Lithium ion battery and manufacturing method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a lithium ion battery and a manufacturing method thereof. The lithium ion battery comprises a positive plate and a negative plate, the positive plate comprises a positive coating layer, and the positive coating layer comprises a positive active material and a positive lithium supplement agent. The negative coating layer comprises a negative active material, the charging N.P of the lithium ion battery is greater than or equal to a first threshold value, the discharging N.P of the lithium ion battery is less than or equal to a second threshold value, and the first threshold value is less than the second threshold value. The charging N.P. Is the ratio of the first negative pole capacity to the first positive pole capacity, the first negative pole capacity is the negative pole capacity in the charging process, and the first positive pole capacity is the positive pole capacity in the charging process; the discharge N.P. Is the ratio of the second negative pole capacity to the second positive pole capacity, the second negative pole capacity is the negative pole capacity in the discharge process, and the second positive pole capacity is the positive pole capacity in the discharge process. The lithium ion battery provided by the invention has relatively good discharge specific capacity and cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery and a method for manufacturing the same. Background Art

[0002] Energy is one of the indispensable materials for the development of human society. With the development of society, energy issues have always attracted much attention, and traditional petrochemical energy is increasingly in short supply. Among all new energy sources, lithium-ion batteries have the characteristics of high energy efficiency, long cycle life, low maintenance cost, and flexible power and energy characteristics. They are becoming more and more popular in automotive power and energy storage.

[0003] With the popularization of automobile electrification, the pursuit of lithium-ion batteries with higher capacity and better cycle performance has become a common goal.

[0004] One method to improve the performance of lithium-ion batteries is to add positive or negative lithium replenishers. Negative lithium replenishers require the introduction of metallic lithium or alkyl lithium, which has high environmental and process requirements and is difficult to implement. Positive lithium replenishers only require a small amount of lithium replenisher to be mixed into the positive active material, without changing any front-end and mid-stage process equipment. The operation is very simple and easy to implement, making it the first choice for many battery companies.

[0005] However, the degree of improvement in lithium ion performance 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

[0006] The present application provides a lithium ion battery and a method for manufacturing the same. The lithium ion battery manufactured by the method has high capacity and cycle performance.

[0007] The technical solutions for this application are as follows:

[0008] In a first aspect, the present application provides a lithium-ion battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material and a positive electrode lithium supplement.

[0009] The negative electrode sheet includes a negative electrode coating layer, and the negative electrode coating layer includes a negative electrode active material.

[0010] 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, and the first threshold is less than the second threshold.

[0011] 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.

[0012] The 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.

[0013] Based on the lithium-ion battery provided in the first aspect, by setting the first threshold and the second threshold, the matching of the negative electrode capacity and the positive electrode capacity of the lithium-ion battery during the charging process and the discharging process can be taken into account, which can help improve the performance of the lithium-ion battery.

[0014] In one possible design, the first positive electrode capacity is determined based on the positive electrode coating layer density, the content of the positive electrode active material in the positive electrode coating layer, the first delithiation capacity of the positive electrode active material, the content of the positive electrode lithium replenisher, and the first delithiation capacity of the positive electrode lithium replenisher;

[0015] The first negative electrode capacity is determined based on the negative electrode coating layer density, the content of the negative electrode active material in the negative electrode coating layer and the first lithium insertion capacity of the negative electrode active material;

[0016] The second positive electrode capacity is determined based on the positive electrode coating layer density, the content of the positive electrode active material in the positive electrode coating layer, the first lithium insertion capacity of the positive electrode active material, the content of the positive electrode lithium replenisher and the first lithium insertion capacity of the positive electrode lithium replenisher.

[0017] The second negative electrode capacity is determined based on the negative electrode coating layer density, the content of the negative electrode active material in the negative electrode coating layer and the first delithiation capacity of the negative electrode active material.

[0018] Based on the lithium-ion battery provided in this embodiment, its charging NP and discharging NP can be determined according to the above parameters.

[0019] In a possible design, the charging NP is NP1:

[0020]

[0021] The discharge NP is NP2:

[0022]

[0023] Among them, CW 负 Indicates the negative electrode coating layer density, L Gr Indicates the mass percentage of negative electrode active material in the negative electrode coating layer, C1 Gr Indicates the initial lithium insertion capacity of the negative electrode active material, C2 Gr Indicates the first lithium removal capacity of the negative electrode active material;

[0024] CW 正 Indicates the density of the positive electrode coating layer, L LFPIndicates the mass percentage of the positive electrode active material in the positive electrode coating layer, C1 LFP Indicates the first lithium removal capacity of the positive electrode active material, C2 LFP Indicates the first lithium insertion capacity of the positive electrode active material;

[0025] L CPAn represents the mass percentage of the nth lithium supplement in the positive electrode coating layer, where n is a natural number greater than or equal to 1, C1 CPAn Indicates the first lithium removal capacity of the nth lithium supplement, C2 CPAn It indicates the initial lithium insertion capacity of the nth lithium supplement.

[0026] Based on the lithium-ion battery provided in this embodiment, its charging NP and discharging NP can be determined according to formula (1) and formula (2).

[0027] In a possible design, the first threshold is 1.05, and the second threshold is 1.25. A lithium-ion battery that meets this condition has good discharge specific capacity and cycle performance.

