一种共溶性磷系阻燃电解液研究

Study on the soluble phosphorus flame retardant electrolyte Co-solvent

选用含1 mol/L LiPF_6/EC+DEC(质量比1∶1)传统二元电解液作为标准电解液,与具有较优性质的磷系阻燃添加剂磷酸三甲酯(TMP)按照不同比例共混,合成制备系列阻燃电解液新体系。对该系列阻燃电解液新体系进行自熄时间、热力学稳定性、离子电导率等测试,得到兼具安全性和电化学性能的最优体系1 mol/L Li PF6/EC+DEC(质量比1∶1)/35%TMP(质量分数)。对该体系进行了电化学稳定窗口测试,并且匹配LiNi_(1/3)Mn_(1/3)Co_(1/3)O_2正极材料、Li_4Ti_5O_(12)负极材料进行恒流充放电测试。结果表明,与标准电解液相比,1mol/L LiPF_6/EC+DEC(质量比1∶1)/35%TMP(质量分数)在保证电池安全性的同时,匹配正负极材料都具有良好的循环性能,具有广阔的应用前景。

The present paper is engaged in a study for a kind of innovative soluble phosphorus flame retardant electrolyte co-solvent. For this research purpose,we have first of all chosen a kind of conventional binary electrolyte which contains 1 mol / L LiPF_6/EC ＋ DEC（ 1 ∶ 1 wt.） as a standard electrolyte,trying to reconstruct a new series of nonflammable electrolytes by adding trimethylphosphate（ TMP） to the base electrolyte in different ratios.And,then,we have gained the 1 mol / L LiPF_6/ EC ＋ DEC（ 1 ∶ 1wt.） /35 wt. % TMP and taken it as the optimized samples by evaluating the average SET（ Self Extinguishing Time） and its thermal stability. Furthermore,we have made measurements and tests over the 35% TMP electrolyte for its ion conductivity,the electrochemical stability window and the compatibility with the raw material for the LiNi_（1 /3）Mn_（1 /3）Co_（1/3）O_2 cathode and Li_4Ti_5O_（12） anode. As a result,we have successfully improved the conductivity of TMP electrolyte at different concentrations of the gradients as compared with the base electrolyte. For example,we have managed to make the ion conductivity of TMP electrolyte 1 mol / L Li PF6/ EC ＋ DEC（ 1 ∶ 1） /in 35% go up by 8. 26 m S/cm at 25 ℃ when we were testing the base electrolyte as 4. 99 m S / cm. Although the electrochemical stability window of the 35% TMP electrolyte seems to be narrower,it can still satisfy the charging and discharging platform demands of the cathode NMC and anode LTO. Besides,the electrochemical NMC / Li half-cells with 35% TMP electrolyte also exhibit their considerable capacity,high coulombian efficiency and nice cycle stability as compared with the base electrolyte. Furthermore,the LTO / Li half-cells also display the first cycle decay though its detrimental effect seems rather weak on the cycling stability. However,LTO / NMC full button cell with the 35 wt. %TMP electrolyte shows better charge-and-discharge tendency,better cycling stabilities and higher capacity retention. Through the42 th cycle,it can also be found that the LTO / NMC full button cell with the 35 wt. % TMP electrolyte may remain capable of110. 7 m Ah / g,that is,12. 6 m Ah / g higher than the full button cells of LTO / NMC with base electrolyte. Therefore,it is just for the aforementioned advantages and some other ones that TMP has been made a promising candidate to the flame-retarding co-solvent,which can combine the efficient flame retardancy with the nice electrochemical performance for safer lithium ion batteries.