posted on 2024-05-14, 13:49authored byChao Zhang, Caixia Li, Kai Zhang, Shenghao Zhang, Jingwen Liu, Minghui Wang, Lei Wang
Flame retardants could improve the safety properties
of lithium
batteries (LBs) with the sacrifice of electrochemical performance
due to parasitic reactions. To concur with this, we designed thermal-response
clothes for hexachlorophosphazene (HCP) additives by the microcapsule
technique with urea-formaldehyde (UF) resin as the shell. HCP@UF combines
with polyacrylonitrile (PAN) by hydrogen bonds successfully to form
PAN–HCP@UF as the flame-retardant solid polymer electrolyte.
The hydrogen bonds ensure excellent mechanical properties of the polymer
electrolyte. The multiscale free radical-annihilating agent HCP effectively
eliminates hydrogen free radicals of electrolytes under high temperature,
showing excellent flame retardation. During the operation of the battery,
functional groups on the UF resin act as active sites to promote the
migration of lithium ions, while the internal HCP is protected from
electrochemical reaction. With 25% HCP@UF addition, the limiting oxygen
index of the PAN–HCP@UF increases to 28% and the Li+ transfer number up to 0.80. By UF protection, the initial capacity
retention rate of the Li||LFP battery that assembles with PAN–HCP@UF
is 88.8% after 500 cycles at 0.5 C. Thus, the microcapsule-encapsulated
approach is deemed to provide an innovative strategy to prepare high-safety
solid-state LB with a stable long cycle life.