High-energy-density lithium-ion battery

Abstract

Provided in the present application is a high-energy-density lithium-ion battery, which comprises a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises lithium iron phosphate and a lithium-rich oxide; in the positive electrode sheet, the mass content of the lithium-rich oxide is 0.2-20%; and the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises artificial graphite.

Description

High energy density lithium-ion batteries

[0001] This application claims priority to Chinese Patent Application No. 202411959799.7, filed with the Chinese Patent Office on December 27, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of batteries, specifically relating to a high-energy-density lithium-ion battery. Background Technology

[0003] Lithium iron phosphate (LFP) batteries are widely favored for their high safety and long cycle life, but the current LFP-graphite system is approaching the conventional energy density limit of 430 Wh / L. However, improving the energy density of lithium-ion batteries is crucial for various applications. For example, by increasing energy density, more electrical energy can be stored without increasing the size and weight of the lithium-ion battery. This promotes the application of lithium-ion batteries. For electric vehicles, high-energy-density lithium-ion batteries can provide longer driving range or stronger energy output after a single charge, meaning that electric vehicles can have greater convenience, faster acceleration, and better hill-climbing ability.

[0004] Therefore, in order to break through the conventional energy density bottleneck of lithium iron phosphate batteries, the industry has adopted a variety of strategies to improve the volumetric energy density of batteries. For example, exploring new positive and negative electrode materials such as silicon-based negative electrode materials. However, silicon will cause volume expansion (up to 300~400%), poor conductivity, and unstable interface with electrolyte during charging and discharging, which affects the commercial application of silicon-based negative electrode materials.

[0005] Alternatively, optimizing the internal structure of lithium-ion batteries can reduce the use of inactive materials, such as electrolytes and separators, to increase the proportion of active materials and improve energy density. However, this approach may affect the thermal stability and cycle life of lithium-ion batteries, requiring rigorous safety and reliability testing to meet market and regulatory requirements. Therefore, this method requires extensive experimental validation and cannot be quickly commercialized.

[0006] Alternatively, increasing the compaction density of the electrode can improve the energy density of the lithium-ion battery. Ideally, increasing the compaction density increases the amount of active material per unit volume, thereby increasing the energy density of the lithium-ion battery. However, excessively increasing the compaction density of the electrode may lead to a series of adverse effects, ultimately reducing the overall performance of the lithium-ion battery. Summary of the Invention

[0007] This application provides a high-energy-density lithium-ion battery to improve the energy density of lithium-ion batteries.

[0008] An embodiment of this application provides a high-energy-density lithium-ion battery, the lithium-ion battery comprising a positive electrode and a negative electrode, the positive electrode comprising a positive electrode active material, the positive electrode active material comprising lithium iron phosphate and lithium-rich oxide; in the positive electrode, the mass content of the lithium-rich oxide is 0.2~20%; the negative electrode comprising a negative electrode active material, the negative electrode active material comprising artificial graphite. Attached Figure Description

[0009] Figure 1 shows the cycle capacity retention rate of processing group 1B, processing group 2B and processing group 3B in this application;

[0010] Figure 2 shows the gram capacity at different magnifications for treatment group 1B, treatment group 2B, and treatment group 3B of this application. Detailed Implementation

[0011] The embodiments of this application provide a high-energy-density lithium-ion battery, which includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode active material, which includes lithium iron phosphate and lithium-rich oxide. In the positive electrode, the mass content of lithium-rich oxide is 0.2-20%. The negative electrode includes a negative electrode active material, which includes artificial graphite.

