CN115986073A - Positive active material and preparation method and application thereof - Google Patents
Positive active material and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a positive active material and a preparation method and application thereof. The positive active material comprises an inner core and a coating layer covering at least part of the surface of the inner core; wherein the inner core comprises a compound represented by formula 1; li a Ni b Co c M 1‑b‑c O 2 In the formula 1, a is more than or equal to 0.8 and less than or equal to 1.2, b is more than or equal to 0.5 and less than or equal to 0.96, b is more than or equal to 0.3 and less than or equal to 0.6, and M is selected from at least one of Mn, al and V; the coating layer comprises at least one of B, al, si, zr, co, ti, mg, W, sn, ce, mn, Y, hf, cu, fe, ag, la, in, sc, rh, V or Zn elements; the Dv50 of the positive electrode active material and the specific surface area BET of the positive electrode active material satisfy: BET/(Dv 50) of 3 ≤ 2 *1000 is less than or equal to 180. The positive electrode has an active materialThe special composition of the material is beneficial to improving the rate capability, the cycle performance and the safety performance of the battery.
Description
Technical Field
The invention relates to a pole piece material, in particular to a positive active material and a preparation method and application thereof, belonging to the technical field of secondary batteries.
Background
In recent years, with the rapid development of new energy automobiles and the increase of endurance mileage, the requirements of people on the rate capability, the cycle performance and the safety performance of power batteries of the new energy automobiles are higher and higher.
The positive active material is the key for improving the comprehensive performance of the battery, and at present, in order to improve the comprehensive performance of the battery, the nickel-cobalt-manganese ternary material is generally improved, wherein one method is to increase the charging voltage of the nickel-cobalt-manganese ternary material, and the other method is to increase the nickel content in the nickel-cobalt-manganese ternary material to more than 80%. The above method can improve the charge/discharge capacity of the battery, but the cycle performance and safety performance of the battery are lost.
Disclosure of Invention
The invention provides a positive active material, and the special composition and structure of the positive active material are beneficial to improving the comprehensive performance (rate capability, cycle performance and safety performance) of a battery.
The invention also provides a preparation method of the positive active material, and the positive active material can be prepared by the preparation method and has a simple preparation process.
The present invention also provides a battery including the above-described cathode active material, and thus the battery has excellent performance in rate performance, cycle performance, and safety performance.
The invention provides a positive active material, wherein the positive active material comprises an inner core and a coating layer covering at least part of the surface of the inner core;
wherein the inner core comprises a compound represented by formula 1;
Li a Ni b Co c M 1-b-c O 2 in the formula 1, the chemical formula is shown in the specification,
in the formula 1, a is more than or equal to 0.8 and less than or equal to 1.2, b is more than or equal to 0.5 and less than or equal to 0.96, b is more than or equal to 0.3 and less than or equal to 0.6, and M is selected from at least one of Mn, al and V;
the coating layer comprises at least one of B, al, si, zr, co, ti, mg, W, sn, ce, mn, Y, hf, cu, fe, ag, la, in, sc, rh, V or Zn elements;
the Dv50 of the positive electrode active material and the specific surface area BET of the positive electrode active material satisfy: BET/(Dv 50) of 3 ≤ 2 *1000 is less than or equal to 180; wherein the BET is measured in g/m 2 The Dv50 is measured in μm.
The positive electrode active material as described above, wherein the Dv50 of the positive electrode active material is 0.2 to 18 μm.
The positive electrode active material as described above, wherein the specific surface area BET of the positive electrode active material is 0.2 to 4.0m 2 /g。
The positive electrode active material as described above, wherein the surface Li of the positive electrode active material 2 CO 3 The content is less than or equal to 3000ppm; and/or the presence of a gas in the atmosphere,
the LiOH content of the surface of the positive electrode active material is less than or equal to 5000ppm; and/or the presence of a gas in the gas,
surface-free Li of the positive electrode active material + The content is less than or equal to 2000ppm.
The positive electrode active material as described above, wherein Dv50 and Dv10 of the core satisfy: dv50/Dv10 is not less than 1.5 and not more than 4.
The positive electrode active material as described above, wherein Dv90 and Dv10 of the core satisfy: dv90/Dv10 is not less than 2 and not more than 12.
