Lithium ion secondary battery, positive electrode active material, preparation method and electric equipment

Abstract

The invention relates to the technical field of secondary batteries, in particular to a lithium ion secondary battery, a positive electrode active material, a preparation method and electric equipment, the positive electrode active material of the lithium ion secondary battery comprises a first part and a second part, in the positive electrode active material, the content of a nickel element in a transition element is greater than or equal to 0.85, and the content of a nickel element in the transition element is greater than or equal to 0.85. In a scanning electron microscope picture with the magnification factor of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; based on the total number of the secondary particles of the positive electrode active material, the number ratio of the secondary particles of the first part is 70%-85%, and the number ratio of the secondary particles of the second part is 15%-30%. Therefore, the volume energy density and the stability of the lithium ion secondary battery are improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to lithium-ion secondary batteries, positive electrode active materials, preparation methods and electrical equipment. Background Art

[0002] In recent years, lithium-ion secondary batteries have been widely used in wireless communications, transportation, aerospace, etc. High-nickel ternary positive electrode active materials have attracted widespread attention due to their advantages such as high energy density and high rate, but the stability of lithium-ion secondary batteries is a problem that needs to be solved urgently. Summary of the invention

[0003] In view of this, the main technical problem to be solved by the present application is how to improve the stability of lithium-ion secondary batteries.

[0004] To solve the above technical problems, the first technical solution adopted in the present application is: to provide a lithium-ion secondary battery, the lithium-ion secondary battery includes a positive electrode plate, a negative electrode plate and an electrolyte; the positive electrode plate includes a positive electrode active material, the positive electrode active material includes a first part and a second part, in the positive electrode active material, the content of nickel in the transition element is greater than or equal to 0.85, and in the scanning electron microscope image of the positive electrode active material with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; based on the total number of secondary particles of the positive electrode active material, the number of secondary particles in the first part accounts for 70% to 85%, and the number of secondary particles in the second part accounts for 15% to 30%.

[0005] In the technical solution of the embodiment of the present application, the active particles in the positive electrode active material include secondary particles of the first part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1.1, and secondary particles of the second part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1 and less than 1.1, the secondary particles of the first part are closer to non-spherical than the secondary particles of the second part, and the secondary particles of the second part are closer to spherical than the secondary particles of the first part. The secondary particles of the first part account for 70% to 85% of the total number of secondary particles of the positive electrode active material, and the secondary particles of the second part account for 15% to 30% of the total number of secondary particles of the positive electrode active material. When the pole piece is coated and cold pressed, the secondary particles in the pole piece that are close to non-spherical can better relieve pressure, reduce pole piece deformation, and reduce the degree of pole piece extension, thereby improving the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the secondary particles that are close to non-spherical can effectively alleviate the stress changes caused by squeezing each other when the particles expand, reduce pole piece expansion and alleviate particle breakage, thereby improving the stability of the lithium-ion secondary battery.

[0006] In one embodiment, the positive electrode sheet has a compaction density of 3.3 g / cm2 under a pressure of 5 T (tons). 3 ~3.8g / cm 3 .

[0007] In an embodiment of the present application, the compaction density of the positive electrode plate is within the above range, and the gap between the secondary particles in the first part and the secondary particles in the second part is smaller, so that the two types of particles account for a larger proportion per unit volume in the positive electrode plate, which can improve the volume energy density of the battery cell.

[0008] In one embodiment, the volume average particle size Dv50 of the secondary particles of the positive electrode active material is 8 μm to 11 μm.

[0009] In the embodiment of the present application, when the volume average particle size Dv50 of the secondary particles of the positive electrode active material is within the above range, the electrochemical performance of the lithium ion secondary battery can be improved.

[0010] In one embodiment, the longest diameter of the secondary particles of the first portion is in the range of 2 μm to 18 μm, and the shortest diameter is in the range of 2 μm to 16.5 μm.

[0011] In the embodiment of the present application, when the longest diameter and the shortest diameter of the secondary particles of the first part are within the above ranges, the electrochemical performance of the lithium ion secondary battery can be improved.

[0012] In one embodiment, the longest diameter of the secondary particles of the second portion is in the range of 2 μm to 18 μm, and the shortest diameter is in the range of 1 μm to 16 μm.

[0013] In the embodiment of the present application, when the longest diameter and the shortest diameter of the secondary particles of the first part are within the above ranges, the electrochemical performance of the lithium ion secondary battery can be improved.

[0014] In one embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently include a main material, and the main material has a structural formula of Li a Ni b Co c Mn d M (1-b-c-d) O n materials, wherein M includes one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti, 0.5≤a≤1.2, 0.85≤b≤0.99, 0 <c≤0.1,0<d≤0.05,b+c+d≤1,1.9≤n≤2.2。

[0015] In the embodiment of the present application, the secondary particles of the positive electrode active material include Li a Nib Co c Mn d M (1-b-c-d) O n The active material of the positive electrode comprises at least 0.85 of the total transition metal content, and the positive electrode active material also comprises transition metal elements Co and Mn, so that the lithium ion secondary battery has better electrochemical performance. In addition, the positive electrode active material can also be doped with any one or more of the metal elements such as Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, etc. to improve the stability of the lithium ion secondary battery.

[0016] In one embodiment, the host material includes lithium nickel cobalt manganese oxide, and the molar content of nickel in all transition metal elements is greater than or equal to 0.85.

[0017] In the embodiment of the present application, the main material of the positive electrode active material includes lithium nickel cobalt manganese oxide, and the molar content of nickel in all transition metal elements is greater than or equal to 0.85, so that the lithium ion secondary battery has better electrochemical performance.

[0018] In one embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently include a first coating layer, and the first coating layer includes one or more of Co, Al, F, and Ti. Based on the mass of the first part and the second part of the positive electrode active material, the mass of the first coating layer accounts for 1.65% to 2.00%.

[0019] In the embodiment of the present application, the residual alkali generated when preparing the positive electrode active material will be consumed during the coating process of the first coating layer. The residual alkali will produce a large amount of gas under high pressure and will also aggravate the side reaction of the positive electrode active material and the electrolyte. Therefore, the reduction of the residual alkali can improve the safety of the lithium-ion secondary battery. In addition, the role of coating the secondary particles of the first part and the second part of the positive electrode active material with a coating layer is that the coating layer can reduce the side reaction on the surface of the positive electrode active material, thereby improving the electrochemical performance of the lithium-ion secondary battery.

[0020] In one embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently include a second coating layer, and the second coating layer includes one or more of B, Al, and Y. Based on the mass of the positive electrode active material, the mass proportion of the second coating layer is 0.1% to 0.25%.

[0021] In an embodiment of the present application, a second coating layer containing one or more of B, Al, and Y is coated on the surface of the positive electrode active material to improve the structural stability of the secondary particles and inhibit side reactions on the surface of the secondary particles, thereby significantly improving the cycle stability and safety of the positive electrode active material.

[0022] In one embodiment, in the first part and / or the second part, the content of nickel in the transition elements is greater than or equal to 0.85.

[0023] In the embodiment of the present application, in the first part and / or the second part, the content of nickel in the transition elements is greater than or equal to 0.85, which can make the lithium-ion secondary battery have better electrochemical performance.

[0024] In one embodiment, the average primary particle size of the first part is 50 nm to 2 μm.

[0025] In an embodiment of the present application, the average particle size of the primary particles of the first part is in the range of 50nm to 2μm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery and making the electrochemical performance of the lithium-ion secondary battery better.

[0026] In one embodiment, the average primary particle size of the first part is 100 nm to 500 nm.

[0027] In an embodiment of the present application, the average particle size of the primary particles of the first part is in the range of 100nm to 500nm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery, and can make the electrochemical performance of the lithium-ion secondary battery better.

[0028] In one embodiment, the average primary particle size of the second part is 50 nm to 2 μm.

[0029] In an embodiment of the present application, the average particle size of the primary particles of the second part is in the range of 50nm to 2μm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery, and can make the electrochemical performance of the lithium-ion secondary battery better.

[0030] In one embodiment, the average primary particle size of the second part is 100 nm to 500 nm.

[0031] In an embodiment of the present application, the average particle size of the primary particles of the second part is in the range of 100nm to 500nm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery, and can make the electrochemical performance of the lithium-ion secondary battery better.

[0032] In a second aspect, the present application provides a positive electrode active material, which includes a first part and a second part. In the positive electrode active material, the content of nickel in the transition elements is greater than or equal to 0.85. In a scanning electron microscope image of the positive electrode active material with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; in the scanning electron microscope image with a magnification of 2K, based on the total number of secondary particles of the positive electrode active material, the number of secondary particles in the first part accounts for 70% to 85%, and the number of secondary particles in the second part accounts for 15% to 30%.

