A silicon-based negative electrode and its battery

Abstract

This invention discloses a silicon-based negative electrode and its battery, comprising a current collector, a non-cyclic expandable active material layer, and a silicon-containing easily cyclic expandable active material layer. The non-cyclic expandable active material layer is deposited on one side of the current collector, and the silicon-containing easily cyclic expandable active material layer is deposited on the other side. The non-cyclic expandable active material layer and the silicon-containing easily cyclic expandable active material layer are respectively coated on both sides of the current collector. The non-cyclic expandable active material layer does not easily expand during battery cycling. When the silicon-containing easily cyclic expandable active material layer expands, the non-cyclic expandable active material layer on one side will offset part of the expansion, slowing down the expansion and breakage of the silicon-based material during cycling, while simultaneously improving the energy density of the lithium-ion battery through the silicon-based material.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more particularly to a silicon-based negative electrode and its battery. Background Technology

[0002] As human industrialization increases, more and more greenhouse gases are being emitted into the atmosphere. The increasingly severe greenhouse effect, leading to extreme weather and adverse consequences, has drawn widespread international attention. Therefore, developing new energy sources has become a crucial task for ensuring the long-term development of all countries. Lithium-ion batteries, due to their advantages such as small size, light weight, high operating voltage, high specific energy, long cycle life, low self-discharge, no memory effect, and environmental friendliness, are widely used in electric vehicles, grid energy storage, portable devices, and other fields, and have experienced rapid development.

[0003] Currently, the graphite anode commonly used in lithium-ion batteries has been largely developed to its theoretical limit, making the development of novel anode materials crucial. Since silicon has a theoretical capacity as high as 4200 mAh / g, silicon-doped anodes are an effective method to improve the energy density of lithium-ion batteries. However, after a battery made from silicon-based anode materials completes charging (lithium intercalation), its volume expands by more than 300%, generating significant stress in the electrode. This stress can cause the active silicon material to fracture and cracks to appear between the silicon and the current collector. Extensive silicon material fracture and the appearance of cracks lead to a rapid decline in the cycle capacity of silicon-based anodes. Therefore, there is an urgent need for silicon-based anode sheets that can overcome the expansion and fracture of silicon material during cycling. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon-based anode sheet and its battery, overcoming the phenomenon of silicon material breakage during cycling.

[0005] This invention discloses a silicon-based negative electrode, comprising a current collector, a non-cyclic expansion type active material layer, and a silicon-containing easily cyclic expansion type active material layer; wherein, the non-cyclic expansion type active material layer is deposited on one side of the current collector, and the silicon-containing easily cyclic expansion type active material layer is deposited on the other side of the current collector.

[0006] Optionally, by mass ratio, the non-cyclic expansion type active material layer comprises 90%–98.5% active material, 0.8%–5% styrene-butadiene rubber, and 0.7%–5% sodium carboxymethyl cellulose.

[0007] Optionally, by mass ratio, the silicon-containing easily cyclic expandable active material layer comprises 95%–96% silicon-containing main material, 2%–4% polyacrylic acid, 0.1%–1% carbon nanotubes, 0.1%–2% Ketjen black, and 1%–2% sodium carboxymethyl cellulose.

[0008] Optionally, the silicon-containing main material is elemental silicon and silicon dioxide, with silicon dioxide encapsulating elemental silicon; or the silicon-containing main material is elemental silicon and carbon, with carbon encapsulating elemental silicon.

[0009] Optionally, the thickness of the non-cyclic expansion type active material layer is 1.4 times the thickness of the silicon-containing cyclic expansion type active material layer.

[0010] Optionally, the thickness of the non-cyclic expansion type active material layer is 70–100 μm.

[0011] Optionally, the thickness of the silicon-containing easily cyclic expandable active material layer is 50–70 μm.

[0012] Optionally, the thickness of the non-cyclic expansion type active material layer is 100 μm, and the thickness of the silicon-containing easily cyclic expansion type active material layer is 70 μm.

[0013] Optionally, the active material is graphite.

[0014] The present invention also discloses a battery comprising a silicon-based negative electrode as described above.

[0015] The silicon-based negative electrode of the present invention includes a current collector, a non-cyclic expandable active material layer, and a silicon-containing easily cyclic expandable active material layer. The non-cyclic expandable active material layer and the silicon-containing easily cyclic expandable active material layer are respectively coated on both sides of the current collector. The non-cyclic expandable active material layer does not easily expand during battery cycling. When the silicon-containing easily cyclic expandable active material layer expands, one side of the non-cyclic expandable active material layer will offset part of the expansion of the silicon-containing easily cyclic expandable active material layer, thereby slowing down the expansion and breakage of the silicon-based material during cycling, and at the same time improving the energy density of the lithium-ion battery through the silicon-based material. Attached Figure Description

[0016] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of the invention and illustrate implementation methods, and together with the textual description, explain the principles of the invention. Obviously, the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort. In the drawings:

[0017] Figure 1 This is a schematic diagram of one side of the silicon-based negative electrode sheet in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the other side of the silicon-based negative electrode sheet in an embodiment of the present invention.

