Lithium-ion battery and manufacturing method therefor

Abstract

The present application relates to the technical field of lithium-ion batteries, and specifically relates to a lithium-ion battery and a manufacturing method therefor. The lithium-ion battery comprises a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprising a positive electrode coating layer, and the positive electrode coating layer comprising a positive electrode active material and a positive electrode pre-lithiation additive. The negative electrode coating layer comprises a negative electrode active material; a charge N / P ratio of the lithium-ion battery is greater than or equal to a first threshold, a discharge N / P ratio of the lithium-ion battery is less than or equal to a second threshold, and the first threshold is less than the second threshold. The charge N / P ratio is a ratio of a first negative electrode capacity to a first positive electrode capacity, the first negative electrode capacity being a negative electrode charge capacity, and the first positive electrode capacity being a positive electrode charge capacity; and the discharge N / P ratio is a ratio of a second negative electrode capacity to a second positive electrode capacity, the second negative electrode capacity being a negative electrode discharge capacity, and the second positive electrode capacity being a positive electrode discharge capacity. The lithium-ion battery provided by the present application exhibits good specific discharge capacity and cycling performance.

Description

A lithium-ion battery and its manufacturing method

[0001] This application claims priority to Chinese Patent Application No. 202411865524.7, filed on December 17, 2024, entitled "A Lithium-ion Battery and a Method for Manufacturing the Same", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery and its manufacturing method. Background Technology

[0003] Energy is an indispensable resource for human societal development. With societal progress, energy issues have consistently garnered significant attention, and traditional fossil fuels are becoming increasingly scarce. Among all emerging energy sources, lithium-ion batteries possess advantages such as high energy efficiency, long cycle life, low maintenance costs, and flexible power and energy characteristics, making them increasingly popular in automotive power and energy storage applications.

[0004] With the increasing popularity of electric vehicles, the pursuit of higher capacity and better cycle performance of lithium-ion batteries is a common goal.

[0005] One method to improve the performance of lithium-ion batteries is by adding a positive or negative electrode lithium supplement. Negative electrode lithium supplements require the introduction of metallic lithium or alkyl lithium, which places high demands on the environment and processes, making implementation difficult. Positive electrode lithium supplements, on the other hand, only require a small amount of lithium supplementation mixed into the positive electrode active material, without requiring any changes to the front-end or mid-end process equipment. This simple and easy-to-implement method has made it the preferred choice for many battery companies.

[0006] However, the improvement in lithium-ion performance by using only positive electrode lithium supplements is relatively limited. Therefore, a method is needed to further improve the performance of lithium-ion batteries. Summary of the Invention

[0007] This application provides a lithium-ion battery and a method for manufacturing the same. The lithium-ion battery prepared by this method has high capacity and cycle performance.

[0008] The technical solution of this application is as follows:

[0009] In a first aspect, this application provides a lithium-ion battery, including a positive electrode and a negative electrode, wherein the positive electrode includes a positive electrode active material and a positive electrode lithium replenishing agent.

[0010] The negative electrode sheet includes a negative electrode coating layer, and the negative electrode coating layer includes a negative electrode active material.

[0011] The charging NP of the lithium-ion battery is greater than or equal to a first threshold, and the discharging NP of the lithium-ion battery is less than or equal to a second threshold, wherein the first threshold is less than the second threshold.

[0012] The charging NP is the ratio of the first negative electrode capacity to the first positive electrode capacity. The first negative electrode capacity is the negative electrode capacity during the charging process, and the first positive electrode capacity is the positive electrode capacity during the charging process.

[0013] Discharge NP is the ratio of the second negative electrode capacity to the second positive electrode capacity. The second negative electrode capacity is the negative electrode capacity during the discharge process, and the second positive electrode capacity is the positive electrode capacity during the discharge process.

[0014] Based on the lithium-ion battery provided in the first aspect, by setting a first threshold and a second threshold, the matching between the negative electrode capacity and the positive electrode capacity of the lithium-ion battery during the charging and discharging processes can be taken into account, which can help improve the performance of the lithium-ion battery.

[0015] In one possible design, the first positive electrode capacity is determined based on the positive electrode coating layer density, the content of positive electrode active material in the positive electrode coating layer, the first delithiation capacity of the positive electrode active material, the content of positive electrode lithium replenishing agent, and the first delithiation capacity of the positive electrode lithium replenishing agent.

[0016] The first negative electrode capacity is determined based on the negative electrode coating layer density, the content of negative electrode active material in the negative electrode coating layer, and the initial lithium intercalation capacity of the negative electrode active material.

[0017] The second positive electrode capacity is determined based on the positive electrode coating layer density, the content of positive electrode active material in the positive electrode coating layer, the initial lithium intercalation capacity of the positive electrode active material, the content of positive electrode lithium supplementer, and the initial lithium intercalation capacity of the positive electrode lithium supplementer.

[0018] The second negative electrode capacity is determined based on the negative electrode coating layer density, the content of negative electrode active material in the negative electrode coating layer, and the initial delithiation capacity of the negative electrode active material.

[0019] Based on the lithium-ion battery provided by this embodiment, its charging NP and discharging NP can be determined according to the above parameters.

[0020] In one possible design, the charging NP is NP1:

[0021] The discharge NP is NP2:

[0022] Among them, CW 负 L represents the density of the negative electrode coating layer. Gr C1 represents the mass percentage of the negative electrode active material in the negative electrode coating layer. Gr Indicates the initial lithium intercalation capacity of the negative electrode active material, C2Gr Indicates the initial delithiation capacity of the negative electrode active material;

[0023] CW 正 L represents the density of the positive electrode coating layer. LFP C1 represents the mass percentage of the positive electrode active material in the positive electrode coating layer. LFP Indicates the initial delithiation capacity of the positive electrode active material, C2 LFP Indicates the initial lithium insertion capacity of the positive electrode active material;

[0024] L CPAn This represents the mass percentage of the nth lithium replenishing agent in the positive electrode coating layer, where n is a natural number greater than or equal to 1. C1 CPAn C2 represents the initial delithiation capacity of the nth lithium replenisher. CPAn This represents the initial lithium insertion capacity of the nth lithium replenisher.