The positive electrode active material as described above, wherein Dv90 and Dv50 of the core satisfy: dv90/Dv50 is not less than 1.2 and not more than 4.
The positive electrode active material as described above, wherein the ratio of the specific surface area BET of the coating layer to the specific surface area BET of the core is not less than 20.
The positive electrode active material as described above, wherein the coating layer is selected from at least one of an oxide, a fluoride, a phosphate, and a sulfate.
The invention also provides a preparation method of the positive active material, which comprises the following steps:
carrying out coprecipitation reaction on a raw material system comprising a precipitator, a nickel source, an M source and a cobalt source to obtain a core precursor;
mixing the core precursor with a lithium source to obtain a mixed system, and calcining the mixed system to obtain a core material;
mixing the core material and the coating material to obtain a second mixed system, and performing second calcination treatment on the second mixed system to obtain a positive electrode active material to be screened;
and screening the positive active material to be screened to obtain a Dv50 and a BET meeting the following conditions: 3 is not more than BET/(Dv 50) 2 * A positive electrode active material of 1000 or less than 180; wherein the BET unit of measurement is g/m 2 The Dv50 is measured in μm.
The present invention also provides a battery comprising the positive electrode active material as described above.
The positive active material has special chemical composition and structure, and after the positive active material is applied to a battery, the rate performance (the ratio of 1C discharge capacity to 0.1C discharge capacity of the battery can reach more than 93 percent), the cycle performance (the capacity retention rate after 300 cycles can reach more than 94 percent) and the safety performance (the gas production can be as low as 0.06 ml/Ah) of the battery are obviously improved.
The preparation method of the cathode active material can be used for preparing the cathode active material, is simple to operate and is convenient to popularize and apply widely.
The battery of the present invention includes the above-described cathode active material, and thus the battery has excellent performance in rate performance, cycle performance, and safety performance.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
A first aspect of the present invention provides a positive electrode active material, wherein the positive electrode active material comprises an inner core and a coating layer covering at least a part of the surface of the inner core;
wherein the inner core comprises a compound represented by formula 1;
Li a Ni b Co c M 1-b-c O 2 the chemical formula of the formula 1,
in the formula 1, a is more than or equal to 0.8 and less than or equal to 1.2, b is more than or equal to 0.5 and less than or equal to 0.96, b is more than or equal to 0.3 and less than or equal to 0.6, and M is selected from at least one of Mn, al and V;
the coating layer comprises at least one of B, al, si, zr, co, ti, mg, W, sn, ce, mn, Y, hf, cu, fe, ag, la, in, sc, rh, V or Zn elements;
the Dv50 of the positive electrode active material and the specific surface area BET of the positive electrode active material satisfy: 3 is not more than BET/(Dv 50) 2 *1000 is less than or equal to 180; wherein the BET is measured in g/m 2 The Dv50 is measured in μm.
It is understood that the positive electrode active material of the present invention is a material of a core-shell structure formed of an inner core and a coating layer covering at least a part of the surface of the inner core. In the present invention, the coating layer may cover a part of the surface of the core or may cover the entire surface of the core. In the charging and discharging process of the battery, the coating layer can prevent the inner core from being eroded by the electrolyte, the stability of the positive active material is improved, the gas generation of the battery is prevented, and the cycle performance and the safety performance of the battery are improved.
The core of the present invention includes a compound represented by formula 1, specifically an oxide including at least lithium, nickel, and cobalt. Further, it may be doped with M, which may be at least one of Mn, al, and V.
The coating layer of the invention comprises at least one of B, al, si, zr, co, ti, mg, W, sn, ce, mn, Y, hf, cu, fe, ag, la, in, sc, rh, V or Zn elements. It is to be understood that the coating layer may be at least one of an oxide, fluoride, phosphate, and sulfate containing the above elements.
In the present invention, the Dv50 of the positive electrode active material means a particle diameter of 50% by volume of the positive electrode active material in the positive electrode active material particles. When the particle size of the anode active material is tested, the method can perform ultrasonic treatment on the anode active material for multiple times so as to disperse the agglomerated anode active material and improve the accuracy of a test result. The specific surface area of the positive electrode active material refers to the surface area per unit mass of the positive electrode active material. The present invention can use N 2 The BET of the positive electrode active material was measured by the adsorption method.
