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Review on Synthesis, Characterizations, and Electrochemical Properties of Cathode Materials for Lithium Ion Batteries | OMICS International
ISSN: 2169-0022
Journal of Material Sciences & Engineering
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Review on Synthesis, Characterizations, and Electrochemical Properties of Cathode Materials for Lithium Ion Batteries

Bensalah N* and Dawood H

Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, Doha, Qatar

Corresponding Author:
Bensalah N
Department of Chemistry and Earth Sciences
College of Arts and Sciences
Qatar University, Doha, Qatar
Tel: 97444036540
E-mail: [email protected]

Received date:April 06, 2016; Accepted date: May 26, 2016; Published date: June 05, 2016

Citation: Bensalah N, Dawood H (2016) Review on Synthesis, Characterizations, and Electrochemical Properties of Cathode Materials for Lithium Ion Batteries. J Material Sci Eng 5:258. doi:10.4172/2169-0022.1000258

Copyright: © 2016 Bensalah N, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

Review on Synthesis, Characterizations, and Electrochemical Properties of Cathode Materials for Lithium Ion Batteries

Keywords

Lithium ion battery; Cathode materials; Insertion; Conversion; Specific capacity

Introduction

Since their commercialization by SONY in 1991 [1], lithium ion batteries (LIBs) have made significant progress in terms of safety, electrochemical properties such as capacity, power, and cycling stability and it has the highest energy density comparing to other secondary batteries such as nickel-cadmium and nickel-metal hydride. A great part of such progress can be attributed to the introduction of new materials with higher capacity, higher potential, and enhanced thermal stability. Along this journey, numerous studies have been conducted in order to find cathode materials for LIBs with higher capacity to allow for practical applications in plug-in hybrid electric vehicles, large-scale power generation systems, and critical space and aeronautical applications.

In this paper, a comprehensive literature review of cathode materials used or proposed for LIBs is attempted. Since the focus is in this paper on capacity, three areas will be highlighted through the review: synthesis methods, characterization techniques, and electrochemical properties related to capacity, namely initial discharge capacity and cyclability. Out of several possible categorization schemes of cathode materials for LIBs, a structure-based scheme (layered, spinel, olivine, etc.) seems to be dominant as used by most reviewers such as Whittingham [2] and Xu et al. [3]. Also other kinds of cathodes have been studied (air, sulfur, organics and conversion like transition metal FeF3).

Different synthesis techniques were developed and utilized to produce cathode materials studied including solid-state reaction, solgel method, hydrothermal synthesis, and co-precipitation, emulsiondrying, spray pyrolysis, and many others (Figure 1 and Table 1). The electrochemical properties of materials formed, such as initial discharge, cyclability, and capacity retention rate, as well as the morphological properties such as surface texture, grain size, size distribution, and crystallinity, are directly affected by the synthesis method (Table 1). Spray pyrolysis method, in particular, allows for controlling the particle size distribution which provides a powerful tool to control the chemical structural and morphology properties of a material.

material-sciences-Different-synthesis-techniques

Figure 1: Different synthesis techniques utilized to produce cathode materials.

Material  Research group (year) Synthesis method Characterization technique Initial capacity (mAhg−1) Number of cycles: Capacity loss
Layered metal oxides          
LixCoO2 (0≤x≤1) Mizushima et al. [6] Electrochemical extraction from the LiCoO2rocksalt structure XRD - -
HT-LiCoO2 Shlyakhtin et al. [18] Freeze-drying method XRD; SEM; TEM; SAED 135-138 10:10-14%
LiCoO2 Gan et al. [14] Carbon combustion synthesis XRD; SEM 148 10:3%
Carbon-coated LiCoO2 Cao et al. [25] Commercial LiCoO2 powder with milling for 24h at 300 rpm XRD; SEM; TEM; EIS 130 at 0.1°C -
Carbon-coated LiCoO2 thin film with PVDF-HFP gel electrolyte Park et al. [11]  Sol-gel process and Screen printing XRD; SEM 110 -
ZnO-coated LiCoO2 Chang et al. [36]  Plasma-enhancedchemicalvapourdeposition XRD; SEM; AAS; TGA; DSC; BET; EIS ~178 at 1°C 30:~33%
Al2O3-coated LiCoO2 Lu et al. [12]  In situ sol-gel process followed by calcination at 1123K for 12h XRD; SEM; TEM; XPS; DSC 195 (1.0wt% Al2O3) 30:15%
Li4Ti5O12-coated LiCoO2 Yi et al. [32]  Commercial LiCoO2 powder and coating with sol-gel process XRD; SEM 142.7 (3wt% Li4Ti5O12) 40:2.7%
FePO4-coated LiCoO2 Li et al. [16]  Co-precipitation method followed by a high-temperature treatment XRD; SEM; TEM; EDS; EIS; AES 146 (3wt% FePO4) 400:11.3%
High-density spherical LiCoO2 Ying et al. [24]  Controlled crystallization method XRD; SEM 148.4 at 0.2°C 40:2.4%
ZnO-coated LiCoO2 Fang et al. [39]  Commercial LiCoO2 powders coated with wet chemical method XRD; SEM; ICP-AES ~188 at 0.1°C (0.2wt% ZnO) 30: 10.4%
ZnO-coated LiCoO2 Fang and Duh [38]  Wet chemical method with a calcination process XRD; SEM ~185 (calcined at 650°C) 30:~13.5%
SrO/Li2O/La2O3/Ta2O5/TiO2-coated LiCoO2 Wang et al. [34]  Commercial LiCoO2 powders coated with Sol-gel method XRD; SEM ~140 at 1°C (1.0wt% SrO/Li2O/La2O3/Ta2O5/TiO2) 900:~25%
M-coated LiCoO2 (M=TiO2 ZrO2 or ZrTiO4) Fey et al. [35]  Sol-gel and mechano-thermal processes XRD; TEM 167 (ZrO2-coated)
165 (TiO2-coated)
168 (ZrTiO4-coated)
110:20%
24:20%
37:20%
Li2PO2N-coated LiCoO2 Choi et al. [31]  RF magnetron sputtering method EDS; SEM; DSC; EIS ~185 at 0.2°C 50:~16%
LiCoO2/LiNi0.8Co0.17Al0.03O2 Lin et al. [236]  Commercial products  - 186 (for pure LiNi0.8Co0.17Al0.03O2)
161.4 (for 50:50 mixture)
20:5%
LiCoO2 thin film Park et al. [237]  Screen-printing method using ethyl-cellulose-based paste SEM 133 -
LiCoO2/polyacrylonitrile/binary conductive additives composite Zhang et al. [238]  Commercial products XRD; SEM; TEM 155.8 at 0.5°C (~12.5wt% binary conductive additives) -
poly(3,4-dioxyethylenethiophene)/LiCoO2 composite Her et al. [239]  Electrochemical deposition process DSC; SEM; EDS - 50:~0%
Ag-doped LiCoO2 Huang et al. [28]  Commercial LiCoO2 powder with milling for 4h in alcohol  XRD; SEM 172.3 at 1°C
133.1 at 10°C
50:22.29% at 1°C
50:4.88% at 10°C
LixMnO2 (0.4≤x≤0.7) Pistoia et al. [240]  Solid-state reaction XRD, TGA, TDA ~108 (x=0.55) 65:~16%
LiNiO2 Yamada et al. [241]  Solid-state reaction at 500-900°C for 5h XRD

197 at 1°C (at 700°C in O2)

173 at 1°C (at 700°C in air)

