Lithium-ion battery and applications

Abstract

The application relates to a lithium ion battery and application. The energy density of the lithium ion battery is greater than or equal to 270 Wh / Kg; the lithium ion battery satisfies the following conditions for the lithium precipitation boundary charging rate of T temperature under the 40%<=SoC<=50% state of charge: when T>=253.15K, 4C<=I1<=10C; when T<253.15K, 1.6C<=I2<=3.9C. The lithium ion battery provided by the application has high energy density, and the lithium precipitation boundary charging rate of the lithium ion battery at different temperatures T is determined by deeply analyzing the thermodynamic and kinetic competition relationship between the negative electrode lithium intercalation reaction and the lithium precipitation side reaction.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to the determination of a fast charging strategy for lithium-ion batteries, and more particularly to a lithium-ion battery and its application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and no memory effect, have been widely used in new energy vehicles, consumer electronics, and energy storage systems. The charging process is a critical stage in the use of lithium-ion batteries. If the charging current is too high, lithium plating can easily occur at the negative electrode. The deposited metallic lithium not only reduces battery capacity and shortens cycle life but may also cause safety hazards such as short circuits and thermal runaway, severely restricting the reliability of lithium-ion batteries. Therefore, accurately calculating the lithium plating boundary current (i.e., the value at which lithium plating does not occur) during the charging process and selecting an appropriate charging regime can resolve the conflict between fast charging, battery aging, and safety. This allows for delaying battery aging and improving fast charging speed while ensuring battery safety.

[0003] CN115146533A discloses a simulation optimization method for the fast charging performance of lithium-ion batteries. The method uses the output charging current to quickly charge the battery cell, which has high accuracy and efficiency, and improves the battery's lifespan. The output charging current when the solid-liquid phase potential at the negative electrode interface is equal to the boundary lithium plating condition can enable the battery cell to maintain a fast charging speed without lithium plating. The output charging current when the battery cell temperature rise is less than or equal to the battery cell temperature critical condition ensures that the battery cell is charged within a suitable temperature range, reducing irreversible capacity decay caused by excessive temperature during fast charging.

[0004] Currently, existing methods for calculating the lithium plating boundary current are mostly based on the maximum charging current-SoC boundary and the threshold voltage-charging current boundary, which have problems such as complex control, poor applicability, and lack of clear parameter acquisition standards, and cannot provide accurate and practical theoretical support for the optimization of charging strategies.

[0005] Therefore, there is an urgent need for a charging boundary current calculation method that balances accuracy, versatility, and feasibility, clarifies the standard testing and acquisition methods for each parameter, expands the applicability of the method, and addresses the shortcomings of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a lithium-ion battery and its applications. The lithium-ion battery provided by this invention possesses high energy density, and through in-depth analysis of the thermodynamic and kinetic competition between the lithium intercalation reaction and the lithium plating side reaction at the negative electrode, the lithium plating boundary charge rate of the lithium-ion battery at different temperatures T is clearly defined.

[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode comprises a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material in the positive active material layer comprises a ternary positive electrode material; the negative electrode comprises a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material in the negative active material layer comprises any one or a combination of at least two of artificial graphite, natural graphite, silicon-oxygen materials, or silicon-carbon materials; the energy density of the lithium-ion battery is ≥270Wh / Kg; the lithium-ion battery, at a state of charge of 40%≤SoC≤50%, has a lithium plating boundary charge rate I at temperature T. 析锂 Satisfies: When T≥253.15K, 4C≤I 析锂 ≤10C; when T<253.15K, 1.6C≤I 析锂 ≤3.9C.

[0008] The lithium-ion battery provided by this invention has an energy density as high as 270 Wh / kg, and confirming the lithium plating boundary charge rate of a high-energy-density lithium-ion battery is particularly important. This invention, through in-depth analysis of the thermodynamic and kinetic competition between the negative electrode lithium intercalation reaction and the lithium plating side reaction, combined with the simplified form of the Tafel equation for the negative electrode lithium intercalation reaction at high rates, and through a series of rigorous mathematical transformations, calculates the lithium plating boundary charge rate of the lithium-ion battery at different temperatures T.

[0009] Preferably, the method for determining the lithium-ion battery's charge rate at the lithium plating boundary at temperature T includes: The thickness of the negative electrode active material layer on one side surface of the negative electrode sheet is L (in meters), and the area is S (in square meters). 2 The D50 radius of the negative electrode active material is r. p The unit is m, and the volume percentage of the negative electrode active material in the negative electrode active material layer is ε. s The Li in the electrolyte + Concentration of c l The unit is mol / L; the stoichiometric coefficient of lithium intercalation at the negative electrode when the state of charge (SoC) of the lithium-ion battery is 100% is sto. max When SoC is 0, the stoichiometry of lithium intercalation in the negative electrode is sto. min SoC and negative open circuit voltage OCP neg The interpolation function is The lithium-ion battery's lithium plating boundary current is I, in amperes (A), and the reference exchange current density is given by a factor of A. i0，ref The unit is A / m 2 The activation energy of the reaction is Ea The units are J / mol, the gas constant R = 8.314 J / mol / K, the Faraday constant F = 96485 C / mol, and the thermodynamic temperature T is in K; the lithium-ion battery lithium plating boundary current I is calculated using formula 1: Formula 1; The lithium plating boundary charge rate = lithium plating boundary current I / nominal capacity Q of the lithium-ion battery.

