Low-temperature positive electrode material, preparation method thereof, positive electrode sheet and lithium ion battery

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a low-temperature cathode material and its preparation method, a cathode sheet, and a lithium-ion battery. The low-temperature cathode material includes a matrix material and a coating layer; the raw materials for preparing the low-temperature cathode material include a first precursor and a second precursor, with a mass ratio of n; n is related to the average single-crystal particle size r of the low-temperature cathode material, the electrode compaction density PD of the cathode sheet containing the low-temperature cathode material, and the particle size d of the low-temperature cathode material. 99 and particle size d min Satisfying 30≤(n×PD×d) 99 ) / (d min ×r)≤100. This low-temperature cathode material has low cost and good low-temperature charge-discharge performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a low-temperature positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have high energy density, long cycle life, low self-discharge rate, no memory effect, fast charging capability, environmental protection and recyclability, low risk of spontaneous combustion and other advantages, and have been widely used in 3C consumer products and power batteries and other fields. With the continuous progress of science and technology, lithium ion batteries will continue to play an important role.

[0003] However, after the temperature drops below-20℃ in winter, especially in the north, the viscosity of the electrolyte increases and the diffusion speed of lithium ions in the electrode material deteriorates, resulting in a significant reduction in the performance of lithium ion batteries. Charging at low temperature can cause lithium precipitation, which seriously affects the safety performance of lithium ion batteries. Moreover, the polarization is large at low temperature, and the discharge easily reaches the cut-off voltage, resulting in a decrease in the endurance capability.

[0004] The positive electrode material plays a crucial role in lithium ion batteries, as it directly determines the energy density, safety and overall performance of the battery. To improve the low-temperature charge-discharge performance of the positive electrode material, existing technologies improve the conductivity of the material, such as increasing the content of Co element. Although increasing the content of Co element can improve the low-temperature performance to some extent, Co resources are relatively scarce, and increasing the content of Co element will lead to an increase in the cost of the positive electrode material. Therefore, it is of great significance to provide a positive electrode material with low cost and good low-temperature performance.

[0005] In addition, with the large-scale application of lithium ion batteries, higher requirements are placed on the high-temperature storage performance of the positive electrode material. The high-temperature storage performance of conventional positive electrode materials is insufficient, limiting the application of lithium ion batteries.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] The first object of the present application is to provide a low-temperature positive electrode material with low cost and excellent low-temperature charge-discharge performance, which is beneficial to the further popularization and use of lithium ion batteries.

[0008] The second object of the present application is to provide a preparation method of a low-temperature positive electrode material, which has the advantages of simple operation, short process, low cost and suitability for mass production.

[0009] The third object of the present application is to provide a positive electrode sheet that exhibits excellent charge-discharge performance at low temperature.

[0010] The fourth objective of this invention is to provide a lithium-ion battery with excellent low-temperature performance.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0012] The present invention first provides a low-temperature cathode material, which includes a matrix material and a coating layer covering the surface of the matrix material.

[0013] The matrix material has the general formula Li x Ni y Co z Mn 1-y-z A q O 2-t Wherein, 0.98≤x≤1.05, 0.55≤y≤0.75, 0.02≤z≤0.15, 0≤q≤0.01, 0≤t≤0.03, and A includes at least one of the elements Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta.

[0014] The coating layer contains the element Q, wherein Q includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta.

[0015] The raw materials for preparing the low-temperature cathode material include nickel cobalt manganese hydroxide precursor materials. The nickel cobalt manganese hydroxide precursor materials include a first precursor and a second precursor. The first precursor is mainly formed by heating and dehydrating the second precursor. The water content in the first precursor is ≤1500ppm, the water content in the second precursor is ≥2000ppm, and the mass ratio of the first precursor to the second precursor is n.

[0016] The morphology of the low-temperature cathode material is single-crystal particles, the average size of the single-crystal particles is r, and the electrode compaction density of the cathode sheet containing the low-temperature cathode material is PD. The morphology of n, r, and PD is related to the particle size d of the low-temperature cathode material. 99 and particle size d min The following relationship must be satisfied: 30 ≤ (n × PD × d) 99 ) / (d min ×r)≤100; where r is in μm and d is the particle size. 99 The unit is μm, and the particle size is d. min The unit is μm, and the unit of PD is g / cm³. 3 .

