A high energy density lithium ion battery
By introducing lithium-rich oxide and artificial graphite anode into the positive electrode of lithium iron phosphate battery, the electrode structure is optimized, solving the problem of improving the energy density of lithium iron phosphate battery and achieving a balance between high energy density and stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- EVE POWER CO LTD
- Filing Date
- 2024-12-27
- Publication Date
- 2026-07-03
AI Technical Summary
The energy density of existing lithium iron phosphate batteries has reached a bottleneck, and it is difficult to improve it. Furthermore, traditional methods may affect battery performance or require long-term verification, making rapid commercialization impossible.
Introducing lithium-rich oxides such as Li5FeO4, Li2NiO2, and Li6CoO4 into the positive electrode, and optimizing the electrode structure by controlling their content and particle size distribution in the positive electrode, combined with the artificial graphite negative electrode, forms a reasonable gradation, thereby improving the filling density of active materials and electrolyte wettability.
Significantly improves the energy density and cycle stability of lithium-ion batteries, enhances rate performance, and maintains high energy density and good cycle performance.
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Figure CN119812434B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of batteries, and particularly relates to a high-energy-density lithium-ion battery. Background Technology
[0002] 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. Specifically, 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.
[0003] 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, problems such as the volume expansion of silicon during charging and discharging (which can reach 300-400%), poor conductivity, and unstable interface with the electrolyte have affected the commercial application of silicon-based negative electrode materials.
[0004] 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.
[0005] 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
[0006] In order to improve the energy density of lithium-ion batteries, the present invention provides a high-energy-density lithium-ion battery.
[0007] According to one aspect of this application, a high-energy-density lithium-ion battery is provided, 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 lithium-rich oxide is 0.2-20%; the negative electrode comprising a negative electrode active material, the negative electrode active material comprising artificial graphite.
[0008] During the first charge and discharge cycle of a lithium-ion battery, the electrode material and electrolyte react at the solid-liquid interface, forming a passivation layer on the electrode material surface. This results in significant loss of active lithium ions, leading to a low energy density. This invention, by combining lithium iron phosphate and lithium-rich oxides and limiting the content of lithium-rich oxides in the positive electrode, promotes the release of active lithium ions from the lithium-rich oxides during the first charge cycle. This effectively compensates for the irreversible lithium loss during the formation of the 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 lithium-rich oxides have the general formula 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.
[0009] Preferably, the mass content of lithium-rich oxide in the positive electrode active material is 0.2% to 10%.
[0010] Preferably, the positive electrode active material satisfies the following conditions: 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 invention, by continuously grading the lithium iron phosphate and lithium-rich oxide particles in the positive electrode active material, that is, combining large, medium, and small particle sizes of the positive electrode active material in a certain proportion, allows for the filling of more lithium iron phosphate and lithium-rich oxide particles within the same electrode volume. Therefore, it can further improve the density of the positive electrode, thereby increasing the energy density of the lithium-ion battery.
[0011] Preferably, the primary particles of lithium-rich oxide have a particle size of 0.05–30 μm.
[0012] Preferably, the lithium-rich oxide includes 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).
[0013] Preferably, 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.
[0014] Different lithium-rich oxides have varying chemical properties, thus requiring control of particle size to further optimize lithium-ion battery performance. Specifically, after the first charge-discharge cycle, LFO's chemical formula transforms from Li5FeO4 to LiFeO2, resulting in irreversible deformation of its crystal structure and subsequent particle shrinkage, leaving larger pores in the electrode. This invention utilizes the volume shrinkage characteristic during the first charge-discharge cycle by selecting ultra-large LFO particles with a primary particle size of 2–30 μm, effectively improving electrolyte wettability on the positive electrode and enhancing cycle stability. Furthermore, selecting ultra-large LFO particles facilitates better gradation, reducing the use of ultra-large lithium iron phosphate particles with poorer cycle characteristics, thereby increasing the energy density and enhancing cycle stability of the lithium-ion battery.
[0015] Furthermore, this invention has discovered that small-particle-size LNO exhibits high rate capability and high capacity characteristics. Introducing LFO or LNO with specific sizes can help improve the cycle stability and rate performance of lithium-ion batteries.
[0016] Preferably, the positive electrode active material satisfies the following conditions: 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 phosphate. This invention achieves high energy density in high-lithium-ion batteries by filling lithium iron phosphate with lithium-rich oxides of different particle sizes.
[0017] Preferably, 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.
[0018] Preferably, the positive electrode active material satisfies the following conditions: in the primary particles of the positive electrode active material with a particle size <0.2 μm, the mass content of lithium-rich oxide is ≤30%; and / or, in the primary particles of the positive electrode active material with a particle size of 0.2 to 2 μm, the mass content of lithium-rich oxide is ≤30%; and / or, in the primary particles of the positive electrode active material with a particle size >2 μm, the mass content of lithium-rich oxide is ≤50%.
