Positive electrode polar plate and lithium ion battery

Abstract

To provide a positive electrode polar plate capable of providing a high energy density and an excellent DCR performance to a lithium battery at the same time.SOLUTION: A positive electrode polar plate contains a positive electrode collector; and a positive electrode active material layer provided to the positive electrode collector. In that, a that is a pressure density of the positive electrode active material layer is 2.9≤a≤3.5; a unit is g / cm3; b that is a surface density of the positive electrode active material layer is 0.012≤b≤0.018; a unit is g / cm2; c that is a mass percentage of a conductive agent in the positive electrode active material layer is 2.4%≤c≤4.4%; and the positive electrode active material layer satisfies a formula of 3.3<a2*b / c<5.5. In the case where the positive electrode polar plate satisfies the above condition, a lithium battery manufactured from the positive electrode polar plate can have a DCR performance as well as secures an energy density of a cell, and thus, can avoid many DOE experiments. The research and development time and cost of the lithium battery can be effectively saved.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to the technical field of batteries, and in particular to positive electrodes and lithium ion batteries. [Background technology]

[0002] With the development of modern society and the progress of science and technology, automobiles have gradually become the mainstream alternative to walking. However, as the number of automobiles increases, traffic gradually becomes more congested, and vertical take-off and landing aircraft gradually attract people's attention. In addition, as the price of crude oil increases year by year, electric vertical take-off and landing (EVTOL) has become a goal pursued by science and technology. At present, lithium-ion batteries are the optimal choice for EVTOL power. Due to its unique characteristics, EVTOL requires lithium-ion batteries to have high energy density, high power output, and long life.

[0003] In light of this, providing lithium-ion batteries that can maintain energy density and provide sustained high output is a requirement for promoting the development of the aircraft industry. Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem to be solved by the present invention is to provide a positive electrode plate and a lithium ion battery, and to provide a lithium battery including the positive electrode plate with high energy density and excellent DCR performance by controlling the areal density, compaction density and conductive agent content of the positive electrode active material layer on the surface of the positive electrode plate. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides the following technical solutions:

[0006] A first aspect of the present invention is a positive electrode plate, A positive electrode current collector; a positive electrode active material layer provided on the positive electrode current collector; The compaction density a of the positive electrode active material layer is 2.9≦a≦3.5 and is expressed in g / cm 3 and b, which is the areal density of the positive electrode active material layer, is 0.012≦b≦0.018 and is expressed in units of g / cm 2 and c, which is a mass percentage of the conductive agent in the positive electrode active material layer, is 2.4%≦c≦4.4%; The positive electrode active material layer is 3.3 2 ×b / c<5.5 A positive electrode plate is provided.

[0007] Furthermore, it is more preferable that the compaction density of the positive electrode active material layer satisfies 3.1≦a≦3.3.

[0008] Furthermore, the areal density of the positive electrode active material layer is more preferably 0.014≦b≦0.016.

[0009] Furthermore, the mass percentage of the conductive agent in the positive electrode active material layer is more preferably 3%≦c≦4%.

[0010] Furthermore, the positive electrode active material layer has a thickness of 3.35 2 It is more preferable that the formula ×b / c<5 is satisfied.

[0011] Furthermore, the conductive agent in the positive electrode active material layer is conductive carbon black.

[0012] Furthermore, the positive electrode current collector is preferably an aluminum foil or a carbon-coated aluminum foil.

[0013] Furthermore, the positive electrode active material contained in the positive electrode active material layer may be one or more selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0014] ​​Furthermore, the positive electrode plate can be manufactured by a wet coating method, which specifically includes: uniformly mixing a positive electrode active material, a conductive agent, a binder, and a solvent to obtain a positive electrode slurry; and uniformly applying the prepared positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it to obtain the positive electrode plate.

[0015] A second aspect of the present invention provides a lithium ion battery comprising the positive electrode plate according to the first aspect.