In some embodiments, since the coating layer is formed by a coating layer material having an extremely small particle size, it is considered that the coating layer has little influence on BET of the core, which is approximately equal to BET of the positive electrode active material; further, since the thickness of the coating layer is extremely thin, the particle size of the core and the particle size of the positive electrode active material are considered to be approximately equal.
According to the above scheme provided by the present invention, dv50 and BET of the positive electrode active material satisfy a specific relationship, and the rate performance, cycle performance, and safety performance of the battery can be improved. The inventors have analyzed the reason, and it is considered that when the Dv50 and BET of the positive electrode active material satisfy a specific relationship, the surface of the positive electrode active material is relatively smooth and compact, which not only contributes to rapid desorption of lithium ions and improvement of rate capability of the battery, but also contributes to improvement of cycle performance and safety performance of the battery due to the fact that the positive electrode active material with a smooth surface is not easily cracked during charge and discharge of the battery, which reduces gas generation of the battery (the gas generation of the battery can be as low as 0.06 ml/Ah).
In the present invention, the relationship between BET and Dv50 may be further specifically selected according to the type of the material of the coating layer in order to further improve the overall performance of the battery. For example, in some embodiments, when the material of the cladding layer comprises Al 2 O 3 And B 2 O 3 When the ratio is 5. Ltoreq. BET/(Dv 50) 2 *1000 is less than or equal to 13; when the material of the clad layer comprises Al 2 O 3 And ZrO 2 When 3.5. Ltoreq. BET/(Dv 50) 2 *1000 is less than or equal to 100; when the material of the cladding layer comprises B 2 O 3 And ZrO 2 When the ratio is 3.5. Ltoreq. BET/(Dv 50) 2 *1000 is less than or equal to 125; when the material of the clad layer comprises Al 2 O 3 、ZrO 2 And CeO 2 When the ratio is 30. Ltoreq. BET/(Dv 50) 2 *1000≤65。
Further, when the Dv50 of the positive electrode active material is 0.2 to 18 μm, the positive electrode active material is less likely to be broken when applied to a battery, and the gas production amount is less, enabling further improvement in the cycle performance of the battery.
When the specific surface area BET of the positive electrode active material is 0.2-4.0 m 2 When the positive active material is used in a battery, the specific surface area is beneficial to leading more lithium ions to be extracted, and further the rate performance of the battery is improved.
The inventor finds in research that the surface residual alkali content of the positive active material also influences the performance of the positive active material, and the surface residual alkali content (Li) of the positive active material 2 CO 3 LiOH and free Li + ) The amount of the acid-base compound can directly influence the gas generation condition of the battery at high temperature, and further influences the safety performance of the battery. The inventors found that when the surface of the positive electrode active material is Li 2 CO 3 The content is less than or equal to 3000ppm; and/or the presence of a gas in the gas,
the LiOH content of the surface of the positive active material is less than or equal to 5000ppm; and/or the presence of a gas in the atmosphere,
surface-free Li of positive electrode active material + When the content is less than or equal to 2000ppm, the positive active material is less prone to generate gas at high temperature when applied to a battery, and the prepared battery has excellent safety performance. The invention can use a potentiometric titrator to test the residual alkali content on the surface of the positive active material.
It can be understood that the positive electrode active material of the present invention is a core-shell material formed by a core and a coating layer, and thus parameters of the core and parameters of the coating layer are critical to the performance of the positive electrode active material.
For example, the particle size distribution of the core may be further selected to enhance the overall performance of the battery. In some embodiments of the invention, dv50 and Dv10 of a kernel satisfy: dv50/Dv10 is not less than 1.5 and not more than 4.
In the present invention, the Dv50 of the core means the particle diameter of 50% by volume of the core particles in the core particles. Dv10 of the core means the particle size of 10% by volume of the core particles. In the preparation process of the positive electrode active material, core particles having Dv50 and Dv10 satisfying the above relationship may be selected to prepare the positive electrode active material. In practical applications, a stack of the positive electrode active material may be decomposed to obtain a stack of core particles, and the Dv50 and Dv10 of the core particles are tested to verify whether the Dv50 and Dv10 of the core particles of the positive electrode active material satisfy the above-mentioned limitations.
