Study On The Effect Of Electrolyte Additives On The Electrochemical Performance Of LiNi_0.8Co_0.15Al_0.05O₂ Ternary Cathode For Lithium-Ion Batteries

Due to the shortage of fossil energy and the increasingly serious environmental problems,lithium-ion batteries have received widespread attention because of high energy density,high power density,wide operating temperature,low self-discharge capability,no memory effect,environmental friendliness and other advantages,especially in 3C electronics,electric vehicles and military industry.In order to further improve their energy density,it is important to develop new cathode materials and more efficient electrolyte systems.Compared to traditional cathodes such as Li Co O₂,Li Mn₂O₄and Li Fe PO₄,LiNi_0.8Co_0.15Al_0.05O₂（NCA）has the advantages of higher theoretical specific capacity,higher operating voltage and lower cost.However,the interphase side reactions result in poor structural stability of NCA.As a result,NCA suffers from faster capacity degradation and worse rate performance.Compared to the modification of NCA material by morphological and structural reorganisation,ion doping and surface coating,the optimization of lithium-ion batteries with NCA cathode by adding electrolyte additives has the advantages of simple operation,efficiency and low cost.In this paper,the electrochemical performance of NCA is enhanced by adding additives to the electrolyte.The electrochemical performance of NCA cathode was investigated using tris（trimethylsilyl）borate（TMSB）as an electrolyte additive.The results show that the oxidation potential of TMSB is lower than that of ethylene carbonate（EC）,dimethyl carbonate（DMC）and methyl ethyl carbonate（EMC）,and the oxidation decomposition products of TMSB are involved in the formation of the cathode electrolyte interface（CEI）film.Trimethylsilyl（TMS-）can react with HF to form trimethylsilyl fluoride（TMSF）and dimethyldifluorosilane（DMDFS）,thus reducing the leaching of transition metals from the NCA cathode by HF.At the same time,the addition of TMSB results in the formation of a thin and uniform interfacial film on the NCA,which contributes to the structural stability of the NCA and inhibits the decomposition of the electrolyte.As a result,the NCA cathode in the electrolyte containing 1%TMSB shows higher cycling stability and rate performance,and has lower impedance.Even after 200 cycles at 1 C,the cell still provides a capacity retention of 86.0%compared to 67.2%for the cathode in the baseline electrolyte.The electrochemical performance of NCA cathode was investigated using tris（2,2,2-trifluoroethyl）borate（TTFEB）as an electrolyte additive.The results show that TTFEB forms a Li F-rich CEI,which not only improves Li⁺transfer for uniform Li deposition but also serves to protect the morphological structure of the NCA cathode.Thus,2%TTFEB suppresses the capacity degradation of Li||NCA cells when cycled at 2 C.After 200 cycles,there is still 144 mAh g^-1of the discharge capacity,a loss of only 35.2 mAh g^-1compared to 69.1 mAh g^-1of the cell without TTFEB.The electrochemical performance of the NCA cathode and Li anode was investigated using 4-aminobenzoic acid（4-ABA）as a multifunctional electrolyte additive.The results of theoretical calculations show that 4-ABA weakens the interaction between Li⁺and solvent molecules so that Li⁺is easier to desolvate.Moreover,4-ABA also has a higher oxidation activity than the electrolyte solvents,and is more likely to form a thin and uniform CEI layer,which inhibits electrolyte corrosion on the NCA cathode and reduces the dissolution of the transition metals Ni and Co.The results of electrochemical performance tests show that the addition of 4-ABA increases the Li⁺transference number,electron gain/loss ability and ionic conductivity of the system,and also extends the cycle life of Li||Li symmetric cells from<400 h to over 600 h.4-ABA also improves the cycling performance of Li||NCA cells.For the cell containing 4-ABA,the discharge capacity remains 164.9 mAh g^-1after 200 cycles at 1 C,while the cell using the baseline electrolyte has a discharge capacity of only 126.3 mAh g^-1.