[0016] Furthermore, the lithium ion battery further includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the compaction density of the negative electrode active material layer is 1.35 g / cm 3 and the surface density of the negative electrode active material layer is preferably 0.0058 g / cm 2 and the mass percentage of the conductive agent in the negative electrode active material layer is preferably 1.6%. Effect of the Invention

[0017] Compared with the prior art, the technical advantages of the present invention are as follows: The present invention provides a positive electrode plate, and the values ​​of the compaction density a, the areal density b and the mass percentage c of the conductive material of the positive electrode active material layer in the positive electrode plate are reasonably controlled, and the three are within the range of 3.3. 2 By satisfying the specific relational expression of ×b / c<5.5, a lithium ion battery including the positive electrode plate can have both high energy density and high output performance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] ​Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. The terms used herein are merely for describing specific examples and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the associated items listed. "Include" or "contain" as described in the present invention means that other components may be included in addition to the above-mentioned components. "Include" or "contain" as described in the present invention may be replaced with the closed "is" or "consisting of".

[0019] As described in the Background Art, in order to promote the development of the aircraft industry, there is a demand for lithium-ion batteries that can maintain energy density and provide sustained high output.

[0020] In order to solve the above technical problems, an embodiment of the present invention provides a positive electrode plate including a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector.

[0021] Here, the compaction density a of the positive electrode active material layer is 2.9≦a≦3.5 and is expressed in units of g / cm 3 The surface density b of the positive electrode active material layer is 0.012≦b≦0.018 and is expressed in g / cm 2 The mass percentage c of the conductive agent in the positive electrode active material layer is 2.4%≦c≦4.4%. 2 ×b / c<5.5.

[0022] Specifically, the inventors discovered that the compaction density, areal density and mass ratio of the conductive agent of the positive electrode active material layer in the positive electrode plate affect the energy density and output performance of the cell, but that the effects have certain limitations and correlations.

[0023] ​When a lithium-ion battery is discharged, lithium ions are released from the negative electrode material and inserted into the positive electrode material. The insertion process of lithium ions into the positive electrode is related to the compaction density, and if the compaction density is too large or too small, it will affect the rate performance of the battery. If the compaction density is too large, the distance between the raw material particles will decrease, the contact will become tighter, and the electronic conductivity will increase accordingly. However, the liquid absorption capacity of the positive electrode active material layer will decrease with an increase in the compaction density, and the ion migration path will be reduced or blocked accordingly, which is unfavorable to the rapid migration of a large amount of ions. As a result, the ion diffusion resistance will increase, which will limit high-current discharge, reduce the discharge voltage, and reduce the discharge capacity. If the compaction density is too small, the distance between the raw material particles will increase, and the absorption capacity of the positive electrode active layer for the electrolyte will be strong, and the ion path will increase accordingly, which is favorable to the rapid migration of ions, but the contact probability and contact area between the particles will decrease with a decrease in the compaction density, which is unfavorable to the conduction of electrons. As a result, the electronic resistance increases, which affects the large current discharge and increases the discharge polarization. In view of this, the inventors have set the compaction density of the positive electrode active material layer to an appropriate range, i.e., 2.9≦a≦3.5, and the unit is g / cm 3 They discovered that by controlling the temperature within a certain range, the ion migration paths can be unblocked and sufficient contact can be achieved between the raw material particles, ensuring both good conductivity and rapid ion migration capability during large current discharge, thereby reducing discharge polarization.

[0024] In some preferred embodiments, the range of the compaction density of the positive electrode active material layer is more preferably 3.1≦a≦3.3, for example, a may be 3.1, 3.12, 3.13, 3.14, 3.15, 3.16, 3.17, 3.18, 3.19, 3.2, 3.25, 3.3, etc., including but not limited to the above values.