[0028] In a possible design, the positive electrode active material includes lithium iron phosphate, and the negative electrode active material includes graphite.

[0029] The lithium-ion battery provided based on this implementation has good discharge specific capacity and cycle performance.

[0030] In a possible design, in the combination of lithium iron phosphate and the positive electrode lithium replenisher, the ratio of lithium iron phosphate to positive electrode lithium replenisher is 95% to 99.9% to 5% to 0.1% by mass.

[0031] Based on the lithium-ion battery provided by this embodiment, the role of the positive electrode lithium supplement is to compensate for the initial efficiency loss of the negative electrode during the first charge and discharge, but the amount of the positive electrode lithium supplement should not be too much, otherwise it will affect the discharge specific capacity of the lithium-ion battery. In the actual test process, when the mass proportion of lithium iron phosphate in the active material is 96% to 99.5%, the mass proportion of the positive electrode lithium supplement 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.

[0032] In one possible design, the positive electrode lithium supplement is one or more of Li5FeO4, Li2NiO2, Li6CoO4, and Li2O.

[0033] Based on the lithium-ion battery provided in this embodiment, the charging NP and discharging NP of the lithium-ion battery are related to the initial charging capacity and the initial discharging capacity of the positive electrode lithium replenisher. When designing and manufacturing the lithium-ion battery, a suitable positive electrode lithium replenisher can be selected according to the type, capacity, charging NP and discharging NP of the battery cell. In this way, it is easy to prepare a lithium-ion battery with good electrochemical performance.

[0034] In one possible design, the positive electrode lithium supplement is a Li5FeO4 / Li2NiO2 composite lithium supplement or a Li2NiO2 / Li6CoO4 composite lithium supplement.

[0035] Based on the lithium-ion battery provided by this embodiment, Li5FeO4 and Li2NiO2 are compounded or Li2NiO2 and Li6CoO4 are compounded. Li5FeO4 / or Li2NiO2 can make up for the problem of low initial charging capacity of Li6CoO4. At the same time, the second is that Li5FeO4 and Li6CoO4 have the risk of gas production. The use of composite lithium supplements is due to the Ni in Li2NiO2. 2+ / Ni 3+ Existence can effectively reduce the risk of gas production.

[0036] In a possible design, in the Li5FeO4 / Li2NiO2 composite lithium supplement, the mass of Li5FeO4 is greater than the mass of Li2NiO2.

[0037] Based on the lithium-ion battery provided by this embodiment, the mass of Li5FeO4 / is greater than the mass of Li2NiO2, so that the capacity of the lithium-ion battery can be minimized while compensating for the initial efficiency loss during the initial charge and discharge of the negative electrode.

[0038] Based on the same inventive concept, the present application also provides a method for manufacturing a lithium-ion battery. During the preparation of the lithium-ion battery, the composition of the slurry and the density of the coating layer are determined according to the following steps:

[0039] A) Preliminary determination of slurry composition:

[0040] According to the type and capacity of the battery cell, the positive electrode slurry composition, the negative electrode slurry composition, 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.

[0041] B) Determine the final slurry composition, positive electrode coating layer density and negative electrode coating layer density:

[0042] Determine one of the positive electrode coating layer density or the negative electrode coating layer density according to the cell type and capacity.

[0043] The charging NP ratio is denoted as NP1, and the discharging NP ratio is denoted as NP2. The parameters in formula (1) and formula (2) are adjusted 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.

[0044]

[0045]

[0046] Record the CW that finally meets the conditions 负 , L Gr , CW 正 , L LFP , L CPAn 、C1 CPAn .

[0047] Among them, CW 负 Indicates the negative electrode coating layer density, L Gr Indicates the mass percentage of negative electrode active material in the solid matter of negative electrode slurry, C1 Gr Indicates the initial lithium insertion capacity of the negative electrode active material, C2 Gr It indicates the first lithium removal capacity of the negative electrode active material.

[0048] CW 正 Indicates the density of the positive electrode coating layer, L LFP Indicates the mass percentage of positive electrode active material in the positive electrode slurry solid matter, C1 LFP Indicates the first lithium removal capacity of the positive electrode active material, C2 LFP It indicates the first lithium insertion capacity of the positive electrode active material.

[0049] L CPAn It represents the mass percentage of the nth positive electrode lithium supplement in the positive electrode slurry solid matter, where n is a natural number greater than or equal to 1, C1 CPAn Indicates the first lithium removal capacity of the nth positive electrode lithium supplement, C2 CPAn It indicates the initial lithium insertion capacity of the nth positive electrode lithium supplement.

[0050] According to the method for manufacturing a lithium-ion battery provided in the second aspect, in the method, NP1 and NP2 can be controlled by adjusting the parameters in formula (1) and formula (2), so that the lithium-ion battery of the first aspect can be manufactured, which helps to improve the electrochemical performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The first cycle charge and discharge curve of LFO, where the curve indicated by a1 is the charge curve, and the curve indicated by a2 is the discharge curve.

[0052] Figure 2 : are the first and second cycle charge and discharge curves of LNO, wherein the curve indicated by b1 is the first cycle charge curve, the curve indicated by b2 is the first cycle discharge curve, the curve indicated by b3 is the second cycle discharge curve, and the curve indicated by b4 is the second cycle charge curve.

