Influence of separator wettability toward nonaqueous electrolyte was investigated in lithium-ion batteries using high-voltage LiNi0.5Mn1.5O4 cathode. A fluorinated ether of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) was introduced as a co-solvent into the control electrolyte and polyolefin separator wettability toward nonaqueous electrolyte was effectively enhanced. Even though conductivity of the electrolyte bulk decreased after HFE was introduced, ionic conductivity of the electrolyte-soaking separator increased due to the enhanced separator wettability. From cycling stability of the half cells using high-voltage LiNi0.5Mn1.5O4 cathode, all electrolytes containing 10%, 20% and 30% HFE have superiority to the control electrolyte, and the 20% HFE containing electrolyte is the optimal. Microscopical analysis revealed that oxidative decomposition of HFE-containing electrolyte on the LiNi0.5Mn1.5O4 cathode was suppressed effectively with the thinner cathode electrolyte interface than that in the control electrolyte. In Li4Ti5O12|LiNi0.5Mn1.5O4 full cells, the 20% HFE containing electrolyte exhibited the enhanced cycling stability and rate capability compared to the control of 1 mol L−1 LiPF6/propylene carbonate. This work here reveals the effect of fluorinated ether co-solvent on separator wettability and further the superior separator wettability is critical to the oxidation stability of the electrolyte in lithium-ion batteries using high-voltage cathode.
Liang Li,Tao Yang,Kaixiang Ren,Xinchun Song,Shilin Wu,Hai-Wen Li,Zhipeng Jiang,Mengjun Sun,Yongtao Li
Lithium-LiNi 0.5 Mn 1.5 O 4 (LNMO) batteries are considered promising candidates for high-energy–density storage due to their high operational voltage and low cost. However, existing electrolytes typically fail to balance high-voltage stability with electrode compatibility, thereby limiting their performance under practical conditions. In this study, we present a synergistic inhibition engineering in which silyl additives—triethylsilyl trifluoromethanesulfonate (TESOTf) and tris(trimethylsiloxy)boron (TMSB)—are incorporated into a conventional carbonate electrolyte, leading to stable cycling of Li-LNMO batteries at voltages as high as 4.9 V. Through in situ techniques and theoretical simulations, we demonstrate that TMSB immobilizes free PF 6 − ions in the electrolyte, while TESOTf preferentially consumes trace amounts of water, thereby shifting the hydrolysis reaction pathway of PF 6 − and reducing side reactions at the cathode. Electrochemical tests show that the addition of small quantities of TESOTf and TMSB significantly enhances the rate capability (10C for 85.2 mAh g −1 ), cycling stability (5C for 500 cycles), and high-temperature performance (60 °C, 5C for 300 cycles) of Li-LNMO cells. More importantly, a practical 3 Ah Li-LNMO pouch cell containing these additives demonstrated stable cycling under practical conditions (20 mg cm −2 , 20 μm Li, 2 g Ah −1 ), achieving an energy density exceeding 300 Wh kg −1 .
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