[0025] In addition, in the embodiment of the present invention, when the lithium ion battery is discharged, lithium ions are desorbed from the negative electrode material and inserted into the positive electrode material, and the movement distance of the lithium ions is related to the surface density. If the surface density is too high, the movement distance of the lithium ions increases with an increase in the surface density, and the ion diffusion resistance increases accordingly, so that the output performance of the cell decreases. If the surface density is too low, the output performance of the cell improves, but the energy density of the cell decreases as the proportion of the cell auxiliary material increases. In view of this, the inventors have set the surface density of the positive electrode active material layer within an appropriate range, that is, 0.012≦b≦0.018, and the unit is g / cm. 2 It has been discovered that by controlling the charge-discharge current (P) within a certain range, it is possible to ensure that the lithium-ion battery has both good power performance and high energy density.

[0026] In some preferred embodiments, the range of the areal density of the positive electrode active material layer is more preferably 0.014≦b≦0.016, and for example, b is 0.014, 0.0142, 0.0143, 0.0144, 0.0145, 0.0146, 0.0147, 0.0148, 0.0149, 0.015, 0.155, 0.016, etc., including but not limited to the above values.

[0027] In the embodiment of the present invention, the content of the conductive agent in the positive electrode active material layer directly affects the electronic impedance of the positive electrode plate and the energy density of the battery. If the content ratio of the conductive agent in the positive electrode active material layer is too high, the electronic impedance of the positive electrode plate decreases, which is favorable for improving the output performance of the cell, but as the content ratio of the conductive agent increases, the proportion of the positive electrode active material in the positive electrode active material layer decreases accordingly, which affects the energy density of the cell. If the content ratio of the conductive agent in the positive electrode active material layer is too low, it is favorable for improving the energy density of the cell, but as the content of the conductive agent decreases, the electronic impedance increases, which affects the output performance of the cell. In view of this, the inventors have found that by controlling the mass percentage of the conductive agent in the positive electrode active material layer to an appropriate range, i.e., 2.4%≦c≦4.4%, a lithium-ion battery can have high energy density and excellent output performance.

[0028] In some preferred embodiments, the range of the value of the mass percentage of the conductive agent in the positive electrode active material layer is more preferably 3%≦c≦4%, for example, c is 3.1%, 3.13%, 3.16%, 3.18%, 3.2%, 3.22%, 3.24%, 3.26%, 3.28%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, etc., including but not limited to the above values.

[0029] By optimizing the compaction density, areal density, or mass ratio of the conductive agent in the positive electrode active material layer, the energy density or output performance of the lithium ion battery can be improved to some extent, but each factor has a large limit in terms of improving both the energy density and the output performance. The inventors have found that the above parameters are within the appropriate value range and 3.3 2 ×b / c<5.5, the lithium ion battery including the positive electrode plate can only achieve high energy density and high output performance. 2 The formula ×b / c<5.5 was obtained by the following method: (1) The logical positive / negative correlation between the magnitude of each factor and the cell energy density and output performance was examined. For example, for both a and b, within their respective preferred ranges, as the values ​​increase, the corresponding cell's energy density increases and output performance decreases (the DCR value increases), while for c, as the value increases (within the preferred range), the cell's energy density decreases and output performance improves (the DCR value decreases). (2) On the premise that the logical positive / negative correlation between the magnitude of each factor and the cell's energy density and output performance is known, the factor's power (e.g., squared, cubed, etc.) is determined based on the importance of the effect of the value of each factor on the cell's performance to construct the formula. (3) The formula is adjusted based on the experimental data obtained by a 100% survey to obtain the preferred range of the formula.

[0030] In some preferred embodiments, the positive electrode active material layer has a thickness of 3.35 2 It is more preferable that the formula: ×b / c<5 is satisfied. For example, 2 ​​​The value of ×b / c may be in the range of 3.5 to 4.0, 4.0 to 4.3, 4.3 to 4.5, or 4.5 to 5.0.

[0031] In some preferred embodiments, the conductive agent in the positive electrode active material layer is conductive carbon black (SP).

