|Patent Cooperation Treaty||Published Application||WO 2023/091715||05/25/2023||2022-856|
Chemical and electrochemical instability between lithium (Li) metal anode and the liquid Li-ion electrolytes result in mossy Li deposit causing severe volume expansion, low Li deposition-stripping efficieency, formation of dead Li and fast depletion of electrolyte. All of these lead to short cycle life and safety concerns. Current strategies to implement Li metal anode use solid-state Li-ion electrolytes including inorganic or organic Li-ion conductors. The disadvantages of solid-state electrolytes include poor producibility, poor stability and low conductivity. The other strategy to implement Li metal anode is to use a new type of liquid electrolytes named localized high concentration electrolytes (LHCEs). The disadvantage of the LHCEs is the expensive co-solvents which are also not readily available.
Prof. Juchen Guo and his research team at UCR have discovered the use of phosphorous pentoxide (P2O5) as an additive to modify the conventional carbonate solvents-based lithium hexa-fluoro-phosphate (LiPF6) electrolytes. P2O5 as an additive, stabilizes the electrolyte/electrode interphases by mitigating the hydrogen fluoride (HF) induced side reactions. The P2O5 additive not only improves th Li metal deposition morphology for a denser deposition layer but also alleviates the transition metal dissolution and NMC622 particle cracking problems.
Mechanisms of P2O5 additive: (I) Decomposition of LiPF6 electrolyte induced by H2O to produce HF and difluorophosphoric acid (HPO2F2); (II) HF scavenging reaction of P2O5; (III) Reactions of products from (II) with P2O5 to generate new species beneficial to the Li metal anode.
Cycling performance of 0.4 Ah Li||NMC622 pouch cell (50 µm Li anode and 3 mAh/cm2 cathode areal capacity) in lean electrolyte (electrolyte to capacity ratio = 3 g per Ah) at C/10 charging and C/3 discharging.
Rechargeable lithium-ion batteries
Inventors have developed and demonstrated a proof-of-concept, rechargeable Li-metal batteries using this new electrolyte.