[0010] This invention, through in-depth analysis of the thermodynamic and kinetic competition between the lithium intercalation reaction and the lithium plating side reaction at the negative electrode, reveals that when the electrode potential at the negative electrode surface is lower than the equilibrium potential for lithium plating, lithium plating is thermodynamically more likely to occur. Combining the simplified form of the Tafel equation for the lithium intercalation reaction at high rates, and through a series of rigorous mathematical transformations, this invention provides a method for determining the lithium plating boundary current in lithium-ion batteries that offers clear physical meaning, standardized parameter acquisition, and high prediction accuracy.

[0011] The method for determining the lithium plating boundary charge rate of a lithium-ion battery provided by this invention considers the structure of the negative electrode, the concentration of lithium ions in the electrolyte, the state of charge (SoC) of the battery, and the open-circuit voltage (OCP) of the negative electrode. neg By establishing a correlation between parameters with clear physical meaning and direct availability, and by pre-setting Formula 1 in the Battery Management System (BMS), a method for determining the lithium plating current boundary can be directly calculated based on the real-time SoC state of the lithium-ion battery. This allows for the adjustment of the maximum current of the lithium-ion battery to below the lithium plating boundary current. The method is highly feasible and applicable to lithium-ion batteries with different structural designs and formulation systems, demonstrating strong versatility.

[0012] Preferably, the compaction density of the negative electrode sheet is ρ0, in g / cm³. 3 The true density of the negative electrode active material is ρ AM The unit is g / cm³ 3 The mass percentage of the negative electrode active material in the negative electrode active material layer is ω. AM The volume percentage of the negative electrode active material in the negative electrode active material layer is ε. s Calculated using Formula 2: Formula 2.

[0013] Preferably, the reference exchange current density of the lithium-ion battery is pre-factor A. i0，ref and activation energy E a The methods for determining this include: Within the temperature range of 253.15K to 333.15K, select more than 5 temperature points to test the exchange current density i of the lithium-ion battery, and compare the exchange current density i with the reference exchange current density using a pre-factor A. i0，ref and activation energy E a Satisfying Formula 3: Formula 3.

[0014] Taking the logarithm of Formula 3 yields Formula 4: Formula 4.

[0015] According to Formula 4, a linear fit is performed on ln(i) and 1 / T. The intercept of the fitted line is ln(A). i0，ref The slope is -E a / R, the precession factor A of the reference exchange current density is calculated. i0，ref and activation energy E a .

[0016] Preferably, the state of charge (SoC) of the lithium-ion battery is related to the open-circuit voltage (OCP) of the negative electrode. neg interpolation function The methods for determining this include: Ⅰ: Perform constant current charging and constant current discharging cycles on the lithium-ion battery, and record the maximum charging capacity Q. max The capacity Q at time t t Open circuit voltage of the negative terminal OCP neg SOC and capacity Q at time t t and maximum capacity Q max Satisfying Formula 5: Formula 5; According to Formula 5, the negative open-circuit voltage OCP at SoC=0 and SoC=100% is obtained using the polynomial interpolation method. neg,0 and OCP neg,100% ; II: A half-cell was fabricated using the same negative electrode material as the negative electrode of the lithium-ion battery. Constant current charging and discharging cycles were performed, and the open-circuit voltage OCP was recorded. neg Using polynomial interpolation, the stoichiometry of lithium intercalation at the negative electrode and the OCP at the negative electrode are obtained. neg The interpolation function OCP neg '(sto); III: The OCP obtained in step I neg，0 and OCP neg，100% Substituting the lithium intercalation sto of the negative electrode with the negative electrode OCP neg The interpolation function OCP negIn '(sto), interpolation yields the corresponding negative electrode lithium intercalation sto s. min and sto max Formula 6 is as follows: Formula 6; Substituting the sto coefficients of lithium intercalation at the negative electrode obtained in step II into the negative electrode OCP neg The interpolation function OCP neg In '(sto), the state of charge (SoC) of the lithium-ion battery and the open-circuit voltage (OCP) of the negative electrode are obtained. neg interpolation function .

[0017] Preferably, the constant current charging and constant current discharging rates in step I and step II are the same, and the constant current charging and constant current discharging rates in step I and step II are each independently below 0.05C.

[0018] Preferably, the constant current charging and constant current discharging are performed at the same temperature, which is 253.15K~333.15K.

[0019] Preferably, the negative open-circuit voltage OCP neg The test was conducted using a three-electrode method.

[0020] Preferably, the number of cycles is more than 2.

[0021] Preferably, in steps I and II, there is a resting period between each consecutive constant current charging and constant current discharging.

[0022] Preferably, the electrolyte includes any one or a combination of at least two of the following: carbonate electrolyte, ether electrolyte, or ionic liquid electrolyte.