When the Dv50 and the Dv10 of the inner core satisfy the above relationship, the gas generation of the battery can be prevented better, and the cycle performance and the safety performance of the battery can be improved. It is worth mentioning that the method is also beneficial to improving the compaction density of the pole piece, and further improving the energy density of the battery.
In some embodiments of the invention, dv90 and Dv10 of a kernel satisfy: dv90/Dv10 is not less than 2 and not more than 12.
In the present invention, dv90 of the core means the particle diameter of 90% by volume of the core particles in the core particles. The test method of Dv90 of the core may refer to the test methods of Dv50 and Dv10 of the core. When the Dv90 and the Dv10 of the core satisfy the above relationship, the positive active material is not easily crushed during actual use, which is helpful to prevent gas generation of the battery better and improve cycle performance and safety performance of the battery.
In some embodiments of the invention, dv90 and Dv50 of the kernel satisfy: when the Dv90/Dv50 is more than or equal to 1.2 and less than or equal to 4, the particle size distribution of the core particles is proper, which is beneficial to improving the rate capability and energy density of the battery under the condition of improving the cycle performance and safety performance of the battery.
The invention can further select the specific surface areas of the inner core and the coating layer so as to better improve the comprehensive performance of the battery. In some embodiments of the invention, the ratio of the specific surface area BET of the coating material to the specific surface area BET of the inner core is 20 or more.
In the present invention, the specific surface area of the clad material means the surface area per unit mass of the clad material. The specific surface area of the core means the surface area per unit mass of the core. In the preparation process of the cathode active material, the core particles and the coating layer material having BET satisfying the above relationship may be selected to prepare the cathode active material. In practical applications, a stack of positive electrode active materials may be decomposed to obtain a stack of core particles and a stack of coating materials, and the BET of the core particles and the BET of the coating materials are tested to verify whether the BET of the core material and the BET of the coating materials satisfy the above-mentioned limitations.
In the invention, when the BET of the core and the BET of the coating layer material satisfy the relationship, the coating thickness of the coating layer is correspondingly thinned, which is beneficial to improving the rate capability of the battery.
A second aspect of the present invention provides a method for preparing the above-described positive electrode active material, comprising the steps of:
carrying out coprecipitation reaction on a raw material system comprising a precipitator, a nickel source, an M source and a cobalt source to obtain a core precursor;
mixing the core precursor with a lithium source to obtain a first mixed system, and performing first calcination treatment on the first mixed system to obtain a core material;
mixing the core material and the coating material to obtain a second mixed system, and performing second calcination treatment on the second mixed system to obtain a positive electrode active material to be screened;
and screening the positive electrode active material to be screened to obtain a Dv50 and a BET meeting the following conditions: BET/(Dv 50) of 3 ≤ 2 * A positive electrode active material of 1000 or less than 180; wherein the BET unit of measurement is g/m 2 The Dv50 is measured in μm.
In some embodiments of the present invention, the core material of the present invention may be prepared by a method comprising the steps of: mixing a nickel source, an M source and water to obtain a first salt solution, adding a cobalt source into the first salt solution to obtain a second salt solution, adding a precipitator into the second salt solution to obtain a raw material system, and performing coprecipitation reaction on the raw material system in a reactor to obtain a kernel precursor NixCoyMz (OH) 2 Wherein x is more than or equal to 0.5, and x + y + z =1;
then mixing the core precursor with a lithium source to obtain a mixed system, and calcining the mixed system to obtain a core material; wherein in the mixed system, the mass ratio of x + y + z to the lithium source is 1 to (0.8-1.2), and preferably, the mass ratio of x + y + z to the lithium source is 1 to (0.95-1.05);
the first calcining treatment can adopt a staged calcining treatment process, and specifically comprises the following steps: firstly, heating the first mixed system to 300-500 ℃ at a heating rate of 1-10 ℃/min, and preserving heat for 2-10 h; heating the first mixed system to 500-600 ℃ at the heating rate of 1-10 ℃/min, and keeping the temperature for 1-2 h; then heating the mixed system to 700-800 ℃ at a heating rate of 1-10 ℃/min, preserving the heat for 1-20 h, and then cooling to room temperature along with the furnace to obtain a core material; and the oxygen concentration is required to be kept between 85 and 100 percent in the sintering process, and preferably between 90 and 95 percent.