[0019] Among them, 1. Current collector; 2. Non-cyclic expansion type active material layer; 3. Silicon-containing easily cyclic expansion type active material layer. Detailed Implementation

[0020] It should be understood that the terminology, specific structural and functional details used herein are merely for describing particular embodiments and are representative. However, the invention can be implemented in many alternative forms and should not be construed as being limited to the embodiments set forth herein.

[0021] The present invention will now be described in detail with reference to the accompanying drawings and optional embodiments.

[0022] like Figure 1 and Figure 2 As shown, as an embodiment of the present invention, a silicon-based negative electrode is disclosed, including a current collector 1, a non-cyclic expansion type active material layer 2, and a silicon-containing easily cyclic expansion type active material layer 3; wherein, the non-cyclic expansion type active material layer 2 is laid on one side of the current collector 1, and the silicon-containing easily cyclic expansion type active material layer 3 is laid on the other side of the current collector 1.

[0023] The silicon-based negative electrode of the present invention includes a current collector 1, a non-cyclic expansion type active material layer 2, and a silicon-containing easily cyclic expansion type active material layer 3. The non-cyclic expansion type active material layer 2 and the silicon-containing easily cyclic expansion type active material layer 3 are respectively coated on both sides of the current collector 1. The non-cyclic expansion type active material layer 2 does not easily expand during battery cycling. When the silicon-containing easily cyclic expansion type active material layer 3 expands, one side of the non-cyclic expansion type active material layer 2 will offset part of the expansion of the silicon-containing easily cyclic expansion type active material layer 3, thereby slowing down the expansion and breakage of the silicon-based material during cycling, and at the same time improving the energy density of the lithium-ion battery through the silicon-based material.

[0024] Specifically, by mass ratio, the non-cyclic expansion type active material layer 2 comprises 90%–98.5% active material, 0.8%–5% styrene-butadiene rubber, and 0.7%–5% sodium carboxymethyl cellulose. More specifically, the active material can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 98.5%; the styrene-butadiene rubber can be 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%; and the sodium carboxymethyl cellulose can be 0.7%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. Specifically, the active material is graphite.

[0025] Specifically, by mass ratio, the silicon-containing easily cyclic expandable active material layer 3 comprises 95%–96% silicon-containing main material, 2%–4% polyacrylic acid (PAA), 0.1%–1% carbon nanotubes (CNTs), 0.1%–2% Ketjenblack, and 1%–2% sodium carboxymethyl cellulose. More specifically, the silicon-containing main material can be 95%, 95.2%, 95.4%, 95.6%, 95.8%, or 96%; the polyacrylic acid can be 2%, 2.4%, 2.8%, 3.2%, 3.6%, or 4%; the carbon nanotubes can be 0.1%, 0.3%, 0.5%, 0.7%, or 1%; the Ketjenblack can be 0.1%, 0.5%, 1%, 1.5%, or 2%; and the sodium carboxymethyl cellulose can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%.

[0026] Specifically, the silicon-containing main material is elemental silicon and silicon dioxide, with silicon dioxide encapsulating elemental silicon; or the silicon-containing main material is elemental silicon and carbon, with carbon encapsulating elemental silicon.

[0027] Specifically, the thickness of the non-cyclic expandable active material layer 2 is 1.4 times the thickness of the silicon-containing easily cyclic expandable active material layer 3. In this scheme, the thickness of the non-cyclic expandable active material layer 2 is 1.4 times the thickness of the silicon-containing easily cyclic expandable active material layer 3. This thickness ratio can be consistent with the corresponding positive electrode thickness, making positive electrode coating convenient. At the same time, the thinner thickness on one side of the silicon-containing easily cyclic expandable active material layer 3 helps to mitigate the breakage of the silicon-based negative electrode during cycling.

[0028] In another embodiment, the thickness of the non-cyclic expandable active material layer 2 and the silicon-containing easily cyclic expandable active material layer 3 can be 70–100 μm, and the thickness of the silicon-containing easily cyclic expandable active material layer 3 can be 50–70 μm. This thickness corresponds to a consistent positive electrode thickness, facilitating positive electrode coating. Simultaneously, the thinner thickness on one side of the silicon-containing easily cyclic expandable active material layer 3 helps to mitigate the breakage of the silicon-based negative electrode during cycling. Specifically, the thickness of the non-cyclic expandable active material layer 2 is 100 μm, and the thickness of the silicon-containing easily cyclic expandable active material layer 3 is 70 μm.

