Negative electrode sheet, method for producing negative electrode sheet, and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and specifically provides a negative electrode sheet, a preparation method of the negative electrode sheet and a lithium ion battery. The negative electrode sheet comprises a current collector and a negative electrode material layer arranged on at least one side of the current collector, and further comprises a first lithium supplementing layer and a second lithium supplementing layer. The negative electrode material layer, the first lithium supplementing layer and the second lithium supplementing layer are sequentially arranged in a direction away from the current collector. Any one of the first lithium supplementing layer and the second lithium supplementing layer comprises a lithium supplementing area and a non-lithium supplementing area, and the other lithium supplementing layer only comprises a continuously distributed lithium supplementing area. The electrode sheet solves the problems of poor electrolyte infiltration, low lithium utilization rate and excessive dead lithium caused by the traditional single-layer lithium supplementing, and the performance of the battery cell is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically providing a negative electrode sheet, a method for preparing the negative electrode sheet, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries (LIBs) possess advantages such as high energy density, high operating voltage, long cycle life, low environmental pollution, low self-discharge, and no memory effect, making them one of the most promising rechargeable batteries. They are currently widely used in mobile phones, laptops, cameras, portable tools, electric vehicles, and energy storage. With the rapid development of electric vehicles and energy storage, the demand for lithium-ion batteries is even stronger.

[0003] However, during the initial activation and early cycling stages of lithium-ion batteries, rapid consumption of active lithium occurs due to factors such as SEI film formation and repair, deactivation of negative electrode active sites, and irreversible lithium metal deposition. This results in low initial efficiency and rapid reversible capacity decay during cycling. Current methods to improve initial efficiency primarily rely on lithium replenishment technology. Commonly used lithium replenishment technologies include: negative electrode lithium replenishment, positive electrode lithium replenishment, electrochemical lithium replenishment, and electrolyte lithium replenishment. These utilize an external lithium source to compensate for the SEI film's consumption during formation, significantly improving the cell's initial efficiency. Simultaneously, a portion of lithium ions can be pre-stored to replenish lithium consumption during cycling, thereby extending the cell's cycle life. Negative electrode lithium replenishment has promising applications due to its significant improvement in lithium replenishment effect, with rolling lithium replenishment technology being particularly widely used.

[0004] The lithium strip rolling and lithium replenishment method involves rolling lithium strips to a thickness of micrometers and then laminating them onto the surface of the negative electrode sheet. The main problems with this method are:

[0005] 1. Full coverage of the electrode surface with lithium strips will increase the electrolyte wetting path, resulting in poor wetting effect, reduced lithium strip utilization and no significant performance improvement;

[0006] 2. Although the striped zebra-shaped lithium bands on the electrode surface improve electrode wetting, the lithium sheet becomes thicker than a fully covered lithium sheet under the same lithium replenishment conditions. After liquid injection, the lithium reaction near the electrode is rapid and achieves a good lithium replenishment effect. The part far from the electrode cannot achieve the lithium replenishment effect due to the obstruction of electron transport path and side reactions, becoming dead lithium and reducing the improvement effect on cycle life.

[0007] Therefore, it is necessary to develop a negative electrode lithium replenishment method to improve the lithium replenishment effect and thus optimize the battery cycle performance. Summary of the Invention

[0008] To overcome the above-mentioned defects, this invention proposes a negative electrode sheet, a method for preparing the negative electrode sheet, and a lithium-ion battery, which improves lithium utilization, significantly reduces lithium residue, and further improves cycle life under the same lithium replenishment design.

[0009] In a first aspect, the present invention provides a negative electrode sheet, comprising a current collector and a negative electrode material layer disposed on at least one side of the current collector, the electrode sheet further comprising: a first lithium replenishment layer and a second lithium replenishment layer; wherein the negative electrode material layer, the first lithium replenishment layer and the second lithium replenishment layer are disposed sequentially in a direction away from the current collector; either the first lithium replenishment layer and the second lithium replenishment layer comprises a lithium replenishment region and a non-lithium replenishment region, and the other lithium replenishment layer comprises only a continuously distributed lithium replenishment region.

[0010] Furthermore, the first lithium replenishment layer only includes continuously distributed lithium replenishment regions, and the lithium replenishment regions of the first lithium replenishment layer completely cover the surface of the negative electrode material layer;

[0011] The second lithium replenishment layer includes a lithium replenishment region and a non-lithium replenishment region, with the lithium replenishment region of the second lithium replenishment layer disposed on the surface of the first lithium replenishment layer.

[0012] Furthermore, the mass Q1 of the lithium replenishment material in the continuously distributed lithium replenishment zone and the total mass Q of the lithium replenishment material in the first and second lithium replenishment layers satisfy the following relationship:

[0013] 5% ≤ Q1 / Q ≤ 50%.