[0017] Furthermore, n = 0.5 to 1.2.

[0018] Furthermore, r = 1.4–1.8 μm, and / or r is measured by scanning electron microscopy.

[0019] Furthermore, the d 99 =9.0~15.0μm.

[0020] Furthermore, the d min =0.2~0.5μm.

[0021] Furthermore, the PD is 3.5–3.8 g / cm³. 3 .

[0022] Furthermore, the water content in the first precursor is 500–1500 ppm.

[0023] Furthermore, the water content in the second precursor is 2000–5000 ppm.

[0024] The present invention further provides a method for preparing the low-temperature cathode material, comprising the following steps: heating and dehydrating a second precursor to obtain a first precursor; mixing the first precursor, the second precursor, a lithium source, and a first additive and then calcining to obtain a matrix material; the first additive includes element A, wherein A includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb, and Ta; mixing the matrix material with the second additive and then sintering to obtain the low-temperature cathode material; the second additive includes element Q, wherein Q includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb, and Ta.

[0025] Furthermore, the heating and dehydration temperature is 100–150°C, and / or the heating and dehydration time is 1–3 hours.

[0026] Furthermore, the calcination temperature is 850–950°C.

[0027] Furthermore, the calcination holding time is 8–16 hours.

[0028] Furthermore, the calcination process also includes a pulverization step.

[0029] Furthermore, the sintering temperature is 300–600°C, and / or the sintering holding time is 3–7 hours.

[0030] The present invention also provides a positive electrode sheet, including the aforementioned low-temperature positive electrode material.

[0031] The present invention also provides a lithium-ion battery, including the positive electrode plate.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) The low-temperature cathode material provided by this invention has high kinetics and high stability, and exhibits excellent low-temperature charge-discharge performance at low temperatures. Furthermore, the low-temperature cathode material has a low cobalt content and is inexpensive.

[0034] (2) The low-temperature cathode material provided by the present invention also has excellent high-temperature storage performance. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0036] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0039] In a first aspect, the present invention provides a low-temperature cathode material, comprising a matrix material and a coating layer covering the surface of the matrix material;

[0040] The matrix material has the general formula Li x Ni y Co z Mn 1-y-z A q O 2-t .

[0041] Wherein, 0.98≤x≤1.05, 0.55≤y≤0.75, 0.02≤z≤0.15, 0≤q≤0.01, and 0≤t≤0.03. Specifically, x includes, but is not limited to, any one of the values ​​of 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, and 1.05, or any range between any two; y includes, but is not limited to, any one of the values ​​of 0.55, 0.58, 0.60, 0.62, 0.65, 0.67, 0.7, 0.73, and 0.75, or any range between any two; z includes, but is not limited to, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.11, 0.12, 0.13, and 0.14. q is a point value of any one of 0.001, 0.002, 0.003, 0.005, 0.006, 0.008, 0.009, 0.01, or a range between any two; t is a point value of any one of 0.001, 0.002, 0.003, 0.005, 0.006, 0.008, 0.009, 0.01, 0.015, 0.02, 0.025, 0.03, or a range between any two.

[0042] A is a doping element, which includes at least one of the elements Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta, preferably at least two, and more preferably at least three.

[0043] In some specific implementations, in order to further improve the low-temperature performance of the cathode material, 0 <q≤0.005。

[0044] The coating layer contains element Q, wherein Q includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta; preferably at least two, more preferably at least three.

[0045] The raw materials for preparing the low-temperature cathode material include nickel-cobalt-manganese hydroxide precursor materials. These precursor materials comprise a first precursor and a second precursor. The first precursor is mainly formed by heating and dehydrating the second precursor. Specifically, the water content in the second precursor is greater than that in the first precursor. The water content in the first precursor is ≤1500 ppm, and the water content in the second precursor is ≥2000 ppm. The mass ratio of the first precursor to the second precursor is n, i.e., n:1. The water content in the first precursor includes, but is not limited to, any one of 1500 ppm, 1300 ppm, 1200 ppm, 1000 ppm, 800 ppm, 600 ppm, 500 ppm, 300 ppm, and 100 ppm, or a range between any two. The water content in the second precursor includes, but is not limited to, any point value or a range between any two of 2000ppm, 2200ppm, 2500ppm, 2800ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, and 6000ppm.

