CN117645323A - Positive electrode material and preparation method and application thereof - Google Patents
Positive electrode material and preparation method and application thereof Download PDFInfo
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- CN117645323A CN117645323A CN202311615954.9A CN202311615954A CN117645323A CN 117645323 A CN117645323 A CN 117645323A CN 202311615954 A CN202311615954 A CN 202311615954A CN 117645323 A CN117645323 A CN 117645323A
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- 238000002360 preparation method Methods 0.000 title abstract description 34
- 230000008859 change Effects 0.000 claims abstract description 16
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a positive electrode material, a preparation method and application thereof, wherein the positive electrode material is subjected to pressure maintaining for 30-80 s at 2-4T, the Dv50 change difference value is delta D, and the specific surface area difference value is delta BET; Δd and Δbet satisfy x=Δd×Δbet, and X is-0.04 to 0; the compaction density of the positive electrode material under the pressure of 2-4T is 3.6-3.8 g/cm 3 . By defining the relation satisfied by the compacted density and Δd and Δbet of the positive electrode material, it is ensured that crack defects are reduced as much as possible while achieving a high compacted density, and the cycle performance and capacity of the battery can be effectively improved by applying the positive electrode material to the battery.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a positive electrode material, a preparation method and application thereof.
Background
In order to increase the energy density of the lithium ion battery, the method generally mixes large particles and small particles at the same time, and improves the compaction density of the pole piece to 3.6g/cm 3 Both aspects improve the energy density. The improvement of the compaction density is usually realized by applying a larger mechanical external force to the particles, but when the large particles and the small particles bear the mechanical external force, the large particles and the small particles are easy to generate stress, so that cracks and even cracks appear on the particles, electrolyte enters the inside of the particles along the cracks, the interface side reaction is increased, the cycle performance is reduced, and therefore, how to improve the crack defects of the particles is particularly important for improving the cycle performance.
Disclosure of Invention
The invention provides a positive electrode material, which ensures that crack defects are reduced as far as possible while realizing high compacted density by limiting a relation formula satisfied by the compacted density and delta D and delta BET of the positive electrode material, and can effectively improve the cycle performance and capacity of a battery when the positive electrode material is applied to the battery.
The invention also provides a preparation method of the positive electrode material, which can prepare the positive electrode material with excellent performance, and the positive electrode material is applied to a battery, thereby being beneficial to improving the cycle performance and capacity of the battery.
The invention also provides a positive plate, which is beneficial to improving the cycle performance and capacity of the battery by applying the positive plate to the battery due to the positive plate.
The invention also provides a battery which has excellent cycle performance and high capacity due to the positive plate.
In a first aspect of the present invention, there is provided a positive electrode material, wherein the difference in Dv50 change of the positive electrode material is Δd and the difference in specific surface area is Δbet before and after pressure maintaining for 30 to 80 seconds under a pressure of 2 to 4T;
Δd and Δbet satisfy x=Δd×Δbet, and X is-0.04 to 0;
the compaction density of the positive electrode material under the pressure of 2-4T is 3.6-3.8 g/cm 3 。
The positive electrode material as described above, wherein the positive electrode material includes at least polycrystalline particles and single crystal particles; the grain diameter change rate of the polycrystalline grains is beta 1 and the specific surface area difference is delta BET before and after pressure maintaining for 30-80 s under the pressure of 2-4T 1 ；
The single crystal grain has a grain diameter change rate of beta 2 and a specific surface area difference of delta BET before and after pressure maintaining for 30-80 s under the pressure of 2-4T 2 The unit of the specific surface area difference is m 2 /g；
β1、ΔBET 1 Satisfy t1=β1×Δ BET 1 And T1 is-0.01-0;
β2、ΔBET 2 satisfy t2=β2×Δ BET 2 And T2 is-0.04-0;
wherein β1 is the ratio of the difference in Dv50 variation of the polycrystalline particles to the average particle diameter of the polycrystalline particles, and β2 is the ratio of the difference in Dv50 variation of the single crystal particles to the average particle diameter of the single crystal particles.
The positive electrode material as described above, wherein the polycrystalline particles have a Dv50 variation difference of-0.90 to-0.05 μm;
the difference of Dv50 of the single crystal particles is-0.15-0 mu m.
The positive electrode material as described above, wherein the difference in specific surface area of the polycrystalline particles is 0 to 0.3m 2 /g；
The specific surface area difference of the single crystal particles is 0-0.2 m 2 /g。
The positive electrode material is characterized in that D104 of single crystal particles in the positive electrode material is 88-105 nm through XRD (X-ray diffraction) test, D104 of polycrystalline particles is 30-65 nm, and D104 refers to the crystal grain size of a 104 crystal face obtained through XRD (X-ray diffraction) test.
The positive electrode material as described above, wherein the mass ratio (1 to 7) of the polycrystalline particles to the single crystal particles: 1, a step of;
the chemical formula of the single crystal particles is LiNi x M (1-x) O 2 Wherein x is more than or equal to 0.7 and less than 1, and M is selected from at least two of Co, mn, B, mg, al, zr, sr, mo, ti; and/or the number of the groups of groups,
the chemical formula of the polycrystalline particles is LiNi y N (1-y) O 2 Wherein y is more than or equal to 0.7 and less than 1, and N is selected from at least two of Co, mn, B, mg, al, zr, sr, mo, ti.
The positive electrode material as described above, wherein the positive electrode material has a compacted density of 3.6 to 3.8g/cm under a pressure of 3.5T 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the number of the groups of groups,
the specific surface area of the positive electrode material is 0.45-0.90 m 2 /g。
The positive electrode material, wherein the gram capacity of the positive electrode material is 200-230 mAh/g under the conditions of 0.2C and 2.5-4.25V).
In a second aspect of the present invention, there is provided a method for preparing the positive electrode material according to the first aspect, comprising the steps of:
mixing a first precursor, a first lithium salt and a first doping agent to obtain a first material; sequentially performing first presintering treatment and first sintering treatment on the first material to obtain polycrystalline particles;
mixing a second precursor, a second lithium salt and a second doping agent to obtain a second material; sequentially performing second presintering treatment and second sintering treatment on the second material to obtain monocrystalline particles;
Mixing the polycrystalline particles and the monocrystalline particles to obtain the positive electrode material;
the first presintering treatment is carried out under an oxygen-containing atmosphere, the first presintering treatment comprises a first stage presintering treatment and a second stage presintering treatment, the temperature of the first stage presintering treatment is 200-400 ℃, the time is 0.5-3 h, the temperature of the second stage presintering treatment is 500-600 ℃, and the time is 3-10 h;
the second presintering treatment is carried out in an oxygen-containing atmosphere, the second presintering treatment comprises a third stage presintering and a fourth stage presintering, the temperature of the third stage presintering is 200-400 ℃, the time is 0.5-3 h, the temperature of the fourth stage presintering is 500-600 ℃, and the time is 3-10 h;
the difference between the temperature of the second stage presintering and the temperature of the first stage presintering is not more than 320 ℃, and the difference between the temperature of the fourth stage presintering and the temperature of the third stage presintering is not more than 350 ℃.
