Li-free Cathode Materials for High Energy Density Lithium Batteries

Lithium-ion batteries (LIBs) have a superior energy density compared to other rechargeable batteries. However, commercial LIBs have challenges to exceed the target of 300 Wh kg−1. Exploring energy storage devices with energy densities higher than 300 Wh kg−1 is highly desired for long-range electric vehicles, advanced portable electronic devices, and many other applications. Because of the renaissance in the study of lithium-metal anodes and the rapid development of solid-state electrolytes, revisiting Li-free cathodes with high energy densities is necessary. Herein, we have screened several of the most promising cathode materials (e.g., S, FeF3, CuF2, FeS2, and MnO2) based on thermodynamic calculations. They have the potential to offer energy densities of 1,000–1,600 Wh kg−1 and 1,500–2,200 Wh L−1 at the cell level. Recent advances regarding their application in rechargeable lithium batteries are reviewed. Their intrinsic limitations, including low practical specific capacity, high voltage hysteresis, and short cycling life, are discussed, and the corresponding solutions are suggested. All of these challenges could be overcome. Therefore, low-cost Li-free cathode materials with a conversion reaction mechanism are competitive and promising components in rechargeable lithium batteries for next-generation high energy density devices. Conversion-type cathode materials, such as transition metal halides, chalcogenides, and oxides, demonstrate high operational voltages and high specific capacities, offering high energy densities for rechargeable lithium-metal batteries. In this review, a series of low-cost, environmentally benign, and high energy density Li-free cathode materials are selected based on thermodynamic calculations. Coupled with Li/C anodes, these cathodes (e.g., S, FeF3, CuF2, FeS2, and MnO2) have the potential to offer energy densities of 1,000–1,600 Wh kg−1 and 1,500–2,200 Wh L−1 at the cell level. Their main challenges, including capacity fading, high voltage hysteresis, large volume change, and parasitic reactions with electrolytes, are discussed. Strategies to circumvent these issues based on the state-of-the-art technologies are summarized. It seems that all of these challenges are able to be solved. We believe that with the development of practical Li-metal-based anodes and solid-state electrolytes, conversion-type cathodes have a promising future for the next-generation high energy density energy storage devices. Conversion-type cathode materials, such as transition metal halides, chalcogenides, and oxides, demonstrate high operational voltages and high specific capacities, offering high energy densities for rechargeable lithium-metal batteries. In this review, a series of low-cost, environmentally benign, and high energy density Li-free cathode materials are selected based on thermodynamic calculations. Coupled with Li/C anodes, these cathodes (e.g., S, FeF3, CuF2, FeS2, and MnO2) have the potential to offer energy densities of 1,000–1,600 Wh kg−1 and 1,500–2,200 Wh L−1 at the cell level. Their main challenges, including capacity fading, high voltage hysteresis, large volume change, and parasitic reactions with electrolytes, are discussed. Strategies to circumvent these issues based on the state-of-the-art technologies are summarized. It seems that all of these challenges are able to be solved. We believe that with the development of practical Li-metal-based anodes and solid-state electrolytes, conversion-type cathodes have a promising future for the next-generation high energy density energy storage devices.