Positive electrode plate and lithium ion battery using same

Abstract

A positive electrode plate, and a lithium ion battery using same. The positive electrode plate comprises a current collector and a positive electrode active material layer. The positive electrode active material layer comprises a first active material layer and a second active material layer, which are arranged in a composite manner. The first active material layer comprises a spinel-type lithium-manganese oxide material and a ternary material composite material. The second active material layer comprises a phosphate material. Individual crystal sizes of the spinel-type lithium-manganese oxide and the ternary material are D1 and D2 respectively, and satisfy formula (I).

Description

A positive electrode sheet and a lithium-ion battery using the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on April 2, 2024, with application number 202410396103.8. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of lithium-ion batteries, and in particular to a positive electrode plate and a lithium-ion battery using the same. Background Art

[0003] Lithium iron manganese phosphate (LMP) has good rate capability and low-temperature performance, but its dual voltage platform makes BMS (Battery Management System) design more difficult. Therefore, it is generally mixed with ternary materials to smooth the charge and discharge curve, improve cycle stability, and thus improve cycle performance. Some researchers are also considering the introduction of lithium manganese oxide, which has lower costs. Higher application voltages can also be mixed with LMP. In this way, the combination of high-energy-density ternary materials, low-cost lithium manganese oxide materials, and long-cycle LMP materials can create a long-cycle, low-cost battery.

[0004] However, in related technologies, the three materials are generally mixed directly and then slurried for coating. However, due to the large differences in particle size, density, and pH value of the three materials, it is difficult to achieve uniform mixing of the three, resulting in difficulties in electrode processing. In addition, the electrode produced by mixing the three materials simultaneously has uneven particle distribution inside, which cannot bring out the advantages of the three materials. There are also methods that prepare separate coatings for the ternary material and the lithium iron manganese material, using a composite coating method, but this method cannot take advantage of the gap-filling effect of lithium iron manganese phosphate on the ternary material, resulting in a lower compaction density. Lithium manganese oxide, as a simple blending material, cannot play its maximum role in reducing costs and improving energy density. Therefore, it is necessary to develop a low-cost, high-compaction electrode system design that meets the energy density and cycle performance requirements. SUMMARY OF THE INVENTION

[0005] The present application provides a positive electrode plate and a lithium-ion battery using the same, which can reduce the production cost of the battery, increase the compaction density of the plate, and improve the volume energy density and cycle performance of the battery.

[0006] The present application provides a positive electrode plate. The positive electrode plate includes a current collector and a positive electrode active material layer coated on at least one side of the current collector; the positive electrode active material layer includes a composite first active material layer and a second active material layer, wherein the first active material layer includes a spinel-type lithium manganate material and a ternary material; the second active material layer includes a phosphate material; the spinel-type lithium manganate material includes lithium manganate single crystal particles, and the ternary material includes ternary single crystal particles; the primary particles of the spinel-type lithium manganate material are D1, and the primary particles of the ternary material are D2, and the spinel-type lithium manganate material and the ternary material meet the following requirements: .

[0007] The present application also provides a lithium-ion battery. The lithium-ion battery includes the positive electrode sheet described above. Beneficial effects

[0008] The beneficial effects of the present application are as follows: the positive electrode provided by the present application designs the morphology of a single crystal of the spinel-type lithium manganate material and simultaneously limits the size of the primary particles of the ternary material and the primary particle size of the lithium manganate. When the stacking density of the pole piece is optimized, the volume energy density of the battery cell can be improved; when , it is impossible to achieve the optimal ratio of ternary material and spinel lithium manganate material, and it is impossible to maximize the compaction density, thereby reducing the volume energy density of the electrode. At the same time, taking advantage of the large pH differences among spinel lithium manganate material (pH 9.4~10.4), ternary material (pH 10.4~12.0), and phosphate material (pH 8.3~9.4), the spinel lithium manganate material is mixed with the ternary material. When the sizes of the two meet the requirements of When the lithium manganese iron phosphate is directly mixed with the ternary material, the instability of the slurry can be avoided, the weighting effect can be maintained, the cost of the positive electrode system can be reduced, and the interface stratification between the phosphate material and the ternary material can be improved, thereby improving the cycle performance. In addition, the introduction of spinel lithium manganese oxide material into the pole piece can also improve the rate performance of the ternary material. Therefore, the positive electrode plate provided by the present application has good cycle performance, rate performance and low cost.