The preparation method comprises the steps of obtaining a first sintered product after a first sintering treatment, and further comprises the step of carrying out a first cladding treatment on the first sintered product to obtain polycrystalline particles;
after the second sintering treatment, obtaining a second sintering product, and further comprising performing a second coating treatment on the second sintering product to obtain monocrystalline particles; and/or the number of the groups of groups,
The molar ratio of the first precursor, the first lithium salt and the first dopant is 1: (0.98-1.08): (0.003-0.02);
the molar ratio of the second precursor, the second lithium salt, and the second dopant is 1: (0.98-1.08): (0.003-0.02).
In a third aspect of the present invention, there is provided a positive electrode sheet comprising the positive electrode material according to the first aspect or the positive electrode material produced by the production method according to the second aspect.
In a fourth aspect of the present invention, there is provided a battery comprising the positive electrode sheet according to the third aspect.
The implementation of the invention has at least the following beneficial effects:
the positive electrode material provided by the invention ensures that the particle size change and the specific surface area of the positive electrode material are mutually matched by limiting the compaction density and the relational expression satisfied by delta D and delta BET of the positive electrode material, ensures the morphology characteristics of positive electrode material particles, furthest reduces crack defects while improving the compaction density, avoids the occurrence of cracks and even cracks of the particles caused by larger applied pressure, and reduces the occurrence of side reaction.
According to the preparation method of the positive electrode material, the doping agent is introduced, the presintering treatment is added before the sintering treatment, so that the lithium salt and the doping agent can enter the surface and the internal structure of the precursor, the lithium intercalation reaction temperature is advanced, the mechanical strength of positive electrode material particles is enhanced, the positive electrode material meeting the relation of X=delta D×delta BET and X being-0.04-0 can be prepared, and the positive electrode material is applied to a lithium ion battery, and the lithium ion battery has excellent gram capacity and cycle performance.
Drawings
FIG. 1 is an SEM image of the positive electrode material of example 1 after dwell at 3.5T;
FIG. 2 is an SEM image of the positive electrode material of comparative example 1 after maintaining the pressure at 3.5T;
FIG. 3 is an SEM image of single crystal grains of example 1 of the present invention after maintaining a pressure of 3.5T;
FIG. 4 is an SEM image of a single crystal grain of comparative example 1 after maintaining a pressure of 3.5T;
FIG. 5 is an SEM image of a polycrystalline table of example 1 after being held at 3.5T;
FIG. 6 is an SEM image of a polycrystalline table of comparative example 1 after being held at 3.5T;
fig. 7 is a plan view projected area diagram of the average particle diameter of the measurement particles at 1K magnification for the positive electrode material in an embodiment of the present invention.
Detailed Description
For the purpose of making 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 in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In a first aspect of the present invention, there is provided a positive electrode material including at least polycrystalline particles and monocrystalline particles; the Dv50 of the positive electrode material is changed before and after pressure maintaining for 30 to 80 seconds under the pressure of 2 to 4TThe difference is DeltaD, and the specific surface area difference is DeltaBET; Δd and Δbet satisfy x=Δd×Δbet, and X is-0.04 to 0; the compaction density of the positive electrode material under the pressure of 2-4T is 3.6-3.8 g/cm 3 。
In the invention, delta D and delta BET are used for representing the particle size change and specific surface area change of the positive electrode material before and after pressure maintaining, so that excessive cracks and exposed crystal boundaries are avoided before and after pressure maintaining, the contact area of the positive electrode material and the electrolyte is reduced as much as possible while the full contact of the positive electrode material and the electrolyte is ensured, side reaction and gas yield are reduced, the rate capability of the lithium ion battery is improved, the compaction density is further improved, the energy density of the lithium ion battery is improved, the strength of the positive electrode material is also improved, and the cycle performance of the lithium ion battery is ensured.
Wherein DeltaD refers to Dv50 after pressure maintaining of the positive electrode material-Dv 50 before pressure maintaining of the positive electrode material, and DeltaBET refers to specific surface area after pressure maintaining of the positive electrode material-specific surface area before pressure maintaining of the positive electrode material.
In the invention, the positive electrode material at least comprises polycrystalline particles and monocrystalline particles, wherein the polycrystalline particles are secondary particle aggregates composed of primary particles, and a large number of crystal boundaries exist in the aggregates. In the charge and discharge process of the battery, due to anisotropic lattice change, crystal boundary cracking is easy to occur, secondary particles are caused to crack, side reactions are rapidly increased, and the impedance is increased, so that the cycle performance of the battery is not facilitated. The monocrystalline particles are primary particles, so that grain boundaries can be reduced, side reactions are reduced, and the monocrystalline particles and the polycrystalline particles are matched with each other, so that the monocrystalline particles effectively fill the pores between the polycrystalline particles, compaction density is improved, and the capacity of the battery is improved. According to the invention, under the mutual coordination of the polycrystalline particles and the monocrystalline particles, the lithium ion transmission path can be improved, the interface impedance is reduced, and the dynamic performance of the positive electrode material is ensured.
In one embodiment, the polycrystalline particles have a particle diameter change rate of β1 and a specific surface area difference of ΔBET after 30 to 80 seconds of holding pressure at a pressure of 2 to 4T 1 The method comprises the steps of carrying out a first treatment on the surface of the The grain diameter of the monocrystalline grains is changed before and after pressure maintaining for 30-80 s under the pressure of 2-4TConversion was β2 and the difference in specific surface area was ΔBET 2 ；β1、ΔBET 1 Satisfy t1=β1×Δ BET 1 And T1 is-0.01-0; beta 2, delta BET 2 Satisfy t2=β2×Δ BET 2 And T2 is-0.04 to 0. By defining the T1 and T2 values of the polycrystalline and monocrystalline particles, it is advantageous to achieve that Δd, Δbet of the positive electrode material satisfies x=Δd×Δbet, and X is-0.04 to 0.
Dv50 of polycrystalline granules 1 The positive electrode material has a particle size corresponding to a volume distribution of 50% of polycrystalline particles, and the specific surface area of the polycrystalline particles is BET 1 The median particle diameter of the polycrystalline particles after pressure maintaining for 30-80 s under the pressure of 2-4T is Dv50 2 Specific surface area is BET 2 At this time, the rate of change in the particle diameter of the polycrystalline particles β1= (Dv 50) 2 -Dv50 1 ) Average particle size of polycrystalline particles, specific surface area difference ΔBET 1 ＝BET 2 -BET 1 . Similarly, dv50 of single crystal particles 3 The positive electrode material is composed of particles having a volume distribution of 50% of the single crystal particles, which may be referred to as average particle size, and the specific surface area of the single crystal particles is BET 3 The method comprises the steps of carrying out a first treatment on the surface of the The average granularity of the monocrystalline particles after pressure maintaining for 30-80 s under the pressure of 2-4T is Dv50 4 Specific surface area is BET 4 At this time, the particle diameter change rate β2= (Dv 50) of the single crystal particles 4 -Dv50 3 ) Average particle diameter of single crystal particles, specific surface area difference of ΔBET 2 ＝BET 4 -BET 3 。
The method for measuring the average particle size comprises the following steps: calculating the overlooking projection area of the dispersed particles with obvious interfaces in the positive electrode material by using the amplification factor of the electron microscope 1K (as shown in fig. 7), equating the overlooking projection area to be a circular area, calculating the diameter corresponding to the circular area, namely the particle size of the particles, calculating the particle sizes of all the polycrystalline particles in the positive electrode material, and taking an average value, namely the average particle size of the polycrystalline particles; and similarly, calculating the particle sizes of all monocrystalline particles in the positive electrode material, and taking an average value as the average particle size of the monocrystalline particles. The average particle diameter is the average particle diameter of the polycrystalline particles and the single crystal particles before the pressure maintaining.