[0025] Based on the lithium-ion battery provided by this embodiment, its charging NP and discharging NP can be determined according to formula (1) and formula (2).

[0026] In one possible design, the first threshold is 1.05 and the second threshold is 1.25. Lithium-ion batteries that meet these conditions exhibit good discharge specific capacity and cycle performance.

[0027] In one possible design, the positive electrode active material comprises lithium iron phosphate, and the negative electrode active material comprises graphite.

[0028] The lithium-ion battery provided by this embodiment has good discharge specific capacity and cycle performance.

[0029] In one possible design, the ratio of lithium iron phosphate to cathode lithium supplement is 95%–99.9% to 5%–0.1% by mass percentage in the combination of lithium iron phosphate and cathode lithium supplement.

[0030] Based on the lithium-ion battery provided by this embodiment, the role of the positive electrode lithium replenisher is to compensate for the initial efficiency loss during the first charge and discharge of the negative electrode. However, the amount of positive electrode lithium replenisher should not be too much, as too much will affect the discharge specific capacity of the lithium-ion battery. In actual testing, when the mass percentage of lithium iron phosphate in the active material is 96% to 99.5%, the mass percentage of the positive electrode lithium replenisher is 4% to 0.5%, and the charging NP is greater than or equal to 1.05 and the discharging NP is less than or equal to 1.25, the lithium-ion battery has good discharge specific capacity and cycle performance.

[0031] In one possible design, the positive electrode lithium supplement is one or more of Li5FeO4, Li2NiO2, Li6CoO4, and Li2O.

[0032] Based on the lithium-ion battery provided by this embodiment, the charging NP and discharging NP of the lithium-ion battery are related to the first charging capacity and first discharging capacity of the positive electrode lithium replenisher. When designing and manufacturing lithium-ion batteries, a suitable positive electrode lithium replenisher can be selected according to the cell type, capacity, charging NP and discharging NP, thus facilitating the preparation of lithium-ion batteries with good electrochemical performance.

[0033] In one possible design, the positive electrode lithium replenisher is a Li5FeO4 / Li2NiO2 composite lithium replenisher or a Li2NiO2 / Li6CoO4 composite lithium replenisher.

[0034] Based on the lithium-ion battery provided by this embodiment, using a composite of Li5FeO4 and Li2NiO2 or a composite of Li2NiO2 and Li6CoO4, Li5FeO4 / or Li2NiO2 can compensate for the low initial charging capacity of Li6CoO4. However, secondly, Li5FeO4 and Li6CoO4 pose a risk of gas generation; using a composite lithium replenishing agent is necessary because of the Ni content in Li2NiO2... 2+ / Ni 3+ Its presence can effectively reduce the risk of gas production.

[0035] In one possible design, the mass of Li5FeO4 in the Li5FeO4 / Li2NiO2 composite lithium supplement is greater than the mass of Li2NiO2.

[0036] Based on the lithium-ion battery provided by this embodiment, the mass of Li5FeO4 / is greater than the mass of Li2NiO2. In this way, the capacity of the lithium-ion battery can be minimized while compensating for the initial efficiency loss of the negative electrode during the first charge and discharge.

[0037] Based on the same inventive concept, this application also provides a method for manufacturing a lithium-ion battery. During the lithium-ion battery preparation process, the determination of the slurry composition and the coating layer density is carried out according to the following steps:

[0038] A) Preliminary determination of slurry composition:

[0039] Based on the type and capacity of the battery cell, the composition of the positive electrode slurry, the composition of the negative electrode slurry, the mass percentage of solid matter in the positive electrode slurry, and the mass percentage of solid matter in the negative electrode slurry are preliminarily determined.

[0040] B) Determine the final slurry composition, positive electrode coating layer density, and negative electrode coating layer density:

[0041] The density of the positive electrode coating layer or the density of the negative electrode coating layer are determined based on the cell type and capacity.

[0042] Let the charging NP ratio be NP1 and the discharging NP ratio be NP2. Adjust the parameters in formula (1) and formula (2) so that NP1 is greater than or equal to the first threshold and NP2 is less than or equal to the second threshold, and the first threshold is less than the second threshold.

[0043] Record the CW that finally meets the conditions. 负 L Gr CW 正 L LFP L CPAn C1 CPAn .

[0044] Among them, CW 负 L represents the density of the negative electrode coating layer. Gr C1 represents the mass percentage of the negative electrode active material in the solid material of the negative electrode slurry. Gr Indicates the initial lithium intercalation capacity of the negative electrode active material, C2 Gr This indicates the initial delithiation capacity of the negative electrode active material.

[0045] CW 正 L represents the density of the positive electrode coating layer. LFP C1 represents the mass percentage of the positive electrode active material in the solid material of the positive electrode slurry. LFP Indicates the initial delithiation capacity of the positive electrode active material, C2 LFP This indicates the initial lithium insertion capacity of the positive electrode active material.

[0046] L CPAn C1 represents the mass percentage of the nth type of positive electrode lithium supplement in the solid material of the positive electrode slurry, where n is a natural number greater than or equal to 1. CPAn C2 represents the initial delithiation capacity of the nth cathode lithium replenishment agent. CPAn This represents the initial lithium insertion capacity of the nth type of positive electrode lithium supplement.

