EP-4738454-A1 - NEGATIVE ELECTRODE SHEET, SECONDARY BATTERY, AND ELECTRICAL DEVICE

EP4738454A1EP 4738454 A1EP4738454 A1EP 4738454A1EP-4738454-A1

Abstract

The present application provides a negative electrode plate, a secondary battery, and an electrical apparatus. The negative electrode plate includes a current collector and a negative electrode film layer, where the negative electrode film layer includes a first film layer, provided on one side or both sides of the current collector; and a second film layer, provided on one side of the first film layer away from the current collector; a negative electrode active material of the first film layer and a negative electrode active material in the second film layer each independently include a silicon-based negative electrode material, the silicon-based negative electrode material in the second film layer includes a porous silicon negative electrode material, and a content of the silicon-based negative electrode material in the first film layer is less than a content of the silicon-based negative electrode material in the second film layer. The charging capability and cycling performance of the secondary battery are improved.

Inventors

WU, KAI
WANG, YUWEN
YOU, Xingyan
BAI, Wenlong
YE, Yonghuang
WU, Baozhen

Assignees

Contemporary Amperex Technology Co., Limited

Dates

Publication Date: 20260506
Application Date: 20231025

Claims (19)

A negative electrode plate, comprising a current collector (01) and a negative electrode film layer, wherein the negative electrode film layer comprises: a first film layer (02), provided on one side or both sides of the current collector (01); and a second film layer (03), provided on one side of the first film layer (02) away from the current collector (01); a negative electrode active material of the first film layer (02) and a negative electrode active material in the second film layer (03) each independently comprise a silicon-based negative electrode material, the silicon-based negative electrode material in the second film layer (03) comprises a porous silicon negative electrode material (10), and a content of the silicon-based negative electrode material in the first film layer (02) is less than a content of the silicon-based negative electrode material in the second film layer (03).
The negative electrode plate according to claim 1, wherein a surface density M1 of the first film layer (02) is in a range of 4.5 mg/cm 2 to 20 mg/cm 2 , and a surface density M2 of the second film layer (03) is in a range of 4.5 mg/cm 2 to 20 mg/cm 2 ; optionally, a weight ratio of the first film layer (02) to the second film layer (03) is 95:5 to 30:70, and further optionally is 90:10 to 40:60; optionally, a porosity of the first film layer (02) is in a range of 20% to 50%, a porosity of the second film layer (03) is 20% to 70%, and a porosity of the negative electrode film layer is 20% to 70%; and optionally, a thickness of the second film layer (03) is 10 µm to 20 µm.
The negative electrode plate according to claim 1 or 2, wherein a mass content of the silicon-based negative electrode material in the first film layer (02) is 0.5% to 50%; and/or a mass content of the porous silicon negative electrode material (10) in the second film layer (03) is 0.5% to 70%; and optionally, a mass content of the porous silicon negative electrode material (10) in the negative electrode film layer is 1% to 60%.
The negative electrode plate according to any one of claims 1 to 3, wherein the second film layer (03) comprises the porous silicon negative electrode material (10), a graphite negative electrode material, a binder, a dispersant, and a conductive agent, and the conductive agent comprises one or more of conductive carbon and carbon nanotubes; optionally, a percentage mass content of the porous silicon negative electrode material (10) in the second film layer (03) is 0.5% to 70%; optionally, a percentage mass content of the graphite negative electrode material in the second film layer (03) is 25% to 90%; optionally, a percentage mass content of the binder in the second film layer (03) is 1% to 8%; optionally, a percentage mass content of the dispersant in the second film layer (03) is 0.5% to 2%; optionally, a percentage mass content of the conductive carbon in the second film layer (03) is 0.5% to 5%; and optionally, a percentage mass content of the carbon nanotubes in the second film layer (03) is 0.05% to 2%.
The negative electrode plate according to any one of claims 1 to 4, wherein the first film layer (02) comprises the silicon-based negative electrode material, a graphite negative electrode material, a binder, a dispersant, and a conductive agent, and the conductive agent comprises one or more of conductive carbon and carbon nanotubes; optionally, a percentage mass content of the silicon-based negative electrode material in the first film layer (02) is 0.5% to 50%; optionally, a percentage mass content of the graphite negative electrode material in the first film layer (02) is 45% to 97.5%; optionally, a percentage mass content of the binder in the first film layer (02) is 1% to 3%; optionally, a percentage mass content of the dispersant in the first film layer (02) is 0.3% to 1.5%; optionally, a percentage mass content of the conductive carbon in the first film layer (02) is 0 to 3%; optionally, a percentage mass content of the carbon nanotubes in the first film layer (02) is 0 to 0.5%; optionally, the silicon-based negative electrode material comprises any one or more of the group consisting of a silicon material, a silicon-oxide material, and a porous silicon negative electrode material (10), and a content of the porous silicon negative electrode material (10) in the first film layer (02) is less than a content of the porous silicon negative electrode material (10) in the second film layer (03).