The inventors have studiedIt is considered that the rate of change in particle diameter and the specific surface area difference of the polycrystalline particles and the single-crystal particles have extremely significant influence on the cycle performance and capacity of the positive electrode material, and that the proper rate of change in particle diameter and the specific surface area difference are key to the positive electrode material to exert the excellent cycle performance and capacity to the maximum extent when t1=β1×Δ BET is satisfied 1 And T1 is-0.01 to 0, T2=β2×ΔBET 2 And when T2 is-0.04-0, the method is beneficial to ensuring the compaction density, reducing cracks as much as possible, avoiding more electrolyte to contact with the positive electrode material along with the progress of the circulation process, and reducing side reactions, thereby being beneficial to improving the circulation performance and capacity of the battery.
The Dv50 of the polycrystalline particles changes by a difference delta D before and after the pressure is maintained for 30 to 80 seconds under the pressure of 2 to 4T 1 ＝Dv50 2 -Dv50 1 . The invention is not limited to ΔD 1 The specific numerical values of (2) may be satisfied by the above-described relational expression. For example, in some embodiments, the polycrystalline grain size varies by a difference ΔD 1 Is-0.90 to-0.05 mu m.
The Dv50 of the monocrystalline particles changes by a difference delta D before and after pressure maintaining for 30-80 s under the pressure of 2-4T 2 ＝Dv50 4 -Dv50 3 . The invention is not limited to ΔD 2 The specific numerical values of (2) may be satisfied by the above-described relational expression. For example, in some embodiments, the particle size of the monocrystalline particles varies by a difference ΔD 2 Is-0.15 to 0 mu m.
The invention is not limited to the size of the polycrystalline particles and monocrystalline particles in the positive electrode material, and in some embodiments, the average particle size of the monocrystalline particles (average particle size measured under SEM (magnification of 3 k)) is 0.5 to 7 μm, and the average particle size of agglomerates formed by agglomeration of part of the monocrystalline particles is 1.5 to 7 μm; SPAN of the monocrystalline particles is 1.2-2.3; and/or, the polycrystalline particles are secondary particle aggregates composed of primary particles, the primary particles have an average particle diameter (average particle diameter measured under SEM (magnification of 10 k)) of 90 to 950nm, the secondary particle aggregates (i.e., the polycrystalline particles) have an average particle diameter (average particle diameter measured under SEM (magnification of 1 k)) of 5 to 18 μm, and the polycrystalline positive electrode material SPAN index range of 0.5 to 1.8. Wherein span= (Dv 90-Dv 10)/Dv 50.
The present invention is not limited toAnd 3.5T of the difference value of the specific surface areas of the polycrystalline particles and the monocrystalline particles before and after pressure maintaining. For example, in some embodiments, the specific surface area difference ΔBET of the polycrystalline particles before and after dwell at a pressure of 3.5T 1 0 to 0.3m 2 /g; the difference of the specific surface areas of the single crystal particles is 0 to 0.2m 2 /g。
D104 is a parameter in XRD testing. In some embodiments, the single crystal particles in the positive electrode material have a D104 of 88 to 105nm and the polycrystalline particles have a D104 of 30 to 65nm as measured by XRD diffraction. Wherein D104 refers to the crystal grain size of the 104 crystal face obtained by XRD ray diffraction test.
The present invention is not limited to the mass ratio of the polycrystalline particles to the single crystal particles, as long as the polycrystalline particles and the single crystal particles are ensured to satisfy the above-described relational expression. In some embodiments, the mass ratio of polycrystalline particles to monocrystalline particles (1-7): 1, e.g., 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or any two of them. In the prior art, as the mechanical strength of the monocrystalline particles and the polycrystalline particles is not matched, collision is not avoided in the compaction process, the polycrystalline particles can crack along the particles, the monocrystalline particles can crack along the structural stacking faults, the volume shrinkage and expansion of the particles of the positive electrode material in the charge-discharge process can enable the particles to be mutually extruded, and the continuous migration of lithium ions is not facilitated due to the trend of forming larger internal stress and more crystal boundaries. The invention is beneficial to further improving the matching degree of the polycrystalline particles and the monocrystalline particles and improving the compressive strength by further limiting the mass ratio of the polycrystalline particles to the monocrystalline particles, and is beneficial to realizing that the delta D and the delta BET of the positive electrode material meet X=delta D×delta BET, and X is-0.04-0.
The present invention is not limited to the chemical formulas of single crystal grains and polycrystalline grains, for example, the chemical formula of single crystal grains is LiNi x M (1-x) O 2 Wherein x is more than or equal to 0.7 and less than 1, and M is selected from at least two of Co, mn, B, mg, al, zr, sr, mo, ti; and/or the polycrystalline grain has a chemical formula of LiNi y N (1-y) O 2 Wherein y is more than or equal to 0.7 and less than 1, and N is selected from at least two of Co, mn, B, mg, al, zr, sr, mo, ti.
In the invention, the positive directionThe polar material D50 values satisfy: d50 Mean particle diameter =x×mean particle diameter of polycrystalline particles + (1-X) X mean particle diameter of primary particles in single crystal particles; the D50 of the positive electrode material is 4-18 mu m, the particle size distribution width SPAN of the positive electrode material is 0.55-2.8, and the specific surface area is 0.45-0.90 m 2 /g。
The invention is not limited to the compacted density, specific surface area, and in some embodiments, the compacted density of the positive electrode material at 3.5T pressure is 3.6-3.8 g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the specific surface area of the positive electrode material is 0.45-0.90 m 2 /g。
In some embodiments, the cathode material has a gram capacity of 200 to 230mAh/g at 0.2C and 2.5 to 4.25V.
In a second aspect of the present invention, there is provided a method for preparing a positive electrode material, comprising the steps of: mixing a first precursor, a first lithium salt and a first doping agent to obtain a first material; sequentially performing first presintering treatment and first sintering treatment on the first material to obtain polycrystalline particles; mixing a second precursor, a second lithium salt and a second doping agent to obtain a second material; sequentially performing second presintering treatment and second sintering treatment on the second material to obtain monocrystalline particles; mixing the polycrystalline particles and the monocrystalline particles to obtain a positive electrode material; the first presintering treatment is carried out in an oxygen-containing atmosphere, the first presintering treatment comprises a first stage presintering treatment and a second stage presintering treatment, the temperature of the first stage presintering treatment is 200-400 ℃, the time is 0.5-3 h, the temperature of the second stage presintering treatment is 500-600 ℃, and the time is 3-10 h; the second presintering treatment is carried out under the oxygen-containing atmosphere, the second presintering treatment comprises a third stage presintering and a fourth stage presintering, the temperature of the third stage presintering is 200-400 ℃, the time is 0.5-3 h, the temperature of the fourth stage presintering is 500-600 ℃, and the time is 3-10 h
Preferably, the difference between the temperature of the second stage presintering and the temperature of the first stage presintering is not more than 320 ℃, and the difference between the temperature of the fourth stage presintering and the temperature of the third stage presintering is not more than 350 ℃. This helps to produce polycrystalline and monocrystalline particles that meet the T1, T2 ranges.
