用于石墨负极的高性能聚丙烯酸锂基复合粘结剂的制备及性能研究

A Lithium Polyacrylate-based High-performance Composite Binder for Graphite Anode

聚丙烯酸锂(LiPAA)由于其较高的离子电导率和良好的化学稳定性被广泛用作锂离子电池负极的粘结剂,但是LiPAA粘度低、硬度大,作为粘结剂时负极极片的粘接性能、柔韧性和可加工性是较大挑战.本工作将LiPAA与多种高分子聚合物复配,通过添加羧甲基纤维素(CMC)或黄原胶(XG)提高粘结剂粘度,采用透明质酸钠(HA)降低粘结剂脆性,添加丁苯橡胶(SBR)提高剥离强度,开发了两款基于LiPAA的复配型粘结剂(Li PAA-CMC-HA-SBR及Li PAA-XG-HA-SBR).与商用负极粘结剂(CMC-SBR)相比,所得两款基于LiPAA的复配粘结剂不仅具有合适的粘接强度及柔韧性,且可显著改善石墨颗粒、导电剂、电解液之间的亲和性,促进锂离子在电极/电解液界面的传输,从而获得高电化学性能.在0.5C的电流密度下,在循环150圈后,采用上述两款复配粘结剂制备的石墨负极容量分别为209m Ah·g^(-1)及191m Ah·g^(-1),远高于使用CMC-SBR粘结剂的石墨负极(108m Ah·g^(-1)).此外,传统配方需添加大量SBR(≈50%),而基于LiPAA的配方中只需少量SBR即可保持极片完整性,且可在低粘结剂含量(≈3%)和高活性物质载量(≈95%)时保持良好力学性能,制备的石墨负极极片也拥有良好的电化学性能,具有较好工业化应用前景.

Lithium polyacrylate(LiPAA)is widely used as a binder for lithium-ion battery anodes due to its high ionic con-ductivity and good chemical stability.However,LiPAA has disadvantages such as low viscosity and high hardness,resulting in the adhesive performance,flexibility and processability of the anode becoming an issue when LiPAA is used as a binder.In this paper,a composite formula was developed by integrating LiPAA with other polymers,including carboxymethyl cellulose(CMC)or Xanthan gum(XG)to tune the viscosity,sodium hyaluronate(HA)to reduce the brittleness,and benzene butadiene rubber(SBR)to improve the stripping strength.On this basis,two LiPAA-based composite binders(LiPAA-CMC-HA-SBR and LiPAA-XG-HA-SBR)were developed.Compared with the commercial anode binder(CMC-SBR),the two LiPAA-based composite binders both demonstrate well-tuned bonding strength and flexibility;more importantly,they also can significantly improve the interfacial affinity between the graphite particles,the conductive agent and the electrolyte,which hence promotes the diffusion kinetics of lithium ions at the electrode/electrolyte interface and thus improves the electrochemical performance of the graphite anode.At the current density of 0.5 C,after 150 cycles,the graphite anode prepared with our two composite binders displayed a capacity of 209 mAh·g^(−1)and 191 mAh·g^(−1),respectively,which was much higher than the graphite anode prepared with the commercial CMC-SBR binder(which is 108 mAh·g^(−1)).The graphite anode prepared with our binder also demonstrates much higher rate capability and better cycling stability compared to the control.Characterizations of the cycled anode reveal that,in the anode prepared with our binders,a much more homogeneous distribution of the conductive carbon and the graphite particles was observed,and a solid electrolyte interphase(SEI)with a higher fraction of LiF was formed.In addition,in the commercial CMC-SBR formula,a mass fraction of SBR up to 50%is required;in comparison,in our two LiPAA-based formulations,only a small fraction of SBR is employed yet which can still maintain the integrity of the anode sheet.It is worth noting that,at a low binder content(≈3%)and high active material load(≈95%),the graphite anode elec-trode prepared by these two composite binders can still maintain remarkable mechanical strength,and it also demonstrates excellent electrochemical performance,showing the promising industrialization potential of such LiPAA-based composite binders.