Conditioning of all solid state Lithium Ion Batteries with LiMPO4 (M=Co, Ni) thin film cathodes

正极材料对锂离子电池的能量密度、安全性和寿命周期起着至关重要的作用。它的热力学稳定性取决于本征电压极限，而本征电压极限是由相关材料内阴离子的固有氧化极限决定的。整个电池的外在稳定性还受到电解液氧化还原电位和阴极/电解液界面的化学相容性的影响。功率能力取决于锂离子和/或电子通过大块阴极材料和跨相边界阴极/电解质的转移速率。因此，要发展稳定的高功率高密度电池，必须解决以下关键问题：a)电池芯在高压充电状态下的热力学稳定性和化学相容性；b) Li+离子通过相和跨相边界的高迁移率；C)高电子导电性的电极和堵塞的电解质界面。由于涉及添加剂的设置的复杂性，这些因素的具体作用很难在经典电池结构中澄清。本课题的目的是制备和研究新型高压固态电池。我们重点研究了橄榄石型结构材料LiMPO4 (M=Fe, Co, Ni)，其中Fe被Co （4.8 V）和Ni （> 5 V）取代，从而增加了电压窗口。应解决以下科学问题：a) LiCoPO4和LiNiPO4橄榄石型正极材料在衰减下热力学稳定吗？它们是否适用于高达未知固有电压极限的高压应用？b) LiCoPO4和LiNiPO4是否与典型的电解质如氟乙烯碳酸酯化学相容，橄榄石/电解质界面在电压约5v时是否稳定？c) LiCoPO4和LiNiPO4是否与固体电解质（如LIPON）化学相容？在特高压条件下制备薄膜阴极材料及其界面，主要利用电子能谱技术对其电子性能进行原位研究。随着这种新的表面科学方法在离子导体上的应用，我们将解决高压橄榄石的内在和外在稳定性范围，并研究避免腐蚀性副反应的可能途径。

The cathode material plays a key role in the determination of energy density, safety and life cycle of Lithium Ion Batteries (LIB). Its thermodynamic stability depends on the intrinsic voltage limit which is defined by the inherent oxidation limit of the anions within the relevant material. The extrinsic stability of the whole battery cell is additionally influenced by the redox potential of the electrolyte and by the chemical compatibility of the cathode/electrolyte interface. Power capability depends on the Li+ and/or electron transfer rates through the bulk cathode material and across the phase boundary cathode/electrolyte. Thus, to develop a stable high power and high density battery, the following key issues have to be solved: a) thermodynamic stability and chemical compatibility of the battery cell operated at a high voltage charged state; b) high migration rate of Li+ ions through the phases and across the phase boundaries; c) high electronic conductivity in the electrode and a blocking electrolyte interface. The specific role of these factors can hardly be clarified in classical battery structures due to the complexity of the set-up involving additives. The aim of our project is the preparation and investigation of novel high voltage solid state batteries. We focus on the olivine type structure material as LiMPO4 (M=Fe, Co, Ni) in which the voltage window is increased by substitution of Fe by Co (4.8 V) and Ni (> 5 V. The following scientific problems shall be addressed: a) Are LiCoPO4 and LiNiPO4 olivine-type cathode materials thermodynamically stable under delithiation and are they suitable for high voltage application up to a still unknown intrinsic voltage limit? b) Are LiCoPO4 and LiNiPO4 chemically compatible with typical electrolytes as fluoroethylene carbonate and is the olivine/electrolyte interface stable at voltage around 5 V? c) Are LiCoPO4 and LiNiPO4 chemically compatible with solid electrolytes (as e. g. LIPON)?The film cathode materials and their interfaces will be prepared under UHV condition and their electronic properties will be studied in situ mostly by using electron spectroscopy. With such a novel surface science approach applied at ion conductors we will address the intrinsic and extrinsic stability range of high voltage Olivines and investigate possible routes to avoid corrosive side reactions.