Positive electrode materials, preparation methods and applications thereof, lithium-ion batteries

Abstract

The present invention relates to the field of positive electrode materials for lithium ion batteries, and discloses a positive electrode material, a preparation method and application thereof, and a lithium ion battery. The positive electrode material is a secondary particle formed by agglomeration of primary particles; the pore size d of the secondary particle is obtained by BJH. 10 d 50 and d 90 Satisfy the following relationship: 10nm≤d 50 ≤40nm; 1≤k 90 ≤8; where k 90 =(d 90 ‑d 10 ) / d 50 The positive electrode material has a specific pore size, pore size distribution, pore size area, and microcrystalline structure, so that the short-term performance, such as the initial charge and discharge capacity, and the long-term performance, such as the capacity retention rate, of the lithium-ion battery prepared from the positive electrode material can be improved during the charge and discharge process.

Description

Technical Field

[0001] The present invention relates to the field of positive electrode materials for lithium-ion batteries, and in particular to a positive electrode material, a preparation method and application thereof, and a lithium-ion battery. Background Art

[0002] With the world's urgent need for new energy, more and more clean energy is being used in power and power equipment. Since Sony pioneered the lithium-ion battery in the 1990s, its advantages, such as high specific energy and recyclability, have attracted the attention of numerous energy storage equipment companies and the scientific research community. Lithium-ion battery cathode materials have evolved through the development of LiCoO2, Li2MnO4, and LiFePO4, with current development focusing on ternary materials.

[0003] As the country's requirements for the range and safety of electric vehicles become increasingly higher, the scientific research community has conducted in-depth research on high-nickel materials in ternary materials. Among them, the direct impact of the pore size on the surface and interior of the positive electrode material on the material performance is becoming increasingly apparent. The larger and more numerous the pore size, the more intuitively the looseness of the surface and interior of the material appears. During the charging and discharging process, it provides enough interfaces for the immersion of electrolyte and the deintercalation of lithium ions, effectively increasing the actual capacity and single-time endurance of the positive electrode material used in the battery. However, the larger and more numerous the pore size, the more likely it is to cause the collapse of the surface crystal structure during the lithium ion deintercalation process, thereby reducing the actual service life of the battery. Therefore, in the preparation process of the positive electrode material, how to effectively control the most suitable pore distribution in the particles, especially the pore size and pore number, is very important.

[0004] CN108123119A discloses a nickel-based active material for a lithium secondary battery, wherein the secondary particles have an external porosity ranging from 6% to 20% and an internal porosity of 5%. This prior art includes positive electrode materials with a higher external porosity than internal porosity. In actual use, electrolyte quickly penetrates the material surface. While the looser external structure can improve initial capacity, the surface easily collapses during repeated charge and discharge cycles, resulting in irreversible "dead lithium." Furthermore, the denser internal structure significantly reduces capacity in the later stages of charge and discharge, an undesirable situation. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of the inability to balance the short-term and long-term performance of lithium-ion batteries during the charge and discharge process in the prior art, and to provide a positive electrode material and its preparation method and application. The positive electrode material has a specific pore size, pore size distribution, pore size area and microcrystalline structure, so that the lithium-ion battery prepared from the positive electrode material can improve both the short-term performance, such as the initial charge and discharge capacity, and the long-term performance, such as the capacity retention rate, during the charge and discharge process.

[0006] In order to achieve the above object, the present invention provides a positive electrode material in a first aspect, characterized in that the positive electrode material is a secondary particle formed by agglomeration of primary particles;

[0007] The pore size d of the secondary particles obtained by BJH 10 d 50 and d 90 Satisfy the following relationship: 10nm≤d 50 ≤40nm; 1≤k 90 ≤8; where k 90 =(d 90 -d 10 ) / d 50 .

[0008] The second aspect of the present invention provides a method for preparing a positive electrode material, characterized by: (1) preparing a mixed salt solution of nickel salt, cobalt salt and M salt according to the molar ratio of Ni:Co:M=(1-xyzm):x:y; preparing a doping element G solution with a doping element;

[0009] (2) adding the mixed salt solution, precipitant, complexing agent and optionally doping element G solution into a reactor, performing a coprecipitation reaction, and then filtering, washing and drying to obtain a positive electrode material precursor;

[0010] (3) mixing and sintering the cathode material precursor, the Li source, and the optional doping element G to obtain a first sintered material;

[0011] (4) coating the first sintered material with a coating element H and then performing a heat treatment to obtain the positive electrode material;

[0012] The total time of the coprecipitation reaction is t, and the pH value at different stages of the coprecipitation reaction is controlled;

[0013] When the coprecipitation reaction is carried out to 0-t / 3, the pH value is Q1; when the coprecipitation reaction is carried out to t / 3-2 / 3t, the pH value is Q2; when the coprecipitation reaction is carried out to 2 / 3t-t, the pH value is Q3;

[0014] Among them, 13>Q1>Q2>Q3>10.

[0015] The third aspect of the present invention provides a positive electrode material prepared by the above preparation method.

[0016] A fourth aspect of the present invention provides a use of the above-mentioned positive electrode material in a lithium-ion battery.

[0017] Through the above technical solution, the positive electrode material provided by the present invention and its preparation method and application achieve the following beneficial effects:

[0018] The positive electrode material provided by the present invention has a special pore size distribution, so that the short-term performance such as the initial charge and discharge capacity and the long-term performance such as the capacity retention rate of the lithium-ion battery prepared by the positive electrode material can be improved during the charge and discharge process. Specifically, the positive electrode material provided by the present invention has a specific pore size distribution, so that in the short term during the charge and discharge process of the lithium-ion battery, the difficulty of the side reactions occurring on the surface and the electrolyte can be controlled, and the surface impedance of the lithium ions during the charge and discharge process can be controlled. Furthermore, the positive electrode material provided by the present invention has a special microcrystalline structure, pore area and pore size, so that after the collapse of the surface crystal structure of the positive electrode material, the increase of "dead lithium" on the surface can effectively compensate for the decrease in surface capacity caused by the reduction in material aging, alleviate the degree of material aging, and extend the service life of the battery.