[0046] The morphology of the low-temperature cathode material is single-crystal particles, the average size of the single-crystal particles is r, and the compaction density of the cathode sheet containing the low-temperature cathode material is PD, wherein n, r, PD, and the particle size d of the low-temperature cathode material are... 99 and particle size d min The following relationship must be satisfied: 30 ≤ (n × PD × d) 99 ) / (d min ×r)≤100.

[0047] In the above formula, r is in μm and d is the particle size. 99 The unit is μm, and the particle size is d. min The unit is μm, and the unit of PD is g / cm³. 3 .

[0048] The low-temperature cathode material provided by this invention has high kinetics and high stability, and exhibits excellent low-temperature charge-discharge performance at low temperatures.

[0049] Furthermore, this low-temperature cathode material has a low cobalt content, resulting in low cost.

[0050] The low-temperature cathode material provided by this invention solves the technical problem that existing technologies cannot balance cost and low-temperature performance.

[0051] Furthermore, the low-temperature cathode material provided by this invention also possesses excellent high-temperature storage performance.

[0052] This invention controls (n×PD×d) 99) / (d min When (n×PD×d) is in the range of 30–100, it can significantly improve low-temperature kinetics. Specifically, when (n×PD×d) 99 ) / (d min When the value of (n×PD×d) is too small, the proportion of small-sized particles is too low to meet the requirement of improving low-temperature kinetics; when the value of (n×PD×d) is too low, the proportion of small-sized particles is too low to meet the requirement of improving low-temperature kinetics. 99 ) / (d min When the value of ×r) is too large, the proportion of small-sized particles is too high, making it impossible to balance long-term and high-temperature stability.

[0053] In some specific embodiments, the general formula of the nickel-cobalt-manganese hydroxide precursor material is Ni. a Co b Mn 1-a-b (OH)2. Wherein, 0.55≤a≤0.75, including but not limited to any one of 0.55, 0.58, 0.60, 0.62, 0.65, 0.67, 0.7, 0.73, 0.75 or any range between any two; 0.02≤b≤0.15, including but not limited to any one of 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15 or any range between any two.

[0054] In some specific implementations, in order to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the n = 0.5 to 1.2 includes, but is not limited to, any one of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 or any range between two of them.

[0055] In some specific implementations, in order to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the r = 1.4 to 1.8 μm includes, but is not limited to, any one of 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, and 1.8 μm, or any range between two of them.

[0056] In some specific embodiments, r is measured by scanning electron microscopy.

[0057] In some specific implementations, the test method for r is as follows: take a picture of the cathode material using a scanning electron microscope (SEM) at a magnification of 5000x, measure the length and width of the particles in the field of view, that is, measure the longitudinal and transverse dimensions respectively, and then take the average of the longitudinal and transverse dimensions, which is the actual size of a certain particle. After measuring the size of several particles (e.g., 200 to 500 particles), take the average of all the measured values, which is the average size r of the single crystal particle.

[0058] In some specific embodiments, in order to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the d 99 = 9.0 to 15.0 μm, including but not limited to point values ​​of any one of 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, and 15.0 μm, or range values ​​between any two.

[0059] In some specific embodiments, in order to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the d min = 0.2 to 0.5 μm, including but not limited to point values ​​of any one of 0.2 μm, 0.3 μm, 0.4 μm, and 0.5 μm, or range values ​​between any two.

[0060] In some specific embodiments, to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the PD is 3.5–3.8 g / cm³. 3 including but not limited to 3.5g / cm 3 3.55g / cm 3 3.6g / cm 3 3.65g / cm 3 3.7g / cm 3 3.75g / cm 3 3.8g / cm 3 The point value of any one of them or the range value between any two.

[0061] In some specific embodiments, in order to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the water content in the first precursor is 500 to 1500 ppm, including but not limited to any one of 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, and 1500 ppm or any range between two of them.

[0062] In some specific embodiments, in order to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the water content in the second precursor is 2000 to 5000 ppm, including but not limited to any one of 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, and 5000 ppm or any range between two of them.

[0063] In some specific embodiments, the test method for the electrode compaction density (PD) of the positive electrode sheet containing the low-temperature positive electrode material is as follows: the finished electrode sheet is rolled under a pressure of 20 MPa for 2 minutes, and the thickness and mass of the electrode sheet are measured to calculate the compaction density of the electrode sheet.