12:~0%
LiNiO2 Kalyani et al. [21]  Microwave synthesis with O2 heat pre-treatment XRD; BET; SEM 163 <5%
Co-coated LiNiO2 Sheng-wen et al. [242]  Co-precipitation method XRD; SEM; TEM; XPS 180 20:0.07%/cycle
Ga-doped LiNiO2 Nishida et al. [243]  Sol-gel method XRD 190 100:5%
LiNi1-xMgxO2 (x=0, 0.1, 0.2, 0.3, or 0.5) Sathiyamoorthi et al. [244]  Solid-state reaction at 600°C for 8h XRD; FTIR; SEM; EDS; TEM 190 (x=0.2) 25:2.4%
LiCo1-xNixO2 (0≤x≤0.2) Gummow and Thackeray [245]  Solid-state reaction at 400°C for 48-120h XRD - -
LiNi0.5Mn0.5O2 Abdel-Ghany et al. [246]  Wet-chemical method XRD; SEM 166 30:5% at 900°C
LiNi0.9Co0.1O2 Shi et al. [247]  Rheological phase reaction method XRD; SEM 199 (synthesized at 800°C) 15:27.1%
LiNi0.8Co0.2O2 powder Sivaprakash et al.[248]  Solid-state reaction at 700-800°C for 15-48h with intermittent grinding XRD ~157 20:~11%
LiMnxCoyNi1-x-yO2 Wang et al. [249]  Solid-state reaction at 800-900°C XRD; SEM 180 (x=0.2 and y=0.25) 50:15%
LiCo1/3Ni1/3Mn1/3O2powder Ogihara et al. [250] Spray pyrolysis SEM; XRD; BET; AAS 170 500:20%
LiNi0.7Co0.2Ti0.05M0.05O2 (M=Mg, Al or Zn) Subramanian and Fey [41]  Solid-state reaction at 800°C for 12h XRD; SEM; ICP-AES 149 30: -2% (Mg-doped)
Li1+xNi0.75Co0.25MgxO2(1+x) Chang et al. [251]  Sol-gel method XRD; TGA; TDA ~170 (x=0.1) 30:~12%
LiAlxCo1−xO2 (0≤x≤0.3) Myung et al. [26]  Emulsion-drying method XRD; TEM 110(x=0.1) -
LiAlxCo1-xO2 (0.1≤x≤0.3) Huang et al. [252]  Solid-state reaction 550°C for 20h and at 750°C for 24h with intermittent grinding XRD 153 (x=0.1) 15% at x=0.1
LiAl0.05Ni0.95-xCoxO2 (x=0.1 or 0.15) Zhu et aL[253]  Solid-state reaction at725°C for 24h  XRD; SEM; TG-TDA 186.2 (x=0.1) 10:3.2%
LiNi1/3Mn1/3Al1/3-xCoxO2 (0≤x≤1/3) Ren et al. [254]  Solid-state reaction at 900°C for 20h XRD; SEM ~170 at x:1/3 20:~0
0.5Li2MnO3-LiNi0.5Mn0.5`O2 Zhong et al. [255]  Low temperature combustion followed by annealing treatment XRD; SEM 139 at 0.1°C 50:-44%
Macroporous LiNi0.5Mn0.5O2 Wang et al. [256]  Solid-state reaction method at 900°C for 10h XRD; SEM; BET; EIS 174 at 1°C 10:<5%
Al2O3-coated LiNi1/3Co1/3Mn1/3O2 Kim et al. [257]  Co-precipitation method at 1000°C for 10h XRD; SEM; EIS 173.8 50:10.9%
Carbon-coated LiNi1/3Mn1/3Co1/3O2 Kim et al. [258]  Co-precipitation at 350°C for 3h XRD; DSC; TGA; SEM; TEM 150 at 1 wt% coating 50:2% at 1 wt% coating
nano-crystalline LiCoO2-coated Li1.05Ni0.35Co0.25Mn0.4O2 Son and Cairns [259]  Sol-gel method XRD; TEM 164.1 at 0.1°C 20:~0% at 0.1°C
        151.2 at 0.2°C 20:7.8% at 0.2°C
Spherical LiNi1/3Mn1/3Co1/3O2 Zhi-min, et al. [260]  Spray-drying method XRD; SEM 153 at 0.2°C 40:~6%
Li1+x(Ni1/3Mn1/3Co1/3)1−xO2 Zhang et al. [261]  Co-precipitation method XRD; SEM; ICP 150 at 1°C 30:5% 
La2O3-coated LiNi0.8Co0.2O2 Fey et al. [262]    XRD; SEM; TEM; XPS; BET    
LiNi0.67Co0.15Mn0.18O2 Sun et al. [263]  Co-precipitation at 750°C for 20h and at 850°C for 15h XRD; EPMA; SEM 207 at 55°C 50:~7% at 55°C
Spinel lithium metal oxides           
LiMn2O4 Pistoia and Rosati[264]  Solid-state reaction at 730°C for 6h SEM ~120 80:~16%
LiMn2O4 Li and Xu Solid-state reaction at 600°C for 6h and 750°C for 72h with intermittent grinding   112 200:6.50%
Carbon/Li1+xMn2O4 (0.9≤x≤1.2) Guyomard and Tarascon[45]  Solid-state reaction at 800°C for 24h TGA ~125 200:~12%
Li1+xMyMn2−(x+y)O4+2 Pistoia et al. [240] Solid-state reaction at 730°C for 72h   ∼100 150:∼7%
(M= Li, Cu, Zn, Ni, Co, Fe, Cr, Ga, Al, B, or Ti)          
Li2CrxMn2−xO4 (0≤x≤2) Davidson et al. [76]  Solid-state reaction at 600°C for 3h and at 1000°C for 72h XRD ~32 at 0.05°C (x=0.5) 25:~28%
LiCrxMn2−xO4 (0≤x≤0.1) Zhang et al. [52]  Solid-state reaction at 600°C for 15h and 650°C for 48h with intermittent grinding followed by slow cooling TGA; XRD; BET 118(x=0.1) 200:6.70%
LiCoxMn2−xO4 (0≤x≤0.33) Arora et al. [58]  Solid-state reaction preheating at 600°C for 6h and heating 750°C for 72h with intermittent grinding followed by slow cooling XRD; SEM; BET 100 85:∼3%
LiCrxMn2−xO4 (x=0), 0.04, 0.06 or 0.1) Wang et al. [75]  Pechini method XRD; neutron diffraction; EDS 122(x=0.04) 50:7%
LiM0.05Mn1.95O4 (M=Li, Al, Co, Ni, or B) Lee et al. [74]  Citrate gel method XRD 125 (Ni-doped) 110:∼2%
        122 (Co-doped) 110:∼4%
LiAl0.24Mn1.76O3.98S0.02 Sun et al. [265]  Sol-gel method XRD; TEM 104 at 50°C 70:2.4% at 50°C
        98.5 at 80°C 70:8.4% at 80°C
LiAlxMn2−xO4 (0≤x≤0.6) Myung et al. [26] Emulsion-drying method   114(x=0.2) 50:4% at 45°C
LiAlxMn2-xO4-δ (x=0.1,0.2,0.3, or 0.4 0δ≤0.07) Cho et al. [266]  Solid-state reaction at 750°C for 72h with intermittent grinding XRD; DSC 125(x=0.1 and δ=0.05)
116 (x=0.2 and δ=0.07)
50:∼5%
50:∼3%
iAlxMn2−xO4−zFz (x=0.1 or 0.2; 0≤z≤0.5) Amatucci et al. [177,187] Solid-state reaction at 800°C for 24h   ∼100 (x=0.2; z=0.5) 400:15% at 55°C
LiAl0.18 Mn1.82O3.97S0.03 Sun et al. [267] Sol-gel method XRD; SEM 107 at 25 and 50°C 50:3% at 25 and 50°C
LiNi0.5Mn1.5O4−xSx (x=0 or 0.05) Sun et al. [268] Co-precipitation at 500°C and 800°C XRD; SEM; TEM 122 (x=0.05 at 500°C) 50:4%
LiMn1.5Ni0.5−xCoxO4 (0≤x≤0.5) Wu et al. [269]  Spray-drying method XRD; SEM 112(x=0.2) 20:1.80%
LiAl0.05Mn1.95O4 Yi et al. [273] Adipic acid-assisted sol-gel method at 800°C   128 (D50=17.3 pm) 50:8.30%
LiGaxMn2−xO4 (0≤x≤0.05) Liu et al. [276] Sol-gel method   118(x=0.05) 50:9%
Agx/LiMn2O4 (0≤x≤0.3) Zhou et al. [77] Thermal decomposition   95 (x=0.2) 40:3.30%
LiNi0.4Mn1.6O4 Patoux et al. Solid-state reaction at 600-900°C for 10h   129 1000:20%
LiMn1.8Li0.1Ni0.1O4−nFn (n=0, 0.1 or 0.15) Luo et al. Solid-state reaction at 450°C for 12h   80 (n=0) 50:∼1%
LiMxMn2−xO4−yBry (0≤x≤0.15; 0≤y≤0.05) Huang et al. Solid-state coordination at 700°C for 10h   104 (x=0.15; y=0.05) 100:14.50%
LiMn1.5Ni0.42Ga0.08O4 Shin and Manthiram[270]  Hydroxide precursor method XRD; EIS; FTIR; TOF-SIMS 124 at 25°C
121 at 55°C
100:∼1%
Li1.15Mn1.96Co0.03Gd0.01O4 Sun et al. [271]  Solid-state reaction at 850°C for 5h and 600°C for 10h XRD; SEM  128.1 at 25°C
126.5 at 50°C
100:0.017%/cycle at 25°C
100:0.098%/cycle at 50°C
LiNi0.5Mn1.5O4 powder  Ogihara et al. [250] Spray pyrolysis SEM; XRD; BET; AAS 130 500:8%
LiNi0.5Mn1.5O4 particles Yang et al. [272] Urea combustion method XRD; FTIR; SEM 133.6 20:0.4%
LiLa0.01Mn1.99O3.99F0.01 Yi et al. [273]  Ultrasonic-assisted sol-gel method XRD; TGA; TG-TDA; SEM 126 50:92.1%
Li1.05M0.02Mn1.98O3.98N3.02 (M=Ga3+,Al3+ or CO3+; N=S2− or F) Amaral et al. [274]  Solid-state reaction at 750°C for 72h XRD; SEM 120 (M=Ga and N=S2-) 300:4% (M=Ga and N=S2-)
LiCrxMn2−xO4 Song et al. [275]  Solid-state reaction at 450-750°C for 2h XRD; SEM; ICP-AES 120(synthesized at 650°C) 100:13%
LiFePO4-coated LiMn1.5Ni0.5O4 Liu et al. [276]  Sol-gel method using citric acid XRD; SEM; TEM; EDS ~110 at 1°C 140:25% at 1°C
Gold-coated LiMn2O4 Tu et al. [277]  Solid-state reaction at 750°C for 20h and coating by ion sputtering method XRD; EIS; EDS ∼126 50: ∼6.3%
Li3PO4-coated LiMn2O4 Li et al. [67]  sol–gel method and coating dryball-milling method XRD; SEM; EIS 112.4 at 55°C 100:15% at 55°C
ZnO-coated LiNi0.5Mn1.5O4 powder Sun et al. [278] Sol-gel method and coating by in situ mixing for 4h XRD; TGA; EDS; SEM; TEM 137 at 55°C 50: ~0 at 55°C
Co-doped LiCoyMn2-yO4 (y=0.05-0.33) Aroraet al. [58]  Solid-state reaction at 600°C for 6h and 750°C for 72h XRD; SEM; BET ~105 (y=0.16) 25:~3%
LiMn2O4/C Huang and Bruce [279]  Modified sol-gel method XRD 150 at 0.5°C (synthesized at 200°C) 300:40%
LiMn2O4 Santiago et al. [47]  Combustion of manganese nitrate tetrahydrate and urea XRD; EIS 107 -
LiMn2O4 Yi et al. [46]  Adipic acid-assisted sol-gel method a XRD; TGA; TG-DTA; XRD; XPS; SEM; ICP-MS 90.7 (synthesized at 350°C)
130.1 (synthesized at 800°C)
50: 6.4% 
50:14.8%
LiZnxMn2−xO4 (0≤x≤0.15) Arumugam et al. [55]  Sol-gel method using aqueous solutions of metal nitrates and succinic acid XRD; SEM; TEM 137 at 0.5°C (x=0)
122 at 0.5°C (x=0.10)
100:41%
100:13%
Olivine transition metal phosphates and silicates          
Mesoporous LiFePO4 Ren and Bruce [280]  Solid-state reaction at 550°C for 5h XRD; TEM; BET 155 at 0.1°C
127 at 1°C
30:~0%
LiFePO4nanorods Changa et al. [281]  Hydrothermal synthesis XRD; SEM; TEM;Mössbauerspectroscopy ~144 at 0.5°C 20:~8%
LiFePO4/graphene/C composite Su et al. [282]  In situsolvothermal method XRD; SEM; TEM 163.7 at 0.1°C
114 at 5°C
30:3% at 0.1°C (LiFePO4/graphene2%/C6%)
nanoporous LiFePO4/C composite Su et al. [283]  Hydrothermal synthesis XRD; SEM; TEM 155.3 50:3%
nanoporous LiFePO4/C composite Yang and Gao[284]  Impregnation from ethanol solution XRD; TGA; DSC; TEM 68 at 50°C 50:12%
LiFePO4/C Yang et al. [83]  Ultrasonic spray pyrolysis XRD; TEM; SEM 150 at 1°C and 50°C (15 wt% C) 30:14.5%
LiFePO4-C/solid polymer electrolyte Jin et al. [285]  Hydrothermal synthesis at 150°C XRD; TEM 128 (5 wt% C) 30:0.78%
C-LiFePO4/polypyrrole composite Boyano et al. [286]  In situelectrodeposition method  XRD; SEM; TGA 154 at 0.1°C(20% PPy) 120:~0%
LiFePO4/C composite fiber Toprakci et al. [287]  Combination of electrospinning and sol–gel methods XRD; SEM; TEM; EDS 166 at 0.05°C(synthesized at 700°C) 50:~0% at 0.1°C
LiFePO4/C composite Huang et al. [288]  Stearic acid-assisted rheological phase reaction at 600°C for 4h XRD; SEM; TEM; SAED 160 at 0.5°C
155 at 1°C
200:<3% at 2°C
         