[0014] Furthermore, in a lithium replenishment layer consisting only of continuously distributed lithium replenishment regions, the area S1 of the lithium replenishment region and the surface area S of the negative electrode material layer satisfy the following relationship:

[0015] S1 / S = 100%.

[0016] Furthermore, in the lithium-replenishing layer, which includes both lithium-replenishing and non-lithiation-replenishing regions, the total area S2 of the lithium-replenishing region and the surface area S of the negative electrode material layer satisfy the following relationship:

[0017] 60% ≤ S² / S ≤ 95%.

[0018] Furthermore, the lithium replenishment layer includes a lithium replenishment region and a non-lithium replenishment region, wherein the distribution of the lithium replenishment region and the non-lithium replenishment region includes any of the following:

[0019] The lithium replenishment area includes multiple strips made of lithium replenishment material, and the non-lithium replenishment area is the gap area between the multiple strips;

[0020] The lithium replenishment area includes a mesh made of lithium replenishment material, and the non-lithium replenishment area is the gap region within the mesh;

[0021] The lithium replenishment area includes multiple blocks made of lithium replenishment material, and the non-lithium replenishment area is the gap area between the multiple blocks.

[0022] Furthermore, the plurality of strips are arranged along the length and / or width direction of the current collector.

[0023] Furthermore, the plurality of strips are arranged along the length and width directions of the current collector, including:

[0024] The strip-shaped objects arranged along the length direction of the current collector and the strip-shaped objects arranged along the width direction of the current collector are arranged perpendicularly to each other.

[0025] Furthermore, in the lithium replenishment layer including the lithium replenishment area and the non-lithium replenishment area, the lithium replenishment material in the lithium replenishment area includes one or more of lithium foil, lithium wire and lithium powder;

[0026] The lithium replenishment layer, which includes only continuously distributed lithium replenishment areas, contains lithium replenishment materials including one or more of lithium foil, lithium wire, and lithium powder.

[0027] In a second aspect, the present invention provides a method for preparing a negative electrode sheet, comprising:

[0028] A negative electrode material layer is formed on at least one side of the current collector;

[0029] Along a direction away from the current collector, a first lithium replenishment layer and a second lithium replenishment layer are sequentially formed on the negative electrode material layer; wherein, either the first lithium replenishment layer or the second lithium replenishment layer includes a lithium replenishment region and a non-lithium replenishment region, and the other lithium replenishment layer includes only a continuously distributed lithium replenishment region.

[0030] In a third aspect, the present invention provides a lithium-ion battery comprising the negative electrode sheet described in the first aspect or a negative electrode sheet prepared by the preparation method described in the second aspect.

[0031] The above-described technical solutions of the present invention have at least one or more of the following beneficial effects:

[0032] This invention proposes an innovative negative electrode lithium replenishment technology. By cleverly fusing two different lithium replenishment methods—a lithium replenishment layer with a continuous lithium replenishment area and a lithium replenishment layer with a discontinuous lithium replenishment area—it achieves a significant improvement in lithium utilization and a substantial reduction in residual lithium. This technology not only optimizes the lithium replenishment process but also further improves the battery cycle life under the same lithium replenishment amount. Attached Figure Description

[0033] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Furthermore, similar numbers in the drawings are used to denote similar components, wherein:

[0034] Figure 1 This is a schematic diagram of the cross-sectional structure of the electrode sheet according to an embodiment 1 of the present invention;

[0035] Figure 2This is a top view schematic diagram of the electrode structure according to an embodiment 1 of the present invention;

[0036] Figure 3 This is a top view schematic diagram of the electrode structure according to an embodiment 5 of the present invention;

[0037] Figure 4 This is a schematic diagram of the structure of a lithium replenishment layer comprising a circular block according to an embodiment of the present invention;

[0038] Figure 5 This is a schematic flowchart of the main steps in the preparation method of the negative electrode sheet according to an embodiment of the present invention.

[0039] List of reference numerals :

[0040] 1: Current collector; 2: Negative electrode active material; 3: First lithium replenishment layer; 4: Second lithium replenishment layer; 5: Tab. Detailed Implementation

[0041] Some embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0042] The present invention provides a negative electrode sheet, comprising a current collector 1 and a negative electrode material layer 2 disposed on at least one side of the current collector 1. The electrode sheet further comprises a first lithium replenishment layer 3 and a second lithium replenishment layer 4. The negative electrode material layer 2, the first lithium replenishment layer 3 and the second lithium replenishment layer 4 are disposed sequentially in a direction away from the current collector 1. Each of the first lithium replenishment layer 3 and the second lithium replenishment layer 4 is composed of lithium replenishment regions in a discontinuous distribution state. The lithium replenishment layer includes lithium replenishment regions and non-lithium replenishment regions, and the other lithium replenishment layer only includes continuously distributed lithium replenishment regions and does not include non-lithium replenishment regions.

