Relevance of LiPF6 as Etching Agent of LiMnPO4 Colloidal Nanocrystals for High Rate Performing Li-ion Battery Cathodes

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• 作者：Lin Chen ; Enrico Dilena ; Andrea Paolella ; Giovanni Bertoni ; Alberto Ansaldo ; Massimo Colombo ; Sergio Marras ; Bruno Scrosati ; Liberato Manna ; Simone Monaco
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：February 17, 2016
• 年：2016
• 卷：8
• 期：6
• 页码：4069-4075
• 全文大小：451K
• ISSN：1944-8252

文摘

LiMnPO₄ is an attractive cathode material for the next-generation high power Li-ion batteries, due to its high theoretical specific capacity (170 mA h g^–1) and working voltage (4.1 V vs Li⁺/Li). However, two main drawbacks prevent the practical use of LiMnPO₄: its low electronic conductivity and the limited lithium diffusion rate, which are responsible for the poor rate capability of the cathode. The electronic resistance is usually lowered by coating the particles with carbon, while the use of nanosize particles can alleviate the issues associated with poor ionic conductivity. It is therefore of primary importance to develop a synthetic route to LiMnPO₄ nanocrystals (NCs) with controlled size and coated with a highly conductive carbon layer. We report here an effective surface etching process (using LiPF₆) on colloidally synthesized LiMnPO₄ NCs that makes the NCs dispersible in the aqueous glucose solution used as carbon source for the carbon coating step. Also, it is likely that the improved exposure of the NC surface to glucose facilitates the formation of a conductive carbon layer that is in intimate contact with the inorganic core, resulting in a high electronic conductivity of the electrode, as observed by us. The carbon coated etched LiMnPO₄-based electrode exhibited a specific capacity of 118 mA h g^–1 at 1C, with a stable cycling performance and a capacity retention of 92% after 120 cycles at different C-rates. The delivered capacities were higher than those of electrodes based on not etched carbon coated NCs, which never exceeded 30 mA h g^–1. The rate capability here reported for the carbon coated etched LiMnPO₄ nanocrystals represents an important result, taking into account that in the electrode formulation 80% wt is made of the active material and the adopted charge protocol is based on reasonable fast charge times.