[0053] Figure 3 The cycle curves of the battery cells prepared in Example 2, Example 3, Example 8, Example 10, Example 11 and Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The embodiments given in this application can be combined with each other without any contradiction. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of this application.

[0055] All raw materials used in this application have no particular limitation on their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0056] All raw materials used in the present application, unless otherwise specified, are raw materials commonly used in the art, and those skilled in the art can purchase them commercially or prepare them using conventional methods based on the names of the raw materials and their corresponding uses.

[0057] The abbreviations of the processes used in this application are all conventional abbreviations in the field. The specific steps and conventional parameters of each abbreviation are clear and definite in its relevant field, and those skilled in the art can implement them in a conventional manner based on the abbreviations.

[0058] Unless otherwise defined, all terms used herein have the same meanings as commonly understood by those skilled in the art unless otherwise specified.

[0059] The following is a detailed description of this application.

[0060] In the prior art, when determining the slurry composition, the charging NP is not considered, only the discharging NP is considered. Among them, the charging NP refers to the ratio of the negative electrode capacity to the positive electrode capacity during the charging process. The charging NP reflects the capacity matching of the negative electrode relative to the positive electrode during the charging process. The discharging NP refers to the ratio of the negative electrode capacity to the positive electrode capacity during the discharging process. The discharging NP reflects the capacity matching of the negative electrode relative to the positive electrode during the discharging process.

[0061] The core idea of ​​the present application is to use charging NP and discharging NP as control conditions to adjust the composition of the slurry and determine the coating layer density when the slurry is coated when manufacturing lithium-ion batteries, so as to improve the performance of lithium-ion batteries.

[0062] Based on the core idea of ​​the present application, the present application provides a lithium-ion battery, including a positive electrode sheet and a negative electrode sheet: the positive electrode sheet includes a positive electrode active material and a positive electrode lithium supplement. The negative electrode sheet includes a negative electrode coating layer, and the negative electrode coating layer includes a negative electrode active material.

[0063] The charging NP of the lithium-ion battery is greater than or equal to the first threshold, and the discharging NP of the lithium-ion battery is less than or equal to the second threshold, and 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, 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. The discharging 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 discharging process, and the second positive electrode capacity is the positive electrode capacity during the discharging process.

[0064] The lithium-ion battery provided in the present application can take into account the matching of the negative electrode capacity and the positive electrode capacity of the lithium-ion battery during the charging process and the discharging process by setting the first threshold and the second threshold, which can help improve the performance of the lithium-ion battery.

[0065] In some embodiments of the present application, the first positive electrode capacity is determined based on the positive electrode coating layer density, the content of the positive electrode active material in the positive electrode coating layer, the first delithiation capacity of the positive electrode active material, the content of the positive electrode lithium replenisher, and the first delithiation capacity of the positive electrode lithium replenisher;

[0066] The first negative electrode capacity is determined based on the negative electrode coating layer density, the content of the negative electrode active material in the negative electrode coating layer and the first lithium insertion capacity of the negative electrode active material.

[0067] The second positive electrode capacity is determined based on the positive electrode coating layer density, the content of the positive electrode active material in the positive electrode coating layer, the first lithium insertion capacity of the positive electrode active material, the content of the positive electrode lithium replenisher and the first lithium insertion capacity of the positive electrode lithium replenisher.

[0068] The second negative electrode capacity is determined based on the negative electrode coating layer density, the content of the negative electrode active material in the negative electrode coating layer and the first delithiation capacity of the negative electrode active material.

[0069] The charging NP is NP1:

[0070]

[0071] The discharge NP is NP2:

[0072]

[0073] Among them, CW 负 Indicates the negative electrode coating layer density, L Gr Indicates the mass percentage of negative electrode active material in the negative electrode coating layer, C1 Gr Indicates the initial lithium insertion capacity of the negative electrode active material, C2 Gr Indicates the first lithium removal capacity of the negative electrode active material;

[0074] CW 正 Indicates the density of the positive electrode coating layer, L LFP Indicates the mass percentage of the positive electrode active material in the positive electrode coating layer, C1 LFP Indicates the first lithium removal capacity of the positive electrode active material, C2 LFP Indicates the first lithium insertion capacity of the positive electrode active material;

[0075] L CPAn represents the mass percentage of the nth lithium supplement in the positive electrode coating layer, where n is a natural number greater than or equal to 1, C1 CPAn Indicates the first lithium removal capacity of the nth lithium supplement, C2 CPAn It indicates the initial lithium insertion capacity of the nth lithium supplement.

[0076] Based on the lithium-ion battery provided in this embodiment, its charging NP and discharging NP can be determined according to formula (1) and formula (2).

[0077] In some embodiments of the present application, the first threshold is 1.05, and the second threshold is 1.25. A lithium-ion battery that meets this condition has good discharge specific capacity and cycle performance.

[0078] In some embodiments of the present 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.

[0079] In some embodiments of the present application, in the combination of lithium iron phosphate and the positive electrode lithium replenisher, according to mass percentage: lithium iron phosphate: positive electrode lithium replenisher = 95% to 99.9%: 5% to 0.1%.

