Lithium-ion secondary battery and negative electrode sheet thereof

Abstract

The invention discloses a lithium ion secondary battery using a water-soluble adhesive and a negative electrode piece of the lithium ion secondary battery. The water-soluble adhesive is a modified polyacrylic acid polymer and is prepared by polymerizing monomers from 1 to 3 shown in the description or monomers 1 and 3 shown in the description through a free radical polymerization initiator. Compared with the prior art, the lithium ion secondary battery disclosed by the invention has the advantages that the adhesive can effectively improve the first-time charging and discharging efficiency of the lithium ion secondary battery, and the high-temperature circulation performance, the high-temperature storage performance and the charging and discharging ratio performance are greatly improved.

Description

technical field [0001] The invention belongs to the field of lithium-ion secondary batteries. More specifically, the invention relates to a silicon-tin alloy lithium-ion secondary battery and a negative electrode sheet thereof with higher charge and discharge rate performance and better high temperature and cycle performance. Background technique [0002] Lithium-ion secondary batteries have been widely used in portable electronic products due to their high voltage and energy density. However, the miniaturization and multi-functional development of electronic products also put forward higher requirements for the energy density of lithium-ion secondary batteries. [0003] At present, the most widely used negative electrode material for lithium-ion secondary batteries is graphite-based carbon material, but its capacity is close to the theoretical value of 376mAh / g. That is to say, even if the carbon material is improved, it is difficult to further increase the energy density. ...

AI Technical Summary

Problems solved by technology

However, due to the presence of free carboxylic acid groups in polyacrylic acid, the battery needs to consume a large amount of lithium ions to neutralize the carboxylate during the initial charge and discharge process, so there will be a large irreversible capacity loss; moreover, due to the heat generated by the free carboxylate The stability is weak, and it will undergo irreversible decarboxylation reaction at high temperature and lose its adhesive ability, thus greatly reducing the high temperature performance of the battery

In addition, according to the research, the acidity of polyacrylic acid itself will also catalyze the decomposition of the electrolyte, which will cause problems such as poor battery cycle performance and flatulence.

[0005] For the above-mentioned technical problems, people in the industry have proposed multiple solutions, but there are irreparable shortcomings in each scheme, for example: 1) someone proposes to neutralize the free carboxylic acid groups in polyacrylic acid with lithium hydroxide, thereby reducing lithium The purpose of the irreversible capacity loss during the first charge and discharge process of the ion secondary battery; however, the lithium salt PAALi generated by the neutralization reaction has a high hydrophilicity, which makes it difficult to dry the prepared pole piece completely, and the remaining crystals in the pole piece Water can cause great damage to the cycle performance of the battery; 2) someone proposes to use the polyacrylic acid copolymer modified by polyvinyl alcohol as the binder of the lithium ion secondary battery negative electrode material with the carboxylic acid group; When it is used in a silicon-tin alloy anode material battery, in order to achieve a good bonding effect, the amount of this type of adhesive is often large, which will undoubtedly lead to a reduction in the energy density of the battery; moreover, the modified polyacrylic acid The copolymer has weak lithium-ion conduction performance, which will increase the internal resistance of the battery and reduce the charge-discharge efficiency and rate performance of the battery; monomer copolymerization to obtain LA-based adhesives with high adhesive properties; however, such adhesives contain strong polar functional groups, resulting in weak wettability with ordinary carbonate electrolytes, so that If it cannot be used together with a suitable electrolyte, the battery is prone to very serious polarization; in addition, the inventors of the present application have also found that the pole pieces made of LA adhesive often have the phenomenon that the pole pieces fall off. When used together with negative electrode materials with large volume changes during charging and discharging, it is easy to reduce the cycle performance of the battery due to the shedding of active materials

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