Long-life lithium ion battery and preparation method of pole piece, pole group and battery

Abstract

The invention discloses a long-life lithium ion battery, a pole piece, pole groups and a preparation method of the battery. The long-life lithium ion battery comprises a plurality of pole groups, the active material coating surface densities of the positive plate and the negative plate in each pole group are the same; and the active material coating surface density of the positive plates and the negative plates of the plurality of pole groups is gradually reduced along with the gradual increase of the distances from the positive plates and the negative plates to the central position in the long-life lithium ion battery. The method is scientific in design, and different gradients of the coating surface densities of the positive plate and the negative plate from the inside of the battery cell to the outside of the battery cell are set by utilizing the principle that the coating surface densities are different and the electrolyte absorption capacities of the pole plates are different; the aggravation trend of electrolyte absorption amount difference caused by different permeation effects of pole pieces inside and outside the battery in the later period of charging and discharging due to different stress of the pole pieces from the inside to the outside in a traditional piece making mode is delayed, the current density of the pole pieces of each part of a battery cell is balanced, reaction interface deterioration is continuously delayed, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a long-life lithium-ion battery and a method for preparing electrodes, electrode assemblies and the battery. Background Technology

[0002] Currently, lithium-ion batteries have advantages such as high specific energy, high cycle life, and long storage time. They are widely used not only in portable electronic devices (such as mobile phones, digital cameras, and laptops), but also in electric vehicles, electric bicycles, power tools, energy storage, and other fields. Therefore, the performance requirements for lithium-ion batteries are becoming increasingly stringent.

[0003] During the charging and discharging process of a battery, the constraints of the battery casing, the shrinkage and expansion of the electrode plates, etc., will cause differences in the forces on the inner and outer electrode plates of the cell, which will affect the absorption of the electrolyte and the actual current density distribution.

[0004] For traditional lithium-ion batteries, the electrodes are usually coated with a uniform (i.e., uniform) areal density. After the electrode assembly is formed, there is no obvious difference between the inside and outside of the cell. This cannot balance the current density of the electrodes in the later stages of charging and discharging due to the difference in the stress on the electrodes inside and outside the cell, which leads to the difference in electrolyte absorption. This results in the difference in current density of the electrodes and ultimately leads to the continuous deterioration of the reaction interface, which in turn affects the cycle life of the battery.

[0005] Therefore, there is an urgent need to develop a technology that can improve battery performance, solve the problem of uneven electrolyte distribution in the later stages of battery charging and discharging, and balance the differences in current density. This is of great significance for improving the cycle life of batteries. Summary of the Invention

[0006] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a method for preparing a long-life lithium-ion battery, as well as electrodes, electrode assemblies, and the battery itself.

[0007] Therefore, the present invention provides a long-life lithium-ion battery comprising multiple electrode groups;

[0008] The active material coating density of the positive and negative electrodes within a single electrode assembly is the same.

[0009] The surface density of the active material coating on the positive and negative electrodes of multiple electrode groups gradually decreases as the distance from the center of the long-life lithium-ion battery increases.

[0010] The long-life lithium-ion battery includes a first cell pack A and a second cell pack B.

[0011] The first battery pack A and the second battery pack B are symmetrically distributed from left to right;

[0012] The first cell pack A includes multiple first electrode groups, and as the distance from the center of the long-life lithium-ion battery gradually decreases, the active material coating density of the positive and negative electrode sheets of the multiple first electrode groups is distributed from small to large.

[0013] The second cell pack B includes multiple second electrode groups, and as the distance from the center of the long-life lithium-ion battery gradually increases, the surface density of the active material coating of the positive and negative electrode sheets of the multiple second electrode groups is distributed from large to small.

[0014] The first electrode group and the second electrode group are prepared in the same way.

[0015] The number of first electrode groups included in the first cell pack A is the same as the number of second electrode groups included in the second cell pack B, and the surface density of the active material coating of each first electrode group is the same as the surface density of the active material coating of a second electrode group.

[0016] Furthermore, the present invention also provides a method for preparing the electrode as described above, characterized by comprising the following steps:

[0017] The first step is to take out the pre-prepared electrode slurry and coat multiple sections of active material onto at least one side of the electrode current collector. After each section of active material is coated, a coating mark is set at the end of the coating.