It will be appreciated that the feedstock system of the present invention may also include a complexing agent, which may be added simultaneously with the precipitating agent. The first calcining treatment can also comprise a crushing treatment, a washing treatment and a filtering treatment to obtain purer core materials, and specifically comprises the following steps: crushing the product obtained by the first calcination treatment, and screening out a product of 200-400 meshes; and (2) mixing the sieved product with water according to the following ratio (1000-1): (1: 1) mixing the raw materials in a ratio of 1-3min for washing, wherein the stirring speed in the washing process can be 5-300r/min, filtering the product after washing to obtain a filter cake, and drying the filter cake to obtain the pure core material, wherein the drying temperature can be 20-500 ℃, and preferably the drying temperature can be 120-240 ℃.
In the invention, the nickel source can be one or more selected from nickel sulfate, nickel nitrate and nickel chloride; the cobalt source can be one or more selected from cobalt sulfate, cobalt nitrate and cobalt chloride; the M source can be one or more selected from sulfuric acid M, nitric acid M and chloride M; the complexing agent can be selected from at least one of ammonia water, EDTA, oxalic acid and ammonium sulfate, and the precipitator can be selected from one or more of sodium hydroxide, sodium carbonate, ammonium carbonate and ammonium oxalate; the lithium source may be selected from Li (OH), li 2 CO 3 、LiNO 3 And CH 3 COOLi or a plurality of COOLi.
In the invention, the core material and the coating material can be mixed in a high-speed mixer, the stirring time of the high-speed mixer is 10-150min, preferably, the stirring time of the high-speed mixer can be 20-50min; the second calcination treatment may include heating the second mixed system to 300-800 deg.c at a heating rate of 1-10 deg.c/min, and then maintaining for 1-15 hr.
Cooling the product obtained after the second calcination treatment to room temperature along with the furnace to obtain the anode active material to be screened; and screening the positive active material to be screened to obtain Dv50 and BET meeting the following requirements: BET/(Dv 50) of 3 ≤ 2 * A positive electrode active material of 1000 or less than 180; wherein the BET unit of measurement is g/m 2 The Dv50 is measured in μm.
The preparation method of the cathode active material can be used for preparing the cathode active material, is simple to operate and is convenient to popularize and apply widely.
A third aspect of the invention provides a battery comprising the above-described positive electrode active material.
The present invention can use the above-described positive electrode active material to prepare a positive electrode sheet, stack the positive electrode sheet, a separator, and a negative electrode sheet to obtain an electrode assembly, place the electrode assembly in an outer package, and inject an electrolyte to obtain a battery.
The battery of the present invention has excellent cycle performance, rate performance, and safety performance because it includes the above-described cathode active material.
The technical solution of the present invention will be further explained with reference to specific examples.
Examples 1 to 5, 46 to 48
The positive electrode active materials of examples 1 to 5, 46 to 48 were prepared by a preparation method including the steps of:
carrying out coprecipitation reaction on a raw material system comprising a precipitator, a nickel source, an M source and a cobalt source to obtain a core precursor;
wherein the precipitator is NaOH, and the nickel source is NiSO 4 The M source is MnSO 4 The cobalt source is CoS0 4 The molar ratio of the nickel source to the M source to the cobalt source is 92: 1: 7;
mixing the core precursor with a lithium source to obtain a first mixed system, and performing first calcination treatment on the first mixed system to obtain a core material;
wherein the lithium source is LiOH, the molar ratio of the kernel precursor to the lithium source is 1: 1.05, the temperature of the first calcination treatment is 750 ℃, and the heat preservation time is 5h;
mixing the core material and the coating material to obtain a second mixed system, and performing second calcination treatment on the second mixed system to obtain a positive electrode active material to be screened;
wherein the coating material is Al 2 O 3 And B 2 O 3 Core material, al 2 O 3 And B 2 O 3 The mass ratio of (1: 0.19: 0.32); the temperature of the second calcination treatment is 350 ℃, and the heat preservation time is 3h;
and screening the positive electrode active material to be screened to obtain a Dv50 and a BET meeting the following conditions: BET/(Dv 50) of 3 ≤ 2 * A positive electrode active material of 1000 or less than 180; wherein the BET unit of measurement is g/m 2 The Dv50 is measured in μm, and specific parameters of the positive electrode active material are shown in table 1.
