A silicon-carbon negative electrode material with core-shell structure and preparation method thereof

Abstract

The invention discloses a core-shell-structured silicon carbon negative electrode material and a preparation method therefor. The silicon carbon negative electrode material comprise a core, a buffer layer and a shell from inside to outside in sequence; the core material consists of SiO, Si, SiO<2> and silicate; the buffer layer material comprises carbon dots or graphene quantum dots; and the shellmaterial is a hard carbon material. The core material disclosed in the invention comprises a modified SiO material; through a high-temperature reaction between SiO and NaOH, nanometer silicon and sodium silicate are generated, so that the shortcoming of low initial coulombic efficiency caused by a reaction between SiO and Li in the initial charging process can be solved; meanwhile, by taking thegenerated sodium silicate as a buffer medium, volume change of the material in the lithium de-intercalation process can be suppressed effectively, and cycle performance of the electrode can be improved; and by taking conductive carbon as a coating layer and by introducing the carbon dots or graphene quantum dots, the material conductivity is improved and a buffer effect can be played, thereby realizing stable cycle performance and high reversible capacity of the battery.

Description

technical field [0001] The invention relates to the field of negative electrode materials for lithium ion batteries, in particular to a silicon-carbon negative electrode material with a core-shell structure and a preparation method thereof. Background technique [0002] Due to the advantages of high specific capacity, high charge-discharge efficiency, good cycle performance and low cost, lithium-ion batteries have gradually become a research hotspot. The rapid development of electronic products and new energy vehicle technology has put forward higher requirements for lithium-ion batteries. As an important part of lithium-ion batteries, anode materials affect the specific energy and cycle life requirements of batteries, and have always been the focus of lithium-ion battery research. [0003] Silicon-based anode materials have high lithium storage capacity and low voltage platform, and are one of the hotspots in the research of anode materials for lithium-ion batteries. Howe...

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Problems solved by technology

[0004] However, SiO also has the following problems: (1) There is a 200% volume expansion during the lithium intercalation process, which generates a large stress, which will lead to electrode pulverization, destroy the conductive network, and rapidly decay the capacity; (2) In the first lithium intercalation process The inert lithium oxide and lithium silicate phases generated in the process make the coulombic efficiency of the first cycle low; (3) in the subsequent charge and discharge process, due to the continuous formation of the solid electrolyte phase interface (SEI) film, the consumption of Li + , the Coulombic efficiency is lower than 100%, which leads to a significant reduction in the delithiation capacity of the negative electrode compared to the positive electrode in the actual battery; (4) SiO is a semiconductor, and its conductivity is much lower than that of graphite, so there will be a larger charge and discharge when the current is large. severe ohmic polarization

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