[0023] Preferably, the lithium salt in the electrolyte includes any one or a combination of at least two of LiPF6, LiBF4, LiClO4, LiFSI, or LiTFSI.

[0024] Preferably, the Li in the electrolyte + Concentration c l The concentration ranges from 0.5 mol / L to 2.0 mol / L.

[0025] Preferably, the negative electrode active material comprises silicon-oxygen materials and / or silicon-carbon materials, in combination with artificial graphite and / or natural graphite.

[0026] Preferably, the positive electrode active material includes a high-nickel ternary positive electrode material.

[0027] Preferably, the mass percentage of silicon-oxygen materials and / or silicon-carbon materials in the negative electrode active material is 5wt% to 35wt%.

[0028] Secondly, the present invention provides an application of the lithium-ion battery as described in the first aspect, wherein the lithium-ion battery is applied in the fields of new energy vehicles, consumer electronics, energy storage, or portable devices.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) The lithium-ion battery provided by the present invention has high energy density, and based on the method for determining the lithium plating boundary charging rate, the lithium plating boundary charging rate is clearly defined, which provides a basis for the application of lithium-ion batteries.

[0030] (2) The method for determining the lithium plating boundary charging rate of lithium-ion batteries provided by the present invention is based on the negative electrode structure of the lithium-ion battery, the concentration of lithium ions in the electrolyte, and the SoC and OCP of the lithium-ion battery. neg The interpolation function and other parameters with clear physical meaning can be used to establish relationships. The parameter acquisition is standardized, the prediction accuracy is high, and the feasibility and versatility are strong. This solves the shortcomings of the current method for determining the lithium plating boundary current, such as complicated operation, large error, and especially poor feasibility. Attached Figure Description

[0031] Figure 1 This is a particle size distribution diagram of the negative electrode active material in the lithium-ion battery negative electrode sheet provided in Example 1.

[0032] Figure 2 It is the fitting curve of ln(i) and 1 / T of the lithium-ion battery provided in Example 1.

[0033] Figure 3 This is the corresponding negative electrode half-cell of the lithium-ion battery provided in Example 1. and stoichiometry The interpolation function graph.

[0034] Figure 4 It is the lithium-ion battery negative electrode provided in Example 1. and SoC Interpolation function graph.

[0035] Figure 5 The boundary current curve is obtained by the lithium-ion battery lithium plating boundary current determination method provided in Example 1.

[0036] Figure 6 This is a comparison chart of the cycle capacity retention rates of Example 1 and Comparative Example 1. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0038] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0039] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0040] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0041] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0042] In one specific embodiment, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material in the positive active material layer comprises a ternary positive electrode material; the negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material in the negative active material layer comprises any one or a combination of at least two of artificial graphite, natural graphite, silicon-oxygen materials, or silicon-carbon materials; the energy density of the lithium-ion battery is ≥270Wh / Kg; the lithium-ion battery has a lithium plating boundary charge rate I at temperature T when the state of charge is 40%≤SoC≤50%. 析锂 Satisfies: When T≥253.15K, 4C≤I 析锂 ≤10C; when T<253.15K, 1.6C≤I 析锂 ≤3.9C.

[0043] The lithium-ion battery provided by this invention has an energy density as high as 270 Wh / kg, and confirming the lithium plating boundary charge rate of a high-energy-density lithium-ion battery is particularly important. This invention, through in-depth analysis of the thermodynamic and kinetic competition between the negative electrode lithium intercalation reaction and the lithium plating side reaction, combined with the simplified form of the Tafel equation for the negative electrode lithium intercalation reaction at high rates, and through a series of rigorous mathematical transformations, calculates the lithium plating boundary charge rate of the lithium-ion battery at different temperatures T.

[0044] In some embodiments, the method for determining the lithium-ion battery's lithium plating boundary charge rate at temperature T includes: The negative electrode active material layer on one side surface of the negative electrode sheet has a thickness of L (m) and an area of ​​S (m²). 2 The D50 radius of the negative electrode active material is r. p The unit is m, and the volume percentage of the negative electrode active material in the negative electrode active material layer is ε. s The Li in the electrolyte + Concentration of c l The unit is mol / L; the stoichiometric coefficient of lithium intercalation at the negative electrode when the state of charge (SoC) of the lithium-ion battery is 100% is sto. max When SOC is 0, the stoichiometric coefficient of lithium intercalation in the negative electrode is sto. min SoC and negative open circuit voltage OCP neg The interpolation function is The lithium-ion battery's lithium plating boundary current is I, in amperes (A), and the reference exchange current density is given by a factor of A. i0，ref The unit is A / m 2The activation energy of the reaction is E a The units are J / mol, the gas constant R = 8.314 J / mol / K, the Faraday constant F = 96485 C / mol, and the thermodynamic temperature T is in K; the lithium-ion battery lithium plating boundary current I is calculated using formula 1: Formula 1.

[0045] The lithium plating boundary charge rate = lithium plating boundary current I / nominal capacity Q of the lithium-ion battery.