[0029] Specifically, the current collector 1 can be a copper foil with a thickness of 6 μm.

[0030] The present invention also discloses a battery comprising a silicon-based negative electrode as described above.

[0031] The technical solution of the present invention will be described below through specific embodiments and comparative examples.

[0032] Example 1

[0033] A non-cyclic expansion type active material layer with a thickness of 100 μm is coated on one side of a 6 μm thick copper foil, and a silicon-containing easily cyclic expansion type active material layer with a thickness of 70 μm is coated on the other side. The formulations of the non-cyclic expansion type active material layer and the silicon-containing easily cyclic expansion type active material layer are as described above. After obtaining the silicon-based negative electrode sheet, it is then made into a battery cell and cycled for 500 cycles under a charge / discharge cycle of 0.7C / 0.5C.

[0034] Comparative Example 1

[0035] A silicon-based anode sheet was prepared by coating both sides of a 6µm thick copper foil with a silicon-containing, easily cyclic, expandable active material layer, each 70µm thick, and then fabricating the cell. The cell was then cycled 500 times under a 0.7C / 0.5C charge / discharge cycle.

[0036] Comparative Example 2

[0037] A non-cyclic expansion type active material layer with a thickness of 100um is coated on both sides of a 6um copper foil to obtain a silicon-based negative electrode sheet, which is then made into a battery cell and cycled for 500 cycles under a charge-discharge system of 0.7C / 0.5C.

[0038] After 500 cycles, the cell expansion rate of Example 1 was 13.2%, that of Comparative Example 1 was 28.3%, and that of Comparative Example 2 was 5.1%. After disassembling the cells, the silicon-based negative electrode of Example 1 cell did not break; the silicon-based negative electrode of Comparative Example 1 cell completely broke; and the silicon-based negative electrode of Comparative Example 2 cell did not break. The coating method in Example 1 reduced the cyclic expansion of the silicon-based negative electrode, solving the problem of electrode breakage after cycling.

[0039] After 500 cycles, the volumetric energy density of Example 1 was 900 Wh / L, that of Comparative Example 1 was 950 Wh / L, and that of Comparative Example 2 was 780 Wh / L. The energy density of the lithium-ion battery in Example 1 was also improved. It should be noted that although Comparative Example 1 had a high energy density, it experienced significant expansion, leading to electrode breakage after cycling, resulting in poor cycle performance and safety. In contrast, Example 1, using a single-sided silicon-containing, easily cyclically expanding active material, exhibited minimal expansion, with no electrode cracking, resulting in superior cycle performance and safety compared to Comparative Example 1. Specifically, the energy density, 300-cycle capacity retention, and 500-cycle electrode expansion rate of Example 1 and Comparative Examples 1-2 are shown in Table 1 below.

[0040] Table 1

[0041]

[0042] The above description, in conjunction with specific optional embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A silicon-based negative electrode sheet, characterized by, The silicon-based negative electrode sheet comprises a current collector, a non-circulating expansion active material layer, and a silicon-containing circulating expansion active material layer. The thickness of the non-circulating expansion active material layer is 70-100 um, and the thickness of the silicon-containing circulating expansion active material layer is 50-70 um. The non-circulating expansion active material layer comprises 90-98.5% active material, 0.8-5% butadiene-styrene rubber, and 0.7-5% sodium carboxymethyl cellulose. The silicon-containing circulating expansion active material layer comprises 95-96% silicon-containing main material, 2-4% polyacrylic acid, 0.1-1% nanometer carbon tube, 0.1-2% Ketjen black, and 1-2% sodium carboxymethyl cellulose.

2. The silicon-based negative electrode sheet according to claim 1, wherein The silicon-containing main material is elemental silicon and silicon dioxide, and the silicon dioxide wraps the elemental silicon.

3. The silicon-based negative electrode sheet according to claim 1, wherein The active material is graphite.

4. A battery, characterized by The thickness of the non-circulating expansion active material layer is 1.4 times the thickness of the silicon-containing circulating expansion active material layer. The thickness of the non-circulating expansion active material layer is 100 um, and the thickness of the silicon-containing circulating expansion active material layer is 70 um. The silicon-based negative electrode sheet comprises a current collector, a non-circulating expansion active material layer, and a silicon-containing circulating expansion active material layer. The silicon-based negative electrode sheet comprises a current collector, a non-circulating expansion active material layer, and a silicon-containing circulating expansion active material layer.

Images