[0018] Among them, the coating density of multiple active substances located on the same side is different;

[0019] The second step is to dry the electrode current collector after the electrode slurry coating is completed, and then roll it to obtain the rolled electrode.

[0020] The third step involves cutting the electrode sheets after rolling according to the coating markings to obtain multiple electrode sheets with different active material coating densities.

[0021] In the first step, the coating density of the multiple active materials on the same side is distributed in ascending order.

[0022] In addition, the present invention also provides a method for preparing the electrode assembly as described above, characterized by comprising the following steps:

[0023] Step S1, positive electrode preparation operation, to prepare multiple positive electrode sheets with different positive electrode active material coating surface densities;

[0024] Step S2, negative electrode preparation operation, to prepare multiple negative electrode sheets with different coating surface densities of negative electrode active materials;

[0025] Step S3: Perform the preparation operation of a single electrode group multiple times to obtain multiple electrode groups of positive and negative electrode sheets with different active material coating surface densities.

[0026] Specifically, the preparation of a single electrode group involves selecting the positive and negative electrode sheets with the same active material coating density from the multiple positive electrode sheets obtained in step S2 and the multiple negative electrode sheets obtained in step S3, placing the separator between the positive and negative electrode sheets, and preparing a single electrode group by winding or stacking. The ratio of the active material coating density of the positive and negative electrode sheets in the single electrode group conforms to the N / P design ratio.

[0027] Specifically, step S1 includes the following steps S101 to S104:

[0028] Step S101: Take out the pre-prepared positive electrode slurry, and coat multiple sections of positive electrode active material onto at least one side surface of the positive electrode current collector in sequence. After each section of positive electrode active material is coated, set a coating mark at the end of the coating.

[0029] Among them, the coating surface density of multiple positive electrode active materials located on the same side is different, and they are distributed in a gradient.

[0030] Step S102: The positive current collector after the positive electrode slurry coating is completed is dried and then rolled to obtain the rolled positive electrode sheet.

[0031] Step S103: For the positive electrode sheet after rolling, cut the sheet according to the coating mark to obtain multiple positive electrode sheets with different positive active material coating surface densities.

[0032] And / or,

[0033] Step S2 specifically includes the following steps S201 to S204:

[0034] Step S201: Take out the pre-prepared negative electrode slurry, and coat multiple sections of negative electrode active material onto at least one side surface of the negative electrode current collector in sequence. After each section of negative electrode active material is coated, set a coating mark at the end of the coating.

[0035] Among them, the coating surface density of multiple negative electrode active materials located on the same side is different;

[0036] Step S202: The negative electrode current collector after the negative electrode slurry coating is completed is dried and then rolled to obtain the rolled negative electrode sheet.

[0037] Step S203: For the negative electrode sheet after rolling, cut the sheet according to the coating mark to obtain multiple negative electrode sheets with different coating surface densities of negative electrode active material.

[0038] In the positive electrode slurry, the mass percentages of the positive electrode active material, conductive agent, and binder are (90%-98%), (1%-5%), and (1%-5%), respectively.

[0039] In the negative electrode slurry, the mass percentages of the negative electrode active material, conductive agent and binder are (90%-98%), (1%-5%) and (1%-5%), respectively.

[0040] Furthermore, the present invention also provides a method for preparing a long-life lithium-ion battery as described above, comprising the following steps:

[0041] First, perform steps S1 to S3 as described in any one of claims 7 to 9 to obtain multiple electrode groups of positive and negative electrode sheets with different active material coating surface densities;

[0042] Then, the cell pack composed of multiple electrode groups is placed into the battery casing, and the surface density of the active material coating of the positive and negative electrode sheets of the multiple electrode groups gradually decreases as the distance from the center of the long-life lithium-ion battery gradually increases.

[0043] Finally, the battery casing undergoes sealing, liquid injection, and formation processes to obtain the finished battery, which is a long-life lithium-ion battery.

