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基于LLZTO@Ag復合層負極改性的硫化物全固態鋰電池及其性能

Novel LLZTO@Ag composite layer for the stable anode of sulfide all-solid-state lithium battery

  • 摘要: 硫化物全固態鋰金屬電池以其高比能和高安全性得到了越來越多的關注,但是電解質與正負極極材料之間嚴重的界面問題仍然限制其進一步發展. 為解決Li6PS5Cl固態電解質對金屬鋰不穩定的難點,許多工作提出引入合金負極、引入中間界面層以及電解質直接改性等策略,但是都和實際應用存在一定的差距. 考慮到石榴石氧化物固態電解質Li6.4La3Zr1.4Ta0.6O12(LLZTO)具有較高的鋰離子電導率和極好的材料穩定性,而Ag金屬具有良好的導鋰性,因此創新性地提出采用LLZTO與Ag的復合界面層來解決Li6PS5Cl全固態電池的金屬負極界面問題,提高全電池的循環穩定性. 研究了LLZTO和Ag簡單分散復合、均勻分散包覆復合以及納米球磨復合等不同組成的LLZTO–Ag復合界面層方式對Li6PS5Cl全固態鋰金屬電池負極界面的改善作用,并探究了優化后的全固態電池的電化學性能. 結果表明,納米球磨復合得到的LLZTO@Ag復合界面層能有效阻止鋰枝晶生長和電池短路. 在最佳工藝下,全固態鋰金屬電池的0.1C首圈效率為77.5%,放電比容量為187.3 mA·h·g?1,經0.3C循環100圈后容量保持率為81.7%.

     

    Abstract: Sulfide all-solid-state lithium metal batteries have received increasing attention owing to their high specific energy density and remarkable safety. However, serious interfacial problems still limit their further development. To solve the problem of instability of the interface between the solid-state electrolyte argyrodite (Li6PS5Cl) and lithium anode, strategies such as introducing an alloy cathode, introducing an intermediate interface layer, and directly modifying the electrolyte have been proposed; however, these methods are not suitable for practical applications. Notably, lithium lanthanum zirconium oxide (LLZTO) exhibits high lithium-ion conductivity and remarkable material stability, and silver (Ag) metal shows satisfactory lithium conductivity. Accordingly, a composite interface layer made of LLZTO and Ag was innovatively proposed to solve the lithium metal anode/Li6PS5Cl interface problem and increase the cycle stability of all-solid-state lithium batteries. We studied the effects of LLZTO–Ag composite interface layers with different combination manners, such as simply dispersed LLZTO–Ag composite, evenly dispersed and coated composite, and ball-milled composite, on the anode interface of Li6PS5Cl all-solid-state lithium metal batteries. The electrochemical performance of an optimized all-solid-state battery was also investigated. The results show that the surface of the LLZTO@Ag composite layer obtained by ball milling is relatively smoother and denser, which can effectively prevent lithium dendrite growth and battery short circuit. Compared with the simply dispersed LLZTO–Ag composite method and the evenly dispersed and coated composite method, the ball-milled composite layer anode method can be used to effectively reduce local lithium deposition current density and successfully solve the short circuit problem of the sulfide solid electrolyte. The first cycle efficiency of the LLZTOpw@Agpw–Lipl all-solid-state battery is 77.5%, and the discharge specific capacity is 187.3 mA·h·g?1. After 100 cycles at 0.3C, the discharge specific capacity is still 125.5 mA·h·g?1, and the capacity retention rate is 81.7%. Additionally, we investigated the electrochemical behavior of all-solid-state lithium metal batteries upon the introduction of the LLZTO–Ag composite interfacial layer by using the AC impedance (EIS) and constant-current intermittent titration technique. The LLZTOpw@Agpw anode shows satisfactory cycle stability for lithium batteries. The impedance of the LLZTOpw@Agpw–Lipl all-solid-state battery exhibits periodic oscillations, indicating that lithium vacancies will be generated in the NCM811 crystal upon extraction of lithium ions, thereby increasing the conductivity of the lithium ions and reducing their migration resistance as well. The effect is most prominent when half of the lithium ions are extracted, but further extraction of lithium ions will lead to too many vacancies in the material, following which extraction of lithium ions will be impeded, thereby increasing the migration resistance of the lithium ions. The interfacial impedance on the cathode side considerably increased during long cycling, thus affecting the subsequent cycling performance, while the interface on the anode side remained essentially stable, highlighting the stabilizing effect of the LLZTO–Ag composite interfacial layer.

     

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