Examples 6 to 15, comparative example 1
The positive active materials of examples 6 to 15 and comparative example 1 were prepared in substantially the same manner as in examples 1 to 5, except that:
in the preparation of the inner core, the molar ratio of the nickel source, the M source and the cobalt source is 90: 5.
Examples 16 to 25, comparative examples 2 to 3
The positive active materials of examples 16 to 25 were prepared in substantially the same manner as in examples 1 to 5, except that:
in the preparation of the inner core, the molar ratio of the nickel source, the M source and the cobalt source is 90: 5, and the coating layer material is B 2 O 3 、ZrO 2 And core material, B 2 O 3 、ZrO 2 The mass ratio of the first calcining treatment to the second calcining treatment is 1: 0.32: 0.4, the temperature of the second calcining treatment is 400 ℃, and the heat preservation time is 5 hours.
Examples 26 to 31, comparative example 4
The positive active materials of examples 26 to 31 and comparative example 4 were prepared in substantially the same manner as in examples 1 to 5, except that:
in the preparation of the inner core, the molar ratio of the nickel source, the M source and the cobalt source is 70: 20: 10, the temperature of the first calcination treatment is 850 ℃, and the heat preservation time is 10 hours;
the coating material is Al 2 O 3 、ZrO 2 、CeO 2 And core material, al 2 O 3 、ZrO 2 、CeO 2 The mass ratio of the first calcining treatment to the second calcining treatment is 1: 0.39: 0.4: 0.12, the temperature of the second calcining treatment is 380 ℃, and the heat preservation time is 5 hours.
Examples 32 to 39, comparative example 5
The positive electrode active materials of examples 32 to 39, comparative example 5 were prepared by substantially the same method as in examples 1 to 5, except that:
in the preparation of the inner core, the molar ratio of the nickel source, the M source and the cobalt source is 60: 30: 10, the temperature of the first calcination treatment is 820 ℃, and the heat preservation time is 12 hours;
the coating material is Al 2 O 3 、ZrO 2 And core material, al 2 O 3 The mass ratio of ZrO is 1: 0.280.34, the temperature of the second calcination treatment is 420 ℃, and the holding time is 5h.
Examples 40 to 45, comparative example 6
The positive active materials of examples 40 to 45 and comparative example 6 were prepared in substantially the same manner as in examples 1 to 5, except that:
in the preparation of the inner core, the molar ratio of the nickel source, the M source and the cobalt source is 88: 2: 10, the temperature of the first calcination treatment is 710 ℃, and the heat preservation time is 12 hours;
the coating material is B 2 O 3 、ZrO 2 And core material, B 2 o 3 The mass ratio of ZrO is 1: 0.32: 0.27, the temperature of the second calcination treatment is 360 ℃, and the heat preservation time is 5h.
Test examples
The battery of this test example was prepared as follows:
(1) Preparation of positive plate
Arranging the positive active slurry on two functional surfaces of the aluminum foil, and drying to obtain a positive plate provided with a positive active layer;
in the positive electrode active layer, the mass ratio of the positive electrode active material (positive electrode active material in examples and comparative examples), the conductive agent SP, the conductive agent KS-6, and the binder PVDF was 94.5% to 2% to 1% to 2.5%, and the parameters related to the positive electrode active material are specifically shown in table 1.
(2) Preparation of negative plate
Arranging the negative active slurry on two functional surfaces of the copper foil, and drying to obtain a negative plate provided with a negative active layer;
wherein, in the negative active layer, the mass ratio of the negative active material graphite, the conductive agent SP, the binder CMC and the binder SBR is 95 percent to 1 percent to 1.5 percent to 2.5 percent.
(3) Preparation of the Battery
Stacking the positive plate and the diaphragm in the step (1) and the negative plate in the step (2) to obtain an electrode assembly, placing the electrode assembly in an aluminum-plastic film, packaging the aluminum-plastic film, and injecting electrolyte into the aluminum-plastic film to obtain a battery of 503048 type;
wherein the electrolyte takes the mixture of EC, EMC and DMC as solvent, the mass ratio of EC, EMC and DMC is 1: 1, liPF of 1mol/L 6 As solutes, and the additives are PS (1, 3-propanesultone) and VC (vinylene sulfate), the mass percent of VC is 1% and the mass percent of DMC is 2% based on the total mass of the electrolyte; the diaphragm is a PE-PP-PE three-layer co-extrusion diaphragm, and the battery capacity is 800mAh.