[0047] The lithium-ion battery manufacturing method provided in the second aspect allows for the control of NP1 and NP2 by adjusting the parameters in formulas (1) and (2), thereby enabling the manufacture of the lithium-ion battery of the first aspect and helping to improve the electrochemical performance of the lithium-ion battery. Attached Figure Description

[0048] Figure 1 shows the first charge and discharge curves of the LFO, where curve a1 indicates the charging curve and curve a2 indicates the discharging curve.

[0049] Figure 2 shows the charge and discharge curves of the LNO in the first and second cycles. Curve b1 indicates the first cycle of charging, curve b2 indicates the first cycle of discharging, curve b3 indicates the second cycle of discharging, and curve b4 indicates the second cycle of charging.

[0050] Figure 3 shows the cycling curves of the battery cells prepared in Examples 2, 3, 8, 10, 11 and Comparative Example 2 of this application. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments given in this application can be combined with each other without contradiction. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] There are no particular restrictions on the source of any raw materials used in this application; they may be purchased from the market or prepared in accordance with conventional methods known to those skilled in the art.

[0053] All raw materials used in this application, unless otherwise specified in their parameters, are commonly used in the field and can be purchased from commercial sources or prepared by conventional methods by those skilled in the art based on the name of the raw material and its corresponding use.

[0054] The processes used in this application are all commonly used abbreviations in the field. The specific steps and conventional parameters of each abbreviation are clear and unambiguous in their respective fields, and those skilled in the art can implement them using conventional methods based on the abbreviations.

[0055] Unless otherwise defined, all terms used herein have the meanings commonly understood by those skilled in the art, unless otherwise specified.

[0056] The following provides a detailed description of this application.

[0057] In existing technologies, when determining the slurry composition, only the discharge NP (capacitance ratio) is considered, not the charging NP (capacitance ratio). The charging NP refers to the ratio of the negative electrode capacity to the positive electrode capacity during charging. The charging NP reflects the capacity matching between the negative and positive electrodes during charging. Similarly, the discharge NP refers to the ratio of the negative electrode capacity to the positive electrode capacity during discharging. The discharge NP reflects the capacity matching between the negative and positive electrodes during discharging.

[0058] The core idea of ​​this application is to adjust the composition of the slurry and determine the coating layer density during the slurry coating process by using charging NP and discharging NP as control conditions during the manufacturing of lithium-ion batteries, thereby improving the performance of lithium-ion batteries.

[0059] Based on the core idea of ​​this application, this application provides a lithium-ion battery, including a positive electrode and a negative electrode: the positive electrode includes a positive active material and a positive lithium replenishing agent. The negative electrode includes a negative coating layer, and the negative coating layer includes a negative active material.

[0060] The charging NP of a lithium-ion battery is greater than or equal to a first threshold, and the discharging NP of a lithium-ion battery is less than or equal to a second threshold, wherein the first threshold is less than the second threshold. Charging NP is the ratio of the first negative electrode capacity to the first positive electrode capacity, where the first negative electrode capacity is the negative electrode capacity during charging, and the first positive electrode capacity is the positive electrode capacity during charging. Discharging NP is the ratio of the second negative electrode capacity to the second positive electrode capacity, where the second negative electrode capacity is the negative electrode capacity during discharging, and the second positive electrode capacity is the positive electrode capacity during discharging.

[0061] The lithium-ion battery provided in this application, by setting a first threshold and a second threshold, can take into account the matching of the negative electrode capacity and the positive electrode capacity during the charging and discharging processes of the lithium-ion battery, thereby contributing to the improvement of lithium-ion battery performance.

[0062] In some embodiments of this application, the first positive electrode capacity is determined based on the positive electrode coating layer density, the content of positive electrode active material in the positive electrode coating layer, the first delithiation capacity of the positive electrode active material, the content of positive electrode lithium replenishing agent, and the first delithiation capacity of the positive electrode lithium replenishing agent.

[0063] The first negative electrode capacity is determined based on the density of the negative electrode coating layer, the content of the negative electrode active material in the negative electrode coating layer, and the initial lithium insertion capacity of the negative electrode active material.

[0064] The second positive electrode capacity is determined based on the positive electrode coating layer density, the content of positive electrode active material in the positive electrode coating layer, the initial lithium intercalation capacity of the positive electrode active material, the content of positive electrode lithium supplementer, and the initial lithium intercalation capacity of the positive electrode lithium supplementer.

[0065] The second negative electrode capacity is determined based on the negative electrode coating layer density, the content of negative electrode active material in the negative electrode coating layer, and the initial delithiation capacity of the negative electrode active material.

[0066] The charging NP is NP1:

[0067] The discharge NP is NP2:

[0068] Among them, CW 负L represents the density of the negative electrode coating layer. Gr C1 represents the mass percentage of the negative electrode active material in the negative electrode coating layer. Gr Indicates the initial lithium intercalation capacity of the negative electrode active material, C2 Gr Indicates the initial delithiation capacity of the negative electrode active material;

[0069] CW 正 L represents the density of the positive electrode coating layer. LFP C1 represents the mass percentage of the positive electrode active material in the positive electrode coating layer. LFP Indicates the initial delithiation capacity of the positive electrode active material, C2 LFP Indicates the initial lithium insertion capacity of the positive electrode active material;

[0070] L CPAn This represents the mass percentage of the nth lithium replenishing agent in the positive electrode coating layer, where n is a natural number greater than or equal to 1. C1 CPAn C2 represents the initial delithiation capacity of the nth lithium replenisher. CPAn This represents the initial lithium insertion capacity of the nth lithium replenisher.

[0071] Based on the lithium-ion battery provided by this embodiment, its charging NP and discharging NP can be determined according to formula (1) and formula (2).

[0072] In some embodiments of this application, the first threshold is 1.05, and the second threshold is 1.25. Lithium-ion batteries that meet these conditions have better discharge specific capacity and cycle performance.

