A Phosphorus-Containing Substance-Coated Cathode Material, Its Preparation Method and Application

Abstract

The present invention discloses a phosphorus-containing substance-coated cathode material, a preparation method thereof, and an application thereof, belonging to the technical field of lithium-ion batteries. The chemical formula of the phosphorus-containing substance-coated cathode material is (1-x)Li 1+a (Ni (1‑m‑n) Co n Mn m ) 1‑b M b M′ y O 2‑y ·xM″ c PO z , where M is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, S, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, Ca, where 0≤a≤0.1, 0

Description

Technical Field

[0001] The present invention relates to a phosphorus-containing substance-coated cathode material, a preparation method thereof and an application thereof, and belongs to the technical field of lithium ion batteries. Background Art

[0002] Lithium batteries are widely used in electric vehicles, energy storage, 3C fields, etc. because of their advantages such as high energy density, low self-discharge, long service life and environmental friendliness. With the development of technology, new requirements have been put forward for the energy density and safety performance of lithium ion batteries. Developing high-energy-density lithium batteries can start from three aspects. One is to develop new anode and cathode materials with high specific capacity. At present, it is difficult to mature the development of materials with higher specific capacity in a short time. The second is to improve the tap density. At present, the tap density has approached the limit and the improvement space is small. The third is to increase the charging cut-off voltage of lithium batteries. Increasing the charging cut-off voltage of lithium batteries indirectly increases the energy density of lithium batteries and reduces the cost of lithium batteries at the same time, which has become an important research direction in the industry.

[0003] As the cut-off voltage of lithium batteries increases, the battery performance deteriorates significantly. The main reason is that as the voltage increases, the amount of lithium deintercalation and intercalation increases, resulting in an increase in volume deformation and stress accumulation, and microcracks are likely to occur on the material surface. The surface of the layered cathode material is more likely to react with the electrolyte. It is mainly reflected in the reaction of trace water in the electrolyte, residual alkali on the surface of the layered material and fluorine in the electrolyte to form inert lithium fluoride and deposit on the surface of the cathode material. Lithium fluoride does not have electrochemical activity, resulting in a decrease in active lithium during the cycling process; the battery interface thickens, resulting in an increase in electronic conductivity impedance and charge transfer impedance, reducing the cycling performance. Therefore, reducing the side reaction at the cathode material interface is a necessary condition for increasing the operating voltage.

[0004] Taking the layered material lithium cobaltate as an example, when the lithium deintercalation gradually increases, Li x CO2 gradually transforms from the hexagonal system H-1 phase to the hexagonal system H-2 phase, and the ratio of the two phases changes with the change of x; when x is from 3 / 4 to 1 / 2, Li x CO2 belongs to the hexagonal system (H-2 phase); both single-phase H-1 and H-2 belong to the R-3m space group and have the same symmetry, but there are differences in the unit cell parameters of the two phases. Single-phase H-1 usually tends to have semiconductor conductivity characteristics, and single-phase H-2 usually tends to have metal conductivity characteristics; when x is about 1 / 2, the charging voltage is about 4.2V, Li x CO2 transforms from the hexagonal system H-2 to the monoclinic system M, belonging to the P12 / m1 space group. This process is accompanied by irregular changes in the unit cell parameters. The possible reason for this phenomenon is that the spatial rules of lithium ions and lithium vacancies change, showing an ordered-disordered-ordered change rule. The change of crystal parameters leads to the change of the volume of material particles, Li xCO2 transforms from the hexagonal system H-2 to the monoclinic system M, and the unit cell of the material expands by about 2.3% along the c-axis; when x is about 1 / 2 to 1 / 3, the monoclinic system M transforms to the second hexagonal system O3, and the occurrence of this phase transition guides the subsequent development of high-voltage lithium cobaltate; when x approaches 0, the second hexagonal system O3 gradually transforms to the second monoclinic system O1, and the two-phase transition occurs near 4.5V. This phase transition undergoes a drastic change along the c-axis, expanding by about 2.6%. During the charge and discharge process of lithium cobaltate, the deintercalation and intercalation of lithium ions are accompanied by changes in the spatial structure, conductivity, and volume, resulting in an unstable crystal structure and stress accumulation, which promotes the generation of microcracks on the surface. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a phosphorus-containing substance-coated cathode material, its preparation method and application; by coating a phosphorus-containing substance on the surface of the bulk material, the P atoms in the surface layer occupy the tetrahedral interstitial sites, and the Li atoms and Co atoms occupy the octahedral interstitial sites; due to the Co-O-P or M-O-P bonds stabilizing the crystal structure, during the + process of lithium deintercalation, the rearrangement of the surface layer crystal is small, and the crystal structure is very stable, which can to a certain extent inhibit the appearance of microcracks, thereby improving the electrical performance of the phosphorus-containing substance-coated cathode material under high voltage.