[0044] As can be seen from the technical solution provided by the present invention above, compared with the prior art, the present invention provides a method for preparing a long-life lithium-ion battery, electrode sheets, electrode groups, and battery. Its design is scientific. It utilizes the principle that the electrode sheet has different electrolyte absorption capacity due to different coating surface densities. By setting different gradients in the coating surface density of the positive and negative electrode sheets from the inside to the outside of the cell, it slows down the increasing trend of electrolyte absorption difference caused by the different stress on the electrode sheets from the inside to the outside of the battery in the later stage of charging and discharging due to different electrode penetration. It balances the current density of the electrode sheets in different parts of the cell, continuously delays the deterioration of the reaction interface, and thus extends the cycle life of the battery, which has significant practical significance. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the coating method in existing traditional film preparation methods;

[0046] Figure 2 A schematic diagram of the coating method for preparing an electrode sheet according to the present invention;

[0047] Figure 3 A schematic diagram of a long-life lithium-ion battery cell structure provided by the present invention (the separator between the positive and negative electrode plates is not shown in this figure, and the separator is omitted from the drawing);

[0048] Figure 4This is a schematic diagram comparing the cycle life of the battery obtained in the embodiments of the present invention with that of a comparative battery obtained using a conventional wafer fabrication method. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0051] In the description of this patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this patent according to the specific circumstances.

[0052] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0053] See Figure 3 As shown, the present invention provides a long-life lithium-ion battery, comprising multiple electrode groups;

[0054] The active material coating density of the positive and negative electrodes within a single electrode assembly is the same.

[0055] The surface density of the active material coating on the positive and negative electrodes of multiple electrode groups gradually decreases as the distance from the internal center position (i.e., the axial center position) of the long-life lithium-ion battery gradually increases.

[0056] It should be noted that, in this invention, the areal density distribution of the positive and negative electrode sheets in the long-life lithium-ion battery gradually decreases from the inner center to the outer side, i.e., it exhibits a gradient distribution.

[0057] In this invention, specifically, the long-life lithium-ion battery includes a first cell pack A and a second cell pack B;

[0058] The first battery pack A and the second battery pack B are symmetrically distributed from left to right;

[0059] The first cell pack A includes multiple first electrode groups (e.g., four electrode groups such as electrode groups A1, A2, A3 and A4), and as the distance from the center position (i.e. the axial center position) inside the long-life lithium-ion battery gradually decreases, the active material coating surface density (i.e. electrode surface density) of the positive and negative electrode sheets of the multiple first electrode groups is distributed from small to large.

[0060] The second cell pack B includes multiple second electrode groups (e.g., four electrode groups such as electrode groups B1, B2, B3, and B4), and as the distance from the center position (i.e., the axial center position) inside the long-life lithium-ion battery gradually increases, the active material coating surface density (i.e., electrode surface density) of the positive and negative electrode sheets of the multiple second electrode groups is distributed from large to small.

[0061] It should be noted that for an electrode assembly, the surface density of the active material coating on the positive and negative electrodes is the same.

[0062] In practice, the first and second electrode groups are prepared in the same way. For example, they are both prepared by stacking or winding. Both the first and second electrode groups include a positive electrode, a negative electrode, and a separator located between the positive and negative electrode.

[0063] In specific implementation, the number of first electrode groups included in the first cell pack A is the same as the number of second electrode groups included in the second cell pack B, and the surface density of the active material coating of each first electrode group is the same as the surface density of the active material coating of a second electrode group.

[0064] In this invention, see Figure 2 As shown, for multiple electrode groups, positive and negative electrode sheets with different active material coating surface densities are obtained by the following preparation method (the following method is a preparation method of multiple electrode sheets with different active material coating surface densities provided by the present invention):

[0065] The first step is to take out the pre-prepared electrode slurry (including positive electrode slurry and negative electrode slurry), and coat multiple segments of active material 2 sequentially on at least one side surface (specifically, the upper surface or the lower surface, or both the upper and lower surfaces) of the electrode current collector 1 (e.g., positive electrode current collector or negative electrode current collector). After each segment of active material 2 is coated, a coating mark 3 is set at the end of the coating (i.e., the right end).

[0066] Among them, the coating surface density of the multiple active substances 2 located on the same side is different;

[0067] In the first step, specifically, the coating density of the multiple active material 2 segments located on the same side is gradient-distributed.

[0068] Furthermore, the coating surface density of the multiple active substances 2 located on the same side is distributed in ascending order.

[0069] In the first step, the specific implementation method of coating mark 3 on electrode current collector 1 (i.e. marking method) is not limited to leaving blank, marking or inkjet printing.