[0012] During the first charge and discharge cycle of a lithium-ion battery, the electrode material and electrolyte react at the solid-liquid interface to form a passivation layer covering the electrode material surface. This results in significant loss of active lithium ions, leading to a low energy density. This application addresses this issue by combining lithium iron phosphate and lithium-rich oxides, and by limiting the content of the lithium-rich oxides in the positive electrode. This promotes the release of active lithium ions from the lithium-rich oxides during the first charge cycle, effectively compensating for the irreversible lithium loss during the formation of the solid electrolyte interface (SEI) film in the artificial graphite negative electrode during the first charge and discharge cycle, thereby significantly improving the energy density of the lithium-ion battery. The general formula for lithium-rich oxides is Li. x M y O z M is a transition metal, including at least one of Fe, Ni, Mn, and Co. When the stoichiometric ratio of lithium atoms to transition metals x / y ≥ 2, it can be called a lithium-rich oxide.

[0013] In some embodiments, the mass content of lithium-rich oxide in the positive electrode active material is 0.2-10%.

[0014] In some embodiments, the following conditions are met in the positive electrode active material: the mass content of primary particles with a particle size <0.2 μm is 35-45%; and / or, the mass content of primary particles with a particle size of 0.2-2 μm is 45-65%; and / or, the mass content of primary particles with a particle size >2 μm is 0-30%. This application achieves continuous gradation of lithium iron phosphate and lithium-rich oxide particles in the positive electrode active material, that is, by combining large, medium, and small particle sizes of the positive electrode active material in a certain proportion, more lithium iron phosphate and lithium-rich oxide particles can be filled within the same electrode volume. Therefore, the density of the positive electrode can be further improved, thereby increasing the energy density of the lithium-ion battery.

[0015] In some embodiments, the primary particles of the lithium-rich oxide have a particle size of 0.05~30 μm.

[0016] In some embodiments, lithium-rich oxides include at least one of lithium-rich lithium iron oxide (Li5FeO4, LFO), lithium-rich lithium nickel oxide (Li2NiO2, LNO), and lithium-rich lithium cobalt oxide (Li6CoO4, LCO).

[0017] In some embodiments, the primary particle size of lithium iron phosphate is 0.05~30 μm; and / or, the primary particle size of lithium nickel phosphate is 0.05~30 μm; and / or, the primary particle size of lithium cobalt phosphate is 0.05~30 μm.

[0018] Different lithium-rich oxides have varying chemical properties, thus requiring control of particle size to further optimize lithium-ion battery performance. After the first charge-discharge cycle, LFO undergoes an irreversible transformation from Li5FeO4 to LiFeO2, resulting in particle shrinkage and larger pores in the electrode. This application utilizes ultra-large LFO particles with a primary particle size of 2-30 μm to effectively improve electrolyte wettability on the positive electrode and enhance cycle stability by leveraging the volume shrinkage characteristic during the first charge-discharge cycle. Furthermore, selecting ultra-large LFO particles facilitates better gradation, reducing the need for using ultra-large lithium iron phosphate particles with poorer cycle characteristics, thereby increasing the energy density and enhancing cycle stability of the lithium-ion battery.

[0019] Furthermore, this application has found that small-particle-size LNO has high rate and high capacity characteristics. Introducing LFO or LNO with specific sizes can help improve the cycle stability and rate performance of lithium-ion batteries.

[0020] In some embodiments, the following conditions are met in the positive electrode active material: in the primary particles of the positive electrode active material with a particle size <0.2 μm, the lithium-rich oxide includes lithium-rich lithium nickel oxide; and / or, in the primary particles of the positive electrode active material with a particle size of 0.2~2 μm, the lithium-rich oxide includes lithium-rich lithium nickel oxide; and / or, in the primary particles of the positive electrode active material with a particle size >2 μm, the lithium-rich oxide includes lithium-rich lithium iron oxide. This application achieves high energy density in high-lithium-ion batteries by filling lithium iron phosphate with lithium-rich oxides of different particle sizes.

[0021] In some embodiments, the lithium-rich oxide includes lithium-rich nickel oxide and lithium-rich iron oxide, with a mass ratio of lithium-rich iron oxide to lithium-rich nickel oxide of 5~8:2~5. This application, by introducing a specific proportion of LFO and LNO into the positive electrode, helps to maintain the high energy density of lithium-ion batteries while improving their rate performance.