[0043] The lithium replenishment zone serves to replenish lithium and is filled with lithium metal products, which are lithium replenishment materials. The non-lithium replenishment zone is an empty area and is not filled with lithium replenishment material.

[0044] The lithium replenishment layer includes both lithium replenishment and non-lithium replenishment areas. The lithium replenishment material in the lithium replenishment area includes one or more of lithium foil, lithium wire, and lithium powder.

[0045] The lithium replenishment layer, which includes only continuously distributed lithium replenishment areas, contains lithium replenishment materials including one or more of lithium foil, lithium wire, and lithium powder.

[0046] The aforementioned lithium replenishment materials can be selected based on the size and shape of the lithium replenishment area.

[0047] In one embodiment, a first lithium replenishment layer 3 and a second lithium replenishment layer 4 are sequentially formed on the negative electrode material layer 2 using methods such as calendering, vapor deposition, or 3D printing.

[0048] The specific method involves using one or more lithium-replenishing materials, such as lithium foil, lithium wire, and lithium powder, to form a first lithium-replenishing layer 3 on the negative electrode material layer 2 through techniques such as calendering, vapor deposition, or 3D printing.

[0049] Then, using one or more lithium replenishing materials such as lithium foil, lithium wire and lithium powder, a second lithium replenishing layer 4 is formed on the first lithium replenishing layer 3 through techniques such as calendering, vapor deposition or 3D printing.

[0050] Calendering, vapor deposition, or 3D printing are common forming processes used for shaping lithium metal. These processes can precisely shape lithium replenishment materials according to the specific shape of a pre-defined lithium replenishment area.

[0051] For the negative electrode sheet, three layers are attached to the current collector 1: negative electrode material layer 2, first lithium replenishment layer 3, and second lithium replenishment layer 4. The specific distribution of the three layers is as follows:

[0052] (1) A negative electrode material layer 2 is coated on the current collector 1. The negative electrode material layer 2 is composed of a negative electrode active material, a binder and a conductive agent. The negative electrode active material can be a common graphite material. The negative electrode material layer 2 can be coated on one or both sides of the current collector 1.

[0053] (2) Then a first lithium replenishment layer 3 is formed on the negative electrode material layer 2.

[0054] (3) Finally, a second lithium replenishment layer 4 is formed on the first lithium replenishment layer 3.

[0055] The first lithium replenishment layer 3 and the second lithium replenishment layer 4 have different distributions of lithium replenishment regions. In one lithium replenishment layer, the lithium replenishment regions are continuously distributed, while in the other, they are discontinuously distributed. The lithium replenishment layer includes lithium replenishment regions and non-lithium replenishment regions, where the lithium replenishment material is provided for lithium replenishment, and the non-lithium replenishment regions separate the lithium replenishment regions.

[0056] This invention proposes an innovative negative electrode lithium replenishment technology that cleverly combines two different lithium replenishment methods, achieving a significant improvement in lithium utilization and a substantial reduction in residual lithium. This technology not only optimizes the lithium replenishment process but also further improves the design cycle life under the same lithium replenishment amount, thus providing new possibilities for improving battery performance.

[0057] In comparing the two types of lithium replenishment layers, the continuously distributed lithium replenishment method has certain advantages and significant disadvantages. Its advantage lies in the larger contact area between the lithium replenishment material and the electrode, which facilitates the chemical reaction and thus improves the lithium replenishment efficiency. However, this method also has a significant disadvantage: the electrolyte wetting effect is negatively affected. Although the portion near the electrode can react rapidly to achieve the purpose of lithium replenishment, the lithium replenishment material further away from the electrode reacts more difficultly, resulting in low utilization of the lithium replenishment material. In this case, a large amount of residual lithium will cover the electrode surface, making the lithium replenishment effect unsatisfactory and failing to achieve the expected lifespan improvement.

[0058] Another discontinuous lithium replenishment method has the advantage of improved electrolyte wetting compared to continuous lithium replenishment. However, this method also has inherent disadvantages: the contact area between the lithium replenishment material and the negative electrode surface is reduced, leading to an increase in the thickness of the lithium replenishment layer for the same amount of lithium replenishment. This makes the reaction of the lithium replenishment material farther from the electrode more difficult, resulting in lower utilization of the material and a large amount of residual lithium covering the electrode surface, leading to poor lithium replenishment and failing to achieve the expected lifespan improvement. Furthermore, the increased thickness of the lithium replenishment material also leads to an increase in the cell thickness, negatively impacting cell design.

[0059] The innovation of this application lies in its creative combination of these two lithium replenishment methods. Through a specific electrode construction technique, it effectively improves lithium utilization, thereby significantly enhancing the battery's cycle life. This technology not only solves the problems in existing technologies but also opens up new avenues for further improvement in battery performance.