[0033] In the technical solution of the embodiment of the present application, the active particles in the positive electrode active material include secondary particles of the first part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1.1, and secondary particles of the second part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1 and less than 1.1. The secondary particles of the first part are closer to non-spherical than the secondary particles of the second part, and the secondary particles of the second part are closer to spherical than the secondary particles of the first part. The secondary particles of the first part account for 70% to 85% of the total number of secondary particles of the positive electrode active material, and the secondary particles of the second part account for 15% to 30% of the total number of secondary particles of the positive electrode active material. When the pole piece is coated and cold pressed, the secondary particles in the pole piece that are close to non-spherical can better relieve pressure, reduce pole piece deformation, and reduce the degree of pole piece extension, thereby improving the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the secondary particles that are close to non-spherical can effectively alleviate the stress changes caused by squeezing each other when the particles expand, reduce pole piece expansion and alleviate particle breakage, thereby improving the stability of the lithium-ion secondary battery.

[0034] The present application provides a method for preparing a lithium-ion secondary battery in a third aspect, comprising: providing a positive electrode sheet, a negative electrode sheet and a separator to prepare a lithium-ion secondary battery; the positive electrode sheet comprises a positive electrode active material, wherein the method for preparing the positive electrode active material comprises: adding a precipitant and a complexing agent to a solution comprising a nickel source, a manganese source and a cobalt source for reaction to obtain a positive electrode active material precursor; sintering the positive electrode active material precursor with a lithium source to obtain the positive electrode active material; in the positive electrode active material, the content of nickel in the transition element is greater than or equal to 0.85; or the method for preparing the positive electrode active material comprises: mixing a first part of the positive electrode active material The positive electrode active material is prepared by mixing a first part of positive electrode active material and a second part of positive electrode active material to obtain a positive electrode active material, wherein, in a scanning electron microscope image of the positive electrode active material at a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1, based on the total number of secondary particles of the positive electrode active material, the number of secondary particles of the first part accounts for 70% to 85%, and the number of secondary particles of the second part accounts for 15% to 30%, and in the positive electrode active material, the content of nickel in the transition elements is greater than or equal to 0.85.

[0035] In the technical scheme of the embodiment of the present application, by adding a precipitant and a chelating agent to a solution containing a nickel source, a manganese source and a cobalt source, it is beneficial to control the morphology of the precursor particles of the positive electrode active material, and then control the morphology of the secondary particles of the positive electrode active material, or, by mixing the first part of the positive electrode active material and the second part of the positive electrode active material with the above morphology to obtain the positive electrode active material, by providing the above-mentioned positive electrode active material, when the electrode is coated and cold pressed, the secondary particles in the electrode that are close to non-spherical can better relieve pressure, reduce electrode deformation, and reduce the degree of extension of the electrode, thereby improving the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the secondary particles that are close to non-spherical can effectively alleviate the stress changes caused by squeezing each other when the particles expand, reduce the expansion of the electrode and alleviate particle breakage, thereby improving the stability of the lithium-ion secondary battery.

[0036] In one embodiment, the precipitating agent comprises at least one of sodium carbonate, sodium hydroxide and potassium carbonate.

[0037] In the technical solution of the embodiment of the present application, the precipitant can react with the nickel source, the manganese source and the cobalt source to generate hydroxide and / or basic salt precipitates corresponding to each of them, and then the precipitates are sintered to obtain a positive electrode active material precursor.

[0038] In one embodiment, the concentration of the precipitant is 1 mol / L to 7 mol / L.

[0039] In the technical solution of the embodiment of the present application, the concentration of the precipitant is within the above range, which is beneficial to controlling the morphology of the positive electrode active material precursor particles.

[0040] In one embodiment, the concentration of the precipitant is 3 mol / L to 6 mol / L.

[0041] In the technical solution of the embodiment of the present application, the concentration of the precipitant is within the above range, which is beneficial to controlling the morphology of the positive electrode active material precursor particles.

[0042] In one embodiment, the complexing agent includes at least one of aqueous ammonia, ammonium chloride and ammonium sulfate.

[0043] In the technical solution of the embodiment of the present application, at least one of ammonia water, ammonium chloride and ammonium sulfate can be used as a complexing agent to effectively complex metal ions such as Ni, Co, Mn, etc. in the liquid, which helps to control the composition of the positive electrode active material precursor.

[0044] In one embodiment, the concentration of the complexing agent is 0.3 mol / L to 0.7 mol / L.

[0045] In the technical solution of the embodiment of the present application, the concentration of the complexing agent is controlled within the range of 0.3 mol / L to 0.7 mol / L, which not only reduces the disturbance of the precipitation equilibrium caused by the addition of raw materials and controls the supersaturation of the precipitate in the solution, but also reduces the rate of nucleation and growth, allowing the crystals to grow slowly, thereby facilitating the regulation of the particle size uniformity of the positive electrode active material precursor.

[0046] In one embodiment, the concentration of the complexing agent is 0.3 mol / L to 0.55 mol / L.

[0047] In the technical solution of the embodiment of the present application, the concentration of the complexing agent is controlled within the range of 0.3 mol / L to 0.55 mol / L, which not only reduces the disturbance of the precipitation equilibrium caused by the addition of raw materials and controls the supersaturation of the precipitate in the solution, but also reduces the rate of nucleation and growth, allowing the crystals to grow slowly, thereby facilitating the regulation of the particle size uniformity of the positive electrode active material precursor.

[0048] In one embodiment, in the step of adding a precipitant and a complexing agent to a solution of a nickel source, a manganese source and a cobalt source for reaction, the pH value is 10-15 and the temperature is 50° C.-70° C.

[0049] In the technical solution of the embodiment of the present application, controlling the pH and reaction temperature of the coprecipitation reaction process within the above range is beneficial to controlling the morphology of the positive electrode active material precursor.

[0050] In one embodiment, in the step of adding a precipitant and a complexing agent to a solution of a nickel source, a manganese source and a cobalt source for reaction, the pH value is 12 to 14.5 and the temperature is 55° C. to 65° C.

[0051] In the technical solution of the embodiment of the present application, controlling the pH and reaction temperature of the coprecipitation reaction process within the above range is beneficial to controlling the morphology of the positive electrode active material precursor.

[0052] In one embodiment, in the step of sintering the positive electrode active material precursor and the lithium source, the sintering temperature is 700° C. to 780° C., and the sintering time is 7 h to 14 h.

[0053] In the technical solution of the embodiment of the present application, the sintering temperature and the sintering time are controlled within the above range, so that lithium can be better diffused into the interior of the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance.

[0054] In one embodiment, in the step of sintering the positive electrode active material precursor and the lithium source, the sintering temperature is 720° C. to 760° C., and the sintering time is 8 h to 13 h.

[0055] In the technical solution of the embodiment of the present application, the sintering temperature and the sintering time are controlled within the above range, so that lithium can be better diffused into the interior of the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance.

[0056] In one embodiment, the step of sintering the positive electrode active material precursor with the lithium source is to sinter the positive electrode active material precursor, the lithium source and the element M source, wherein M includes one or more of the elements Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti.

[0057] In the technical solution of the embodiment of the present application, adding one or more metal elements such as Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, etc. into the positive electrode active material can improve the crystal structure of the material, reduce the distortion of the layered structure, and thus improve the structural stability and cycle life of the positive electrode active material.

[0058] In one embodiment, after the step of sintering the positive electrode active material precursor and the lithium source, it further includes: adding a first coating element source for sintering, and the first coating element source includes one or more of Co, Al, F, and Ti.

[0059] In the embodiment of the present application, the residual alkali generated when preparing the positive electrode active material will be consumed during the coating process of the first coating layer. The residual alkali will produce a large amount of gas under high pressure and will also aggravate the side reaction between the positive electrode active material and the electrolyte. Therefore, the reduction of the residual alkali can improve the safety of the lithium-ion secondary battery. In addition, the role of coating the secondary particles of the positive electrode active material with a coating layer is that the coating layer can reduce the side reaction on the surface of the positive electrode active material, thereby improving the electrochemical performance of the lithium-ion secondary battery.

[0060] In one embodiment, after the step of sintering the positive electrode active material precursor and the lithium source, the step further includes: adding a second coating element source for sintering, wherein the second coating element includes one or more of B, Al, and Y.

[0061] In an embodiment of the present application, a second coating layer containing one or more of B, Al, and Y is coated on the surface of the positive electrode active material to improve the structural stability of the secondary particles and inhibit side reactions on the surface of the secondary particles, thereby significantly improving the cycle stability and safety of the positive electrode active material.

[0062] A fourth aspect of the present application provides an electrical device, comprising the lithium ion secondary battery of the first aspect or / and the positive electrode active material of the second aspect or / and the method for preparing the lithium ion secondary battery of the third aspect.

