A battery

Abstract

This invention belongs to the field of lithium-ion battery technology, specifically relating to a battery. This invention controls the percentage of the total molar amount of trivalent and tetravalent nickel elements in the total molar amount of nickel in the nickel-based cathode material, the molar ratio of nickel-based cathode material to the cathode active material, and the H of the cathode electrode sheet in the lithium-ion battery. + The increased growth rate can significantly reduce battery gas production, ensure close contact between battery electrodes and separators, thereby reducing battery internal resistance and improving battery cycle performance.

Description

[0001] This application is a divisional application of the invention filed on October 30, 2024, entitled "A Battery", with application number 202411525404.2. Technical Field

[0002] This invention belongs to the field of lithium-ion battery technology, and specifically relates to a battery. Background Technology

[0003] Lithium manganese iron phosphate (LMFP) is composed of manganese (Mn), iron (Fe), phosphorus (P) and lithium (Li). As a cathode material for lithium batteries, LMFP has become a highly regarded material in new energy vehicles and energy storage systems due to its advantages such as high performance, stability and economy.

[0004] However, LMFP materials have a large specific surface area and a large contact area with the electrolyte, which can exacerbate the protonation of hydrogen in the electrolyte. Protonated hydrogen is reduced to hydrogen gas at the negative electrode, causing severe gas production. This gas production causes the electrode to expand, resulting in poor contact between the electrode and the separator, increased impedance, and black spots on the electrode.

[0005] Therefore, providing a lithium-ion battery that can reduce gas production has become a problem that needs to be solved. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a battery that can significantly reduce gas production, ensure close contact between the battery electrodes and the separator, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0007] This invention provides a battery, including a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes lithium manganese iron phosphate material and a nickel-based positive electrode material, the nickel-based positive electrode material includes trivalent nickel and tetravalent nickel, and the molar ratio of the nickel-based positive electrode material to the positive electrode active material is c; in the battery at 100% SOC, the percentage of the total molar amount of trivalent and tetravalent nickel to the total molar amount of nickel in the nickel-based positive electrode material is a; the H of the positive electrode sheet... + The growth rate is b, and a, c, and b satisfy the relationship shown in equation I:

[0008] 0.008<(a×c) / b≤8.290, formula I.

[0009] Compared with existing technologies, this invention controls the percentage of the total molar amount of trivalent and tetravalent nickel elements in the total molar amount of nickel in the nickel-based cathode material, the molar ratio of nickel-based cathode material to cathode active material, and the H of the cathode electrode sheet. +The increased growth rate can significantly reduce battery gas production, ensure close contact between battery electrodes and separators, thereby reducing battery internal resistance and improving battery cycle performance. Detailed Implementation

[0010] This invention provides a battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising lithium manganese iron phosphate material and a nickel-based positive electrode material, wherein the molar ratio of the nickel-based positive electrode material to the positive electrode active material is c; in the 100% SOC state of the battery, the nickel-based positive electrode material comprises trivalent nickel and tetravalent nickel, wherein the total molar amount of trivalent and tetravalent nickel comprises a percentage of the total molar amount of nickel in the nickel-based positive electrode material; and the H of the positive electrode sheet... + The growth rate is b, and a, c, and b satisfy the relationship shown in equation I:

[0011] 0.008<(a×c) / b≤8.290, formula I.

[0012] In this invention, when a, b, and c satisfy the relationship shown in Equation I, the battery gas generation and expansion problems are significantly improved, and there is no black spot problem. The battery gas generation problem is comprehensively related to the values ​​of a, b, and c, H + The higher the ion growth rate, the larger b becomes, and the more severe the gas production. At this time, introducing an appropriate amount of high-valence Ni ions (a) is beneficial. Ni ions have stronger catalytic oxidation activity than Mn ions, which can further oxidize protonated hydrogen to produce absorbable gases such as CO and CO2, thereby changing the gas production pathway and reducing hydrogen production.

[0013] When the calculated value of (a×c) / b exceeds the upper limit of the expression, i.e., exceeds the maximum value, it may be due to an excessive amount of tetravalent and trivalent nickel elements, which can affect the battery capacity and reduce it. It could also be due to H... + If the growth rate b is too small, it indicates a small positive electrode surface active area, resulting in high lithium-ion diffusion resistance and poor battery kinetics. When the growth rate b exceeds the lower limit of the relationship, i.e., exceeds the minimum value, it may indicate an imbalance. + Excessive ion growth rate results in a large positive electrode active area, leading to severe dissolution of transition metal ions, damaging the SEI, and thus causing poor kinetics, increased DCR, and worsened cycle performance. Alternatively, the low content of trivalent and tetravalent nickel elements in the positive electrode material may prevent them from altering the gas production pathway, resulting in excessive hydrogen production and affecting battery safety.

[0014] Therefore, by controlling the values ​​of a, b, and c to satisfy the range of 0.008 < (a × c) / b ≤ 8.290, this invention can significantly reduce battery gas production, ensure tight contact between the battery electrodes and the separator, thereby reducing the battery's internal resistance and improving its cycle performance. In this invention, (a × c) / b can be any value between 0.008 and 8.290, such as 0.009, 0.010, 0.02, 0.025, 0.03, 0.05, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.5, 2.0, 2.5, 2.86, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.290.