[0009] The lithium-ion battery provided in the present application has good cycle performance, rate performance and low cost by adopting the above-mentioned positive electrode plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG1 is a positive electrode sheet provided in the present application, wherein the first active material layer is arranged on the side close to the current collector.

[0011] FIG2 is a diagram of the positive electrode sheet provided in this application, wherein the second active material layer is disposed on the side close to the current collector. Modes for Carrying Out the Invention

[0012] In order to enable people in this technical field to better understand the technical solutions in this application, the technical solutions of this application will be clearly and completely described below in combination with the embodiments of this application and the drawings in the embodiments. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments.

[0013] Example 1

[0014] 1. Preparation of positive electrode sheet

[0015] (1) Preparation of positive electrode sheet materials

[0016] The positive electrode sheet provided in this embodiment is prepared. The positive electrode active materials that can be used in each active material layer are shown in Table 1. Among them, the phosphate material used is LiMn 0.6 Fe 0.4 D3 of PO4=200nm.

[0017] Table 1 Materials for preparing positive electrode sheets

[0018]

[0019] (2) Method for preparing positive electrode sheet

[0020] The spinel lithium manganate material and the ternary material shown in Table 1 were mixed in a mass ratio of 1:1, and then the mixed material, conductive carbon black, CNT, and PVDF were mixed in a weight ratio of 96:1:1:2. After these materials were mixed and stirred evenly using NMP as a solvent, a first active material layer slurry was obtained.

[0021] The phosphate material, conductive carbon black, CNT, and PVDF shown in Table 1 were mixed in a weight ratio of 96:1:1:2, and NMP was used as a solvent to mix and stir the materials to obtain a second active material layer slurry.

[0022] The first active material layer slurry and the second active material layer slurry are simultaneously coated on the carbon-coated aluminum foil, wherein the first active material layer is on the side close to the aluminum foil, and the surface density of the first active material layer is 40g / m 2 The second active material layer has a density of 160 g / m 2 After drying, cold pressing (elongation of the electrode is between 0.5% and 0.7%), and die cutting, the positive electrode is obtained.

[0023] 2. Preparation of negative electrode sheet

[0024] The negative electrode material graphite, conductive agent acetylene black, binder CMC, and SBR were prepared into a slurry in a mass ratio of 94:1:2:3 and coated on a copper foil current collector, which was then vacuum-dried to obtain a negative electrode sheet.

[0025] 3. Battery assembly

[0026] The positive electrode sheet, separator (Enjie 14μm separator) and negative electrode sheet prepared above are stacked in order, with the separator acting as an isolation between the positive and negative electrode sheets. Then, the battery cell is obtained by stacking or winding. The wound core is placed in an outer packaging shell (such as an aluminum shell or soft pack). After drying, the electrolyte (Zhonghua Lantian ZP507 type) is injected at a liquid injection volume of 5.0g / Ah. After vacuum packaging, standing, formation, capacity separation and other processes, the secondary battery to be tested is obtained.

[0027] In this embodiment, the positive electrode active materials selected in the first active material layer and the second active material layer and their primary particle sizes are used as variables to set different treatment groups and comparison groups. Among them, the variables of treatment groups 1A~4A and comparison groups 1A~2A of Example 1 are shown in Table 2. Except for the above differences, the steps of preparing the positive electrode sheet and lithium-ion battery in this embodiment are consistent with the method provided above.

[0028] The positive electrode sheet prepared by treatment group 1A of Example 1 is shown in FIG1 , and the positive electrode sheet prepared by treatment group 5A of Example 1 is shown in FIG2 .

[0029] Table 2 Variables of treatment groups 1A to 4A and control groups 1A to 2A in Example 1

[0030]

[0031] Treatment group 5A

[0032] This treatment group prepared the positive electrode sheet with reference to the formula provided by treatment group 1A of Example 1. The difference between this treatment group and treatment group 1A of Example 1 is that the second active material layer slurry is applied to the side close to the aluminum foil when preparing the positive electrode sheet. Apart from the above difference, the lithium ion battery prepared by this treatment group is strictly consistent with treatment group 1A of Example 1. Among them, the positive electrode active material used in the second active material layer close to the aluminum foil is LiMn 0.6 Fe 0.4 PO4, D3 = 200nm; in the first active material layer on the side away from the aluminum foil, the positive electrode active materials used are LiMn2O4, D1 = 0.5μm, LiNi 0.8 Co 0.1 Mn 0.1 O2, D2=3μm.