[0064] In some specific embodiments, the mass of the coating layer accounts for 0.5% to 2% of the mass of the matrix material, including but not limited to any one of 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, and 2%, or a range between any two.

[0065] Secondly, the present invention provides a method for preparing the aforementioned low-temperature cathode material, specifically comprising the following steps:

[0066] The second precursor is heated and dehydrated to obtain the first precursor. Here, dehydration refers to reducing the water content in the second precursor.

[0067] The first precursor, the second precursor, the lithium source, and the first additive are mixed and calcined to obtain the matrix material. The first additive includes element A, which includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb, and Ta. It is understood that the first additive is a dopant.

[0068] The matrix material is mixed with the second additive and then sintered to obtain the low-temperature cathode material. The second additive includes the element Q, wherein Q includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb, and Ta. It is understood that the second additive is a coating agent.

[0069] The method for preparing low-temperature cathode materials provided by this invention has the advantages of simple operation, short process, low cost, and mass production.

[0070] In some specific embodiments, the lithium source includes any lithium-containing compound commonly used in the art, such as lithium carbonate, lithium hydroxide, etc., but is not limited thereto.

[0071] In some specific embodiments, the second precursor and the first precursor have the same general molecular formula, which is Ni. a Co b Mn 1-a-b(OH)2. Wherein, 0.55≤a≤0.75, including but not limited to any one of 0.55, 0.58, 0.60, 0.62, 0.65, 0.67, 0.7, 0.73, 0.75 or any range between any two; 0.02≤b≤0.15, including but not limited to any one of 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15 or any range between any two.

[0072] In some specific embodiments, the first additive includes a compound containing A, such as an oxide, hydroxide, or a salt thereof. A includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb, and Ta.

[0073] In some specific embodiments, the second additive includes a compound containing Q, such as an oxide, hydroxide, or a salt thereof. Q includes at least one selected from Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb, and Ta.

[0074] In some specific implementations, in order to further improve the low-temperature performance and high-temperature storage performance of the cathode material, the first additive and the second additive contain different types of elements.

[0075] In some specific embodiments, the mass of the second additive accounts for 0.5% to 2% of the mass of the matrix material, including but not limited to a point value of any one of 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, and 2%, or a range between any two.

[0076] In some specific embodiments, the heating and dehydration temperature is 100-150°C, including but not limited to any one of 100°C, 110°C, 120°C, 130°C, 140°C, and 150°C, or a range between any two.

[0077] In some specific embodiments, the heating and dehydration is carried out in a dry atmosphere.

[0078] In some specific embodiments, the heating and dehydration time is 1 to 3 hours, including but not limited to any one of 1 hour, 1.5 hours, 2 hours, 2.5 hours, and 3 hours, or any range between two of them.

[0079] In some specific embodiments, the calcination temperature is 850–950°C; including but not limited to any one of 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, and 950°C, or a range between any two.

[0080] In some specific embodiments, the calcination holding time is 8 to 16 hours; including but not limited to any one of 8 hours, 10 hours, 12 hours, 13 hours, 15 hours, and 16 hours, or any range between two of them.

[0081] In some specific embodiments, the calcination atmosphere includes an air atmosphere and / or an oxygen atmosphere.

[0082] In some specific embodiments, the calcination process further includes a pulverization step. Preferably, the pulverization includes air jet milling. Air jet milling disperses the particles into single-crystal particles.

[0083] In some specific embodiments, the sintering temperature is 300 to 600°C, including but not limited to any one of 300°C, 350°C, 400°C, 450°C, 500°C, and 600°C, or a range between any two.

[0084] In some specific embodiments, the sintering holding time is 3 to 7 hours, including but not limited to any one of 3 hours, 4 hours, 5 hours, 6 hours, and 7 hours, or any range between two of them.

[0085] In some specific embodiments, the sintering atmosphere includes an air atmosphere and / or an oxygen atmosphere.

[0086] Thirdly, the present invention provides a positive electrode sheet comprising the aforementioned low-temperature positive electrode material.

[0087] The positive electrode exhibits excellent charge and discharge performance at low temperatures.

[0088] Optionally, the positive electrode may further include a binder and / or a conductive agent, which is not limited in this invention.

[0089] Fourthly, the present invention provides a lithium-ion battery, including the positive electrode sheet.