[0063] The lithium-ion secondary battery of the embodiment of the present application has at least the same advantages as the lithium-ion secondary battery of the first aspect, or / and at least the same advantages as the positive electrode active material of the second aspect, or / and at least the same advantages as the lithium-ion secondary battery prepared by the preparation method of the lithium-ion secondary battery of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 is a schematic structural diagram of a vehicle according to an embodiment of the present application;

[0065] Figure 2 is a schematic diagram of the exploded structure of a secondary battery according to one embodiment of the present application;

[0066] Figure 3 is a schematic diagram of the exploded structure of a battery cell according to an embodiment of the present application;

[0067] Figure 4 1 is a scanning electron microscope image of a positive electrode active material according to an embodiment of the present application. DETAILED DESCRIPTION

[0068] Below, the battery cells, batteries and electrical equipment of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0069] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination 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 "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0071] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0072] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0073] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, "include" and "comprising" may represent that other components not listed may also be included or only listed components may be included or only listed components may be included.

[0074] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0075] High-nickel ternary positive electrode active materials are widely used in lithium-ion secondary batteries due to their advantages such as high energy density and high rate. In order to improve the volume energy density of lithium-ion secondary batteries, high-nickel ternary positive electrode active materials are usually prepared into spherical shapes so that the compaction density of the positive electrode sheets can be increased when they are prepared as positive electrode sheets and cold pressed. However, although the compaction density of the positive electrode sheets is increased after cold pressing in this method, the degree of elongation of the positive electrode sheets is relatively high, which significantly reduces the volume energy density of the lithium-ion secondary battery. In addition, when the lithium-ion secondary battery is cyclically charged and discharged, the particles of the high-nickel ternary positive electrode active materials will expand and contract, which will cause the particles to break and increase side reactions, ultimately resulting in a lower capacity and poorer cycle performance of the lithium-ion secondary battery.

[0076] Based on the above problems, the first aspect of the present application provides a lithium-ion secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte; the positive electrode plate includes a positive electrode active material, the positive electrode active material includes a first part and a second part, in the positive electrode active material, the content of nickel in the transition elements is greater than or equal to 0.85, and in a scanning electron microscope image of the positive electrode active material with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; based on the total number of secondary particles of the positive electrode active material, the number of secondary particles in the first part accounts for 70% to 85%, and the number of secondary particles in the second part accounts for 15% to 30%.

[0077] Secondary particles are formed by the agglomeration of primary particles, and primary particles are crystals that grow from a crystal nucleus.

[0078] The active particles in the positive electrode active material include secondary particles of the first part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1.1, and secondary particles of the second part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1 and less than 1.1. The secondary particles of the first part are closer to non-spherical than the secondary particles of the second part, and the secondary particles of the second part are closer to spherical than the secondary particles of the first part. The secondary particles of the first part account for 70% to 85% of the total number of secondary particles of the positive electrode active material, and the secondary particles of the second part account for 15% to 30% of the total number of secondary particles of the positive electrode active material. Compared with the secondary particles of the second part that tend to be spherical, the secondary particles of the first part that tend to be non-spherical account for a larger proportion in the positive electrode active material, and the secondary particles of the first part and the secondary particles of the second part cooperate with each other to form a "rivet-like" effect, so that the secondary particles of the first part and the secondary particles of the second part are more firmly combined. When the electrode is coated and cold pressed, the non-spherical secondary particles in the electrode can better relieve pressure, reduce electrode deformation, and reduce the extension of the electrode, thereby increasing the load of the positive electrode, thereby increasing the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the non-spherical secondary particles can effectively alleviate the stress changes caused by the expansion of the particles, reduce the expansion of the electrode and alleviate the crushing of the particles, thereby improving the stability of the lithium-ion secondary battery. Among them, the total number of secondary particles of the positive electrode active material refers to the total number of secondary particles of all positive electrode active materials in the field of view of a scanning electron microscope with a magnification of 2K times.

[0079] Among them, in the positive electrode active material, the content of nickel in the transition element can be 0.85, 0.88, 0.9, 0.95, 0.99, etc., or a range consisting of any two of the above values, for example, 0.85-0.9, 0.9-0.95, 0.95-0.99, etc. The ratio of the longest diameter to the shortest diameter of the secondary particles of the first part can be 1.1, 1.2, 1.5, 2, etc., or a range consisting of any two of the above values, for example, 1.1-1.2, 1.2-1.5, 1.5-2, etc.

[0080] The ratio of the longest diameter to the shortest diameter of the secondary particles of the first part may be 1.1, 1.2, 1.5, 2, etc., or a range consisting of any two of the above values, for example, 1.1-1.2, 1.2-1.5, 1.5-2, etc. The ratio of the longest diameter to the shortest diameter of the secondary particles of the second part may be 1, 1.02, 1.05, 1.09, etc., or a range consisting of any two of the above values, for example, 1-1.05, 1.05-1.09, etc.

[0081] The amount of secondary particles in the first part may be 70%, 75%, 80%, 85%, etc., or a range consisting of any two of the above values, for example, 70% to 75%, 75% to 80%, 80% to 85%, etc. The amount of secondary particles in the second part may be 15%, 20%, 25%, 30%, etc., or a range consisting of any two of the above values, for example, 15% to 25%, 25% to 30%, etc.

[0082] In one embodiment, the positive electrode sheet has a compaction density of 3.3 g / cm2 under a pressure of 5 T (tons). 3 ~3.8g / cm 3 .

[0083] When the compaction density of the positive electrode sheet is within the above range, the gap between the secondary particles in the first part and the secondary particles in the second part is smaller, so that the two types of particles account for a larger proportion per unit volume in the positive electrode sheet, which can improve the volume energy density of the battery cell.

[0084] Among them, the compaction density of the positive electrode sheet can be 3.3g / cm under a pressure of 5T (tons). 3 、3.4g / cm 3 、3.6g / cm 3 、3.7g / cm 3 、3.8g / cm 3 etc., or a range consisting of any two of the above values, for example, 3.3 g / cm 3 ~3.4g / cm 3 、3.4g / cm 3 ~3.6g / cm 3 、3.6g / cm 3 ~3.8g / cm 3 wait.

[0085] In one embodiment, the volume average particle size Dv50 of the secondary particles of the positive electrode active material is 8 μm to 11 μm.

[0086] By controlling the volume average particle size Dv50 of the secondary particles of the positive electrode active material to be 8 μm to 11 μm, the electrochemical performance of the lithium ion secondary battery can be improved.

[0087] Specifically, by controlling the volume average particle size Dv50 of the secondary particles of the positive electrode active material to be 8μm to 11μm, the specific surface area of ​​the secondary particles of the positive electrode active material is within a preferred range, so that the positive electrode active material has more sites for lithium insertion and delithiation, ensuring a higher energy density of the lithium-ion secondary battery.

[0088] The volume average particle size Dv50 of the positive electrode active material may be 8 μm, 8.5 μm, 8.9 μm, 9.4 μm, 9.8 μm, 10.5 μm, 11 μm, etc. or a range consisting of any two of the above values, for example, 8.5 μm to 9.8 μm, 9.8 μm to 11 μm, etc.

[0089] In one embodiment, the longest diameter of the secondary particles of the first portion is in the range of 2 μm to 18 μm, and the shortest diameter is in the range of 2 μm to 16.5 μm.

[0090] When the longest diameter and the shortest diameter of the secondary particles of the first part are within the above ranges, the electrochemical performance of the lithium ion secondary battery can be improved.

[0091] The longest diameter of the secondary particles of the first part may be 2 μm, 5 μm, 10 μm, 14.5 μm, 18 μm, etc., or a range consisting of any two of the above values, for example, 2 μm to 10 μm, 10 μm to 14.5 μm, 14.5 μm to 18 μm, etc. The shortest diameter of the secondary particles of the first part may be 2 μm, 2.5 μm, 5 μm, 10 μm, 16.5 μm, etc., or a range consisting of any two of the above values, for example, 2 μm to 5 μm, 5 μm to 10 μm, 10 μm to 16.5 μm, etc.

[0092] In one embodiment, the longest diameter of the secondary particles of the second portion is in the range of 2 μm to 18 μm, and the shortest diameter is in the range of 1 μm to 16 μm.

[0093] When the longest diameter and the shortest diameter of the secondary particles of the first part are within the above ranges, the electrochemical performance of the lithium ion secondary battery can be improved.

[0094] The longest diameter of the secondary particles of the second part may be 2 μm, 5 μm, 10 μm, 14.5 μm, 18 μm, etc., or a range consisting of any two of the above values, for example, 2 μm to 10 μm, 10 μm to 14.5 μm, 14.5 μm to 18 μm, etc. The shortest diameter of the secondary particles of the second part may be 1 μm, 2.5 μm, 5 μm, 10 μm, 16 μm, etc., or a range consisting of any two of the above values, for example, 1 μm to 5 μm, 5 μm to 10 μm, 10 μm to 16 μm, etc.