[0033] Comparative group 3A

[0034] The positive electrode sheet of this comparative group was prepared by referring to the formula provided by the treatment group 1A of Example 1. The difference between this comparative group and the treatment group 1A of Example 1 is that the first active material layer of this comparative group only uses NCM811 when preparing the positive electrode sheet, and the second active material layer mixes lithium manganese iron phosphate material and lithium manganese oxide material. Except for the above differences, the lithium ion battery prepared by this comparative group is strictly consistent with the treatment group 1A of Example 1. Among them, in the first active material layer close to the aluminum foil side, the positive electrode active material used is LiNi 0.8 Co 0.1 Mn 0.1 O2, D2 = 3μm; in the second active material layer on the side away from the aluminum foil, the positive electrode active material used is LiMn2O4, D1 = 0.5μm, LiMn 0.6 Fe 0.4 PO4, D3=200nm.

[0035] Control group 4A

[0036] The positive electrode sheet of this comparison group was prepared by referring to the formula provided by treatment group 1A. The difference between this comparison group and treatment group 1A is that the material used in the preparation of the first active material layer of the positive electrode sheet of this comparison group is NCM811, and the material used in the second active material layer is lithium manganese iron phosphate. Except for the above differences, the lithium ion battery prepared by this comparison group is strictly consistent with the treatment group 1A of Example 1. Among them, in the first active material layer close to the aluminum foil side, the positive electrode active material used is LiNi 0.8 Co 0.1 Mn 0.1 O2, D2 = 3μm; in the second active material layer on the side away from the aluminum foil, the positive electrode active material used is LiMn 0.6 Fe 0.4 PO4, D3=200nm.

[0037] Control group 5A

[0038] The positive electrode sheet of this comparative group was prepared by referring to the formula provided by the treatment group 1A of Example 1. The difference between this comparative group and the treatment group 1A of Example 1 is that the material used in the first active material layer of the positive electrode sheet of this comparative group is NCM811, and the material used in the second active material layer is lithium manganate. Except for the above differences, the lithium ion battery prepared by this comparative group is strictly consistent with the treatment group 1A of Example 1. Among them, in the first active material layer close to the aluminum foil side, the positive electrode active material used is LiNi 0.8 Co 0.1 Mn 0.1 O2, D2=3μm; in the second active material layer on the side away from the aluminum foil, the positive electrode active material used is LiMn2O4, D1=0.5μm.

[0039] Control group 6A

[0040] The positive electrode sheet was prepared by the formula provided by the treatment group 1A of Example 1 in this comparative group. The difference between this comparative group and the treatment group 1A of Example 1 is that this comparative group has only one active material layer when preparing the positive electrode sheet. The material layer is prepared by mixing NCM811 and lithium iron manganese phosphate material. The surface density ratio of NCM811 and lithium iron manganese phosphate material is 2:8. Except for the above differences, the preparation of lithium-ion batteries in this comparative group is strictly consistent with the treatment group 1A of Example 1. Among them, in the active material layer, the positive electrode active material used is LiNi 0.8 Co 0.1 Mn 0.1 O2, D2=3μm, LiMn 0.6 Fe 0.4 PO4, D3=200nm.

[0041] Control group 7A

[0042] The positive electrode sheet of this comparative group was prepared by referring to the formula provided by the treatment group 1A of Example 1. The difference between this comparative group and the treatment group 1A of Example 1 is that this comparative group has only one active material layer when preparing the positive electrode sheet. The material layer is a mixture of NCM811, lithium manganese iron phosphate, and lithium manganate. Except for the above difference, the lithium ion battery prepared by this comparative group is strictly consistent with the treatment group 1A of Example 1. Among them, in the active material layer, the positive electrode active material used is LiMn2O4, D1=0.5μm, LiNi 0.8 Co 0.1 Mn 0.1 O2, D2=3μm, LiMn 0.6 Fe 0.4 PO4, D3=200nm. Specifically, the steps for preparing the electrode in this comparative group are: spinel lithium manganate material (LiMn2O4), ternary material (LiNi 0.8 Co 0.1 Mn 0.1 O2), phosphate materials (LiMn 0.6 Fe 0.4 PO4) in a 1:1:1 mass ratio. The mixed positive electrode active material, conductive carbon black, CNT, and PVDF are then mixed in a 96:1:1:2 weight ratio. These materials are then mixed and stirred uniformly in NMP as a solvent to produce a positive electrode active material layer slurry. The positive electrode active material layer slurry is then coated on an aluminum foil surface. After drying, cold pressing, and die-cutting, the positive electrode sheet is obtained.

