Lithium ion cells and lithium ion batteries for electrochemical prelithiation

Abstract

The application discloses a lithium ion cell and a lithium ion battery for electrochemical prelithiation, the lithium ion cell comprises a negative electrode sheet and a separator, and is characterized in that the negative electrode sheet is divided into n regions in a direction perpendicular to the direction of the tab, n is an odd number not less than 3; the negative electrode sheet is coated in a gradient mode from the middle region to the two side regions; and / or the separator is a stripe-coated separator, the interval between the stripes is equal, and the stripe width of the stripe-coated separator gradually decreases from the middle to the two sides. The lithium ion cell can effectively solve the problems of small prelithiation amount, low prelithiation rate and poor prelithiation effect in the electrochemical prelithiation of the laminated cell.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical pre-lithiation technology for lithium-ion cells, specifically relating to a lithium-ion cell for electrochemical pre-lithiation and a lithium-ion battery including the lithium-ion cell. Background Technology

[0002] Lithium-ion batteries (LIBs) have become one of the most widely used electrochemical energy storage systems due to their high energy density, high operating voltage, and lack of memory effect. However, the commonly used graphite anode has a relatively low capacity (372 mAh·g). -1 However, these technologies are insufficient to fully meet the ever-increasing market demand. Currently developed high-capacity anode materials, such as silicon and lithium metal, all suffer from various problems. Silicon, in particular, has been hampered by significant volume expansion and low conductivity, hindering its further commercialization. Lithium metal anodes, on the other hand, present safety risks due to irregular lithium dendrite growth. Furthermore, both anode materials exhibit irreversible lithium loss. Therefore, to address these issues, pre-lithiation technology has emerged. This technology replenishes lithium in the electrode material through pre-lithiation, offsetting the irreversible lithium loss caused by the formation of the SEI film, thereby improving the battery's overall capacity and energy density.

[0003] Electrochemical pre-lithiation technology has significant advantages, such as minimal modification to production lines, compatibility with existing equipment and processes, substantial performance improvements that can effectively increase capacity and improve cycle life, and no safety hazards due to the absence of lithium metal residue at the time of cell delivery and the absence of lithium plating during cycling. However, traditional electrochemical pre-lithiation technology suffers from drawbacks such as small pre-lithiation amounts and slow pre-lithiation rates, resulting in insignificant pre-lithiation effects. This is mainly because the lithium source for external pre-lithiation is located on the outside of the cell and needs to be transported to the inside of the cell using an electrolyte as a carrier. After passing through the separator, active materials, and conductive agents, the internal chemical system of the cell is complex and variable, so the force generated by a single potential difference is insufficient to achieve the desired production effect. Summary of the Invention

[0004] In view of this, the present invention needs to provide a lithium-ion cell for electrochemical pre-lithiation, which solves the problems of low pre-lithiation amount, low pre-lithiation rate and poor pre-lithiation effect in electrochemical pre-lithiation of stacked cells by designing the coating structure and process of the negative electrode and / or separator.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The present invention first provides a lithium-ion battery cell for electrochemical pre-lithiation, which includes a negative electrode and a separator. In a direction perpendicular to the tab direction, the negative electrode is divided into n regions, where n is an odd number not less than 3. The negative electrode is coated in a gradient manner from the middle region to the two side regions.

[0007] And / or, the diaphragm is a strip-coated diaphragm, and the spacing between the stripes is equal, and the stripe width of the strip-coated diaphragm gradually decreases from the middle to both sides.

[0008] Further options include n = 3 or 5.

[0009] In a further embodiment, the gradient coating refers to the N / P ratio of the negative electrode gradually increasing from the middle region to the two sides in a direction perpendicular to the tab direction.

[0010] In a further embodiment, the gradient coating refers to the gradient coating of the active material in the negative electrode slurry on the surface of the negative electrode sheet, from the middle region to the two sides, in a direction perpendicular to the tab direction. The active material includes graphite particles and / or conductive agents and / or Li. + Conductor additives.

[0011] In a further embodiment, the graphite particles are derived from raw petroleum coke, the conductive agent is conductive carbon black, and the Li... + The conductor additive is copper-tin nanowires.