[0015] The structural formula of lithium manganese iron phosphate in this invention is LiMn x Fe y M z n PO4, where M is a doping metal element, 0 < x < 1, 0 < y < 1, 0 ≤ z < 1, and 2(x + y) + n × z = 2, where n is the valence state of the doping metal element M. The doping element M is selected from at least one of Be, Ca, Mg, Ba, and Sr. In the embodiments of this invention, the lithium manganese iron phosphate material used is LiMn 0.6 Fe 0.4 Taking PO4 as an example, but not limited to this type of lithium manganese iron phosphate material.

[0016] As a preferred embodiment of the present invention, the percentage of the total molar amount of trivalent and tetravalent nickel elements in the total molar amount of nickel in the nickel-based cathode material, the molar ratio of nickel-based cathode material to cathode active material, and the H of the cathode electrode sheet are all specified. + The growth rate satisfies the following relationship:

[0017] 0.025 ≤ (a × c) / b ≤ 2.860

[0018] In this invention, the positive electrode active material includes lithium manganese iron phosphate material and nickel-based positive electrode material. In a fully charged state (100% SOC), the nickel-based positive electrode material includes trivalent nickel and tetravalent nickel. The percentage of the total molar amount of trivalent and tetravalent nickel in the total molar amount of nickel in the nickel-based positive electrode material is denoted as 'a'. A larger value of 'a' indicates a larger percentage of the total molar amount of trivalent and tetravalent nickel in the total molar amount of nickel in the nickel-based positive electrode material; a smaller value of 'a' indicates a smaller percentage of the total molar amount of trivalent and tetravalent nickel in the total molar amount of nickel in the nickel-based positive electrode material.

[0019] Compared to other valence states of nickel, trivalent and tetravalent nickel exhibit higher catalytic oxidation activity and are more easily reduced. The catalytic oxidation activity of trivalent and tetravalent nickel ions is stronger than that of Mn ions, allowing for further oxidation of protonated hydrogen to produce gases such as CO and CO2, which can be absorbed by the electrode, thus altering the gas production pathway and reducing hydrogen production. The a value is related to the amount of lithium nickel oxide (LNO) cathode material and nickel-containing ternary cathode material added. A high a value increases battery manufacturing costs; a low a value fails to achieve the desired effect of altering the gas production pathway.

[0020] In this invention, 0.3% ≤ a ≤ 23% can be any value between 0.3%, 0.5%, 0.7%, 1%, 3%, 5%, 7%, 9%, 10%, 12%, 14%, 15%, 17%, 19%, 20%, 21%, 23%, or 0.3% to 23%. In some preferred embodiments of this invention, 1% ≤ a ≤ 20%.

[0021] Therefore, by controlling the value of a to be within the range of 0.3%≤a≤23%, this invention can ensure that the effect of changing the gas generation path of the battery is achieved under the condition of low-cost battery preparation.

[0022] The test method for 'a' is not limited in this invention. Those skilled in the art can use conventional techniques to detect the percentage of the total molar amount of trivalent and tetravalent nickel elements in the total molar amount of nickel in the nickel-based cathode material. For example, the test method for 'a' includes the following steps:

[0023] With the battery at 100% SOC and fully charged, after cleaning the positive electrode, the peak areas of each valence state of nickel in the positive electrode were measured using XPS. 'a' was calculated according to formula II.

[0024] a=(S Ni 4+ +S Ni 3+ ) / S 总面积 Formula II;

[0025] In Equation II, S Ni 4+ This represents the area of ​​tetravalent nickel obtained from XPS testing;

[0026] S Ni 3+ This represents the area of ​​trivalent nickel obtained from XPS testing;

[0027] S 总面积 This represents the sum of the peak areas of nickel across all valence states obtained from XPS testing.

[0028] Specifically, the testing method includes the following steps:

[0029] The positive electrode sheet was disassembled when the battery was fully charged at 100% SOC. The positive electrode sheet was cleaned with DMC (dimethyl carbonate) and then dried to obtain the treated positive electrode sheet.

[0030] The present invention does not impose any particular limitation on the drying method; any drying method known to those skilled in the art is acceptable. In this invention, vacuum drying is preferred, the drying temperature is preferably 25°C, and the drying time is preferably 24 hours.

[0031] After the positive electrode is processed, it is etched by X-ray photoelectron spectroscopy (XPS) at a rate of 0.7 nm / s and an etching time of 60 s. The peak areas of each valence state are fitted according to the binding energy. The sum of the peak areas of trivalent nickel and tetravalent nickel and the total peak area of ​​nickel in all valence states are measured. The value of a is calculated according to the formula shown in Equation II.

[0032] In some preferred embodiments of the present invention, the molar ratio of trivalent nickel to tetravalent nickel is 1:10 to 6:10, and can be 1:10, 1.5:10, 2:10, 2.5:10, 3:10, 3.5:10, 4:10, 4.5:10, 5:10, 5.5:10, 6:10, or any value between 1:10 and 6:10. If the molar ratio of trivalent nickel to tetravalent nickel is too large, it indicates an excessive amount of trivalent nickel, resulting in a poor effect on changing the gas production path and failing to reduce hydrogen production; if the ratio is too small, it indicates an insufficient amount of trivalent nickel, leading to a significant decrease in battery life. When the molar ratio of trivalent nickel to tetravalent nickel is within the range of 1:10 to 6:10, it can not only effectively change the gas production path, thereby reducing hydrogen production, but also maintain battery life and prevent the battery life from decreasing too rapidly.