[0022] In some embodiments, the following conditions are met in the positive electrode active material: the mass content of lithium-rich oxide is ≤30% in the primary particles of the positive electrode active material with a particle size <0.2 μm; and / or, the mass content of lithium-rich oxide is ≤30% in the primary particles of the positive electrode active material with a particle size of 0.2~2 μm; and / or, the mass content of lithium-rich oxide is ≤50% in the primary particles of the positive electrode active material with a particle size >2 μm.

[0023] In some embodiments, the compaction density of the positive electrode is 2.2~3.1 g / cm³. 3 .

[0024] In some embodiments, the method for preparing the positive electrode sheet includes the following steps: First, positive electrode homogenization: A conductive agent is added to N-methylpyrrolidone (NMP), and the mixture is stirred at a low speed of 2.0~5.0 m / s for 0.5 hours to 3 hours; then, lithium iron phosphate and lithium-rich oxide are added to the reaction system in the above proportions, and the mixture is stirred at a low speed of 2.0~5.0 m / s for 0.5 hours to 3 hours; then the stirring speed is increased to 10 m / s~25 m / s, and the mixture is stirred for 0.5 hours to 3 hours; PVDF is added to the reaction system, and the mixture is stirred at a high speed of 10 m / s~25 m / s for 1.0 hour to 8 hours; then, the viscosity is adjusted to 5000~25000 by adding NMP. The positive electrode slurry is obtained at mPa·s; the second step is positive electrode coating: the above positive electrode slurry is coated on both sides of the carbon-coated aluminum foil to obtain a positive electrode wet film, wherein the thickness of the carbon-coated aluminum foil is 10~15μm; after drying the positive electrode wet film, a positive electrode sheet is obtained, which can be stored in rolls.

[0025] In some embodiments, the median particle size D of artificial graphite 50 The size is 3~25μm.

[0026] In some embodiments, the compaction density of the negative electrode is 1.4~1.9 g / cm³. 3 .

[0027] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: First, negative electrode homogenization: artificial graphite and conductive agent are added sequentially to deionized water, and then stirred at a linear speed of 2.0~5.0 m / s for 0.5~3 hours; CMC is added to the reaction system, and stirring is continued at a linear speed of 5~15 m / s for 0.5~3 hours; then SBR is added to the reaction system, and stirring is carried out at a linear speed of 5~20 m / s for 1~8 hours; by adding deionized water, the viscosity is adjusted to 3000~8000 mPa·s to obtain the negative electrode slurry; Second, negative electrode coating: the above negative electrode slurry is coated on both sides of a copper foil to obtain a negative electrode wet film, wherein the thickness of the copper foil is 4.5~8 μm; after drying the negative electrode wet film, a negative electrode sheet is obtained, which can be stored in rolls.

[0028] The following are relevant examples of preparing positive and negative electrode sheets under different gradation conditions.

[0029] Example 1

[0030] Processing group 1A

[0031] 1. Raw materials for preparing positive and negative electrode sheets

[0032] The materials required for preparing the positive and negative electrode sheets in this embodiment are shown in Table 1, and prepared according to the formula provided in Table 1. The proportions in Table 1 refer to the mass ratio of the material used to prepare the positive electrode sheet to the mass ratio of the material used to prepare the negative electrode sheet to the mass ratio of the material used to prepare the negative electrode sheet. Furthermore, the gradation of the primary particles in the positive electrode active material is shown in Table 2, wherein the primary particle size range of lithium iron ferrite (LFO) is 2~5 μm.