[0012] In a further embodiment, in a direction perpendicular to the tab direction, from the middle region to the two sides, the proportion of single particles in the graphite particles gradually decreases, while the proportion of secondary particles gradually increases.

[0013] In a further embodiment, the content of the conductive agent gradually increases from the middle region to the two sides in a direction perpendicular to the tab direction.

[0014] A further embodiment, in a direction perpendicular to the tab direction, from the middle region to the two side regions, the portion including Li... + The content of conductor additives gradually increases.

[0015] In a further embodiment, along the tab direction, the stripes of the strip-coated diaphragm are vertical stripes, horizontal stripes, or diagonal stripes;

[0016] Preferably, the stripes of the striped diaphragm are diagonal stripes.

[0017] The present invention further provides a lithium-ion battery comprising the lithium-ion cell as described above.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention solves the problems of low pre-lithiation amount, low pre-lithiation rate, and poor pre-lithiation effect in the electrochemical pre-lithiation of stacked battery cells. Specifically, in the electrochemical pre-lithiation process of traditional stacked batteries, lithium ions diffuse from the periphery of the electrode to the center. The lithium intercalation pathway includes two types: solid-phase diffusion and liquid-phase diffusion. Solid-phase diffusion involves lithium ions diffusing from the outside to the inside of the negative electrode active material, while liquid-phase diffusion involves the diffusion of lithium ions in the electrolyte within the separator or on the surface of the active material. The diffusion medium is singular, and the driving force of diffusion (the potential difference generated between the negative electrode and the lithium band) gradually weakens as the degree of lithium intercalation increases. Therefore, using different diffusion media can improve the lithium ion diffusion rate. Because secondary particles have more active sites and larger pores than single particles, they can adsorb more electrolyte; the addition of conductive agents facilitates electron transport; and Li... + Conductors facilitate lithium-ion transport, while strip-coated separators promote electrolyte adsorption, increasing the electrolyte retention capacity of the battery cell. Therefore, this invention starts with the negative electrode slurry process, utilizing gradient coating of negative electrode active materials in the negative electrode slurry and / or optimization of strip-coated separators to increase the pre-lithiation capacity of the battery cell, improve the pre-lithiation rate, and enhance the overall pre-lithiation effect. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the negative electrode sheet with partitioned coating (divided into 3 and 5 regions) in some typical embodiments of the present invention;

[0021] Figure 2 Li is used in some typical embodiments of the present invention. + Schematic diagram of a gradient zone coating structure for conductor additives;

[0022] Figure 3 This is a schematic diagram of the strip-coated diaphragm used during stacking in some typical embodiments of the present invention. Detailed Implementation

[0023] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0025] The first aspect of this invention provides a lithium-ion battery cell for electrochemical pre-lithiation. Here, a lithium-ion battery cell refers to a stacked battery cell comprising a positive electrode, a negative electrode, a separator, and an electrolyte, assembled through a stacking process. This invention addresses the problems of low pre-lithiation rate and poor pre-lithiation effect in conventional stacked battery cells during the electrochemical pre-lithiation process by optimizing the coating structure of the negative electrode and / or separator in the lithium-ion battery cell.

[0026] In some specific embodiments of the present invention, the above-mentioned objectives are achieved by improving the negative electrode sheet. Specifically, one end of the negative electrode sheet is provided with a tab. In this text, the end closer to the tab and the end farther away from the tab is called the tab direction, also known as the first direction. The direction perpendicular to the tab direction (first direction) is called the second direction. The negative electrode sheet is divided into n regions along the second direction, where n ≥ 3 and n is an odd number. In the second direction, from the middle region to the two side regions, the negative electrode sheet is coated in a gradient manner between the regions, and the coating state is the same in the same region. The number of n can be adjusted according to specific circumstances. Taking into account factors such as cost, preferably, n = 3 or 5.