[0033] In this invention, the nickel-based cathode material is selected from one or more of lithium nickel oxide cathode materials or nickel-containing ternary cathode materials.

[0034] In some specific embodiments of the present invention, the nickel-containing ternary cathode material is selected from nickel-cobalt-manganese ternary cathode materials, wherein the nickel-cobalt-manganese ternary material is LiNi. x Co y Mn 1-x-y O2, where 0.9 < x < 1, 0 < y < 0.1, and x + y ≠ 1.

[0035] In this invention, there are no special restrictions on the source of the lithium nickel oxide cathode material or the nickel-containing ternary cathode material. It can be a commercially available product or a preparation method known to those skilled in the art.

[0036] In this invention, the preparation method of the lithium nickel-oxygen cathode material is not limited, and those skilled in the art can prepare the cathode active material using conventional techniques. Exemplarily, the preparation method of the lithium nickel-oxygen cathode material includes the following steps:

[0037] First, the lithium source and nickel source required for synthesizing lithium nickel oxide material are weighed in proportion and added to deionized water. After grinding and washing, the materials are spray-dried to obtain dry powder of lithium nickel oxide material. The dry powder is sintered under a protective atmosphere and cooled to obtain lithium nickel oxide cathode material.

[0038] In this invention, for LiNi x Co y Mn 1-x-y The preparation method of O2 is not limited, and those skilled in the art can prepare nickel-based cathode materials using conventional techniques. For example, a nickel-based cathode material precursor and a lithium source are mixed and sintered to obtain the nickel-based cathode material.

[0039] The nickel-based cathode material precursor can be one or more of oxides, hydroxides, and carbonates containing Ni, Co, and Mn in stoichiometric proportions, such as hydroxides containing Ni, Co, and Mn in stoichiometric proportions. The cathode active material precursor can be obtained by methods known in the art, such as co-precipitation, gelation, or solid-state methods.

[0040] As an example, Ni, Co, and Mn sources are dispersed in a solvent to obtain a mixed solution. Using a continuous co-current reaction, the mixed solution, strong alkali solution, and complexing agent solution are simultaneously pumped into a stirred reactor. The pH of the reaction solution is controlled at 10–13, and the temperature inside the reactor is maintained at 25°C–90°C. An inert gas is purged during the reaction for protection. After the reaction is complete...

[0041] After aging, filtration, washing and vacuum drying, a hydroxide containing Ni, Co and Mn is obtained.

[0042] In some embodiments of the present invention, the Ni source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, or nickel acetate; and / or the Co source includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, or cobalt acetate; and / or the Mn source includes at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, or manganese acetate; and / or the Li source includes at least one of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), or lithium nitrate (LiNO3).

[0043] The positive electrode active material precursor and lithium source can be mixed using a ball mill or high-speed mixer. The mixed material is then added to an atmosphere sintering furnace for sintering. The sintering atmosphere is an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere.

[0044] In addition, a coating process can be applied to nickel-based cathode materials. Specifically, a dry coating method (high-temperature solid-state method) is used to coat the surface of the nickel-based cathode material with a coating material, so that the surface of the nickel-based cathode material is partially or completely covered with a coating layer formed by the coating material. The coating layer contains at least one element selected from the following (hereinafter referred to as the "coating element"): aluminum (Al), titanium (Ti), tungsten (W), boron (B), phosphorus (P), cobalt (Co), yttrium (Y), and silicon (Si).

[0045] Furthermore, the particle size of the nickel-based cathode material is 40~200nm.

[0046] In this invention, the positive electrode active material further includes lithium manganese iron phosphate material, wherein the particle size of the lithium manganese iron phosphate material is 50~170nm.

[0047] In this invention, there are no special restrictions on the source of the lithium manganese iron phosphate material; it can be a commercially available product or a preparation method known to those skilled in the art.

[0048] In this invention, the preparation method of the lithium manganese iron phosphate material is not limited, and those skilled in the art can prepare the lithium manganese iron phosphate material using conventional techniques. Exemplarily, the preparation method of the lithium manganese iron phosphate material includes the following steps:

[0049] First, the lithium source, manganese source, iron source and phosphorus source required for synthesizing lithium manganese iron phosphate material are weighed in proportion and added to deionized water, and then ground to obtain lithium manganese iron phosphate precursor slurry.

[0050] A carbon source is added and mixed evenly with lithium manganese iron phosphate precursor slurry, then ground, and the solid content is adjusted and spray dried to obtain dry powder; the dry powder is sintered under a protective atmosphere and cooled to obtain positive electrode active material.

[0051] In this invention, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate; the manganese source is selected from at least one of manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate; the iron source is selected from at least one of ferrous oxalate, ferric hydroxide, ferrous hydroxide, ferric phosphate, ferrous phosphate, ferric acetate, ferrous acetate, ferric carbonate, ferrous carbonate, ferric oxide, magnetite, and ferric oxalate; the phosphorus source is selected from at least one of diammonium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate, and lithium phosphate. Preferably, ferric manganese phosphate is used as the manganese, iron, and phosphorus source simultaneously; or, preferably, ferric phosphate is used as the iron and phosphorus source simultaneously; the carbon source includes glucose.

[0052] The raw materials can be mixed using a ball mill or a high-speed mixer. The mixed raw materials are then dried to obtain the precursor.