Performance testing
1. The following tests were performed on the positive electrode active materials of examples and comparative examples, respectively, and the test results are shown in table 1;
1) Particle size test
Testing the Dv50 of the positive active material and the Dv10, the Dv50 and the Dv90 of the inner core respectively by using a Malvern laser particle size analyzer; in the specific test, the material to be tested is dispersed in water, ultrasonic treatment is carried out for 10s, a Malvern laser particle size analyzer is used for testing, and the test error is controlled to be not more than 0.1 mu m.
2) BET test
Using N 2 Respectively testing BET of the positive active material, the coating material and the core by an adsorption method;
the method specifically comprises the following steps: baking the sample in a 120 ℃ oven for 1h, weighing a certain mass of the sample, placing the sample into a sample tube, controlling the volume of the sample to be about 1/2 to 2/3 of the volume of the sample tube at the lower end of the sample tube, mounting the sample tube on a vacuum connector on a degassing station port, degassing for 2h at 200 ℃, cooling after that, weighing, mounting the sample tube on a test bench, cooling N by adopting liquid nitrogen 2 The mode of adsorption was tested.
3) Residual alkali
Testing of surface Li of positive active material using potentiometric titration 2 CO 3 Content, liOH content and free Li + Content (c);
the method specifically comprises the following steps: 30g of the positive electrode active material was weighed, and a sample of test residual alkali (Li) was charged into the cell using a 100mL measuring cylinder 2 CO 3 Or LiOH) into a conical flask, placing the positive active material into the conical flask, placing on a magnetic stirrer, stirring at normal temperature for 30min, transiting with filter paper, collecting filtrate, titrating, and collecting the titrated solutionAnd (3) the solution is hydrochloric acid solution with a certain concentration, titration equipment is a potentiometric titrator, data are processed after titration, and residual alkali is calculated.
2. Test of comprehensive performance of battery
The following tests were performed on the lithium ion batteries prepared in the examples and comparative examples, respectively, and the test results are shown in table 1;
1) Cycle performance test
Charging the battery at 1C, discharging the battery at 1C, performing charge-discharge circulation on the battery at the cut-off current of 0.05C and the ambient temperature of 25 +/-2 ℃, wherein the voltage range is 2.8V-4.25V (the battery with the mass percentage of Ni in the positive active material being more than or equal to 80%) or 2.8-4.4V (the battery with the mass percentage of Ni in the positive active material being less than 80%), and calculating the capacity retention rate of the battery after circulating for 300 weeks;
the capacity retention rate is the ratio of the discharge capacity at the 300 th week to the discharge capacity at the first week.
2) Rate capability test
Charging the battery to cut-off voltage at 0.5C and cut-off current at 0.05C at the ambient temperature of 25 +/-2 ℃, discharging the battery to 2.8V at 0.1C, charging and discharging for 3 weeks, and taking and placing the maximum value of the capacitance; charging the battery to cut-off voltage at 0.5C, cutting off current at 0.05C, discharging the battery to 2.8V at 1C, charging and discharging for 3 weeks, and taking and placing the maximum value of the capacitance;
the rate capability is obtained by dividing the discharge capacity of 1C by the discharge capacity of 0.1C.
3) Flatulence test
The method comprises the steps of charging the battery to a cut-off voltage at 1C, enabling the cut-off current to be 0.05C, testing the volume of the battery cell by using a drainage method after the battery cell is fully charged, controlling the temperature to be 25 +/-2 ℃, recording the volume of the battery cell, placing the battery cell in a 70 ℃ environment for 7 days, testing the volume of the battery cell by using the drainage method again, controlling the temperature to be 70 +/-3 ℃, and obtaining the ratio of the volume difference of the battery cell to the capacity of the battery cell as a gas production value after the test of the volume of the battery cell is completed.