Wherein, the polycrystal particles and the monocrystal particles are mixed for 10 to 20 minutes by a batch mixer at the temperature of 20 to 30 ℃ to obtain the anode material.
In the prior art, in the synthesis process of the ternary positive electrode material, a doping agent is required to be added for sintering treatment, and in the sintering treatment, lithium salt and the doping agent can be combined with a precursor, so that the sintering temperature is required to be higher, otherwise, irregular morphology and agglomeration of the ternary positive electrode material can be caused. The inventors have studied that by increasing the burn-in treatment before the sintering treatment and defining the difference in the burn-in temperature, the mechanical strength of the polycrystalline particles and the single crystal particles is directly affected, and the particle diameter change rate and the specific surface area difference of the particles before and after the pressure maintaining are further affected. This is because, by adding two-stage pre-sintering treatment before sintering treatment, lithium intercalation reaction can be advanced, lithium is preferentially doped into the precursor, and at the same time, even distribution of dopant and lithium salt in particles can be promoted, so that the mechanical strength of polycrystalline particles and monocrystalline particles is improved, crack defects are reduced as much as possible while high compaction density is realized, and the cycle performance and capacity of the battery can be effectively improved by applying the positive electrode material to the battery.
After the first sintering treatment, obtaining a first sintering product, and further comprising performing a first cladding treatment on the first sintering product to obtain polycrystalline particles; after the second sintering treatment, obtaining a second sintered product, and further comprising performing a second coating treatment on the second sintered product to obtain monocrystalline particles; and/or the molar ratio of the first precursor, the first lithium salt and the first dopant is 1: (0.98-1.08): (0.003-0.02); the molar ratio of the second precursor, the second lithium salt, and the second dopant is 1: (0.98-1.08): (0.003-0.02).
The method comprises the steps of mixing a first sintering product after washing and drying with a first coating agent in a high-speed mixer, putting the mixture into a muffle furnace, carrying out first coating treatment in an oxygen or nitrogen atmosphere, cooling along with the furnace, crushing and sieving to obtain polycrystalline particles.
And the method further comprises the steps of washing and drying the second sintering product, mixing the washed and dried second sintering product with a second coating agent in a high-speed mixer, putting the mixture into a muffle furnace, carrying out second coating treatment in an oxygen or nitrogen atmosphere, cooling along with the furnace, crushing and sieving to obtain monocrystalline particles.
The present invention is not limited to the specific choice of the above-described reaction starting materials and preparation parameters, for example, in some embodiments, the chemical formula of the first precursor is Ni x M (1-x) (OH) 2 Wherein x is more than or equal to 0.7 and less than 1, and M is any one or more than one of Co, mn, B, mg, al, zr, sr, mo; the first lithium source is selected from one of lithium hydroxide and lithium carbonate; the first dopant is selected from at least one of compounds composed of Zr, sr, al, nb, Y; the first sintering treatment may be two-stage sintering, for example, heating to 600 ℃ for 4 hours, and then heating to 680-800 ℃ for 6-10 hours; the water washing adopts cold water washing, and the water washing temperature is 0-10 ℃; drying can be performed in vacuum equipment at 120-180 ℃; the temperature of the first cladding treatment is 150-400 ℃, the time is 6-10 h, and the sintering atmosphere is oxygen or nitrogen with the volume concentration of more than or equal to 85%; the first coating agent is at least one compound formed by P, al, co, ti, W, Y, mg, preferably at least one of aluminum phosphate, aluminum oxide, titanium dioxide, yttrium oxide, cobalt oxide and magnesium oxide.
In some embodiments, the second precursor has the formula Ni y N (1-y) (OH) 2 Wherein y is more than or equal to 0.7 and less than 1, and M is any one or more than one of Co, mn, B, mg, al, zr, sr, mo; the second lithium source is selected from one of lithium hydroxide and lithium carbonate; the second dopant is selected from at least one of compounds formed by Zr, sr, al, nb; the second sintering treatment is two-stage sintering, for example, heating to 600 ℃ for 4 hours, and then continuously heating to 700-1000 ℃ for 6-10 hours; the temperature of the second coating treatment is 450-750 ℃, the time is 5-10 h, and the sintering atmosphere is oxygen or nitrogen with the volume concentration of more than or equal to 85%; the second coating agent is at least one compound formed by P, al, co, ti, W, Y, mg, preferably at least one of aluminum phosphate, aluminum oxide, titanium dioxide, yttrium oxide, cobalt oxide and magnesium oxide.
In some embodiments, the first sintering process and the second sintering process may be one-stage sintering, where the temperature of the first sintering process is 720-780 ℃ and the time is 5-15 h; the temperature of the second sintering treatment is 795-830 ℃ and the time is 5-15 h.
In a third aspect of the present invention, there is provided a positive electrode sheet comprising the positive electrode material of the first aspect or the positive electrode material produced by the production method of the second aspect.
In some embodiments, the positive electrode sheet includes a current collector, a positive electrode active material layer on at least one functional surface of the current collector; the positive electrode active material layer contains a positive electrode material, a conductive agent, and a binder.
The positive plate can also be prepared by adopting the conventional technical means in the field, specifically, the positive electrode material, the conductive agent and the binder can be uniformly dispersed in a solvent to obtain positive electrode active layer slurry, then the positive electrode active layer slurry is coated on at least one functional surface of a positive electrode current collector, and the positive electrode plate can be obtained after drying.
The specific types of the conductive agent and the adhesive are not particularly limited, and the conductive agent, the adhesive and the like can be conventional materials in the field, for example, the conductive agent can be one or more selected from conductive carbon black, carbon nano tubes, conductive graphite and graphene, and the adhesive can be one or more selected from polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber and styrene-acrylic rubber.
The coating method is not particularly limited, and the coating of the positive electrode active layer slurry can be realized by adopting any coating method such as gravure coating, extrusion coating, spray coating, screen printing and the like.
In a fourth aspect of the present invention, there is provided a lithium ion battery including the positive electrode sheet provided in the third aspect.
In addition to the positive electrode sheet, in some embodiments, the lithium ion battery of the present invention further comprises a separator, a negative electrode sheet, and an electrolyte. The composition of the negative electrode sheet can refer to a conventional negative electrode sheet in the field, and the separator can also adopt a separator conventionally used in the field, such as a PP film, a PE film and the like. The negative electrode sheet is at least one selected from lithium sheet, graphite and silicon carbon negative electrode.