[0095] In one embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently include a main material, and the main material has a structural formula of Li a Ni b Co c Mn d M (1-b-c-d) O nmaterials, wherein M includes one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti, 0.5≤a≤1.2, 0.85≤b≤0.99, 0 <c≤0.1,0<d≤0.05,b+c+d≤1,1.9≤n≤2.2。

[0096] The secondary particles of the positive electrode active material include Li a Ni b Co c Mn d M (1-b-c-d) O n The active material of the positive electrode comprises at least 0.85 of the total transition metal content, and the positive electrode active material also comprises transition metal elements Co and Mn, so that the lithium ion secondary battery has better electrochemical performance. In addition, the positive electrode active material can also be doped with any one or more of the metal elements such as Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, etc. to improve the stability of the lithium ion secondary battery.

[0097] Among them, Li a It is used to provide Li intercalation and deintercalation on the positive and negative electrodes during the cycle charge and discharge process of lithium-ion secondary batteries. + The value of a can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, etc., or a range consisting of any two of the above values, for example, 0.5≤a≤0.7, 0.7≤a≤0.9, 0.9≤a≤1.2, etc.

[0098] Ni b Co c Mn dThat is, the ternary material of the ternary material. The presence of nickel ions increases the unit cell parameters, which helps to increase the gram capacity of the positive electrode active material. Cobalt ions can inhibit the problem of cation mixing in the material, improve the electronic conductivity of the material, and improve the cycle performance of the lithium-ion secondary battery. However, too high a cobalt content will also lead to a decrease in the actual capacity. Manganese ions can stabilize the material structure, increase the safety of lithium-ion secondary batteries, and reduce costs. However, excessive cobalt and manganese content will reduce the gram capacity of lithium-ion secondary batteries. The value of b can be 0.85, 0.87, 0.9, 0.93, 0.96, 0.99, etc., or a range composed of any two of the above values, for example, 0.85-0.9, 0.9-0.96, 0.96-0.99, etc. The value of c can be 0.02, 0.05, 0.07, 0.1, etc., or a range composed of any two of the above values, for example, 0.02-0.05, 0.05-0.1, etc. The value of d can be 0.02, 0.03, 0.04, 0.05, etc., or a range consisting of any two of the above values, for example, 0.02-0.03, 0.03-0.04, 0.04-0.05, etc.

[0099] M (1-b-c-d) That is, doping elements, which include one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti. Doping the positive electrode active material with the above metal elements can improve the ionic conductivity and structural stability, thereby improving the electrochemical properties of the positive electrode active material.

[0100] The value of n may be 1.9, 2, 2.1, 2.2, etc., or a range consisting of any two of the above values, for example, 1.9-2, 2-2.1, 2.1-2.2, etc.

[0101] In one embodiment, the host material includes lithium nickel cobalt manganese oxide, and the molar content of nickel in all transition metal elements is greater than or equal to 0.85.

[0102] The main material of the positive electrode active material includes lithium nickel cobalt manganese oxide, and the molar content of nickel element in all transition metal elements is greater than or equal to 0.85, so that the lithium ion secondary battery has better electrochemical performance.

[0103] Specifically, the nickel element in lithium nickel cobalt manganese oxide has a high redox potential. By controlling the molar content of nickel element in lithium nickel cobalt manganese oxide to be greater than or equal to 0.85 in all transition metal elements, the nickel content is high, so that the lithium-ion secondary battery has a higher energy density. The molar content of nickel element in all transition metal elements can be 0.85, 0.88, 0.93, 0.96, 0.99, etc., or a range consisting of any two of the above values, for example, 0.85-0.93, 0.93-0.99.

[0104] In one embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently include a first coating layer, and the first coating layer includes one or more of Co, Al, F, and Ti. Based on the mass of the first part and the second part of the positive electrode active material, the mass of the first coating layer accounts for 1.65% to 2.00%.

[0105] In the embodiment of the present application, the residual alkali generated when preparing the positive electrode active material will be consumed during the coating process of the first coating layer. The residual alkali will produce a large amount of gas under high pressure and will also aggravate the side reaction of the positive electrode active material and the electrolyte. Therefore, the reduction of the residual alkali can improve the safety of the lithium-ion secondary battery. In addition, the role of coating the secondary particles of the first part and the second part of the positive electrode active material with a coating layer is that the coating layer can reduce the side reaction on the surface of the positive electrode active material, thereby improving the electrochemical performance of the lithium-ion secondary battery.

[0106] The mass percentage of the first coating layer may be 1.65%, 1.75%, 1.85%, 1.95%, 2.00%, etc., or a range consisting of any two of the above values, for example, 1.65% to 1.85%, 1.85% to 1.95%, 1.95% to 2.00%, etc.

[0107] In one embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently include a second coating layer, and the second coating layer includes one or more of B, Al, and Y. Based on the mass of the positive electrode active material, the mass proportion of the second coating layer is 0.1% to 0.25%.

[0108] A second coating layer containing one or more of B, Al, and Y is coated on the surface of the positive electrode active material to improve the structural stability of the secondary particles and inhibit side reactions on the surface of the secondary particles, thereby significantly improving the cycle stability and safety of the positive electrode active material.

[0109] The mass percentage of the second coating layer may be 0.1%, 0.12%, 0.17%, 0.21%, 0.25%, etc., or a range consisting of any two of the above values, for example, 0.1% to 0.17%, 0.17% to 0.25%, etc.

[0110] In one embodiment, in the first part and / or the second part, the content of nickel in the transition elements is greater than or equal to 0.85.

[0111] In the first part and / or the second part, the content of nickel in the transition elements is greater than or equal to 0.85, which can make the lithium-ion secondary battery have better electrochemical performance.

[0112] In one embodiment, the average primary particle size of the first part is 50 nm to 2 μm.

[0113] The average particle size of the primary particles of the first part is controlled within the range of 50nm to 2μm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery, and can make the electrochemical performance of the lithium-ion secondary battery better.

[0114] The average particle size of the primary particles of the first part can be 50nm, 300nm, 500nm, 1μm, 1.5μm, 1.7μm, 2μm, etc., or a range consisting of any two of the above values, 50nm~1000nm, 1000nm~1500nm, 1500nm~2000nm, etc.

[0115] In one embodiment, the average primary particle size of the first part is 100 nm to 500 nm.

[0116] The average particle size of the primary particles of the first part is in the range of 100nm to 500nm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery and making the electrochemical performance of the lithium-ion secondary battery better.

[0117] The average particle size of the primary particles of the first part can be 100nm, 200nm, 300nm, 350nm, 500nm, etc., or a range consisting of any two of the above values, 100nm~300nm, 300nm~500nm, etc.

[0118] In one embodiment, the average primary particle size of the second part is 50 nm to 2 μm.

[0119] The average particle size of the primary particles in the second part is controlled within the range of 50nm to 2μm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery, and can make the electrochemical performance of the lithium-ion secondary battery better.

[0120] The average particle size of the primary particles of the second part can be 50nm, 300nm, 500nm, 1μm, 1.5μm, 1.7μm, 2μm, etc., or a range consisting of any two of the above values, 50nm~1000nm, 1000nm~1500nm, 1500nm~2000nm, etc.

[0121] In one embodiment, the average primary particle size of the second part is 100 nm to 500 nm.

[0122] The average particle size of the primary particles of the second part is in the range of 100nm to 500nm, so that the primary particles have a shorter electron transmission path, which helps to improve the electron transmission efficiency, thereby improving the charge and discharge performance of the battery and making the electrochemical performance of the lithium-ion secondary battery better.

[0123] The average particle size of the primary particles of the second part can be 100nm, 200nm, 300nm, 350nm, 500nm, etc., or a range consisting of any two of the above values, 100nm~300nm, 300nm~500nm, etc.

[0124] According to a second aspect of the present application, a positive electrode active material is provided, which includes a first part and a second part. In the positive electrode active material, the content of nickel in the transition elements is greater than or equal to 0.85. In a scanning electron microscope image of the positive electrode active material at a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; based on the total number of secondary particles of the positive electrode active material, the number of secondary particles in the first part accounts for 70% to 85%, and the number of secondary particles in the second part accounts for 15% to 30%.

[0125] In the technical solution of the embodiment of the present application, the active particles in the positive electrode active material include secondary particles of the first part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1.1, and secondary particles of the second part whose ratio of the longest diameter to the shortest diameter is greater than or equal to 1 and less than 1.1. The secondary particles of the first part are closer to non-spherical than the secondary particles of the second part, and the secondary particles of the second part are closer to spherical than the secondary particles of the first part. The secondary particles of the first part account for 70% to 85% of the total number of secondary particles of the positive electrode active material, and the secondary particles of the second part account for 15% to 30% of the total number of secondary particles of the positive electrode active material. When the pole piece is coated and cold pressed, the secondary particles in the pole piece that are close to non-spherical can better relieve pressure, reduce pole piece deformation, and reduce the degree of pole piece extension, thereby improving the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the secondary particles that are close to non-spherical can effectively alleviate the stress changes caused by squeezing each other when the particles expand, reduce pole piece expansion and alleviate particle breakage, thereby improving the stability of the lithium-ion secondary battery.