[0019] Furthermore, in the preparation method of the positive electrode material provided by the present invention, by controlling the pH value at different stages during the co-precipitation reaction, a suitable precursor can be obtained, and then by controlling the subsequent doping and sintering processes, as well as the coating and post-treatment processes, the battery material can have a suitable pore size distribution, ensuring good short-term and long-term performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a graph showing the pore size distribution and cumulative pore size percentage of the positive electrode material prepared in Example 1;

[0021] Figure 2 is a SEM image of a cross section of the positive electrode material prepared in Example 1;

[0022] Figure 3 is a SEM image of the cross section of the positive electrode material prepared in Comparative Example 1;

[0023] Figure 4 is a SEM image of the cross section of the positive electrode material prepared in Comparative Example 2;

[0024] Figure 5 1 is a cycle curve diagram of a lithium-ion battery made from the positive electrode materials of Example 1 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0025] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0026] A first aspect of the present invention provides a positive electrode material, characterized in that the positive electrode material is a secondary particle formed by agglomeration of primary particles;

[0027] The pore size d of the secondary particles obtained by BJH 10 d 50 and d 90 Satisfy the following relationship: 10nm≤d 50 ≤40nm; 1≤k 90 ≤8; where k 90 =(d 90 -d 10 ) / d 50 .

[0028] In the present invention, d 10 The average pore size d of the cathode material obtained by BJH is arranged from small to large, and the cumulative distribution of particles is 10% of the pore size; d 50 The average pore size d of the cathode material obtained by BJH is arranged from small to large, and the cumulative distribution of particles is 50% of the pore size; d 90 It refers to the pore size of the cathode material obtained by BJH, which is arranged from small to large, and the cumulative distribution of particles is 90%.

[0029] In the present invention, the positive electrode material having the above-mentioned specific pore size and pore size distribution can improve the short-term performance, such as the initial charge and discharge capacity, and the long-term performance, such as the capacity retention rate, of the lithium-ion battery prepared from the positive electrode material during the charge and discharge process.

[0030] In the present invention, the pore size d 50 The positive electrode material has both excellent initial charge and discharge capacity and cycle performance. Specifically, when d 50 When the pore size is less than 10 nm, the internal pore size is small, and the internal Li ion shuttle is blocked by multiple obstacles, which is not conducive to the capacity of the entire material. 50 When the pore size is larger than 40nm, the internal pore size is larger and the particle strength of the material deteriorates. When the positive electrode of the battery is rolled, the particles are prone to breakage and pulverization.

[0031] In the present invention, the pore size distribution k 90 The positive electrode material has both excellent initial charge and discharge capacity and cycle performance. Specifically, when k 90 When k is less than 1, the pore size distribution tends to be consistent, which is difficult in actual production; when k 90 When it is greater than 8, the pore size inside the material is unevenly dispersed, and the degree of electrolyte infiltration is different, resulting in different charge and discharge depths, and ultimately causing the cycle to deteriorate.

[0032] Furthermore, the pore size d obtained by BJH of the secondary particles is 10 d50 and d 90 Satisfy the following relationship: 12nm≤d 50 ≤35nm; 2≤k 90 ≤6.

[0033] According to the present invention, the average size of the pore area S of the secondary particles is II The average area S of the primary particles I The ratio γ satisfies the following relationship: 0.01%≤γ≤0.2%.

[0034] In the present invention, the area of ​​the average pore size of the secondary particles refers to the area calculated based on the average pore size.

[0035] In the present invention, the area S of the average pore size II Calculate according to the following formula: II =π(d 50 / 2) 2 ; Average area of ​​primary particles S I Calculate according to the following formula: I =a×b, where a is the major axis length of the primary particle and b is the minor axis length of the primary particle. a and b are obtained through the SEM electron microscope image of the primary particles. Specifically, at least 10 primary particles of the positive electrode material cross section are selected to obtain the major axis length and minor axis length of the primary particles. The average area of ​​at least 10 primary particles is calculated, which is S I .

[0036] In the present invention, when the average size of the pore area S of the secondary particles is II The average area of ​​primary particles S I When the ratio γ satisfies the above relationship, the role of the pores can be maximized without affecting the capacity, so that the battery made of the positive electrode material has both high initial charge and discharge capacity and excellent cycle performance.

[0037] Furthermore, the average pore size area S of the secondary particles is II The average area S of the primary particles I The ratio γ satisfies the following relationship: 0.05%≤γ≤0.20%.

[0038] According to the present invention, the intensity of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the peak intensity I of (104) crystal plane 104 Satisfies the following relationship: 1≤I 003 / I 104 ≤1.8.

[0039] In the present invention, the intensity of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the peak intensity I of (104) crystal plane 104 The XRD diffractometer was used for step scanning and small angle testing.

[0040] In the present invention, when the intensity of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the peak intensity I of (104) crystal plane 104 When the above relationship is satisfied, it indicates that the layered structure in the microcrystalline structure of the positive electrode material is better, thereby making it easier for lithium ions to be intercalated and deintercalated in the positive electrode material during the charge and discharge cycle, thereby improving the performance of the lithium ion battery made from the positive electrode material.

[0041] Furthermore, the intensity of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the peak intensity I of (104) crystal plane 104 Satisfy the following relationship: 1.1≤I 003 / I 104 ≤1.7.