The lithium ion battery can be prepared by adopting a conventional method in the art, specifically, the positive plate, the diaphragm and the negative plate are sequentially stacked and placed, the battery core is obtained through lamination or winding process, and then the lithium ion battery is obtained through the procedures of baking, liquid injection, formation, encapsulation and the like.
The present invention will be further illustrated by the following specific examples and comparative examples. The reagents, materials and instruments used in the following are all conventional reagents, conventional materials and conventional instruments, which are commercially available, and the reagents and materials involved can be synthesized by conventional synthesis methods, unless otherwise specified.
Example 1
1. Preparation of polycrystalline granules
Ni is a first precursor 93 Co 6 Mn 1 (OH) 2 Fully mixing lithium hydroxide and yttrium oxide in a high-speed mixer according to the mol ratio of 1:1.06:0.003 to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 380 ℃ in an oxygen atmosphere, preserving heat for 3 hours, continuously heating to 500 ℃ and preserving heat for 7 hours, performing presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a first presintering material;
then the first presintering material is put into a muffle furnace, and is subjected to high-temperature sintering treatment for 10 hours at 780 ℃ in the atmosphere of oxygen, and is cooled, crushed and sieved along with the furnace to obtain a sintered material;
after washing and drying the sintered material, mixing 1kg of the dried sintered material with 10g of aluminum oxide in a high-speed mixer, putting into a muffle furnace, preserving heat for 10 hours under a nitrogen atmosphere at 300 ℃ for coating treatment, cooling along with the furnace, crushing, and sieving to obtain polycrystalline particles A1.
2. Preparation of monocrystalline particles
Ni as second precursor 93.5 Co 5.5 Mn 1 (OH) 2 Fully mixing lithium carbonate and zirconia in a high-speed mixer according to the mol ratio of 1:1.04:0.004 to obtain a second mixture;
placing the second mixture into a muffle furnace, heating to 320 ℃ in an oxygen atmosphere, preserving heat for 3 hours, continuously heating to 580 ℃ and preserving heat for 7 hours, carrying out second presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a second presintering material;
Placing the second presintering material into a muffle furnace, carrying out heat preservation at 810 ℃ for 13 hours under the atmosphere of oxygen, carrying out high-temperature sintering treatment, cooling along with the furnace, crushing, and sieving to obtain a sintered material;
mixing 1kg of sintered material and 15g of titanium dioxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 500 ℃ for 10 hours under the atmosphere of nitrogen, carrying out cladding treatment, cooling along with the furnace, crushing, and sieving to obtain single crystal particles B1.
3. Preparation of cathode Material
The mass ratio is 1:1 and monocrystalline particles B1 were mixed at 25 ℃ for 15min using a batch mixer to obtain a positive electrode material.
Example 2
1. Preparation of polycrystalline granules
Ni is a first precursor 91.5 Co 2.5 Mn 6 (OH) 2 Fully mixing lithium hydroxide and niobium trioxide in a high-speed mixer according to the mol ratio of 1:1.03:0.012 to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 300 ℃ in an oxygen atmosphere, preserving heat for 2 hours, continuously heating to 590 ℃ and preserving heat for 7 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a first presintering material;
then the first presintering material is put into a muffle furnace, and is subjected to heat preservation at 725 ℃ for 10 hours under the atmosphere of oxygen for high-temperature sintering treatment, and is cooled, crushed and sieved along with the furnace to obtain a sintering product;
Washing and drying the sintered product, mixing 1kg of the dried sintered product with 20g of titanium dioxide in a high-speed mixer, placing the mixture into a muffle furnace, preserving the temperature for 10 hours at 390 ℃ in an oxygen atmosphere, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain polycrystalline particles A2.
2. Preparation of monocrystalline particles
Ni as second precursor 92.5 Co 2.5 Mn 5 (OH) 2 Fully mixing lithium hydroxide and strontium carbonate in a high-speed mixer according to the mol ratio of 1:1.04:0.003 to obtain a second mixture;
placing the second mixture into a muffle furnace, heating to 300 ℃ in an oxygen atmosphere, preserving heat for 1.5 hours, continuously heating to 600 ℃ and preserving heat for 6 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a second presintering material;
placing the second presintering material into a muffle furnace, carrying out high-temperature sintering treatment at 795 ℃ for 10 hours in an oxygen atmosphere, cooling along with the furnace, crushing, and sieving to obtain a sintered product;
mixing 1kg of sintered product, 12g of cobalt oxide and 5g of magnesium oxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 570 ℃ for 10 hours under the atmosphere of oxygen for coating treatment, cooling along with the furnace, crushing and sieving to obtain single crystal particles B2.
3. Preparation of cathode Material
The mass ratio is 4:1 and monocrystalline particles B2 were mixed at 25 ℃ for 15min using a batch mixer to obtain a positive electrode material.
Example 3
1. Preparation of polycrystalline granules
Ni is a first precursor 88 Co 6 Mn 6 (OH) 2 Fully mixing lithium hydroxide and niobium trioxide in a high-speed mixer according to the mol ratio of 1:1.08:0.015 to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 270 ℃ in an oxygen atmosphere, preserving heat for 1 hour, continuously heating to 590 ℃ and preserving heat for 7 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a first presintering material;
then the first presintering material is put into a muffle furnace, and is subjected to high-temperature sintering treatment at 750 ℃ for 10 hours under the atmosphere of oxygen, and is cooled, crushed and sieved along with the furnace to obtain a sintered material;
washing and drying the sintered material, mixing 1kg of the dried sintered material with 13g of alumina in a high-speed mixer, placing into a muffle furnace, preserving heat for 10 hours in an oxygen or nitrogen atmosphere at 390 ℃, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain polycrystalline particles A3.
2. Preparation of monocrystalline particles
Ni as second precursor 90 Co 5 Mn 5 (OH) 2 Fully mixing lithium hydroxide and strontium carbonate in a high-speed mixer according to the mol ratio of 1:1.00:0.018 to obtain a second mixture;
Placing the second mixture into a muffle furnace, heating to 250 ℃ in an oxygen atmosphere, preserving heat for 1 hour, continuously heating to 600 ℃ and preserving heat for 6 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a second presintering material;
placing the second presintering material into a muffle furnace, carrying out heat preservation at 830 ℃ for 10 hours under the atmosphere of oxygen, carrying out high-temperature sintering treatment, cooling along with the furnace, crushing, and sieving to obtain a sintered material;
mixing 1kg of sintered material, 12g of aluminum phosphate and 10g of yttrium oxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 570 ℃ for 10 hours in an oxygen or nitrogen atmosphere for coating treatment, cooling along with the furnace, crushing, and sieving to obtain single crystal particles B3.
3. Preparation of cathode Material
And mixing the polycrystalline particles A3 and the monocrystalline particles B3 with the mass ratio of 7:1 at the temperature of 25 ℃ for 15min by using a batch mixer to obtain the positive electrode material.