The negative electrode plate according to any one of claims 1 to 5, wherein Dv 50 of the porous silicon negative electrode material (10) is between 3 µm and 20 µm, and optionally is between 4 µm and 15 µm; and/or a BET specific surface area of the porous silicon negative electrode material (10) is between 1 m 2 /g and 30 m 2 /g, and optionally is between 6 m 2 /g and 20 m 2 /g.
The negative electrode plate according to any one of claims 1 to 6, wherein the porous silicon negative electrode material (10) comprises: a core (11), wherein the core (11) is porous silicon, the porous silicon comprises elemental silicon and a compound of silicon, and the compound of silicon comprises an oxide of silicon; and a cladding layer, wherein the cladding layer is cladded on a surface of the core (11).
The negative electrode plate according to claim 7, wherein the cladding layer comprises any one or more of a metal compound of silicon, lithium silicate, amorphous carbon, and carbon nanotubes.
The negative electrode plate according to claim 8, wherein the cladding layer comprises: a first cladding layer (12), wherein the first cladding layer (12) is cladded on the surface of the core (11), and the first cladding layer (12) comprises lithium silicate; a second cladding layer (13), wherein the second cladding layer (13) is cladded on a surface of the first cladding layer (12), the second cladding layer (13) comprises a metal compound of silicon, and optionally, metal elements of the metal compound of silicon comprise Ti, Mg, and/or Al; and a third cladding layer (14), wherein the third cladding layer (14) is cladded on a surface of the second cladding layer (13), the third cladding layer (14) comprises amorphous carbon, and optionally, a material of the amorphous carbon comprises hard carbon and/or soft carbon.
The negative electrode plate according to claim 8, wherein the cladding layer comprises: a first cladding layer (12), wherein the first cladding layer (12) is cladded on the surface of the core (11), and the first cladding layer comprises the lithium silicate; and a third cladding layer (14), wherein the third cladding layer (14) is cladded on a surface of the first cladding layer (12), the third cladding layer (14) comprises the amorphous carbon, and optionally, a material of the amorphous carbon comprises hard carbon and/or soft carbon.
The negative electrode plate according to any one of claims 7, 8, and 10, wherein the compound of silicon further comprises a metal compound of silicon, the metal compound of silicon is cladded on a surface of the elemental silicon, and optionally, metal elements of the metal compound of silicon comprise Ti, Mg, and/or Al.
The negative electrode plate according to any one of claims 9 to 11, wherein the third cladding layer further comprises the carbon nanotubes.
The negative electrode plate according to claim 12, wherein mass of the porous silicon negative electrode material (10) in the first film layer (02) and the second film layer (03) is m1 and m2, respectively; percentage mass contents of carbon nanotubes belonging to the porous silicon negative electrode material (10) in the first film layer (02) and the second film layer (03) are C1 and C2, respectively; and excluding the carbon nanotubes in the porous silicon negative electrode material (10), mass of remaining carbon nanotubes in the first film layer (02) and the second film layer (03) is S1 and S2, respectively, the first film layer (02) and the second film layer (03) are a first film layer (02) per unit area and a second film layer (03) per unit area respectively, and the following relationships: (m2×C2+S2)/M2=(m1×C1+S1)/M1, m2≥m1, S1>S2, and S2=m1×m2×(C2-C1)/(m2-m1) are satisfied.
The negative electrode plate according to any one of claims 7 to 13, wherein Dv50 of the elemental silicon is in a range of 0<Dv50≤10 nm; and optionally, the Dv50 of the elemental silicon is in a range of 2 nm<Dv50≤8 nm.
The negative electrode plate according to any one of claims 7 to 14, wherein a chemical formula of the oxide of silicon is SiOx, and in the formula, 0<x≤2; and Dv50 of the oxide of silicon is in a range of 2 µm≤Dv50≤13 µm.
The negative electrode plate according to claim 9 or 10, wherein the lithium silicate comprises one or more of Li 2 SiO 3 , Li 2 Si 2 O 5 , Li 4 SiO 4 , Li 2 Si 3 O 7 , Li 8 SiO 6 , Li 6 Si 2 O 7 , Li 4 Si 2 O 7 , Li 2 Si 4 O 7 , and LiSiO 3 ; and optionally, the lithium silicate comprises at least Li 2 SiO 3 , and further optionally, mass of the Li 2 SiO 3 is at least 50% of mass of the first cladding layer, and more optionally, the mass of the Li 2 SiO 3 is at least 70% of the mass of the first cladding layer.
The negative electrode plate according to any one of claims 9 to 16, wherein a thickness of the first cladding layer is 10% to 80% of a particle radius of the porous silicon negative electrode material (10), optionally, a thickness of the second cladding layer is 1 nm to 50 nm, and optionally, a thickness of the third cladding layer is 1 nm to 1000 nm, and optionally is 5 nm to 300 nm.