[0032] In some preferred embodiments, the positive current collector is preferably aluminum foil or carbon coated aluminum foil.

[0033] In some preferred embodiments, the positive electrode active material contained in the positive electrode active material layer is preferably one or more selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide, and is more preferably an NCM-based or NCA6-based positive electrode active material, for example, an NCM8-based positive electrode active material LiNi 0.83 Co 0.12 Mn 0.05 O 2 It is more preferable that:

[0034] An embodiment of the present invention further provides a method for manufacturing the above-mentioned positive electrode plate, the method comprising: uniformly mixing a positive electrode active material, a conductive agent, a binder, and a solvent to obtain a positive electrode slurry; and uniformly applying the prepared positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it to obtain the positive electrode plate.

[0035] In some preferred embodiments, the binder may be one or more of polyacrylic acid, polyvinylidene fluoride, polyvinylidene difluoride, carboxymethyl cellulose, and styrene butadiene latex, and the solvent may be N-methylpyrrolidone (NMP).

[0036] An embodiment of the present invention further provides a lithium ion battery including the positive electrode plate described above.

[0037] Specifically, the lithium ion battery includes a case, a positive electrode plate, a separator, a negative electrode plate, and an electrolyte solution, and the positive electrode plate, the separator, and the negative electrode plate are stacked and laminated or wound to form a bare cell, and the tabs are ultrasonically welded, and the bare cell is placed in a case, dried to remove moisture, and then the electrolyte solution is injected and sealed to obtain a battery.

[0038] In some preferred embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, where the negative electrode current collector may be a copper foil.

[0039] In some preferred embodiments, the packed density of the negative electrode active material layer is 1.35 g / cm 3 and the surface density of the negative electrode active material layer is preferably 0.0058 g / cm 2 and the mass percentage of the conductive agent in the negative electrode active material layer is preferably 1.6%.

[0040] In some preferred embodiments, the negative electrode active material contained in the negative electrode active material layer may be one or more selected from graphite, soft carbon, hard carbon, mesocarbon microbeads, and silicon materials, but the present invention is not limited to these materials, and other well-known negative electrode active materials for lithium ion batteries may also be used.

[0041] In some preferred embodiments, the separator may be a polypropylene film or other separator materials available for lithium ion batteries. The electrolyte includes a lithium salt and a solvent, the lithium salt may be LiPF6, LiBF4, LiTFSI, etc., and the solvent may be a mixed solvent selected from ethylene carbonate, propylene carbonate, butylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate, for example, a mixed solvent in which ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 1:1:1.

[0042] The present invention will be further described below with reference to examples in order to enable those skilled in the art to better understand and practice the present invention, but the examples listed are not intended to limit the present invention.

[0043] <Example 1> This embodiment relates to the manufacture of a lithium ion battery, and specifically includes the following steps: (1) Manufacturing of positive electrode plate: Positive electrode active material LiNi 0.83 Co 0.12 Mn 0.05 O 2 The conductive agent SP and the binder PVDF are mixed in a mass ratio of 95.5:3.5:1, and NMP is added and stirred to obtain a uniformly mixed positive electrode slurry. The positive electrode slurry is uniformly applied to a positive electrode current collector, dried, and cold pressed to obtain a positive electrode plate. The positive electrode active material layer formed by the positive electrode slurry on the surface of the positive electrode plate has a compaction density of 3.2 g / cm. 3 and the surface density is 0.015 g / cm 2 It is. (2) Manufacturing of negative electrode plate: Graphite and silicon oxide (SiO x ) in a mass ratio of 81:19, a conductive agent in which SP and CNT are mixed in a mass ratio of 82:3, and a binder in which PAA and SBR are mixed in a mass ratio of 2:1 are mixed in a mass ratio of 95.1:1.6:3.3, and deionized water is added and stirred to obtain a homogeneously mixed negative electrode slurry. The negative electrode slurry is applied to a negative electrode current collector, dried, and cold pressed to obtain a negative electrode plate. The negative electrode active material layer formed by the negative electrode slurry on the surface of the negative electrode plate has a compaction density of 1.35 g / cm 3 and the surface density is 0.0058 g / cm 2 It is. (3) Separator: A polyethylene film having a porosity of 45% is used. (4) Electrolyte: Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and lithium salt LiPF 6 Add LiPF 6 An electrolyte solution having a concentration of 1.2 mol / L is obtained. (5) Assembly of lithium-ion batteries: Positive electrodes, separators, and negative electrodes are stacked and wound to form a bare cell. The bare cell is then placed in an exterior case, dried, and then an electrolyte is injected. After vacuum sealing, standing, formation, shaping, and other processes, a lithium-ion battery is obtained.