[0126] The present application provides a method for preparing a lithium-ion secondary battery in a third aspect, comprising: providing a positive electrode sheet, a negative electrode sheet and a separator to prepare a lithium-ion secondary battery; the positive electrode sheet comprises a positive electrode active material, wherein the method for preparing the positive electrode active material comprises: adding a precipitant and a complexing agent to a solution comprising a nickel source, a manganese source and a cobalt source for reaction to obtain a positive electrode active material precursor; sintering the positive electrode active material precursor with a lithium source to obtain the positive electrode active material; in the positive electrode active material, the content of nickel in the transition element is greater than or equal to 0.85; or the method for preparing the positive electrode active material comprises: mixing a first part of the positive electrode active material The positive electrode active material is prepared by mixing a first part of positive electrode active material and a second part of positive electrode active material to obtain a positive electrode active material, wherein, in a scanning electron microscope image of the positive electrode active material at a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1, based on the total number of secondary particles of the positive electrode active material, the number of secondary particles of the first part accounts for 70% to 85%, and the number of secondary particles of the second part accounts for 15% to 30%, and in the positive electrode active material, the content of nickel in the transition elements is greater than or equal to 0.85.

[0127] In the technical scheme of the embodiment of the present application, by adding a precipitant and a chelating agent to a solution containing a nickel source, a manganese source and a cobalt source, it is beneficial to control the morphology of the precursor particles of the positive electrode active material, and then control the morphology of the secondary particles of the positive electrode active material, or, by mixing the first part of the positive electrode active material and the second part of the positive electrode active material with the above morphology to obtain the positive electrode active material, by providing the above-mentioned positive electrode active material, when the electrode is coated and cold pressed, the secondary particles in the electrode that are close to non-spherical can better relieve pressure, reduce electrode deformation, and reduce the degree of extension of the electrode, thereby improving the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the secondary particles that are close to non-spherical can effectively alleviate the stress changes caused by squeezing each other when the particles expand, reduce the expansion of the electrode and alleviate particle breakage, thereby improving the stability of the lithium-ion secondary battery.

[0128] The nickel source is selected from one or more of nickel carbonate, nickel hydroxide, nickel acetate, nickel sulfate, nickel chloride, nickel nitrate and nickel oxalate. The cobalt source is selected from one or more of cobalt carbonate, cobalt hydroxide, cobalt acetate, cobalt sulfate, cobalt chloride, cobalt nitrate and cobalt oxalate. The manganese source is selected from one or more of manganese dioxide, electrolytic manganese dioxide, manganese tetraoxide and the like.

[0129] In one embodiment, the precipitating agent comprises at least one of sodium carbonate, sodium hydroxide and potassium carbonate.

[0130] The precipitant can react with the nickel source, the manganese source and the cobalt source to generate hydroxides and / or basic salt precipitates corresponding to each of them, and then the precipitates can be sintered to obtain a positive electrode active material precursor.

[0131] In one embodiment, the concentration of the precipitant is 1 mol / L to 7 mol / L.

[0132] The precipitant has a great influence on the nucleation rate and growth rate of the crystal of the positive electrode active material precursor. By controlling the concentration of the precipitant within the above range, the positive electrode active material precursor has a suitable particle size range and morphology. The concentration of the precipitant can be 1 mol / L, 3 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, etc., or a range consisting of any two of the above values, for example, 1 mol / L to 5 mol / L, 5 mol / L to 7 mol / L, etc.

[0133] In one embodiment, the concentration of the precipitant is 3 mol / L to 6 mol / L.

[0134] The precipitant has a great influence on the nucleation rate and growth rate of the crystals of the positive electrode active material precursor. By controlling the concentration of the precipitant within the above range, the positive electrode active material precursor has a suitable particle size range and morphology. The concentration of the precipitant can be 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, etc., or a range consisting of any two of the above values, for example, 3 mol / L to 4 mol / L, 4 mol / L to 5 mol / L, 5 mol / L to 6 mol / L, etc.

[0135] In one embodiment, the complexing agent includes at least one of aqueous ammonia, ammonium chloride and ammonium sulfate.

[0136] At least one of ammonia water, ammonium chloride and ammonium sulfate as a complexing agent can effectively complex metal ions such as Ni, Co, Mn, etc. in the liquid, which helps to control the composition of the positive electrode active material precursor.

[0137] In one embodiment, the concentration of the complexing agent is 0.3 mol / L to 0.7 mol / L.

[0138] Ammonia water as a complexing agent can effectively complex metal ions such as Ni, Co, and Mn in the mixed liquid to complex the free metal ions in the mixed liquid, thereby helping to control the proportion of metal ions in the positive electrode active material precursor.

[0139] The concentration of the complexing agent is controlled within the range of 0.3 mol / L to 0.7 mol / L, which not only slows down the disturbance of the precipitation equilibrium caused by the addition of raw materials, controls the supersaturation of the precipitate in the solution, but also reduces the speed of nucleation and growth, allowing the crystal to grow slowly, and facilitates the regulation of the particle size uniformity of the positive electrode active material precursor. The concentration of the complexing agent can be 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, etc., or a range consisting of any two of the above values, such as 0.3 mol / L to 0.5 mol / L, 0.5 mol / L to 0.7 mol / L, etc.

[0140] In one embodiment, the concentration of the complexing agent is 0.3 mol / L to 0.55 mol / L.

[0141] The concentration of the complexing agent is controlled within the range of 0.3 mol / L to 0.55 mol / L, which not only slows down the disturbance of the precipitation equilibrium caused by the addition of raw materials, controls the supersaturation of the precipitate in the solution, but also reduces the speed of nucleation and growth, allowing the crystal to grow slowly, and facilitates the regulation of the particle size uniformity of the positive electrode active material precursor. The concentration of the complexing agent can be 0.3 mol / L, 0.35 mol / L, 0.45 mol / L, 0.55 mol / L, etc., or a range consisting of any two of the above values, such as 0.3 mol / L to 0.45 mol / L, 0.45 mol / L to 0.55 mol / L, etc.

[0142] In one embodiment, in the step of adding a precipitant and a complexing agent to a solution of a nickel source, a manganese source and a cobalt source for reaction, the pH value is 10-15 and the temperature is 50° C.-70° C.

[0143] Controlling the pH and reaction temperature of the coprecipitation reaction process within the above range is beneficial to controlling the morphology of the positive electrode active material precursor.

[0144] Specifically, pH can control the growth rate and nucleation rate of the positive electrode active material particles. The pH of the coprecipitation reaction process is controlled within the range of pH = 10 to 15. The nucleation rate of the positive electrode active material precursor particles is slow, and the growth rate of the particles is fast, which is helpful for the subsequent control of the distribution of the secondary particle size in the positive electrode active material precursor, and is also beneficial for controlling the morphology of the positive electrode active material precursor. Controlling the reaction temperature within the range of 50°C to 70°C can accelerate the reaction speed without affecting the crystal growth and nucleation. Among them, pH can be 10, 11, 12, 13, 14, 15, etc., or a range composed of any two of the above values, such as 10 to 12, 12 to 13, 13 to 15, etc. The reaction temperature can be 55°C, 60°C, 65°C, 70°C, etc., or a range composed of any two of the above values, such as 55°C to 65°C, 65°C to 70°C, etc.

[0145] In one embodiment, in the step of adding a precipitant and a complexing agent to a solution of a nickel source, a manganese source and a cobalt source for reaction, the pH value is 12 to 14.5 and the temperature is 55° C. to 65° C.

[0146] Controlling the pH and reaction temperature of the coprecipitation reaction process within the above range is beneficial to controlling the morphology of the positive electrode active material precursor.

[0147] In one embodiment, in the step of sintering the positive electrode active material precursor and the lithium source, the sintering temperature is 700° C. to 780° C., and the sintering time is 7 h to 14 h.

[0148] The positive electrode active material precursor is sintered with a lithium source to obtain a positive electrode active material that can embed and extract active lithium in the transition metal oxide lattice. The sintering temperature is controlled within the range of 700°C to 780°C, and the sintering time is controlled within the range of 7h to 14h, so that lithium can be better diffused into the interior of the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance. The sintering temperature can be 700°C, 720°C, 730°C, 740°C, 750°C, 760°C, 780°C, etc., or a range composed of any of the above values, such as 700°C to 730°C, 730°C to 750°C, 750°C to 780°C, etc. The sintering time can be 7h, 9h, 11h, 12h, 13h, 14h, etc., or a range composed of any of the above values, such as 7h to 11h, 11h to 13h, 13h to 14h, etc.

[0149] In one embodiment, in the step of sintering the positive electrode active material precursor and the lithium source, the sintering temperature is 720° C. to 760° C., and the sintering time is 8 h to 13 h.

[0150] By controlling the sintering temperature and sintering time within the above range, lithium can be better diffused into the interior of the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance.