[0053] The precursor is added to an atmosphere sintering furnace for sintering. The sintering atmosphere is an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere.

[0054] In addition, a coating process can be applied to lithium manganese iron phosphate materials. Specifically, a dry coating method (high-temperature solid-state method) is used to coat the surface of the lithium manganese iron phosphate material with a coating material, so that the surface of the lithium manganese iron phosphate material is partially or completely covered with a coating layer formed by the coating material. The coating layer contains at least one element selected from the following (hereinafter referred to as the "coating element"): aluminum (Al), titanium (Ti), tungsten (W), boron (B), phosphorus (P), cobalt (Co), yttrium (Y), and silicon (Si).

[0055] In this invention, the molar ratio c of nickel-based cathode material to cathode active material can also affect the gas production and performance of the battery.

[0056] A higher c-value indicates a higher content of nickel-based materials in the entire active material and a lower content of LMFP. Although this can change the gas production path of the battery and reduce hydrogen production, the lower LMFP content results in a significant reduction in battery capacity. Conversely, a lower c-value indicates a lower content of nickel-based materials in the entire active material, which cannot uniformly suppress gas production across the entire electrode, leading to excessive hydrogen production and affecting battery safety.

[0057] Therefore, by controlling the c value range to 0.5%≤c≤40%, this invention can ensure battery capacity while uniformly suppressing gas generation across the entire electrode.

[0058] In this invention, the value of c ranges from 0.5% to 40%, and can be 0.5%, 1%, 3%, 5%, 6%, 7%, 10%, 12%, 14%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 34%, 35%, 37%, or 40%. In some preferred embodiments of this invention, the value of c ranges from 5% to 30%.

[0059] The method for testing c is not limited in this invention. Those skilled in the art can detect the molar ratio of nickel-based cathode material to cathode active material using conventional techniques. For example, the method for testing c includes the following steps:

[0060] At 25°C, the battery was discharged from 0.33C to 2.5V. The battery was disassembled to obtain positive and negative electrode sheets. 2g of positive electrode powder and 2g of negative electrode powder were obtained from the positive electrode sheet and the negative electrode sheet, respectively. The molar percentage of Ni and Mn elements in the positive and negative electrode powders was determined by inductively coupled plasma (ICP). The selected element detection wavelengths were 257.61nm for Mn and 232.0nm for Ni. Based on the characteristics of the sample and the elements to be detected, appropriate ICP instrument operating conditions were set, including a gas flow rate of 0.5L / min and a power of 1150W. The content of Mn and Ni elements was determined by ICP, and the molar percentage c of the nickel-based positive electrode material in the positive electrode active material was calculated according to the formula shown in Equation VI.

[0061] c = (Total molar percentage of Ni in positive and negative electrode powders / Total molar percentage of nickel and manganese in positive and negative electrode powders) × 100% Equation VI

[0062] In this invention, H + The growth rate b can also affect the gas production of the battery and the battery performance.

[0063] H + The growth rate b represents the size of the active area of ​​the electrode, H + The larger the growth rate b, the larger the active area of ​​the electrode. + The smaller the growth rate b, the smaller the active area of ​​the electrode. + The growth rate b is related to factors such as the degree of carbon coating, particle size, and distribution of the active material. A high b value indicates that the electrochemical reaction on the electrode is easier to carry out or the reaction rate is faster. When the b value is too high, the reaction between the active material and the electrolyte is too high, which can easily trigger too many side reactions, leading to excessive gas production in the battery and black spots on the electrode. When the b value is too low, it indicates that the electrochemical reaction is difficult to carry out effectively. This may be due to the large particle size of the positive electrode active material and the large solid-phase diffusion resistance caused by the excessively thick carbon layer, resulting in poor overall battery kinetics.

[0064] Therefore, in this invention, it is necessary to control H. + The growth rate b ranges from 0.01 to 0.18, and can be any value between 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, and 0.18. In some preferred embodiments of the present invention, the value of b is 0.02 to 0.15.

[0065] By controlling the range of b to 0.01≤b≤0.18, this invention can ensure the effective conduct of the electrochemical reaction while maximizing the reaction rate.

[0066] The present invention does not limit the testing method for b; those skilled in the art can use conventional technical means to test H. + Growth rate detection, for example, H + The testing method for growth rate b includes the following steps:

[0067] Two sets of positive electrode sheets with the same area from a fully charged battery at 100% SOC were immersed in the same volume of solution. One set of positive electrode sheets was stored at 60℃ for 48 hours, and the H2O in the solution was measured. + The content of [unspecified substance] is m1, in ppm; another set of positive electrode plates were stored at 60℃ for 72 hours, and the H [unspecified substance] in the solution was measured. + The content of m2 is expressed in ppm; H + The growth rate b is calculated according to the formula shown in Equation III:

[0068] b=(m2-m1) / m1 Equation III;

[0069] The tested area of ​​the positive electrode sheet is 147 cm². 2 The test area was 147cm². 2 It can be the total area of ​​the positive electrode plates of multiple fully charged batteries. In some specific embodiments of the present invention, it can be three 7×7cm plates. 2 The positive electrode of a fully charged battery.

[0070] The solution is a mixed solution of ethylene carbonate EC, methyl ethyl carbonate EMC and lithium perchlorate. In the mixed solution, the concentration of lithium perchlorate is 1M, the volume ratio of ethylene carbonate EC to methyl ethyl carbonate EMC is 3:7, and the volume of the solution used is 20ml.