[0070] The second step is to dry the electrode current collector 1 after the electrode slurry coating is completed, and then roll it to obtain the rolled electrode.

[0071] The third step is to cut the electrode sheets after rolling according to the coating mark 3 to obtain multiple electrode sheets with different active material coating surface densities.

[0072] For specific implementation details, please refer to [link / reference]. Figure 2 As shown, multiple electrode groups with different active material coating areal densities are obtained by the following preparation method (i.e., the following method is a preparation method for multiple electrode groups with different active material coating areal densities):

[0073] Step S1, positive electrode preparation operation, to prepare multiple positive electrode sheets with different positive electrode active material coating areal densities, specifically including the following steps S101 to S104:

[0074] Step S101: Take out the pre-prepared positive electrode slurry and sequentially coat at least one side surface of the positive electrode current collector with multiple segments of positive electrode active material (e.g., Figure 2 The active material segments shown are a1, a2, a3 and a4, and after each segment of positive electrode active material is coated, a coating mark 3 is set at the end of the coating.

[0075] Among them, the coating surface density of multiple positive electrode active materials located on the same side is different, and they are distributed in a gradient.

[0076] In step S101, specifically, the coating surface density of multiple positive electrode active materials located on the same side is gradient-distributed.

[0077] Furthermore, the coating surface density of the multiple positive electrode active materials located on the same side is distributed in ascending order.

[0078] In step S101, the specific implementation of the method of setting the coating mark 3 on the positive current collector (i.e., the marking method) is not limited to leaving blank, marking or inkjet printing.

[0079] Step S102: The positive current collector after the positive electrode slurry coating is completed is dried and then rolled to obtain the rolled positive electrode sheet.

[0080] Step S103: For the positive electrode sheet after rolling, cut the sheet according to the coating mark 3 to obtain multiple positive electrode sheets with different coating surface densities of positive active material.

[0081] Step S2, negative electrode preparation operation, to prepare multiple negative electrode sheets with different coating areal densities of negative electrode active materials, specifically including the following steps S201 to S204:

[0082] Step S201: Take out the pre-prepared negative electrode slurry and sequentially coat at least one side surface of the negative electrode current collector with multiple segments of negative electrode active material (e.g., Figure 2 The active material segments shown are a1, a2, a3 and a4, and after each segment of negative electrode active material is coated, a coating mark 3 is set at the end of the coating.

[0083] Among them, the coating surface density of multiple negative electrode active materials located on the same side is different;

[0084] In step S201, specifically, the coating surface density of the multiple negative electrode active materials located on the same side is gradient-distributed and conforms to the n / p design ratio with the positive electrode surface density.

[0085] Furthermore, the surface density of the coating of the multiple negative electrode active materials located on the same side is distributed in ascending order.

[0086] In step S201, the specific implementation of the method of setting the coating mark 3 on the negative electrode current collector (i.e., the marking method) is not limited to leaving blank, marking or inkjet printing.

[0087] Step S202: The negative electrode current collector with the negative electrode slurry coating completed is dried and then rolled.

[0088] Step S203: For the negative electrode sheet after rolling, cut the sheet according to the coating mark 3 to obtain multiple negative electrode sheets with different coating surface densities of negative electrode active material.

[0089] It should be noted that the surface density range of the active material coating on the positive and negative electrodes should conform to the N / P safety design range, and the N / P should be between 1.04 and 1.2 to prevent lithium plating on the negative electrode.

[0090] It should be noted that the surface density of the active material coating on both the positive and negative electrode sheets should be within the engineering capacity range of a conventional coating machine, and the surface density of the active material coating on the positive electrode sheet should be between 20 mg / cm³. 2 ~40mg / cm 2 The surface density of the active material coating on the negative electrode should be between 15 mg / cm³. 2 ~20mg / cm 2 Between these steps, it is necessary to prevent large deviations in coating precision from causing abnormalities at the cell interface and affecting the final evaluation results;

[0091] Furthermore, the surface density gradient of the active material coating on the positive and negative electrodes is set in the transverse length direction of the electrodes;

[0092] Furthermore, the positive and negative electrodes are coated according to the designed areal density gradient, and the coating areal density is kept consistent in each gradient cycle.

