摘要
The LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(Ni-rich NCM)cathode materials suffer from electrochemical performance degradation upon cycling due to detrimental cathode interface reactions and irreversible surface phase transition when operating at a high voltage(≥4.5 V).Herein,a traditional carbonate electrolyte with lithium difluoro(oxalato)borate(Li DFOB)and tris(trimethylsilyl)phosphate(TMSP)as dual additives that can preferentially oxidize and decompose to form a stable F,B and Si-rich cathode-electrolyte interphase(CEI)that effectively inhibits continual electrolyte decomposition,transition metal dissolves,surface phase transition and gas generation.In addition,TMSP also removes trace H_(2)O/HF in the electrolyte to increase the electrolyte stability.Owing to the synergistic effect of Li DFOB and TMSP,the Li/LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) half cells exhibit the capacity retention 76.3%after 500 cycles at a super high voltage of 4.7 V,the graphite/LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)full cells exhibit high capacity retention of 82.8%after 500 cycles at 4.5 V,and Li/LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)pouch cells exhibit high capacity retention 94%after 200 cycles at 4.5 V.This work is expected to provide an effective electrolyte optimizing strategy compatible with high energy density lithium-ion battery manufacturing systems.
为进一步提高高镍三元放电比容量,将充电截止电压从4.3 V提高到4.5/4.7 V,放电比容量可从200 mAh g^(-1)提高到230 mAh g^(-1),这对提高能量密度是非常有利的,但同时会导致界面稳定性进一步降低.本文在商业电解液(1 mol L^(-1)LiPF_(6)/EC:DEC=1:1,体积比)基础上,加入双添加剂二氟草酸硼酸锂(LiDFOB)和三甲基硅基磷酸酯(TMSP),一方面形成富含F,B,Si等元素的无机组分界面膜增加高电压下界面稳定性;另一方面,TMSP中的Si-O键具有清除电解液中高腐蚀性HF的作用,以此增加电解液的稳定性.在成膜和除HF的双重作用下,抑制了4.5/4.7 V高截止电压下的界面反应、过渡金属溶出、表面相变及产气.组装的LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)/Li电池在4.5 V下具有800圈的循环寿命,在4.7 V下具有500圈的循环寿命.
基金
supported by the National Natural Science Foundation of China(52172201,51732005,51902118,and 52102249)
China Postdoctoral Science Foundation(2019M662609 and 2020T130217)。