[0073] In some embodiments of this application, the positive electrode active material includes lithium iron phosphate, and the negative electrode active material includes graphite. The lithium-ion battery provided based on this embodiment has good discharge specific capacity and cycle performance.

[0074] In some embodiments of this application, the ratio of lithium iron phosphate to cathode lithium supplement is 95% to 99.9% to 5% to 0.1% by mass percentage.

[0075] Specifically, in this application, the role of the positive electrode lithium replenisher is to compensate for the initial efficiency loss during the first charge and discharge of the negative electrode. However, the amount of positive electrode lithium replenisher should not be too high, as excessive amounts will affect the discharge specific capacity of the lithium-ion battery. In actual testing, when the mass percentage of lithium iron phosphate and positive electrode lithium replenisher in the combination is 96%–99.5%, and the mass percentage of positive electrode lithium replenisher is 4%–0.5%, and the charging NP is greater than or equal to 1.05 and the discharging NP is less than or equal to 1.25, the lithium-ion battery exhibits good discharge specific capacity and cycle performance. Its electrochemical performance will be verified subsequently through test results of specific embodiments.

[0076] In some embodiments of this application, the positive electrode lithium replenishing agent is one or more of Li5FeO4, Li2NiO2, Li6CoO4, and Li2O.

[0077] The abbreviation for Li5FeO4 is LFO, the abbreviation for Li2NiO2 is LNO, and the abbreviation for Li6CoO4 is LCO.

[0078] Please refer to Figure 1. Curve a1 indicates the first charge curve of LFO, and curve a2 indicates the first discharge curve of LFO. The first delithiation capacity and first lithium insertion capacity vary depending on the cathode lithium replenishment agent. The first charge capacity of LFO is 700-750 mAh / g, and the first discharge capacity is 30-35 mAh / g. Please refer to Figure 2. The first charge capacity of LNO is 400-420 mAh / g, and the first discharge capacity is 150-160 mAh / g. The first charge capacity of LCO is 790-810 mAh / g, and the first discharge capacity is 30-40 mAh / g.

[0079] The charging capacity (NP) and discharging capacity (NP) of a lithium-ion battery are related to the initial charging capacity and initial discharging capacity of the positive electrode lithium replenisher. When designing and manufacturing lithium-ion batteries, a suitable positive electrode lithium replenisher can be selected according to the cell type, capacity, charging capacity (NP), and discharging capacity (NP). This makes it easier to prepare lithium-ion batteries with good electrochemical performance.

[0080] In some embodiments of this application, the positive electrode lithium replenisher is a Li5FeO4 / Li2NiO2 composite lithium replenisher or a Li2NiO2 / Li6CoO4 composite lithium replenisher.

[0081] Specifically, both LFO and LCO have relatively high initial charge capacity and relatively low initial discharge capacity. LNO, on the other hand, has a slightly smaller initial charge capacity but a larger initial discharge capacity. Therefore, there is a certain complementary relationship between LFO and LNO, and between LNO and LCO.

[0082] In the design and manufacturing of lithium-ion batteries, LFO is often combined with LNO or LNO with LCO. LFO or LNO can compensate for the low initial charge capacity of LCO. However, LFO and LCO pose a risk of gas generation. Using composite lithium supplementers is problematic because of the Ni content in LNO. 2+ / Ni 3+ Its presence can effectively reduce the risk of gas production.

[0083] In some embodiments of this application, in the Li5FeO4 / Li2NiO2 composite lithium supplement, the mass of Li5FeO4 is greater than the mass of Li2NiO2.

[0084] Specifically, as mentioned above, Li5FeO4 has a higher initial charge capacity, while Li2NiO2 has a lower initial charge capacity. In some embodiments of this application, the mass of Li5FeO4 is greater than that of Li2NiO2. In this way, the capacity of the lithium-ion battery can be minimized while compensating for the loss of initial charge-discharge efficiency of the negative electrode.

[0085] Based on the same inventive concept, this application also provides a method for manufacturing a lithium-ion battery. The method for manufacturing a lithium-ion battery provided by this invention, in the process of preparing the lithium-ion battery, involves determining the composition of the slurry and the density of the coating layer, according to the following steps:

[0086] A) Preliminary determination of slurry composition:

[0087] Based on the type and capacity of the battery cell, the composition of the positive electrode slurry, the composition of the negative electrode slurry, the mass percentage of solid matter in the positive electrode slurry, and the mass percentage of solid matter in the negative electrode slurry are preliminarily determined.

[0088] B) Determine the final slurry composition, positive electrode coating layer density, and negative electrode coating layer density:

[0089] B1) Determine either the positive electrode coating density or the negative electrode coating density based on the cell type and capacity.

[0090] B2) Let the charging NP ratio be NP1 and the discharging NP ratio be NP2. Adjust the parameters in formula (1) and formula (2) so that NP1 is greater than or equal to the first threshold and NP2 is less than or equal to the second threshold. The first threshold is less than the second threshold.

[0091] Record the CW that finally meets the conditions. 负 L Gr CW 正 L LFP L CPAn C1 CPAn .

[0092] Among them, CW 负 L represents the density of the negative electrode coating layer. Gr C1 represents the mass percentage of the negative electrode active material in the solid material of the negative electrode slurry. Gr Indicates the initial lithium intercalation capacity of the negative electrode active material, C2 Gr This indicates the initial delithiation capacity of the negative electrode active material.

[0093] CW 正 L represents the density of the positive electrode coating layer. LFP C1 represents the mass percentage of the positive electrode active material in the solid material of the positive electrode slurry. LFPIndicates the initial delithiation capacity of the positive electrode active material, C2 LFP This indicates the initial lithium insertion capacity of the positive electrode active material.

[0094] L CPAn C1 represents the mass percentage of the nth type of positive electrode lithium supplement in the solid material of the positive electrode slurry, where n is a natural number greater than or equal to 1. CPAn C2 represents the initial delithiation capacity of the nth cathode lithium replenishment agent. CPAn This represents the initial lithium insertion capacity of the nth type of positive electrode lithium supplement.