[0027] In a typical embodiment of the present invention, the gradient coating refers to the gradual increase of the N / P ratio of the negative electrode sheet along the second direction, from the middle region to the two side regions. For example, when n=3, the negative electrode sheet is evenly divided into a first region in the middle and a second region located on both sides of the first region. In this case, the N / P ratio of each region is: first region < second region. Similarly, when n=5, the negative electrode sheet is evenly divided into a first region in the middle, a second region located on both sides of the first region, and a third region located on the side of the second region away from the first region. In this case, the N / P ratio of each region is: first region < second region < third region. Since N / P represents the capacity of the extra space between the negative electrode active material and the positive electrode active material, this extra space is a key point in electrochemical pre-lithiation. A fixed N / P means that the amount of lithium ions accommodated remains constant, and the diffusion rate from the outer electrode sheet to the middle electrode sheet is fixed. Therefore, further pre-lithiation can only proceed after lithium ions have diffused and created space. More space means more lithium ions can be accommodated; therefore, a larger N / P ratio in the outer region results in a larger pre-lithiation capacity, and it can continue to accommodate new lithium ions during the migration towards the inner side. As the gradient changes, lithium ions can continuously migrate from the outside to the inside of the electrode. Therefore, the gradient design with gradually increasing N / P ratio from the middle region to both sides can effectively improve the problems of insufficient pre-lithiation, slow pre-lithiation rate, and poor pre-lithiation effect in electrochemical pre-lithiation.

[0028] In another typical embodiment of the present invention, the gradient coating refers to the gradient coating of the active material in the negative electrode slurry coated on the surface of the negative electrode sheet along the second direction, from the middle region to the two sides. The active material here includes graphite particles and / or conductive agents and / or Li.+ Conductor additives, it is understood that the types of active substances can be based on conventional compositions in the art, and the specific formulation and composition of the negative electrode slurry can be adjusted according to those well known to those skilled in the art. Preferably, the graphite particles are derived from raw petroleum coke, the conductive agent is conductive carbon black, and the Li... + The conductor additive is copper-tin nanowires.

[0029] Furthermore, compared to single particles, secondary particles, prepared from the same raw materials, have a slightly lower specific capacity but higher porosity and more reaction sites. Increased porosity allows for the inclusion of more electrolyte, which is crucial for lithium-ion transport during pre-lithiation. More reaction sites enhance lithium-ion transport efficiency. Therefore, for graphite particles in the negative electrode slurry, the gradient coating refers to a gradual decrease in the proportion of single particles and a gradual increase in the proportion of secondary particles along the second direction, from the central region to both sides. A high proportion of secondary particles (preferably pure secondary particles) is used on the outer side of the electrode to accelerate lithium-ion transport, while a high proportion of single particles (preferably pure single particles) is used on the inner side to ensure the cell's capacity and energy density. This gradient distribution accelerates pre-lithiation efficiency and improves the pre-lithiation effect. For example, when n=3, the negative electrode is divided into a central first region and a second region located on both sides of the first region. The graphite particles in the first region are single particles or a mixture of single particles and secondary particles, and the graphite particles in the second region are secondary particles. As another example, when n=5, the negative electrode is divided into a central first region, a second region located on both sides of the first region, and a third region located on the side of the second region away from the first region. The graphite particles in the first region are single particles or a mixture of single particles and secondary particles, the graphite particles in the second region are a mixture of single particles and secondary particles, and the graphite particles in the third region are secondary particles. The content of secondary particles in the second region is higher than that in the first region.

[0030] Furthermore, the increase in conductive agent in the negative electrode slurry enhances the overall conductivity of the material. The increase in conductive agent per unit area increases the number of electrons per unit area, thereby increasing the electron transfer rate and indirectly improving the lithium-ion transport rate. Therefore, in this invention, the gradient coating of the conductive agent in the negative electrode slurry refers to a gradual increase in the content of the conductive agent along the second direction, from the middle region to both sides. While designing a higher conductive agent content on the outer side of the electrode can reduce the proportion of active material and affect capacity, this can be mitigated by correspondingly reducing the amount of conductive agent on the inner side. This ensures the overall capacity of the electrode and the energy density of the cell. This gradient coating of the conductive agent addresses the problems associated with electrochemical pre-lithiation.

