Highly safe lithium-ion batteries (LIBs) are required for large-scale applications such as electrical vehicles and energy storage systems. A highly stable cathode is essential for the development of safe LIBs. LiFePO₄ is one of the most stable cathodes because of its stable structure and strong bonding between P and O. However, it has a lower energy density than lithium transition metal oxides. To investigate the high energy density of phosphate materials, vanadium phosphates were investigated. Vanadium enables multiple redox reactions as well as high redox potentials. LiVPO₄O has two redox reactions (V⁵⁺/V⁴⁺/V³⁺) but low electrochemical activity. In this study, LiVPO₄O is doped with fluorine to improve its electrochemical activity and increase its operational redox potential. With increasing fluorine content in LiVPO₄O_1-xF_x, the local vanadium structure changed as the vanadium oxidation state changed. In addition, the operating potential increased with increasing fluorine content. Thus, it was confirmed that fluorine doping leads to a strong inductive effect and high operating voltage, which helps improve the energy density of the cathode materials.

High performance lithium-ion batteries (LIBs) have attracted considerable attention as essential energy sources for high-technology electrical devices such as electrical vehicles, unmanned drones, uninterruptible power supply, and artificial intelligence robots because of their high energy density (150-250 Wh/kg), long lifetime (> 500 cycles), low toxicity, and low memory effects. Of the high-performance LIB components, cathode materials have a significant effect on the capacity, lifetime, energy density, power density, and operating conditions of high-performance LIBs. This is because cathode materials have limitations with respect to a lower specific capacity and cycling stability as compared to anode materials. In addition, cathode materials present difficulties when used with LIBs in electric vehicles because of their poor rate performance. Therefore, this study summarizes the structural and electrochemical properties of cathode materials for LIBs used in electric vehicles. In addition, we consider unique strategies to improve their structural and electrochemical properties.

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• Estimation of Representative Mechanical Property of Porous Electrode for Secondary Batteries with Homogenization Method
  Changmin Pyo, Jaewoong Kim
  Journal of the Korean Society of Manufacturing Process Engineers.2022; 21(9): 85.     CrossRef

Layered LiNi_0.83Co_0.11Mn_0.06O₂ cathode materials single- and dual-doped by the rare-earth elements Ce and Nd are successfully fabricated by using a coprecipitation-assisted solid-phase method. For comparison purposes, nondoping pristine LiNi_0.83Co_0.11Mn_0.06O₂ cathode material is also prepared using the same method. The crystal structure, morphology, and electrochemical performances are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) mapping, and electrochemical techniques. The XRD data demonstrates that all prepared samples maintain a typical α-NaFeO₂-layered structure with the R-3m space group, and that the doped samples with Ce and/or Nd have lower cation mixing than that of pristine samples without doping. The results of SEM and EDS show that doped elements are uniformly distributed in all samples. The electrochemical performances of all doped samples are better than those of pristine samples without doping. In addition, the Ce/Nd dualdoped cathode material shows the best cycling performance and the least capacity loss. At a 10 C-rate, the electrodes of Ce/Nd dual-doped cathode material exhibit good capacity retention of 72.7, 58.5, and 45.2% after 100, 200, and 300 cycles, respectively, compared to those of pristine samples without doping (24.4, 11.1, and 8.0%).

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• Numerical approach for lithium-ion battery performance considering various cathode active material composition for electric vehicles using 1D simulation
  Heewon Choi, Nam-gyu Lim, Seong Jun Lee, Jungsoo Park
  Journal of Mechanical Science and Technology.2021; 35(6): 2697.     CrossRef
• Synthesis of CeVO4-V2O5 nanowires by cation-exchange method for high-performance lithium-ion battery electrode
  Xueliu Xu, Shiying Chang, Taofang Zeng, Yidan Luo, Dong Fang, Ming Xie, Jianhong Yi
  Journal of Alloys and Compounds.2021; 887: 161237.     CrossRef