[0095] Specifically, the positive electrode slurry includes solid substances and solvents. The solid substances in the positive electrode slurry include positive electrode active materials, positive electrode lithium supplements, conductive agents, and binders.

[0096] Negative electrode slurry also includes solid substances and solvents. The solid substances in negative electrode slurry include negative electrode active materials, conductive agents, dispersants, and binders.

[0097] In this field, given the cell type and capacity, those skilled in the art can preliminarily determine the composition and approximate proportions of lithium iron phosphate, conductive agent, binder, and positive electrode lithium replenishing agent in the positive electrode slurry, and can also determine the composition and approximate proportions of graphite, conductive agent, dispersant, and binder in the negative electrode slurry.

[0098] It should be noted that in this application, the positive electrode slurry forms a positive electrode coating layer after undergoing relevant manufacturing processes. Therefore, in this application, L LFP L represents the mass percentage of the positive electrode active material in the solid material of the positive electrode slurry. LFP It also indicates the mass percentage of the positive electrode active material in the positive electrode coating layer.

[0099] Similarly, in this application, the negative electrode slurry forms a negative electrode coating layer after undergoing relevant manufacturing processes. Therefore, in this application, L Gr L represents the mass percentage of the negative electrode active material in the solid material of the negative electrode slurry. Gr It also indicates the mass percentage of the negative electrode active material in the negative electrode coating layer.

[0100] After initially determining the composition of the positive electrode slurry and the negative electrode slurry, it is necessary to use charging NP and discharging NP as control conditions to determine the positive electrode coating layer density, the negative electrode coating layer density, and the positive electrode lithium replenishing agent.

[0101] Generally speaking, step B) is a process of trying to input parameters into formulas (1) and (2) and continuously adjusting them. Specifically

[0102] In one embodiment of this application, the process can be performed as follows:

[0103] B1) The negative electrode coating layer density range can be determined based on the cell type and capacity, and a negative electrode coating layer density CW can be set within this range. 负 .

[0104] B2) The negative electrode surface density CW 负 The mass percentage L of the positive electrode active material initially determined in step A) LFP The initial delithiation capacity of the positive electrode active material C1 LFP The initial lithium intercalation capacity of the positive electrode active material (C2) LFP The mass percentage of negative electrode active material in the solid material of the negative electrode slurry (L) Gr The initial lithium intercalation capacity of the negative electrode active material C1 Gr The initial delithiation capacity of the negative electrode active material (C2) Gr The mass percentage L of the nth type of positive electrode lithium supplement in the solid material of the positive electrode slurry CPAn The initial delithiation capacity C1 of the nth type of positive electrode lithium replenishing agent CPAn And represents the initial lithium insertion capacity C2 of the nth cathode lithium supplement. CPAn Substitute into formulas (1) and (2).

[0105] B3) Under the condition that NP1 is greater than or equal to the first threshold, NP1 is given a fixed value. Thus, CW can be calculated according to formula (1). 正 The value of NP2 can then be calculated using formula (2).

[0106] B4) If NP2 does not meet the conditions, then the negative electrode coating layer density CW can generally be adjusted. 负 Re-determine NP2. Alternatively, adjust the value of NP1 and recalculate CW. 正 And the value of NP2, re-evaluate.

[0107] If it still doesn't work, you can adjust the type and amount of lithium supplement in the positive electrode, or adjust NP1, and repeat the adjustments until you get the parameters that meet the requirements.

[0108] It is understandable that adjustments to the types of lithium replenishers include changing one type of lithium replenisher to another, replacing one type of lithium replenisher with multiple types of lithium replenishers, and reducing or increasing the number of types of lithium replenishers.

[0109] It should be noted that the parameter C1 in formulas (1) and (2) Gr、 C2 Gr、 C1 LFP、 C2 LFP、 C1 CPAn and C2CPAn The values ​​are determined by the properties of the active material itself and can be determined beforehand using half-cell testing, through charging curves and capacity analysis. Specific testing methods can be found using existing techniques, and will not be elaborated upon here.

[0110] In some embodiments of this application, the preparation of the positive electrode slurry during the preparation of a lithium-ion battery includes the following steps:

[0111] The positive electrode active material, the first conductive agent, the binder, and the positive electrode lithium supplement agent are mixed to form a mixture.

[0112] Add the second conductive agent slurry to the mixture, along with a solvent, and stir to knead the conductive agent slurry into the mixture.

[0113] Add solvent again and stir to form a suspension.

[0114] In this process, two conductive agents are used to improve the conductivity of the positive electrode. The two conductive agents have different physical properties and are added in two different ways to facilitate the uniform mixing of the positive electrode active material, the first conductive agent, the binder and the positive electrode lithium supplement.

[0115] In one embodiment of this application, the first conductive agent is Super P, and the second conductive agent can be a CNT slurry. The CNT slurry is a carbon nanotube slurry. The first conductive agent can also be carbon black, Ketjen black, etc.

[0116] The technical solution and effects of this application are illustrated below through several embodiments.

[0117] Example 1:

[0118] A) Preliminary determination of slurry composition.

[0119] Positive electrode slurry: In Example 1, the battery's design capacity is 5Ah, and the battery type is a pouch cell. Based on the battery's design capacity and type, the composition and proportion range of solid materials in the positive electrode slurry are preliminarily determined. Within this range, the tentative proportions of solid materials and their mass ratios in the positive electrode slurry are as follows:

[0120] Cathode material: Lithium iron phosphate, mass percentage (L) LFP It is 94.67%.

[0121] Cathode lithium supplement: Li5FeO4, abbreviated as LFO, mass percentage L CPA1 It is 1.94%.