[0071] Specifically, the H in the solution stored for 48 hours + The test method for the content includes the following steps:

[0072] Prepare a 0.05 mol / L triethylamine titration solution using triethylamine and EMC;

[0073] EC and EMC were mixed in a volume ratio of 3:7 to form a 20 mL mixture. 2.13 g of lithium perchlorate was added to the mixture to obtain the soaking solution.

[0074] The test area is 147cm² 2 The positive electrode of a fully charged battery is mixed with an immersion solution and immersed at 60°C for 48 hours to obtain a 48-hour positive electrode immersion solution. 10-30 drops of methyl red are added to the 48-hour positive electrode immersion solution as an indicator. Triethylamine titrant is then added to the 48-hour positive electrode immersion solution containing methyl red. The amount of triethylamine titrant used, V1, is recorded when the 48-hour positive electrode immersion solution turns orange. The H2 content in the 48-hour solution is calculated using formula IV. + The content of m1;

[0075] m1=M×V1×20010 / m Equation IV

[0076] In Formula IV, M is the concentration of the titrant, in mol / L;

[0077] V1 is the volume of titrant consumed, in mL;

[0078] m represents the mass of the soaking solution, in grams.

[0079] Similarly, H in the solution stored for 72 hours + The test method for the content includes the following steps:

[0080] Prepare a 0.05 mol / L triethylamine titration solution using triethylamine and EMC;

[0081] EC and EMC were mixed in a volume ratio of 3:7 to form a 20 mL mixture. 2.13 g of lithium perchlorate was added to the mixture to obtain the soaking solution.

[0082] The test area is 147cm² 2 The positive electrode of a fully charged battery is mixed with an immersion solution and immersed for 72 hours at 60°C to obtain a 72-hour positive electrode immersion solution. 10-30 drops of methyl red are added to the 72-hour positive electrode immersion solution as an indicator. Triethylamine titrant is then added to the 72-hour positive electrode immersion solution containing methyl red. The amount of triethylamine titrant used, V2, is recorded when the 72-hour positive electrode immersion solution turns orange. The H2 concentration in the 72-hour solution is calculated using formula V. + The content of m2;

[0083] m1=M×V2×20010 / m (Formula V)

[0084] In Formula IV, M is the concentration of the titrant, in mol / L;

[0085] V2 is the volume of titrant consumed, in mL;

[0086] m represents the mass of the soaking solution, expressed in grams.

[0087] Substituting the obtained m1 and m2 into Equation III, we can calculate H. + The growth rate b.

[0088] In this invention, values ​​a and b are measured when the battery is at 100% SOC, and c is measured when the battery is at 0% SOC. Specifically, this invention defines 0% SOC as the battery being discharged from 0.33C to 2.5V at 25°C.

[0089] In the formula shown in Equation I, a×c can reflect the content of trivalent and tetravalent nickel elements in the entire positive electrode active material to a certain extent. The larger the value of a×c, the more trivalent and tetravalent nickel elements are present, and the smaller the value of a×c, the less trivalent and tetravalent nickel elements are present in the entire positive electrode active material.

[0090] In this invention, the value of a×c is controlled to satisfy the range of 0.001 ≤ a×c ≤ 0.092. When the value of a×c is lower than 0.01, it indicates that the content of trivalent and tetravalent nickel elements in the electrode is low, resulting in a decrease in the performance of the nickel-containing material in improving the gas generation path after the nickel-containing material is added to the electrode, that is, a decrease in the performance of the nickel-containing material in suppressing hydrogen generation. When the value of a×c is higher than 2.6, it indicates that the content of trivalent and tetravalent nickel elements in the electrode is excessive. This affects the content of lithium manganese iron phosphate in the positive electrode material, thereby reducing the cell capacity and the energy density of the battery.

[0091] Therefore, by controlling the value range of a×c to satisfy 0.001≤a×c≤0.092, the present invention can enable nickel-containing materials to have good performance in changing the gas production path of the battery, that is, reducing the production of hydrogen, while ensuring a good energy density of the battery.

[0092] In this invention, 0.001≤a×c≤0.092 can be any value between 0.001, 0.002, 0.003, 0.004, 0.005, 0.007, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.092, or 0.001~0.092. In some preferred embodiments of this invention, 0.003≤a×c≤0.06.

[0093] In this invention, the battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0094] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material. In addition to the positive active material, the positive active material layer may also contain a conductive agent and a binder.

[0095] Conductive agents are used to provide conductivity in the electrodes. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Preferred materials include carbon fibers such as carbon nanofibers, carbon black such as acetylene black and Ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, and carbon nanotubes.

[0096] The binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Therefore, the binder suitable for use in the embodiments is a fluorinated polyolefin binder, which may include, but is not limited to, polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives.

[0097] The present invention does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0098] In this invention, the positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material, conductive agent and binder are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector, and after drying, rolling and other processes, the positive electrode sheet is obtained.

[0099] The negative electrode sheet of the present invention includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and may also include a conductive agent and / or a binder.

[0100] The present invention does not impose any particular limitation on the negative electrode current collector, as long as it has high conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium or silver, or aluminum-cadmium alloy can be used.

[0101] For the negative electrode active material, the embodiments of the present invention do not specifically limit the type of the negative electrode active material, and it can be selected according to actual needs. As an example, the negative electrode active material can be natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO m (0 < m < 2, such as m = 1), lithium titanate Li4Ti5O with a spinel structure 12 or one or more of them.