[0006] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0007] In the first aspect, a phosphorus-containing substance-coated cathode material is provided, and the chemical formula of the phosphorus-containing substance-coated cathode material is (1-x)Li 1+a (Ni (1-m-n) Co n Mn m ) 1-b M b M′ y O 2-y ·xM″ c PO z ,

[0008] where M is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, S, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, Ca;

[0009] where 0≤a≤0.1, 0<b≤0.1, 0<c≤3, 0≤m≤1, 0≤n≤1, 3≤z≤4, 0.001≤x≤0.05;

[0010] where M′ is one or two of F, Se, S, and 0.0001≤y≤0.1;

[0011] Wherein M″ is at least one of La, Al, Ti, Y, Zr, Co, Ni, Mn, Mg, and B.

[0012] In the present invention, through the co-doping of multiple elements and the synergistic effect of various elements, the transformation of H1-3 to the O1 phase of lithium cobaltate is inhibited under high voltage, and the structural stability of the positive electrode material coated with a phosphorus-containing substance is improved. In the positive electrode material coated with a phosphorus-containing substance of the present invention, M′ doping occupies the O site, improving the conductivity of the positive electrode material; M doping occupies the Co site, enhancing the ionization of the Co-O-P bond and making it easier for lithium ions to migrate; M″ is coated on the surface layer to stabilize the interface structure. M″ c PO z has a good lithium ion transmission rate, coats the positive electrode material lithium cobaltate, improves the structural stability of highly delithiated lithium cobaltate, delays the transformation of O3 to the H1-3 phase of lithium cobaltate under high voltage, inhibits the transformation of H1-3 to the O1 phase, reduces the grain boundary dislocations and internal stress in the highly delithiated state, and further reduces the charge transfer impedance at the interface between lithium cobaltate and the electrolyte. Therefore, it is beneficial to the electrochemical stability of the positive electrode material of the lithium ion battery, and solves the problems of cycling, storage, gas generation, etc. faced in the development of high-voltage materials.

[0013] M″ c PO z reacts with lithium in the positive electrode material to form a cobalt-lithium phosphate compound. Since the conductivity of the cobalt-lithium phosphate compound is very low, coating the cobalt-lithium phosphate compound will significantly increase the impedance of lithium cobaltate in the battery, increase the internal resistance of the battery, and sacrifice the battery capacity. The particle size of the cobalt-lithium phosphate compound is at the nanometer level. It can not only delay or inhibit the redox reaction between the electrolyte and the surface of lithium cobaltate, but also, due to the nanometer size of the nanoscale cobalt-lithium phosphate compound, greatly shorten the lithium ion transmission path, significantly improve the conductivity of the cobalt-lithium phosphate compound, build a good lithium ion transmission channel on the surface of lithium cobaltate, and achieve the goal of neither sacrificing the battery capacity of the lithium cobaltate battery nor improving the battery cycle performance under high voltage.

[0014] Preferably, the particle size of the positive electrode material coated with a phosphorus-containing substance is 2-26 μm.

[0015] Within the above particle size range, the electrochemical performance of the positive electrode material coated with a phosphorus-containing substance is better.

[0016] In a second aspect, a method for preparing the positive electrode material coated with a phosphorus-containing substance is provided, including the following steps:

[0017] Prepare the bulk material: Mix and stir evenly a lithium source, a precursor, a compound containing M, and a substance containing M′, then calcine and crush to obtain the bulk material;

[0018] Prepare a phosphorus-containing substance suspension:

[0019] S1: Mix the lithium source, phosphorus source, and the substance containing M″ evenly, then calcine and crush them to obtain a phosphorus-containing substance powder;

[0020] S2: Add the phosphorus-containing substance powder obtained in S1 into deionized water and stir evenly to obtain a phosphorus-containing substance suspension;

[0021] Prepare a phosphorus-containing substance-coated cathode material: Spray the phosphorus-containing substance suspension onto the bulk material under rotating conditions, mix evenly, then sinter and pulverize to obtain the phosphorus-containing substance-coated cathode material.