[0044] <Example 2> This embodiment differs from Example 1 in the manufacture of a lithium ion battery only in the manufacture of a positive electrode plate, and the rest is the same. The manufacture of the positive electrode plate is specifically as follows. Cathode active material LiNi 0.83 Co 0.12 Mn 0.05 O 2 The conductive agent SP and the binder PVDF are mixed in a mass ratio of 95.6:3.4:1, NMP is added and stirred to obtain a uniformly mixed positive electrode slurry, which is then uniformly applied to a positive electrode current collector, dried, and cold pressed to obtain a positive electrode plate. The positive electrode active material layer formed by the positive electrode slurry on the surface of the positive electrode plate has a compaction density of 3.3 g / cm. 3 and the surface density is 0.014 g / cm 2 It is.

[0045] <Example 3> This embodiment differs from Example 1 in the manufacture of a lithium ion battery only in the manufacture of a positive electrode plate, and the rest is the same. The manufacture of the positive electrode plate is specifically as follows. Cathode active material LiNi 0.83 Co 0.12 Mn 0.05 O 2 The conductive agent SP and the binder PVDF are mixed in a mass ratio of 95.4:3.6:1, NMP is added and stirred to obtain a uniformly mixed positive electrode slurry, which is then uniformly applied to a positive electrode current collector, dried, and cold pressed to obtain a positive electrode plate. The positive electrode active material layer formed by the positive electrode slurry on the surface of the positive electrode plate has a compaction density of 3.1 g / cm 3 and the surface density is 0.016 g / cm 2 It is.

[0046] <Example 4> This example relates to the manufacture of a lithium ion battery, and is characterized in that the compaction density of the positive electrode active material layer is 2.9 g / cm 3 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0047] <Example 5> This example relates to the manufacture of a lithium ion battery, and is characterized in that the compaction density of the positive electrode active material layer is 3.5 g / cm 3 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0048] <Example 6> This example relates to the manufacture of a lithium ion battery, and is a method for manufacturing a lithium ion battery having a positive electrode active material layer with a surface density of 0.012 g / cm 2 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0049] <Example 7> This example relates to the manufacture of a lithium ion battery, and is a method for manufacturing a lithium ion battery having a positive electrode active material layer with a surface density of 0.018 g / cm 2 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0050] <Example 8> This embodiment differs from Example 1 in the manufacture of the lithium ion battery only in that the mass ratio of the conductive agent in the positive electrode active material layer is 4%, and all other procedures are the same.

[0051] <Example 9> This embodiment differs from Example 1 in the manufacture of the lithium ion battery only in that the mass ratio of the conductive agent in the positive electrode active material layer is 4.4%, and all other procedures are the same.

