Lithium-ion battery and electrical apparatus

Abstract

Provided in the present application are a lithium-ion battery and an electrical apparatus. The lithium-ion battery comprises a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The surface of the positive electrode sheet is covered with a positive electrode active material layer comprising positive electrode material particles, and the surface of the negative electrode sheet is covered with a negative electrode active material layer comprising negative electrode material particles. When a measured first capacity retention ratio of the battery is x, 78%≤x≤89%, the diameter of the positive electrode material particles is D, and the depth of an F‑element intrusion layer of the positive electrode material particles is L, the obtained thickness ratio of the F‑element intrusion layer is m=L / D and further satisfies: m≤1‑x, and the statistical proportion of the negative electrode material particles among the negative electrode material particles into which F element intrudes is n and satisfies: n≤(1‑x) / 2. The present application optimizes the particle size distribution of the positive electrode material particles and the negative electrode material particles, enhances the interface stability of the positive and negative electrode sheets, inhibits side reactions with the electrolyte, and improves the high-rate cycle performance of the battery.

Description

A lithium-ion battery and power device

[0001] Cross-reference of related applications

[0002] This application claims priority to Chinese Patent Application No. 2024119199858, filed on December 25, 2024, entitled "A Lithium-ion Battery and an Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of electrical device technology, and in particular to a lithium-ion battery and an electrical device. Background Technology

[0004] Lithium-ion batteries play a crucial role in portable devices, electric vehicles, and renewable energy storage systems due to their excellent energy storage capacity and wide range of applications. However, as application demands increase, the performance requirements for lithium-ion batteries are also becoming more stringent, such as maintaining high energy density and high-rate charge / discharge capabilities while simultaneously achieving longer cycle life and enhanced safety.

[0005] In the existing electrochemical system of lithium-ion batteries, lithium ions are extracted from the lattice of the positive electrode active material, pass through the electrolyte and the separator, and then embed into the lattice of the negative electrode active material to complete the charging of the battery; lithium ions are extracted from the lattice of the negative electrode active material, pass through the electrolyte and the separator, and then embed into the lattice of the positive electrode active material to complete the discharging of the battery.

[0006] However, under high-rate charge and discharge conditions, the transport and migration of lithium ions in lithium-ion batteries is often not timely enough. This can lead to uneven lithium insertion and extraction in the active material layers on the positive and negative electrodes, causing the surface particles of the active material layer to crack due to asymmetrical stress. The electrolyte can then penetrate into the inner layer of the active material layer through these cracks and react with the particles in the inner layer, generating a large number of byproducts. This damages the electrochemical performance of the active material layer, causing irreversible damage to the battery's capacity, deteriorating the battery's cycle stability, and even creating safety hazards. Summary of the Invention

[0007] To address the aforementioned issues, optimize the particle size distribution of the positive and negative electrode materials, and enhance the interfacial stability of the positive and negative electrode sheets, the first aspect of this application provides a lithium-ion battery, comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte for transporting lithium ions. The surface of the positive electrode sheet is covered with a positive active material layer comprising positive electrode material particles, and the surface of the negative electrode sheet is covered with a negative active material layer comprising negative electrode material particles. When the first capacity retention rate of the lithium-ion battery is measured to be x, and 78% ≤ x ≤ 89%, the diameter of the positive electrode material particles is D, and the depth of the F element penetration layer of the positive electrode material particles is L. The thickness percentage of the F element penetration layer in the radial direction of the positive electrode material particles is obtained as m = L / D, and the thickness percentage m of the F element penetration layer and the first capacity retention rate x also satisfy: m ≤ 1 - x; and

[0008] The percentage n of the negative electrode material particles that are invaded by F element is statistically determined, and the following condition is met: n≤(1-x) / 2.

[0009] By optimizing the particle size distribution of the positive electrode material particles and constraining the particle size and F element penetration depth, the structural strength of the surface layer in contact with the electrolyte is improved, thereby increasing the tolerance to local stress caused by uneven lithium insertion and / or delithiation, reducing the probability of cracking, and effectively suppressing the side reactions between the inner positive electrode material particles and the electrolyte. On the other hand, by constraining the proportion of negative electrode material particles penetrated by F element, the uniformity of the negative electrode active material layer is improved, avoiding local accumulation of lithium ions, delaying the deactivation of positive and negative electrode active materials, and improving the cycle performance of lithium-ion batteries.