Lithium silicate, a lithium-ion conducting ceramic, is coated on a layer-structured lithium nickel manganese oxide (LiNi_0.7Mn_0.3O₂). Residual lithium compounds (Li₂CO₃ and LiOH) on the surface of the cathode material and SiO₂ derived from tetraethylorthosilicate are used as lithium and silicon sources, respectively. Powder X-ray diffraction and scanning electron microscopy with energy-dispersive spectroscopy analyses show that lithium silicate is coated uniformly on the cathode particles. Charge and discharge tests of the samples show that the coating can enhance the rate capability and cycle life performance. The improvements are attributed to the reduced interfacial resistance originating from suppression of solid-electrolyte interface (SEI) formation and dissolution of Ni and Mn due to the coating. An X-ray photoelectron spectroscopy study of the cycled electrodes shows that nickel oxide and manganese oxide particles are formed on the surface of the electrode and that greater decomposition of the electrolyte occurs for the bare sample, which confirms the assumption that SEI formation and Ni and Mn dissolution can be reduced using the coating process.

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• Artificial cathode-electrolyte interphases on nickel-rich cathode materials modified by silyl functional group
  Hye Ji Song, Seol Heui Jang, Juhyeon Ahn, Si Hyoung Oh, Taeeun Yim
  Journal of Power Sources.2019; 416: 1.     CrossRef

Ni_1/3Co_1/3Mn_1/3(OH)₂ powders have been synthesized in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH using NH₄OH as a chelating agent. The co-precipitation temperature is varied in the range of 30-80°C. Calcination of the prepared precursors with Li₂CO₃ for 8 h at 1000°C in air results in Li Ni_1/3Co_1/3Mn_1/3O₂ powders. Two kinds of obtained powders have been characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analyzer, and tap density measurements. The co-precipitation temperature does not differentiate the XRD patterns of precursors as well as their final powders. Precursor powders are spherical and dense, consisting of numerous acicular or flaky primary particles. The precursors obtained at 70 and 80°C possess bigger primary particles having more irregular shapes than those at lower temperatures. This is related to the lower tap density measured for the former. The final powders show a similar tendency in terms of primary particle shape and tap density. Electrochemical characterization shows that the initial charge/discharge capacities and cycle life of final powders from the precursors obtained at 70 and 80°C are inferior to those at 50°C. It is concluded that the optimum co-precipitation temperature is around 50°C.

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• A kinetic descriptor to optimize Co-precipitation of Nickel-rich cathode precursors for Lithium-ion batteries
  Seon Hwa Lee, Ki Young Kwon, Byeong Kil Choi, Hyun Deog Yoo
  Journal of Electroanalytical Chemistry.2022; 924: 116828.     CrossRef

As precursors of cathode materials for lithium ion batteries, Ni_1/3Co_1/3Mn_1/3(OH)₂ powders are prepared in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH in the presence of NH4OH in air or nitrogen ambient. Calcination of the precursors with Li₂CO₃ for 8 h at 1,000°C in air produces dense spherical cathode materials. The precursors and final powders are characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analysis, tap density measurement, and thermal gravimetric analysis. The precursor powders obtained in air or nitrogen ambient show XRD patterns identified as Ni_1/3Co_1/3Mn_1/3(OH)₂. Regardless of the atmosphere, the final powders exhibit the XRD patterns of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM). The precursor powders obtained in air have larger particle size and lower tap density than those obtained in nitrogen ambient. NCM powders show similar tendencies in terms of particle size and tap density. Electrochemical characterization is performed after fabricating a coin cell using NCM as the cathode and Li metal as the anode. The NCM powders from the precursors obtained in air and those from the precursors obtained in nitrogen have similar initial charge/discharge capacities and cycle life. In conclusion, the powders co-precipitated in air can be utilized as precursor materials, replacing those synthesized in the presence of nitrogen injection, which is the usual industrial practice.