[0042] According to the present invention, the interlayer spacing d of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the interlayer spacing d of the (104) crystal plane 104 Satisfies the following relationship: d 003 / d 104 ≥1.

[0043] In the present invention, the interlayer spacing d of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the interlayer spacing d of the (104) crystal plane 104 Calculated by Scherrer's formula: d = kλ / (βcosθ).

[0044] In the present invention, when the interlayer spacing d of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the interlayer spacing d of the (104) crystal plane 104 When the above relationship is met, it can be ensured that the material has a suitable contact area and angle when in contact with the electrolyte, thereby effectively improving the capacity cycle performance of the final material.

[0045] Furthermore, the interlayer spacing d of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the interlayer spacing d of the (104) crystal plane 104 Satisfy the following relationship: 1.2≤d 003 / d 104 ≤3.

[0046] According to the present invention, the particle sizes D5 and D 50 and D 95 The following relationship is satisfied:

[0047] 5μm≤D 50 ≤20μm; 0.5≤K 95 ≤2, where K 95 =(D 95 -D5) / D 50 .

[0048] In the present invention, the particle size D of the positive electrode material 50 The above range must be met. If the D 50 When the particle size is less than 5 μm, the particle fluidity is poor, and the environmental humidity and temperature requirements are high during the material preparation and battery manufacturing process. 50 When the particle size is larger than 20 μm, the capacity of the battery cannot be fully utilized when the positive electrode material is used to prepare the battery, and the positive electrode material particles are easily crushed during the battery rolling process.

[0049] In the present invention, the particle sizes D5 and D 50 and D 95 Measured by laser particle size analyzer.

[0050] Furthermore, 8μm≤D 50 ≤15μm; 0.6≤K 95 ≤1.8.

[0051] According to the present invention, the particle strength MCT of the positive electrode material satisfies the following relationship: 60 MPa≤MCT≤200 MPa.

[0052] In the present invention, when the particle strength (MCT) of the positive electrode material falls within the above range, the material has relatively suitable strength. If the MCT is less than 60 MPa, it is easily crushed during the battery electrode manufacturing process. If the MCT is greater than 200 MPa, it also prevents the intercalation and deintercalation of lithium ions. Only when the particle strength of the positive electrode material falls within the above range can the overall performance of the material be improved.

[0053] In the present invention, the particle strength MCT of the positive electrode material is measured by a micro compression tester.

[0054] Further, 80MPa≤MCT≤180MPa.

[0055] According to the present invention, the BET of the positive electrode material satisfies the following relationship: 0.25m 2 / g≤BET≤0.95m 2 / g.

[0056] In the present invention, when the specific surface area (BET) of the cathode material meets the above range, the pores on the surface of the cathode material effectively increase the contact area when the material contacts the electrolyte, effectively improving the initial capacity of the material. However, if the BET of the cathode material is too high and the surface pores are too large, the surface crystal structure is more likely to collapse during long-term charge and discharge cycles, resulting in rapid attenuation of the reversible capacity. Therefore, having a suitable BET can ensure that the overall performance of the material is improved.

[0057] Furthermore, 0.3m 2 / g≤BET≤0.85m 2 / g.

[0058] According to the present invention, the composition of the positive electrode material is as shown in Formula I:

[0059] Li e (Ni 1-x-y-z-m Co x M y G z H m )O2 Formula I;

[0060] Among them, 0.9≤e≤1.3, x≤(1-xyzm), y≤(1-xyzm), 0.5≤1-xyzm<1, 0≤y<0.2, 0≤z<0.05, 0≤m<0.05, y and z are not 0 at the same time;

[0061] M is selected from Al and / or Mn, G is selected from at least one element in Groups IIA-IIIA of Periods 2-5, and H is selected from at least one element of B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

[0062] In the present invention, the positive electrode material contains a doping element G and a coating element H, and specific types of doping elements G and coating elements H are selected, thereby forming different bonds between the transition metal in the positive electrode material and different doping and coating elements. In particular, after being treated under appropriate process conditions, the battery made from the positive electrode material has a high initial charge and discharge capacity and excellent cycle performance.

[0063] Furthermore, 0.95≤e≤1.1, 0.53≤1-xyzm<0.99, 0 <y<0.15,0<z<0.03,0<m<0.03。

[0064] Furthermore, M is Mn, G is at least one element selected from Al, Mg, Ca, Sr, Zr, Nb and Mo, and H is at least one element selected from B, Zr, Nb, Al and Y.

[0065] The preparation method of the positive electrode material in the present invention includes a design in which the pH value of the precursor is continuously changed during preparation. Specifically, the pH value varies within the range of 10-13.

[0066] The preparation method of the positive electrode material in the present invention also includes the design of the sintering temperature and sintering time during the sintering process, wherein the sintering temperature is 650-900° C. and the sintering time is 6-30 hours.

[0067] The preparation method of the positive electrode material in the present invention also includes designing the treatment temperature and treatment time during the surface heat treatment process, wherein the heat treatment temperature is 200-500° C. and the heat treatment time is 5-18 hours.

[0068] A second aspect of the present invention provides a method for preparing a positive electrode material, characterized in that the preparation method comprises the following steps:

[0069] (1) preparing a mixed salt solution of nickel salt, cobalt salt and M salt according to the molar ratio of Ni:Co:M=(1-xyzm):x:y; preparing a doping element G solution by adding a doping element;

[0070] (2) adding the mixed salt solution, precipitant, complexing agent, and optionally doping element G solution and optionally doping element N solution into a reactor, performing a coprecipitation reaction, and then filtering, washing, and drying to obtain a positive electrode material precursor;

[0071] (3) mixing and sintering the cathode material precursor, the Li source, and the optional doping element G to obtain a first sintered material;

[0072] (4) coating the first sintered material with a coating element H and then performing a heat treatment to obtain the positive electrode material;

[0073] The total time of the coprecipitation reaction is t, and the pH value at different stages of the coprecipitation reaction is controlled;

[0074] When the coprecipitation reaction is carried out to 0-t / 3, the pH value is Q1; when the coprecipitation reaction is carried out to t / 3-2 / 3t, the pH value is Q2; when the coprecipitation reaction is carried out to 2 / 3t-t, the pH value is Q3;

[0075] Among them, 13>Q1>Q2>Q3>10.