[0060] In one embodiment, reference is made to Figure 1 The first lithium replenishment layer 3 includes only a continuously distributed lithium replenishment area, and the lithium replenishment area of ​​the first lithium replenishment layer 3 completely covers the surface of the negative electrode material layer 2.

[0061] The second lithium replenishment layer 4 includes lithium replenishment regions and non-lithium replenishment regions, which are distributed alternately. The lithium replenishment regions of the second lithium replenishment layer 4 are disposed on the surface of the first lithium replenishment layer 3.

[0062] In one embodiment, there exists a specific proportional relationship between the mass Q1 of the lithium replenishment material in the continuously distributed lithium replenishment zone and the total mass Q of the lithium replenishment material in the first lithium replenishment layer 3 and the second lithium replenishment layer 4. This relationship can be expressed by the following mathematical formula:

[0063] 5% ≤ Q1 / Q ≤ 50%.

[0064] This continuously distributed lithium replenishment layer is fully laid and covered on the entire surface of the electrode, rather than selectively laid in parts. The rate at which the continuously distributed lithium replenishment layer is consumed affects the wetting effect of the electrolyte. Under the mass ratio of this embodiment, it can be ensured that the first lithium replenishment layer 3 and the second lithium replenishment layer 4 can better complement each other and jointly improve the lithium replenishment effect.

[0065] In one embodiment, in a lithium replenishment layer comprising only continuously distributed lithium replenishment regions, the area S1 of the lithium replenishment regions and the surface area S of the negative electrode material layer 2 satisfy the following relationship:

[0066] S1 / S = 100%.

[0067] This mathematical expression shows that the continuously distributed lithium replenishment layer is uniformly covered on the entire surface of the negative electrode material layer 2. In other words, the lithium replenishment layer achieves full-area coverage of the surface of the negative electrode material layer 2.

[0068] Method for calculating the area of ​​the lithium replenishment zone: The lithium replenishment material in the lithium replenishment zone is laid flat. If a lithium replenishment zone of a certain shape is laid on a plane, then the area occupied by this flat area filled by the lithium replenishment material is the area calculated by the above formula.

[0069] The negative electrode material layer 2 is a slurry made of negative electrode active material, conductive agent and binder, which is laid or coated on the current collector. The area laid or coated is the surface area S of the negative electrode material layer 2. For example, if the negative electrode material layer 2 is square, then the surface area S of the negative electrode material layer 2 is the product of the length and the width.

[0070] In one embodiment, the lithium replenishment layer includes both lithium replenishment and non-lithium replenishment regions, meaning the lithium replenishment layer simultaneously includes both lithium replenishment and non-lithium replenishment regions. The total area S2 of the lithium replenishment regions and the surface area S of the negative electrode material layer 2 satisfy the following relationship:

[0071] 60% ≤ S² / S ≤ 95%.

[0072] For lithium replenishment layers where the lithium replenishment area is discontinuously distributed, the area calculation method is to calculate each segmented lithium replenishment area separately, and then obtain the total area. Specifically, for each segmented lithium replenishment area, the lithium replenishment area under the lithium replenishment material is calculated, and then the areas are summed to obtain the total area S2 of the lithium replenishment area of ​​the entire lithium replenishment layer.

[0073] In this embodiment, the focus is on the lithium replenishment layer when the lithium replenishment region is discontinuously distributed. The relationship between the area S2 of the lithium replenishment region and the surface area S of the negative electrode active material 2 is given, and a clear numerical range is provided.

[0074] Specifically, the relationship between the area S2 of the lithium replenishment region and the surface area S of the negative electrode material layer 2 satisfies the following mathematical expression:

[0075] When the lithium replenishment layer includes both lithium replenishment and non-lithium replenishment areas, the total area S2 of all lithium replenishment areas used for lithium replenishment accounts for a proportion of the surface area S of the negative electrode material layer 2 between 60% and 95%.

[0076] S2 refers to the total area of ​​all areas filled with lithium replenishment material in the lithium replenishment layer.

[0077] By setting a specific ratio of S2 to the surface area S of the negative electrode material layer 2, the size of the lithium replenishment area in the lithium replenishment region can be effectively controlled, thereby ensuring that the first lithium replenishment layer 3 and the second lithium replenishment layer 4 can better complement each other and jointly improve the lithium replenishment effect.

[0078] The following describes the distribution pattern of the lithium replenishment layer when it includes both lithium replenishment and non-lithium replenishment regions.

[0079] The distribution patterns of lithium replenishment areas and non-lithiation replenishment areas include any of the following:

[0080] The lithium replenishment area includes multiple strips made of lithium replenishment material, and the non-lithium replenishment area is the gap area between the multiple strips;

[0081] The lithium replenishment area includes a mesh made of lithium replenishment material, and the non-lithium replenishment area is the gap region within the mesh;

[0082] The lithium replenishment zone consists of multiple blocks made of lithium replenishment material, and the non-lithium replenishment zone is the gap area between the multiple blocks.