[0046] In this invention, the nominal capacity Q refers to the discharge specific capacity obtained after multiple corrections based on test results, using the theoretical capacity Q0 calculated from the design parameters of the lithium-ion battery as a benchmark and performing low-rate charge-discharge cycles. For example, first, using the theoretical capacity Q0 as a benchmark, it is charged at a constant current and constant voltage rate of 0.33C~1C, with the cutoff voltage set to 0.02C~0.1C. Then, it is discharged at a constant current rate of 0.33C~1C to obtain the discharge capacity Q1. If Q1 is close to the theoretical capacity Q0, then Q1 is used as the nominal capacity Q. If Q1 deviates significantly from the theoretical capacity Q0, then Q1 is used as the new benchmark, and the above charge-discharge process is repeated until Q0 is reached. n With Q n-1 Approaching, with Q n The nominal capacity is Q.

[0047] The "lithium plating boundary current" mentioned in this invention refers to the maximum charging current that ensures the lithium-ion battery does not plating lithium.

[0048] This invention derives an analytical expression for the lithium plating boundary current by deeply analyzing the thermodynamic and kinetic competition between the lithium intercalation reaction and the lithium plating side reaction at the negative electrode. When the electrode potential at the negative electrode surface is lower than the equilibrium potential for lithium plating, lithium plating is thermodynamically predisposed. Combining the simplified form of the Tafel equation for the lithium intercalation reaction at high rates, and through a series of rigorous mathematical transformations, this invention provides a method for determining the lithium plating boundary charging rate of lithium-ion batteries that is physically clear, has standardized parameter acquisition, and offers high prediction accuracy.

[0049] The method for determining the lithium plating boundary charging rate of a lithium-ion battery provided by this invention considers the structure of the negative electrode, the concentration of lithium ions in the electrolyte, the state of charge (SOC) of the battery, and the open-circuit voltage (OCP) of the negative electrode. negBy establishing a correlation between parameters with clear physical meaning and direct availability, and by pre-setting Formula 1 in the Battery Management System (BMS), a method for determining the lithium plating current boundary can be directly calculated based on the real-time SOC state of the lithium-ion battery. This allows for the adjustment of the maximum current of the lithium-ion battery to below the lithium plating boundary current. The method is highly feasible and applicable to lithium-ion batteries with different structural designs and formulation systems, demonstrating strong versatility.

[0050] In this invention, the D50 radius of the negative electrode active material is r. p The D50 particle size is half of the D50 particle size, and the testing method for the D50 particle size of the negative electrode active material is no longer specifically limited. Specifically, for negative electrode active material particles, a laser particle size analyzer can be used for testing, and the testing method can be performed according to the national standard GB / T24533-2019. For the negative electrode sheet, SEM can be used for testing. For example, the SEM testing method includes: selecting at least three different regions on the negative electrode sheet, taking at least five SEM images of each region, measuring the diameter of at least 100 negative electrode active material particles using ImageJ software, statistically analyzing the measured diameters, and calculating the D50 particle size of the negative electrode active material. p That is, half the D50 particle size.

[0051] In this invention, the method for testing the thickness L of the negative electrode active material layer on one side of the negative electrode sheet is not particularly limited. For example, the thickness L of the negative electrode active material layer on one side of the negative electrode sheet can be obtained by using a micrometer or a thin film thickness gauge. The testing method includes: selecting at least 5 different test points on the negative electrode sheet for thickness measurement, repeating the measurement at each test point more than 3 times, and taking the average value as the final value of L1. When the negative electrode sheet has a negative electrode active material layer on only one side, L = (L1 - L0). When the negative electrode sheet has negative electrode active material layers of the same thickness on both sides, L = (L1 - L0) / 2, where L0 is the thickness of the negative electrode current collector, and the testing accuracy is not less than 0.1 μm.

[0052] In some embodiments, the compaction density of the negative electrode is ρ0, in g / cm³. 3 The true density of the negative electrode active material is ρ AM The unit is g / cm³ 3 The mass percentage of the negative electrode active material in the negative electrode active material layer is ω, and the volume percentage of the negative electrode active material in the negative electrode active material layer is ε. s Calculated using Formula 2: Formula 2.

[0053] In some embodiments, the reference exchange current density of the lithium-ion battery is pre-factored by a factor A.i0，ref and activation energy E a The methods for determining this include: Within the temperature range of 253.15K to 333.15K, select more than 5 temperature points to test the exchange current density i of the lithium-ion battery, and compare the exchange current density i with the reference exchange current density using a pre-factor A. i0，ref and activation energy E a Satisfying Formula 3: Formula 3.

[0054] Taking the logarithm of Formula 3 yields Formula 4: Formula 4.

[0055] According to Formula 4, a linear fit is performed on ln(i) and 1 / T. The intercept of the fitted line is ln(A). i0，ref The slope is -E a / R, the precession factor A of the reference exchange current density is calculated. i0，ref and activation energy E a .

[0056] In this invention, the test method for the exchange current density i is the EIS Rct method. Specifically, a half-cell made of the same negative electrode material as the negative electrode of the lithium-ion battery is used for EIS testing at a temperature T. The test amplitude is 10mV, and the test frequency is 10Hz~500KHz. Rct is obtained through equivalent circuit fitting. Based on the relationship between Rct and exchange current density... The exchange current density i at temperature T is calculated, where S is the area of ​​the negative electrode active material layer.