[0010] In some optional embodiments, the lithium-ion battery is cycled at a 2C charge rate and a 5C discharge rate until a first capacity retention rate x is reached, and then the following tests are performed:

[0011] The lithium-ion battery after cyclic charging and discharging was placed at 25°C and discharged at a rate of 0.2C to the discharge cutoff voltage of 2.5V. After standing for 0.5 hours, the lithium-ion battery was disassembled and the positive electrode and the negative electrode were obtained. The cross-section was prepared and observed using a scanning electron microscope. The EDS signal was captured and acquired at a magnification of 1000x to obtain the surface scan distribution map of the F element.

[0012] For the surface scan distribution map of the positive electrode sheet cross section: select at least 100 positive electrode material particles sequentially from left to right and from top to bottom, and calculate the average diameter D of all the selected positive electrode material particles and the average thickness L of the F element intrusion layer in its radial direction.

[0013] For the surface scan distribution map of the cross-section of the negative electrode sheet: select at least 100 negative electrode material particles sequentially from left to right and from top to bottom. Define negative electrode material particles in which the area ratio of F element in a single negative electrode material particle is greater than 5% as negative electrode material particles invaded by F element. Count the number of negative electrode material particles invaded by F element among all the negative electrode material particles and calculate n.

[0014] Following the experimental method described above, the measured data are highly accurate.

[0015] In some optional embodiments, the separator is disposed between the positive electrode and the negative electrode, the positive electrode material particles comprise a high-nickel ternary material, and the peak intensity ratio of the XRD diffraction peak of the positive electrode is y, the ratio of I003 / I104 is y, and the porosity of the separator is η, satisfying: y≥0.3*(2-lnη). By constraining the relationship between the I003 / I104 ratio in high-nickel ternary materials and the membrane porosity, it is observed that in high-rate applications, the activity decay of I104-crystal high-nickel ternary materials is faster than that of I003-crystal high-nickel ternary materials, meaning that the I003 / I104 ratio gradually increases. Meanwhile, the membrane porosity gradually decreases during application, i.e., the value of (2-lnη) gradually increases. The rate of porosity reduction is positively correlated with the degree of interfacial side reactions between the positive and negative electrode material particles. By limiting the I003 / I104 ratio y ≥ 0.3*(2-lnη), the rate of porosity reduction in the membrane is controlled to match the composition of the positive electrode material particles, preventing a sharp decrease in porosity during high-rate applications. This improves the uniformity of lithium insertion / extraction at the positive electrode interface, further optimizing the high-rate cycle performance and safety performance of the battery.

[0016] In some alternative embodiments, the ratio y of I003 / I104 satisfies the following relationship with the porosity η: y ≥ 0.5 * (2 - lnη)

[0017] In some optional embodiments, the methods for testing the XRD diffraction peaks of the positive electrode and the porosity η of the separator in the lithium-ion battery include:

[0018] S1: Take one of the lithium-ion batteries, place it at 25°C for more than 2 hours, discharge it at a rate of 0.2C to the cutoff voltage of 2.5V, then let it stand for 10 minutes, and disassemble it to obtain the positive electrode and the separator.

[0019] S2: After rinsing the positive electrode and the separator three times with dimethyl carbonate, bake them in a vacuum oven at 60°C for 2 hours;

[0020] S3: Remove the positive electrode and the separator and allow them to cool;

[0021] S4: Test the positive electrode with XRD to obtain the diffraction peak pattern of the positive electrode and calculate the peak intensity ratio I003 / I104.

[0022] S5: Take the membrane and test the porosity η.

[0023] In some optional embodiments, when the first capacity retention rate of the lithium-ion battery is x, the porosity of the separator corresponds to η. x It also satisfies: x*y≥0.3*(2-lnη) x ).

[0024] In some optional embodiments, the lithium salt concentration of the electrolyte is E mol / L. After the lithium-ion battery is discharged at a rate of 0.2C to the discharge cutoff voltage of 2.5V, its negative electrode is removed and XRD test is performed to obtain a test spectrum. The highest peak and the second highest peak are selected from the test spectrum. The ratio of the peak intensity of the highest peak to the peak intensity of the second highest peak is P, and satisfies: 3P / 2≥E≥P / 6.