[0083] This configuration results in a discontinuous distribution of the lithium replenishment material on the electrode, allowing the discontinuous lithium replenishment area between the two lithium replenishment layers to replenish lithium ions together with the continuously distributed lithium replenishment area during battery charging and discharging.

[0084] In one embodiment, the plurality of strips are arranged along the length and / or width direction of the current collector.

[0085] by Figure 2 For example, the strip-shaped material is a lithium strip. The first lithium replenishment layer 3 is designed as a lithium replenishment layer, such as a lithium sheet, consisting of continuous lithium replenishment regions, while the second lithium replenishment layer 4 is designed as a lithium replenishment layer including both lithium replenishment and non-lithium replenishment regions. Specifically, the lithium replenishment regions of the second lithium replenishment layer 4 are composed of multiple spaced-apart strip-shaped lithium strips, which are spaced apart along the horizontal direction (width direction) of the current collector 1 on the surface of the first lithium replenishment layer 3. This design makes the distribution of lithium strips more uniform.

[0086] In addition, to more completely demonstrate the overall structure of the electrode, Figure 2The diagram also shows tab 5. Tab 5 is connected to the electrode plate, specifically to the current collector 1. This connection method not only ensures good contact between tab 5 and the electrode plate, but also makes the current transmission of the battery more stable during charging and discharging.

[0087] In one embodiment, reference is made to Figure 3 The plurality of strips are arranged along the length and width directions of the current collector 1, including:

[0088] The strip-shaped objects arranged along the length direction of the current collector 1 and the strip-shaped objects arranged along the width direction of the current collector 1 are arranged perpendicularly to each other.

[0089] In one embodiment, reference is made to Figure 4 The lithium replenishment zone consists of multiple circular blocks made of lithium powder, a lithium replenishment material, and the non-lithium replenishment zone is the gap area between the multiple circular blocks.

[0090] This invention also provides a method for preparing a negative electrode sheet, referring to... Figure 5 The preparation methods include:

[0091] S1, a negative electrode material layer 2 is formed on at least one side of the current collector 1;

[0092] S2, along the direction away from the current collector 1, a first lithium replenishment layer 3 and a second lithium replenishment layer 4 are sequentially formed on the negative electrode material layer 2; wherein, either the first lithium replenishment layer 3 or the second lithium replenishment layer 4 includes a lithium replenishment region and a non-lithium replenishment region, and the other lithium replenishment layer only includes a continuously distributed lithium replenishment region.

[0093] The present invention also provides a lithium-ion battery, including the negative electrode sheet or the negative electrode sheet prepared by the preparation method.

[0094] The following examples illustrate the preparation of lithium-added negative electrode sheets and their fabrication into lithium-ion batteries for cycle performance testing.

[0095] Example 1:

[0096] Positive electrode preparation: Lithium iron phosphate (LiFePO4), conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are uniformly dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 96.5%:1.5%:2% to form a positive electrode slurry. The slurry is then coated, dried, and rolled onto a current collector aluminum foil to form a positive electrode sheet.

[0097] Negative electrode preparation: Artificial graphite, SP, CMC, and styrene-butadiene rubber are uniformly dispersed in deionized water at a mass ratio of 96%:1.2%:1%:1.8% to form a negative electrode slurry, i.e., a negative electrode material layer. This slurry is then coated onto copper foil, dried, and rolled. The rolled negative electrode sheet undergoes a lithium strip calendering and lithium replenishment process, which is performed twice, as described above. Figure 1-2 The structure involves firstly covering the surface of the negative electrode material layer with a first lithium replenishment layer, and secondly forming a second lithium replenishment layer on the first lithium replenishment layer. The second lithium replenishment layer includes lithium replenishment areas and non-lithium replenishment areas that are spaced apart. The mass Q1 of the lithium replenishment material in the lithium replenishment area of ​​the first lithium replenishment layer accounts for 20% of the total lithium replenishment amount Q. Finally, the negative electrode sheet after lithium replenishment is made.

[0098] Diaphragm: Polyethylene film is selected as the diaphragm.

[0099] The positive electrode, separator, and lithium-added negative electrode are arranged in sequence, with the separator positioned between the positive and negative electrodes, to form a dry cell. Then, the cells are assembled, injected with electrolyte, aged, formed, and capacity-tested to produce a lithium-ion secondary battery.

[0100] Example 2:

[0101] The only difference from Example 1 is that the mass of the lithium replenishing material Q1 in the lithium replenishing region of the first lithium replenishing layer accounts for 5% of the total lithium replenishment amount Q (Q1 / Q).

