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

doi:10.6023/A24050160

摘要/Abstract

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(LiPAA-CMC-HA-SBR及LiPAA-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0.5 C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209 mAh•g⁻¹及191 mAh•g⁻¹, 远高于使用CMC-SBR粘结剂的石墨负极(108 mAh•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.

关键词: 锂离子电池, 石墨负极, 复合粘结剂, 聚丙烯酸锂

Lithium polyacrylate (LiPAA) is widely used as a binder for lithium-ion battery anodes due to its high ionic conductivity 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.

Key words: lithium-ion battery, graphite anode, composite binder, lithium polyacrylate

引用此文

郑坤贵, 刘君珂, 胡轶旸, 尹祖伟, 周尧, 李君涛, 孙世刚. 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[J]. 化学学报, 2024, 82(8): 833-842.

Kungui Zheng, Junke Liu, Yiyang Hu, Zuwei Yin, Yao Zhou, Juntao Li, Shigang Sun. A Lithium Polyacrylate-based High-performance Composite Binder for Graphite Anode[J]. Acta Chimica Sinica, 2024, 82(8): 833-842.

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图/表 9

图1. 本工作选用的粘结剂分子结构: (a)聚丙烯酸锂(LiPAA); (b)羧甲基纤维素钠(CMC); (c)黄原胶(XG); (d)透明质酸钠(HA); (e)苯乙烯-丁二烯橡胶(SBR)

Figure 1. The molecular structure of the binders selected in this work: (a) lithium polyacrylate (LiPAA); (b) sodium carboxymethyl cellulose (CMC); (c) xanthan gum (XG); (d) sodium hyaluronate (HA); (e) styrene-butadiene rubber (SBR)

图2. (a)不同粘结剂2%溶液的粘度测试结果; (b)静置24 h后商业CMC-SBR粘结剂与基于LiPAA的复合粘结剂溶液的电子照片; (c)不同粘结剂薄膜的应力-应变曲线; (d)纳米压痕及相应的模量和硬度

Figure 2. (a) Viscosity test results of 2% solutions of different binders; (b) electronic photographs of commercial CMC-SBR binders and LiPAA-based composite binders solutions after stand 24 h; (c) stress-strain profiles of films with different binders; (d) nanoindentation and corresponding modulus and hardness

图3. 不同粘结剂制备的极片和粘结剂薄膜的弯折测试结果

Figure 3. Bending test results of anode sheets and films prepared with different binders

图4. (a)不同粘结剂的剥离强度曲线; (b)不同粘结剂的剥离力; (c, d)不同粘结剂的红外谱图; (e)使用不同粘结剂制备的石墨负极在嵌锂至0.01 V之后电极厚度变化率; (f)使用不同粘结剂制备的石墨负极在电解液中浸泡5 d后的电极厚度变化率

Figure 4. (a) Peel strength profiles of different binders; (b) peel strength of different binders; (c, d) infrared spectra of different binders; (e) change rate of electrode thickness of graphite anode prepared with different binders after lithium insertion to 0.01 V; (f) the change rate of electrode thickness of graphite anode prepared with different binders after soaking in electrolyte for 5 d

图5. 不同粘结剂制备的石墨极片与电解液之间的接触角测试结果: (a) CMC-SBR; (b) LiPAA-CMC-HA-SBR; (c) LiPAA-XG-HA-SBR; (d)使用不同粘结剂的石墨电极组装电池在循环前的交流阻抗谱和电荷转移阻抗(Rct)的拟合结果

Figure 5. Contact angle between graphite anode sheet prepared with different binders and electrolyte: (a) CMC-SBR; (b) LiPAA-CMC-HA-SBR; (c) LiPAA-XG-HA-SBR; (d) electrochemical impedance spectra of batteries assembled with graphite anode of different binders before cycling and fitting results of charge transfer impedance (Rct)

图6. (a)不同粘结剂涂覆在铜箔上时的LSV曲线; 基于不同粘结剂的石墨负极组装的电池的(b)循环性能; (c)倍率性能; (d) 1 C下的充放电曲线; (e) 2 C下的充放电曲线和(f)循环伏安曲线

Figure 6. (a) LSV curve of copper foil coated with different binders; (b) cycle performance of batteries with different graphite anodes; (c) rate performance; (d) charge and discharge curve at 1 C; (e) charge and discharge curve at 2 C and (f) cyclic voltammetry curve

图7. (a)基于不同粘结剂的石墨负极组装的电池在循环10圈后的交流阻抗谱; (b)基于交流阻抗测试结果计算的Zre-ω-1/2图和(c) Warburg因子的计算结果

Figure 7. (a) Electrochemical impedance spectra of batteries with graphite anode with different binders after 10 cycles; (b) the relevant Zre-ω-1/2 plot and (c) the resulting Warburg factor

图8. 基于不同粘结剂的石墨负极在(a, b)循环前和(c)循环10圈后的扫描电镜图片

Figure 8. SEM images of graphite anode prepared with different binders before (a, b) cycle and after (c) 10 cycles

图9. 基于不同粘结剂的石墨负极在循环10圈后表面的XPS精细谱: (a) C 1s; (b) F 1s; (c)极片表面和刻蚀50 nm后的C和F的原子占比

Figure 9. Fine XPS spectra of different graphite anodes after 10 cycles: (a) C 1s; (b) F 1s; (c) the atomic fraction of C and F on the electrode surface and after etching up to 50 nm

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