[0080] Specifically, in this application, the role of the positive electrode lithium replenisher is to make up for the initial loss of the negative electrode during the first charge and discharge, but the amount of the positive electrode lithium replenisher should not be too much, otherwise it will affect the discharge specific capacity of the lithium-ion battery. In the actual test process, in the combination of lithium iron phosphate and the positive electrode lithium replenisher, the mass proportion of lithium iron phosphate is 96% to 99.5%, the mass proportion 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 discharge NP is less than or equal to 1.25. The lithium-ion battery has a good discharge specific capacity and cycle performance. Its electrochemical performance will be verified later through the test results of specific embodiments.

[0081] In some embodiments of the present application, the positive electrode lithium supplement is one or more of Li5FeO4, Li2NiO2, Li6CoO4, and Li2O.

[0082] Li5FeO4 is abbreviated as LFO, Li2NiO2 is abbreviated as LNO, and Li6CoO4 is abbreviated as LCO.

[0083] Please refer to Figure 1 The curve indicated by a1 is the first charge curve of LFO, and the curve indicated by a2 is the first discharge curve of LFO. Different positive electrode lithium supplements have different first lithium removal capacity and first lithium insertion capacity. The first charge capacity of LFO is 700-750mAh / g, and the first discharge capacity is 30-35mAh / g. Please refer to Figure 2 , the first charge capacity of LNO is 400-420mAh / g, and the first discharge capacity is 150-160mAh / g. The first charge capacity of LCO is 790-810mAh / g, and the first discharge capacity is 30-40mAh / g.

[0084] The charge NP and discharge NP of lithium-ion batteries are related to the first charge capacity and first discharge capacity of the positive electrode lithium supplement. When designing and manufacturing lithium-ion batteries, suitable positive electrode lithium supplements can be selected according to the type, capacity, charge NP and discharge NP of the battery cell. This makes it easier to prepare lithium-ion batteries with good electrochemical properties.

[0085] In some embodiments of the present application, the positive electrode lithium supplement is a Li5FeO4 / Li2NiO2 composite lithium supplement or a Li2NiO2 / Li6CoO4 composite lithium supplement.

[0086] Specifically, the first charge capacity of LFO and LCO is relatively high, and the first discharge capacity is relatively low. The first charge capacity of LNO is slightly smaller, but the first discharge capacity is relatively large. Therefore, there is a certain complementary relationship between LFO and LNO, and between LNO and LCO.

[0087] When designing and manufacturing lithium-ion batteries, LFO and LNO are used in combination or LNO and LCO are used in combination. LFO or LNO can make up for the low initial charging capacity of LCO. At the same time, LFO and LCO have the risk of gas production. 2+ / Ni 3+ Existence can effectively reduce the risk of gas production.

[0088] In some embodiments of the present application, in the Li5FeO4 / Li2NiO2 composite lithium supplement, the mass of Li5FeO4 is greater than the mass of Li2NiO2.

[0089] Specifically, as mentioned above, the initial charge capacity of Li5FeO4 is higher, while the initial charge capacity of Li2NiO2 is lower. In some embodiments of the present application, the mass of Li5FeO4 is greater than the mass of Li2NiO2, so that the capacity of the lithium-ion battery can be minimized while compensating for the initial charge and discharge efficiency loss of the negative electrode.

[0090] Based on the same inventive concept, the present application also provides a method for manufacturing a lithium-ion battery. In the method for manufacturing a lithium-ion battery provided by the present invention, during the preparation of the lithium-ion battery, the composition of the slurry and the determination of the coating surface density are carried out according to the following steps:

[0091] A) Preliminary determination of slurry composition:

[0092] According to the type and capacity of the battery cell, the positive electrode slurry composition, the negative electrode slurry composition, 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.

[0093] B) Determine the final slurry composition, positive electrode coating layer density and negative electrode coating layer density:

[0094] B1) Determine one of the positive electrode coating layer density or the negative electrode coating layer density according to the type and capacity of the battery cell.

[0095] B2) The charging NP ratio is recorded as NP1, and the discharging NP ratio is recorded as NP2. The parameters in formula (1) and formula (2) are adjusted so that NP1 is greater than or equal to a first threshold value, and NP2 is less than or equal to a second threshold value, and the first threshold value is less than the second threshold value.

[0096]

[0097] Record the CW that finally meets the conditions 负 , L Gr , CW 正 , L LFP , L CPAn 、C1CPAn .

[0098] Among them, CW 负 Indicates the negative electrode coating layer density, L Gr Indicates the mass percentage of negative electrode active material in the solid matter of negative electrode slurry, C1 Gr Indicates the initial lithium insertion capacity of the negative electrode active material, C2 Gr It indicates the first lithium removal capacity of the negative electrode active material.

[0099] CW 正 Indicates the density of the positive electrode coating layer, L LFP Indicates the mass percentage of positive electrode active material in the positive electrode slurry solid matter, C1 LFP Indicates the first lithium removal capacity of the positive electrode active material, C2 LFP It indicates the first lithium insertion capacity of the positive electrode active material.

