Deriving Structure‐Performance Relations of Chemically Modified Chitosan Binders for Sustainable High‐Voltage LiNi0.5Mn1.5O4 Cathodes. Issue 2 (12th November 2019) - Kuenzel, Matthias
Abstract: The implementation of aqueous electrode processing for lithium‐ion positive electrodes is key towards the realization of environmentally benign and cheap battery production. One of the water‐soluble binders that has attracted most attention is chitosan, the second‐most abundant natural biopolymer. Herein, the use of chitosan for high‐voltage, cobalt‐free LiNi0.5 Mn1.5 O4 cathodes is reported for the first time. A detailed comparison of three different grades of chitosan with varying chain length and degrees of deacetylation (DD) is provided to explore the impact of these properties on the electrochemical performance. In fact, bio‐derived chitosan with a relatively lower DD outperforms synthetic chitosan‐especially after crosslinking with citric acid‐yielding about 10 % higher capacities. Higher molecular weight appears additionally advantageous for the cycling stability. Finally, guar gum is employed as slurry thickener, co‐crosslinking with chitosan. This allows for achieving 50 % higher mass loadings than for chitosan only and stable capacities above 130 and 120 mAh g −1 at C/3 and 1 C, respectively. Abstract : The secret ingredient? Acid or gum : Bio‐derived chitosan serves as environmentally benign binding agent for high‐voltage LiNi0.5 Mn1.5 O4 positive electrodes. The electrochemical performance of such electrodes depends strongly on the chain length and degree of deacetylation of the water‐processable biopolymer and can be improved significantly through chemical modification by means of crosslinking with citric acid or the incorporation of a second water‐soluble polymer like guar gum.