[0031] Furthermore, regarding Li in the negative electrode slurry+ The conductor additive, wherein the gradient coating refers to the coating applied along the second direction from the middle region to both sides, including Li + The content of conductor additives gradually increases. Li + The role of conductor additives is to provide channels for lithium ions, facilitating their transport. Adding this substance to the electrode from the outside in promotes lithium ion migration from the edges to the center. A higher content on the outer side increases the lithium ion transfer rate in the initial pre-lithiation stage, preventing lithium ion accumulation at the edges. Adding a small amount of this substance to the transition zone in the middle of the electrode also accelerates lithium ion migration towards the center. Therefore, through this Li... + Gradient coating of conductor additives is beneficial to improving the rate of electrochemical pre-lithiation.

[0032] In some specific embodiments of the present invention, the above-mentioned objectives are achieved through improvements to the separator structure. Specifically, the separator used is a strip-coated separator. As described herein, a strip-coated separator refers to a separator with a discontinuous adhesive layer coated on the surface of a base film, i.e., formed by several stripes spaced apart from each other. The composition of the adhesive layer is conventional in the art and is not particularly limited. The spacing between the stripes in the strip-coated separator is equal, and the stripe width gradually decreases from the middle to both sides. Specifically, the strip-coated separator can be divided into different regions according to the stripe width, and the stripe width is the same within the same region. Along the tab direction (first direction), the stripes of the strip-coated separator are vertical stripes, horizontal stripes, or diagonal stripes; preferably, the stripes of the strip-coated separator are diagonal stripes. In this invention, the strip-coated separator is used, where the coated area facilitates contact between the electrode and the separator, while the uncoated area has recessed gaps, which is beneficial for electrolyte storage. More electrolyte is more conducive to lithium ion transport; therefore, the strip-coated separator is the preferred choice for electrochemical pre-lithiation. Furthermore, to ensure contact between the electrode and the separator, the coating area gradually increases from the outside to the inside, ensuring the electrolyte level without reducing the contact area, thereby further improving the pre-lithiation effect.

[0033] The above-mentioned negative electrode sheet and / or separator are assembled into a lithium-ion cell through conventional stacking processes in the art, and relevant performance tests are conducted. The lithium-ion cell has excellent electrochemical pre-lithiation effect and can significantly improve the first-efficiency and cycle performance of the lithium-ion cell.

[0034] A second aspect of the present invention provides a lithium-ion battery comprising a lithium-ion cell as described in the first aspect of the present invention. This lithium-ion battery has all the beneficial effects of the aforementioned lithium-ion cell, and therefore will not be described in detail here.

[0035] The present invention will be described below through specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods that do not specifically describe conditions or steps are conventional methods, and the reagents and materials used can be obtained commercially.

[0036] The specific information regarding the raw materials used in the following examples and comparative examples is as follows:

[0037] Raw petroleum coke graphite single particles, D50 is 15μm; raw petroleum coke graphite secondary particles, D50 is 15μm;

[0038] The conductive agent is conductive carbon black;

[0039] Li + The conductor additive is copper-tin nanowires.

[0040] Comparative Example 1

[0041] In this comparative example, the battery cell has a designed capacity of 10Ah and an N / P ratio of 1.1. Its assembly process is as follows:

[0042] (1) Preparation of negative electrode slurry: Prepare the slurry according to the mass ratio of graphite particles / conductive agent / dispersant / binder of 95.5 / 1.5 / 1.2 / 1.8.

[0043] (2) The negative electrode current collector uses a copper foil with a thickness of 8 μm. The above-mentioned negative electrode slurry is coated on both sides of the surface of the negative electrode current collector to obtain a negative electrode sheet, wherein the coating surface density is 161.32 g / m². 2 The compaction density is 1.5 g / cm³. 3 ;

[0044] (3) The cell is assembled using a stacking process (15 positive electrode sheets and 16 negative electrode sheets). The composition of the positive electrode sheet is (mass ratio): lithium iron phosphate / graphene / conductive agent / binder = 96 / 1 / 0.5 / 2.5; the thickness of the PE base film is 14μm; the electrolyte is 1mol / L lithium hexafluorophosphate, and the solvent is DMC / EC = 1:1 (v / v); the cell liquid injection coefficient is 5g / Ah.