[0025] In the XRD diffraction peak pattern of the negative electrode, each diffraction peak represents a crystal form in the negative electrode material particles. The ratio of the peak intensity of the highest peak to the intensity of the second highest peak reflects the stability of the negative electrode material particles to a certain extent. The higher the stability of the negative electrode material particles, the weaker their kinetic performance for lithium ion migration. The higher the lithium salt concentration of the electrolyte, the faster the lithium ion migration rate. By controlling the lithium salt concentration E to the ratio P of the highest peak intensity to the second highest peak intensity of the negative electrode as: 3P / 2≥E≥P / 6, the stability and kinetic performance of the negative electrode can be balanced. The negative electrode can efficiently and persistently complete the high-flux lithium ion insertion and extraction reactions, ensuring that the interface stability and rate performance of the negative electrode are in the optimal range, thus achieving the optimal rate performance of the battery.

[0026] In some optional embodiments, the positive electrode material particles located on the surface of the positive electrode active material layer are further doped with element Z, wherein element Z is one or more selected from Al, B, Zr, Ti, Ba, Mn, Co, Y, La, Ca, Sr, and Sb. Doping the positive electrode material particles with the above chemical elements is used to improve the structural stability of the positive electrode active material.

[0027] In some alternative embodiments, the element Z accounts for 0.05%-2% of the weight of the positive electrode material particles located on the surface.

[0028] A second aspect of this application provides an electrical device including the lithium-ion battery described above. Due to the beneficial effects of lithium-ion batteries as described above, the electrical device provided by this application exhibits good structural stability of the positive electrode active material layer and the negative electrode active material layer during high-power charging and discharging, effectively suppressing electrolyte side reactions, improving battery cycle performance, and extending the service life of the electrical device. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 is a schematic diagram of the structure of a lithium-ion battery according to an optional embodiment of this application;

[0031] Figure 2 is a schematic diagram of the structure of the positive electrode, separator and negative electrode of a lithium-ion battery according to an optional embodiment of this application after the core portion is unfolded.

[0032] Figure 3 is a schematic diagram of the longitudinal section of the core of a lithium-ion battery according to an optional embodiment of this application.

[0033] Reference numerals: 2-core, 21-positive electrode sheet, 212-positive electrode current collector, 210-positive electrode active material layer, 2101-positive electrode material particles, 23-separator, 25-negative electrode sheet, 252-negative electrode current collector, 250-negative electrode active material layer, 2501-negative electrode material particles, 3-electrolyte. Detailed Implementation

[0034] The embodiments of this implementation are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this implementation, and should not be construed as limiting this implementation.

[0035] In the description of this embodiment, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this embodiment and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this embodiment.

[0036] In the description of this embodiment, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0037] In the description of this embodiment, unless otherwise explicitly limited, terms such as setting, installing, and connecting should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this embodiment in conjunction with the specific content of the technical solution.

[0038] A common structure for existing lithium-ion batteries includes a casing with an opening at one end, a core 2 assembled into the casing through the opening, an electrolyte 3 injected into the casing, and a cap covering the opening of the casing. It is understood that the lithium-ion battery can be a cylindrical lithium-ion battery or a prismatic lithium-ion battery.

[0039] Please refer to Figures 1-3. Figure 1 shows a schematic diagram of the structure of a lithium-ion battery according to an embodiment of this application. Figure 2 shows a three-dimensional structural schematic diagram of the core portion after unfolding. Figure 3 shows the cross-section of the positive electrode sheet and the negative electrode sheet. Referring to Figure 2, the core 2 is formed by winding a positive electrode sheet 21, a separator 23, and a negative electrode sheet 25 stacked together. Referring to Figure 3, the positive electrode sheet 21 includes a positive current collector 212 and a positive active material layer 210 coated on both sides of the positive current collector 212. The negative electrode sheet 25 includes a negative current collector 252 and a negative active material layer 250 coated on both sides of the negative current collector 252. The thickness of the active material coating is greater than the thickness of the current collector. Charged particles in the electrolyte 3 undergo insertion or deintercalation reactions on the surfaces of the positive active material layer 210 and the negative active material layer 250.

[0040] The first aspect of this application provides a lithium-ion battery, including a positive electrode 21, a separator 23, a negative electrode 25, and an electrolyte 3 for transporting lithium ions. The surface of the positive electrode 21 is covered with a positive active material layer 210 including positive electrode material particles 2101, and the surface of the negative electrode 25 is covered with a negative active material layer 251 including negative electrode material particles 2501.

[0041] Take one of the lithium-ion batteries and cycle it at a 2C charging rate and a 5C discharging rate to achieve a first capacity retention rate x, where 78% ≤ x ≤ 89%.