[0076] The preparation method of the cathode material of the present invention includes a design that continuously changes the pH during the precursor preparation process. Specifically, the pH value varies within the range of 10-13. By controlling the pH value at different stages of the coprecipitation reaction, a suitable precursor can be obtained. Then, through the control of the subsequent doping and sintering processes, as well as the coating and post-treatment processes, the battery material has a suitable pore size distribution, ensuring good short-term and long-term performance.

[0077] According to the present invention, the nickel salt is selected from at least one of nickel sulfate, nickel nitrate, and nickel chloride; the cobalt salt is selected from at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride; the M salt is selected from Al salts and / or Mn salts, more preferably, the Al salt is selected from at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride, and the Mn salt is selected from at least one of manganese sulfate, manganese nitrate, and manganese chloride. The precipitant is an alkaline solution, such as sodium hydroxide solution; and the complexing agent is aqueous ammonia.

[0078] According to the present invention, 10h≤t≤120h, preferably 15h≤t≤100h.

[0079] According to the present invention, the temperature of the coprecipitation reaction is 30-100°C, preferably 40-70°C.

[0080] Furthermore, in order to further make the positive electrode material have specific pore size distribution and pore size as well as appropriate particle size, particle strength and other characteristics, Q1, Q2 and Q3 are made to decrease in an arithmetic progression.

[0081] According to the present invention, the coprecipitation reaction is carried out in the presence of nitrogen and / or oxygen.

[0082] Furthermore, when the coprecipitation reaction is carried out to 0-t / 3, the coprecipitation reaction is carried out in the presence of nitrogen and oxygen, and the volume fraction of the oxygen is 0-5 vol% based on the total volume of the nitrogen and oxygen; when the coprecipitation reaction is carried out to t / 3-2 / 3t, the coprecipitation reaction is carried out in the presence of nitrogen and oxygen, and the volume fraction of the oxygen is 0-3 vol% based on the total volume of the nitrogen and oxygen; when the coprecipitation reaction is carried out to 2 / 3t-t, the coprecipitation reaction is carried out in the presence of nitrogen.

[0083] In the present invention, the 0-t / 3 stage and t / 3-2 / 3t of the coprecipitation reaction are carried out in the presence of oxygen, and when the volume fraction of oxygen is controlled to meet the above range, a precursor with a specific structure and pore size can be obtained.

[0084] Furthermore, in the 0-t / 3 stage of the coprecipitation reaction, the volume fraction of the oxygen is 0-3 vol% based on the total volume of nitrogen and oxygen; in the t / 3-2 / 3t stage of the coprecipitation reaction, the volume fraction of the oxygen is 0-2 vol% based on the total volume of nitrogen and oxygen.

[0085] In the present invention, the cathode material precursor has a composition shown in Formula II:

[0086] (Ni 1-x-y Co x M y )(OH)2 Formula II;

[0087] Among them, x≤(1-xy), y≤(1-xy), 0.5≤1-xy<1, 0≤y<0.2.

[0088] According to the present invention, the amount of the Li source added is such that: 0.9≤[n(Li)] / [n(Ni)+n(Co)+n(M)]≤1.3.

[0089] Furthermore, the amount of the Li source added is such that: 0.95≤[n(Li)] / [n(Ni)+n(Co)+n(M)]≤1.2.

[0090] In the present invention, the doping element G can be introduced during the coprecipitation reaction process described in step (2) or during the sintering process described in step (3). There is no particular requirement for the amount of the doping element G solution added in step (2) and / or the amount of the doping element G added in step (3), as long as the amount of the doping element G is less than 5000 ppm based on the total weight of the positive electrode material precursor. The preparation method adopted in the present invention includes the design of the doping element in the sintering process and the sintering temperature and sintering time in the sintering procedure, wherein the sintering temperature is 650-900°C and the sintering time is 6-30h.

[0091] The sintering conditions include: a sintering temperature of 650-900° C.; and a sintering time of 6-30 hours.

[0092] According to the present invention, the doping element G is selected from at least one element selected from Groups IIA-IIIA of Periods 2-5.

[0093] In the present invention, by controlling the type of doping element G and the sintering conditions, especially the sintering temperature, the growth of the primary particles can be further controlled, thereby controlling the average area of ​​the primary particles, and then the average pore area and the primary particle area of ​​the prepared positive electrode material meet the limitations of this application, and can maximize the role of pores without affecting the performance of capacity. Specifically, by using the above-mentioned specific type of doping element G, it is possible to increase the material of the crystal particles during the reaction process, control the direction of growth and the crystal plane, thereby controlling the ratio of the major diameter to the minor diameter of the grains, and controlling the interface contact and pores between the grains. By controlling the content of the doping element G and the sintering temperature to meet the above range, the porosity on the surface of the positive electrode material can be reduced, and the residual alkali on the surface of the positive electrode material can be controlled.

[0094] Furthermore, the doping element G solution and the added amount of the doping element G are such that, based on the total weight of the positive electrode material precursor, the amount of the doping element G is 0-3000 ppm.

[0095] Furthermore, the sintering conditions include: a sintering temperature of 700-890° C.; and a sintering time of 8-25 hours.

