硼酸锂包覆改性尖晶石锰酸锂的研究

尖晶石型锰酸锂由于具有优异的安全性能且成本低廉，成为锂离子电池正极材料的研究热点。然而，由于锰溶解所导致的循环性能衰退是锰酸锂发展的主要障碍。随着温度的升高，锰溶解加剧，因而电池在高温条件下衰退更加严重。将硼酸锂包覆于锰酸锂表面，可以抑制锰的溶解。通过高能球磨的方法可将硼酸锂均匀地包覆于锰酸锂表面。X射线衍射与电化学阻抗表征结果表明，硼酸锂不会引起锰酸锂结构的变化和电池阻抗的增加。通过对界面转移电阻的研究发现，硼酸锂包覆量超过2%（质量分数）时电池的极化会增加，因此将硼酸锂的最佳包覆量控制在2%。相比于未经包覆的锰酸锂，经包覆的锰酸锂不论是对锂半电池还是对石墨全电池均表现出优异的循环性能，尤其是在60 ℃下的循环性能大大改善。软包全电池体积能量密度达到308 W·h/L，1C循环200次后容量保持率可达到94.7%。通过硼酸锂包覆可有效抑制锰酸锂的锰溶解，改善其循环性能。

Study on modification of spinel lithium manganate coated with lithium borate

Spinel lithium manganate is a research hotspot of cathode materials for lithium?ion batteries because of its excellent safety performance and low cost.However，the degradation of cycle performance caused by manganese dissolution is the main obstacle to the development of lithium manganite.With the increase of temperature，the dissolution of manganese intensifies，so the deterioration of the battery is more serious under high temperature conditions.Coating lithium borate on the surface of lithium manganate can inhibit the dissolution of manganese.Lithium borate can be uniformly coated on the surface of lithium manganate by high?energy ball milling.X-ray diffraction and electrochemical impedance spectroscopy showed that lithium borate would not cause the change of lithium manganate structure and the increase of battery impedance.Through the study of interface transfer resistance，it was found that the polarization of the battery would increase when the coating amount of lithium borate exceeded 2%（mass fraction），so the optimal coating amount of lithium borate was controlled at 2%.Compared with uncoated lithium manganate，coated lithium manganate showed excellent cycle performance for both lithium half battery and graphite full battery.especially at 60 ℃，the cycle performance was greatly improved.The volume energy density of soft packed full battery reached 308 W·h/L，and the capacity retention rate could reach 94.7% after 200 cycles at 1C.The coating of lithium borate could effectively inhibit the dissolution of manganese in lithium manganate and improve its cycle performance.