A secondary battery, comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte solution, wherein the negative electrode plate is the negative electrode plate according to any one of claims 1 to 17.
An electrical apparatus, comprising a secondary battery, wherein the secondary battery is selected from the secondary battery according to claim 18.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims the priority of Chinese patent application No. 202310798399.1, filed on June 30, 2023, and entitled "NEGATIVE ELECTRODE PLATE, SECONDARY BATTERY, AND ELECTRICAL APPARATUS", the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present application relates to the technical field of batteries, and in particular, to a negative electrode plate, a secondary battery, and an electrical apparatus. BACKGROUND Lithium-ion batteries have the advantages such as high energy density, high power density, and long cycle life, and thus are widely used in portable electronic devices such as laptops, mobile phones, digital cameras and other electronic products. In recent years, with rapid development of new energy and clean energy vehicles, higher requirements have been placed on the performance and safety of new power batteries and energy storage batteries, and the demand for batteries to withstand various extreme working conditions is also increasing. At present, in order to improve the performance of the lithium-ion batteries, many studies are focused on the development and improvement of electrode materials and electrolytes. For example, silicon materials have a higher theoretical specific capacity (>4000 mAh/g), which is much higher (about 10 times) than the limit capacity of graphite, and has a low voltage to lithium. Therefore, the silicon materials are expected to become the first choice for batteries with high energy density. Although using a silicon negative electrode to replace part of the traditional graphite negative electrode can increase the gram capacity of the negative electrode active material, silicon may produce dramatic volume expansion during the lithium intercalation/de-intercalation process, which causes the silicon material to be rapidly pulverized and fall off from the electrode plate during the cycling process, thereby losing contact with the current collector and failing to fully exert the activity of the silicon material. SUMMARY OF THE INVENTION The present application provides a negative electrode plate, a secondary battery, and an electrical apparatus to improve the charging capability and cycling performance of the secondary battery. In a first aspect of the present application, a negative electrode plate is provided, and includes a current collector and a negative electrode film layer, where the negative electrode film layer includes a first film layer, provided on one side or both sides of the current collector; and a second film layer, provided on one side of the first film layer away from the current collector; a negative electrode active material of the first film layer and a negative electrode active material in the second film layer each independently include a silicon-based negative electrode material, the silicon-based negative electrode material in the second film layer includes a porous silicon negative electrode material, and a content of the silicon-based negative electrode material in the first film layer is less than a content of the silicon-based negative electrode material in the second film layer. In the negative electrode plate of the present application, the lower-layer first film layer also includes the silicon-based negative electrode material, thereby improving the energy density of the negative electrode plate. At the same time, the content of a silicon-based negative electrode in the first film layer on a lower layer is relatively small, which effectively alleviates the problem of stripping from the current collector caused by pulverization of the silicon-based negative electrode material during the cycling process. The second film layer on a surface layer has the porous silicon negative electrode material, thus effectively avoiding the problem of a reduced gram capacity of a battery caused by the use of pore-forming agents such as porous carbon. In addition, the porous silicon negative electrode material can increase surface layer pores, thereby overcoming the defect that due to damage to the surface layer pores caused by rolling, lithium ions cannot be intercalated into a negative electrode of the electrode plate. Moreover, the content of the silicon-based negative electrode material in the second film layer on an upper layer is greater than the content of the silicon-based negative electrode material in the first film layer on the lower layer, especially the upper layer has the porous silicon negative electrode material, such that lithium is preferentially intercalated in the upper layer, a lithium intercalating path is shorter, the kinetic performance is better, then the charging capability of the negative electrode plate is improved, and lithium precipitation is effectively alleviated, thereby improving the cycling performance of the battery. In any embodiment of the first aspect, a surface density M1 of the above first film layer is in a range of 4.5 mg/cm2 to 2