[0045] The obtained lithium-ion cells were charged at 0.02C for 4 hours at 45℃ and then charged at 0.1C for 2 hours for formation. After capacity testing at 25℃, the capacity testing capacity, the first efficiency of the cell and the capacity retention rate after 500 cycles were recorded (25℃, test current 0.33C / 0.33C, voltage range 2.0-3.65V). The results are shown in Table 1.

[0046] Comparative Example 2

[0047] The battery cell and assembly process in this comparative example are implemented in the same way as in Comparative Example 1. The difference is that after the battery cell is assembled in this comparative example, electrochemical pre-lithiation is performed.

[0048] The electrochemical pre-lithiation process is as follows:

[0049] A lithium source with the same negative electrode size was combined with the lithium-ion cell in this comparative example. After the cell was sized and tested, the time taken to reach 2.5V after liquid injection, the capacity, the cell's first efficiency and capacity retention rate after 500 cycles, and the remaining amount of lithium strip after disassembly were recorded. The results are shown in Table 1.

[0050] Example 1

[0051] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0052] In this embodiment, the negative electrode sheet is divided into three equal parts along the second direction (e.g., ...). Figure 1 As shown in Figure a), it is divided into a first region in the middle and a second region located on both sides of the first region. The N / P ratio of the first region is designed to be 1.1, and the coating surface density is 161.32 g / m². 2 The negative electrode sheet is compacted to 1.5 g / cm³. 3 The N / P ratio for the second region is designed to be 1.14, with a coating surface density of 166.42 g / m². 2 The negative electrode sheet is compacted to 1.55 g / cm³. 3 .

[0053] Example 2

[0054] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0055] In this embodiment, the negative electrode sheet is divided into 5 equal parts along the second direction (e.g., ...). Figure 1 As shown in b), it is divided into a first region in the middle, second regions located on both sides of the first region, and a third region located on the side of the second region away from the first region. The N / P ratio of the first region is designed to be 1.1, and the coating surface density is 161.32 g / m². 2 The negative electrode sheet is compacted to 1.5 g / cm³. 3 The N / P ratio for the second region is designed to be 1.12, and the coating surface density is 163.5 g / m². 2 The negative electrode sheet is compacted to 1.52 g / cm³. 3 The N / P ratio for the third region is designed to be 1.15, and the coating surface density is 167.88 g / m². 2 The negative electrode sheet is compacted to 1.56 g / cm³. 3 .

[0056] Example 3

[0057] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0058] In this embodiment, the negative electrode sheet is divided into three equal parts along the second direction (e.g., ...). Figure 1 As shown in (a), it is divided into a first region in the middle and a second region located on both sides of the first region. The graphite particles in the first region are raw petroleum single particles; the graphite particles in the second region are raw petroleum coke secondary particles.

[0059] Example 4

[0060] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0061] In this embodiment, the negative electrode sheet is divided into three equal parts along the second direction (e.g., ...). Figure 1 As shown in a), it is divided into a first region in the middle and a second region located on both sides of the first region. The graphite particles in the first region are 20wt% raw petroleum coke single particles mixed with 80wt% raw petroleum coke secondary particles; the graphite particles in the second region are raw petroleum coke secondary particles.

[0062] Example 5

[0063] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0064] In this embodiment, the negative electrode sheet is divided into 5 equal parts along the second direction (e.g., ...). Figure 1 As shown in b), it is divided into a first region in the middle, a second region located on both sides of the first region, and a third region located on the side of the second region away from the first region. The graphite particles in the first region are single raw petroleum coke particles; the graphite particles in the second region are 50wt% single raw petroleum coke particles mixed with 50wt% secondary raw petroleum coke particles; and the graphite particles in the third region are secondary raw petroleum coke particles.

[0065] Example 6

[0066] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0067] In this embodiment, the negative electrode sheet is divided into 5 equal parts along the second direction (e.g., ...). Figure 1 As shown in b), it is divided into a first region in the middle, a second region located on both sides of the first region, and a third region located on the side of the second region away from the first region. The graphite particles in the first region are 80wt% raw petroleum coke single particles mixed with 20wt% raw petroleum coke secondary particles; the graphite particles in the second region are 50wt% raw petroleum coke single particles mixed with 50wt% raw petroleum coke secondary particles; and the graphite particles in the third region are raw petroleum coke secondary particles.

