Study On The Destruction Mechanism Of Li/MCMB Battery By Transition Metal Ion

Lithium-ion batteries have become a potential energy source for electric vehicles,hybrid vehicles,and grid energy storage due to their long service life and large energy density.However,the capacity attenuation has seriously troubled its develop ment.The study found that the dissolution of the transition metal ions from the cathode material will seriously damage the battery performance,especially when the battery is stored or cycled under extreme conditions such as high voltage and high temperat ure,the dissolved transition metal will cause the battery capacity to decline sharply.Therefore,revealing the mechanism of transition metal ions impairing battery capacity and finding corresponding solutions have become the key points of current research.The main research contents of this thesis are as follows:1.Study on the destruction mechanism of single transition metal ion to battery performance.First,the solid-phase method is used to synthesize manganese bisoxalate borate（Mn（BOB）₂）,cobalt bisoxalate borate（Co（BOB）₂）,and nickel oxalate borate（Ni（BOB）₂）,using these three salts as a source of transition metal ions.Secondly,using LiBOB-sulfolane（SL）/diethyl carbonate（DEC）electrolyte as the reference electrolyte,using electrolyte systems of 0.7 M LiBOB-SL/DEC+50 ppm Mn²⁺,0.7 M LiBOB-SL/DEC+50 ppm Co²⁺and 0.7 M LiBOB-SL/DEC+50 ppm Ni²⁺to study the effects of a single transition metal ion in LiBOB-based electrolyte on the performance of lithium-ion batteries.The results show that in Li/MCMB（mesophase carbon microsphere）batteries,the 0.7 M LiBOB-SL/DEC+50 ppm Mn²⁺system is more likely to damage the cycling performance of the battery,while the 0.7M LiBOB-SL/DEC+50 ppm Ni²⁺system has relatively good rate performance,this is mainly due to Ni²⁺increasing the battery capacity,and Li⁺and Ni²⁺will first be exchanged on the surface of MCMB.The thickness of the SEI film formed by different electrolyte systems during the cycle(Mn²⁺>Co²⁺>Ni²⁺)decreases in turn,and the deposition of transition metal ions on the surface of the negative electrode will cause the continuous thickening of the SEI film and the increase the battery impedance.2.Research on the destruction mechanism of various transition metal ions on battery performance.Using LiBOB-SL/DEC electrolyte as reference electrolyte,0.7M LiBOB-SL/DEC 50 ppm Mn²⁺+Ni²⁺+Co²⁺（each 16.7 ppm）system to study the effects of various transition metal ions in LiBOB-based electrolyte on the performance of lithium-ion batteries.The results show that the catalytic decomposition of transition metal ions on the electrolyte causes more decomposition products deposited on the SEI film,resulting in the continuous growth of the interface film,consuming lithium ions while hindering the deintercalation of lithium ions in the material,and ultimately causing rapid decay of capacity.And the order of transition metal ions entering the surface of MCMB is Ni²⁺,Co²⁺,Mn²⁺,which is mainly due to the difference in ion radius and electrochemical adsorption.In summary,the destruction mechanisms of single and multiple transition metal ions on battery performance are studied,and the mechanism of transition metal ions damaging the battery capacity is summarized from the perspective of the interface film of the negative electrode material.It provides a new idea for inhibiting the destruction of the battery performance by the transition metal ions in the electrolyte.