[0042] The test method for the first capacity retention rate x is as follows:

[0043] Take a lithium-ion battery prepared according to any of the above embodiments, place it in a constant temperature chamber at 25°C for more than 4 hours, and test it according to the following steps:

[0044] S01: Charge the battery at a constant current to 4.2V under a 2C charging rate, and charge it at a constant voltage to a current of 0.025C, then let it stand for 15 minutes; discharge the battery at a constant current to 2.5V under a 5C discharging rate, and let it stand for 30 minutes.

[0045] S02: Repeat step S01 above N times (2≤N≤2000); record the first discharge capacity as the initial capacity, denoted as a1, and record the discharge capacity at the Nth cycle, denoted as b1;

[0046] S03: When b1 / a1×100% is within the range of x, perform the following test.

[0047] S11: The lithium-ion battery after the above-mentioned cycle charge and discharge is placed at 25°C and discharged at a rate of 0.2C to the cutoff voltage of 2.5V. After standing for 0.5 hours, the lithium-ion battery is disassembled to obtain the positive electrode 21 and the negative electrode 25, and a cross-section is prepared (see Figure 3). The cross-section is observed using a scanning electron microscope, and the surface scan distribution map of the F element is obtained by taking pictures and acquiring EDS signals at a magnification of 1000x.

[0048] For the cross-sectional area scan distribution of the positive electrode 21: at least 100 positive electrode material particles 2101 are selected sequentially from left to right and from top to bottom. The average diameter D of all the selected positive electrode material particles 2101 and the average thickness L of the F element intrusion layer in its radial direction are statistically analyzed. The thickness ratio m of the F element intrusion layer in the radial direction of the positive electrode material particles 2101 is calculated as m = L / D.

[0049] For the surface scan distribution of the cross-section of the negative electrode sheet 25: at least 100 negative electrode material particles 2501 are selected sequentially from left to right and from top to bottom. Negative electrode material particles 2501 with an F element area ratio greater than 5% in a single negative electrode material particle 2501 are defined as negative electrode material particles 2501 invaded by F element. The number of negative electrode material particles 2501 invaded by F element in all the negative electrode material particles 2501 is counted and screened, and the proportion n of negative electrode material particles 2501 invaded by F element in all the screened negative electrode material particles 2501 is calculated.

[0050] Furthermore, the thickness percentage m of the F element and the capacity retention rate x also satisfy: m ≤ 1 - x; and

[0051] Furthermore, the proportion n of the negative electrode material particles 2501 that are invaded by F element is limited to satisfying: n≤(1-x) / 2.

[0052] It should be noted that a CEI film (Cathode Electrolyte Interphase, a passivation film formed when the positive electrode active material layer 210 contacts the electrolyte 3) will be formed at the interface. A SEI film (Solid Electrolyte Interface, a passivation layer formed on the surface of the negative electrode material during the first charge and discharge process of a lithium-ion battery) will be formed at the interface between the negative electrode active material layer 251 and the electrolyte 3. The stability of the CEI film and the SEI film is the interface stability between the positive electrode sheet 21 and the negative electrode sheet 25. Specifically, the content of element F in the positive electrode active material layer 210 and the negative electrode active material layer 251 can be used to evaluate the interfacial stability of the positive and negative electrode sheets. The specific principle is as follows: element F is the most electronegative element, and fluoride has stable chemical properties. It forms a protective layer on the surface of the positive and negative electrodes of the battery, inertly protecting the active materials in the electrolyte 3, thereby preventing the continuous decomposition of the electrolyte 3 and reducing the risk of battery thermal runaway and safety hazards. It can be understood that the depth L of the F element penetration layer of the positive electrode material particles 2101 and the proportion of F element penetration exceeding 5% of the area of ​​the negative electrode material particles 2501 can both be used to measure the content of element F at the interface of the positive and negative electrode sheets. Furthermore, the degree of interaction between element F and the positive electrode material particles 2101 or the negative electrode material particles 2501 is further limited, which can more accurately reflect the content of element F that has a passivating effect on the electrolyte 3. Therefore, the achieved technical effect is more reliable.

[0053] Referring to Figure 3, by optimizing the particle size distribution of the positive electrode material particles 2101 and constraining the particle size of the positive electrode material particles 2101 and the depth of their F element penetration layer, the interfacial structural strength between the positive electrode active material layer 210 and the electrolyte 3 is improved. This enhances the tolerance to local stress caused by uneven lithium insertion and / or delithiation, reduces the probability of cracking, and effectively suppresses side reactions between the inner positive electrode material particles 2101 and the electrolyte 3. On the other hand, by constraining the proportion of negative electrode material particles 2501 penetrated by F element, the uniformity of the negative electrode active material layer 251 is improved, preventing local accumulation of lithium ions, delaying the deactivation of the positive and negative electrode active materials, and improving the cycle performance of the lithium-ion battery.