[0151] The positive electrode active material precursor is sintered with a lithium source to obtain a positive electrode active material capable of embedding and extracting active lithium in a transition metal oxide lattice. The sintering temperature is controlled within the range of 720°C to 760°C, and the sintering time is controlled within the range of 8h to 13h, so that lithium can be better diffused into the interior of the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance. The sintering temperature can be 720°C, 730°C, 740°C, 750°C, 760°C, etc., or a range consisting of any of the above values, such as 720°C to 730°C, 730°C to 750°C, 750°C to 760°C, etc. The sintering time can be 8h, 9h, 10h, 12h, 13h, etc., or a range consisting of any of the above values, such as 8h to 10h, 10h to 12h, 12h to 13h, etc.

[0152] The lithium source is selected from one or more of LiOH·H2O, Li2CO3, Li2SO4, LiNO3, LiC2O4, and CH3COOLi.

[0153] In one embodiment, the step of sintering the positive electrode active material precursor with the lithium source is to sinter the positive electrode active material precursor, the lithium source and the element M source, wherein M includes one or more of the elements Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti.

[0154] Adding one or more of the metal elements such as Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, etc. into the positive electrode active material can improve the crystal structure of the material, reduce the distortion of the layered structure, and thus improve the structural stability and cycle life of the positive electrode active material.

[0155] In one embodiment, after the step of sintering the positive electrode active material precursor and the lithium source, it further includes: adding a first coating element source for sintering, and the first coating element source includes one or more of Co, Al, F, and Ti.

[0156] In the process of coating the first coating layer, the residual alkali generated when preparing the positive electrode active material will be consumed. The residual alkali will produce a large amount of gas under high pressure and will also aggravate the side reaction between the positive electrode active material and the electrolyte. Therefore, the reduction of residual alkali can improve the safety of lithium-ion secondary batteries. In addition, the role of coating the secondary particles of the positive electrode active material with a coating layer is that the coating layer can reduce the side reaction on the surface of the positive electrode active material, thereby improving the electrochemical performance of the lithium-ion secondary battery.

[0157] In the embodiment of the present application, the temperature when the first coating element is added for sintering is 400° C. to 650° C., and the sintering time is 5 h to 11 h.

[0158] By controlling the temperature and time during the coating process of the first coating source within the above range, the thickness, uniformity and structure of the coating layer can be optimized, thereby improving the overall performance and stability of the lithium-ion battery. Among them, the temperature when the first coating element is added for sintering can be 400°C, 440°C, 480°C, 520°C, 560°C, 600°C, 650°C, etc., or a range composed of any of the above values, such as 400°C to 480°C, 480°C to 560°C, 560°C to 650°C, etc. The sintering time can be 5h, 7h, 9h, 10h, 11h, etc., or a range composed of any of the above values, such as 5h to 7h, 7h to 10h, 10h to 11h, etc.

[0159] In one embodiment, after the step of sintering the positive electrode active material precursor and the lithium source, the step further includes: adding a second coating element source for sintering, wherein the second coating element includes one or more of B, Al, and Y.

[0160] A second coating layer containing one or more of B, Al, and Y is coated on the surface of the positive electrode active material to improve the structural stability of the secondary particles and inhibit side reactions on the surface of the secondary particles, thereby significantly improving the cycle stability and safety of the positive electrode active material.

[0161] In the embodiment of the present application, the temperature when the second coating element is added for sintering is 250° C. to 400° C., and the sintering time is 5 h to 12 h.

[0162] By controlling the temperature and time during the coating process of the second coating source within the above range, the thickness, uniformity and structure of the coating layer can be optimized, thereby improving the overall performance and stability of the lithium-ion battery. Among them, the temperature when the second coating element is added for sintering can be 250°C, 280°C, 310°C, 350°C, 370°C, 400°C, etc., or a range composed of any of the above values, such as 250°C to 280°C, 280°C to 350°C, 350°C to 400°C, etc. The sintering time can be 5h, 7h, 9h, 10h, 12h, etc., or a range composed of any of the above values, such as 5h to 7h, 7h to 10h, 10h to 12h, etc.

[0163] The fourth aspect of the present application provides an electrical device, including the lithium-ion secondary battery of the first aspect or / and the positive electrode active material of the second aspect or / and the preparation method of the lithium-ion secondary battery of the third aspect. The lithium-ion secondary battery of the embodiment of the present application has at least the same advantages as the lithium-ion secondary battery of the first aspect, or / and at least the same advantages as the positive electrode active material of the second aspect, or / and at least the same advantages as the lithium-ion secondary battery prepared by the preparation method of the lithium-ion secondary battery of the third aspect.

[0164] The battery disclosed in the embodiments of the present application can be used in electrical equipment that uses the battery as a power source or various energy storage systems that use the battery as an energy storage element. Electrical equipment can be, but is not limited to, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecrafts, etc.

[0165] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device in an embodiment of the present application.

[0166] Please refer to Figure 1 , Figure 1A schematic diagram of the structure of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A secondary battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The secondary battery 100 may be used to power the vehicle 1000, for example, the secondary battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the secondary battery 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0167] In some embodiments of the present application, the secondary battery 100 can be used not only as an operating power source for the vehicle 1000 , but also as a driving power source for the vehicle 1000 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000 .

[0168] Please refer to Figure 2 , Figure 2 Schematic diagram of the exploded structure of the battery 100 provided for some embodiments of the present application. The secondary battery 100 includes a box 10 and a battery cell 20, and the battery cell 20 is contained in the box 10. Among them, the box 10 is used to provide a storage space for the battery cell 20, and the box 10 can adopt a variety of structures. In some embodiments, the box 10 may include a first part 11 and a second part 12, the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one end open, the first part 11 may be a plate-like structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a storage space; the first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the box 10 formed by the first part 11 and the second part 12 may be in a variety of shapes, such as a cylinder, a cuboid, etc.

[0169] In the secondary battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. The multiple battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, the secondary battery 100 may also be a battery module formed by connecting multiple battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple secondary battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The secondary battery 100 may also include other structures, for example, the secondary battery 100 may also include a busbar component for realizing electrical connection between the multiple battery cells 20.

[0170] Each battery cell 20 may be a battery or a primary battery, or a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 may be cylindrical, flat, rectangular, or in other shapes.

[0171] Please refer to Figure 3 , Figure 3 The schematic diagram of the exploded structure of the battery cell 20 provided in some embodiments of the present application. The battery cell 20 refers to the smallest unit that constitutes the battery. Figure 3 The battery cell 20 includes an end cover 21, a shell 22, a battery cell assembly 23 and other functional components.

[0172] The end cap 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the shell 22 to match the shell 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 21 is not easily deformed when squeezed and collided, so that the battery cell 20 can have a higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals 21a can be provided on the end cap 21. The electrode terminal 21a can be used to electrically connect to the battery cell assembly 23 for outputting or inputting electrical energy of the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The material of the end cap 21 can also be a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose special restrictions on this. In some embodiments, an insulating member may be provided inside the end cap 21, and the insulating member may be used to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, or the like.

[0173] The shell 22 is a component used to cooperate with the end cover 21 to form the internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the battery cell assembly 23, electrolyte and other components. The shell 22 and the end cover 21 can be independent components, and an opening can be set on the shell 22, and the internal environment of the battery cell 20 is formed by covering the opening with the end cover 21 at the opening. Without limitation, the end cover 21 and the shell 22 can also be integrated. Specifically, the end cover 21 and the shell 22 can form a common connection surface before other components are put into the shell, and when the interior of the shell 22 needs to be encapsulated, the end cover 21 covers the shell 22. The shell 22 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the battery cell assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0174] The cell assembly 23 is a component in the battery cell 100 where electrochemical reactions occur. One or more cell assemblies 23 may be contained in the housing 22. The cell assembly 23 is mainly formed by winding or stacking the positive electrode sheet and the negative electrode sheet, and a separator is usually provided between the positive electrode sheet and the negative electrode sheet. The parts of the positive electrode sheet and the negative electrode sheet with active materials constitute the main body of the cell assembly, and the parts of the positive electrode sheet and the negative electrode sheet without active materials each constitute a tab 23a. The positive tab and the negative tab may be located together at one end of the main body or respectively at both ends of the main body. During the charge and discharge process of the battery, the positive active material and the negative active material react with the electrolyte, and the tab 23a connects the electrode terminals to form a current loop.

[0175] Typically, the secondary battery 100 includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0176] [Positive electrode]

[0177] In some embodiments, the positive electrode sheet includes a positive electrode current collector, and the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector.

[0178] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0179] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0180] In some embodiments, the positive electrode active material layer may further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0181] In some embodiments, the positive electrode active material layer may further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0182] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the phosphate composite material and the spinel structure lithium manganese oxide, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0183] [Negative electrode]

[0184] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0185] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0186] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0187] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0188] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0189] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0190] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0191] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0192] [Isolation film]

[0193] In some embodiments, the battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0194] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0195] [Electrolytes]

[0196] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0197] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0198] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0199] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0200] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into a battery cell assembly by a winding process or a lamination process.