As can be seen from the examples and comparative examples, when the Dv50 of the positive electrode active material and the specific surface area BET of the positive electrode active material satisfy: 3 is not more than BET/(Dv 50) 2 * When the temperature is more than or equal to 1000 and less than or equal to 180, the battery has more excellent cycle performance and rate capability, less gas production and excellent safety performance.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A positive electrode active material, comprising an inner core and a coating layer covering at least a part of a surface of the inner core;
wherein the inner core comprises a compound represented by formula 1;
Li a Ni b Co c M 1-b-c O 2 the chemical formula of the formula 1,
in the formula 1, a is more than or equal to 0.8 and less than or equal to 1.2, b is more than or equal to 0.5 and less than or equal to 0.96, b is more than or equal to 0.3 and less than or equal to 0.6, and M is selected from at least one of Mn, al and V;
the coating layer comprises at least one of B, al, si, zr, co, ti, mg, W, sn, ce, mn, Y, hf, cu, fe, ag, la, in, sc, rh, V or Zn elements;
dv50 of the positive electrode active material and a positive electrode active materialThe specific surface area BET satisfies: BET/(Dv 50) of 3 ≤ 2 *1000 is less than or equal to 180; wherein the BET unit of measurement is g/m 2 The Dv50 is measured in μm.
2. The positive electrode active material according to claim 1, wherein the Dv50 of the positive electrode active material is 0.2-18 μm.
3. The positive electrode active material according to claim 1 or 2, wherein the specific surface area BET of the positive electrode active material is 0.2 to 4.0m 2 /g。
4. The positive electrode active material according to any one of claims 1 to 3, wherein the surface Li of the positive electrode active material 2 CO 3 The content is less than or equal to 3000ppm; and/or the presence of a gas in the gas,
the LiOH content of the surface of the positive electrode active material is less than or equal to 5000ppm; and/or the presence of a gas in the gas,
surface-free Li of the positive electrode active material + The content is less than or equal to 2000ppm.
5. The positive electrode active material according to any one of claims 1 to 4, wherein Dv50 and Dv10 of the core satisfy: dv50/Dv10 is not less than 1.5 and not more than 4.
6. The positive electrode active material according to any one of claims 1 to 5, wherein Dv90 and Dv10 of the core satisfy: dv90/Dv10 is not less than 2 and not more than 12; and/or the presence of a gas in the gas,
dv90 and Dv50 of the kernel satisfy: dv90/Dv50 is not less than 1.2 and not more than 4.
7. The positive electrode active material according to any one of claims 1 to 6, wherein the ratio of the specific surface area BET of the coating material to the specific surface area BET of the core is not less than 20.
8. The positive electrode active material according to any one of claims 1 to 7, wherein the coating layer is at least one selected from the group consisting of an oxide, a fluoride, a phosphate, and a sulfate.
9. A method for preparing a positive electrode active material according to any one of claims 1 to 8, comprising the steps of:
carrying out coprecipitation reaction on a raw material system comprising a precipitator, a nickel source, an M source and a cobalt source to obtain a core precursor;
mixing a core precursor with a lithium source to obtain a first mixed system, and performing first calcination treatment on the first mixed system 5 to obtain a core material;
mixing the core material and the coating material to obtain a second mixed system, and performing second calcination treatment on the second mixed system to obtain a positive electrode active material to be screened;
and screening the positive active material to be screened to obtain a Dv50 and a BET meeting the following requirements: BET/(Dv 50) of 3 ≤ 2 * A positive electrode active material of 1000 or less than 180; wherein the BET is measured in g/m 2 The measurement unit of 0Dv50 is μm.
10. A battery comprising the positive electrode active material according to any one of claims 1 to 8.
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| CN117790763A (en) * | 2024-02-28 | 2024-03-29 | 江苏众钠能源科技有限公司 | Composite positive electrode material, preparation method thereof, positive electrode plate, secondary battery and application |
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| CN117790763A (en) * | 2024-02-28 | 2024-03-29 | 江苏众钠能源科技有限公司 | Composite positive electrode material, preparation method thereof, positive electrode plate, secondary battery and application |
| CN117790763B (en) * | 2024-02-28 | 2024-05-14 | 江苏众钠能源科技有限公司 | Composite positive electrode material, preparation method thereof, positive electrode plate, secondary battery and application |
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