[0043] Test Example 1

[0044] 1. Test subjects

[0045] Batteries prepared in each treatment group and control group of Example 1.

[0046] 2. Test Method

[0047] Room temperature cycle performance: At 25°C, the lithium-ion battery is charged at a constant current of 0.5C (nominal capacity) to a voltage of 4.2V, then charged at a constant voltage of 4.2V to a current of ≤0.05C. After 10 minutes of storage, it is discharged at a constant current of 1C or 2C to a cut-off voltage of 2.5V. The above is considered one charge and discharge cycle. The lithium-ion battery is charged and discharged at 25°C according to the above conditions, and the number of cycles at which the capacity retention rate is 80% at different discharge rates is recorded. The capacity retention rate is calculated according to formula (1).

[0048] (1)

[0049] 3. Test results and analysis

[0050] The test results of this test example are shown in Table 3. Among them, this test example mainly explores the effects of different spinel-type lithium manganese oxide materials, ternary materials, phosphate materials, and the settings of the first active material layer and the second active material layer on the prepared positive electrode sheet. In treatment groups 1A to 4A of Example 1, the effects of different D1 and D2 and ternary materials were mainly explored. Among them, the battery prepared by treatment group 1A has good rate performance and cycle performance. Compared with treatment group 1A, treatment group 5A has two layers of positive electrode active layers interchanged, and the electrical performance of the lithium-ion battery prepared by treatment group 5A still remains at a good level.

[0051] In comparison groups 1A to 2A, , which causes the cycle performance of the battery to which it is applied to decrease.

[0052] In Comparative Group 3A, the first active material layer was a ternary material, while the second active material layer mixed lithium iron manganese phosphate and lithium manganese oxide. The rate performance and cycle performance of the battery using this material were significantly reduced. Compared with Comparative Group 3A, the battery using Comparative Group 4A, in which the second active material layer was made of only lithium iron manganese phosphate, also showed a significant decline in cycle performance.

[0053] In the comparison group 5A, the pole pieces were prepared by coating ternary materials and lithium manganese oxide materials respectively, and the rate performance and cycle performance of the batteries using them were significantly reduced.

[0054] In Comparative Group 6A, the battery using a mixture of ternary materials and phosphate materials, coated to prepare the electrode, showed reduced rate performance. This may be because the slurry obtained by mixing the phosphate material with lithium manganese oxide is not as dispersible as the slurry obtained by mixing the ternary materials with lithium manganese oxide.

[0055] In Comparative Group 7A, the positive electrode sheet was prepared by mixing and coating a spinel lithium manganese oxide material, a ternary material, and a phosphate material. However, this method made the positive active slurry difficult to mix evenly, resulting in a sharp decline in the rate capability and cycle performance of the lithium-ion battery using it.

[0056] Table 3 Test results of test case 1

[0057]

[0058] Example 2

[0059] This example sets up treatment groups 1B-5B with reference to treatment group 2A in Example 1. Furthermore, in Example 2, treatment groups 1B-5B use m1 and P1 of the first active material layer and m2 and P2 of the second active material layer as variables. The variables for treatment groups 1B-5B are shown in Table 4. Aside from the aforementioned differences, the steps for preparing positive electrode sheets and lithium-ion batteries for treatment groups 1B-5B in Example 2 strictly follow those for treatment group 2A in Example 1.

[0060] Table 4 Variables of each treatment group in Example 2

[0061]

[0062] Test Example 2

[0063] 1. Test subjects

[0064] Batteries prepared in each treatment group of Example 2.

[0065] 2. Test Method

[0066] Refer to the test method of Test Example 1.