[0201] In some embodiments, the housing 22 may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.

[0202] The present application has no particular limitation on the shape of the battery cell 20 , which may be cylindrical, square, or any other shape.

[0203] The beneficial effects of the present application are further illustrated below in conjunction with embodiments.

[0204] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0205] Example 1

[0206]

Preparation of positive electrode active materials

[0207] Step (1): a 2 mol / L mixed solution of Ni, Co, and Mn sulfates is prepared in a molar ratio of 93:6:1, the mixed solution, sodium carbonate, and ammonia water are added to a reactor, the ammonia concentration is 0.5 mol / L, the sodium carbonate concentration is 3.5 mol / L, the pH in the reactor is controlled to be maintained at 12.5, the temperature is maintained at 60°C, and a coprecipitation reaction is performed. After the reaction is completed, the positive electrode active material precursor (Ni 0.93 Co 0.06 Mn 0.01 (OH)2), the precursor particle Dv50 is about 8.3μm.

[0208] Step (2): The above-mentioned positive electrode active material precursor is mixed with LiOH in a molar ratio of 1:1.05, and then 1000 ppm of Y2O3 and 1000 ppm of ZrO2 are added and mixed. Then the mixed powder is added into a sintering furnace, kept at 725°C for 13 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the main material of the positive electrode active material.

[0209] Step (3): The main material of the positive electrode active material obtained in step (2) is crushed and mixed with 10000 ppm of CoOOH, and the mixed powder is added to a sintering furnace for sintering at a temperature of 620°C for 7.5 hours, and then cooled to room temperature at a rate of 5°C / min.

[0210] Step (4): 300 g of the powder obtained in step (3) was added to 300 mL of deionized water and stirred for 5 min, then filtered to obtain a solid powder, which was then dried in a 60° C. forced air oven.

[0211] Step (5): Add the powder obtained in step (4) into a sintering furnace and mix thoroughly with 1000 ppm of H2BO3. Sinter the mixed powder at 350°C for 6 hours and cool to room temperature at a rate of 1.5°C / min to obtain a positive electrode active material.

[0212]

Preparation of positive electrode

[0213] The positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) prepared above were dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 98:0.5:1.5, and the mixture was fully stirred and mixed to obtain a positive electrode slurry; the positive electrode slurry was then evenly coated on both sides of a 60 μm aluminum foil, dried and cold pressed to obtain a positive electrode sheet with a thickness of 120 μm.

[0214]

Preparation of negative electrode sheet

[0215] Artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) are added to deionized water solvent in a mass ratio of 90:5:2:2:1, stirred and mixed thoroughly, and then coated on both sides of copper foil, dried, cold pressed and other processes to obtain a negative electrode sheet.

[0216]

Preparation of electrolyte

[0217] In an argon atmosphere glove box, ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain a solvent, LiPF6 was added and dissolved in the above solvent, and stirred evenly to obtain a 1 mol / L LiPF6 electrolyte.

[0218]

Diaphragm

[0219] A polyethylene film with a thickness of 13 μm was used as the separator.

[0220]

Battery preparation

[0221] The separator, negative electrode sheet, and positive electrode sheet are stacked in the order of "separator-negative electrode sheet-separator-positive electrode sheet", processed and formed, packaged in an aluminum-plastic bag, injected with 1 mol / L electrolyte, and then packaged and formed to obtain a soft-pack lithium-ion secondary battery. The length of the battery cell assembly is 50 mm, the width is 42 mm, and the thickness is 0.4 mm.

[0222] Example 2

[0223] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the molar ratio of the nickel source, the manganese source and the cobalt source is 88:6:6, the concentration of sodium carbonate is 7 mol / L, the reaction temperature is 50°C, PH=10, and the concentration of ammonia water is 0.3 mol / L. The sintering temperature of the precursor and the lithium source, Y2O3 and ZrO2 is 780°C, and the sintering time is 7h. The temperature of the first sintering is 400°C, the time of the first sintering is 5h, the temperature of the second sintering is 250°C, and the time of the second sintering is 5h. The others are similar to Example 1 and will not be repeated here.

[0224] Example 3

[0225] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the molar ratio of the nickel source, the manganese source and the cobalt source is 92:6:2, the concentration of sodium carbonate is 4 mol / L, the reaction temperature is 55°C, the pH is 12, and the concentration of ammonia is 0.55 mol / L. The sintering temperature of the precursor and the lithium source, Y2O3 and ZrO2 is 720°C, and the sintering time is 10h. The temperature of the first sintering is 500°C, the time of the first sintering is 11h, the temperature of the second sintering is 400°C, and the time of the second sintering is 8h. Others are similar to Example 1 and will not be repeated here.

[0226] Example 4

[0227] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the molar ratio of the nickel source, the manganese source and the cobalt source is 96:3:1, the concentration of sodium carbonate is 1 mol / L, the reaction temperature is 65°C, the pH is 14.5, and the concentration of ammonia water is 0.7 mol / L. The sintering temperature of the precursor and the lithium source, Y2O3 and ZrO2 is 740°C, and the sintering time is 14h. The second sintering time is 12h. Others are similar to Example 1 and will not be repeated here.

[0228] Example 5

[0229] The lithium ion secondary battery and the method for preparing the lithium ion secondary battery of the present embodiment are different from those of Example 1 in that: the pH in step (2) is 15, and the reaction temperature is 70°C. The sintering temperature in step (2) is 760°C. Steps (3) to (5) are eliminated. The rest are similar to Example 1 and will not be described in detail here.

[0230] Example 6

[0231] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery in the present embodiment are different from those in Example 1 in that the precipitant is sodium hydroxide and only 1000 ppm of Y2O3 is added in step 2. The rest is similar to Example 1 and will not be described again.

[0232] Example 7

[0233] The lithium ion secondary battery and the method for preparing the lithium ion secondary battery of the present embodiment are different from those of Example 1 in that the concentration of the sulfate in step (1) is 2.5 mol / L and the precipitant is potassium carbonate. Only 1000 ppm of ZrO2 is added in step (2). The rest is similar to Example 1 and will not be described in detail here.

[0234] Example 8

[0235] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the concentration of sulfate in step (1) is 3 mol / L and the complexing agent is ammonium chloride. In step (2), Y2O3 and ZrO2 are replaced with 1000 ppm of Ta2O5 and 1000 ppm of WO3. The rest is similar to Example 1 and will not be repeated here.

[0236] Example 9

[0237] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that: the complexing agent in step (1) is ammonium sulfate. In step (3), 800 ppm of Ti2O3 is added on the basis of CoOOH. In step (4), 500 ppm of Al2O3 is added on the basis of H2BO3. The rest is similar to Example 1 and will not be repeated here.

[0238] Example 10

[0239] The lithium ion secondary battery and the method for preparing the lithium ion secondary battery of the present embodiment are different from those of Example 1 in that: in step (3), 1000 ppm of AlF3 is added on the basis of CoOOH. In step (4), 800 ppm of Y2O3 is added on the basis of H2BO3. The rest is similar to Example 1 and will not be described here.

[0240] Comparative Example 1

[0241] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the comparative example of the present application are different from those of Example 1 in that: the precipitant in step (1) is potassium carbonate, the concentration of potassium carbonate is 0.5 mol / L, the complexing agent is ammonium sulfate, the concentration of ammonium sulfate is 0.8 mol / L, pH=15, and the reaction temperature is 49°C. The sintering temperature in step (2) is 730°C, and the sintering time is 9h. Others are similar to Example 1 and will not be repeated here.

[0242] Comparative Example 2

[0243] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the comparative example of the present application are different from those of Example 1 in that: the precipitant in step (1) is potassium carbonate, the concentration of potassium carbonate is 8 mol / L, the complexing agent is ammonium sulfate, the concentration of ammonium sulfate is 0.2 mol / L, pH=9.5, and the reaction temperature is 71°C. The sintering temperature in step (2) is 715°C, and the sintering time is 13h. Others are similar to Example 1 and are not repeated here.

[0244] The relevant parameter testing methods in the above embodiments and comparative examples are as follows:

[0245] 1. Powder compaction density test

[0246] A certain amount of powder is placed in a special compaction mold, and then the mold is placed on a compaction density instrument. Different pressures are set to compact the powder. After the pressure is released, the thickness of the powder under different pressures is read on the device, from which the compaction density can be calculated. The powder compaction density test uses a compaction density instrument model CARVER4350.

[0247] 2. Particle size test of primary particles

[0248] The particle size test adopts the SEM scanning electron microscope test method. The scanning electron microscope model used in the SEM test is Philips XL30. The test method is: place the sample on the scanning electron microscope sample stage for testing. The scanning range is 100nm~2μm. The ruler marks the size of the primary particles. The average particle size of the primary particles = the sum of the particle sizes of all measured particles / the sum of the number of all measured particles.