[0054] In some alternative embodiments, referring to Figures 2 and 3, the separator 23 is disposed between the positive electrode 21 and the negative electrode 25, the positive electrode material particles 2101 comprise a high-nickel ternary material, and the peak intensity ratio of the XRD diffraction peaks in the positive electrode is y, and the porosity of the separator 23 is η, satisfying: y≥0.3*(2-lnη). By analyzing the relationship between the peak intensity ratio I003 / I104 of the XRD diffraction peaks in the positive electrode and the porosity of the separator 23, it is found that in high-rate applications, the activity decay of the high-nickel ternary material with the I104 crystal form is faster than that of the high-nickel ternary material with the I003 crystal form, meaning that I003 / I104 gradually increases. Meanwhile, the porosity of the separator 23 gradually decreases during application, meaning that the value of (2-lnη) gradually increases. The rate of decrease in porosity is positively correlated with the degree of interfacial side reactions between the positive and negative electrodes. By limiting the I003 / I104 ratio y ≥ 0.3*(2-lnη), the rate of decrease in the porosity of the separator 23 can be controlled to match the composition of the positive electrode material particles 2101, preventing a sharp decrease in porosity during high-rate applications. This improves the uniformity of lithium insertion / extraction at the interface of the positive electrode 21, further optimizing the high-rate cycle performance and safety performance of the battery. It should be noted that the peak intensity ratios I003 / I104 of the positive electrode and the peak intensity ratio of the negative electrode were obtained by testing according to the general rules of X-ray diffraction analysis and the methods for determining the lattice parameters of graphite, JIS K 0131-1996 and JB / T4220-2011.

[0055] Specifically, the XRD diffraction peaks of the positive electrode and the porosity η of the separator in the lithium-ion battery include:

[0056] S1: Take a fresh lithium-ion battery, place it at 25°C for more than 2 hours, discharge it at a rate of 0.2C to the discharge cutoff voltage of 2.5V, then let it stand for 10 minutes, and disassemble it to obtain the positive electrode 21 and the separator 23.

[0057] S2: After rinsing the positive electrode 21 and the separator 23 three times with dimethyl carbonate, bake them in a vacuum oven at 60°C for 2 hours.

[0058] S3: Remove the positive electrode 21 and the separator 23 and allow them to cool;

[0059] S4: Test the positive electrode 21 with XRD to obtain the diffraction peak pattern of the positive electrode 21, and calculate the peak intensity ratio I003 / I104.

[0060] S5: Take the diaphragm 23 and test the porosity η (test method refers to national standard GB / T36363-2018).

[0061] Understandably, in high-rate applications, the porosity of the separator 23 will gradually decrease, while the active materials on the positive and negative electrodes will gradually deactivate. Furthermore, the ratio y of I003 / I104 and the porosity η further satisfy: y ≥ 0.5*(2-lnη), which further constrains the rate of change of the porosity of the separator 23, adapting to the lithium insertion and de-lithiation activity of the positive electrode material particles 2101. This ensures that during high-rate applications, the rate at which lithium ions pass through the separator 23 matches the rate at which lithium ions are inserted or de-inserted at the interface of the positive electrode 21, preventing the local accumulation of lithium ions in the positive electrode 21, reducing the risk of cracking, and suppressing the occurrence of side reactions.

[0062] In some alternative embodiments, when the first capacity retention rate of the lithium-ion battery is x, the porosity of the separator 23 corresponds to η. x It also satisfies: x*y≥0.3*(2-lnη) x Matching the porosity of the separator 23 with the capacity retention rate of the battery ensures that the predetermined capacity retention rate can still be maintained in high-rate application scenarios, thereby improving the cycle performance of the battery and extending its life.