[0068] Example 7

[0069] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0070] In this embodiment, the negative electrode sheet is divided into three equal parts along the second direction (e.g., ...). Figure 1 As shown in Figure a), it is divided into a first region in the middle and a second region located on both sides of the first region. The amount of conductive agent added to the negative electrode slurry in the first region is 1.2 wt%; the amount of conductive agent added to the negative electrode slurry in the second region is 1.7 wt%.

[0071] Example 8

[0072] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0073] In this embodiment, the negative electrode sheet is divided into 5 equal parts along the second direction (e.g., ...). Figure 1 As shown in b), it is divided into a first region in the middle, a second region located on both sides of the first region, and a third region located on the side of the second region away from the first region. The amount of conductive agent added in the negative electrode slurry of the first region is 1.2 wt%; the amount of conductive agent added in the negative electrode slurry of the second region is 1.5 wt%; and the amount of conductive agent added in the negative electrode slurry of the third region is 1.7 wt%.

[0074] Example 9

[0075] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0076] In this embodiment, the negative electrode sheet is divided into three equal parts along the second direction (e.g., ...). Figure 1 As shown in (a), it is divided into a first region in the middle and a second region located on both sides of the first region. The negative electrode slurry in the first region contains Li... + The amount of conductor additive added is 1 wt%; Li in the negative electrode slurry of the second region + The amount of conductor additive added is 2wt%, and the effect after coating is shown in the diagram. Figure 2 As shown in a.

[0077] Example 10

[0078] In this embodiment, the overall method of assembling the battery cell is the same as in Comparative Example 2, except that the negative electrode sheet is different.

[0079] In this embodiment, the negative electrode sheet is divided into 5 equal parts along the second direction (e.g., ...). Figure 1 As shown in b), it is divided into a first region in the middle, a second region located on both sides of the first region, and a third region located on the side of the second region away from the first region. The negative electrode slurry in the first region contains Li... +The amount of conductor additive added is 1 wt%; Li in the negative electrode slurry of the second region + The amount of conductor additive added is 2wt%; Li in the negative electrode slurry of the third region + The amount of conductor additive added is 3wt%, and the effect after coating is shown in the diagram. Figure 2 As shown in b.

[0080] Example 11

[0081] In this embodiment, the overall method of assembling the battery cells is the same as that in Comparative Example 2, except that the diaphragm used during the stacking process is different.

[0082] In this embodiment, the diaphragm used is a horizontal striped coated PE diaphragm, such as... Figure 3 As shown in b, the widths (mm) of each stripe are 1 / 1 / 2 / 2 / 3 / 3 / 4 / 5 / 6 / 5 / 4 / 3 / 3 / 2 / 2 / 1 / 1, and the interval between the stripes is 3mm.

[0083] Example 12

[0084] In this embodiment, the overall method of assembling the battery cells is the same as that in Comparative Example 2, except that the diaphragm used during the stacking process is different.

[0085] In this embodiment, the diaphragm used is a vertically striped PE diaphragm, such as... Figure 3 As shown in Figure a, the widths (mm) of each stripe are 1 / 1 / 2 / 2 / 3 / 3 / 4 / 4 / 5 / 5 / 6 / 5 / 5 / 4 / 4 / 3 / 3 / 2 / 2 / 1 / 1, and the interval between the stripes is 3mm.

[0086] Example 13

[0087] In this embodiment, the overall method of assembling the battery cells is the same as that in Comparative Example 2, except that the diaphragm used during the stacking process is different.

[0088] In this embodiment, the diaphragm used is a diagonal striped coating diaphragm, such as... Figure 3 As shown in c, the widths (mm) of each stripe are 1 / 1 / 1 / 2 / 2 / 2 / 3 / 3 / 4 / 4 / 5 / 6 / 5 / 4 / 4 / 3 / 3 / 2 / 2 / 2 / 1 / 1 / 1, and the interval between the stripes is 3mm.

[0089] The cell and pre-lithiation performance test results of Examples 1-13 and Comparative Examples 1-2 are shown in Table 1.