[0096] Furthermore, the doping element G is at least one element selected from Al, Mg, Ca, Sr, Zr, Nb and Mo.

[0097] The preparation method employed in the present invention includes designing a coating element during the surface heat treatment process and the treatment temperature and treatment time in the heat treatment procedure. The heat treatment temperature is 200-500°C and the heat treatment time is 5-18 hours. The amount of the coating element H is less than 5000 ppm based on the total weight of the first sintered material.

[0098] In the present invention, when the amount of coating element H meets the above range, the transition metal and the doping element on the surface can be bonded to each other to stabilize the crystal structure, while ensuring that the appropriate addition amount does not block the entry and exit of lithium ions on the surface of the material, effectively ensuring the initial capacity of the material.

[0099] Furthermore, based on the total weight of the first sintered material, the amount of the coating element H is 0-3000 ppm.

[0100] According to the present invention, the coating element H is selected from at least one element of B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

[0101] In the present invention, the use of the above-mentioned special type of element as the coating element H can enable the coating element to further react with the residual alkali on the surface to generate lithium metal oxide, forming a coating layer on the surface of the material, stabilizing the structure of the material surface, and improving the cycle performance.

[0102] Furthermore, the coating element H is at least one element selected from B, Al, Zr, Nb and Y.

[0103] According to the present invention, the heat treatment conditions include: heat treatment temperature of 300-500° C.; heat treatment time of 5-18 hours.

[0104] In the present invention, the heat treatment is carried out under the above-mentioned specific conditions, so that the material only reacts with the residual alkali on the surface without further entering the interior of the crystal lattice, and does not form an internal crystal structure that blocks the shuttle of lithium ions. Only a thin coating layer is formed on the surface of the material, which effectively improves the cycle performance without reducing the capacity of the material.

[0105] Furthermore, the heat treatment conditions include: heat treatment temperature of 300-480° C.; heat treatment time of 5-12 hours.

[0106] The third aspect of the present invention provides a positive electrode material prepared by the above preparation method.

[0107] According to the present invention, the positive electrode material is a secondary particle formed by agglomeration of primary particles;

[0108] The pore size d of the secondary particles obtained by BJH 10 d 50 and d 90 Satisfy the following relationship: 10nm≤d 50 ≤40nm; 1≤k 90 ≤8; where k 90 =(d 90 -d 10 ) / d 50 .

[0109] According to the present invention, the average pore size area S of the secondary particles is II The average area S of the primary particles I The ratio γ satisfies the following relationship: 0.01%≤γ≤0.2%.

[0110] According to the present invention, the intensity of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the peak intensity I of (104) crystal plane 104 Satisfies the following relationship: 1≤I 003 / I 104 ≤1.8.

[0111] According to the present invention, the interlayer spacing d of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the interlayer spacing d of the (104) crystal plane 104 Satisfies the following relationship: d 003 / d 104 ≥1.

[0112] According to the present invention, the particle sizes D5 and D 50 and D 95 The following relationship is satisfied:

[0113] 5μm≤D 50 ≤20μm; 0.5≤K 95 ≤2, where K 95 =(D 95 -D5) / D 50 .

[0114] According to the present invention, the particle strength MCT of the positive electrode material satisfies the following relationship: 60 MPa≤MCT≤200 MPa.

[0115] According to the present invention, the BET of the positive electrode material satisfies the following relationship: 0.25m 2 / g≤BET≤0.95m 2 / g.

[0116] According to the present invention, the composition of the positive electrode material is as shown in Formula I:

[0117] Li e (Ni 1-x-y-z-m Co x M y G z H m )O2 Formula I;

[0118] Among them, 0.9≤e≤1.3, x≤(1-xyzm), y≤(1-xyzm), 0.5≤1-xyzm<1, 0≤y<0.2, 0≤z<0.05, 0≤m<0.05, y and z are not 0 at the same time;

[0119] M is selected from Al and / or Mn, G is selected from at least one element in Groups IIA-IIIA of Periods 2-5, and H is selected from at least one element of B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

[0120] A fourth aspect of the present invention provides a use of the above-mentioned positive electrode material in a lithium-ion battery.

[0121] The present invention will be described in detail below through examples.

[0122] (1) X-ray diffraction test

[0123] The sample was measured using an XRD diffractometer (SmartLab 9KV) using a Cu Ka radiation source and step-scan technology for small-angle testing. The diffraction patterns for the 003 and 104 peaks were measured. First, excess material was added to the glass sample holder. Under LED light, the surface was gently pressed and scraped flat. The parameters were set, the test type was selected, and the BB optical path was adjusted. The hatch was opened, the sample was placed on the sample stage, and the "Execute" button was clicked to perform the test. The data was saved to complete the test.

[0124] (2) BET and pore size distribution test

[0125] The test was performed using a Tri-star 3020 surface area analyzer. A 3g sample was weighed and the sample tube was installed on the vacuum connector on the degassing station. The heating temperature was set to 300°C and the degassing time was set to 120 minutes. After degassing, the sample tube was cooled. The mass of the empty sample tube and the mass of the degassed sample and sample tube were entered into the analyzer software interface. The specific surface area data (BET method and BJH pore size test method) calculated by the software was recorded to complete the specific surface area and pore size distribution test of the cathode material sample.

[0126] (3) Particle size test

[0127] Use a Mastersizer 2000 laser particle size analyzer for testing. In the "Measurement" section of the software, change the "Sample Test Time" and "Background Test Time" settings to 6 seconds. In the "Measurement Cycles" section, change the number of cycles to 3 and the delay to 5 seconds. Click "Create Average Results from Measurement" to record the average results. Next, click "Start" to automatically measure the background. After the automatic measurement is complete, add 40 ml of sodium pyrophosphate, then use a medicine spoon to add a small amount of sample until the obscuration reaches 1 / 2 of the visual 10-20% area. Click "Start." Finally, record the three results and the average.