Comparative example 1
1. Preparation of polycrystalline granules
Ni is a first precursor 92 Co 5 Mn 3 (OH) 2 Fully mixing lithium hydroxide and yttrium oxide in a high-speed mixer according to the mol ratio of 1:1.03:0.02 to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 300 ℃ in an oxygen atmosphere, preserving heat for 1 hour, continuously heating to 710 ℃ and preserving heat for 7 hours, cooling along with the furnace, crushing, and sieving to obtain a first sintered material;
After washing and drying the first sintering material, adding 1kg of the dried first sintering material and 10g of titanium dioxide into a high-speed mixer, mixing, putting into a muffle furnace, preserving heat for 10 hours in an oxygen or nitrogen atmosphere at 390 ℃, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain polycrystalline particles A11.
2. Preparation of monocrystalline particles
Ni as second precursor 93 Co 5 Mn 2 (OH) 2 Fully mixing lithium carbonate and strontium carbonate in a high-speed mixer according to the mol ratio of 1:0.98:0.012 to obtain a second mixture;
placing the second mixture into a muffle furnace, heating to 220 ℃ in an oxygen atmosphere, preserving heat for 1 hour, continuously heating to 790 ℃ and preserving heat for 10 hours, carrying out sintering treatment, cooling along with the furnace, crushing, and sieving to obtain a sintered product;
mixing 1kg of sintered product, 20g of cobalt oxide and 5g of aluminum oxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 570 ℃ for 10 hours in an oxygen or nitrogen atmosphere for coating treatment, cooling along with the furnace, crushing, and sieving to obtain single crystal particles B11.
3. Preparation of cathode Material
And mixing the polycrystalline particles A11 and the monocrystalline particles B11 with the mass ratio of 8:1 at the temperature of 25 ℃ for 15min by using a batch mixer to obtain the positive electrode material.
Comparative example 2
1. Preparation of polycrystalline granules
Ni is a first precursor 80 Co 10 Mn 10 (OH) 2 Fully mixing lithium hydroxide and niobium trioxide in a high-speed mixer according to the mol ratio of 1:1.01:0.010 to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 270 ℃ in an oxygen atmosphere, preserving heat for 1 hour, continuously heating to 600 ℃ and preserving heat for 3.5 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a first presintering material;
then the first presintering material is put into a muffle furnace, and is subjected to high-temperature sintering treatment for 9 hours at 780 ℃ in the atmosphere of oxygen, and is cooled, crushed and sieved along with the furnace to obtain the first sintering material;
washing and drying the first sintering material, mixing 1kg of the dried first sintering material with 5g of alumina in a high mixer, putting into a muffle furnace, preserving heat for 7 hours in an oxygen or nitrogen atmosphere at 390 ℃, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain polycrystalline particles.
2. Preparation of monocrystalline particles
Ni as second precursor 80 Co 10 Mn 10 (OH) 2 Fully mixing lithium hydroxide and strontium carbonate in a high-speed mixer according to the mol ratio of 1:1.03:0.008 to obtain a second mixture;
placing the second mixture into a muffle furnace, heating to 270 ℃ in an oxygen atmosphere, preserving heat for 3 hours, continuously heating to 620 ℃ and preserving heat for 6 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a second presintering material;
Placing the second presintering material into a muffle furnace, carrying out high-temperature sintering treatment at 880 ℃ for 8 hours in an oxygen atmosphere, cooling along with the furnace, crushing, and sieving to obtain a second sintering material;
mixing 1kg of second sintering material and 12g of yttrium oxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 530 ℃ for 10 hours under the atmosphere of oxygen or nitrogen, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain single crystal particles.
3. Preparation of cathode Material
And mixing the polycrystalline particles and the monocrystalline particles with the mass ratio of 4:1 at the temperature of 25 ℃ for 15 minutes by using a batch mixer to obtain the anode material.
Comparative example 3
1. Preparation of polycrystalline granules
Ni is a first precursor 82 Co 6 Mn 12 (OH) 2 Fully mixing lithium hydroxide and molybdenum dioxide in a high-speed mixer according to the mol ratio of (1:1.04:0.011) to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 220 ℃ in an oxygen atmosphere, preserving heat for 1.5 hours, continuously heating to 600 ℃ and preserving heat for 3.5 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a first presintering material;
then the first presintering material is put into a muffle furnace, heat preservation is carried out for 9 hours at 790 ℃ under the atmosphere of oxygen, high-temperature sintering treatment is carried out, cooling is carried out along with the furnace, crushing is carried out, and the first sintering material is obtained after sieving;
Washing and drying the first sintering material, mixing 1kg of dried sintering material with 5g of alumina in a high-speed mixer, placing into a muffle furnace, preserving heat for 7 hours in an oxygen or nitrogen atmosphere at 390 ℃, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain polycrystalline particles.
2. Preparation of monocrystalline particles
Ni as second precursor 83 Co 6 Mn 11 (OH) 2 Fully mixing lithium hydroxide and strontium carbonate in a high-speed mixer according to the mol ratio of (1:1.03:0.008) to obtain a second mixture;
placing the second mixture into a muffle furnace, heating to 280 ℃ in an oxygen atmosphere, preserving heat for 3 hours, continuously heating to 600 ℃ and preserving heat for 6 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a second presintering material;
placing the second presintering material into a muffle furnace, carrying out high-temperature sintering treatment at 893 ℃ for 8 hours under the atmosphere of oxygen, cooling along with the furnace, crushing, and sieving to obtain a second sintering material;
mixing 1kg of second sintering material and 16g of boron oxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 535 ℃ for 10 hours under the atmosphere of oxygen or nitrogen, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain single crystal particles.
3. Preparation of cathode Material
And mixing the polycrystalline particles and the monocrystalline particles with the mass ratio of 4:1 at the temperature of 25 ℃ for 15 minutes by using a batch mixer to obtain the anode material.
Comparative example 4
1. Preparation of polycrystalline granules
Ni is a first precursor 82 Co 12 Mn 6 (OH) 2 In a high-speed mixer, lithium hydroxide and zirconium dioxide are mixed according to the mol ratio of (1:1.07:0.009)Fully mixing to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 210 ℃ in an oxygen atmosphere, preserving heat for 1.5 hours, continuously heating to 650 ℃ and preserving heat for 6 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a first presintering material;
then the first presintering material is put into a muffle furnace, the high-temperature sintering treatment is carried out at 785 ℃ for 10 hours under the atmosphere of oxygen, and the first presintering material is obtained after cooling, crushing and sieving along with the furnace;
and (3) washing and drying the first sintering material, weighing 1kg of the first sintering material and 15g of the first sintering material, mixing the first sintering material with an alumina high-speed mixer, putting the mixture into a muffle furnace, carrying out coating treatment at 480 ℃ in an oxygen or nitrogen atmosphere for 7 hours, cooling the first sintering material along with the furnace, crushing the first sintering material, and sieving the first sintering material to obtain polycrystalline particles.