[0057] In this invention, the precession factor A for determining the reference exchange current density is... i0，ref and activation energy E a The temperature range is 253.15K to 333.15K, for example, it can be 253.15K, 258.15K, 263.15K, 268.15K, 273.15K, 278.15K, 283.15K, 288.15K, 293.15K, 298.15K, 303.15K, 308.15K, 313.15K, 318.15K, 323.15K, 328.15K or 333.15K. The number of selected temperature points can be, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15, preferably including at least 263.15K, 273.15K, 298.15K and 333.15K.

[0058] In some embodiments, the state of charge (SoC) of the lithium-ion battery is related to the open-circuit voltage (OCP) of the negative electrode. neg interpolation function The methods for determining this include: Ⅰ: Perform constant current charging and constant current discharging cycles on the lithium-ion battery, and record the maximum charging capacity Q. max The capacity Q at time t t Open circuit voltage of the negative terminal OCP neg SOC and capacity Q at time t t and maximum capacity Q max Satisfying Formula 5: Formula 5; According to Formula 5, the negative open-circuit voltage OCP at SOC=0 and SOC=100% is obtained using polynomial interpolation. neg，0 and OCP neg，100% ; II: A half-cell was fabricated using the same negative electrode material as the negative electrode of the lithium-ion battery. Constant current charging and discharging cycles were performed, and the open-circuit voltage OCP was recorded. neg Using polynomial interpolation, the stoichiometry of lithium intercalation at the negative electrode and the OCP at the negative electrode are obtained. neg The interpolation function OCP neg '(sto); III: The OCP obtained in step I neg，0 and OCP neg，100% Substituting the lithium intercalation sto of the negative electrode with the negative electrode OCP neg The interpolation function OCP neg In '(sto), interpolation yields OCP. neg，0 and OCP neg，100% The corresponding negative electrode lithium intercalation sto sto max and sto min Formula 6 is as follows: Formula 6; Substituting the sto coefficients of lithium intercalation at the negative electrode obtained in step II into the negative electrode OCP neg The interpolation function OCP neg In '(sto), the state of charge (SOC) of the lithium-ion battery and the open-circuit voltage (OCP) of the negative electrode are obtained. neg interpolation function .

[0059] In some implementations, the constant current charging and constant current discharging rates in step I and step II are the same, and the constant current charging and constant current discharging rates in step I and step II are each independently below 0.05C, for example, 0.05C, 0.04C, 0.03C, 0.02C, 0.01C or 0.005C.

[0060] In some embodiments, the constant current charging and constant current discharging temperatures are the same, both ranging from 253.15K to 333.15K, for example, 253.15K, 263.15K, 273.15K, 283.15K, 293.15K, 303.15K, 313.15K, 323.15K, or 333.15K.

[0061] In this invention, the temperature for constant current charging and constant current discharging is selected according to the temperature corresponding to the lithium plating boundary current to be measured. For example, the lithium plating boundary current at 298.15K is tested, that is, 298.15K is selected for constant current charging and constant current discharging.

[0062] In some embodiments, the negative open-circuit voltage OCP neg The test was conducted using a three-electrode method.

[0063] In some implementations, the number of cycles is more than two, for example, two, three, four, or five. By performing more than two cycles of constant current charging and discharging, the State of Charge (SOC) and OCP (Optical Content) are ensured. neg Accuracy of data acquisition and interpolation function The accuracy.

[0064] In some embodiments, a resting period is included between each consecutive constant current charging and discharging cycle in steps I and II. In this invention, the resting time is not specifically limited, but aims to completely eliminate voltage polarization caused by the charging or discharging current. For example, after constant current charging, it is preferable to allow the voltage to remain stationary until it no longer decreases over time; during constant current discharging, it is preferable to allow the voltage to remain stationary until it no longer rises over time. Preferably, the resting period is 0.5 hours or more, such as 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0065] In some embodiments, the electrolyte includes any one or a combination of at least two of carbonate electrolytes, ether electrolytes, or ionic liquid electrolytes.

[0066] In some embodiments, the lithium salt in the electrolyte includes any one or a combination of at least two of LiPF6, LiBF4, LiClO4, LiFSI, or LiTFSI. Typical but non-limiting combinations include combinations of LiPF6 and LiFSI, LiPF6 and LiTFSI, LiPF6 and LiBF4, or LiPF6, LiBF4, and LiFSI.

[0067] In this invention, the concentration of lithium ions in the electrolyte of the lithium-ion battery is measured using an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0068] In some embodiments, the Li in the electrolyte + Concentration c l The concentration ranges from 0.5 mol / L to 2.0 mol / L, for example, it can be 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, or 2.0 mol / L.

[0069] In some embodiments, the negative electrode active material includes silicon-oxygen materials and / or silicon-carbon materials, in combination with artificial graphite and / or natural graphite.

[0070] In some embodiments, the positive electrode active material includes a high-nickel ternary positive electrode material.