[0093] Furthermore, the positive current collector is aluminum foil, and the negative current collector is copper foil.

[0094] Furthermore, the main material of the positive electrode slurry is lithium iron phosphate, and the main material of the negative electrode slurry is graphite;

[0095] Furthermore, in the positive electrode slurry, the mass percentages of the positive electrode active material, conductive agent, and binder are (90%-98%), (1%-5%), and (1%-5%), respectively.

[0096] In the negative electrode slurry, the mass percentages of negative electrode active material, conductive agent and binder are (90%-98%), (1%-5%) and (1%-5%), respectively, which are in line with conventional electrode formulation design and prevent the electrode formulation from affecting the electrode interface reaction and ultimately affecting the evaluation results.

[0097] Step S3: Perform the preparation operation of a single electrode group multiple times to obtain multiple electrode groups of positive and negative electrode sheets with different active material coating surface densities.

[0098] The preparation of a single electrode group is specifically as follows: For the multiple positive electrode sheets obtained in step S2 and the multiple negative electrode sheets obtained in step S3, select the positive and negative electrode sheets with the same active material coating density, and place the separator between the positive and negative electrode sheets. A single electrode group is prepared by winding or stacking. The ratio of the active material coating density of the positive and negative electrode sheets in the single electrode group meets the N / P design ratio (e.g., N / P = 1.1), where N / P = (the proportion of negative active material content × the negative electrode surface density × the negative electrode specific capacity) / (the proportion of positive active material content × the positive electrode surface density × the positive electrode specific capacity).

[0099] Based on the above-mentioned method for preparing multiple electrode groups with positive and negative electrode sheets having different active material coating surface densities provided by the present invention, the present invention also provides a method for preparing a long-life lithium-ion battery, which includes the following steps:

[0100] First, perform steps S1 to S3 as described above to obtain multiple electrode groups of positive and negative electrode sheets with different active material coating surface densities.

[0101] Then, the cell pack composed of multiple electrode groups is placed into the battery casing, and the surface density of the active material coating of the positive and negative electrode plates of the multiple electrode groups gradually decreases as the distance from the internal center position (i.e., the axial center position) of the long-life lithium-ion battery gradually increases.

[0102] Finally, the battery casing undergoes sealing, liquid injection, and formation processes to obtain the finished battery, which is a long-life lithium-ion battery.

[0103] In this invention, after obtaining a long-life lithium-ion battery, a lifespan test and evaluation can be performed.

[0104] To better understand the technical solution of the present invention, the technical solution of the present invention will be described below through specific embodiments and comparative examples.

[0105] Example.

[0106] In this invention, the prepared positive electrode slurry (main material is lithium iron phosphate) and negative electrode slurry (main material is graphite) are continuously coated and marked in segments according to a pre-designed areal density gradient. Then, according to the coating markings, the electrodes are rolled and cut into sheets, and electrodes with the same areal density are made into the same electrode group. Following a design where the areal density distribution of the positive and negative electrodes gradually decreases from the center of the battery cell to the outside, the battery cell is manufactured. After completing subsequent processes such as electrolyte filling, the finished battery is produced and its lifespan is evaluated. Specifically, the following operations are included:

[0107] 1. According to the electrode formula, the ratio of active material: conductive agent: binder = 95%: 2%: 3%, positive and negative electrode slurries were prepared respectively;

[0108] 2. The prepared positive and negative electrode slurries were coated according to Table 1, "Design Table of Coating Area Density for Positive and Negative Electrodes," to obtain the positive and negative electrode sheets of the comparative examples and embodiments, respectively.

[0109] In this embodiment, the active material is coated according to the density gradient of each coating surface, and a mark is made at the end, with a coating identifier 3, such as... Figure 2 As shown;

[0110] In the comparative example, the coating length of each electrode segment follows the coating length of each electrode segment in the embodiment, and a mark is made at the end, such as... Figure 1 As shown. Note: N / P = 1.1.

[0111] Table 1. Design Table of Coating Surface Density for Positive and Negative Electrodes

[0112]

[0113] 3. According to the coating mark 3, the positive and negative electrode sheets of the comparative example and the embodiment are cut and rolled into 4 segments a1, a2, a3 and a4.