[0102] Example 3:

[0103] The only difference from Example 1 is that the mass ratio (Q1 / Q) of the lithium replenishment material Q1 in the lithium replenishment region of the first lithium replenishment layer to the total lithium replenishment amount Q is 50%.

[0104] Example 4

[0105] The difference from Example 1 is that the first lithium replenishment layer includes spaced lithium replenishment areas and non-lithium replenishment areas. The lithium replenishment areas are composed of multiple strip-shaped lithium strips, which are evenly spaced on the surface of the negative electrode material layer. The first lithium replenishment layer appears to be attached to the surface of the negative electrode material layer like zebra stripes. The second lithium replenishment layer includes continuously distributed lithium replenishment areas, and lithium metal is rolled and laid on the entire surface of the first lithium replenishment layer. The continuously distributed lithium replenishment areas, i.e., the lithium replenishment area S1 of the second lithium replenishment layer in this example, satisfy S1 / S = 100% with the surface area S of the negative electrode active material. In this example, the lithium replenishment amount Q1 of the second lithium replenishment layer accounts for 20% of the total lithium replenishment amount Q. The area S2 of the lithium replenishment area of ​​the first lithium replenishment layer satisfies the relationship S2 / S = 70% with the surface area S of the negative electrode active material.

[0106] Example 5

[0107] The only difference from Example 1 is that, referring to Figure 3The second lithium replenishment layer is composed of multiple lithium strips. Part of the lithium strips are distributed at intervals along the length direction of the current collector of the electrode, and another part of the lithium strips are distributed at intervals along the width direction of the current collector of the electrode. The lithium strips in the two directions are arranged perpendicularly to each other.

[0108] Example 6

[0109] The only difference from Example 1 is that the area S2 of the lithium replenishment region of the second lithium replenishment layer 4 satisfies the relationship S with the surface area S of the negative electrode active material: S2 / S = 95%.

[0110] Example 7

[0111] The only difference from Example 1 is that the area S2 of the lithium replenishment region of the second lithium replenishment layer 4 and the surface area S of the negative electrode active material satisfy the relationship: S2 / S = 60%.

[0112] Comparative Example 1:

[0113] The only difference from Example 1 is that in Comparative Example 1, there is only a continuous lithium replenishment area, namely the first lithium replenishment layer, which is fully laid out and formed on the negative electrode active material. There are no other lithium replenishment layers, and the total lithium replenishment amount Q is designed on the first lithium replenishment layer.

[0114] Comparative Example 2:

[0115] The only difference from Example 1 is that Comparative Example 1 only has a discontinuously distributed lithium replenishment region, that is, the second lithium replenishment layer. The lithium bands in the lithium replenishment region of the second lithium replenishment layer are spaced on the negative electrode material layer. Comparative Example 2 has a continuous first lithium replenishment layer without a lithium replenishment region. The lithium replenishment amount Q is designed on the lithium replenishment region of the second lithium replenishment layer. The second lithium replenishment layer includes a lithium replenishment region and a non-lithium replenishment region.

[0116] Comparative Example 3:

[0117] The only difference from Example 1 is that in Comparative Example 3, the mass ratio of the lithium replenishment amount Q1 of the first lithium replenishment layer to the total lithium replenishment amount Q is 3%.

[0118] Comparative Example 4:

[0119] The only difference from Example 1 is that the mass ratio of the lithium replenishing material Q1 in the lithium replenishing region of the first lithium replenishing layer to the total lithium replenishing amount Q is 80%.

[0120] The negative electrode lithium replenishment design pre-stores a portion of lithium at the negative electrode. This pre-stored lithium can promptly replenish the lithium loss during cycling, which manifests as a continuously flattening cycle curve. Therefore, it is possible to monitor the cycle curves of cells with different lithium replenishment designs under the same lithium replenishment conditions and compare the number of cycles at the start of degradation. A higher number of cycles at the start of degradation indicates a better lithium replenishment effect and a higher lithium band utilization rate, resulting in a longer cycle life in the later stages.

[0121] The lithium-ion secondary batteries prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to cycle capacity retention tests.

[0122] The specific testing method is as follows: under 25℃ conditions, the battery is cycle-tested according to the following steps: 1. The secondary battery is charged at a constant current rate of 0.5C, and the charging cut-off voltage is 3.65V.

[0123] 2. Let the secondary battery stand for 5 minutes;

[0124] 3. Discharge the secondary battery at a constant current rate of 0.5C, with a discharge cutoff voltage of 2.5V;

[0125] 4. Let the lithium-ion secondary battery stand for 5 minutes.

[0126] The above steps 1-4, the charge-discharge process, constitute one cycle. The discharge capacity is recorded as the initial battery capacity. Repeat the above steps and calculate the capacity retention rate: Capacity retention rate = Discharge capacity / Initial capacity × 100%. The test results are shown in Table 1.