[0052] <Comparative Example 1> This comparative example relates to the manufacture of a lithium ion battery, and the compaction density of the positive electrode active material layer is 2.4 g / cm 3 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0053] <Comparative Example 2> This comparative example relates to the manufacture of a lithium ion battery, and the compaction density of the positive electrode active material layer is 3.6 g / cm 3 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0054] <Comparative Example 3> This comparative example relates to the manufacture of a lithium ion battery, and is based on a positive electrode active material layer having an areal density of 0.01 g / cm 2 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0055] <Comparative Example 4> This comparative example relates to the manufacture of a lithium ion battery, and is based on a positive electrode active material layer having an areal density of 0.02 g / cm 2 This embodiment differs from the first embodiment only in that, and everything else is the same.

[0056] <Comparative Example 5> This comparative example differs from Example 1 in the manufacture of the lithium ion battery only in that the mass ratio of the conductive agent in the positive electrode active material layer is 2%, and all other procedures are the same.

[0057] <Comparative Example 6> This comparative example differs from Example 1 in the manufacture of the lithium ion battery only in that the mass ratio of the conductive agent in the positive electrode active material layer is 5.5%, and all other procedures are the same.

[0058] <Comparative Example 7> This comparative example differs from Example 1 in the manufacture of the lithium ion battery only in that the mass ratio of the conductive agent in the positive electrode active material layer is 2.4%, and all other procedures are the same.

[0059] <Performance test> The energy density and DCR performance of the lithium ion batteries prepared in the above examples and comparative examples are tested, and the specific procedures are as follows:

[0060] Energy density test: At 25°C, the lithium ion batteries prepared in the examples and comparative examples are fully charged at 1C rate, then fully discharged at 1C rate, and the actual discharge energy is recorded. The ratio of the actual discharge energy to the weight of the lithium ion battery (weighed at 25°C) is the actual energy density of the lithium ion battery.

[0061] DCR performance test: At 25°C, the lithium ion batteries manufactured in the examples and comparative examples are fully charged at a constant current and constant voltage of 1C, left for 5 minutes, then discharged at a constant current of 1C for 30 minutes, left to stand for 5 minutes, and the voltage value V1 at the end of the standing time is recorded. Pulse discharge is performed at 2C for 30 seconds, and the voltage value V2 at the end of the pulse discharge is recorded. The ratio of the voltage difference between V1 and V2 to the 2C current value is the DCR of the battery at SOC50% discharge.

[0062] The results of the above performance tests are shown in Table 1 below.

[0063] [Table 1]

[0064] As can be seen from the comparison of the data of Examples 1 to 9 and Comparative Examples 1 to 7 in the above table, the compaction density of the positive electrode active material layer in the positive electrode plate is controlled to be between 2.9 and 3.5, the areal density is controlled to be between 0.012 and 0.018, the mass ratio of the conductive agent is controlled to be between 2.4% and 4.4%, and the above parameters are controlled to be between 3.3 and 4.4%. 2 When the relationship ×b / c<5.5 is satisfied, a lithium-ion battery manufactured from the positive electrode plate has both high energy density and excellent DCR performance (i.e., excellent output performance).

[0065] As can be seen from Example 1 and Comparative Examples 1 and 2, either the compaction density being too low (Comparative Example 1) or being too high (Comparative Example 2) affects the DCR performance of the lithium ion battery, and the formula a 2 The value calculated by ×b / c is not within the range of 3.3 to 5.5, and the overall performance of the battery is inferior.

[0066] ​As can be seen from Example 1 and Comparative Examples 3 and 4, a surface density that is too low (Comparative Example 3) or too high (Comparative Example 4) affects the energy density and DCR performance of a lithium-ion battery. If the surface density is too low, the DCR value is small, i.e., it has good output performance, but the energy density of the battery is low to 239 Wh / Kg. If the surface density is too high, the energy density of the battery is significantly improved, but the DCR value is too large and the output performance is poor. In addition, if the energy density of the battery is too low or the DCR value is too large, the overall performance of the battery is poor. In this case, the formula a 2 The value calculated by ×b / c does not fall within the range 3.3 to 5.5.