[0090] This lithium-ion battery exhibits excellent low-temperature performance, low cost, and good high-temperature storage performance.

[0091] Optionally, the lithium-ion battery may further include a negative electrode, an electrolyte, and a separator, but the present invention does not limit these components.

[0092] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0093] Example 1

[0094] The low-temperature cathode material provided in this embodiment includes a matrix material and a coating layer covering the surface of the matrix material. The matrix material has the general formula Li. 1.00 Ni 0.55 Co 0.05 Mn 0.4 Mg 0.003 Sr 0.002 Mo 0.001 O 2.0065 The main components of the coating layer are Nb2O5 and Ta2O5. The preparation method of this low-temperature cathode material includes the following steps:

[0095] (1) The second precursor Ni 0.55 Co 0.05 Mn 0.4 (OH)₂ was heated at 125°C for 1 hour in a dry atmosphere to remove water, yielding the first precursor Ni. 0.55 Co 0.05 Mn 0.4 (OH)2. The water content in the first precursor is 1622 ppm, and the water content in the second precursor is 3259 ppm.

[0096] (2) The first precursor, the second precursor, lithium hydroxide, MgO, SrO, and MoO2 are mixed uniformly according to the proportions in the target chemical formula, wherein the mass ratio n of the first precursor and the second precursor is 0.5 (i.e., 0.5:1). Then, the mixture is calcined at 900°C for 12 hours in an air atmosphere, and after cooling, the particles are dispersed into single crystal particles by air jet milling to obtain the matrix material.

[0097] (3) The above matrix material is mixed evenly with Nb2O5 and Ta2O5, wherein the mass of Nb2O5 accounts for 0.5% of the mass of the matrix material and the mass of Ta2O5 accounts for 0.3% of the mass of the matrix material. Then, it is sintered at 350°C for 7 hours in an air atmosphere to obtain a low-temperature cathode material.

[0098] The low-temperature cathode material prepared in this embodiment has the morphology of single-crystal particles, and the average size r of the single-crystal particles and the particle size d of the low-temperature cathode material are... 99 The particle size d of the low-temperature cathode material minThe electrode compaction density (PD) of the cathode sheet made from this low-temperature cathode material is shown in Table 1. Define (n×PD×d99) / (dmin×r)=DR, and the calculation results of DR are shown in Table 1, where r is in μm and d is the particle size. 99 The unit is μm, and the particle size is d. min The unit is μm, and the unit of PD is g / cm³. 3 .

[0099] The method for testing the average size r of single crystal particles of low-temperature cathode material is as follows: Take a picture of the cathode material using a scanning electron microscope (SEM) at a magnification of 5000x, measure the length and width of the particles in the field of view, that is, measure the longitudinal and transverse dimensions respectively, and then take the average of the longitudinal and transverse dimensions, which is the actual size of a certain particle. After measuring the size of several (300) particles, take the average of all the measured values ​​to obtain r.

[0100] The test method for the electrode compaction density (PD) of the cathode sheet made of low-temperature cathode material is as follows: the finished electrode sheet is rolled under a pressure of 20 MPa for 2 minutes, and the thickness and mass of the electrode sheet are measured to calculate the compaction density of the electrode sheet.

[0101] The preparation method of the positive electrode sheet made of low temperature positive electrode material is as follows: The low temperature positive electrode material is uniformly mixed with conductive carbon black SuperP, carbon nanotubes CNT, polyvinylidene fluoride PVDF and N-methylpyrrolidone NMP in a mass ratio of 97.2:1.0:0.8:1.0:100 to obtain a slurry. Then, the slurry is uniformly coated on aluminum foil and dried to obtain the positive electrode sheet.

[0102] Examples 2-7

[0103] The preparation methods of the low-temperature cathode materials provided in Examples 2-7 are basically the same as those in Example 1, except that the heating and dehydration temperature, the heating and dehydration time, or the mass ratio n of the first precursor and the second precursor are different, as shown in Table 1 below.

[0104] The average size r and particle size d of the single crystal particles of the low-temperature cathode materials prepared in Examples 2-7 99 The particle size d of the low-temperature cathode material min The electrode compaction density (PD) results and DR values ​​of the cathode sheets prepared from various low-temperature cathode materials are shown in Table 1. The testing methods for r and PD, as well as the preparation methods for the cathode sheets, are the same as in Example 1.