[0100] L CPAn It represents the mass percentage of the nth positive electrode lithium supplement in the positive electrode slurry solid matter, where n is a natural number greater than or equal to 1, C1 CPAn Indicates the first lithium removal capacity of the nth positive electrode lithium supplement, C2 CPAn It indicates the initial lithium insertion capacity of the nth positive electrode lithium supplement.

[0101] Specifically, the positive electrode slurry includes solid matter and a solvent, and the solid matter in the positive electrode slurry includes a positive electrode active material, a positive electrode lithium supplement, a conductive agent and a binder.

[0102] The negative electrode slurry also includes solid matter and a solvent. The solid matter in the negative electrode slurry includes a negative electrode active material, a conductive agent, a dispersant and a binder.

[0103] In this field, if the type and capacity of the battery cell are given, then those skilled in the art can preliminarily determine the composition and approximate ratio of lithium iron phosphate, conductive agent, binder and positive electrode lithium supplement in the positive electrode slurry, and can also determine the composition and approximate ratio of graphite, conductive agent, dispersant and binder in the negative electrode slurry.

[0104] It should be noted that, in the present application, the positive electrode slurry is subjected to relevant manufacturing processes to form a positive electrode coating layer. Therefore, in the present application, L LFP It indicates the mass percentage of positive electrode active material in the positive electrode slurry solid matter, L LFP It also represents the mass percentage of the positive electrode active material in the positive electrode coating layer.

[0105] Similarly, in the present application, the negative electrode slurry is subjected to relevant manufacturing processes to form a negative electrode coating layer. Therefore, in the present application, L Gr It indicates the mass percentage of negative electrode active material in the solid matter of negative electrode slurry, L GrIt also indicates the mass percentage of the negative electrode active material in the negative electrode coating layer.

[0106] After preliminarily determining the positive electrode slurry composition and the negative electrode slurry composition, it is necessary to use the 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 supplement.

[0107] Generally speaking, step B) is a process of trying to substitute parameters into formula (1) and formula (2) and making continuous adjustments.

[0108] Specifically

[0109] In one embodiment of the present application, the process can be performed as follows:

[0110] B1) The negative electrode coating layer density range can be determined according to the cell type and capacity, and a negative electrode coating layer density CW can be set within the negative electrode coating layer density range. 负 .

[0111] B2) The negative electrode surface density CW 负 , the mass percentage L of the positive electrode active material preliminarily determined in step A) LFP 、First lithium removal capacity of positive electrode active material C1 LFP , the first lithium insertion capacity of the positive electrode active material C2 LFP , the mass percentage of negative electrode active material in the solid matter of negative electrode slurry L Gr 、The first lithium insertion capacity of negative electrode active material C1 Gr 、The first lithium removal capacity of negative electrode active material C2 Gr , the mass percentage of the nth positive electrode lithium supplement in the positive electrode slurry solid matter L CPAn 、The first lithium removal capacity C1 of the nth positive electrode lithium supplement CPAn and represents the first lithium insertion capacity C2 of the nth positive electrode lithium supplement CPAn , substitute into formula (1) and formula (2).

[0112] B3) When NP1 is greater than or equal to the first threshold, a fixed value is given to NP1. Thus, CW can be calculated according to formula (1). 正 Then, the value of NP2 can be calculated according to formula (2).

[0113] B4) If NP2 does not meet the conditions, then it can generally be solved by adjusting the negative electrode coating layer density CW 负 , re-determine NP2. You can also adjust the value in NP1 and recalculate CW 正 and the value of NP2, and re-judge.

[0114] If it still doesn't work, you can adjust the type and amount of the positive electrode lithium supplement, or adjust NP1, and adjust it repeatedly until the parameters that meet the conditions are obtained.

[0115] It is understandable that the adjustment of the types of lithium supplements includes the situation of replacing one lithium supplement with another, the situation of replacing one lithium supplement with multiple lithium supplements, and the situation of reducing or increasing the types of lithium supplements.

[0116] It should be noted that the parameter C1 in formulas (1) and (2) is Gr、 C2 Gr、 C1 LFP、 C2 LFP、 C1 CPAn and C2 CPAn The values ​​are determined by the properties of the active material itself, and can be determined in advance by using a half-battery test, through the charging curve and capacity. The specific test method can adopt the existing method, which will not be repeated here.

[0117] In some embodiments of the present application, in the preparation process of the lithium ion battery, the preparation of the positive electrode slurry includes the following steps:

[0118] The positive electrode active material, the first conductive agent, the binder and the positive electrode lithium supplement agent are mixed to form a mixture.

[0119] The second conductive agent slurry is added to the mixture, and a solvent is added, followed by stirring to knead the conductive agent slurry and the mixture.

[0120] The solvent was added again and stirred to form a suspension.

[0121] In this process, two conductive agents are used. The purpose of using the two conductive agents is to improve the conductivity of the positive electrode sheet. The two conductive agents have different physical properties and are added in two different ways. The purpose is to facilitate uniform mixing of the positive electrode active material, the first conductive agent, the binder and the positive electrode lithium supplement.

[0122] In one embodiment of the present application, the first conductive agent is Super P, and the second conductive agent can be CNT slurry. The CNT slurry is carbon nanotube slurry. The first conductive agent can also be carbon black, Ketjen black, etc.

[0123] The technical solution and effects of the present application are described below through multiple embodiments.