[0128] (4) MCT test

[0129] Measurements were performed using an MCT-210 micro compression tester. First, open the MCT-210 testing software and clamp the sample stage to the center of the platen, ensuring it remains at least 3 cm below the objective lens. Turn on the LED light on the main unit and adjust the stage height until the sample particle image is clear in the CCD image display window by turning the handwheel on the lower right. Click "Start Testing," measure the particle diameter, and save the pre-compression image. Rotate the handwheel to bring the particle's apex to the lens's focal point. Push the sample stage right under the platen to begin the compression test. After compression is complete, push the stage left under the objective lens and rotate the handwheel until the compressed image is clear. Save the image.

[0130] (5) Morphology of cathode materials

[0131] The morphology of the cathode material was examined using a scanning electron microscope (SEM). The cathode material was first embedded and then thinned in an ion milling apparatus to obtain a cross-section sample of the ion-milled particles. Finally, the cross-section sample was mounted on the SEM sample stage for SEM analysis.

[0132] (6) Battery performance test

[0133] After making the button battery, let it stand for 2 hours. After the open circuit voltage stabilizes, charge the positive electrode with a current density of 0.1C to a cutoff voltage of 4.3V, then charge it at a constant voltage for 30 minutes, and then discharge it with the same current density to a cutoff voltage of 3V; repeat the same process once more and regard the battery at this time as an activated battery.

[0134] The cycle performance test is as follows: using an activated battery, the capacity retention rate is measured by cycling 50 times at a current density of 1C (200mA / g) in the voltage range of 3-4.3V at a temperature of 45°C.

[0135] The raw materials used in the examples and comparative examples are all commercially available products.

[0136] Example 1

[0137] (1) Nickel sulfate, cobalt sulfate, and manganese sulfate are added to water at a molar ratio of nickel sulfate: cobalt sulfate: manganese sulfate = 85:9:6 to prepare a mixed salt solution.

[0138] (2) Sodium hydroxide aqueous solution is added to the synthesis reactor as a precipitant, ammonia water is used as a complexing agent, the temperature of the synthesis reactor is controlled at 45°C, and the total time t of the coprecipitation reaction is 90h. In the first stage, the pH in the synthesis reactor is controlled to be 12.5, the reaction residence time is 30h (the coprecipitation reaction is carried out to t / 3), and 97vol% nitrogen and 3vol% oxygen are introduced throughout the process; in the second stage, the pH of the reactor is controlled to be 11.9, the reaction residence time is 30h (the coprecipitation reaction is carried out to 2t / 3), and 98vol% nitrogen and 2vol% oxygen are introduced throughout the process; in the third stage, the pH is 11.3, the reaction residence time is 30h (the coprecipitation reaction is carried out to t), and nitrogen is introduced throughout the process. After the reaction is completed, it is filtered and separated with a filter press, and then washed with sodium hydroxide solution and dried at 200°C for 8 hours to obtain the positive electrode material precursor Ni 0.85 Co 0.09 Mn 0.06 (OH)2.

[0139] (3) The cathode material precursor and LiOH were dry premixed at a molar ratio of 1:1.03. After the premixing was completed, Nb2O5 was used as a dopant, and the Nb content was 3000 ppm based on the total weight of the cathode material precursor. The mixture was sintered at 765°C for 20 hours in an oxygen atmosphere to obtain a first sintered material.

[0140] (4) The first sintered material was further surface-coated and heat-treated. The coating elements were H₃BO₃ and Y₂O₃. The amount of B was 2000 ppm, and the amount of Y was 1000 ppm, based on the mass of B and Y, based on the total weight of the first sintered material. These materials were mixed using a dry process. The heat treatment temperature was controlled at 350°C for 12 hours. After the heat treatment, the material was cooled and sieved to obtain positive electrode material A1.

[0141] Example 2-10

[0142] Positive electrode materials were prepared according to the method of Example 1. The raw material ratios and specific process conditions are shown in Table 1. Positive electrode materials A2-A10 were prepared.

[0143] Comparative Examples 1-4

[0144] The positive electrode material was prepared according to the method of Example 1. The raw material ratios and specific process conditions are shown in Table 1. Positive electrode materials D1-D4 were prepared.

[0145] Table 1

[0146]

[0147] Table 1 (continued)

[0148]

[0149]

[0150] Table 1 (continued)

[0151]

[0152]

[0153] Table 1 (continued)

[0154]

[0155] Test Case

[0156] The compositions of the positive electrode materials prepared in the examples and comparative examples are shown in Table 2. The structures and properties of the positive electrode materials were tested, and the test results are shown in Table 3.

[0157] Table 2

[0158]

[0159]

[0160] Table 3

[0161] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 <![CDATA[d 50 / nm]]> 22.1 17.5 18.5 30.3 16.7 26.7 20.2 33.2 <![CDATA[k 90 ]]> 3.2 3.8 5.7 3.4 3.1 4.5 2.8 6.2 <![CDATA[S II / nm 2 ]]> 383.6 240.5 268.8 721.1 219.0 559.9 320.5 865.7 <![CDATA[S I / nm 2 ]]> 406958 389004 748980 425278 412846 592812 385624 452685 γ 0.094％ 0.062％ 0.036％ 0.170％ 0.053％ 0.094％ 0.08％ 0.19％ <![CDATA[D 50 / μm]]> 12.8 12.5 11.7 13.5 16.5 15.2 13 12.5 <![CDATA[K 95 ]]> 0.52 0.64 1.2 0.95 0.58 0.65 0.57 0.60 MCT / MPa 112 125 95 126 150 98 135 88 <![CDATA[I 003 / I 104 ]]> 1.47 1.26 1.57 1.64 1.38 1.59 1.52 1.68 <![CDATA[d 003 / d 104 ]]> 1.55 1.52 1.38 1.62 1.59 1.48 1.65 1.75 <![CDATA[BET / m 2 / g]]> 0.49 0.56 0.54 0.60 0.48 0.55 0.50 0.36