Carbon-coated LiFePO4 Dong et al. [81]  Solid-state reaction at 650-800°C for 10h followed by slow cooling XRD; SEM 156.7 at 0.1°C (synthesized at 650°C) 50:3.5%
Carbon-coated LiFePO4 Shin et al. [84]  Mechanochemical activation method XRD; SEM; TEM; EIS 150 at 0.05°C 0.1–0.3 mAhg−1/cycle
        135 at 1°C  
Carbon-coated nanocrystalline LiFePO4 Zhecheva et al. [86]  Freeze-drying method XRD; BET; SEM; XPS 122 at 0.1°C and 500°C 85:11.5%
SiO2-coated LiFePO4 Li et al. [289]  Sol-gel method XRD; TEM; SEM; EIS 158 at 0.1°C and 55°C 100:6% at 0.5°C and 55°C
        145 at 1°C and 55°C  
ZrO2-nanocoated LiFePO4 Liu et al. [290]  Precipitation method XRD; TEM; SAED 146 at 0.1°C 100:1.8% at 0.1°C
        97 at 1°C 100:3.1% at 1°C
CeO2-coated LiFePO­4/C Yao et al. [291]  Commercially LiFePO4/C powder  XRD, SEM, TEM; EDS; EIS 153.8 at 0.1°C and 20°C 30:1.4% at -20°C
        99.7 at 0.1°C and -20°C  
Ru-doped LiFePO4/C Wang et al. [292]  Rheological phase reaction at 350◦C for 10h and at 750◦C for a few hours XRD; SEM; EIS 156 at 0.1°C 30:~0%
Cu-doped LiFe1−xCuxPO4/C (x=0, 0.01, 0.015, 0.02, or 0.025) Chang et al. [293]  Solid-state reaction at 500◦C for 6h then at 750◦C for 18h XRD; SEM 150 at 0.1°C (x=0.02)
127 at 2°C
-
Co-doped LiFe1−xCoxPO4 Zhao et al. [294]  Hydrothermal synthesis XRD; XPS; TEM; EDS; Raman spectroscopy 170 at 0.1°C (x=1/4) -
LiAlxV1-xPO4F (x=0, 0.03, or 0.06) Zhong et al. [295]  Carbothermal reduction XRD; SEM 118 at x=0.03 30:14.4%
Al-doped LiAlxV1-xPO4F (x=0, 0.03, or 0.06) Shengkui et al. [295] Carbothermal reduction process XRD; SEM ~118 (x=0.03) 30:~14.4%
Li3Fe2−2xTixMnx(PO4)3/C (0≤x≤0.2) Sun et al. [296]  Solid-state reaction at 850°C for 80h followed by milling at 220 rpm for 10h XRD; SEM 112.3 (x=0.1) 20:25.8%
LiFePO4 powders Meligrana et al. [297]  Hydrothermal synthesis XRD; ICP-AES, BET; SEM ~137 at 0.5°C 20:~0 at 0.5°C
        ~130 at 1°C 20:~0 at 1°C
LiFePO4/C nanocomposites Fey et al. [298] Combination of carbothermal reduction and molten salt XRD; SEM; TEM; DLS; EIS; SAED; EDS; Raman spectroscopy 141 at 0.2°C -
LiCoPO4/C Xing et al. [85]  Sol-gel method XRD; SEM; TEM; EIS 136.2 30:32%
LiCoPO4/C nanocomposites Doan and Tangiuschi[299]  Combination of spray pyrolysis and wet ball-milling techniques followed by heat treatment XRD; SEM; TEM; TG-TDA; EDS 109 at 0.05°C
142 at 20°C
40:13% at 0.1°C
Vanadium-based compounds          
LiV3O8 West et al. [121]  Freeze-drying and spray-drying XRD; TGA - 50: 0.5%/cycle
Li6V10O28 Xie et al. [151]  Hydrothermal synthesis and annealing dehydration treatment XRD; TGA; TG-TDA; ICP-AES; SEM; TEM 132 15:~24%
LiV3O8 Xiong et al. [120]  Spray-drying method XRD; SEM 340.2 at 25 mAg-1 100:15.2% at 125 mAg−1
LiV3O8 Kannan and Manthiram[105] Low-temperature solution dispersion method XRD; SEM; DSC; TGA ~250 at 60°C 100:~-4%
Li3V2(PO4)3/C Ge et al. [300]  Sol-gel method XRD; SEM; TEM; EIS 179.8 at 700°C (d=30-50 nm and L=~800nm) 50:~21%
Li3V2(PO4)3/C  Wang et al. [140]  Electrostatic spray deposition XRD; SEM; TEM     
Li3V2(PO4)3/C Yuan et al. [301]  Sol-gel method XRD; SEM; TEM 127.9 at 1°C (synthesized at at 750°C)
124.1 at 5°C(synthesized at at 750°C)
100:~0% at 1°C and 5°C
Li3V2(PO4)3/C Chen et al. [302]  Carbothermal reduction process XRD, FTIR, XPS, EIS 122 at 0.5°C at -25°C 100:5% at 20°C
Cr-doped LiV3O8 Fenget al. [122]  Sol-gel method XRD; SEM 269.9 at 150 mAg−1 100:5.6%
Polypyrrole–LiV3O8 composite Feng et al. [123]  Solution dispersion in ethanol followed by co-heating process  SEM 292 at 40 mAg−1(20% PPy) 40:~14
Mixed amorphous-nanocrystalline LiV3O8 Shi et al. [127]  RF magnetron sputtering XRD; TEM; SEM; SAED 382 100:21.2%
LiV3O8/C nanosheet Idris et al. [129] Hydrothermal synthesis followed by carbon coating  XRD; TGA; SEM; TEM; EIS 227 at 0.2°C 100:14.5% 
LiV3O8nanocrystallites Li et al. [124]  Solid-state reaction at 120°C for 20h with intermittent grinding XRD; SEM; TEM; TGA; TG-TDA 342 at 300°C 30:11.7%
nanoporous LiV3O8 Ma et al. [126]  Tartaric acid-assisted sol-gel process XRD; SEM; TEM 301 at 40 mAg−1 50:3.7%
Polypyrrole-LiV3O8 composite Tian et al. [125]  Oxidative poly-merization of pyrrole using ferric chloride XRD; FTIR; SEM 169 at 0.5°C 50:~0%
LiV3O8nanorods Xu et al. [128]  Hydrothermal synthesis XRD; TGA; TEM; FTIR 302 at 300°C 30:~8%
Li3V2(PO4)3nanocrystals-graphene oxide nanosheets Rui et al. [138]  Modified Hummers method XRD; TEM; SEM; TGA; Raman spectroscopy 128 at 0.5°C 100:~0%
amorphous Fe2V4O13 Si et al. [128]  Liquid precipitation method XRD; SEM 235 40:~14.5%
MnxV2O5 (x=0.02, 0.04, 0.09, or 0.19) Park [303]  Sol-gel method with ion exchange resin XRD; SEM; TGA 120 (x=0.09) 50:~0%
Nanostructured composites           
K2FeO4 Wang et al. [304]  Hypochlorite oxidation method XRD; CCD ~350 50:~35%
LiFePO4 powder Ogihara et al. [250] Spray pyrolysis SEM; XRD; BET; AAS 150 500:16%
LiF/Fe nanocomposites Li et al. [305]  Mechanical ball-milling method XRD ~568 20:46%
Polypyrrole-sulfur nanocomposites Liang et al. [306]  Self-degraded template  for polypyrrole followed by co-heating process XRD; FTIR; TEM; SEM; BET; TG-DSC 1151.7 (30 wt% sulfur) 80:43.6% (30 wt% sulfur)
LiMn2O4/CNT nanocomposites Ding et al. [73]  In-situ hydrothermal method XRD; SEM 116 at 1°C
84 at 10°C
100:0.009% at 1°C
100:5.8% at 10°C
LiMn2O4/CNT nanocomposites Xia et al. [307]  In-situ hydrothermal method XRD; TEM; SEM; TGA 124 at 1°C
106 at 10°C
500:8% at 1°C
1000:23% at 10°C
LiFePO4/multiwalled CNT nanocomposites Li et al. [308]  Solid-state reaction at 700°C for 12h and hydrogen arc discharge method followed by mixing  XRD; TEM; SEM; EIS 155at 0.1°C
147 at 1°C
50: ~5% at 0.1°C
50: ~6% at 1°C
Li[Li0.2Mn0.54Ni0.13Co0.13]O2–V2O5composites Gao et al.[110] Co-precipitation method XRD 300 at 0.05°C (10 wt% V2O5) 25:~12%
V2O5/polypyrrole composites Ren et al. [104]  Sol-gel method using XRD; FTIR; SEM; TGA 271.8 at 0.1°C (2.5 wt% PPy) 50:17.1%
TEOS/[Bmim][NTf2]/Carbon–titania composites Wang and Dai [165]  Sol-gel method using STEM microscope; MicromeriticsTristar analyzer; BET; TEM, XRD, XPS - -