[0127] Table 1. Main design parameters and test results for each embodiment and comparative example.

[0128]

[0129] By analyzing and comparing the data from Examples 1 to 5 with those from Comparative Examples 1 to 4, it can be seen that the traditional lithium replenishment methods, namely using either a continuously distributed lithium replenishment layer or a discontinuously distributed lithium replenishment layer, are not ideal. When using a continuously distributed lithium replenishment layer, although the contact area between the lithium replenishment material and the electrode is larger, which is beneficial for lithium-ion reaction and thus improves replenishment efficiency, this design leads to a deterioration in electrolyte wetting. While the lithium replenishment material near the electrode can react quickly to achieve the replenishment effect, the lithium replenishment material further away from the electrode has a more difficult reaction, resulting in a reduced utilization rate of the lithium replenishment material. This inefficient utilization ultimately leads to a large amount of residual lithium covering the electrode surface, negatively impacting the overall performance of the cell. On the other hand, when using a discontinuously distributed lithium replenishment layer, although the electrolyte wetting is improved compared to a continuously distributed lithium replenishment layer, the contact area between the lithium replenishment material and the surface of the negative electrode active material is reduced. This results in an increased thickness of the lithium replenishment layer under the same amount of lithium replenishment, making the reaction of the lithium replenishment material farther from the electrode more difficult, and the utilization rate of the lithium replenishment material is also low. This low utilization rate also leads to a large amount of residual lithium covering the electrode surface, affecting the performance of the cell.

[0130] This invention proposes an innovative lithium replenishment design method, which combines lithium replenishment layers with continuous and discontinuous distributions in the lithium replenishment region. By adjusting the lithium mass ratio of these two types of lithium replenishment layers, this invention significantly improves the lithium replenishment effect and effectively enhances the battery's cycle performance. This combination not only optimizes the lithium-ion reaction efficiency but also improves the electrolyte wettability, ensuring good contact between the lithium replenishment material and the electrode, thereby increasing the utilization rate of the lithium replenishment material and reducing the adverse effects of residual lithium on cell performance.

[0131] The structure of Example 1 shows the most significant improvement in battery cycle performance, and its mechanism of action is analyzed as follows:

[0132] The first lithium replenishment layer, with its continuously distributed lithium replenishment areas, provides complete coverage of the entire surface of the negative electrode active material, rather than selectively covering only a portion. This comprehensive coverage ensures maximum contact area between the first lithium replenishment layer and the negative electrode active material, significantly improving lithium replenishment efficiency. The lithium replenishment amount in the first layer is completely consumed before the lithium replenishment reaction is fully completed, thus exposing the non-overlapping area of ​​the negative electrode active material between the first and second lithium replenishment layers. This exposure helps improve electrolyte wettability. Subsequently, the second lithium replenishment layer comes into play, specifically comprising lithium replenishment and non-lithium replenishment areas, which are alternately distributed, allowing the lithium replenishment reaction to continue. Furthermore, because the area of ​​the lithium replenishment area in the first lithium replenishment layer is larger than that in the second lithium replenishment layer, the thickness of the second lithium replenishment layer is reduced, increasing the lithium band reaction efficiency away from the negative electrode active material, thereby improving cell performance.

[0133] In Example 4, multiple spaced-apart strip-shaped lithium strips are placed below the full-area lithium replenishment layer. However, this results in a lower lithium replenishment effect compared to placing the strip-shaped lithium strips above the full-area lithium replenishment layer. The main reason is the low hardness of lithium metal itself. If the strip-shaped lithium strips are used as the first layer and the sheet-like full-coverage lithium metal is used as the second layer, during the fabrication process, the second layer will partially fuse with the first layer of strip-shaped lithium replenishment material under pressure, causing some damage to the intended structure and resulting in a less effective lithium replenishment compared to other examples.

[0134] In the continuously distributed lithium replenishment layers, there is a certain proportional relationship between the mass Q1 of the lithium replenishing agent used and the total mass Q of the lithium replenishing agent used in the first lithium replenishment layer 3 and the second lithium replenishment layer 4. When this ratio Q1 / Q reaches 20%, the lithium replenishment effect becomes more obvious and effective. The discovery of this proportional relationship has important guiding significance for optimizing the performance of the lithium replenishment layer.

[0135] Even when Comparative Examples 3 and 4 used the same structure as Example 1 to construct the first lithium replenishment layer 3 and the second lithium replenishment layer 4, if the mass Q1 of the lithium replenishing agent used in the continuously distributed lithium replenishment layers was too large or too small, a problem would arise: the lithium replenishing agent could not achieve good compatibility with the other lithium replenishment layer (including the lithium replenishment region and the non-lithium replenishment region). This poor compatibility would directly result in poor wetting effect of the electrolyte and insufficient utilization of the lithium replenishment layer, thus failing to achieve the expected battery performance improvement effect.