2. Preparation of monocrystalline particles
Ni as second precursor 83 Co 12 Mn 6 (OH) 2 Fully mixing lithium hydroxide and zirconium dioxide in a high-speed mixer according to the mol ratio of 1:0.99:0.017 to obtain a second mixture;
Placing the second mixture into a muffle furnace, heating to 290 ℃ in an oxygen atmosphere, preserving heat for 3 hours, continuously heating to 650 ℃ and preserving heat for 8 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a second presintering material;
placing the second presintering material into a muffle furnace, carrying out high-temperature sintering treatment at 900 ℃ for 9 hours in an oxygen atmosphere, cooling along with the furnace, crushing, and sieving to obtain a second sintering material;
mixing 1kg of second sintering material and 30g of cobalt oxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 550 ℃ for 7 hours under the atmosphere of oxygen or nitrogen for coating treatment, cooling along with the furnace, crushing and sieving to obtain single crystal particles.
3. Preparation of cathode Material
And mixing the polycrystalline particles and the monocrystalline particles with the mass ratio of 4:1 at the temperature of 25 ℃ for 15 minutes by using a batch mixer to obtain the anode material.
Comparative example 5
The procedure was substantially identical to that of example 2, except that in the preparation of the positive electrode material, polycrystalline particles A2 and single crystal particles B2 in a mass ratio of 0.5:1 were mixed at a temperature of 25 ℃ for 15 minutes using a batch mixer, to obtain a positive electrode material of this comparative example.
Comparative example 6
1. Preparation of polycrystalline granules
Ni is a first precursor 90 Co 5 Mn 5 (OH) 2 Fully mixing lithium hydroxide and zirconium dioxide in a high-speed mixer according to the mol ratio of (1:0.98:0.019) to obtain a first mixture;
placing the first mixture into a muffle furnace, heating to 215 ℃ in an oxygen atmosphere, preserving heat for 2.5 hours, continuously heating to 550 ℃ and preserving heat for 7 hours, cooling along with the furnace, crushing, and sieving to obtain a first presintering material;
then the first presintering material is put into a muffle furnace, and is subjected to heat preservation at 725 ℃ for 12 hours under the atmosphere of oxygen for high-temperature sintering treatment, and is cooled, crushed and sieved along with the furnace to obtain the first sintering material;
washing and drying the first sintering material, mixing 1kg of the dried first sintering material with 19g of strontium oxide in a high-speed mixer, placing into a muffle furnace, preserving heat for 7 hours in an oxygen or nitrogen atmosphere at 480 ℃, carrying out coating treatment, cooling along with the furnace, crushing, and sieving to obtain polycrystalline particles.
2. Preparation of monocrystalline particles
Ni as second precursor 90 Co 5 Mn 5 (OH) 2 Fully mixing lithium hydroxide and titanium dioxide in a high-speed mixer according to the mol ratio of (1:0.99:0.017) to obtain a second mixture;
placing the second mixture into a muffle furnace, heating to 290 ℃ in an oxygen atmosphere, preserving heat for 3 hours, continuously heating to 650 ℃ and preserving heat for 8 hours, carrying out first presintering treatment, cooling along with the furnace, crushing, and sieving to obtain a second presintering material;
Placing the second presintering material into a muffle furnace, carrying out high-temperature sintering treatment at 900 ℃ for 9 hours in an oxygen atmosphere, cooling along with the furnace, crushing, and sieving to obtain a second sintering material;
mixing 1kg of second sintering material, 30g of strontium oxide and 5g of aluminum oxide in a high-speed mixer, putting into a muffle furnace, carrying out heat preservation at 500 ℃ for 10 hours in an oxygen or nitrogen atmosphere for coating treatment, cooling along with the furnace, crushing and sieving to obtain single crystal particles.
3. Preparation of cathode Material
And mixing the polycrystalline particles and the monocrystalline particles with the mass ratio of 4:1 at the temperature of 25 ℃ for 15 minutes by using a batch mixer to obtain the anode material.
Comparative example 7
The single crystal particles B1 in example 1 were used as the positive electrode material of this comparative example.
Comparative example 8
The polycrystalline particle A1 in example 1 was used as the positive electrode material of this comparative example.
Test examples
1. The polycrystalline pellets, single crystal pellets, and positive electrode materials of examples and comparative examples were subjected to pressure maintaining at 3.5T for 60s, respectively, and Dv50, specific surface area, and average particle diameters of the polycrystalline pellets, single crystal pellets, and positive electrode materials before and after the pressure maintaining were recorded, respectively.
2. Cycle performance test
Preparation of a positive plate: the positive electrode materials of the examples and the comparative examples, the conductive carbon black SP, the conductive graphite KS-6 and the polyvinylidene fluoride PVDF are mixed according to the mass ratio of 94.5 percent to 2 percent to 1.0 percent to 2.5 percent, and are dissolved in N-methyl pyrrolidone by magnetic stirring to obtain positive electrode slurry, then the positive electrode slurry is coated on an aluminum foil current collector with the thickness of 15 mu m by a coating machine, rolled and formed, dried in an oven at the temperature of 125 ℃ and cut into positive electrode sheets with the required size;
Preparing a negative plate: graphite, conductive carbon black SP, sodium carboxymethylcellulose CMC and styrene-butadiene rubber SBR are dissolved in deionized water through magnetic stirring according to the mass ratio of 95.5 percent to 1.5 percent to 2.0 percent to obtain negative electrode slurry, the obtained negative electrode slurry is coated on a copper foil current collector with the thickness of 10 mu m by a coating machine, the copper foil current collector is rolled and formed, and the negative electrode slurry is dried in an oven at 115 ℃ and cut into negative electrode plates with the required size.
Assembling a battery: and winding the positive plate, the polypropylene diaphragm PP and the negative plate into required battery cells, baking the battery cells in an oven at 85 ℃ for 10 hours, packaging an aluminum plastic film, welding the electrode lugs, continuously baking the battery cells for 20 hours after short circuit testing, and performing the procedures of liquid injection, air exhaust, sealing, pre-charging, formation and aging after moisture is tested to be qualified to obtain the required battery. The capacity retention rate of the battery was measured at 2.8 to 4.25V for 300 weeks by performing a 1C charge-discharge cycle.
3. Capacity testing
The positive electrode material, acetylene black and polyvinylidene fluoride (PVDF) are mixed according to the following ratio of 94:3:3, weighing and uniformly mixing the materials according to the mass ratio, adding N-methyl pyrrolidone, stirring for 2 hours to obtain positive electrode slurry, uniformly coating the positive electrode slurry on an aluminum foil, baking the aluminum foil in vacuum at 80 ℃, tabletting, and cutting a positive electrode plate with the diameter of 14 mm;
in a glove box filled with argon, a button-type half cell with the specification of CR2032 (electrolyte comprises electrolyte and solvent, the electrolyte is LiPF6 with the concentration of 1mol/L, the solvent is a mixed solution of diethyl carbonate and ethylene carbonate with the volume ratio of 1:1, a counter electrode is a pure lithium sheet with the diameter of 16mm, a diaphragm is Celgard 2500) is arranged, and the button-type half cell with the specification of CR2032 is obtained after standing for 24 hours. The half-cell capacity was tested at 2.5-4.25 v,0.2c charge-discharge. Among them, the test data of the polycrystalline particles and the monocrystalline particles are shown in table 1, and the test data of the positive electrode material and the performance of the assembled battery are shown in table 2.