[0114] 4. Based on the areal density gradient group, positive and negative electrode sheets with the same active material coating areal density as those in the comparative example and the embodiment are made into the same electrode group. Two electrode groups are prepared for each active material coating areal density segment, i.e., 8 electrode groups in the comparative example and 8 electrode groups in the embodiment. Specifically, both the comparative example and the embodiment include four electrode groups A1 to A4 and four electrode groups B1 to B4. For the embodiment, the active material coating areal densities of the four electrode groups A1 to A4 are the same as those of the four electrode groups B1 to B4. For the comparative example, there is no difference in the active material coating areal densities of the four electrode groups A1 to A4 and the four electrode groups B1 to B4.

[0115] 5. First, the four electrode groups (A1-A4) in the embodiment are assembled into a first cell pack A in order of increasing areal density gradient (A1-A2-A3-A4). Then, the other four electrode groups in the embodiment are assembled into a second cell pack B in order of decreasing areal density (B4-B3-B2-B1). Finally, the two first cell packs are assembled into a battery cell of the embodiment. Figure 3 As shown;

[0116] exist Figure 3 The long-life battery includes a battery casing 4, and a first cell pack A and a first cell pack B are disposed inside the battery casing 4.

[0117] The first battery pack A and the second battery pack B are symmetrically distributed from left to right;

[0118] See Figure 3 As shown, the first cell pack A includes four electrode groups: A1, A2, A3, and A4. The electrode groups gradually decrease in size as the distance from the center position (i.e., the axial center position) inside the long-life lithium-ion battery increases. The surface density of the active material coating on the positive electrode 5 and the negative electrode 6 of the electrode groups A1, A2, A3, and A4 is distributed from small to large (i.e., distributed from the outside to the inside according to A1-A2-A3-A4).

[0119] The second cell pack B includes four electrode groups: B1, B2, B3, and B4. The electrode groups gradually decrease in size as their distance from the center position (i.e., the axial center position) of the long-life lithium-ion battery increases. The surface density of the active material coating on the positive electrode 5 and negative electrode 6 of the electrode groups B1, B2, B3, and B4 is distributed from small to large (i.e., distributed from the inside to the outside according to B4-B3-B2-B1).

[0120] 6. The active material coating surface density of the 8 electrode groups in the comparative example is the same. Randomly select 4 electrode groups to form cell pack A, and form cell pack B with the remaining 4 electrode groups. Finally, combine the two cell packs to form the battery cell of the comparative example.

[0121] 7. Simultaneously process the comparative and example cells with the same process parameters for liquid injection, formation and other post-processing to produce the comparative lithium-ion battery and the example lithium-ion battery.

[0122] 8. Perform cycle life tests on the comparative and example batteries under the same test conditions and plot the capacity retention curves.

[0123] See Figure 4 As shown, compared with the comparative battery (i.e., the battery obtained by the conventional uniform surface density fabrication method), the battery of the embodiment provided by the present invention has a significantly better energy retention rate curve and trend than the comparative battery. This fully demonstrates that the cycle life of the battery is significantly improved after using the battery preparation method provided by the present invention.

[0124] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A long-life lithium-ion battery, characterized in that, Includes multiple pole groups; The active material coating density of the positive and negative electrodes within a single electrode assembly is the same. The surface density of the active material coating on the positive and negative electrodes of multiple electrode groups gradually decreases as the distance from the center of the long-life lithium-ion battery increases.

2. The long-life lithium-ion battery as described in claim 1, characterized in that, Including the first cell pack A and the second cell pack B; The first battery pack A and the second battery pack B are symmetrically distributed from left to right; The first cell pack A includes multiple first electrode groups, and as the distance from the center of the long-life lithium-ion battery gradually decreases, the active material coating density of the positive and negative electrode sheets of the multiple first electrode groups is distributed from small to large. The second cell pack B includes multiple second electrode groups, and as the distance from the center of the long-life lithium-ion battery gradually increases, the surface density of the active material coating of the positive and negative electrode sheets of the multiple second electrode groups is distributed from large to small.

3. The long-life lithium-ion battery as described in claim 2, characterized in that, The preparation methods for the first and second electrode groups are the same.

4. The long-life lithium-ion battery as described in claim 2, characterized in that, The number of first electrode groups included in the first cell pack A is the same as the number of second electrode groups included in the second cell pack B, and the surface density of the active material coating of each first electrode group is the same as the surface density of the active material coating of a second electrode group.