[0124] Embodiment 1:

[0125] A) Preliminary determination of slurry composition.

[0126] Positive electrode slurry: In Example 1, the design capacity of the battery is 5Ah, and the type of the battery is a soft-pack laminated battery. The composition and ratio range of the solid matter in the positive electrode slurry are preliminarily determined according to the design capacity of the battery and the type of the battery. Within this range, the solid matter and mass ratio in the positive electrode slurry are tentatively determined as follows:

[0127] Positive electrode material: lithium iron phosphate, mass percentage L LFP is 94.67%,

[0128] Positive lithium supplement: Li5FeO4, referred to as LFO, mass percentage L CPA1 It is 1.94%.

[0129] The first conductive agent: SuperP, with a mass percentage of 1.0%.

[0130] The second conductive agent: carbon nanotubes, CNT for short, with a mass percentage of 0.4%.

[0131] Binder: PVDF, mass percentage is 2.0%.

[0132] Similarly, the composition and ratio range of the solid matter in the negative electrode slurry are preliminarily determined according to the design capacity of the battery and the type of battery. Within this range, the mass percentage of graphite is tentatively determined as L Gr The mass percentage of the first conductive agent Super P 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%.

[0133] Among them, the first lithium removal capacity of lithium iron phosphate is C1 LFP The first lithium insertion capacity of lithium iron phosphate is C2, which is 162mAh / g. LFP It is 144mAh / g.

[0134] The first lithium removal capacity C1 of the positive electrode lithium supplement LFO CPA1 The first lithium insertion capacity C2 of the positive electrode lithium supplement LFO is 720mAh / g. CPA1 It is 35mAh / g.

[0135] Graphite first lithium insertion capacity C1 Gr The first lithium removal capacity of graphite is 382mAh / g, C2 Gr It is 355mAh / g.

[0136] B) Determine the final slurry composition, positive electrode coating layer density and negative electrode coating layer density.

[0137] The design capacity of the battery is 5Ah, the battery type is a soft-pack laminated battery, and the negative electrode coating layer density is determined to be 7.81mg / cm 2 .

[0138] After that, the charge NP ratio was recorded as NP1, the discharge NP ratio was recorded as NP2, NP1 was set to 1.05, and the negative electrode coating layer density was set to 7.81 mg / cm 2 The parameters determined in step A) are substituted into formula (1) and formula (2). The positive electrode coating layer density obtained by formula (1) is 16.49 mg / cm 2 , the NP2 obtained by calculation using formula (2) is 1.18.

[0139]

[0140] Finalization:

[0141] NP1 is 1.05 and NP2 is 1.18.

[0142] In cathode slurry: L LFP is 94.67%, L CPAn It is 1.94%.

[0143] In negative electrode slurry: L Gr 97%

[0144] The density of the positive electrode coating layer is 16.49 mg / cm 2 The negative electrode coating layer density is 7.81 mg / cm 2 .

[0145] In this embodiment, the positive electrode coating layer density and NP2 calculated by formula (1) and formula (2) meet the requirements, so no further adjustment is made.

[0146] If the positive electrode coating layer density and NP2 calculated by formula (1) and formula (2) do not meet the requirements, then it is necessary to adjust the amount of the positive electrode lithium supplement agent, the type of the positive electrode lithium supplement agent, the negative electrode coating layer density and one or more of NP1 until the obtained positive electrode coating layer density and NP2 meet the requirements. It should be noted that whether the positive electrode coating layer density meets the requirements can be judged by those skilled in the art based on experience.

[0147] C) Slurry preparation.

[0148] C1) Preparation of positive electrode slurry:

[0149] 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 using a planetary stirring kettle at a stirring speed of 800 rpm for 30 minutes.

[0150] The second conductive agent CNT slurry was added, and then a certain amount of NMP was added. After the addition of NMP, the solid content of the mixture was about 74%. The mixture was stirred at a stirring speed of 300 rpm for 30 minutes.

[0151] NMP was added again. After the addition of NMP, the solid content of the mixture was about 63%. The mixture was stirred at a stirring speed of 3000 rpm for 240 min. The slurry was then filtered out for later use.

[0152] C2) Preparation of negative electrode slurry.

[0153] 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 speed is 1800rpm, and the time is 120min. Then the slurry is filtered out for use.

[0154] D) Coating.

[0155] The positive electrode coating layer density determined in step B) is used to coat the prepared positive electrode slurry using a transfer coater or an extrusion coater to form a positive electrode sheet. The positive electrode current collector is aluminum foil.

[0156] The negative electrode coating layer density determined in step B) is used to coat the prepared negative electrode slurry using a transfer coater or an extrusion coater to form a negative electrode sheet. The negative electrode current collector is a copper foil.

[0157] E) Rolling, slitting, assembly and forming.

[0158] The positive electrode sheets and negative electrode sheets are rolled and cut according to certain specifications, and then assembled into battery cells, which are then injected with liquid at a rate of 3.5g / Ah. The prepared battery cells are then chemically formed.

[0159] Other embodiments:

[0160] Table 1 is a list of embodiments and comparative examples of this application, please refer to Table 1:

[0161] Table 1

[0162]

[0163]

[0164]

[0165] 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 replenisher. The mass percentage of LFO in the positive electrode active material in Table 1 is the mass of the positive electrode lithium replenisher divided by the mass sum of the positive electrode lithium replenisher 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 of the mass percentage of LNO in the positive electrode active material is the same as that of LFO.