[0105] Example 8

[0106] The low-temperature cathode material provided in this embodiment includes a matrix material and a coating layer covering the surface of the matrix material. The matrix material has the general formula Li.1.04 Ni 0.75 Co 0.13 Mn 0.12 Nb 0.005 Ta 0.002 B 0.002 O 2.029 The main components of the coating layer are SrO and MoO2. The preparation method of this low-temperature cathode material includes the following steps:

[0107] (1) The second precursor Ni 0.75 Co 0.13 Mn 0.12 (OH)₂ was heated at 145°C for 2.5 h in a dry atmosphere to remove water, yielding the first precursor Ni. 0.75 Co 0.13 Mn 0.12 (OH)2. The water content in the first precursor is 614 ppm, and the water content in the second precursor is 2820 ppm.

[0108] (2) The first precursor, the second precursor, lithium hydroxide, Nb2O5, Ta2O5, and B2O3 are mixed uniformly according to the proportions in the target chemical formula, wherein the mass ratio n of the first precursor and the second precursor is 1 (i.e., 1:1). Then, the mixture is calcined at 950°C for 8 hours in an air atmosphere, and after cooling, the particles are dispersed into single crystal particles by air jet milling to obtain the matrix material.

[0109] (3) The above matrix material is mixed evenly with SrO and MoO2, wherein the mass of SrO accounts for 0.4% of the mass of the matrix material and the mass of MoO2 accounts for 0.8% of the mass of the matrix material. Then, it is sintered at 450°C for 4 hours in an air atmosphere to obtain a low-temperature cathode material.

[0110] The low-temperature cathode material prepared in this embodiment has the morphology of single-crystal particles, and the average size r of the single-crystal particles and the particle size d of the low-temperature cathode material are... 99 The particle size d of the low-temperature cathode material min The results of the electrode compaction density (PD) and the calculated DR of the cathode sheet prepared from the low-temperature cathode material are shown in Table 1. The testing methods for DR and PD, as well as the preparation method of the cathode sheet, are the same as in Example 1.

[0111] Example 9

[0112] The low-temperature cathode material provided in this embodiment includes a matrix material and a coating layer on the surface of the matrix material. The chemical formula of the matrix material is the same as that in Example 1. The main components of the coating layer are ZrO2, Al2O3 and WO3. The preparation method of the low-temperature cathode material is basically the same as that in Example 1, except that in step (3), Nb2O5 and Ta2O5 are replaced with ZrO2, Al2O3 and WO3. The mass of ZrO2 accounts for 0.7% of the mass of the matrix material, the mass of Al2O3 accounts for 1% of the mass of the matrix material, and the mass of WO3 accounts for 0.3% of the mass of the matrix material.

[0113] The low-temperature cathode material prepared in this embodiment has the morphology of single-crystal particles, and the average size r of the single-crystal particles and the particle size d of the low-temperature cathode material are... 99 The particle size d of the low-temperature cathode material min The results of the electrode compaction density (PD) and the calculated DR of the cathode sheet prepared from the low-temperature cathode material are shown in Table 1. The testing methods for DR and PD, as well as the preparation method of the cathode sheet, are the same as in Example 1.

[0114] Comparative Example 1

[0115] The preparation method of the low-temperature cathode material provided in this comparative example is basically the same as that in Example 1, except that the second precursor is not heated and dehydrated, that is, the first precursor is not added, but only the second precursor (n=0) is added according to the proportion of the target chemical formula.

[0116] The low-temperature cathode material prepared in this comparative example has the morphology of single-crystal particles. The average size r of the single-crystal particles and the particle size d of the low-temperature cathode material are shown in the figure. 99 The particle size d of the low-temperature cathode material min The results of the electrode compaction density (PD) and the calculated DR of the cathode sheet prepared from the low-temperature cathode material are shown in Table 1. The testing methods for DR and PD, as well as the preparation method of the cathode sheet, are the same as in Example 1.

[0117] Comparative Examples 2-5

[0118] The preparation methods of the low-temperature cathode materials provided in Comparative Examples 2-5 are basically the same as those in Example 1, except that the heating and dehydration temperature, the heating and dehydration time, or the mass ratio n of the first precursor and the second precursor are different, as shown in Table 1 below.