[0102] The embodiments of the present invention do not specifically limit the types of the conductive agent and the binder in the negative electrode active material layer, and they can be selected according to actual needs. As an example, the conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder is one or more of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, water-based acrylic resin, and carboxymethyl cellulose. The negative electrode active material layer may also optionally include a thickening agent, such as carboxymethyl cellulose.

[0103] The electrolyte of the present invention can be various electrolytes in the art suitable for electrochemical energy storage devices. The electrolyte includes an electrolyte and a solvent, and the electrolyte usually includes a lithium salt.

[0104] Specifically, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte can be 0.5 - 5 mol / L.

[0105] Specifically, the solvent includes at least one selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). Based on the weight of the electrolyte, the weight content of the solvent can be 70-98%.

[0106] In addition, the electrolyte may also include additives. Specifically, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0107] The electrochemical device may further include a separator located between the positive and negative electrode plates to separate them and prevent short circuits. The separator can be any material suitable for separators in electrochemical energy storage devices. Specifically, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0108] This invention provides an electronic device comprising the battery described above. The electrochemical device serves as the power source for the electronic device.

[0109] The electronic device refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other energy forms, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, e-cigarettes, etc.; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0110] To further understand the present invention, the battery provided by the present invention will be described below with reference to embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0111] Example 1

[0112] 1) Preparation of LMFP cathode material:

[0113] According to LiMn 0.6 Fe 0.4 In the chemical formula PO4, the molar proportions of Li, Mn, Fe, and P were respectively measured as follows: 1 mol of lithium carbonate, 0.6 mol of manganese carbonate, 0.4 mol of ferrous oxalate, and 1 mol of diammonium hydrogen phosphate. These were added to deionized water and mixed. The mixture was then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 30% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. After preliminary filtration, the precursor was obtained. The precursor was then calcined in a tube furnace at a heating rate of 5 °C / min to 600 °C for 300 min, followed by a heating rate of 10 °C / min to 800 °C for 720 min. After natural cooling, LiMn was obtained. 0.6 Fe 0.4 PO4 aggregates. Then LiMn... 0.6 Fe 0.4 PO4 aggregates were crushed and ground for 8 hours, and then screened to obtain LiMn. 0.6 Fe 0.4 PO4 cathode material.

[0114] 2) Cathode preparation: Lithium manganese iron phosphate (LiMn) is used to prepare the cathode. 0.6 Fe 0.4 The main material is a homogeneous mixture of PO4 and lithium nickel oxide (LNO) cathode material at a molar ratio of 17.01:3.79. The main material is then homogeneously mixed with conductive agent SP and PVDF adhesive at a mass ratio of 96.5:1.5:2 in NMP. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode sheet is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C. It is then slit and dried in a vacuum furnace at 100°C. After that, it is rolled and cut to obtain the positive electrode sheet.

[0115] 3) Negative electrode preparation: Artificial graphite, conductive agent SP, and PVDF adhesive system were mixed uniformly at a mass ratio of 96.4:0.6:3 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry was then prepared with an areal density of 173 g / m³. 2 The coating is evenly applied to copper foil and dried in a vacuum environment at 100℃ for 12 hours. The resulting product is then slit and cut to a density of 1.65 g / cm³. 3 The compaction density is subjected to cold pressing to obtain the negative electrode sheet.

[0116] 4) Electrolyte preparation: The electrolyte uses EC:EMC=3:7 wt% as the solvent system, 1.15M LiPF6 as the lithium salt, and 1% VC (ethylene carbonate) and 1% MMDS (methylene disulfonate) as film-forming additives.

[0117] 5) Preparation of the separator: PP was selected as the separator.

[0118] 6) Battery assembly, formation, and capacity setting to form SEI / CEI: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. The electrolyte injection coefficient is adjusted. Formation is performed at 0.02C to 3.5V and 0.1C to 4.25V, forming a stable SEI on the negative electrode side. Excess gas is extracted through a second seal, and the battery is charged at 0.33C to the upper limit voltage. It is then charged at a constant voltage for 0.05C to the cutoff point and discharged at 0.33C to the lower limit voltage of 2.5V. This charge-discharge cycle is repeated twice to form a stable CEI on the positive electrode side.

[0119] Examples 2-18 and Comparative Examples 1-4

[0120] Examples 2-18 and Comparative Examples 1-4 each provide a lithium-ion battery, the preparation method of which is similar to that of Example 1, the difference being the type of nickel-based cathode material and the lithium manganese iron phosphate (LiMn) used in preparing the cathode sheet. 0.6 Fe 0.4 The ratio of PO4 and nickel-based cathode materials is shown in Table 1.

[0121] The testing methods for various parameters of the batteries prepared in each embodiment and comparative example are as follows:

[0122] ①The specific testing method for the value of a is as follows:

[0123] The positive electrode sheet was disassembled when the battery was fully charged at 100% SOC. The positive electrode sheet was cleaned with DMC (dimethyl carbonate) and then dried at 25°C for 24 hours to obtain the treated positive electrode sheet.

