US-12626913-B2 - Negative electrode for secondary batteries, and secondary battery

US12626913B2US 12626913 B2US12626913 B2US 12626913B2US-12626913-B2

Abstract

This negative electrode for secondary batteries is provided with a negative electrode mixture layer which comprises a binder material and a negative electrode active material that contains graphite particles and an Si-containing material; the Si-containing material contains an Si-containing material A which comprises a carbon phase and silicon particles that are dispersed in the carbon phase; in cases where the negative electrode mixture layer is divided into equal halves in the thickness direction, the average intraparticle void fraction of the graphite particles contained in the upper half region is 13% or less, and is smaller than the average intraparticle void fraction of the graphite particles contained in the lower half region.

Inventors

Tatsuro Sasa
Yuta Kuroda

Assignees

PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20210909
Priority Date: 20200930

Claims (8)

1 . A negative electrode for a secondary battery comprising: a negative electrode mixture layer including a negative electrode active material including graphite particles and a Si-containing material, wherein the Si-containing material includes a Si-containing material A including a carbon phase and silicon particles dispersed in the carbon phase, and when the negative electrode mixture layer is divided into two equal parts in a thickness direction, an average value of particle internal porosities of the graphite particles included in an upper half region is less than or equal to 13%, and is smaller than an average value of particle internal porosities of the graphite particles included in a lower half region, wherein the Si-containing material includes a Si-containing material B including a silicate phase and silicon particles dispersed in the silicate phase.
2 . The negative electrode for a secondary battery according to claim 1 , wherein the average value of the particle internal porosities of the graphite particles included in the upper half region is greater than or equal to 2.5% and less than or equal to 13%, and the average value of the particle internal porosities of the graphite particles included in the lower half region is greater than or equal to 8% and less than or equal to 20%.
3 . The negative electrode for a secondary battery according to claim 1 , wherein a mass ratio (A/B) of the Si-containing material A to the Si-containing material B is greater than or equal to 0.2 and less than or equal to 20.
4 . The negative electrode for a secondary battery according to claim 1 , wherein a total content of the Si-containing material is greater than or equal to 5 mass % and less than or equal to 20 mass % with respect to a total mass of the negative electrode active material.
5 . The negative electrode for a secondary battery according to claim 1 , wherein the carbon phase of the Si-containing material A contains crystalline carbon.
6 . The negative electrode for a secondary battery according to claim 1 , wherein the silicate phase of the Si-containing material B contains at least one element of an alkali metal element and an alkaline earth metal element.
7 . The negative electrode for a secondary battery according to claim 1 , wherein the silicate phase of the Si-containing material B contains lithium silicate represented by a general formula Li 2z SiO (2+z) , wherein 0<z<2.
8 . A secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is the negative electrode for a secondary battery according to claim 1 .

Description

CROSS REFERENCE TO RELATED APPLICATIONS This Application is the National Stage of International Application No. PCT/JP2021/033089, filed Sep. 9, 2021, which claims priority from Application No. 2020-165625 filed on Sep. 30, 2020 in Japan. The entire contents of these applications are incorporated herein by reference in their entirety. TECHNICAL FIELD The present disclosure relates to a negative electrode for a secondary battery and a secondary battery. BACKGROUND A non-aqueous electrolyte secondary battery using a carbon material as a negative electrode active material is widely used as a secondary battery having a high energy density. For example, Patent Literature 1 discloses a non-aqueous electrolyte secondary battery using densified carbon having a particle internal porosity of less than or equal to 5% as a negative electrode active material. In addition, for example, Patent Literature 2 discloses a non-aqueous electrolyte secondary battery using graphite and a Si-containing material having different particle internal porosities as a negative electrode active material. CITATION LIST Patent Literature Patent Literature 1: JP H09-320600 APatent Literature 2: WO 2019/239947 A SUMMARY When the Si-containing material is used as the negative electrode active material, a capacity of the secondary battery can be increased, but charge/discharge cycle characteristic of the secondary battery tends to be deteriorated. According to one aspect of the present disclosure, there is provided a negative electrode for a secondary battery including a negative electrode mixture layer including a negative electrode active material including graphite particles and a Si-containing material, in which the Si-containing material includes a Si-containing material A including a carbon phase and silicon particles dispersed in the carbon phase, and when the negative electrode mixture layer is divided into two equal parts in a thickness direction, an average value of particle internal porosities of the graphite particles included in an upper half region is less than or equal to 13%, and is smaller than an average value of particle internal porosities of the graphite particles included in a lower half region. In addition, according to another aspect of the present disclosure, a secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, in which the negative electrode is the negative electrode for a secondary battery. According to one embodiment of the present disclosure, charge/discharge cycle characteristic of the secondary battery can be improved using a negative electrode active material including a Si-containing material. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a cross-sectional view of a secondary battery as an example of an embodiment. FIG. 2 is a cross-sectional view of a negative electrode as an example of an embodiment. FIG. 3 is an enlarged view illustrating a cross section of a graphite particle in a negative electrode mixture layer. DESCRIPTION OF EMBODIMENTS According to one aspect of the present disclosure, there is provided a negative electrode for a secondary battery including a negative electrode mixture layer including a negative electrode active material including graphite particles and a Si-containing material, in which the Si-containing material includes a Si-containing material A including a carbon phase and silicon particles dispersed in the carbon phase, and when the negative electrode mixture layer is divided into two equal parts in a thickness direction, an average value of particle internal porosities of the graphite particles included in an upper half region is less than or equal to 13% or less, and is smaller than an average value of particle internal porosities of the graphite particles included in a lower half region. Further, according to the negative electrode for a secondary battery as one aspect of the present disclosure, charge/discharge cycle characteristic of the secondary battery can be improved. Although the mechanism that exerts the above effects is not clear, the following is conceivable. It is considered that when graphite particles having a particle internal porosity of less than or equal to 13% and a Si-containing material A in which silicon particles are dispersed in a carbon phase are mixed, inter-particle friction is specifically increased, and a layer that is hardly crushed is obtained. Such a layer that is hardly crushed is disposed in the upper half region when the negative electrode mixture layer is divided into two equal parts in the thickness direction, such that liquid absorption of an electrolyte used in a secondary battery. Therefore, it is considered that the charge/discharge cycle characteristic of the secondary battery can be improved. In addition, since an internal porosity of the graphite particles is higher in the lower half region than in the upper half region when the negative electrode mixture layer is divided into two equal part