Structural characterization of cathode materials synthesized have been done by using different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic light scattering (DLS), and Raman spectroscopy. These techniques have been utilized to determine crystal structures, chemical and phase compositions, surface morphological characteristics, and microstructural features of synthesized materials.

Although LIB’s have many advantages, it has its drawbacks since it needs high protection circuit to keep both current and voltage within the safe limits, costly to manufacture and have aging issues, especially in hot places.

Lithium-ion rechargeable batteries have great achievement because of their characteristics as high energy density, long-term stability and its effectiveness as a solution for huge applications. This journal is completed to motivate reviewers who are interested in LIB, types of cathodes specifically and looking for environment-friendly, inexpensive and charge/discharge long-term cycles materials. Also, open the challenges front of researchers to discover new materials with better properties, characteristics, and features for LIB.

Electrochemistry

The basic working mechanism based on which LIBs functions is associated with the transfer of lithium ions from the positive electrode (cathode) to the negative one (anode) and vice versa. During discharging process, lithium ions travel through an electrolyte, often an organic solution of lithium salt such as LiPF6, from the cathode side to the anode side. The exact opposite occurs during charging as an external current is applied. Although all LIBs work according to this basic mechanism, there are two different processes by which lithium ions associate with cathodes or anodes: intercalation and reversible chemical reaction or alloying. Since the focus here is on the cathode side, a straightforward explanation of both processes follows.

Lithium transition metal oxides in the form of LiMO2 or LiM2O4, where M is usually Co, Ni or Mn, allow only for the intercalation of lithium ions around potential of 4 V [4]. Reversible intercalation of lithium ions virtually without structural changes of cathode materials makes the operational safety of LIBs superior to other types of secondary batteries such as lead acid and metal hydride nickel batteries. From other hand, in reversible alloying, insertion and extraction of lithium into the crystal structure of cathode with changes in the volume of the structural.

Reversible conversion reaction are lithiation reactions, it’s proceed rapidly where the structural’s are well-dispersed by lithium to metal structure (Figure 2) [5].

material-sciences-Structural-changes

Figure 2: Structural changes during charge-discharge of Insertion, alloying and conversion cathodes materials.