[0124] After obtaining the processed positive electrode, etching was performed using X-ray photoelectron spectroscopy (XPS). The instrument used was a NEXSA G2. In the instrument's manual control window, the test beam was set to 400 micrometers. Based on the element to be measured, the instrument automatically supplemented the test pass energy range. The etching dwell time was 50 ms, the step size was 1 eV, the etching rate was 0.7 nm / s, and the etching time was set to 60 s. After the test, the instrument automatically provided the results, and the peak areas of each valence state were calculated based on the binding energy.

[0125] a is calculated according to the formula shown in Equation II:

[0126] a=(S Ni 4+ +S Ni 3+ ) / S 总面积 Formula II;

[0127] In Equation II, S Ni 4+ This represents the area of ​​tetravalent nickel obtained from XPS testing;

[0128] S Ni 3+ This represents the area of ​​trivalent nickel obtained from XPS testing;

[0129] S 总面积 This represents the sum of the peak areas of nickel across all valence states obtained from XPS testing.

[0130] The calculated values ​​of 'a' are shown in Table 1.

[0131] ②The test method for the b value is as follows:

[0132] The positive electrode of a fully charged battery at 100% SOC was immersed in a solution and stored at 60°C for 48 hours. The H2 content in the solution was measured. + The content of [agent] m1 is expressed in ppm; then, the solution is stored at 60°C for 72 hours, and the H2 content is measured. + The content of m2 is expressed in ppm, H + The growth rate b is calculated according to the formula shown in Equation III:

[0133] b=(m2-m1) / m1 Equation III;

[0134] The tested area of ​​the positive electrode sheet is 147 cm². 2 Specifically, it consists of 3 pieces, each 7×7cm. 2 The positive electrode of a fully charged battery;

[0135] The solution is a mixed solution of ethylene carbonate EC, methyl ethyl carbonate EMC and lithium perchlorate. In the mixed solution, the concentration of lithium perchlorate is 1M, the volume ratio of ethylene carbonate EC to methyl ethyl carbonate EMC is 3:7, and the volume of the solution used is 20ml.

[0136] H in the solution after 48 hours of storage + The test method for the content includes the following steps:

[0137] Prepare a 0.05 mol / L triethylamine titration solution using triethylamine and EMC;

[0138] EC and EMC were mixed in a volume ratio of 3:7 to form a 20 mL mixture. 2.13 g of lithium perchlorate was added to the mixture to obtain the soaking solution.

[0139] Take 3 pieces of 7×7cm 2 The positive electrode of a fully charged battery is mixed with an immersion solution and immersed at 60°C for 48 hours to obtain a 48-hour positive electrode immersion solution. 10-30 drops of methyl red are added to the 48-hour positive electrode immersion solution as an indicator. Triethylamine titrant is then added to the 48-hour positive electrode immersion solution containing methyl red. The amount of triethylamine titrant used, V1, is recorded when the 48-hour positive electrode immersion solution turns orange. The H2 content in the 48-hour solution is calculated using formula IV. + The content of m1;

[0140] m1=M×V1×20010 / m Equation IV

[0141] In Formula IV, M is the concentration of the titrant, in mol / L;

[0142] V1 is the volume of titrant consumed, in mL;

[0143] m represents the mass of the soaking solution, in grams.

[0144] Similarly, H in the solution stored for 72 hours + The test method for the content includes the following steps:

[0145] Prepare a 0.05 mol / L triethylamine titration solution using triethylamine and EMC;

[0146] EC and EMC were mixed in a volume ratio of 3:7 to form a 20 mL mixture. 2.13 g of lithium perchlorate was added to the mixture to obtain the soaking solution.

[0147] Take 3 pieces of 7×7cm 2 The positive electrode of a fully charged battery is mixed with an immersion solution and immersed for 72 hours at 60°C to obtain a 72-hour positive electrode immersion solution. 10-30 drops of methyl red are added to the 72-hour positive electrode immersion solution as an indicator. Triethylamine titrant is then added to the 72-hour positive electrode immersion solution containing methyl red. The amount of triethylamine titrant used, V2, is recorded when the 72-hour positive electrode immersion solution turns orange. The H2 concentration in the 72-hour solution is calculated using formula V. + The content of m2;

[0148] m2=M×V2×20010 / m (Equation V)

[0149] In Formula IV, M is the concentration of the titrant, in mol / L;

[0150] V2 is the volume of titrant consumed, in mL;

[0151] m represents the mass of the soaking solution, expressed in grams.

[0152] Substituting the obtained m1 and m2 into Equation III, we can calculate H. + The growth rate b.

[0153] ③The test method for the c value is as follows:

[0154] Under conditions of 25℃, the battery was discharged from 0.33C to 2.5V. The battery was disassembled to obtain positive and negative electrode sheets. 2g of positive electrode powder was obtained from the positive electrode sheet and 2g of negative electrode powder was obtained from the negative electrode sheet. The molar percentage of Ni and Mn elements in the positive and negative electrode powders was tested by inductively coupled plasma (ICP). The molar percentage c of nickel-based positive electrode material in the positive electrode active material was calculated according to the formula shown in Equation VI.

[0155] c = (Total molar percentage of Ni in positive and negative electrode powders / Total molar percentage of nickel and manganese in positive and negative electrode powders) × 100% Equation VI

[0156] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the specific items and methods are as follows:

[0157] ① Room temperature cycling test method:

[0158] At 45℃, charge at 0.33C to 4.3V, discharge at 0.33C to 2.5V, and after two cycles of constant capacity, charge at 1C constant current and constant voltage to 4.3V at 45℃, and discharge at 1C constant current to 2.5V. Repeat this cycle 200 times. Record the discharge capacity of the 3rd cycle as C1, and the discharge capacity of the 200th cycle as C2. The capacity retention rate after 200 cycles is (C2 / C1)×100%.