[0063] In some optional embodiments, the lithium salt concentration of the electrolyte 3 is E mol / L. The lithium-ion battery is discharged at a rate of 0.2C to the discharge cutoff voltage of 2.5V. The negative electrode 25 is taken out and XRD test is performed to obtain the test spectrum. The highest peak and the second highest peak are selected from the test spectrum. The ratio of the peak intensity of the highest peak to the peak intensity of the second highest peak is P, and satisfies: 3P / 2≥E≥P / 6. The diffraction peaks in the XRD diffraction peak test spectrum of the negative electrode 25 represent a crystal form of the negative electrode material particles 2501. The ratio of the peak intensity of the highest peak to the peak intensity of the second highest peak reflects the stability of the negative electrode material particles 2501 to a certain extent. The higher the stability of the negative electrode material particles 2501, the weaker their kinetic performance for lithium ion migration. The higher the lithium salt concentration of the electrolyte 3, the faster the lithium ion migration rate. By controlling the lithium salt concentration E and the ratio P of the peak intensity of the highest peak to the peak intensity of the second highest peak of the negative electrode 25 to be: 3P / 2≥E≥P / 6, the stability and kinetic performance of the negative electrode 25 can be balanced. The negative electrode 25 can efficiently and persistently complete the high-throughput lithium ion insertion and extraction reaction, ensuring that the interface stability and rate performance of the negative electrode 25 are in the optimal range, and achieving the optimal rate performance of the battery.

[0064] In some optional embodiments, referring to Figure 3, the positive electrode material particles 2101 located on the surface of the positive electrode active material layer 210 are also doped with element Z. Element Z is one or more of Al, B, Zr, Ti, Ba, Mn, Co, Y, La, Ca, Sr, and Sb. Doping the positive electrode material particles 2101 with the above chemical element improves the structural stability of the positive electrode active material. Specifically, the above chemical element is doped on the surface of the positive electrode material particles 2101 to form a physical barrier, thereby reducing side reactions between the positive electrode active material layer 210 and the electrolyte 3.

[0065] In some optional embodiments, referring to Figure 3, the element Z accounts for 0.05%-2% of the weight of the positive electrode material particles 2101 located on the surface. By doping with element Z in an appropriate amount, on the one hand, it synergistically forms a passivation layer with element F, improving the interfacial stability of the positive electrode active material layer 210; on the other hand, it reduces the impact on the content of energy storage material in the positive electrode active material, ensuring battery capacity.

[0066] A second aspect of this application provides an electrical device including the aforementioned lithium-ion battery. Due to the beneficial effects of lithium-ion batteries as described above, the electrical device provided by this application exhibits good structural stability of the positive and negative electrode active material layers during high-power charging and discharging, effectively suppressing electrolyte side reactions, improving battery cycle performance, and extending the service life of the electrical device.

[0067] The technical solution of this application will be described below with reference to Examples 1-9 and Comparative Examples 1-5.

[0068] The above Examples 1-9 and Comparative Examples 1-5 were subjected to 600-cycle retention rate tests, hot box tests, and EDS elemental analysis tests, respectively.

[0069] The method for testing retention rate over 600 cycles is as follows:

[0070] Take a lithium-ion battery prepared according to any of the above embodiments, place it in a constant temperature chamber at 25°C for more than 4 hours, and test it according to the following steps:

[0071] S31: Charge the battery at a constant current to 4.2V under a 3C charging rate, and then charge it at a constant voltage to a current of 0.025C. Let it stand for 15 minutes. Discharge the battery at a constant current to 2.5V under a 10C discharging rate, and let it stand for 30 minutes. Record the first discharge capacity as the initial capacity, denoted as a.

[0072] S32: Repeat step S31 above 600 times; record the discharge capacity at the 600th cycle, denoted as b;

[0073] S33: Calculate the retention rate after 600 cycles as b / a×100%.

[0074] The hot box test method is as follows:

[0075] Take a lithium-ion battery prepared according to any of the above embodiments, cycle it 500 times, place it in a constant temperature chamber at 25°C for more than 4 hours, and test it according to the following steps:

[0076] S41: Discharge the battery at a constant current rate of 0.1C until it is cut off at 2.5V, and let it stand for 5 minutes;

[0077] S42: Charge the battery at a constant current rate of 0.2C until it reaches 4.2V, then charge it at a constant voltage rate until it reaches 0.05C, and let it stand for 5 minutes.

[0078] S43: Place the battery into the heating chamber, set the heating rate to 5K / min, heat to 130℃, and hold for 1 hour. Then stop heating and allow it to cool down to below 30℃.

[0079] S44: A battery that does not catch fire or emit smoke is considered to have passed; otherwise, it is considered to have failed. At least 6 batteries should be tested in parallel for each embodiment or comparative example, and the pass rate should be recorded.

[0080] Qualitative and / or quantitative analyses of element Z were performed using energy dispersive spectroscopy (EDS).

[0081] The EDS elemental analysis method is as follows:

[0082] S51: Prepare cross-sectional slices of positive electrode 21 or negative electrode 25;

[0083] S52: Check the operating environment of the EDS detector and calibrate the EDS system;

[0084] S53: Sample loading, under predetermined electron beam conditions, acquiring the EDS spectrum of the sample to be tested.