[0033] Table 1. Raw materials for preparing positive and negative electrode sheets in treatment group 1A

[0034]

[0035] Table 2. Gradation of positive electrode active material in treatment group 1A

[0036]

[0037] 2. Preparation of positive electrode sheet

[0038] The first step is positive electrode homogenization: the conductive agent is added to N-methylpyrrolidone (NMP) and stirred at a low speed of 2.0 m / s for 1.5 hours; then, lithium iron phosphate and lithium-rich oxide are added to the reaction system in the above ratio, and stirred at a low speed of 3.0 m / s for 2 hours; then the stirring speed is increased to 18 m / s and stirred for 3 hours; PVDF is added to the reaction system and stirred at a high speed of 20 m / s for 6 hours; then, NMP is added to adjust the viscosity to 15000 mPa·s to obtain the positive electrode slurry;

[0039] The second step is positive electrode coating: the above positive electrode slurry is coated on both sides of the carbon-coated aluminum foil to obtain a positive electrode wet film, wherein the thickness of the carbon-coated aluminum foil is 12μm; after drying the positive electrode wet film, a positive electrode sheet is obtained, which can be stored in rolls.

[0040] 3. Preparation of negative electrode sheet

[0041] Step 1, negative electrode homogenization: Artificial graphite and conductive agent are added sequentially to deionized water, and then stirred at a linear speed of 2.0 m / s for 1.5 hours; CMC is added to the reaction system, and stirring is continued at a linear speed of 10 m / s for 2 hours; then SBR is added to the reaction system, and stirring is carried out at a linear speed of 15 m / s for 6 hours; by adding deionized water, the viscosity is adjusted to 5000 mPa·s to obtain the negative electrode slurry;

[0042] The second step is negative electrode coating: the above negative electrode slurry is coated on both sides of the copper foil to obtain a negative electrode wet film, wherein the thickness of the copper foil is 6μm; after drying the negative electrode wet film, a negative electrode sheet is obtained, which can be stored in rolls.

[0043] 4. Preparation of lithium-ion batteries

[0044] The above positive and negative electrode sheets are rolled and pressed into electrode sheets with a certain porosity; wherein, the porosity of the positive electrode sheet is 22.5% (corresponding to a compacted density of 2.65 g / cm³). 3 The porosity of the negative electrode is 17.2% (corresponding to a compacted density of 1.80 g / cm³). 3Both types of electrode sheets were stored in rolls. Subsequently, the positive and negative electrode sheets were sequentially slit / formed, wound, had tabs welded, baked, and encapsulated. Then, an appropriate amount of electrolyte was injected into the aluminum-plastic encapsulation shell, followed by vacuum settling, edge sealing, formation, degassing, sealing, high-temperature aging, capacity testing, and screening to obtain the lithium-ion battery. The electrolyte formulation was as follows: a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as the organic solvent; vinylene carbonate (VC), fluoroethylene carbonate (FEC), and ethylene sulfate (DTD) as additives; and the concentration of LiPF6 in the electrolyte was 1 mol / L.

[0045] Processing group 2A

[0046] This treatment group prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 1A of Example 1. The difference between this treatment group and Treatment Group 1A is that, in preparing the positive electrode sheet, the mass content of LFO in this treatment group is 2.5% (achieved by correspondingly reducing the content of LFP). Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 1A of Example 1.

[0047] Processing Group 3A

[0048] This treatment group prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 1A of Example 1. The difference between this treatment group and Treatment Group 1A of Example 1 is that, in preparing the positive electrode sheet, the mass content of LFO in this treatment group is 5% (achieved by correspondingly reducing the content of LFP). Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 1A of Example 1.

[0049] Processing group 4A

[0050] This treatment group prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 1A of Example 1. The difference between this treatment group and Treatment Group 1A of Example 1 is that, in preparing the positive electrode sheet, the mass content of LFO in this treatment group is 10% (achieved by correspondingly reducing the LFP content). Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 1A of Example 1.

[0051] Processing Group 5A

[0052] This treatment group prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 1A of Example 1. The difference between this treatment group and Treatment Group 1A of Example 1 is that, in preparing the positive electrode sheet, the mass content of LFO in this treatment group is 20% (achieved by correspondingly reducing the LFP content). Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 1A of Example 1.