[0122] First conductive agent: SuperP, 1.0% by mass.

[0123] The second conductive agent is carbon nanotubes (CNTs), with a mass percentage of 0.4%.

[0124] Adhesive: PVDF, 2.0% by weight.

[0125] Similarly, based on the battery's design capacity and type, the composition and proportion range of solid materials in the negative electrode slurry are initially determined. Within this range, the mass percentage of graphite is tentatively set as L. Gr The content is 96.6%, the mass percentage of the first conductive agent Super P is 0.5%, the mass percentage of the dispersant is 1.1%, and the mass percentage of the binder is 1.8%.

[0126] Among them, the initial delithiation capacity of lithium iron phosphate C1 LFP The initial lithium iron phosphate (LFP) lithium-ionization capacity (C2) is 162 mAh / g. LFP It has a capacity of 144 mAh / g.

[0127] The initial delithiation capacity C1 of the positive electrode lithium replenisher LFO CPA1 The initial lithium intercalation capacity (C2) of the positive electrode lithium supplement LFO is 720 mAh / g. CPA1 It is 35mAh / g.

[0128] Graphite's first lithium intercalation capacity C1 Gr The first delithiation capacity of graphite is 382 mAh / g, C2. Gr It has a capacity of 355mAh / g.

[0129] B) Determine the final slurry composition, positive electrode coating layer density, and negative electrode coating layer density.

[0130] The battery is designed with a capacity of 5Ah and is a pouch cell battery. The negative electrode coating density is determined to be 7.81 mg / cm³. 2 .

[0131] Next, the charging NP ratio is denoted as NP1, the discharging NP ratio as NP2, and NP1 is set to 1.05. The negative electrode coating layer density is 7.81 mg / cm². 2 Substitute the parameters determined in step A) into formulas (1) and (2). The positive electrode coating layer density obtained by formula (1) is 16.49 mg / cm³. 2 The NP2 obtained by calculation using formula (2) is 1.18.

[0132] Final determination:

[0133] NP1 is 1.05, and NP2 is 1.18.

[0134] In the positive electrode slurry: LLFP It is 94.67%, L CPAn It is 1.94%.

[0135] In the negative electrode slurry: L Gr 97%

[0136] The density of the positive electrode coating layer is 16.49 mg / cm³. 2 The density of the negative electrode coating layer is 7.81 mg / cm³. 2 .

[0137] In this embodiment, the positive electrode coating layer density and NP2 calculated by formula (1) and formula (2) meet the requirements, therefore, no further adjustments are made.

[0138] If the positive electrode coating layer density and NP2 calculated by formulas (1) and (2) do not meet the requirements, then it is necessary to adjust one or more of the following: the amount of positive electrode lithium supplement, the type of positive electrode lithium supplement, the negative electrode coating layer density, and NP1, until the obtained positive electrode coating layer density and NP2 meet the requirements. It should be noted that those skilled in the art can judge whether the positive electrode coating layer density meets the requirements based on experience.

[0139] C) Slurry preparation.

[0140] C1) Preparation of positive electrode slurry:

[0141] According to the positive electrode slurry composition determined in step B), the positive electrode active material, the first conductive agent (Super P), and the binder (PVDF) are mixed. The mixture is stirred in a planetary mixer at a speed of 800 rpm for 30 minutes.

[0142] Add the second conductive agent CNT slurry, and then add a certain amount of NMP. After adding NMP, the solid content of the mixture is about 74%. Stir the mixture at 300 rpm for 30 minutes.

[0143] Add NMP again. After adding NMP, the solid content of the mixture is about 63%. Stir the mixture at 3000 rpm for 240 minutes. Then filter the slurry for later use.

[0144] C2) Preparation of negative electrode slurry.

[0145] According to the negative electrode slurry composition determined in step B), graphite (Gr), conductive agent (Super P), dispersant, and binder are mixed, and a certain amount of deionized water is added to make the solid content about 50%. The rotation speed is 1800 rpm and the time is 120 min. Then the slurry is filtered out for later use.

[0146] D) Coating.

[0147] Using the positive electrode coating layer density determined in step B), the prepared positive electrode slurry is coated using a transfer coating or extrusion coating machine to form a positive electrode sheet. The positive electrode current collector is aluminum foil.

[0148] Using the negative electrode coating layer density determined in step B), the prepared negative electrode slurry is coated using a transfer coating or extrusion coating machine to form a negative electrode sheet. The negative electrode current collector is copper foil.

[0149] E) Roll forming, slitting, assembly and chemical formation.

[0150] The positive and negative electrode sheets are rolled and cut according to specific specifications, then assembled into battery cells, and electrolyte is injected into the cells at an injection rate of 3.5 g / Ah. The prepared battery cells are then subjected to formation.

[0151] Other embodiments:

[0152] Table 1 lists the embodiments and comparative examples of this application. Please refer to Table 1:

[0153] Table 1

[0154] It should be noted that the positive electrode active material in Table 1 is a combination of lithium iron phosphate and a positive electrode lithium supplement. The mass percentage of LFO in the positive electrode active material in Table 1 is calculated by dividing the mass of the positive electrode lithium supplement by the sum of the masses of the positive electrode lithium supplement and lithium iron phosphate. Taking Example 1 as an example, the mass percentage of LFO in the positive electrode active material is 2%, and the mass percentage of lithium iron phosphate in the positive electrode active material is 98%. The calculation method for the mass percentage of LNO in the positive electrode active material is the same as that for LFO.

[0155] The remaining embodiments and comparative examples of this application are described below.

[0156] Examples 2 to 4:

[0157] Compared with Example 1, Examples 2, 3, and 4 use the same materials in the positive and negative electrode slurries, and the preparation methods of the lithium-ion batteries are basically the same. NP1 and NP2 are different, but all satisfy the condition that NP1 is greater than or equal to 1.05 and NP2 is less than or equal to 1.25.

