High-Temperature Storage Deterioration Mechanism of Cylindrical 21700-Type Batteries Using Ni-Rich Cathodes under Different SOCs

Abstract

The safety and energy density of lithium-ion batteries (LIBs) are important concerns. The use of high-capacity cathode materials, such as Ni-rich cathodes, can greatly improve the energy density of LIBs, but it also brings some safety hazards. Cylindrical 21700-type batteries using Ni-rich cathodes were employed here to investigate their high-temperature storage deterioration mechanism under different states of charge (SOCs). Electrolyte decomposition was identified as the main problem. It can be worsened by elevated storage temperatures and battery SOCs, with the latter having a more significant influence. Specifically, the decomposition of the LiPF 6 solute and the carbonate solvent will induce hydrofluoric acid (HF) formation and solid−electrolyte interphase (SEI) film regeneration, respectively. HF erosion will aggravate the dissolution of transition metal ions and structural degradation of cathode materials, while the destruction/regeneration of SEI films will consume active lithium and hinder Li + diffusion at the anode side. Besides, the self-discharge behavior will also enlarge the graphite layer spacing, thus decreasing the graphitization degree of graphite anodes and causing anode failure. These findings will aid in the development of strategies for improving the safety of LIBs with high energy density.

A Review of Degradation Mechanisms and Recent Achievements for Ni‐Rich Cathode‐Based Li‐Ion Batteries

“…[ 61 ] Numerous studies have proven that thermodynamic instability can develop at higher temperatures, also under storage conditions without cycling. [ 62 ] As shown in Figure 15 a, a capacity decay upon storage is strongly temperature‐dependent. In postmortem analysis, it is noted that storage at high temperatures leads to a loss of electric contact between the electrodes and current collectors.…”

“…a) Reproduced with permission. [ 62 ] Copyright 2021, American Chemical Society. b) Reproduced with permission.…”

Elucidating the Effect of the Dopant Ionic Radius on the Structure and Electrochemical Performance of Ni-Rich Layered Oxides for Lithium-Ion Batteries

“…One of the high-priority criteria for a cathode used in an electric vehicle is its safety property, which can be evaluated by the thermal stability of the oxide materials . Here, the thermal stability of the Ni-rich cathodes is investigated using high-temperature XRD, which is an effective technique to probe the bulk structural change during thermal decomposition .…”

Facile and Powerful In Situ Polymerization Strategy for Sulfur-Based All-Solid Polymer Electrolytes in Lithium Batteries

“…It is well known that the serious capacity degradation of lithium batteries at high temperatures is a long-standing issue. High temperatures accelerate the occurrence of parasitic side reactions. − Interestingly, the Li/CPE/LiFePO 4 battery at 55 °C presented improved capacity retention without detectable degradation over 100 cycles (Figure f) due to the high-temperature electrochemical stability of the obtained P­(EGDMA-EDT)-based electrolyte.…”