[0053] Processing group 6A

[0054] This treatment group prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 3A of Example 1. The difference between this treatment group and Treatment Group 3A of Example 1 is that, in preparing the positive electrode sheet, no primary particles larger than 2 μm are introduced into the positive electrode active material. Specifically, the gradation is as follows: the mass content of primary particles with a particle size <0.2 μm is 50%, and the mass content of primary particles with a particle size of 0.2~2 μm is 50%. The gradation of the positive electrode active material satisfies the conditions shown in Table 3. This treatment group replaces 2~5 μm LFO with an equal mass fraction of 0.2~2 μm LFO, and the mass content of LFO in the positive electrode sheet in this treatment group is 5%. Apart from the above differences, the operation steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 3A of Example 1.

[0055] Table 3. Gradation of positive electrode active material in treatment group 6A

[0056]

[0057] Processing group 7A

[0058] This treatment group prepared positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 3A of Example 1. The difference between this treatment group and Treatment Group 3A of Example 1 is that, in preparing the positive electrode sheet, the gradation of the positive electrode active material meets the conditions shown in Table 4, and the mass content of LFO in the positive electrode sheet is 5%. Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 3A of Example 1.

[0059] Table 4. Gradation of positive electrode active material in treatment group 7A

[0060]

[0061] Control group 1A

[0062] This comparative group prepared positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in treatment group 3A of Example 1. The difference between this comparative group and treatment group 3A of Example 1 is that, in preparing the positive electrode sheet, an equal mass fraction of LFP was used instead of LFO; and in preparing the negative electrode sheet, an equal mass fraction of graphite was used instead of artificial graphite. Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this comparative group were strictly consistent with those in treatment group 3A of Example 1.

[0063] Test Example 1

[0064] 1. Test Object

[0065] The lithium-ion batteries, positive electrode sheets, and negative electrode sheets prepared by the multiple treatment groups and the control group in Example 1.

[0066] 2. Testing Methods

[0067] (1) Volumetric energy density: refers to the volumetric energy density of a single cell, which is calculated using equations ① and ②.

[0068] Volumetric energy density (Wh / L) = Total battery capacity (Wh) / Volume (L) ①

[0069] Total battery capacity (Wh) = Discharge plateau voltage (V) × Capacity (Ah) ②

[0070] (2) Compacted density of the positive electrode: The compacted density is calculated by formula ③.

[0071] The compaction density of the positive electrode sheet = the surface density of the positive electrode coating / the thickness after cold pressing ③

[0072] 3. Test Results

[0073] The test results for this test example are shown in Table 5. Based on the test data from multiple treatment groups and control groups 1A to 3A of this test example, it can be seen that the lithium-ion battery provided in this application can further improve the energy density of the lithium-ion battery by introducing lithium iron phosphate and lithium-rich oxide into the positive electrode and artificial graphite into the negative electrode. This demonstrates that the lithium-ion battery provided in this application can significantly enhance its energy density through the combination of positive and negative electrodes.

[0074] Data from processing groups 1A-5A and control group 1A show that as the mass content of lithium-rich oxide in the positive electrode active material increases, the energy density of lithium-ion batteries initially increases and then decreases. When the lithium-rich oxide content is too low, the release of active lithium ions during the initial charge is insufficient to compensate for irreversible lithium loss, resulting in an energy density similar to the control group. Conversely, when the lithium-rich oxide content is too high, the energy density of the lithium-ion battery decreases due to the reduction in the mass proportion of lithium iron phosphate in the active material from 97% to 77-87%. When the mass content of lithium-rich oxide in the positive electrode active material is 2.5%-10%, the energy density of the lithium-ion battery remains at a relatively good level.