[0067] 3. Test results and analysis

[0068] The test results of this test example are shown in Table 5. This test example primarily explored the effects of the compaction density and mass ratio of the first and second active material layers on the resulting positive electrode sheet. The test data revealed that in treatment groups 1B to 5B, by manipulating the mass ratio and compaction density of the first and second active material layers, the compaction density of the positive electrode sheet could be further optimized, thereby improving the volumetric energy density and cycling performance of the positive electrode.

[0069] Table 5 Test results of test case 1

[0070]

Claims

1. A positive electrode plate, comprising a current collector and a positive electrode active material layer coated on at least one side of the current collector; The positive electrode active material layer includes a first active material layer and a second active material layer which are compositely arranged, wherein: The first active material layer includes spinel lithium manganate material and ternary material; the second active material layer includes phosphate material; The spinel lithium manganate material includes lithium manganate single crystal particles, and the ternary material includes ternary single crystal particles; the primary particles of the spinel lithium manganate material are D1, and the primary particles of the ternary material are D2. The spinel lithium manganate material and the ternary material meet 。 2. The positive electrode sheet according to claim 1, wherein: The primary particles D1 of the spinel lithium manganate material are 0.5-2 μm.

3. The positive electrode sheet according to claim 1 or 2, wherein: The ternary material includes LiNi 0.8 Co 0.1 Mn 0.1 O2 and LiNi 0.8 Co 0.1 Al 0.1 At least one of O2; the spinel lithium manganate material includes LiMn2O4; the phosphate material includes LiMn 0.6 Fe 0.4 PO4.

4. The positive electrode sheet according to claim 3, wherein: The ternary material is LiNi 0.8 Co 0.1 Mn 0.1 O2, D2 are 3 μm; the spinel lithium manganate material is LiMn2O4, and D1 is 0.5 μm.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein: The primary particles of the phosphate material are D3, and D3 is 100nm~600nm.

6. The positive electrode sheet according to claim 5, wherein: The phosphate material is LiMn 0.6 Fe 0.4 PO4, D3 is 200nm.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein: In the positive electrode active material layer, the mass proportion of the first active material layer is m1, the compaction density of the first active material layer is P1, the mass proportion of the second active material layer is m2, the compaction density of the second active material layer is P2, the compaction density of the positive electrode sheet is P, and the positive electrode sheet satisfies the following relationship: ;m1:m2=0.1~10:1, and m1+m2=1.

8. The positive electrode sheet according to claim 7, wherein: Calculated by mass ratio, in the first active material layer, the ratio of the spinel-type lithium manganese oxide material to the ternary material is 0.1-5:

1.

9. The positive electrode sheet according to claim 7 or 8, wherein: The compaction density P1 of the first active material layer is 2.9-3.8 g / cm 3 , and / or, the compaction density P2 of the second active material layer is 2.0-2.5 g / cm 3 .

10. The positive electrode sheet according to claim 9, wherein: The mass ratio m1 of the first active material layer is 0.9, and the compaction density P1 of the first active material layer is 3.2 g / cm 3 The mass ratio m2 of the second active material layer is 0.1, and the compaction density P2 of the second active material layer is 2.3 g / cm 3 .

11. The positive electrode sheet according to claim 9 or 10, wherein: The compaction density P of the positive electrode sheet is 2.3-3.6 g / cm 3 .

12. The positive electrode sheet according to claim 7 or 8, wherein: The area density ratio of the first active material layer to the second active material layer is 5-60:50-200.

13. The positive electrode sheet according to claim 12, wherein: The coating area density of the first active material layer is 5-60 g / m 2 .

14. The positive electrode sheet according to claim 13, wherein: The first active material layer has a surface density of 40 g / m 2 The second active material layer has a surface density of 160 g / m 2 .

15. The positive electrode sheet according to any one of claims 1 to 14, wherein: The first active material layer is coated on a side close to the current collector, and the second active material layer is coated on a side of the first active material layer away from the current collector.

16. The positive electrode sheet according to any one of claims 1 to 14, wherein: The second active material layer is coated on a side close to the current collector, and the first active material layer is coated on a side of the second active material layer away from the current collector.

17. A lithium-ion battery, comprising the positive electrode sheet according to any one of claims 1 to 16.

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