[0166] The remaining embodiments and comparative examples of the present application are described below.

[0167] Embodiment 2 to Embodiment 4:

[0168] Compared with Example 1, the materials used in the positive electrode slurry and the negative electrode slurry are the same, and the preparation methods of the lithium-ion batteries are basically the same. NP1 and NP2 are different, but both satisfy that NP1 is greater than or equal to 1.05 and NP2 is less than or equal to 1.25.

[0169] Embodiment 5, embodiment 6 and embodiment 7:

[0170] Compared with Example 1, the type and amount of the positive electrode lithium supplement in the positive electrode slurry are changed, but the other substances selected in the positive electrode slurry and the negative electrode slurry are the same, and the battery preparation process is basically the same. In addition, in Example 5, Example 6 and Example 7, NP1 is greater than or equal to 1.05, and NP2 is less than or equal to 1.25.

[0171] Embodiment 8, Embodiment 9, Embodiment 10, Embodiment 11, Embodiment 12 and Embodiment 13:

[0172] Compared with Example 1, in Examples 8 to 13, the positive electrode lithium replenisher of the positive electrode slurry uses a composite lithium replenisher, and the type and amount of the lithium replenisher are changed, but the other substances used in the positive electrode slurry and the negative electrode slurry are the same, and the preparation process of the battery is basically the same. In addition, in Examples 8 to 13, NP1 is greater than or equal to 1.05, and NP2 is less than or equal to 1.25.

[0173] Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4:

[0174] Compared with Example 1, no positive electrode lithium supplement is added to the positive electrode slurry, but the other materials selected in the positive electrode slurry and the negative electrode slurry are the same, and the battery preparation process is basically the same. In addition, in Comparative Examples 1 to 4, NP1 is greater than or equal to 1.05, and NP2 is less than or equal to 1.25.

[0175] Comparative Example 5, Comparative Example 6, Comparative Example 7, Comparative Example 8, Comparative Example 9, Comparative Example 10 and Comparative Example 11:

[0176] Compared with Example 1, the materials used in the positive electrode slurry and the negative electrode slurry in Comparative Examples 5 to 9 are the same, and the battery preparation process is basically the same. However, in Comparative Examples 5 to 11, at least one of NP1 and NP2 does not meet the conditions specified in this application.

[0177] Effect analysis of embodiments and comparative examples:

[0178] The lithium-ion batteries prepared in Examples 1 to 13 and Comparative Examples 1 to 11 were tested, and the test items included the actual discharge specific capacity and cycle performance of the battery cells.

[0179] The actual discharge specific capacity of the battery cell is tested by charging and discharging at 0.33C / 0.33C at room temperature (25°C).

[0180] The cycle test is to first test the 0.33C capacity of the battery cell at room temperature (25°C), then adjust the temperature to 45°C and perform a 1C / 1C charge and discharge test.

[0181] During the test, the test environment and test standards selected for the comparative example and the embodiment are basically the same, and the test results can be compared.

[0182] Please refer to Table 1 and Figure 3 :

[0183] It can be seen from the test data of Examples 1 to 13 in Table 1 that the actual discharge specific capacity of the battery cells prepared in Examples 1 to 13 is greater than 143 mAh / g, the discharge voltage platform after 100 cycles is greater than or equal to 3.29, and the 45°C retention rate after 1000 cycles is greater than 93%.

[0184] From the test data of Comparative Examples 1 to 4 in Table 1, it can be seen that the actual discharge specific capacity of the battery cells prepared in Comparative Examples 1 to 4 is less than 143 mAh / g, the discharge voltage platform after 100 cycles is less than 3.29, and the 45°C retention rate after 1000 cycles is less than 90%.

[0185] By comparing the test data of Comparative Examples 1 to 4 with those of Examples 1 to 13 as a whole, it can be seen that in Comparative Examples 1 to 4 without adding the positive electrode lithium supplement, although the NP1 of the lithium ion battery is greater than or equal to 1.05 and the NP2 is less than or equal to 1.25, the actual discharge specific capacity of the battery cell is not as good as that of Examples 1 to 13, and the cycle performance is also not as good as that of Examples 1 to 13.

[0186] From this group of comparisons, it can be seen that the positive electrode lithium supplement has an impact on the actual discharge capacity and cycle performance of lithium-ion batteries. The actual discharge capacity and cycle performance of lithium-ion batteries with the addition of positive electrode lithium supplement will be better.

[0187] It can be seen from the test data of Comparative Examples 5 to 11 in Table 1 that the actual discharge specific capacity of the battery cells prepared in Comparative Examples 5 to 11 is less than 140 mAh / g, and the actual discharge specific capacity of the battery cells is relatively low.

[0188] By comparing Comparative Examples 5 to 9 with Examples 1 to 13 as a whole, it can be seen that although Comparative Examples 5 to 11 also use positive electrode lithium replenishers, the actual discharge specific capacity of the battery cells cannot meet the requirements.