[0119] The average size r and particle size d of the single crystal particles of the low-temperature cathode materials prepared in Comparative Examples 2-5 99 The particle size d of the low-temperature cathode material minThe electrode compaction density (PD) results and DR values ​​of the cathode sheets prepared from various low-temperature cathode materials are shown in Table 1. The testing methods for r and PD, as well as the preparation methods for the cathode sheets, are the same as in Example 1.

[0120] Table 1. Preparation parameters and performance parameters of low-temperature cathode materials

[0121]

[0122]

[0123] Experimental Example

[0124] Using the low-temperature positive electrode materials prepared in each embodiment and comparative example as positive electrode active materials, soft-pack battery cells were fabricated according to the following method: Positive electrode active materials, conductive carbon black Super P, carbon nanotubes (CNTs), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) were uniformly mixed in a mass ratio of 97.2:1.0:0.8:1.0:100 to obtain a positive electrode slurry. This positive electrode slurry was uniformly coated onto aluminum foil and dried to obtain a positive electrode sheet. The electrode sheet was then rolled to a compaction density of 3.45 g / cm³. 3 A rolled positive electrode sheet was obtained. The negative electrode active material (natural graphite), conductive agent (acetylene black), thickener (sodium carboxymethyl cellulose), and binder (styrene-butadiene rubber) were mixed at a mass ratio of 96.4:1:1.2:1.4. Deionized water was then added as a solvent, and the mixture was thoroughly stirred to obtain a negative electrode slurry. This negative electrode slurry was uniformly coated onto copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet was obtained. Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a volume ratio of 1:1:1 to form an organic solvent system. Fully dried lithium hexafluorophosphate was dissolved in this organic solvent system to prepare an electrolyte with a concentration of 1 mol / L. The separator was a porous polyethylene membrane with a thickness of 11 μm. The rolled positive electrode sheet, negative electrode sheet, separator, and electrolyte were combined to form a 1 Ah soft-pack battery cell, and its electrical performance was measured according to the following method. The results are shown in Table 2.

[0125] The low-temperature discharge performance test method is as follows: Each pouch cell is placed at 25℃ and charged to 4.35V using a constant current of 0.33A, then charged to a cutoff current of 50mA using a constant voltage of 4.35V; then discharged to 2.8V using a constant current of 0.33A, and this discharge capacity is recorded as the 25℃ discharge capacity. The pouch cell is then placed at 25℃ and charged to 4.35V using a constant current of 0.33A, then charged to a cutoff current of 50mA using a constant voltage of 4.35V; finally, the pouch cell is placed at -20℃ for 3 hours to reach a stable state, and then discharged to 2.5V using a constant current of 0.33A, and this discharge capacity is recorded as the -20℃ discharge capacity. Low-temperature discharge performance = -20℃ discharge capacity / 25℃ discharge capacity × 100%.

[0126] The high-temperature storage gas generation test method is as follows: At room temperature, charge the battery to 4.35V at a rate of 0.33C, and record the initial volume V1 using the water displacement method. Then, store the battery in a 60℃ constant temperature oven. Every 7 days, remove the battery from the oven, allow it to cool to room temperature, and measure its volume, recording it as V7. Then, charge the battery again to 4.35V at a rate of 0.33C, and again store it in a 60℃ constant temperature oven. Every 7 days, remove the battery from the oven, allow it to cool to room temperature, and measure its volume, recording it as V7. x Where x is the number of days the battery was stored (28 days in Table 2). The test was conducted sequentially, and the change in battery volume compared to V1 corresponds to the amount of gas produced during cell storage. The formula for calculating the amount of gas produced by the battery is: (V... x -V1) / V1×100%.

[0127] Table 2 Electrochemical performance test results

[0128] Group Discharge capacity at -20°C / 25°C discharge capacity (%) Gas generation amount after 28 days storage (%) Example 1 72 5 Example 2 69 3 Example 3 71 1 Example 4 71 1 Example 5 68 6 Example 6 69 5 Example 7 70 3 Example 8 75 4 Example 9 73 2 Comparative Example 1 53 12 Comparative Example 2 59 11 Comparative Example 3 62 13 Comparative Example 4 53 10 Comparative Example 5 55 8

[0129] As shown in Tables 1 and 2, the cathode materials of Comparative Examples 1 to 5 do not satisfy 30 ≤ (n × PD × d) 99 ) / (d min The value of ×r)≤100 results in poor low-temperature discharge performance and poor gas generation performance.

