No abstract

While silicon is considered one of the most promising anode materials for the next generation of high‐energy lithium‐ion batteries (LIBs), the industrialization of Si anodes is hampered by the anode's large volume change during the charging and discharging process. In comparison to the traditional graphite anode used in LIBs, the Si anode places more stringent demands on the binder, which must maintain intimate contact between the electrode components and the integrity of the ion and electron transport channels when subjected to frequent large volume changes. The purpose of this review is to cover the recent advances in binder design strategies by examining the molecular structure, chemical functionalities, physical and mechanical properties of the binder materials, as well as the working strategies involved. The challenges in the design of the innovative polymer binder for commercializing Si anodes are discussed, as well as the future development direction and application prospects.

Binders play a crucial role in the development of silicon (Si) anodes for lithium-ion batteries with high specific energy. The large volume change of Si (∼300%) during repeated discharge and charge processes causes the destruction and separation of electrode materials from the copper (Cu) current collector and ultimately results in poor cycling performance. In the present study, we design and prepare hydrogen-bonding cross-linked thiourea-based polymeric binders (denoted CMC-co-SN) in consideration of their excellent binding interaction with the Cu current collector and low cost as well. The CMC-co-SN binders are formed through in situ thermopolymerization of chain-type carboxymethylcellulose sodium (CMC) with thiourea (SN) in the drying process of Si electrode disks. A tight and physical interlocked layer between the CMC-co-SN binder and Cu current collector is derived from a dendritic nonstoichiometric copper sulfide (Cu x S) layer on the interface and enhances the binding of electrode materials with the Cu current collector. When applying the CMC-co-SN binders to micro- (∼3 μm) (μSi) and nano- (∼50 nm) (nSi) Si particles, the Si anodes exhibit high initial Coulomb efficiency (91.5% for μSi and 83.2% for nSi) and excellent cyclability (1121 mA h g–1 for μSi after 140 cycles and 1083 mA h g–1 for nSi after 300 cycles). The results demonstrate that the CMC-co-SN binders together with a physical interlocked layer have significantly improved the electrochemical performance of Si anodes through strong binding forces with the current collector to maintain electrode integrity and avoid electric contact loss.

A composite consisting of cobalt and graphitic porous carbon (Co@GC-PC) is synthesized from bimetallic metal-organic frameworks and employed as the sulfur host for high-performance Li-S batteries. Because of the presence of a large surface area (724 m g) and an abundance of macro-/mesopores, the Co@GC-PC electrode is able to alleviate the debilitating effect originating from the volume expansion/contraction of sulfur species during the cycling process. Our in situ UV/vis analysis indicates that the existence of Co@GC-PC promotes the adsorption of polysulfides during the discharge process. Density functional theory calculations show a strong interaction between Co and LiS and a low decomposition barrier of LiS on Co(111), which is beneficial to the following LiS oxidation in the charge process. As a result, at 0.2C, the discharge capacity of the S/Co@GC-PC cathode is stabilized at 790 mAh g after 220 cycles, much higher than that of a carbon-based cathode, which delivers a discharge capacity of 188 mAh g.