[0158] Examples 5, 6, and 7:

[0159] Compared with Example 1, Examples 5, 6, and 7 show changes in the type and amount of positive electrode lithium replenishing agent in the positive electrode slurry, but the other substances used in the positive and negative electrode slurries are the same, and the battery preparation process is basically the same. Furthermore, in Examples 5, 6, and 7, NP1 is greater than or equal to 1.05, and NP2 is less than or equal to 1.25.

[0160] Examples 8, 9, 10, 11, 12, and 13:

[0161] Compared with Example 1, Examples 8 to 13 use a composite lithium replenishing agent in the positive electrode slurry, with changes in type and amount. However, the other substances used in the positive and negative electrode slurries are the same, and the battery preparation process is basically the same. Furthermore, in Examples 8 to 13, NP1 is greater than or equal to 1.05, and NP2 is less than or equal to 1.25.

[0162] Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4:

[0163] Compared with Example 1, Comparative Examples 1 to 4 did not add a positive electrode lithium replenishing agent to the positive electrode slurry, but the other substances used in the positive and negative electrode slurries were the same, and the battery preparation process was basically the same. In addition, in Comparative Examples 1 to 4, NP1 was greater than or equal to 1.05, and NP2 was less than or equal to 1.25.

[0164] Comparative Examples 5, 6, 7, 8, 9, 10, and 11:

[0165] Compared with Example 1, Comparative Examples 5 to 9 use the same materials in both the positive and negative electrode slurries, and the battery fabrication processes are basically the same. However, in Comparative Examples 5 to 11, at least one of NP1 and NP2 does not meet the conditions defined in this application.

[0166] Analysis of the effects of the examples and comparative examples:

[0167] The lithium-ion batteries prepared in Examples 1 to 13 and Comparative Examples 1 to 11 were tested. The test items included the actual discharge specific capacity and cycle performance of the cells.

[0168] The actual discharge specific capacity of the battery cell was tested at room temperature (25℃) using a charge / discharge cycle of 0.33C / 0.33C.

[0169] The cycle test first tests the 0.33C capacity of the cell at room temperature (25℃), and then adjusts the temperature to 45℃ and performs a 1C / 1C charge and discharge test.

[0170] During testing, the test environment and test standards used in the comparative and example examples are basically the same, and the test results can be compared.

[0171] Please refer to Table 1 and Figure 3:

[0172] As can be seen from the test data of Examples 1 to 13 in Table 1, the actual discharge specific capacity of the battery cells prepared in Examples 1 to 13 is greater than 143 mAh / g, the discharge voltage plateau after 100 cycles is greater than or equal to 3.29, and the retention rate at 45°C after 1000 cycles is greater than 93%.

[0173] The test data from Comparative Examples 1 to 4 in Table 1 show that the actual discharge specific capacity of the cells prepared by Comparative Examples 1 to 4 is less than 143 mAh / g, the discharge voltage plateau after 100 cycles is less than 3.29, and the retention rate at 45℃ after 1000 cycles is less than 90%.

[0174] A comprehensive comparison of the test data of Comparative Examples 1 to 4 with those of Examples 1 to 13 shows that, although the lithium-ion batteries of Comparative Examples 1 to 4, which did not add positive electrode lithium replenishment agent, had NP1 greater than or equal to 1.05 and NP2 less than or equal to 1.25, their actual discharge specific capacity and cycle performance were not as good as those of Examples 1 to 13.

[0175] The comparison shows that positive electrode lithium replenishment agents affect the actual discharge specific capacity and cycle performance of lithium-ion batteries. Lithium-ion batteries with added positive electrode lithium replenishment agents have better actual discharge specific capacity and cycle performance.

[0176] As can be seen from the test data of Comparative Examples 5 to 11 in Table 1, the actual discharge specific capacity of the cells prepared by Comparative Examples 5 to 11 is less than 140mAh / g, indicating that the actual discharge specific capacity of the cells is low.

[0177] By comparing Comparative Examples 5 to 9 with Examples 1 to 13, it can be seen that although Comparative Examples 5 to 11 also used positive electrode lithium replenishment agents, the actual discharge specific capacity of the battery cells could not meet the requirements.

[0178] Meanwhile, Comparative Examples 6 and 7 also show that the amount of positive electrode lithium replenishing agent used is not necessarily better the more it is used. Excessive use of positive electrode lithium replenishing agent will seriously affect the actual discharge specific capacity of the cell. As can be seen from Formulas (1) and (2), the type and amount of positive electrode lithium replenishing agent are related to NP1 and NP2.

[0179] The above comparison shows that although the positive electrode lithium replenisher affects the actual discharge specific capacity and cycle performance of lithium-ion batteries, NP1 and NP2 also affect the actual discharge specific capacity and cycle performance of lithium-ion batteries. When using the positive electrode lithium replenisher, the actual discharge specific capacity and cycle performance of lithium-ion batteries can be improved by controlling NP1 and NP2.

[0180] Please continue to refer to Table 1. Specifically, please take Examples 1 to 4 as the first group, Examples 5 to 7 as the second group, and Examples 8 to 13 as the third group. By comparing the test data of the first group, the second group, and the third group, it can be seen that the effect of using LNO alone as a positive electrode lithium supplement is slightly inferior to the effect of using LFO alone as a positive electrode lithium supplement, and also inferior to the effect of LFO / LNO composite lithium supplement.