Cathode materials

Despite the fact that layered LiCoO2 has been the dominant cathode materials in commercialized LIBs, many important alternatives have attracted many researchers for potential use. Such substitutes, some of which have been already introduced to the market, include layered LiNiO2 and LiMnO2 along with their derivatives such as LiNixCoyO2, LiCoxNiyMn1-x-yO2, spinel-structured LiMn2O4 along with its derivatives such as LiNixMn2-xO4 and LiCrxMn2-xO4, and olivine-structured LiFePO4. However, for any of these substitutes to be widely adapted, some challenges have to be overcome (Figure 3).

material-sciences-Voltage-specific-capacity

Figure 3: Voltage and specific capacity of different cathode materials.

Layered Lithium Transition Metal Oxides

The layered lithium transition metal oxide with the formula LiMO2, where M=Co, Mn, Ni or a combination of two or more, have been arguably the most successful category of cathode materials for LIBs. Their superior electrochemical behavior can be ascribed to their layered structure which allows for a large number of diffusion paths for lithium ions (Figure 4).

material-sciences-Charging-discharging

Figure 4: Charging and discharging processes of the lithium ion battery using insertion cathode materials.

LiCoO2

As stated earlier, LiCoO2 is the earliest and the most commonlyused cathode material for commercial LIBs. Suggested first by Mizushima et al. [6] in 1980, this material has several desirable features including high discharge potential, low molecular weight, high energy capacity, good charge/discharge performance, relative ease of synthesis and treatment, and stable and high discharge voltage [7]. However, extensive research has been conducted during the last two decades to find cathode materials with larger capacity and higher potential than LiCoO2. This was further motivated by the high cost, chemical hazards, and the environmental impact associated with cobalt. The preparation of LiCoO2 was done by means of solid state reaction [8-10], sol-gel technique [11,12], ultrasonic spray pyrolysis process [13], combustion synthesis [14,15], co-precipitation method [16], molten salt synthesis [17], freeze-drying method [18], complex formation method [19], hydrothermal synthesis [20], mechanochemical, and microwave synthesis [21,22], and other methods. Depending on the synthesis method, LiCoO2 could have either hexagonal layered for hightemperature LiCoO2 or cubic spinel-like structure for low-temperature LiCoO2 [23]. A comprehensive review of high- and low-temperature synthetic methods and their effects on the electrochemical properties of LiCoO2 was conducted by Antolini [23].

Despite its high theoretical capacity of 274 mAhg-1, reported practical discharge capacities of LiCoO2 are relatively low, in the range of 135-150 mAhg-1 [14,18,24], only 50-55% of its theoretical capacity. In order to enhance the ionic conductivity and cycling performance of the cathode, some approaches such as carbon coating [11,25], coatings with oxide compounds such as Al2O3, ZnO, and LiTiO12, and cationic doping on aluminum [26], chromium [27] and sliver [28] have been applied. Among these, Al doping has received the greatest deal of attention as it has been proven to produce significant improvement on the capacity retention of upon cycling, which was attributed to an increase of the diffusion coefficient of lithium ions in Al-doped cathodes [26].

Various oxide coatings of LiCoO2 cathodes have been studied including AlPO4, Al2O3 [29,30], CePO4, FePO4 [16], Li2CO3, Li2PO2N [31], Li4Ti5O12 [32], MgO [33], SrHPO4, SrO [34], SnO2, TiO2 [34,35], ZnO [36], and ZrO2 [35,37]. Having achieved a mixed record of success, some coatings remarkably increased the initial discharge capacity of LiCoO2 as high as 190 mAhg-1 while others significantly enhanced the cycling behavior. For instance, Lu et al. [11] reported an initial discharge capacity of 195 mAhg-1 for Al2O3-co ated LiCoO2 (1.0 wt% Al2O3) prepared by in situ sol-gel method with a good capacity retention upon cycling (85% after 30 cycles) [12]. In another study by Li et al. [16], 11.3% capacity loss was reported after 400 cycles for 3.0 wt% FePO4-coated LiCoO2 cathodes. Other coatings which have produced significant improvements on the electrochemical behavior of LiCoO2 include ZnO [38,39], ZrO2 [35], Li2PO2N [31], and Li4Ti5O12 [32].

LiMnO2

Although LiMnO2 has been proposed as a cathode material in LIBs almost as early as LiCoO2, its use has not spread mainly due to performance limitations such as low capacity, difficulty of mass production, and power charge/discharge performance, especially at high temperatures. However, years of extensive research has led to significant improvement of its performance. Compared to LiCoO2, LiMnO2 has major advantages such as high safety and low cost which make it a promising substitute in the future.

LiNiO2

One of the early cathode materials to be explored was lithium nickel oxide (LiNiO2) which has a comparable layered structure and charge-discharge characteristics to those of LiCoO2. Although nickelbased cathodes are currently feasible for commercial use, their major drawback is poor solubility in organic electrolyte solutions, particularly at high temperature. Also, synthesis and treatment of LiNiO2 often require harsh temperature conditions which further limit its current use in commercial LIBs despite its superior capacity [40]. Nickel has higher energy density than cobalt does; 50% of lithium ions can be transferred between anode and cathode for cobalt at the maximum voltage of a typical battery (4.7 V), while 70% of lithium ions can be mobilized for nickel at only 4.2 V.

Derivative compounds

The electrochemical behaviors of various layered derivative compounds haven been extensively studied by numerous research groups. For more than two decades, researchers have been working on developing derivatives of nickel, cobalt, and/or manganese oxides in order to enhance the stability and improve the electrochemical behavior of layered cathode materials. Some of these derivatives are as LiNixCo1-xO2, LiCoxM1-xO2, LiNixMxO2, and LiNixMyCo1-x-yO2 (where M=Al or Mn). Substantial improvement on the cycling performance has been reported by optimizing the composition of these derivative materials. Also, since manganese is less expensive and safer to use than cobalt or nickel, these derivatives could provide low-cost alternatives.

Surface modification by either coating with metal oxides or doping with metal cations proved to be an effective method for improving the chemical stability of layered derivative compounds. For instance, Subramanian and Fey (2002) reported a significant enhancement of the cycling behavior by cationic doping of LiNi0.7Co0.2Ti0.05Mg0.05O2 (~ 0% afte 20 cycles) [41].

Spinel Lithium Transition Metal Oxides (LiMn2O4) LiMn2O4

The spinel lithium manganese oxide LiMn2O4 has been one of the most prospective cathode materials as a non-toxic, environmentallyfriendly, the high natural abundance of Mn and low-cost candidate [42]. This material has a theoretical capacity of 148 mAh/g for an equivalent weight (M) is 180.8 g/mol [43].

A more detailed study of the electrical, thermal, and structural properties of LiMn2O4 as well as the conduction mechanism for this material can be found somewhere else [44]. Many researchers [45-47], who investigated the electrochemical properties of LiMn2O4 reported discharge capacity in the range of 100-120 mAhg−1 which represent 67-81% of its theoretical capacity (148 mAhg−1) [48].] A wide variety of synthetic approaches have been applied to develop spinel LiMn2O4 including solid-state reaction [49], sol-gel method [50], hydrothermal synthesis [42], combustion synthesis, solution-phase, flame-assisted spray technology [51], and templating method.

Within the spinel lithium manganese oxide system, two approaches have been often proposed to improve the structural stability and electrochemical performance of the system: cationic substitution and surface modification. Manganese-substituted spinels of the structural formula LiMxMn2-xO4 (M=Al, B, Cr, Co, Cu, Fe, Ga, Ge, Na, Ni, Ti, Sc or Zn) have been extensively investigated by different research groups to improve the cycling performance of LiMn2O4 [52-61]. Among these derivatives, LiNixMn2-xO4 showed significant improvement on cycling behavior of LiMn2O4. For example, Wang and Xiao et al. showed a relatively good cycling behavior and higher reversible capacity of LiNi0.05Mn1.95O4 electrode prepared by sol-gel method [62]. It was reported that lithium substituted used to make almost all commercial manganese oxide spinel materials (LMOs), since the cycling behavior is improved than LiMn2O4. The theoretical capacities of 100-120 mAh/g, slightly lower than that for LiMn2O4 [63].