5. A method for preparing an electrode as described in claim 1, characterized in that, Includes the following steps: First, take out the pre-prepared electrode slurry and coat multiple active materials (2) on at least one side of the electrode current collector (1). After each active material (2) is coated, a coating mark (3) is set at the end of the coating. Among them, the coating surface density of the multiple active substances (2) located on the same side is different; The second step is to dry the electrode current collector (1) after the electrode slurry coating is completed, and then roll it to obtain the rolled electrode. The third step is to cut the electrode sheets after rolling according to the coating mark (3) to obtain multiple electrode sheets with different active material coating surface densities.

6. The method for preparing the electrode sheet as described in claim 5, characterized in that, In the first step, the coating surface density of the multiple active materials (2) located on the same side is distributed in ascending order.

7. A method for preparing an electrode assembly as described in claim 1, characterized in that, Includes the following steps: Step S1, positive electrode preparation operation, to prepare multiple positive electrode sheets with different positive electrode active material coating surface densities; Step S2, negative electrode preparation operation, to prepare multiple negative electrode sheets with different coating surface densities of negative electrode active materials; Step S3: Perform the preparation operation of a single electrode group multiple times to obtain multiple electrode groups of positive and negative electrode sheets with different active material coating surface densities. Specifically, the preparation of a single electrode group involves selecting the positive and negative electrode sheets with the same active material coating density from the multiple positive electrode sheets obtained in step S2 and the multiple negative electrode sheets obtained in step S3, placing the separator between the positive and negative electrode sheets, and preparing a single electrode group by winding or stacking. The ratio of the active material coating density of the positive and negative electrode sheets in the single electrode group conforms to the N / P design ratio.

8. The method for preparing the electrode assembly as described in claim 7, characterized in that, Step S1 specifically includes the following steps S101 to S104: Step S101: Take out the pre-prepared positive electrode slurry, coat multiple sections of positive electrode active material on at least one side surface of the positive electrode current collector, and set a coating mark (3) at the end of each coating after the coating of each section of positive electrode active material is completed. Among them, the coating surface density of multiple positive electrode active materials located on the same side is different, and they are distributed in a gradient. Step S102: The positive current collector after the positive electrode slurry coating is completed is dried and then rolled to obtain the rolled positive electrode sheet. Step S103: For the positive electrode sheet after rolling, cut the sheet according to the coating mark (3) to obtain multiple positive electrode sheets with different positive active material coating surface densities; And / or, Step S2 specifically includes the following steps S201 to S204: Step S201: Take out the pre-prepared negative electrode slurry, coat multiple sections of negative electrode active material on at least one side surface of the negative electrode current collector, and set a coating mark at the end of each section of negative electrode active material after coating is completed (3). Among them, the coating surface density of multiple negative electrode active materials located on the same side is different; Step S202: The negative electrode current collector after the negative electrode slurry coating is completed is dried and then rolled to obtain the rolled negative electrode sheet. Step S203: For the negative electrode sheet after rolling, cut the sheet according to the coating mark (3) to obtain multiple negative electrode sheets with different coating surface densities of negative electrode active material.

9. The method for preparing the electrode assembly as described in claim 8, characterized in that, In the positive electrode slurry, the mass percentages of the positive electrode active material, conductive agent, and binder are (90%-98%), (1%-5%), and (1%-5%), respectively. In the negative electrode slurry, the mass percentages of the negative electrode active material, conductive agent and binder are (90%-98%), (1%-5%) and (1%-5%), respectively.

10. A method for preparing a long-life lithium-ion battery as described in claim 1, characterized in that, It includes the following steps: First, perform steps S1 to S3 as described in any one of claims 7 to 9 to obtain multiple electrode groups of positive and negative electrode sheets with different active material coating surface densities; Then, the cell pack composed of multiple electrode groups is placed into the battery casing, and the surface density of the active material coating of the positive and negative electrode sheets of the multiple electrode groups gradually decreases as the distance from the center of the long-life lithium-ion battery gradually increases. Finally, the battery casing undergoes sealing, liquid injection, and formation processes to obtain the finished battery, which is a long-life lithium-ion battery.

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