The results are shown in Table 1
TABLE 1
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TABLE 2
As can be seen from fig. 1 to 6, the positive electrode material, the polycrystalline particles and the single crystal particles of the comparative example all had chipping after the pressure maintaining, whereas the positive electrode material, the polycrystalline particles and the single crystal particles of the examples remained original appearance after the pressure maintaining, without chipping.
As is clear from tables 1 and 2, the present invention can effectively improve cycle performance and capacity of a battery by limiting the compacted density of a positive electrode material and the relationship x=Δd×Δbet satisfied by Δd and Δbet of the positive electrode material, wherein X is-0.04 to 0, ensuring that crack defects are reduced as much as possible while achieving a high compacted density, and applying the positive electrode material to a battery. Furthermore, the present invention is defined by defining β1, ΔBET of the polycrystalline particles 1 Single crystal particles β2, Δbet 2 Is advantageous for achieving a positive electrode material having the specific compacted density and relationship described above.
Comparative examples 1 to 3 and comparative examples 2 to 4 and 6 are useful for preparing polycrystalline particles satisfying T1 of-0.01 to 0 when the difference between the temperature satisfying the second stage burn-in and the temperature satisfying the first stage burn-in is not more than 320 ℃, and comparative examples 1 to 3 and comparative examples 2 to 4 and 6 are useful for preparing single crystal particles satisfying T2 of-0.04 to 0 when the difference between the temperature satisfying the fourth stage burn-in and the temperature satisfying the third stage burn-in is not more than 350 ℃. By combining the polycrystalline particles and the monocrystalline particles, the positive electrode material can meet the relation of X=delta D×delta BET and X is-0.04-0 while achieving high compaction density, so that the electrochemical performance of the battery is improved.
Preferred embodiments of the present invention and experimental verification are described in detail above. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention without requiring creative effort by one of ordinary skill in the art. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (12)
1. The positive electrode material is characterized in that the Dv50 variation difference value of the positive electrode material is delta D and the specific surface area difference value is delta BET before and after pressure maintaining for 30-80 s under the pressure of 2-4T;
Δd and Δbet satisfy x=Δd×Δbet, and X is-0.04 to 0;
the compaction density of the positive electrode material under the pressure of 2-4T is 3.6-3.8 g/cm 3 。
2. The positive electrode material according to claim 1, wherein the positive electrode material includes at least polycrystalline particles and single crystal particles; the grain diameter change rate of the polycrystalline grains is beta 1 and the specific surface area difference is delta BET before and after pressure maintaining for 30-80 s under the pressure of 2-4T 1 ；
The single crystal grain has a grain diameter change rate of beta 2 and a specific surface area difference of delta BET before and after pressure maintaining for 30-80 s under the pressure of 2-4T 2 The unit of the specific surface area difference is m 2 /g；
β1、ΔBET 1 Satisfy t1=β1×Δ BET 1 And T1 is-0.01-0;
β2、ΔBET 2 satisfy t2=β2×Δ BET 2 And T2 is-0.04-0;
wherein β1 is the ratio of the difference in Dv50 variation of the polycrystalline particles to the average particle diameter of the polycrystalline particles, and β2 is the ratio of the difference in Dv50 variation of the single crystal particles to the average particle diameter of the single crystal particles.
3. The positive electrode material according to claim 2, wherein the difference in Dv50 variation of the polycrystalline particles is-0.90 to-0.05 μm;
the difference of Dv50 of the single crystal particles is-0.15-0 mu m.
4. The positive electrode material according to claim 2, wherein the difference in specific surface area of the polycrystalline particles is 0 to 0.3m 2 /g；
The specific surface area difference of the single crystal particles is 0-0.2 m 2 /g。
5. The positive electrode material according to claim 2, wherein D104 of single crystal particles in the positive electrode material is 88 to 105nm and D104 of polycrystalline particles is 30 to 65nm as measured by XRD ray diffraction, wherein D104 means a crystal grain size of 104 crystal planes as measured by XRD ray diffraction.
6. The positive electrode material according to any one of claims 1 to 5, wherein a mass ratio (1 to 7) of the polycrystalline particles to the single crystal particles: 1, a step of;
The chemical formula of the single crystal particles is LiNi x M (1-x) O 2 Wherein x is more than or equal to 0.7 and less than 1, and M is selected from at least two of Co, mn, B, mg, al, zr, sr, mo, ti; and/or the number of the groups of groups,
the chemical formula of the polycrystalline particles is LiNi y N (1-y) O 2 Wherein y is more than or equal to 0.7 and less than 1, and N is selected from at least two of Co, mn, B, mg, al, zr, sr, mo, ti.
7. The positive electrode material according to claim 6, wherein the positive electrode material has a compacted density of 3.6 to 3.8g/cm under a pressure of 3.5T 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the number of the groups of groups,
the specific surface area of the positive electrode material is 0.45-0.90 m 2 /g。
8. The positive electrode material according to claim 7, wherein the positive electrode material has a gram capacity of 200 to 230mAh/g at 0.2C and 2.5 to 4.25V.
9. A method for producing the positive electrode material according to any one of claims 1 to 8, comprising the steps of:
mixing a first precursor, a first lithium salt and a first doping agent to obtain a first material; sequentially performing first presintering treatment and first sintering treatment on the first material to obtain polycrystalline particles;
mixing a second precursor, a second lithium salt and a second doping agent to obtain a second material; sequentially performing second presintering treatment and second sintering treatment on the second material to obtain monocrystalline particles;
Mixing the polycrystalline particles and the monocrystalline particles to obtain the positive electrode material;
the first presintering treatment is carried out under an oxygen-containing atmosphere, the first presintering treatment comprises a first stage presintering treatment and a second stage presintering treatment, the temperature of the first stage presintering treatment is 200-400 ℃, the time is 0.5-3 h, the temperature of the second stage presintering treatment is 500-600 ℃, and the time is 3-10 h;
the second presintering treatment is carried out in an oxygen-containing atmosphere, the second presintering treatment comprises a third stage presintering and a fourth stage presintering, the temperature of the third stage presintering is 200-400 ℃, the time is 0.5-3 h, the temperature of the fourth stage presintering is 500-600 ℃, and the time is 3-10 h;
the difference between the temperature of the second stage presintering and the temperature of the first stage presintering is not more than 320 ℃, and the difference between the temperature of the fourth stage presintering and the temperature of the third stage presintering is not more than 350 ℃.
10. The method of claim 9, wherein after the first sintering process, a first sintered product is obtained, further comprising subjecting the first sintered product to a first coating process to obtain polycrystalline particles;
after the second sintering treatment, obtaining a second sintering product, and further comprising performing a second coating treatment on the second sintering product to obtain monocrystalline particles; and/or the number of the groups of groups,
The molar ratio of the first precursor, the first lithium salt and the first dopant is 1: (0.98-1.08): (0.003-0.02);
the molar ratio of the second precursor, the second lithium salt, and the second dopant is 1: (0.98-1.08): (0.003-0.02).
11. A positive electrode sheet comprising the positive electrode material according to any one of claims 1 to 8 or a positive electrode material produced by the production method according to claim 9 or 10.
12. A battery comprising the positive electrode sheet according to claim 11.
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