[0085] S54: Use EDS analysis software to process and analyze the acquired spectra to obtain the types and contents of elements.

[0086] Examples 1-2 and Comparative Example 1 serve as control groups with the particle size D of the positive electrode material 2101 and the F element penetration depth L as variables. Examples 1 and 3 and Comparative Examples 2-3 serve as control groups with the F element penetration ratio in the negative electrode material 2501 as a variable. Examples 4 and Comparative Example 4 serve as control groups with the I003 / I104 ratio in the positive electrode material 2101 as a variable. Examples 5-6 and Comparative Example 5 serve as control groups with the crystal structure of the negative electrode sheet 25 and the lithium salt concentration in the electrolyte 3 as variables. Examples 7-8 serve as control groups with porosity as a variable. Examples 7-9 serve as control groups with the type of dopant element Z as a variable. Specific comparison results are shown in Tables 1-5.

[0087] Table 1

[0088] As shown in Table 1, the ratio m of the radial depth L of F element penetration into the positive electrode material particle 2101 to the particle size D of the positive electrode material particle 2101 can significantly affect the cycle performance and safety of the battery. When m ≤ 1-x, the cycle retention rate is relatively higher. At the same time, ensuring the n value of the negative electrode material particle 2501, n ≤ (1-x) / 2, results in a better cycle retention rate. When m > 1-x, the cycle retention rate of the battery is low and the safety of use is low, and the pass rate of the temperature chamber test drops to 0.

[0089] Table 2

[0090] As shown in Table 2, the proportion of particles with an area of ​​more than 5% infiltrated by F element in the negative electrode material particles 2501 has a significant impact on the cycle retention rate of the battery. Specifically, the higher the proportion of F element infiltrated into the negative electrode material particles 2501 (n ≤ (1-x) / 2), the higher the cycle retention rate of the battery. When n > (1-x) / 2, the cycle retention rate of the battery will decrease relatively, and the decrease will increase with the increase of the difference between n and (1-x) / 2. When the difference between n and (1-x) / 2 reaches 4.5 or above, the cycle retention rate drops to 60%, and the safety also decreases significantly, with a temperature chamber test pass rate of 0. In actual production, the optimal proportion of F element infiltrated into the negative electrode material particles 2501 is around 7%.

[0091] Table 3:

[0092] As can be seen from Table 3, the ratio y of the two crystal forms I003 / I104 in the cathode material particles 2101 has a certain impact on the cycle performance of the battery. When y≥0.3*(2-lnη), or further y≥0.5*(2-lnη), the cycle performance is better, and further, when x*y≥0.3*(2-lnη), the safety performance is guaranteed.

[0093] Table 4:

[0094] As shown in Table 4, the lithium salt concentration E in electrolyte 3 has a significant impact on the cycle performance and safety performance of the battery. Specifically, when 3P / 2≥E≥P / 6, i.e. 0.16≤E / P≤1.5, the cycle retention rate and safety test pass rate of the battery are relatively high.

[0095] Table 5:

[0096] As shown in Table 5, the choice of dopant element Z has a relatively low impact on the cycle retention rate of the battery, with Zr being the preferred chemical element. Specifically, the content of element Z has a relatively low impact on the cycle retention rate and safety performance of the battery. The porosity η of the separator 23 alone has a relatively low impact on the cycle performance and safety of the battery.

[0097] In summary, this application, on the one hand, by constraining the cross-linking effect of the positive electrode material particles 2101 and the negative electrode material particles 2501 with the F element, effectively enhances the structural stability of the interface between the positive electrode, negative electrode, and electrolyte 3, reduces the probability of cracking, and suppresses the occurrence of side reactions. On the other hand, by controlling the crystal form of the positive electrode material particles 2101 and the negative electrode material particles 2501 at the microscopic level, it enhances their ability to insert and extract lithium ions to meet the requirements of high-rate applications of batteries. On the third hand, by limiting the porosity of the separator 23 to match the activity of the positive and negative electrode material particles 2501, it achieves orderly conduction of lithium ions, avoids local accumulation and stress formation, further reduces the risk of interface cracking, and suppresses the occurrence of side reactions. Ultimately, it achieves high-rate operation and high-cycle performance of lithium-ion batteries while ensuring safety in use.

[0098] In the description of this specification, references to the terms "some embodiments," "an embodiment," or similar descriptions mean that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment or example. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0099] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.