[0019] Preferably, the compaction density of the positive electrode sheet is 2.2–3.1 g / cm³. 3 .
[0020] Preferably, 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 0.5–3 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 0.5–3 hours; immediately afterward, 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 stirred at a high speed of 10 m / s to 25 m / s for 1.0 hour to 8 hours; then NMP is added to adjust the viscosity to 5000 to 25000 mPa·s to obtain the positive electrode slurry; 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 to 15 μm; after drying the positive electrode wet film, a positive electrode sheet is obtained, which can be stored in rolls.
[0021] Preferably, the median particle size D of the artificial graphite is... 50 The size ranges from 3 to 25 μm.
[0022] Preferably, the compaction density of the negative electrode sheet is 1.4–1.9 g / cm³. 3 .
[0023] Preferably, 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. Attached Figure Description
[0024] Figure 1 This is a diagram showing the cycle capacity retention rate of processing groups 1B, 2B, and 3B of the present invention.
[0025] Figure 2 This is a graph showing the gram capacity at different magnification ratios for treatment groups 1B, 2B, and 3B of the present invention. Detailed Implementation
[0026] To enable those skilled in the art to better understand the technical solutions of this application, the technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.
[0027] Example 1
[0028] Processing group 1A
[0029] 1. Raw materials for preparing positive and negative electrode sheets
[0030] 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, where the primary particle size range of lithium iron ferrite (LFO) is 2–5 μm.
[0031] Table 1. Raw materials for preparing positive and negative electrode sheets in treatment group 1A
[0032]
[0033] Table 2. Gradation of positive electrode active material in treatment group 1A
[0034] Particle size mass content materials <0.2μm 40％ LFP 0.2~2μm 30％ LFP >2μm 30％ LFP+LFO
[0035] 2. Preparation of positive electrode sheet
[0036] 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;
[0037] 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.
[0038] 3. Preparation of negative electrode sheet
[0039] 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;
[0040] 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.
[0041] 4. Preparation of lithium-ion batteries
[0042] 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). 3 Both 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 consisted of a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as the organic solvent; and vinylene carbonate (VC), fluoroethylene carbonate (FEC), and ethylene sulfate (DTD) as additives. The concentration of LiPF6 in the electrolyte was 1 mol / L.
[0043] Processing group 2A
[0044] 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 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.
[0045] Processing Group 3A
[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 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 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.
[0047] Processing group 4A
[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 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.
[0049] Processing Group 5A
[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 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.
[0051] Processing group 6A
[0052] 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. Specifically, 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.
[0053] Table 3. Gradation of positive electrode active material in treatment group 6A
[0054] Particle size mass content materials <0.2μm 50％ LFP 0.2~2μm 50％ LFP+LFO >2μm 0％ /
[0055] Processing group 7A
[0056] 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.
[0057] Table 4. Gradation of positive electrode active material in treatment group 7A
[0058] Particle size mass content materials <0.2μm 60％ LFP 0.2~2μm 10％ LFP >2μm 30％ LFP+LFO
[0059] Control group 1A
[0060] 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.
[0061] Test Example 1
[0062] 1. Test Object
[0063] The lithium-ion batteries, positive electrode sheets, and negative electrode sheets prepared in each treatment group and the control group in Example 1.
[0064] 2. Testing Methods
[0065] (1) Volumetric energy density: refers to the volumetric energy density of a single cell, which is calculated using equations ① and ②.
[0066] Volumetric energy density (Wh / L) = Total battery capacity (Wh) / Volume (L) ①
[0067] Total battery capacity (Wh) = Discharge plateau voltage (V) × Capacity (Ah) ②
[0068] (2) Compacted density of the positive electrode: The compacted density is calculated by formula ③.
[0069] The compaction density of the positive electrode sheet = the surface density of the positive electrode coating / the thickness after cold pressing ③3. Test results
[0070] The test results for this test example are shown in Table 5. Based on the test data of each treatment group and control groups 1A to 3A in this test example, it can be seen that the lithium-ion battery provided by this invention 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 shows that the lithium-ion battery provided by this invention can significantly enhance its energy density by combining the positive and negative electrodes.
[0071] 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%. Furthermore, 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.
[0072] 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.
[0073] Table 5. Experimental data for Test Example 1
[0074] Group <![CDATA[Battery energy density / Wh L -1 > <![CDATA[The compaction density of the positive electrode sheet g / cm 3 > Processing group 1A 445 2.65 Processing group 2A 462 2.70 Processing Group 3A 470 2.75 Processing group 4A 438 2.75 Processing Group 5A 405 2.75 Processing group 6A 440 2.64 Processing group 7A 403 2.60 Control group 1A 430 2.65
[0075] Example 2
[0076] Processing Group 1B
[0077] In this embodiment, processing group 1B prepares positive electrode sheets, negative electrode sheets, and lithium-ion batteries using the formula 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 formula for preparing the positive electrode sheet is different, 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.
