氧化锂基复合正极补锂材料的制备及对电池电化学性能的影响

Preparation of Lithium Oxide-Based Composite Cathode Lithium-Supplementing Material and Its Influence on the Electrochemical Performance of the Battery

摘要:

锂离子电池在首次充放电过程中，其负极表面形成的固态电解质界面（SEI）膜会消耗部分正极材料的活性锂，导致不可逆的容量损失，降低锂离子电池能量密度。为解决此问题，选用氧化锂作为牺牲锂盐以补偿锂离子电池的首次不可逆容量损失，提高电池容量和循环性能。通过将催化剂LiMnO₂、Li₂O和导电炭黑(SP)按一定质量比研磨混合，制备了Li₂O基正极补锂材料LiMnO₂/Li₂O/SP。为研究其补锂性能，选用磷酸铁锂作为正极，石墨作为负极，TCGG-Si作为电解液，组装了2032扣式全电池，通过充放电测试，研究了该正极补锂材料对电池电化学性能的影响。结果表明，当LiMnO₂/Li₂O/SP的质量分数分别为50%、45%和5%时，在 10 mA?g^-1的电流密度下充电至4.3 V，LiMnO₂/Li₂O/SP 复合材料的首次充电比容量可达526.5 mAh?g^-1，首次库伦效率为14.63%，其在首次充电过程中分解释放活性锂的过程是不可逆的，并在第4次后完全丧失容量，说明 Li₂O/LiMnO₂/SP复合材料可以作为补锂材料添加到正极材料中。将质量分数为3.6%的Li₂O/LiMnO₂/SP复合材料加入到磷酸铁锂半电池中，半电池的首次充电比容量为186.5 mAh·g^-1，相较 LiFePO₄比容量（166.8 mAh·g^-1）提高了19.7 mAh·g^-1，说明补锂剂已发挥作用，该部分多余的容量可用于形成石墨SEI膜。将Li₂O/LiMnO₂/SP添加到磷酸铁锂-石墨全电池体系中作为正极补锂剂，不仅可补偿石墨负极的首次不可逆容量损失，还可提高全电池的循环性能。全电池的首次可逆容量为158.2 mAh?g^-1，循环100次的可逆比容量为108.0 mAh?g^-1；相较于未添加情况，全电池首次充电比容量增加了12.9 mAh?g^-1，可逆比容量提高了11.6 mAh?g^-1，经100次循环后容量保持率提升了13.90%。

Abstract:

During the first charge-discharge cycle of lithium-ion batteries，the formation of solid electrolyte interface（SEI） films on the negative electrode surface consumes some of the active lithium in the cathode material，resulting in irreversible capacity loss and subsequently reducing the energy density of lithium-ion batteries. To address this issue，lithium oxide（Li₂O） is chosen as sacrificial lithium salt to compensate for the first irreversible capacity loss in lithium-ion batteries，aiming to improve the capacity and cycling performance of the battery. In order to investigate the prelithiation performance，the catalytic material LiMnO₂ is ground and mixed with Li₂O and conductive carbon black（SP）in certain mass ratios， iron phosphate（LiFePO₄ ）is selected as the cathode，graphite is selected as the negative electrode，TCGG-Si is selected as the electrolyte， and a 2032 coin cell is assembled. The effect of the prelithiation additive（LiMnO₂/Li₂O/SP）on the electrochemical performance of the battery is studied through charge-discharge tests. The results show that when the mass fractions of LiMnO₂，Li₂O，and SP are 50%，45%，and 5% respectively，the first charge capacity of the LiMnO₂/Li₂O/SP composite material can reach 526.5 mAh?g^-1 at a current density of 10 mA?g^-1 during charging to 4.3 V. The decomposition and release of active lithium in the first charge cycle are irreversible，with a Coulombic efficiency of only 14.63% in the first cycle. After the fourth cycle，the capacity is completely lost，indicating that LiMnO₂/Li₂O/SP composite material can be used as a prelithiation material added to the cathode material. When the composite material LiMnO₂/Li₂O/SP with a mass fraction of 3.6% is added to the iron phosphate half-cell，the first cycle charge capacity of the half-cell is 186.5 mAh·g^-1. Compared to LiFePO₄（166.8 mAh·g^-1），the capacity is increased by 19.7 mAh·g^-1，indicating that the prelithiation agent has played a role，and this excess capacity can be used for the formation of graphite SEI film. Adding LiMnO₂/Li₂O/SP to the iron phosphate-graphite full battery system as a cathode prelithiation agent not only compensates for the first-cycle irreversible capacity loss of the graphite negative electrode but also improves the cycling performance of the full battery. The first reversible capacity of the full battery is 158.2 mAh?g^-1，and the reversible capacity after 100 cycles is 108.0 mAh?g^-1 . Compared to the situation without the additive，the first charge capacity of the full battery increases by 12.9 mAh?g^-1，and the reversible capacity increases by 11.6 mAh?g^-1 after 100 cycles，with a capacity retention rate increased by 13.90%.