[0071] In some embodiments, the mass percentage of silicon-oxygen materials and / or silicon-carbon materials in the negative electrode active material is 5wt% to 35wt%, for example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt% or 35wt%.

[0072] In some embodiments, the separator is disposed between the positive electrode and the negative electrode, and the separator is made of any one of polyethylene, polypropylene, or polyacrylonitrile.

[0073] In another specific embodiment, the present invention provides an application of a lithium-ion battery as described in the aforementioned other specific embodiment, wherein the lithium-ion battery is applied in the fields of new energy vehicles, consumer electronics, energy storage, or portable devices.

[0074] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0075] Example 1 This embodiment provides a lithium-ion battery, including a positive electrode, a polyethylene separator, and a negative electrode. The positive electrode includes an aluminum foil and positive active material layers disposed on both sides of the aluminum foil. In the positive active material layers, the mass ratio of lithium nickel cobalt manganese oxide, conductive carbon black, and polyvinylidene fluoride is 95:2:3. The negative electrode includes a copper foil and negative active material layers disposed on both sides of the copper foil. In the negative active material layers, the mass ratio of graphite, silicon, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber is 93.45:3:1.55:1:1. The rated capacity of the lithium-ion battery is 5Ah, and the compaction density ρ0 = 1.516 g·cm³. -3 .

[0076] The method for determining the lithium-ion battery lithium plating boundary charging rate includes: (1) SEM testing was used. Three different regions of the negative electrode sheet were selected, and five SEM images were taken for each region. The diameter of 100 negative electrode active material particles was measured using ImageJ software. The particle size distribution diagram is shown below. Figure 1 As shown, D50 is 11.497 μm, and r is calculated. p =5.749×10 -6 m.

[0077] (2) Measure the length and width of the negative electrode and calculate the area of ​​the negative electrode: S = 0.188518 m². 2 The thickness of the negative electrode active material layer on one side of the negative electrode sheet was measured using a thin film thickness gauge. Five test points were selected, and each test point was measured three times. The average value was taken, and the copper foil thickness was subtracted to calculate L = 3.7 × 10⁻⁶. -5 m.

[0078] (3) Measure the true density ρ of the negative electrode active material (graphite and silicon with a mass ratio of 86.45:10). AM =2.19 g·cm -3 In the negative electrode active material layer, the mass ratio of the negative electrode active material is ω. AM =96.45%, according to Formula 2: ε was calculated s =66.77%.

[0079] (4) The concentration of lithium ions in the electrolyte was tested using ICP-OES, and the concentration of lithium ions was obtained from the test. l =1.450mol / L.

[0080] (5) The exchange current density i was measured at five temperature points: 263.15K, 273.15K, 298.15K, 218.15K, and 333.15K. According to Formula 3: Taking the logarithm, we get Formula 4: According to Formula 4, a linear fit is performed on ln(i) and 1 / T, and the fitting result is as follows: Figure 2 As shown, the fitted relationship is: y = -2062.9962x + 7.0092, and the intercept of the fitted line is ln(A). i0，ref =7.0092, slope -E a / R=-2062.9962, A is calculated. i0，ref =exp(7.0092)≈1106.73A / m 2 E a =2062.9962×8.314≈17151J / mol.

[0081] (6) Determine the state of charge (SoC) of the lithium-ion battery and the open-circuit voltage (OCP) of the negative electrode. neg interpolation function ,include: I: In a 298.15K environment, constant current charging and discharging cycles were performed at a rate of 0.02C for a total of 3 cycles, and the maximum charging capacity Q was obtained. max =5.13Ah, SoC and capacity Q at time t t and maximum capacity Q max satisfy: The negative open-circuit voltage OCP at SoC=0 and SoC=100% was obtained using a polynomial interpolation method. neg，0 and OCP neg，100% .

[0082] II: A half-cell was fabricated using the same negative electrode material as the negative electrode of the lithium-ion battery. Constant current charging and discharging cycles were performed, and the open-circuit voltage OCP was recorded. neg Using polynomial interpolation, the stoichiometry of lithium intercalation at the negative electrode and the OCP at the negative electrode are obtained. neg The interpolation function OCP neg '(sto), such as Figure 3 As shown; III: The OCP obtained in step I neg，0 and OCP neg，100% Substituting the lithium intercalation sto of the negative electrode with the negative electrode OCP neg The interpolation function OCP neg '(sto) interpolation yields OCP neg，0 and OCP neg，100% The corresponding negative electrode lithium intercalation sto sto min =0.0917 and sto max =0.89529; Formula 6: Substituting the sto coefficients of lithium intercalation at the negative electrode obtained in step II into the negative electrode OCP negThe interpolation function OCP neg In '(sto), the state of charge (SoC) of the lithium-ion battery and the open-circuit voltage (OCP) of the negative electrode are obtained. neg interpolation function ,like Figure 4 As shown.