Surface modification has been a second way to improve the electrochemical performance of LiMn2O4. Different salts have been studied such as Al2O3, AlPO4, Cr2O3 [64], La2O3 [65,66], Li3PO4 [67], SrF2 [68], TiO2 [69], ZnO [70,71] and ZrO2 [69]. Further nanostructural modifications have been examined such as encapsulation of LiMn2O4nanowires in ZnO nanotubes by Liu et al. [72] and homogenous dispersion of LiMn2O4 nanoparticles in carbon nanotubes (CNT) composites by Ding et al. [73]. The latter approach demonstrated a significant improvement on the cycling behavior of LiMn2O4 approaching 100% after 100 cycles [73].

Derivative Compounds

Much research work has been conducted on the electrochemical properties of derivatives of LiMn2O4 in order to enhance the specific capacity and power and optimize the operational range of temperature for the original spinel compound. Two derivatives which have attracted many researchers since the early 90’s, LiNixMn2-xO4 [74], and LiCrxMn2-xO4 [52,75,76], have demonstrated a remarkable improvement on the cyclability of spinel magnesium oxides.

Olivine Lithium Transition Metal Phosphates and Silicates (LiMPO4 and LiMSiO4)

LiMPO4

The electrochemical behavior of olivine-structured transition poly anion compounds of the structural formulas of LiMPO4 and LiMSiO4 (M=Co, Fe, Mn, Ni or V) have been attracted a great deal of interest as potential cathode materials. A comparative study of lithium intercalation potential in olivine-structured transition metal compounds has been reported by Zhou et al. [77].

Olivine-structured compounds have several advantages over other cathode materials including its structure of material hardly changes while Li ion intercalation and deintercalation; (2). It holds a long voltage platform.

Among phosphate compounds, LiFePO4 has received the greatest amount of attention due to a number of desirable features such as low cost, non-toxicity, and good thermal and chemical stability [78]. For example, the main drawback of lithium iron phosphates, LiFePO4, is their low electrochemical performance at room temperature due to low lithium ion diffusion and poor electronic conductivity [78]. In order to overcome this drawback, several material processing techniques, including solid solution doping in metals and nanocoatings of phosphate particles with carbon, have been proposed.

LiFePO4 has been prepared through different synthetic methods as reviewed by Zhang et al. [79] such as solid-state reaction, sol-gel synthesis, hydrothermal synthesis, carbothermal reduction, microwave synthesis, and spray pyrolysis. A comparative study of the synthetic routes of LiFePO4 and their effect of the electrochemical properties was conducted by Franger et al. [80].

Another widely-investigated phosphate compound that has recently attained strong interest is LiCoPO4. LiCoPO4 has been prepared by means of solid-state reaction, sol–gel synthesis, coprecipitation, hydrothermal synthesis, optical floating zone method, radio frequency magnetron sputtering, spray pyrolysis, and microwave synthesis. Zhao et al. [81] reported an initial capacity of 156.7 mAhg−1 and a capacity loss of 3.5% after 50 cycles for LiFePO4 prepared by solid state reaction at 650°C.

Yang et al. studied mesoporous FePO4 as a potential cathode material reporting an initial discharge capacity of 160 mAhg-1 with a capacity loss of 10% after 20 cycles. A significant amount of research has suggested that the migration of lithium ions, and consequently charge/discharge performance LiFePO4, can be greatly enhanced by carbon coating [81,82-86].

LiMSiO4

Another group of poly-anionic compounds, silicates, have been examined for their interesting electrochemical potential as cathode materials including Li2MnSiO4 [87-89], Li2CoSiO4 [90-92], Li2FeSiO4 [78,88,93-102], and LiFeSO4F [103]. However, several limitations have to be overcome before a wide use of such materials becomes feasible.

Nanostructured Metal Oxides

Vanadium oxides

The vanadium-based oxides have attracted strong interest from researchers due to their good electronic conductivity, excellent chemical stability in polymeric electrolytes, and high energy density [104]. Since vanadium can exist in a number of oxidation states from 2+ in VO to 5+ in V2O5, vanadium oxides could offer a wide range of capacities as cathode materials [105]. Vanadium oxides which have been studied as potential cathode materials in LIBs are VO2 [106], V2O5 [104,106-117], V3O6 [118], V3O7·H2O [119-125], LiV3O8 [104,126-139], Li3V2(PO4)3 [140-146], V4O11 [147], Fe2V4O13 [148], V6O13 [149,150], and Li6V10O28 [151]. Chernova et al. [152] reviewed in detail the structural and electrochemical features of different vanadium oxides as well as the process of lithium insertion in them [153-156]. Among these oxides, V2O5, LiV3O8 and Li3V2(PO4)3 have shown the most promising electrochemical behavior as indicated by their high discharge capacities and good capacity retention. Li3V2(PO4)3 has been previously reviewed along with other phosphate compounds.

V2O5

As layered compounds with a high theoretical capacity of 442 mAhg−1, V2O5 compounds are among the most promising high-capacity cathode materials under development. Several synthetic methods have been employed to prepare V2O5 including sol-gel method, solvothermal route, precipitation process, and electrodeposition. A novel synthetic approach by Pomerantseva et al. enabled for nanostructured V2O5 thin films by biotemplated synthesis using Tobacco mosaic virus particles [114].

Studies on V2O5 have shown high discharge capacity mostly in the range of 250-300 mAhg−1 for V2O5/polypyrrole composites which represent 57-67% of its theoretical capacity with good capacity retention (15-20% after 50 cycles) [104]. When the structure and composition of lithiated V2O5 nanocomposites are optimized, their electrochemical behavior can be significantly enhanced. For example, in a study by Semenenko et al. [153] thin LixV2O5 (x~0.8) nanorods with thickness of 5-10 μm were synthesized using hydrothermal treatment of V2O5 gel and lithium ions [157]. An initial discharge capacity of 490 mAhg-1 was reported with capacity loss of about 18% after 50 cycles [158].

Despite these advantages of V2O5 compounds, two drawbacks still persist: low power density due to their intrinsic low ionic conductivity, and poor cyclability as a result of microstructural failure upon cyclic lithium ion intercalation-deintercalation [104]. Since thermal stability in polymeric electrolytes is one of the main advantages for vanadium oxide, a variety of conductive polymeric materials have been suggested to be used as hybrid hosts of V2O5 such as polypyrrole [104,112,114], poly(ethylene glycol) [116], polythiophene [109], polyphosphazene [159], and polyaniline [115]. Such polymeric hybrid materials have been found to increase the electronic conductivity of the original oxides and improve the cycling behavior by enhancing the microstructural stability. Among these polymeric materials, polypyrrole has been the most extensively studied due to its high electric conductivity once doped with oxidizing agents and good electrochemical activity with a theoretical capacity of 72 mAhg-1 [160].

LiV3O8

Another lithium vanadium oxide that has been widely investigated over the last two decades for its good electrochemical properties is LiV3O8. Such good electrochemical properties include high discharge capacity, high specific energy density, and long cycle life [120].

A wide range of synthetic routes have been used to prepare LiV3O8 in different forms including spherical particles [120], polymeric composites [123,125], and nanostructured materials of various morphologies such as nanorods [128], thin films [127,161] nanocrystals [162], and porous nanoparticles [126]. The synthetic routes studied in literature include solid-state reaction [124], spray pyrolysis method [163], sol–gel process [126], hydrothermal synthesis [105,122], radio frequency magnetron sputtering [156,127], hydrothermal treatment [128], rheological phase reaction method [164] and microwave synthesis [165]. In order to enhance the electrochemical properties of the material synthesized by increasing surface porosity and lowering crystallinity, several techniques have been suggested such as ultrasonic treatment [166] and partial crystalline modification by introducing small amounts of H2O, CO2 and NH3 [167]. Such techniques, although have improved the electrochemical behavior of LiV3O8 to some degree, need further optimization in order to produce satisfactory power and cycling efficiency and to be applicable in large-scale production systems [159].

It was found by several researchers that the synthetic routes affect greatly the capacity of LiV3O8cathodes [159]. Even though the initial discharge capacity could even reach more than 100% of its theoretical capacity (280 mAhg-1) [157] when certain nanostructuring techniques or polymeric alloying are applied. Idris et al. [129] reported an initial discharge capacity of 227 mAhg-1 with low capacity loss (~ 15% after 100 cycles) for LiV3O8/carbon nanocomposites prepared by hydrothermal synthesis followed by a carbon-coating process. Other researchers such as Feng et al. [123] and Tian et al. [125] obtained higher initial discharge capacity (~ 300 mAhg-1) with good cycling efficiency (8-14% capacity loss after 30-40 cycles) for polypyrrole-LiV3O8 composites.