[0078] Table 6. Raw materials for preparing the positive and negative electrode sheets of treatment group 1B
[0079]
[0080] Table 7. Mass content of each particle size in the positive electrode active material of treatment group 1B
[0081]
[0082] Processing Group 2B
[0083] 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 each grade of the formulation is adjusted by increasing or decreasing 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 1B of Example 2.
[0084] Processing Group 3B
[0085] 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 each grade of the formulation is adjusted by increasing or decreasing 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 1B of Example 2.
[0086] Test Example 2
[0087] 1. Test Object
[0088] The lithium-ion batteries prepared by each treatment group in Example 2.
[0089] 2. Testing Methods
[0090] The energy density of the battery and the compaction density of the positive electrode were determined using the method provided in Test Example 1.
[0091] (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 using formula ④.
[0092] Capacity retention rate (%) = Discharge capacity at the nth cycle (Ah) * 100% / Maximum discharge capacity (Ah) ④
[0093] (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.
[0094] Calibrated quantile capacity (mAh / g) at different expansion rates = Q / mass of active substance ⑤3. Test results
[0095] The results of this test case are shown in Table 8.
[0096] The inventors discovered during experiments that, in order to improve the energy density of lithium-ion batteries, designing high compaction density on the electrodes can affect the cycle performance or rate performance of the lithium-ion batteries. This was achieved by processing test data from groups 1B to 3B and... Figures 1-2 Test data shows 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. Specifically, although the cathode compaction density gradually decreases, leading to a slight decrease in battery energy density, the addition of LNO significantly improves the rate performance of treatment groups 1B to 3B compared to treatment group 3A, with an approximately 1% improvement in capacity retention at 1400 cyc during long cycles. Therefore, a suitable LFO and LNO ratio helps improve battery cycle stability and rate performance while maintaining the high energy density of lithium-ion batteries.
[0097] Table 8. Experimental data of treatment groups 1B-3B in Example 2
[0098]
[0099]
[0100] 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 in detail with reference to preferred 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, characterized in that: The lithium-ion battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode active material, which is composed of lithium iron phosphate and lithium-rich oxide. The lithium-rich oxide is composed of lithium-rich nickel oxide and lithium-rich iron oxide. The following conditions must be met in the positive electrode active material: The primary particles of the positive electrode active material, including the lithium iron phosphate and the lithium-rich oxide, have a particle size of <0.2 μm and a mass content of 35-45%. In the primary particles of the positive electrode active material with a particle size of <0.2 μm, the mass content of the lithium-rich oxide is ≤30%, and the lithium-rich oxide is lithium-rich nickel oxide. In the primary particles of the positive electrode active material comprising the lithium iron phosphate and the lithium-rich oxide, which have a particle size of 0.2~2μm, the mass content of the lithium-rich oxide is ≤30%, and the lithium-rich oxide is lithium-rich nickel oxide. The primary particles of the positive electrode active material, including the lithium iron phosphate and the lithium-rich oxide, with a particle size >2 μm, have a mass content greater than 0 and less than or equal to 30%. In the primary particles of the positive electrode active material with a particle size >2 μm, the mass content of the lithium-rich oxide is ≤50%, and the lithium-rich oxide is lithium iron phosphate. In the positive electrode, the mass content of the lithium-rich oxide is 0.2-20%, and the mass ratio of lithium-rich lithium iron oxide to lithium-rich lithium nickel oxide is 5-8:2-5. The negative electrode sheet includes a negative electrode active material, which includes artificial graphite.
2. The high energy density lithium-ion battery as described in claim 1, characterized in that: The positive electrode active material consists of primary particles with a particle size of 0.2~2μm and a mass content of 45~65%.
3. The high energy density lithium-ion battery as described in claim 1, characterized in that: The primary particle size of the lithium iron ferrite rich in lithium is 0.05~30μm; And / or, the primary particle size of the lithium-rich nickel oxide is 0.05~30μm.
4. The high energy density lithium-ion battery as described in claim 1, characterized in that: The primary particle size of the lithium iron phosphate is 0.02~6μm.
5. The high energy density lithium-ion battery as described in claim 1, characterized in that: The compacted density of the positive electrode sheet is 2.2 to 3.1 g / cm 3 .
6. The high energy density lithium-ion battery as described in claim 1, characterized in that: The median particle size D50 of the artificial graphite is 3 to 25 μm. 50 is 3 to 25 μm.
7. The high energy density lithium-ion battery as described in claim 1 or 6, characterized in that: The compacted density of the negative electrode sheet is 1.4~1.9 g / cm³. 3 .