Abstract
Silicon is a highly promising electrode material for Li-ion batteries because of its high theoretical capacity, but severe volume changes during cycling leads to pulverization and rapid capacity fading. The use of alternative and water-soluble polymer binders such as poly(vinyl alcohol) (PVA) or poly(acrylic acid) (PAA) can improve the cycling performance of Si-based Li-ion batteries. Here, we investigate the effect of the substitution of the hydroxyl groups of PVA chains by carboxylic acid and acetate groups on the electrochemical performance of Si anodes in Li-ion batteries. Using modified PVAs, a model system is created spanning the chemical space between PVA and PAA, and the role of different Si-adhering functionalities is investigated. When comparing the electrochemical performance of Li-ion battery cells using Si anodes and the investigated binder systems, PVA with the highest degree of hydrolysis exhibits a superior performance (100 cycles with 1019 mAh g–1) compared to modified PVAs and PAA as a binder for Si anodes. An increased degree of hydrolysis of PVA is also seen to be beneficial for high capacity retention. These effects can be largely explained by the crystallinity of the binder system, which renders an improved electrode integrity during cycling and less swelling of the Si particles.
Highlights
Rechargeable lithium-ion batteries (LIBs) are today widely used as electrochemical energy storage devices in consumer electronics, smart grids, and electric vehicles because of their high energy density and long cycle life.[1,2] The components of the electrodes play a significant role in the electrochemical performance of a battery
Severe problems in terms of capacity fading, poor rate capability, and short cycle life limit the commercial adoption of Si-based electrodes.[6−8] Some of these are connected to the severe volume changes that the silicon particles experience during cycling which lead to pulverization of the active material particles, continuous growth of the SEI layer thickness, and loss of electrical contact with the current collector and to a fast capacity drop after a limited number of cycles
In contrast to much of the other work published on similar systems in literature, we investigate the electrochemical performance of Si anodes using a low binder content, to better put these electrodes in the context of industrial applications
Summary
Rechargeable lithium-ion batteries (LIBs) are today widely used as electrochemical energy storage devices in consumer electronics, smart grids, and electric vehicles because of their high energy density and long cycle life.[1,2] The components of the electrodes play a significant role in the electrochemical performance of a battery. Article the performance of the electrodes, and the properties such as the molecular weight and the rheological properties during processing are important parameters to consider.[23,24] While poly(vinylidene fluoride) (PVdF) has traditionally been used for conventional graphite electrodes,[25] for Si, hydrogenbonding polymers that are soluble in water and can interact with the silanol groups on the surface of the Si particles are preferred.[26] This could be polymers bearing either carboxyl (−COOH) groups, such as in poly(acrylic acid) (PAA),[23,27,28] or hydroxyl (−OH) groups, such as in carboxymethyl cellulose (CMC)[29,30] or poly(vinyl alcohol) (PVA).[31]. The polymer was dried in vacuum for 3 days (degree of modification = 6% according to NMR) Another three reactions were carried out (using 0.5, 1.0, and 2.0 equiv of maleic anhydride with respect to the molar ratios of PVA) under similar reaction conditions, resulting in degrees of modification of 2%, 5%, and 11% respectively. A steady-state flow experiment was performed at a series of controlled shear rates
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