Coatings of Cathode Materials

A comprehensive review of surface coatings of cathodes in LIBs was conducted by Li et al. [163]. Such coatings were found to enhance the structural stability of the cathode material by limiting the contact with electrolyte solution, suppress phase transition, and stabilize the cations in their crystal sites. Nanocoatings of LiMn2O4 include SiO2 [168-172].

Nanostructured Composites

Nanostructured carbon-oxide composites

Wang and Dai [165] developed an approach towards functionalized porous carbon–oxide composite materials by using ionic liquid (ILs) as solvents in nonhydrolytic sol–gel processing and this to limited and oxide-catalyzed carbonization of ILs trapped within an oxide framework. BET, TEM, XRD and XPS characterization measurements were applied.

Nanostructured polymer-oxide composites

Zhang et al. prepared LiFePO4/C composite fibers by a combination of electrospinning and sol-gel techniques using Polyacrylonitrile (PAN) as an electrospinning media. XRD and SEM measurements were carried out to characterize the structure of the fibers formed [173].

Lithium/Air

Recently, a growing attention has been directed to lithium/air batteries which utilize mesoporous carbon as cathode materials. These devices represent a special category of LIBs as they enjoy very high energy density compared to other conventional types of lithium-ion batteries.

Organosulfur Materials

Nowadays, organosulfur compounds usually with the organothiol (–SH)/disulfide (S–S) redox couple, it's characterized by their ability to store big amounts of charges per unit mass to use as cathode materials for rechargeable lithium batteries and featuring of being safety, cheap, synthetic it easily and chemically stable. The theoretical energy of organosulfur compounds goes beyond that of as intercalation compounds, conducting polymers and conventional battery materials [166,167]. Organosulfur compounds containing disulfide bonds showed a high discharge capacity equal to 500 mAh/g [168].

Advanced Cathode Material

Organic cathodes

Most of the recent lithium batteries made of inorganic compounds as a cathode are produced from nonrenewable resources and because of that they are highly cost [174-177]. Scientists searched for another candidate to improve the power and energy density, safety of Liion cells and greener Li-ion batteries. Organic electrodes have been proposed as one of the best electrodes for Li-ion batteries due to its inherently flexible, non-toxic, cheap, abundant nature and also their limitation of cycle life, thermal stability, low energy density values and rate capability led to a huge improvement of it [170]. Nakahara et al. proposed a high-energy organic cathode material; poly(2,2,6,6- tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) for use in lithium rechargeable batteries, it is obtained good power capability, cycling efficiency (retaining more than half of original capacity after 1000 cycles), fast charging and discharging (less than 1.5 min) and can transfer specific capacity over 100 mAh.g−1 [171].

Sulfur compounds Li2S

Except the air cathode, the sulfur element has the cheapest cathode material for lithium batteries and top theoretical capacity density of 1672 mA/g between all known cathode materials [172]. Li2S cathode material shows a great potential of high-performance rechargeable lithium batteries comparing with other resources of elemental sulfur in nature, like micro-batteries for power sources for electric vehicles and small-size electronic devices emphasizing high charge density [169]. However, because sulfur element has the dissolution of its reaction product polysulfides into the electrolytes and highly insulating nature, it cannot be used directly at low temperature as an electrode material for lithium batteries, which caused various problems, such as rapid fall of the capacity and short utilization of active material [178]. Yang et al. [174] found that Li2S can be an active material and reached a large potential barrier (∼ 1 V) at the beginning of charging by applying a higher voltage cutoff. It’s obtained a greater initial discharge capacity (~ 800 mAh/g) which becomes stabilized after (10 cycles with around 500–550 mAh/g, ~ 0.25% per cycle capacity decay rate).

Conversion cathodes

To improve cathode materials, electrochemical conversion reactions have been used as another way to accomplishing the utilization of all the oxidation phases of a transition metal [179-182]. Fluorides metal are one of greatest transition metals that commonly studied in the research because of its stability and its ion considered as a strong and suitable ionic character of the (M-F bond) to transfer charges between two electrodes and produce high operating voltages and reversible capacity [176]. Iron fluoride (FeF3) is one of the derivative of transition metal fluorides that safety and inexpensive, it is characterized by high theoretical capacity (712 mAh/g) [177,175]. In 1990, Arai et al. were the first researcher who reported the electrochemical activity of trifluorides with its high theoretical voltage and a specific capacity equal to 80 mAh/g [178].

Among various studies of fluorinated, fluorinated solvents are the most studied since it’s used for increasing the safety and stability in LIB [183-186]. Different fluorine-doped intercalation cathodes are produced from fluorine which has been used as a dopant like layered transition metal oxyfluorides (Li1+xNi1−xO2−yFy), spinel lithium manganese oxyfluorides (Li1+xMn2−xO4−yFy) and orthorhombic lithium manganese oxyfluorides (Li1.07Mn0.93O1.92F0.08) [187].

Layered transition metal oxyfluoride: As have been mentioned before about layered lithium transition metal oxides owing to their electrochemial performance for secondary Li-ion batteries as high potential electrode materials. However, fluoride cathodes have the highest average voltage between conversion reactions [179].

Li1-xNi1−xO2−yFy : Kubo et al. [180] discussed metal oxyfluoride as cathode materials by studying the synthesized of Li1-xNi1−xO2−yFy, through solid state reaction that led to substitute nickel and oxygen positions for LiNiO2. X-ray diffractometry and electrochemical technology were used to examine the cycle properties and show initial charging capacity around 240 mAh/g. Li1.08Ni0.92O1.9F0.1 possessed excellent features on charge/discharge cycling compared to LiNiO2 and showed enhanced in the capacity retention during cycling [188-190].

Spinel lithium manganese oxyfluorides: Spinel lithium manganese oxide LiMn2O4 has been studied widely as cathode materials due to its features of being non-toxic, inexpensive and environmentally-friendly material. Spinel LiMn2O4 can deliver 120 mAh/g capacity. Choi and Manthiram [182] reported the synthesized of spinel Li4Mn5O12-nFn oxyfluoride cathodes at 500 and 600°C by substituted F-ions from employing LiF for oxygen (O2) ions in the spinel Li4Mn5O12. XRD, electrochemical cycling, and chemical analysis measurements were carried out to characterize Li4Mn5O12-nFn and it has been found the useful of oxyfluoride cathodes to increase and enhance the capacity [181]. However, many different types of research discussed different ways to improve the Spinel lithium manganese oxyfluorides [182-184].

Metal fluorides: Conversion reactions start to attract attention recently, like fluorides, nitrides, sulfides and phosphides. Fluoride showed a great reversible cathode electrode that used to react with Li at 2.5 V and produced 800 mWh/g of energy density [191-193]. Poizot et al. [179] studied the mechanism of Li reactivity depend on involves the formation and decomposition of Li2O, escorting the oxidation and reduction of metal nanoparticles. However, in the past and due to metal fluorides characteristic such as insulating nature and apparent irreversibility in structural conversion [175], it has been ignored as rechargeable cathode materials for lithium batteries. Malini et al. [186] reported two ways to exploit the electrochemical efficiency of metal fluorides: first one, by mixing metal fluorides with conducting carbon materials to improve electrical conductivity and the second one, mechanical ball milling of metal fluoride to reduce the particle size [194- 197]. VF3 and TiF3 are also transition metal fluoride, they demonstrated their effectiveness with Li and generated as high as 500-600 mAh/g [175]. Amatucci et al. [187] studied the basic reactions of alkali nitrides with metal fluorides by prepared pre-lithiation agent, Li3N, to (FeF3, FeF2, and BiF3) metal fluorides. XRD, DMC, and TEM measurements were carried out to characterize the structure of the nanocomposite product and showed 243mAh/g initial charge capacity.

Carbon fluorides: Carbon fluorides consider as a great theoretically materials for high energy batteries because of its high theoretical potential, low equivalent weight and also most of them produce a very low self-discharge and extraordinary stability which pays high attention for carbon fluorides [177].