[0075] Furthermore, compared to treatment group 2A, the primary particles in the cathode sheets provided by treatment group 6A are all less than or equal to 2μm. The lack of large particles reduces the particle packing effect, resulting in a significant decrease in the cathode sheet compaction density, which in turn leads to a decrease in the energy density of the lithium-ion battery. In treatment group 7A, due to the change in the interval range of continuous gradation, the unreasonable particle interval ratio cannot achieve the optimal packing effect, resulting in a decrease in the cathode sheet compaction density, which in turn affects the energy density of the lithium-ion battery.

[0076] Table 5. Experimental data for Test Example 1

[0077]

[0078] Example 2

[0079] Processing Group 1B

[0080] In this embodiment, processing group 1B prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in processing group 3A of embodiment 1. The difference between this embodiment and processing group 3A of embodiment 1 is that the formulation for preparing the positive electrode sheet differs, as shown in Table 6. Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this embodiment are strictly consistent with those in processing group 3A of embodiment 1. The proportions in Table 6 refer to the mass ratio of the materials used to prepare the positive electrode sheet in the positive electrode sheet and the mass ratio of the materials used to prepare the negative electrode sheet in the negative electrode sheet. Furthermore, the gradation of primary particles in the positive electrode active material is shown in Table 7.

[0081] Table 6. Raw materials for preparing the positive and negative electrode sheets of treatment group 1B

[0082]

[0083] Table 7. Mass content of each particle size in the positive electrode active material of treatment group 1B

[0084]

[0085] Processing Group 2B

[0086] This treatment group prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 1B of Example 2. The difference between this treatment group and Treatment Group 1B of Example 2 is that, in preparing the positive electrode sheet, the mass ratio of LFO to LNO in the lithium-rich oxide (LFO and LNO) is calculated as 20:80 (the total mass fraction of lithium-rich oxide remains constant, and the content of LFO and LNO in multiple gradations is adjusted by increasing or decreasing the content of LFP in multiple gradations). Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 1B of Example 2.

[0087] Processing Group 3B

[0088] This treatment group prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formulation and method provided in Treatment Group 1B of Example 2. The difference between this treatment group and Treatment Group 1B of Example 2 is that, in preparing the positive electrode sheet, the mass ratio of LFO to LNO in the lithium-rich oxide (LFO and LNO) is calculated as 80:20 (the total mass fraction of lithium-rich oxide remains constant, and the content of LFO and LNO in multiple gradations is adjusted by increasing or decreasing the content of LFP in multiple gradations). Apart from the above differences, the operational steps for preparing the positive electrode sheet, negative electrode sheet, and lithium-ion battery in this treatment group are strictly consistent with those in Treatment Group 1B of Example 2.

[0089] Test Example 2

[0090] 1. Test Object

[0091] Lithium-ion batteries prepared by multiple processing groups in Example 2.

[0092] 2. Testing Methods

[0093] The energy density of the battery and the compaction density of the positive electrode were determined using the method provided in Test Example 1.

[0094] (1) Cycle capacity retention rate: refers to the percentage of the discharge capacity in the nth cycle relative to the maximum discharge capacity in the entire cycle. The capacity retention rate in the nth cycle is calculated by formula ④.

[0095] Capacity retention rate (%) = Discharge capacity at cycle n (Ah) * 100% / Maximum discharge capacity (Ah) ④

[0096] (2) Calibrated capacity at different rates: At the calibration temperature of 25℃, constant current discharge was performed using six different rates of 0.1C, 0.33C, 0.5C, 1C, 2C and 3C, with a cutoff voltage of 2.5V. The discharge capacity Q was recorded. The calibrated capacity at different rates was calculated using formula ⑤.

[0097] Calibrated gram capacity (mAh / g) at different expansion rates = Q / mass of active material ⑤

[0098] 3. Test Results

[0099] The results of this test case are shown in Table 8.