[0067] As can be seen from Example 1 and Comparative Examples 5 and 6, if the mass ratio of the conductive agent in the positive electrode active material layer is too low (Comparative Example 5) or too high (Comparative Example 6), it affects the energy density and DCR performance of the lithium ion battery. If the mass ratio of the conductive agent in the positive electrode active material layer is too low, the battery has a high energy density, but the DCR value is large and the output performance is accordingly poor. If the mass ratio of the conductive agent in the positive electrode active material layer is too high, the DCR value is significantly reduced, which is advantageous for improving the output performance of the battery, but the energy density is low.

[0068] As can be seen from Comparative Example 7, the compaction density, areal density and conductive agent content of the positive electrode plate are all within the preferred ranges, but 2 The calculated value of ×b / c is 6.40, which does not meet the preferred range. The battery manufactured from this positive electrode plate has a high energy density, but the DCR value of the battery is too high, so the overall performance is relatively poor. Meanwhile, it is difficult in the battery field to further reduce the DCR value while maintaining the same energy density.

[0069] In addition, the compaction density of the positive electrode active material layer in the positive electrode plate is controlled to be between 3.1 and 3.3, the areal density is controlled to be between 0.014 and 0.016, the mass ratio of the conductive agent is controlled to be between 3% and 4%, and the above parameters are controlled to be 3.35 2 ​When the relational expression ×b / c<5 is satisfied, for example, the above-mentioned Examples 1, 2, 3, and 8 can have both a relatively high energy density and a low DCR value, and have better overall performance.

[0070] As can be seen from the above, the compaction density, areal density, and mass ratio of the conductive agent of the positive electrode active material layer in the positive electrode plate are all optimized, and the above parameters are set to 3.3. 2 By satisfying the formula b / c<5.5, a lithium ion battery including the positive electrode plate has both high energy density and high output performance.

[0071] The above embodiments are merely preferred embodiments enumerated to fully explain the present invention, and the scope of protection of the present invention is not limited thereto. Those skilled in the art will recognize that any equivalent replacement or conversion made based on the present invention falls within the scope of protection of the present invention. The scope of protection of the present invention is subject to the scope of the claims.​

Claims

1. A positive electrode plate, A positive electrode current collector; a positive electrode active material layer provided on the positive electrode current collector; The compaction density a of the positive electrode active material layer is 2.9≦a≦3.5 and is expressed in g / cm ３ and The surface density b of the positive electrode active material layer is 0.012≦b≦0.018 and is expressed in g / cm ２ and the mass percentage c of the conductive agent in the positive electrode active material layer is 2.4%≦c≦4.4%, The positive electrode active material layer has a ２ × b / c < 5.5 is satisfied. A positive electrode plate characterized by:

2. The compaction density of the positive electrode active material layer is 3.1≦a≦3.

3. The positive electrode plate according to claim 1 .

3. The areal density of the positive electrode active material layer is 0.014≦b≦0.

016. The positive electrode plate according to claim 1 .

4. The mass percentage of the conductive agent in the positive electrode active material layer is 3%≦c≦4%. The positive electrode plate according to claim 1 .

5. The positive electrode active material layer has a ２ × b / c < 5 is satisfied. The positive electrode plate according to claim 1 .

6. The conductive agent in the positive electrode active material layer is conductive carbon black. The positive electrode plate according to claim 1 .

7. The positive electrode current collector is an aluminum foil or a carbon-coated aluminum foil. The positive electrode plate according to claim 1 .

8. The positive electrode active material contained in the positive electrode active material layer is one or more selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. The positive electrode plate according to claim 1 .

9. The positive electrode plate according to any one of claims 1 to 8 is included. A lithium-ion battery characterized by:

10. The lithium ion battery further includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, The compaction density of the negative electrode active material layer is 1.35 g / cm ３ and The surface density of the negative electrode active material layer is 0.0058 g / cm ２ and The mass percentage of the conductive agent in the negative electrode active material layer is 1.6%.

10. The lithium ion battery according to claim 9.

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