Two main groups are classified carbon fluorides: high temperature (HT) up to 300°C and room or low temperature (LT). HT fabricated graphite fluorides compounds consisting of two stages, (CF)n and (C2F)n respectively while LT fabricated fluorine-graphite intercalation compounds of CFx [198,199]. Various studies have been studied the lithium batteries contained graphite fluoride as cathode material [200-205]. Therefore, the specific energy densities of covalent graphite fluorides of the (C-F bond) reached 900 W h kg−1 [191]. Many researchers have been discussed graphite fluorides in their both categories: HT [193,194], and at LT [195-197]. Electrochemical performance of LT fluorinated graphite’s studied by Delabarre et al [198] where the compounds prepared at room temperature under fluorine gas, XRD, FT-IR, NMR and EPR measurements were carried out to characterize the electrochemical properties.

Fluorophosphates

New studies of cathodes materials for LIBs have been conducting about poly-anionic materials containing fluorine as part of their compounds, known as fluorophosphate. LiMPO4F and Li2MPO4F (M=Fe, Ni, Co) were the general formulas of fluorophosphate containing Li and crystallized materials that have been discovered as high-potential cathode materials [199], and thermal stability [71] for rechargeable lithium batteries. Three structured compounds have been widely studies, LiVPO4F, NaVPO4F, and LiFePO4F [63].

LiVPO4F: Lithium vanadium fluorophosphate it is a new class of cathode material that produced high voltage, long cycle life, excellent thermally stability, stable crystalline structure with good quality [201-204]. Carbothermal reduction method used mainly to prepare LiVPO4F, also it is synthesized through one or two-step solid reactions [201], chemical lithiation [206-210], sol–gel method [206] and postannealing [211-215].

Theoretical capacity (156 mAh/g) with potential equal to 4 V was reported by Saidi and Barker [150]. Gover et al. [210] prepared LiVPO4 as a cathode electrode in LIB using carbothermal reduction method, DSC, and electrochemical measurements were performed. The discharge capacity is about 140 mAhg-1 for the positive electrode with average discharge voltage around 4V [200]. Other research done by Zhang et al. [208] depended on prepared LiVPO4F/C nanosheets with homogeneous carbon coating by applying a hydrothermal approach and calcinations respectively. X-ray diffraction, SEM, TEM measurements and electrochemical tests have been performed and showed initial discharge capacity (143 mAh/g) with potential between (3.0-4.5 V) [216].

NaVPO4F: Sodium vanadium fluorophosphate characterized as a safer, economical and higher work potential comparing to other materials [209,210]. This includes Na3V2(PO4)2F3 with theoretical capacity equal to 128 mAh/g [170,211,212], NaVPO4F [209] and Na1.5VOPO4F0.5 [213]. Generally, NaVPO4F materials synthesis required VPO4 as the reaction intermediate phase, also it’s successfully synthesized by three strategies: first, solid-state which require high temperature, long time-consuming process and complex operation procedure [209,212], second ion exchange or third, hydrothermal approach that considered as a complicated system to collect the results of compounds after the procedures finished [209]. Na3V2(PO4)2F3 classified as the most important among fluorophosphate materials due to the high theoretical capacity 192 mAh/g and its flexibility to be used as a cathode in both Li-ion batteries and Na-ion batteries [214]. While Na1.5VOPO4F0.5 delivered through 3.6 and 4 V vs. Na+/Na theoretical capacity equal to 156 mAh/g [217-221].

LiFePO4F: Another option about olivine-type, tavorite-structured lithium-metal-fluorophosphate as cathode material achieved a good alternative for LIBs [216]. In lithium iron fluorophosphate, one Li+ can be cycled charge/discharge with the theoretical capacity of 153 mAh/g [222-225]. LiFePO4F was conducted by Ramesh et al. [218] as a new adequate material of fluorophosphate because of Li+ feature that migrates easily without any barriers. LiFePO4F prepared by solid-state routes and produced a reversible capacity approximately 145 mAh.g-1, with stable electrochemical cycling (40 cycles at room temperature and 55°C) [218]. In another study by Wang et al. [219] LiFePO4F prepared by a novel sol-gel process, EIS and galvanostatic were unambiguously performed and showed reversible capacity equal to 145 mAh.g-1, with outstanding cyclic performance and fast transfer of Li+ comparing to raw LiFePO4. Other various fluorophosphate materials have been studied including Li2FePO4F [218,226-230], Li2MPO4F (M=Co, Ni) [231-235], and Na3V2(PO4)2F3 Hybrid Ion Cathode [204,210].

Fluorosulfates

New material of cathode materials reported first by Sebastian et al. was LiMgSO4F, they presented the benefit of LiMSO4F (M=Mn, Fe, Co) for redox extraction/insertion of lithium involving MII/MIII oxidation states [236-240]. Then reported by the Sauvage [213], who prepared in the tavorite type structure LiFePO4OH. Investing the large electronegativity of sulfur and fluorine of LiMSO4F in produce high-voltage cathode materials such as LiFeSO4F transfer around 140 mAh/g with a high redox potential of 3.6 V [241-244]. Different Li metal fluorosulfate compounds (M=Mg, Mn, Fe, Co, Ni, Zn, Cu) were studied and shown a great electrochemistry and crystal chemistry counting on the type of metal ions and on the synthesis methods [227].

LiFeSO4F: Ionothermal was the first method to produce LiFeSO4F, it can be reused repeatedly for synthesizing although it is very high cost ionic liquid media [245-250]. LiFeSO4F has been prepared through various synthetic processes such as solid-state reaction [140], polymerassisted [228], tradition ceramic preparation [229], electronically conductive coatings, high-energy ball milling [251-255], and solvothermal reaction [224]. The recent synthesizing methods found that tavorite-type LiFeSO4F has low thermodynamic stability, unstable at temperatures above 350°C, because of that, producing single-phase of tavorite LiFeSO4F It is difficult to occur [103,256-259]. LiFeSO4F has a theoretical capacity of 148 mA h/g and produced an energy density (543 Wh/kg) as good as LiFePO4 (581 Wh/kg) [260-263]. Rosati et al. [264] reported the reversible capacity of approximately 85 mA h.g− 1 of LiFeSO4F which prepared in the triplite structure by the ceramic method at 300°C [265-269]. LiFeSO4F has numerous advantages as cathode material such as it can be prepared from plentiful FeSO4·nH2O precursor and synthesized at low temperature [270-276].

LiMSO4F (M=Co, Ni, Mn, Zn): Fluorosulfate polyanionic LiMSO4F electrode materials represent a wide family of a good combine of properties, especially, both electrochemical and safety issues. LiMSO4F showed a redox potential of 4.25, 4.95, and 5.25 V, respectively [277- 281]. Li2CoP2O7 is considered as a 4.9 V while Li2NiP2O7 is considered as a 5.4-V cathode [231,281-285]. In contrast with Fe2+/Fe3+ redox reaction, Ni2+/Ni3+, Mn2+/Mn3+ and CO2+/CO3+ redox reactions do not take place within the explored galvanostatic cycling potential window [286-291].

LiMSO4F (M=Co, Ni, Mn, Zn) synthesized at low temperature similarly to LiFeSO4F by using solid-state [291-296] and polymerassisted methods [297-300]. Other various fluorosulfates materials have been studied including Li(Fe1-xMx)SO4F (M=Mn, Zn), NaMSO4F (M=Fe, Co, Ni, Mn, Mg, Zn, Cu), NaMSO4F·2H2O (M=Fe, Co, Ni, Zn) [301-306].

Conclusion

Rechargeable batteries are considered of crucial role nowadays and become mandatory for most important electronics devices that most of the people use in communication, transportation, and monitoring. LIBs need an improvement in their characteristics for future applications where high energy and power density with long-term stability are required [307-310]. This paper summarized the characteristics of different types of cathode materials for LIBs and compare between their electrochemical performance such as specific capacity, thermal stability, synthesis method, and characterization techniques. The best cathode materials for LIBs should have high capacity, inexpensive, environment-friendly and charge/discharge long-term cycles for large and practical applications. However, as much as material exist, as well as challenges present, challenges of cathode materials include nanostructuring, switching from insertion to alloying and conversion materials, and improving cyclability and life types. Therefore, better understanding the mechanisms involved in charge-discharge of different cathode materials will certainly help scientists to overcome volume changes and hysteresis phenomena encountered with alloying and conversion materials. LIBs are expected to reach more commercial production in the future with better improvements in energy density and capacity.

Reference

  1. Zhang D, Popov BN, White RE (1998) Electrochemical investigation of CrO2.65 doped LiMn2O4 as a cathode material for lithium-ion batteries. Journal of Power Sources 76: 81-90.
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