[0249] 3. Volume average particle size Dv50 test

[0250] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009, specific test process: take an appropriate amount of the sample to be tested (the sample concentration is guaranteed to be 8%-12% shading), add 20ml of deionized water, and ultrasonicate for 5min (53KHz / 120W) to ensure that the sample is completely dispersed, and then measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard.

[0251] 4. Electrochemical performance test

[0252] 4.1g capacity test

[0253] After assembling the above-mentioned positive electrode and negative electrode into a soft-pack battery, let it stand for 120 minutes, then charge it to 4.25V at a constant current of 0.1C in a constant temperature environment of 25°C, then charge it at a constant voltage of 4.25V until the current drops to 0.05mA, let it stand for 5 minutes, and then discharge it to 2.8V at a constant current of 0.1C to obtain the gram capacity C1.

[0254] 4.2 Cyclic performance test

[0255] The secondary battery was charged to 4.25V at a constant current of 0.33C at a constant temperature of 25°C, then charged to 0.05mA at a constant voltage of 4.25V, and then discharged to 2.8V at a constant current of 0.33C, and the first cycle discharge capacity D1 was obtained. This charge and discharge was repeated until the 100th cycle, and the discharge capacity D100 after 100 cycles was obtained. The 100-cycle cycle capacity retention rate = D100 / D1.

[0256] Capacity retention rate = discharge capacity after 500 cycles (D100) / first cycle discharge capacity (D1).

[0257] 4.3 Volume energy density test

[0258] Referring to the 4.1 gram capacity test, through the constant current charge and discharge test of the battery cell, the capacity of the battery cell is obtained as Cp, the voltage platform corresponding to the battery cell is U1, the volume of the measured battery cell is V1, and then the volume energy density of the battery cell is calculated.

[0259] The volume energy density is calculated as:

[0260] Vd=(Cp×U1) / V1

[0261]

[0262]

[0263] like Figure 4 As shown, Figure 4 1 is a scanning electron microscope image of a positive electrode active material according to an embodiment of the present application. Figure 4 The figure shows a scanning electron microscope image of the positive electrode active material at a magnification of 2K. Figure 4 It can be clearly seen that the positive electrode active material particles include particles that are close to spherical, and also particles that are quite different from spherical particles. The particles that are close to non-spherical cooperate better with the spherical particles, forming a "rivet"-like effect. Then, when the pole piece is under pressure, the particles that are close to spherical and the particles that are close to non-spherical can cooperate with each other to achieve better pressure relief, reduce pole piece deformation, and reduce the degree of pole piece extension. In addition, the two shapes of particles can also cooperate well in particle size, and the particles with smaller particle size are dispersed between the particles with larger particle size. This can help to increase the tap density of the positive pole piece.

[0264] As shown in Table 1 and Table 2, Table 1 shows the preparation process parameters of Examples 1 to 10 and Comparative Examples 1 to 2. Table 2 shows the performance test results of Examples 1 to 10 and Comparative Examples 1 to 2. Examples 1 to 10 control the preparation process parameters of the precursor and the positive electrode active material in order to prepare a lithium-ion secondary battery with better test performance. Compared with Examples 1 to 10, Comparative Examples 1 to 2 have the problem that the precipitant concentration, complexing agent concentration, pH and temperature of the reaction environment of the precursor preparation process parameters of Comparative Examples 1 and 2 are too large or too low, while the preparation process parameters of Examples 1 to 10 are all within a suitable range. Therefore, the secondary particles of the first part and the secondary particles of the second part of the positive electrode active material prepared according to the preparation process parameters of Examples 1 to 10 are respectively within a suitable range with respect to the number of the total secondary particles. Especially in Example 1, the secondary particles in the first part account for 72.5% of the total secondary particles, and the secondary particles in the second part account for 27.5% of the total secondary particles, so that the secondary particles in the first part and the secondary particles in the second part can be better matched to relieve the pressure during cold pressing of the pole piece, reduce the degree of extension of the pole piece, and then increase the load of the positive pole piece, and finally achieve the purpose of increasing the volume energy density of the battery cell. And the molar content of nickel element in all transition metal elements accounts for 0.918, which is a positive active material with a high nickel content. In addition, Example 1 also has a first coating layer and a second coating layer with a relatively suitable mass ratio. In summary, Example 1 has better gram capacity, capacity retention rate and volume energy density.

[0265] The above are only implementation methods of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A lithium ion secondary battery, characterized in that: Including positive electrode sheet, negative electrode sheet and electrolyte; The positive electrode sheet includes a positive electrode active material, the positive electrode active material includes a first part and a second part, in the positive electrode active material, the content of nickel in the transition element is greater than or equal to 0.85, in the scanning electron microscope image of the positive electrode active material with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; based on the total number of secondary particles of the positive electrode active material, the number of secondary particles of the first part accounts for 70% to 85% ， The secondary particles in the second part account for 15% to 30%.

2. The lithium ion secondary battery according to claim 1, characterized in that: The volume average particle size Dv50 of the secondary particles of the positive electrode active material is 8 μm to 11 μm.

3. The lithium ion secondary battery according to claim 1 or 2, characterized in that: The longest diameter of the secondary particles of the first part is in the range of 2 μm to 18 μm, and the shortest diameter is in the range of 2 μm to 16.5 μm.

4. The lithium ion secondary battery according to any one of claims 1 to 3, characterized in that: The longest diameter of the secondary particles of the second part is in the range of 2 μm to 18 μm, and the shortest diameter is in the range of 1 μm to 16 μm.

5. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: The secondary particles of the first part and the second part of the positive electrode active material independently also include a first coating layer, and the first coating layer includes one or more of the elements Co, Al, F, and Ti. Based on the mass of the positive electrode active material, the mass proportion of the first coating layer is 1.65% to 2.00%.

6. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: The secondary particles of the first part and the second part of the first coating layer independently also include a second coating layer, and the second coating layer includes one or more of the elements B, Al, and Y. Based on the mass of the positive electrode active material, the mass proportion of the second coating layer is 0.1% to 0.25%.

7. The lithium ion secondary battery according to any one of claims 1 to 6, characterized in that: In the first part and / or the second part, the content of nickel in the transition elements is greater than or equal to 0.

85.

8. The lithium ion secondary battery according to any one of claims 1 to 7, characterized in that: The average primary particle size of the first part is 50 nm to 2 μm.

9. The lithium ion secondary battery according to any one of claims 1 to 8, characterized in that: The average primary particle size of the first part is 100 nm to 500 nm.

10. The lithium ion secondary battery according to any one of claims 1 to 9, characterized in that: The average primary particle size of the second part is 50 nm to 2 μm.

11. The lithium ion secondary battery according to any one of claims 1 to 10, characterized in that: The average primary particle size of the second part is 100 nm to 500 nm.

12. A positive electrode active material, characterized in that: The positive electrode active material includes a first part and a second part. In the positive electrode active material, the content of nickel in the transition elements is greater than or equal to 0.

85. In a scanning electron microscope image of the positive electrode active material with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; based on the total number of secondary particles of the positive electrode active material, the number of secondary particles in the first part accounts for 70% to 85%, and the number of secondary particles in the second part accounts for 15% to 30%.

13. A method for preparing a lithium ion secondary battery, characterized in that: include: Providing positive electrode sheets, negative electrode sheets and separators to make lithium-ion secondary batteries; The positive electrode sheet includes a positive electrode active material, wherein: The preparation method of the positive electrode active material comprises: A precipitant and a complexing agent are added to a solution including a nickel source, a manganese source and a cobalt source to react and obtain a positive electrode active material precursor; Sintering the positive electrode active material precursor with a lithium source to obtain the positive electrode active material, wherein the content of nickel in the transition elements is greater than or equal to 0.85; or The preparation method of the positive electrode active material comprises: A first portion of positive electrode active material and a second portion of positive electrode active material are mixed to obtain the positive electrode active material, wherein, in a scanning electron microscope image of the positive electrode active material at a magnification of 2K, a ratio of the longest diameter to the shortest diameter of the secondary particles of the first portion is greater than or equal to 1.1, and a ratio of the longest diameter to the shortest diameter of the secondary particles of the second portion is greater than or equal to 1 and less than 1.1; based on the total number of secondary particles of the positive electrode active material, the number of secondary particles of the first portion accounts for 70% to 85%, and the number of secondary particles of the second portion accounts for 15% to 30%.

14. The method for preparing a lithium ion secondary battery according to claim 13, characterized in that: The complexing agent includes at least one of ammonia water, ammonium chloride and ammonium sulfate.

15. An electrical equipment, characterized in that: A lithium ion secondary battery comprising the lithium ion secondary battery according to any one of claims 1 to 11, the positive electrode active material according to claim 12, and / or a lithium ion secondary battery prepared by the method for preparing a lithium ion secondary battery according to claim 13 or 14.

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