[0083] (7) According to Formula 1: Based on the relevant parameters obtained from steps (1) to (6), the charging boundary current curves of the lithium-ion battery at calculated temperatures of 253.15K, 273.15K, 298.15K, and 313.15K are shown below. Figure 5 As shown, Formula 1 and the relevant parameters obtained from steps (1) to (6) are preset in the BMS to set the fast charging strategy. The lithium-ion battery is charged at 298.15K. The charging current controlled by the BMS at 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC and 80% SOC are obtained. The calculated lithium plating boundary current, i.e. the corresponding rate, is compared with the charging current controlled by the BMS. The comparison results are shown in Table 1.

[0084] Table 1 Based on the fast charging strategy set by the BMS in step (7) of this embodiment, the total charging time from 10% SoC to 80% SoC is only 14.84 minutes. Under this fast charging strategy, after 600 charge-discharge cycles, the capacity retention rate (the ratio of the capacity of the 600th discharge cycle to the capacity of the first discharge cycle) can reach 73.78%.

[0085] Comparative Example 1 This comparative example provides a lithium-ion battery that is exactly the same as the lithium-ion battery provided in Example 1.

[0086] This comparative example uses a constant current charging strategy with a single current for charging and charging cycles, and charges from 10% SoC to 80% SoC in the same time as in Example 1. The calculated charging current of this comparative example should be 14.14A.

[0087] According to the calculation results in Example 1, if lithium plating is to be prevented in the lithium-ion battery, the charging current should have dropped below 9.87A when charged to 70% SoC. Obviously, 14.14A is greater than the lithium plating boundary current value. Therefore, the lithium-ion battery in this comparative example has a greater risk of lithium plating during charge-discharge cycles, and after 600 charge-discharge cycles, the capacity retention rate is only 49.77%.

[0088] like Figure 6 The graph shows a comparison of the cycle capacity retention rates of the comparative example and Example 1. After 200 charge-discharge cycles, Comparative Example 1 showed a clear deterioration trend, with capacity decay accelerating significantly.

[0089] In summary, based on the comparison of the cycle performance of Example 1 and Comparative Example 1, it can be determined that the lithium-ion battery calculated by the lithium-ion boundary charging rate determination method provided by the present invention can achieve rapid charging of lithium-ion batteries while controlling the charging current within the lithium-ion boundary current, thus significantly improving the cycle performance and safety performance of lithium-ion batteries.

[0090] The high accuracy of the lithium plating boundary current calculation provided by this invention is attributed to the fact that this invention uses the theoretical formula derived from the kinetic and thermodynamic characteristics of the lithium intercalation reaction and the lithium plating reaction as the charging boundary current calculation model. It comprehensively considers the influence of multiple factors such as temperature, SoC, electrode structure parameters, and reaction kinetic parameters, and overcomes the problem of large calculation deviation in existing methods. It can accurately calculate the maximum charging current under different operating conditions without lithium plating.

[0091] Furthermore, the method for determining the lithium plating boundary charging rate provided by this invention clarifies the standard testing and acquisition methods for each calculation parameter, ensuring the accuracy and consistency of parameter values ​​and improving the repeatability of the method. Moreover, the method for determining the lithium plating boundary charging rate provided by this invention can be directly applied to lithium-ion battery management systems, providing theoretical support for the dynamic adjustment of charging current. It can avoid the risk of lithium plating, improve battery safety and cycle life, and maximize charging speed, balancing safety and charging efficiency. It is highly feasible and has significant engineering application value.

[0092] Furthermore, the method for determining the lithium plating boundary charging rate provided by this invention is based on structural parameters such as the radius, thickness, and volume fraction of the active material of the negative electrode particles, as well as kinetic parameters such as the reaction activation energy and the OCP interpolation function. It is applicable to lithium-ion batteries with various positive electrode active materials, negative electrode active materials, different types of electrolytes, and various application scenarios. It breaks through the limitation of the narrow applicability of existing methods and can be widely used in the optimization of charging strategies for various lithium-ion batteries.

[0093] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, wherein the positive active material in the positive active material layer includes a ternary positive electrode material. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material in the negative electrode active material layer includes any one or a combination of at least two of artificial graphite, natural graphite, silicon-oxygen materials or silicon-carbon materials. The energy density of the lithium-ion battery is ≥270Wh / Kg; The lithium-ion battery, under a state of charge of 40% ≤ SoC ≤ 50%, has a lithium plating boundary charge rate I at temperature T. 析锂 satisfy: When T≥253.15K, 4C≤I 析锂 ≤10C; When T < 253.15 K, 1.6 C ≤ I 析锂 ≤3.9C.

2. The lithium-ion battery as described in claim 1, characterized in that, The method for determining the lithium-ion battery's lithium plating boundary charge rate at temperature T includes: The thickness of the negative electrode active material layer on one side surface of the negative electrode sheet is L (in meters), and the area is S (in square meters). 2 ; The D50 radius of the negative electrode active material is r. p The unit is m, and the volume percentage of the negative electrode active material in the negative electrode active material layer is ε. s ; Li in the electrolyte + Concentration of c l The unit is mol / L; When the state of charge (SoC) of the lithium-ion battery is 100%, the stoichiometry of the lithium intercalation electrode is sto. max When SoC is 0, the stoichiometry of lithium intercalation in the negative electrode is sto. min SoC and negative open circuit voltage OCP neg The interpolation function is ; The lithium-ion battery has a lithium plating boundary current of I, in amperes (A), and a reference exchange current density pre-factor of A. i0，ref The unit is A / m 2 The activation energy of the reaction is E a The unit is J / mol, the gas constant R = 8.314 J / mol / K, the Faraday constant F = 96485 C / mol, and the thermodynamic temperature T is in K. The lithium-ion battery lithium plating boundary current I is calculated using formula 1: Official 1; The lithium plating boundary charge rate = lithium plating boundary current I / nominal capacity Q of the lithium-ion battery.

