Deriving Structure‐Performance Relations of Chemically Modified Chitosan Binders for Sustainable High‐Voltage LiNi_0.5Mn_1.5O₄ Cathodes

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 LiNi 0.5 Mn 1.5 O 4 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 acidyielding 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 À 1 at C/3 and 1 C, respectively.

Co‐Crosslinked Water‐Soluble Biopolymers as a Binder for High‐Voltage LiNi0.5Mn1.5O4|Graphite Lithium‐Ion Full Cells

“…This superior electrochemical performance compared to that of the electrodes based on CMC only is ascribed to the ability of GG to coordinate to oxide‐based active materials to form a rather stable (electrode) network, which thus enables increased active material mass loadings . This beneficial behavior is further amplified by CA‐induced crosslinking . GG‐based electrodes with increased mass loadings do not significantly differ in their appearance.…”

“…SBR, for instance, is not sufficiently stable at such elevated potentials, which means that new (bio)polymers need to be identified to realize mechanically stable, high‐mass‐loading, high‐voltage electrodes for LIBs . Recently, it has been shown that the detrimental side effects of aqueous cathode processing, which especially include lithium leaching, aluminum current collector corrosion, and improvable adhesion of (high loading) electrode coating layers to the current collector, can be mitigated by implementing suitable processing additives, such as phosphoric acid (PA) and citric acid (CA), and by modifying the current collector . These strategies have effectively prevented corrosion of the aluminum current collector and have led to stabilized current collector–active material–electrolyte interfaces by forming a protective metal phosphate layer on the active material surface as well as the current collector that allows an improved binder network that is tethered covalently to the carbon‐coated aluminum current collector.…”

Comparative Study on Chitosans as Green Binder Materials for LiMn2O4 Positive Electrodes in Lithium Ion Batteries

“…stated that acetic acid residues from the solvent might remain in already dried samples and can react with the chitosan's amine groups, leading to branching and less cross‐linking of chitosan. CA is a tricarboxylic acid, which can react with amine groups of chitosans in a temperature‐induced amine condensation, as reported by Kuenzel et al., when using chitosan/CA as binder for LiNi 0.5 Mn 1.5 O 4 (LNMO)‐based positive electrodes [29] …”

“…The dashed line shows the position of C=O stretching vibration (1725 cm À 1 ), [29] indicating the formation of an Nalkylamide (RÀ (HNÀ C=O)À R') by cross-linking with citric acid on the free amine groups (À NH 2 ). As citric acid does not display a band at this wavenumber, the new band arises rather because of a reaction than through plain mixing.…”

“…CA is a tricarboxylic acid, which can react with amine groups of chitosans in a temperature-induced amine condensation, as reported by Kuenzel et al, when using chitosan/CA as binder for LiNi 0.5 Mn 1.5 O 4 (LNMO)-based positive electrodes. [29] In this work, different chitosan materials as environmentally friendly binders in combination with LiMn 2 O 4 (LMO) as sustainable positive electrode (cathode) active material were evaluated to understand the impact of the characteristics of the respective chitosan binders on their electrochemical cell performance. Therefore, chitosan materials with different degrees of acetylation (DA) and different degrees of polymerization (DP) were prepared from commercial sources.…”