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• Stabilization of High Nickel Cathode Materials with Core-Shell Structure via Co-precipitation Method
  Minjeong Kim, Soonhyun Hong, Heongkwon Jeon, Jahun Koo, Heesang Lee, Gyuseok Choi, Chunjoong Kim
  Korean Journal of Materials Research.2022; 32(4): 216.     CrossRef
• Spherical agglomeration of nickel-manganese-cobalt hydroxide in turbulent Batchelor vortex flow
  Xiaotong Sun, Jinsoo Kim, Woo-Sik Kim
  Chemical Engineering Journal.2021; 421: 129924.     CrossRef
• Design strategies for development of nickel-rich ternary lithium-ion battery
  Kyu Hwan Choi, Xuyan Liu, Xiaohong Ding, Qiang Li
  Ionics.2020; 26(3): 1063.     CrossRef
• Effect of Single and Dual Doping of Rare Earth Metal Ce and Nd Elements on Electrochemical Properties of LiNi_0.83 Co_0.11Mn_0.06O₂ Cathode Lithium-ion Battery Material
  Yoo-Young Kim, Jong-Keun Ha, Kwon-Koo Cho
  Journal of Korean Powder Metallurgy Institute.2019; 26(1): 49.     CrossRef
• Effects of Precursor Co-Precipitation Temperature on the Properties of LiNi1/3Co1/3Mn1/3O2 Powders
  Woonghee Choi, Chan Hyoung Kang
  Journal of Korean Powder Metallurgy Institute.2016; 23(4): 287.     CrossRef

The electrochemical properties of cells assembled with the LiNiO₂ (LNO) recycled from cathode materials of waste lithium secondary batteries (Li[Ni,Co,Mn]O₂), were evaluated in this study. The leaching, neutralization and solvent extraction process were applied to produce high-purity NiSO₄ solution from waste lithium secondary batteries. High-purity NiO powder was then fabricated by the heat-treatment and mixing of the NiSO₄ solution and H₂C₂O₄. Finally, LiNiO₂ as a cathode material for lithium ion secondary batteries was synthesized by heat treatment and mixing of the NiO and Li₂CO₃ powders. We assembled the cells using the LiNiO₂ powders and evaluated the electrochemical properties. Subsequently, we evaluated the recycling possibility of the cathode materials for waste lithium secondary battery using the processes applied in this work.

FeS₂ has been widely used for cathode materials in thermal battery because of its high stability and current capability at high operation temperature. Salts such as a LiCl-KCl were added as a binder for improving electrical performance and formability of FeS₂ cathode powder. In this study, the effects of the addition of Li₂O in LiCl-KCl binder on the formability of FeS₂ powder compact were investigated. With the increasing amount of Li₂O addition to LiCl-KCl binder salts, the strength of the pressed compacts increased considerably when the powder mixture were pre-heat-treated above 350°C. The heat-treatment resulted in promoting the coating coverage of FeS₂ particles by the salts as Li₂O was added. The observed coating as Li₂O addition might be attributed to the enhanced wettability of the salt rather than its reduced melting temperature. The high strength of compacts by the Li₂O addition and pre-heat-treatment could improve the formability of FeS₂ raw materials.

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• Effects of Particle Size and Binder Phase Addition on Formability of Li-Si Alloy Powder for Thermal Battery Anode
  Sung-Soo Ryu, Hui-Sik Kim, Seongwon Kim, Hyung-Tae Kim, Hae-Won Cheong, Sung-Min Lee
  Journal of Korean Powder Metallurgy Institute.2014; 21(5): 331.     CrossRef

Cathode materials and their precursors are prepared with transition metal solutions recycled from the the waste lithium-ion batteries containing NCM (nickel-cobalt-manganese) cathodes by a H₂ and C-reduction process. The recycled transition metal sulfate solutions are used in a co-precipitation process in a CSTR reactor to obtain the transition metal hydroxide. The NCM cathode materials (Ni:Mn:Co=5:3:2) are prepared from the transition metal hydroxide by calcining with lithium carbonate. X-ray diffraction and scanning electron microscopy analyses show that the cathode material has a layered structure and particle size of about 10 μm. The cathode materials also exhibited a capacity of about 160 mAh/g with a retention rate of 93~96% after 100 cycles.