[0130] Each embodiment satisfies 30 ≤ (n × PD × d) 99 ) / (d min With a particle size of ×r)≤100, the cathode material exhibits good uniformity in particle distribution, excellent low-temperature charge-discharge performance, and superior high-temperature storage performance.

[0131] Specifically, by comparing Example 1 with Examples 2-7, it can be seen that the heating and dehydration temperature, the heating and dehydration time, and the mass ratio n of the first precursor and the second precursor all affect the DR value, thereby affecting the low-temperature discharge performance and high-temperature storage performance.

[0132] Furthermore, a comparison of Example 1 and Example 9 shows that the composition and mass percentage of the coating layer also affect the low-temperature discharge performance and high-temperature storage performance of the battery.

[0133] In summary, this invention improves the low-temperature charge-discharge performance of the cathode material by controlling the cobalt content to reduce the cost of the cathode material. It also enhances the high-temperature stability of the cathode material.

[0134] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A low temperature cathode material, characterized in that, The substrate material and a cladding layer cladded on the surface of the substrate material; The general formula of the base material is Li x Ni y Co z Mn 1-y-z A q O 2-t , wherein, 0.98≤x≤1.05, 0.55≤y≤0.75, 0.02≤z≤0.15, 0≤q≤0.01, 0≤t≤0.03, A includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta elements. The cladding layer contains an oxide of Q element, wherein Q includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta; The preparation raw material of the low-temperature cathode material includes a nickel-cobalt-manganese hydroxide precursor material, the nickel-cobalt-manganese hydroxide precursor material includes a first precursor and a second precursor, the first precursor is mainly formed by heating and dehydrating the second precursor, the water content in the first precursor is ≤1500 ppm, the water content in the second precursor is ≥2000 ppm, and the mass ratio of the first precursor to the second precursor is n; The morphology of the low-temperature cathode material is single-crystal particles, the average size of the single-crystal particles is r, and the electrode compaction density of the cathode sheet containing the low-temperature cathode material is PD. The morphology of n, r, and PD is related to the particle size d of the low-temperature cathode material. 99 and particle size d min The following relationship must be satisfied: 30 ≤ (n × PD × d) 99 ) / (d min ×r)≤100; where r is in μm and d is the particle size. 99 The unit is μm, and the particle size is d. min The unit is μm, and the unit of PD is g / cm³. 3 ; The n = 0.5~1.2; The r = 1.4~1.8 μm; The d 99 = 9.0-15.0 μm; The d min = 0.2-0.5 μm; The PD = 3.5-3.8 g / cm 3 ; The water content in the first precursor is 500~1500 ppm; The water content in the second precursor is 2000~5000 ppm.

2. The low temperature cathode material of claim 1, wherein, The r is measured by a scanning electron microscope.

3. The method for preparing the low-temperature cathode material according to any one of claims 1 to 2, characterized in that, The method comprises the following steps: The second precursor is heated and dehydrated to obtain the first precursor; the first precursor, the second precursor, a lithium source and a first additive are mixed and calcined to obtain the substrate material; the first additive includes an A element, wherein A includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta; The substrate material is mixed with a second additive and sintered to obtain the low-temperature cathode material; the second additive includes a Q element, wherein Q includes at least one of Ti, Zr, Al, W, B, Mg, Sr, Mo, Nb and Ta.

4. The method for preparing the low-temperature cathode material according to claim 3, characterized in that, The heating and dehydration temperature is 100~150 ℃, and / or the heating and dehydration time is 1~3 h.

5. The method for preparing the low-temperature cathode material according to claim 3, characterized in that, At least one of the following conditions is met: (1) The calcination temperature is 850~950 ℃; (2) The holding time of the calcination is 8~16 h; (3) The calcination further includes a crushing step.

6. The method for preparing the low-temperature cathode material according to claim 3, characterized in that, The sintering temperature is 300~600 ℃, and / or the holding time of the sintering is 3~7 h.

7. A positive electrode sheet characterized by comprising: The low-temperature cathode material according to any one of claims 1~2.

8. A lithium-ion battery, characterized by The cathode sheet according to claim 7.

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