[0100] The inventors discovered during experiments that designing high compaction density on the electrodes to improve the energy density of lithium-ion batteries can affect their cycle performance or rate performance. Test data from treatment groups 1B-3B and Figures 1-2 show that introducing specific proportions of LFO and LNO not only helps maintain the high energy density of lithium-ion batteries but also improves their cycle stability and rate performance. Although the decreasing compaction density of the positive electrode leads to a slight decrease in battery energy density, the addition of LNO significantly improves the rate performance of treatment groups 1B-3B compared to treatment group 3A, with an approximately 1% improvement in capacity retention at 1400 cyc during long cycles. Therefore, a suitable LFO / LNO ratio helps improve the cycle stability and rate performance of batteries while maintaining high energy density.

[0101] Table 8. Experimental data of treatment groups 1B~3B in Example 2

[0102]

[0103] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described with reference to some embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A high-energy-density lithium-ion battery, comprising a positive electrode and a negative electrode, wherein the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises lithium iron phosphate and lithium-rich oxide; In the positive electrode, the mass content of the lithium-rich oxide is 0.2% to 20%. The negative electrode sheet includes a negative electrode active material, which includes artificial graphite.

2. The high energy density lithium-ion battery of claim 1, wherein, The positive electrode active material satisfies at least one of the following conditions: The positive electrode active material consists of primary particles with a particle size of <0.2μm, and its mass content is 35~45%. The positive electrode active material consists of primary particles with a particle size of 0.2~2μm and a mass content of 45~65%. The positive electrode active material consists of primary particles with a particle size >2μm, and its mass content is 0~30%.

3. The high energy density lithium-ion battery of claim 1, wherein, The lithium-rich oxide includes at least one of lithium-rich lithium iron oxide, lithium-rich lithium nickel oxide, and lithium-rich lithium cobalt oxide.

4. The high energy density lithium-ion battery as described in claim 3, wherein, The primary particle size of the lithium iron ferrite rich in lithium is 0.05~30μm; Alternatively, the primary particle size of the lithium-rich nickel oxide is 0.05~30μm; Alternatively, the primary particle size of the lithium cobalt oxide rich in lithium is 0.05~30μm; Alternatively, the particle size of the primary particles of the lithium iron phosphate and the primary particles of the lithium nickel phosphate are both 0.05~30μm. Alternatively, the particle size of the primary particles of the lithium iron oxide rich lithium and the primary particles of the lithium cobalt oxide rich lithium are both 0.05~30μm. Alternatively, the primary particle size of the lithium nickel oxide and the primary particle size of the lithium cobalt oxide are both 0.05~30μm. Alternatively, the particle size of the primary particles of the lithium iron phosphate, the lithium nickel phosphate, and the lithium cobalt phosphate is all 0.05~30μm.

5. The high energy density lithium-ion battery of any one of claims 1 to 4, wherein, The positive electrode active material satisfies at least one of the following conditions: In the primary particles with a particle size <0.2 μm of the positive electrode active material, the lithium-rich oxide includes lithium-rich nickel oxide; In the primary particles with a particle size of 0.2~2μm of the positive electrode active material, the lithium-rich oxide includes lithium-rich nickel oxide; In the primary particles with a particle size >2 μm of the positive electrode active material, the lithium-rich oxide includes lithium-rich lithium iron oxide.

6. The high energy density lithium-ion battery of claim 5, wherein, Among lithium-rich oxides, including lithium-rich nickel oxide and lithium-rich iron oxide, the mass ratio of lithium-rich iron oxide to lithium-rich nickel oxide is 5~8:2~5.

7. The high energy density lithium-ion battery of claim 1, wherein, The primary particle size of the lithium iron phosphate is 0.02~6μm.

8. The high energy density lithium-ion battery of claim 1, wherein, The compacted density of the positive electrode sheet is 2.2 to 3.1 g / cm 3 .

9. The high energy density lithium-ion battery of claim 1, wherein, The median particle size D50 of the artificial graphite is 3 to 25 μm. 50 is 3 to 25 μm.

10. The high energy density lithium-ion battery of claim 1 or 9, wherein, The compacted density of the negative electrode sheet is 1.4 to 1.9 g / cm 3 .

Images