[0090] Table 1 Cell Test Results

[0091]

[0092] Analysis of the test results in Table 1: Comparative Example 1 is a traditional non-pre-lithiated battery, and Comparative Example 2 is a traditional electrochemical pre-lithiated battery. Comparing Comparative Examples 1 and 2, it was found that pre-lithiation can improve the cell's capacity and first-time efficiency, as well as the cell's cycle performance. However, the residual lithium content of traditional pre-lithiated cells is still very high, which may pose a safety hazard.

[0093] Comparing Comparative Example 2, Example 1, and Example 2, it can be found that increasing the N / P ratio can effectively improve the pre-lithiation rate of the cell, while also improving the capacity grading result and first efficiency, and improving the cell cycle performance. Gradient coating significantly improves the overall performance of the cell, and it can be seen that the effect of 5 coating lines is significantly better than that of 3 coating lines.

[0094] Comparing Comparative Example 2 with Examples 3, 4, 5, and 6, it can be found that increasing the content of secondary particles can improve the pre-lithiation effect, and the gradient distribution further enhances the pre-lithiation effect. This is because secondary particles have more voids and reaction sites than single particles of the same particle size, which is beneficial for the electrolyte to carry lithium ions from the outside to the inside of the cell. At the same time, more reaction sites provide the possibility for more lithium ions to land.

[0095] Comparing Comparative Example 2 with Examples 7 and 8, it can be found that the addition of conductive agent can improve the pre-lithiation effect, but the effect is not very obvious. The reason is that the conductive agent is mainly used to conduct electrons but not ions, and does not improve the lithium ion transport rate.

[0096] Comparing Comparative Example 2 with Examples 9 and 10, it can be found that Li + Conductors can effectively enhance the pre-lithiation effect, and gradient addition further enhances this effect, because Li + Conductors can provide an efficient transport channel for lithium ions, allowing them to reach the inside of the cell in a shorter time.

[0097] Comparing Comparative Example 2 with Examples 11, 12, and 13, it can be found that striped separators can improve the pre-lithiation effect, but the horizontal and vertical stripes are not as effective as the diagonal stripes. This is because the lithium insertion path of the cell is in all directions, while the limitation of a single direction is greater. Therefore, the pre-lithiation effect of the diagonal striped separator is more obvious.

[0098] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A lithium-ion electric cell for electrochemical prelithiation comprising a negative electrode sheet and a separator, characterized in that, In a direction perpendicular to the direction of the tab, the negative electrode sheet is divided into n regions, n being an odd number not less than 3; from the middle region to the two side regions, the N / P of the negative electrode sheet and the active material in the negative electrode slurry are gradiently coated; and the separator is a strip-coated separator with equal spacing between the stripes, and from the middle to the two sides, the stripe width of the strip-coated separator gradually decreases. In a direction perpendicular to the direction of the tab, the negative electrode sheet is divided into n regions, n being an odd number not less than 3; from the middle region to the two side regions, the N / P of the negative electrode sheet and the active material in the negative electrode slurry are gradiently coated; and the separator is a strip-coated separator with equal spacing between the stripes, and from the middle to the two sides, the stripe width of the strip-coated separator gradually decreases. The active material includes graphite particles and / or a conductive agent and / or Li + The conductive additive; the gradient coating of the active material means that 1) the proportion of single particles in the graphite particles gradually decreases, and the proportion of secondary particles gradually increases, or 2) the content of the conductive agent gradually increases, or 3) the content of the Li + The content of the conductive additive gradually increases.

2. The lithium-ion electric cell of claim 1, wherein, n = 3 or 5.

3. The lithium-ion electric cell of claim 1, wherein, The graphite particles are derived from green petroleum coke, the conductive agent is conductive carbon black, and the Li + The conductor additive is copper tin nanowires.

4. The lithium-ion electric cell of claim 1, wherein, In the direction of the tab, the stripes of the strip-coated separator are vertical stripes, horizontal stripes or diagonal stripes.

5. The lithium-ion electric cell of claim 4, wherein, The stripes of the strip-coated separator are diagonal stripes.

6. A lithium-ion battery, characterized by, It comprises the lithium ion cell as claimed in any one of claims 1-5.

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