3. The lithium-ion battery as described in claim 1, characterized in that, The compaction density of the negative electrode sheet is ρ0, in g / cm³. 3 The true density of the negative electrode active material is ρ AM The unit is g / cm³ 3 The mass percentage of the negative electrode active material in the negative electrode active material layer is ω. AM The volume percentage of the negative electrode active material in the negative electrode active material layer is ε. s Calculated using Formula 2: Official 2.

4. The lithium-ion battery as described in claim 1, characterized in that, The reference exchange current density of the lithium-ion battery, with a pre-factor A. i0，ref and activation energy E a The methods for determining this include: Within the temperature range of 253.15K to 333.15K, select more than 5 temperature points to test the exchange current density i of the lithium-ion battery, and compare the exchange current density i with the reference exchange current density using a pre-factor A. i0，ref and activation energy E a Satisfying Formula 3: Official 3; Taking the logarithm of Formula 3 yields Formula 4: Official 4; According to Formula 4, a linear fit is performed on ln(i) and 1 / T. The intercept of the fitted line is ln(A). i0，ref The slope is -E a / R, the precession factor A of the reference exchange current density is calculated. i0，ref and activation energy E a .

5. The lithium-ion battery as described in claim 1, characterized in that, The state of charge (SoC) and open-circuit voltage (OCP) of the lithium-ion battery neg interpolation function The methods for determining this include: Ⅰ: Perform constant current charging and constant current discharging cycles on the lithium-ion battery, and record the maximum charging capacity Q. max The capacity Q at time t t Open circuit voltage of the negative terminal OCP neg SoC and capacity Q at time t t and maximum capacity Q max Satisfying Formula 5: Official 5; According to Formula 5, the negative open-circuit voltage OCP at SoC=0 and SoC=100% is obtained using the polynomial interpolation method. neg，0 and OCP neg，100% ; II: A half-cell was fabricated using the same negative electrode material as the negative electrode of the lithium-ion battery. Constant current charging and discharging cycles were performed, and the open-circuit voltage OCP was recorded. neg Using polynomial interpolation, the stoichiometry of lithium intercalation at the negative electrode and the OCP at the negative electrode are obtained. neg The interpolation function OCP neg '(sto); III: The OCP obtained in step I neg，0 and OCP neg，100% Substituting the lithium intercalation sto of the negative electrode with the negative electrode OCP neg The interpolation function OCP neg In '(sto), interpolation yields the corresponding negative electrode lithium intercalation sto s. min and sto max Formula 6 is as follows: Official 6; Substituting the sto coefficients of lithium intercalation at the negative electrode obtained in step II into the negative electrode OCP neg The interpolation function OCP neg In '(sto), the state of charge (SoC) of the lithium-ion battery and the open-circuit voltage (OCP) of the negative electrode are obtained. neg interpolation function .

6. The lithium-ion battery as described in claim 5, characterized in that, The constant current charging and constant current discharging rates described in Step I and Step II are the same, and the constant current charging and constant current discharging rates in Step I and Step II are each independently below 0.05C. And / or, the constant current charging and constant current discharging are at the same temperature, which is 253.15K~333.15K; And / or, the negative open-circuit voltage OCP neg The test was conducted using a three-electrode method. And / or, the number of cycles is more than 2; And / or, in steps I and II, there is also a resting period between each adjacent constant current charging and constant current discharging cycle.

7. The lithium-ion battery as described in claim 1, characterized in that, The electrolyte includes any one or a combination of at least two of the following: carbonate electrolyte, ether electrolyte, or ionic liquid electrolyte; And / or, the lithium salt in the electrolyte includes any one or a combination of at least two of LiPF6, LiBF4, LiClO4, LiFSI or LiTFSI; And / or, the Li in the electrolyte + Concentration c l The concentration ranges from 0.5 mol / L to 2.0 mol / L.

8. The lithium-ion battery as described in claim 1, characterized in that, The negative electrode active material includes silicon-oxygen materials and / or silicon-carbon materials, in combination with artificial graphite and / or natural graphite; And / or, the positive electrode active material includes a high-nickel ternary positive electrode material.

9. The lithium-ion battery as described in claim 1, characterized in that, In the negative electrode active material, the mass percentage of silicon-oxygen material and / or silicon-carbon material is 5wt%~35wt%.

10. An application of the lithium-ion battery as described in claim 9, characterized in that, The lithium-ion batteries are used in the fields of new energy vehicles, consumer electronics, energy storage, or portable devices.

Images