[0162] Note: γ=S II / S I ×100% Table 3 (continued)

[0163]

[0164]

[0165] Note: γ=S II / S I ×100%

[0166] Application Examples

[0167] The positive electrode materials of the embodiment and the comparative example are used to prepare lithium-ion batteries. The specific preparation method is as follows: a composite nickel-cobalt-manganese multi-element positive electrode active material for non-aqueous electrolyte secondary batteries, acetylene black and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:3:2, coated on aluminum foil and dried, and stamped into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. The positive electrode sheet is then placed in a vacuum drying oven and dried at 120°C for 12 hours.

[0168] The negative electrode uses a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator uses a polyethylene porous membrane with a thickness of 25 μm; and the electrolyte uses an equal mixture of 1 mol / L LiPF6, ethylene carbonate (EC) and diethyl carbonate (DEC).

[0169] The performance of the lithium-ion battery was tested, and the results are shown in Table 4.

[0170] Table 4

[0171]

[0172]

[0173] Figure 1 1 is a graph showing the pore size distribution and cumulative pore size ratio of the positive electrode material A1 obtained in Example 1. As can be seen from FIG1 , the trend graph of the pore size ratio is close to a logarithmic form. Figure 2 is a SEM image of the cross section of the positive electrode material A2 obtained in Example 1, Figure 3This is a SEM image of the cross section of the positive electrode material D1 prepared in Comparative Example 1. Figure 4 This is a SEM image of the cross section of the positive electrode material D3 obtained in Comparative Example 2. Figure 2-4 It can be seen that the cross-section of the cathode material has different pore sizes and pore size distributions. Figure 5 The cycle curve of the lithium-ion battery made of positive electrode material A1, positive electrode material D1 and positive electrode material D2 is shown in FIG. Figure 5 It can be seen that the electrochemical performance of the lithium-ion battery prepared by using the positive electrode material with specific pore size and pore size distribution of the present invention is more excellent.

[0174] It can be seen from Table 2, Table 3 and Table 4 that the lithium-ion battery prepared by using the positive electrode material with specific pore size and pore size distribution of the present invention not only has a high initial charge and discharge capacity, but also has a high capacity retention rate.

[0175] Furthermore, when the positive electrode material has a specific microstructure, particle strength, etc., it can further improve the initial charge and discharge capacity and capacity retention rate of the lithium-ion battery, so that the overall performance of the battery is further improved.

[0176] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material is a secondary particle formed by agglomeration of primary particles; The pore size d of the secondary particles obtained by BJH 10 d 50 and d 90 Satisfy the following relationship: 16.7nm≤d 50 ≤40nm; 1≤k 90 ≤8; where k 90 =(d 90 -d 10 ) / d 50 ; The average size of the pore area of ​​the secondary particles S II The average area S of the primary particles I The ratio γ satisfies the following relationship: 0.01%≤γ≤0.2%; The area of ​​the average size of the pores S II Calculate according to the following formula: II =π(d 50 / 2) 2 ; Average area of ​​primary particles S I Calculate according to the following formula: I =a×b, where a is the major axis length of the primary particle and b is the minor axis length of the primary particle. a and b are obtained through the SEM electron microscope image of the primary particles. Specifically, at least 10 primary particles of the positive electrode material cross section are selected to obtain the major axis length and minor axis length of the primary particles. The average area of ​​at least 10 primary particles is calculated, which is S I ; The BET of the positive electrode material satisfies the following relationship: 0.25m 2 / g≤BET≤0.95m 2 / g; The composition of the positive electrode material is shown in Formula I: Li e (Ni 1-x-y-z-m Co x M y G z H m )O₂ of formula I; Among them, 0.9≤e≤1.3, x≤(1-xyzm), y≤(1-xyzm), 0.5≤1-xyzm<1, 0≤y<0.2, 0≤z<0.05, 0≤m<0.05, y and z are not 0 at the same time; M is selected from Al and / or Mn, G is selected from at least one element in Groups IIA-IIIA of Periods 2-5, and H is selected from at least one element of B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

2. The positive electrode material according to claim 1, wherein The pore size d of the secondary particles obtained by BJH 10 d 50 and d 90 Satisfy the following relationship: 16.7nm≤d 50 ≤35nm; 2≤k 90 ≤6.

3. The positive electrode material according to claim 1 or 2, wherein The average size of the pore area of ​​the secondary particles S II The average area S of the primary particles I The ratio γ satisfies the following relationship: 0.05%≤γ≤0.20%.

4. The positive electrode material according to claim 1 or 2, wherein The intensity of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the peak intensity I of (104) crystal plane 104 Satisfies the following relationship: 1≤I 003 / I 104 ≤1.8; And / or, the interlayer spacing d of the (003) crystal plane of the positive electrode material obtained by XRD 003 and the interlayer spacing d of the (104) crystal plane 104 Satisfies the following relationship: d 003 / d 104 ≥1; And / or, the particle size D5, D 50 and D 95 The following relationship is satisfied: 5μm≤D 50 ≤20μm; 0.5≤K 95 ≤2, where K 95 =(D 95 -D5) / D 50 ; And / or, the particle strength MCT of the positive electrode material satisfies the following relationship: 60 MPa≤MCT≤200 MPa; The BET of the positive electrode material satisfies the following relationship: 0.3m 2 / g≤BET≤0.85 m 2 / g.