Claims

1. A lithium-ion battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte for transporting lithium ions, wherein the surface of the positive electrode is covered with a positive active material layer comprising positive electrode material particles, and the surface of the negative electrode is covered with a negative active material layer comprising negative electrode material particles, characterized in that, When the first capacity retention rate of the lithium-ion battery is measured to be x, 78% ≤ x ≤ 89%, the diameter of the positive electrode material particle is D, and the depth of the F element penetration layer of the positive electrode material particle is L, the thickness percentage of the F element penetration layer in the radial direction of the positive electrode material particle is m = L / D, and the thickness percentage m of the F element penetration layer also satisfies the following condition with respect to the first capacity retention rate x: m ≤ 1 - x; and The percentage n of the negative electrode material particles that are invaded by F element is statistically determined, and the following condition is met: n≤(1-x) / 2.

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery was cycled at a 2C charging rate and a 5C discharging rate until the first capacity retention rate x was reached, at which point the following tests were performed: The lithium-ion battery after cyclic charging and discharging was placed at 25°C and discharged at a rate of 0.2C to the discharge cutoff voltage of 2.5V. After standing for 0.5 hours, the lithium-ion battery was disassembled and the positive electrode and the negative electrode were obtained. The cross-section was prepared and observed using a scanning electron microscope. The EDS signal was captured and acquired at 1000x magnification to obtain the surface scan distribution map of the F element. For the surface scan distribution map of the positive electrode sheet cross section: select at least 100 positive electrode material particles sequentially from left to right and from top to bottom, statistically screen out the average diameter D of all the positive electrode material particles and the average thickness L of the F element intrusion layer in its radial direction, and calculate m; For the surface scan distribution map of the cross-section of the negative electrode sheet: select at least 100 negative electrode material particles sequentially from left to right and from top to bottom. Define negative electrode material particles in which the area ratio of F element in a single negative electrode material particle is greater than 5% as negative electrode material particles invaded by F element. Count the number of negative electrode material particles invaded by F element among all the negative electrode material particles and calculate n.

3. The lithium-ion battery according to claim 1, characterized in that, The separator is disposed between the positive electrode and the negative electrode. The positive electrode material particles contain high-nickel ternary material, and the peak intensity ratio of the XRD diffraction peak of the positive electrode is y (I003 / I104). The porosity of the separator is η, which satisfies: y≥0.3*(2-lnη).

4. The lithium-ion battery according to claim 3, characterized in that, The ratio y of I003 / I104 and the porosity η satisfy: y≥0.5*(2-lnη).

5. The lithium-ion battery according to claim 3 or 4, characterized in that, The XRD diffraction peaks of the positive electrode of the lithium-ion battery and the methods for testing the porosity η of the separator include: S1: Take one of the lithium-ion batteries, place it at 25°C for more than 2 hours, discharge it at a rate of 0.2C to the cutoff voltage of 2.5V, then let it stand for 10 minutes, and disassemble it to obtain the positive electrode and the separator. S2: After rinsing the positive electrode and the separator three times with dimethyl carbonate, bake them in a vacuum oven at 60°C for 2 hours; S3: Remove the positive electrode and the separator and allow them to cool; S4: Test the positive electrode with XRD to obtain the diffraction peak pattern of the positive electrode and calculate the peak intensity ratio I003 / I104. S5: Take the membrane and test the porosity η.

6. The lithium-ion battery according to claim 3, characterized in that, When the first capacity retention rate of the lithium-ion battery is x, the porosity of the separator is η. x It also satisfies: x*y≥0.3*(2-lnη) x ).

7. The lithium-ion battery according to claim 1, characterized in that, The lithium salt concentration of the electrolyte is E mol / L. After discharging the lithium-ion battery at a rate of 0.2C to the cutoff voltage of 2.5V, the negative electrode is removed and XRD test is performed to obtain the test spectrum. The highest peak and the second highest peak in the test spectrum are selected. The ratio of the peak intensity of the highest peak to the peak intensity of the second highest peak is P, which satisfies: 3P / 2≥E≥P / 6.

8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material particles located on the surface of the positive electrode material layer are also doped with element Z, which is one or more of Al, B, Zr, Ti, Ba, Mn, Co, Y, La, Ca, Sr and Sb.

9. The lithium-ion battery according to claim 8, characterized in that, The element Z accounts for 0.05%-2% of the weight of the positive electrode material particles located on the surface.

10. An electrical device, characterized in that, Including the lithium-ion battery according to any one of claims 1-9.

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