Claims

1. A lithium-ion battery, characterized in that, include: A positive electrode sheet, wherein the positive electrode sheet includes a positive electrode coating layer, and the positive electrode coating layer includes a positive electrode active material and a positive electrode lithium supplementing agent; A negative electrode sheet, wherein the negative electrode sheet includes a negative electrode coating layer, and the negative electrode coating layer includes a negative electrode active material; The charging NP of the lithium-ion battery is greater than or equal to a first threshold, and the discharging NP of the lithium-ion battery is less than or equal to a second threshold, wherein the first threshold is less than the second threshold; The charging NP is the ratio of the first negative electrode capacity to the first positive electrode capacity, where the first negative electrode capacity is the negative electrode capacity during the charging process, and the first positive electrode capacity is the positive electrode capacity during the charging process. Discharge NP is the ratio of the second negative electrode capacity to the second positive electrode capacity. The second negative electrode capacity is the negative electrode capacity during the discharge process, and the second positive electrode capacity is the positive electrode capacity during the discharge process.

2. The lithium-ion battery according to claim 1, characterized in that, The first positive electrode capacity is determined based on the positive electrode coating layer density, the content of positive electrode active material in the positive electrode coating layer, the initial delithiation capacity of the positive electrode active material, the content of positive electrode lithium replenishing agent, and the initial delithiation capacity of the positive electrode lithium replenishing agent. The first negative electrode capacity is determined based on the negative electrode coating layer density, the content of negative electrode active material in the negative electrode coating layer, and the initial lithium intercalation capacity of the negative electrode active material; The second positive electrode capacity is determined based on the positive electrode coating layer density, the content of positive electrode active material in the positive electrode coating layer, the initial lithium intercalation capacity of the positive electrode active material, the content of positive electrode lithium supplementer, and the initial lithium intercalation capacity of the positive electrode lithium supplementer. The second negative electrode capacity is determined based on the negative electrode coating layer density, the content of negative electrode active material in the negative electrode coating layer, and the initial delithiation capacity of the negative electrode active material.

3. The lithium-ion battery according to claim 1, characterized in that, The charging NP is NP1: The discharge NP is NP2: Among them, CW 负 L represents the density of the negative electrode coating layer. Gr C1 represents the mass percentage of the negative electrode active material in the negative electrode coating layer. Gr Indicates the initial lithium intercalation capacity of the negative electrode active material, C2 Gr Indicates the initial delithiation capacity of the negative electrode active material; CW 正 L represents the density of the positive electrode coating layer. LFP C1 represents the mass percentage of the positive electrode active material in the positive electrode coating layer. LFP Indicates the initial delithiation capacity of the positive electrode active material, C2 LFP Indicates the initial lithium insertion capacity of the positive electrode active material; L CPAn This represents the mass percentage of the nth lithium replenishing agent in the positive electrode coating layer, where n is a natural number greater than or equal to 1. C1 CPAn C2 represents the initial delithiation capacity of the nth lithium replenisher. CPAn This represents the initial lithium insertion capacity of the nth lithium replenisher.

4. The lithium-ion battery according to claim 3, characterized in that, The first threshold is 1.05, and the second threshold is 1.

25.

5. The lithium-ion battery according to any one of claims 1 to 4, characterized in that, The positive electrode active material includes lithium iron phosphate, and the negative electrode active material includes graphite.

6. The lithium-ion battery according to claim 5, characterized in that, Based on mass percentage, in the combination of lithium iron phosphate and cathode lithium supplement, the ratio is: lithium iron phosphate : cathode lithium supplement = 95%~99.9% : 5%~0.1%.

7. The lithium-ion battery according to claim 1, characterized in that, The positive electrode lithium replenishing agent is one or more of Li5FeO4, Li2NiO2, Li6CoO4, and Li2O.

8. The lithium-ion battery according to claim 7, characterized in that, The positive electrode lithium replenishing agent is a Li5FeO4 / Li2NiO2 composite lithium replenishing agent or a Li2NiO2 / Li6CoO4 composite lithium replenishing agent.

9. The lithium-ion battery according to claim 8, characterized in that, In the Li5FeO4 / Li2NiO2 composite lithium supplement, the mass of Li5FeO4 is greater than the mass of Li2NiO2.

10. A method for manufacturing a lithium-ion battery, characterized in that, In the process of lithium-ion battery manufacturing, the composition of the slurry and the density of the coating layer are determined according to the following steps: A) Preliminary determination of slurry composition: Based on the type and capacity of the battery cell, the composition of the positive electrode slurry, the composition of the negative electrode slurry, the mass percentage of solid matter in the positive electrode slurry, and the mass percentage of solid matter in the negative electrode slurry are preliminarily determined. B) Determine the final slurry composition, positive electrode coating layer density, and negative electrode coating layer density: The density of the positive electrode coating layer or the density of the negative electrode coating layer are determined based on the cell type and capacity. Let the charging NP ratio be NP1 and the discharging NP ratio be NP2. Adjust the parameters in formula (1) and formula (2) to make NP1 greater than or equal to the first threshold and NP2 less than or equal to the second threshold. The first threshold is less than the second threshold. Record the CW that finally meets the conditions. 负 L Gr CW 正 L LFP L CPAn C1 CPAn ; Among them, CW 负 L represents the density of the negative electrode coating layer. Gr C1 represents the mass percentage of the negative electrode active material in the solid material of the negative electrode slurry. Gr Indicates the initial lithium intercalation capacity of the negative electrode active material, C2 Gr Indicates the initial delithiation capacity of the negative electrode active material; CW 正 L represents the density of the positive electrode coating layer. LFP C1 represents the mass percentage of the positive electrode active material in the solid material of the positive electrode slurry. LFP Indicates the initial delithiation capacity of the positive electrode active material, C2 LFP Indicates the initial lithium insertion capacity of the positive electrode active material; L CPAn C1 represents the mass percentage of the nth type of positive electrode lithium supplement in the solid material of the positive electrode slurry, where n is a natural number greater than or equal to 1. CPAn C2 represents the initial delithiation capacity of the nth cathode lithium replenishment agent. CPAn This represents the initial lithium insertion capacity of the nth type of positive electrode lithium supplement.

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