5. The positive electrode material according to claim 4, wherein The intensity of the (003) crystal plane of the positive electrode material obtained by XRD is 003 and the peak intensity I of (104) crystal plane 104 Satisfy the following relationship: 1.1≤I 003 / I 104 ≤1.7; And / or, the interlayer spacing d of the (003) crystal plane of the positive electrode material obtained by XRD 003 and the interlayer spacing d of the (104) crystal plane 104 Satisfy the following relationship: 1.2≤d 003 / d 104 ≤3; And / or, the particle size D5, D 50 and D 95 The following relationship is satisfied: 8μm≤D 50 ≤15μm; 0.6≤K 95 ≤1.8, where K 95 =(D 95 -D5) / D 50 ; And / or, the particle strength MCT of the positive electrode material satisfies the following relationship: 80 MPa≤MCT≤180 MPa.

6. The positive electrode material according to claim 1 or 2, wherein In formula I, 0.95≤e≤1.1, 0.53≤1-xyzm<0.99, 0 <y<0.15,0<z<0.03,0<m<0.03; M is Mn, G is at least one element selected from the group consisting of Al, Mg, Ca, Sr, Zr, Nb, and Mo, and H is at least one element selected from the group consisting of B, Zr, Nb, Al, and Y.

7. A method for preparing the positive electrode material according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: (1) nickel salt, cobalt salt and M salt are prepared into a mixed salt solution according to the molar ratio of Ni:Co:M=(1-xyzm):x:y; and doping element G solution is prepared; (2) adding the mixed salt solution, precipitant, and complexing agent into a reactor, or adding the mixed salt solution, precipitant, complexing agent, and doping element G solution into a reactor, performing a coprecipitation reaction, and then filtering, washing, and drying to obtain a cathode material precursor; (3) mixing and sintering the cathode material precursor and the Li source, or mixing and sintering the cathode material precursor, the Li source and the doping element G to obtain a first sintered material; (4) coating the first sintered material with a coating element H and then performing a heat treatment to obtain the positive electrode material; The total time of the coprecipitation reaction is t, and the pH value at different stages of the coprecipitation reaction is controlled; When the coprecipitation reaction is in the 0-t / 3 stage, the pH value is controlled to be Q1; when the coprecipitation reaction is in the t / 3-2 / 3t stage, the pH value is controlled to be Q2; when the coprecipitation reaction is in the 2 / 3t-t stage, the pH value is controlled to be Q3; Wherein, 13>Q1>Q2>Q3>10; Q1, Q2 and Q3 decrease in an arithmetic progression; In step (4), the heat treatment conditions include: heat treatment temperature of 200-500°C; heat treatment time of 5-18h.

8. The preparation method according to claim 7, wherein 10h≤t≤120h; And / or, the temperature of the coprecipitation reaction is 30-100°C.

9. The preparation method according to claim 7 or 8, wherein 15h≤t≤100h; And / or, the temperature of the coprecipitation reaction is 40-70°C.

10. The preparation method according to claim 7 or 8, wherein In step (2), the coprecipitation reaction is carried out in the presence of nitrogen and / or oxygen.

11. The preparation method according to claim 7 or 8, wherein In step (2), when the coprecipitation reaction is carried out to 0-t / 3, the coprecipitation reaction is carried out in the presence of nitrogen and oxygen, and the volume fraction of the oxygen is 3-5 vol% based on the total volume of nitrogen and oxygen.

12. The preparation method according to claim 7 or 8, wherein In step (2), when the coprecipitation reaction is carried out to t / 3-2 / 3t, the coprecipitation reaction is carried out in the presence of nitrogen and oxygen, and the volume fraction of the oxygen is 2-3 vol% based on the total volume of nitrogen and oxygen.

13. The preparation method according to claim 7 or 8, wherein In step (2), when the coprecipitation reaction is carried out to 2 / 3t-t, the coprecipitation reaction is carried out in the presence of nitrogen.

14. The preparation method according to claim 7 or 8, wherein In step (3), the amount of the Li source added is such that: 0.9≤[n(Li)] / [n(Ni)+n(Co)+n(M)]≤1.3; and / or, in step (2) and step (3), the amount of the doping element G solution and the doping element G added is such that, based on the total weight of the positive electrode material precursor, the total amount of the doping element G is less than 5000 ppm; And / or, in step (3), the sintering conditions include: sintering temperature of 650-900°C; sintering time of 6-30h; and / or, in step (4), the amount of the coating element H is less than 5000 ppm based on the total weight of the first sintered material; And / or, in step (4), the heat treatment conditions include: heat treatment temperature of 300-480°C; heat treatment time of 5-12h; And / or, the nickel salt is selected from at least one of nickel sulfate, nickel nitrate and nickel chloride; And / or, the cobalt salt is selected from at least one of cobalt sulfate, cobalt nitrate and cobalt chloride; And / or, the M salt is selected from Al salt and / or Mn salt; And / or, the doping element G is selected from at least one element in Groups IIA-IIIA of Periods 2-5; And / or, the coating element H is selected from at least one of B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

15. The preparation method according to claim 14, wherein In step (2) and step (3), the amount of the doping element G solution and the doping element G added is such that, based on the total weight of the positive electrode material precursor, the total amount of the doping element G is 0-3000 ppm; And / or, in step (3), the sintering conditions include: sintering temperature of 700-890°C; sintering time of 8-25h; And / or, in step (4), the amount of the coating element H is 0-3000 ppm based on the total weight of the first sintered material; And / or, the Al salt is selected from at least one of aluminum sulfate, aluminum nitrate and aluminum chloride, and the Mn salt is selected from at least one of manganese sulfate, manganese nitrate and manganese chloride.

16. Use of the positive electrode material according to any one of claims 1 to 6 in a lithium ion battery.

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