Composite Cathode for All Solid-State Lithium Batteries: A Gear up Towards Co-Sintering
Authors: Valiyaveettil SobhanRaj Sona , Casas-Cabanas Montserrat , Cid Barreno Rosalía , Bonilla Francisco , Thompson Travis , Cabelguen Pierre-Etienne , Vasseur Karolien , Aguesse Frederic 
Published: July 2021

The demand for energy storage systems has exponentially grown over the last decade. Li-ion battery, containing liquid electrolyte, is the most advanced and implemented technology for transport and stationary markets.[1] However, safety limitations of these systems mainly due to flammable and volatile electrolyte represent the major threat to reach complete market maturity.[2] Replacing liquid by safe solid electrolyte is foreseen as a realistic strategy while maintaining high energy and power densities.
Among solid-state electrolyte materials, oxide-based ceramic electrolytes show high ionic conductivity, intrinsic safety and wide electrochemical window. The development of all-inorganic solid batteries is still at its infancy and presents various challenges due to the mechanical properties and processing of these materials.[3] High processing temperatures is certainly needed leading to chemical reactions and elemental diffusion, detrimental to maintain the battery performances.
Developing a fully inorganic solid-state battery, consisting of a composite cathode, solid electrolyte and lithium metal anode by co-sintering the first two components, remains a great challenge. The composite cathode comprises the active material, and an ionic and an electronic conductive filler, that should form stable interfaces under processing as well as during cycling. But densification of oxide-based ceramic electrolytes requires temperatures as high as 1000 °C and co-sintering at these temperatures can induce numerous chemical side- reactions at composite cathode[4] which is detrimental to maintain the battery performance. To control the sintering process, the threshold temperature at which the material is stable and maintains the electrochemical performance needs to be defined and the reaction byproducts need to be identified to prevent and control their impact. In this work we will present the impact of heat treatment on the stability of composite cathode mixture with LiNi0.6Co0.2Mn0.2O2 (NMC), Li1+xAlxTi2-xP3O12 (LATP) and Ketjen black (KB). The study optimizes the threshold conditions such as heating atmosphere and temperature in determining the chemical and electrochemical compatibility of the composite and explains the reaction mechanism at threshold limits. Surface based analysis of the active material demonstrates that the NMC surface reconstruction acts as barrier to electrochemistry after heat treatment at temperatures above threshold limits. Also, it underlines the fact that each element of the composite has inevitable contribution to the reaction mechanism and is determined by both heating atmosphere and temperature. Alternatives to enhance the threshold limits will be proposed.

Reference:

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[4] L. Miara et al., “About the Compatibility between High Voltage Spinel Cathode Materials and Solid Oxide Electrolytes as a Function of Temperature,” vol. 8, no. 40, pp. 26842–26850, Oct. 2016, doi: 10.1021/acsami.6b09059.