[0159] ②DCR growth rate test method:

[0160] At 45℃, the battery was charged at 0.33C to 4.3V, then discharged at 0.33C to 2.5V, and subjected to two cycles of capacitance adjustment. At 45℃, it was then charged at 0.33C with constant current and constant voltage to 4.3V, then discharged at 0.33C to adjust the charge to 80% SOC. After standing for two hours, the 1C discharge for 18 seconds was measured and recorded as R0. The battery was then discharged at 0.33C to 2.5V at 45℃. This cycle was repeated at 45℃ with constant current and constant voltage at 1C to 4.3V, then discharged at 1C with constant current to 2.5V, for 200 cycles of 1C / 1C charge / discharge. Finally, at 45℃, the battery was charged again at 0.33C to 4.3V, then discharged at 0.33C to 2.5V, and subjected to two cycles of capacity adjustment. The battery was then discharged at 0.33C to adjust the charge to 80% SOC, and placed to stand for two hours. The 1C discharge for 18 seconds was measured and recorded as R0. DCR is denoted as R1, and the DCR growth rate over 200 laps is calculated as [(R1-R0) / R0]×100%.

[0161] The test results are shown in Table 1.

[0162] Table 1

[0163]

[0164] For the lithium-ion batteries prepared in the various embodiments of the present invention, their 200cls cycle capacity retention rate is ≥91.81% and their DCR growth rate is ≤10.25%. It can be seen that the lithium-ion batteries of the present invention reduce the gas production, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0165] The data from Examples 1-5 and Examples 10-11, combined with those from Examples 6-9, Examples 12-18, and Comparative Examples 1-4, show that when a, b, c, and a×c meet the preferred parameter range defined in this invention, the lithium-ion battery has lower internal resistance and relatively better cycle performance.

[0166] From Examples 1-5 and Examples 6-9, it can be seen that when the battery satisfies 0.008 < (a×c) / b ≤ 8.290, the lithium-ion battery has lower internal resistance and relatively higher cycle performance.

[0167] As can be seen from the results of Comparative Examples 1 to 4, even when a, b, c, and a×c meet the parameter ranges defined in this invention, lithium-ion batteries have high internal resistance and poor cycle performance when the battery does not meet the range of 0.008 < (a×c) / b ≤ 8.290.

[0168] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A battery, characterized in that, The cathode includes a positive electrode sheet, which comprises a positive electrode active material, including lithium manganese iron phosphate material and a nickel-based positive electrode material. The nickel-based positive electrode material includes trivalent and tetravalent nickel elements. The nickel-based positive electrode material is selected from nickel-containing ternary positive electrode materials, specifically nickel-cobalt-manganese ternary positive electrode materials, where the nickel-cobalt-manganese ternary material is LiNi. x Co y Mn 1-x-y O2, where 0.9 < x < 1, 0 < y < 0.1; The molar ratio of the nickel-based cathode material to the cathode active material is c; in the 100% SOC state of the battery, the percentage of the total molar amount of trivalent and tetravalent nickel elements to the total molar amount of nickel in the nickel-based cathode material is a; the H of the cathode sheet + The growth rate is b, and a, c, and b satisfy the relationship shown in equation I: 0.025<(a×c) / b≤2.860, formula I; In Formula I, 0.3%≤a≤23%, 0.01≤b≤0.18, and 0.5%≤c≤40%; The values ​​of a and b are measured when the battery is at 100% SOC, and the value of c is measured when the battery is at 0% SOC. H + The testing method for growth rate b includes the following steps: Two sets of positive electrode sheets with the same area from a fully charged battery at 100% SOC were immersed in the same volume of solution. One set of positive electrode sheets was stored at 60℃ for 48 hours, and the H2O in the solution was measured. + The content of [unspecified substance] is m1, in ppm; another group of positive electrode sheets were stored at 60℃ for 72 hours, and the H2 content in the solution was measured. + The content of m2 is expressed in ppm; H + The growth rate b is calculated according to the formula shown in Equation III: b= (m2-m1) / m1 Formula III The tested area of ​​the positive electrode is 147 cm². 2 .

2. The battery according to claim 1, characterized in that, 1%≤a≤20%。 3. The battery according to claim 1, characterized in that, 0.02≤b≤0.15。 4. The battery according to claim 1, characterized in that, 5%≤c≤30%。 5. The battery according to claim 1, characterized in that, 0.001≤a×c≤0.

092.

6. The battery according to claim 1, characterized in that, 0.003≤a×c≤0.

06.

7. The battery according to claim 1, characterized in that, The molar ratio of trivalent nickel to tetravalent nickel is 1:10 to 6:

10.

8. The battery according to claim 1, characterized in that, The battery also includes a negative electrode, a separator, and an electrolyte; The negative electrode sheet includes a negative electrode active material, which is selected from natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon-carbon composites, and SiO2. m 0 <m<2、Li4Ti5O 12 One or more of the following; The diaphragm is selected from PP, PE, and PP / PF. The electrolyte comprises a lithium salt and a solvent, wherein the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, or lithium bis(oxalate borate), and the solvent is selected from one or more of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, or dimethyl carbonate.

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