[0136] Example 5 uses an upper layer (second layer) with multiple lithium strips arranged in a cross-sectional structure. This structure is a derivative of the strip-shaped lithium replenishment structure, and its performance is similar to that of the strip-shaped lithium replenishment structure, and it also has a good lithium replenishment effect.

[0137] It should be noted that although the steps in the above embodiments are described in a specific order, those skilled in the art will understand that in order to achieve the effects of the present invention, different steps do not necessarily have to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders, and these variations are all within the scope of protection of the present invention.

[0138] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The electrode includes a current collector (1) and a negative electrode material layer (2) disposed on at least one side of the current collector (1), characterized in that the electrode further includes a first lithium replenishment layer (3) and a second lithium replenishment layer (4); wherein the negative electrode material layer (2), the first lithium replenishment layer (3) and the second lithium replenishment layer (4) are disposed sequentially in a direction away from the current collector (1); either the first lithium replenishment layer (3) or the second lithium replenishment layer (4) includes a lithium replenishment region and a non-lithium replenishment region, and the other lithium replenishment layer includes only a continuously distributed lithium replenishment region.

2. The electrode sheet according to claim 1, characterized in that, The first lithium replenishment layer (3) consists only of continuously distributed lithium replenishment regions, and the lithium replenishment regions of the first lithium replenishment layer (3) completely cover the surface of the negative electrode material layer (2); The second lithium replenishing layer (4) includes lithium replenishing regions and non-lithium replenishing regions spaced apart, and the lithium replenishing regions of the second lithium replenishing layer (4) are disposed on the surface of the first lithium replenishing layer (3).

3. The electrode sheet according to claim 1, characterized in that, The mass Q1 of the lithium replenishment material in the continuously distributed lithium replenishment zone satisfies the following relationship with the total mass Q of the lithium replenishment material in the first lithium replenishment layer (3) and the second lithium replenishment layer (4): 5% ≤ Q1 / Q ≤ 50%.

4. The electrode sheet according to claim 1, characterized in that, In the lithium replenishment layer that only includes continuously distributed lithium replenishment regions, the area S1 of the lithium replenishment regions and the surface area S of the negative electrode material layer (2) satisfy the following relationship: S1 / S = 100%.

5. The electrode sheet according to claim 1, characterized in that, In the lithium-replenishing layer, which includes both lithium-replenishing and non-lithiation-replenishing regions, the total area S2 of the lithium-replenishing region and the surface area S of the negative electrode material layer (2) satisfy the following relationship: 60% ≤ S² / S ≤ 95%.

6. The electrode sheet according to claim 1, characterized in that, The lithium replenishment layer includes a lithium replenishment region and a non-lithium replenishment region, wherein the distribution of the lithium replenishment region and the non-lithium replenishment region includes any of the following: The lithium replenishment area includes multiple strips made of lithium replenishment material, and the non-lithium replenishment area is the gap area between the multiple strips; The lithium replenishment area includes a mesh made of lithium replenishment material, and the non-lithium replenishment area is the gap region within the mesh; The lithium replenishment area includes multiple blocks made of lithium replenishment material, and the non-lithium replenishment area is the gap area between the multiple blocks.

7. The electrode sheet according to claim 6, characterized in that, The plurality of strips are arranged along the length and / or width of the current collector (1).

8. The electrode sheet according to claim 7, characterized in that, The plurality of strips are arranged along the length and width directions of the current collector (1), including: The strips arranged along the length direction of the current collector (1) and the strips arranged along the width direction of the current collector (1) are arranged perpendicularly to each other.

9. The electrode sheet according to claim 1, characterized in that, The lithium replenishment layer, which includes both lithium replenishment and non-lithiation replenishment areas, includes lithium replenishment materials in the lithium replenishment area, which include one or more of lithium foil, lithium wire, and lithium powder. The lithium replenishment layer, which includes only continuously distributed lithium replenishment areas, contains lithium replenishment materials including one or more of lithium foil, lithium wire, and lithium powder.

10. A method for preparing a negative electrode sheet, characterized in that, include: A negative electrode material layer (2) is formed on at least one side of the current collector (1); Along a direction away from the current collector (1), a first lithium replenishment layer (3) and a second lithium replenishment layer (4) are sequentially formed on the negative electrode material layer (2); wherein either the first lithium replenishment layer (3) or the second lithium replenishment layer (4) includes a lithium replenishment region and a non-lithium replenishment region, and the other lithium replenishment layer includes only a continuously distributed lithium replenishment region.

11. A lithium-ion battery, characterized in that, Includes the negative electrode sheet according to any one of claims 1-9 or the negative electrode sheet prepared by the preparation method according to claim 10.

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