[0189] At the same time, it can be seen from Comparative Examples 6 and 7 that the amount of positive electrode lithium supplement is not necessarily the more the better. When the positive electrode lithium supplement is used too much, the actual discharge capacity of the battery cell will be seriously affected. It can be seen from Formula (1) and Formula (2) that the type and amount of positive electrode lithium supplement are related to NP1 and NP2.

[0190] From the above comparison, it can be seen that although the positive electrode lithium supplement has an impact on the actual discharge capacity and cycle performance of lithium-ion batteries, NP1 and NP2 will also have an impact on the actual discharge capacity and cycle performance of lithium-ion batteries. When using a positive electrode lithium supplement, the actual discharge capacity and cycle performance of lithium-ion batteries can be improved by controlling NP1 and NP2.

[0191] 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 replenisher is slightly inferior to the effect of using LFO alone as a positive electrode lithium replenisher, and is also inferior to the effect of the LFO / LNO composite lithium replenisher.

Claims

1. A lithium ion battery, characterized in that: include: A positive electrode sheet, the positive electrode sheet comprising a positive electrode coating layer, the positive electrode coating layer comprising a positive electrode active material and a positive electrode lithium supplement; A negative electrode sheet, the negative electrode sheet comprising a negative electrode coating layer, the negative electrode coating layer comprising 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, and 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, 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; The discharge NP is a ratio of the second negative electrode capacity to the second positive electrode capacity, wherein 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 the positive electrode active material in the positive electrode coating layer, the first lithium desorption capacity of the positive electrode active material, the content of the positive electrode lithium replenisher and the first lithium desorption capacity of the positive electrode lithium replenisher; The first negative electrode capacity is determined based on the negative electrode coating layer density, the content of the negative electrode active material in the negative electrode coating layer and the first lithium insertion 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 the positive electrode active material in the positive electrode coating layer, the first lithium insertion capacity of the positive electrode active material, the content of the positive electrode lithium supplement and the first lithium insertion capacity of the positive electrode lithium supplement; The second negative electrode capacity is determined based on the negative electrode coating layer density, the content of the negative electrode active material in the negative electrode coating layer and the first 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 Indicates the negative electrode coating layer density, L Gr Indicates the mass percentage of negative electrode active material in the negative electrode coating layer, C1 Gr Indicates the initial lithium insertion capacity of the negative electrode active material, C2 Gr Indicates the first lithium removal capacity of the negative electrode active material; CW 正 Indicates the density of the positive electrode coating layer, L LFP Indicates the mass percentage of the positive electrode active material in the positive electrode coating layer, C1 LFP Indicates the first lithium removal capacity of the positive electrode active material, C2 LFP Indicates the first lithium insertion capacity of the positive electrode active material; L CPAn represents the mass percentage of the nth lithium supplement in the positive electrode coating layer, where n is a natural number greater than or equal to 1, C1 CPAn Indicates the first lithium removal capacity of the nth lithium supplement, C2 CPAn It indicates the initial lithium insertion capacity of the nth lithium supplement.

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: According to the mass percentage, in the combination of lithium iron phosphate and positive electrode lithium replenisher: lithium iron phosphate: positive electrode lithium replenisher = 95% to 99.9%: 5% to 0.1%.

7. The lithium-ion battery according to claim 1, characterized in that: The positive electrode lithium supplement 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 supplement agent is a Li5FeO4 / Li2NiO2 composite lithium supplement agent or a Li2NiO2 / Li6CoO4 composite lithium supplement 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 preparation process of lithium-ion batteries, 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: According to the type and capacity of the battery cell, preliminarily determine the positive electrode slurry composition, the negative electrode slurry composition, the mass percentage of solid matter in the positive electrode slurry, and the mass percentage of solid matter in the negative electrode slurry; B) Determine the final slurry composition, positive electrode coating layer density and negative electrode coating layer density: Determine one of the positive electrode coating layer density or the negative electrode coating layer density according to the cell type and capacity; The charging NP ratio is recorded as NP1, and the discharging NP ratio is recorded as NP2. The parameters in formula (1) and formula (2) are adjusted so that NP1 is greater than or equal to a first threshold value, and NP2 is less than or equal to a second threshold value, and the first threshold value is less than the second threshold value; Record the CW that finally meets the conditions 负 , L Gr , CW 正 , L LFP , L CPAn 、C1 CPAn ; Among them, CW 负 Indicates the negative electrode coating layer density, L Gr Indicates the mass percentage of negative electrode active material in the solid matter of negative electrode slurry, C1 Gr Indicates the initial lithium insertion capacity of the negative electrode active material, C2 Gr Indicates the first lithium removal capacity of the negative electrode active material; CW 正 Indicates the density of the positive electrode coating layer, L LFP Indicates the mass percentage of positive electrode active material in the positive electrode slurry solid matter, C1 LFP Indicates the first lithium removal capacity of the positive electrode active material, C2 LFP Indicates the first lithium insertion capacity of the positive electrode active material; L CPAn It represents the mass percentage of the nth positive electrode lithium supplement in the positive electrode slurry solid matter, where n is a natural number greater than or equal to 1, C1 CPAn Indicates the first lithium removal capacity of the nth positive electrode lithium supplement, C2 CPAn It indicates the initial lithium insertion capacity of the nth positive electrode lithium supplement.

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