[0022] In the preparation of the bulk material, adding a compound containing M can achieve the bulk doping of the M element, improve the electronic conductivity and charge transfer ability of the phosphorus-containing substance-coated cathode material, and inhibit the irreversible phase change of the phosphorus-containing substance-coated cathode material under high voltage; at the same time, the substance containing M′ can inhibit oxygen loss for the oxygen vacancies of the bulk material and improve the stability of the phosphorus-containing substance-coated cathode material. The substance containing M″ reacts with the phosphorus source and acts together to improve the interfacial performance of the phosphorus-containing substance-coated cathode material and alleviate the corrosion rate of the surface layer of the phosphorus-containing substance-coated cathode material.

[0023] During the preparation of the phosphorus-containing substance suspension, the crushing step of the sintered product is as follows: Place the sintered product in a micro-nano crusher, add ethanol, and then crush it at a power of 200W for 10 minutes. In the above crushing process, the role of ethanol is to wet, and the added amount can be added according to actual needs as long as the purpose of wetting is achieved.

[0024] Through the above method, a phosphorus-containing substance-coated cathode material with high stability and good electrochemical performance is prepared.

[0025] Preferably, at least one of the following (a) to (e):

[0026] (a) The lithium source is at least one of lithium hydroxide, lithium carbonate, and lithium oxalate;

[0027] (b) The precursor is a compound containing at least one element of nickel, cobalt, and manganese, and the compound is an oxide, hydroxide, carbonate, or hydroxy-oxide;

[0028] (c) The compound containing M is at least one of an oxide containing M, a hydroxide containing M, an acetate containing M, and a carbonate containing M; M is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, S, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, Ca;

[0029] (d) The substance containing M′ is at least one of an oxide containing M′, a fluoride containing M′, a lithium salt containing M′, and M′ in its elemental form; M′ is one or two of F, Se, and S.

[0030] (e) The substance containing M″ is at least one of an oxide containing M″, a hydroxide containing M″, a carbonate containing M″, and a hydroxyoxide containing M″, and M″ is at least one of La, Al, Ti, Y, Zr, Co, Ni, Mn, Mg, and B.

[0031] Preferably, the calcination temperature for preparing the bulk material is 800 - 1100 °C, and the sintering time is 8 - 12 h.

[0032] Preferably, the calcination temperature for preparing the phosphorus-containing substance powder is 500 - 700 °C, and the sintering time is 3 - 6 h.

[0033] Preferably, the sintering temperature for preparing the phosphorus-containing substance-coated cathode material is 300 - 800 °C, and the sintering time is 3 - 8 h.

[0034] For different materials, different sintering temperatures and sintering times are required. At a temperature of 800 - 1100 °C, the M element and M′ element can be well doped into the bulk material; and the electrochemical capacity of the bulk material can be achieved.

[0035] In the method for preparing the phosphorus-containing substance-coated cathode material, the calcination can be carried out in an oxygen atmosphere. For example, the calcination can be carried out in an oxygen atmosphere, but the implementation mode is not limited to this condition, and the conditions can be appropriately selected within the range that can provide improved physical properties for the phosphorus-containing substance-coated cathode material considering the type of metal.

[0036] Preferably, the particle size of the phosphorus-containing substance powder is 10 - 500 nm.

[0037] The particle size of the phosphorus-containing powder affects the performance of the phosphorus-containing substance-coated cathode material. The inventors found that when the particle size of the phosphorus-containing substance powder is within the above range, the phosphorus-containing substance-coated cathode material has better performance.

[0038] Preferably, the weight ratio of the phosphorus-containing substance powder to deionized water is 1:5 - 1:50.

[0039] In a third aspect, a lithium battery is provided, and the lithium battery includes the phosphorus-containing substance-coated cathode material described above.

[0040] In a fourth aspect, an electrochemical energy storage device is provided, and the electrochemical energy storage device includes the phosphorus-containing substance-coated cathode material or the lithium battery described above.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] 1. Through the co-doping of multiple elements and the synergistic effect of various elements, the irreversible phase transformation of the phosphorus-containing substance-coated cathode material at high voltages is inhibited, and the structural stability of the phosphorus-containing substance-coated cathode material is improved.

[0043] 2. By introducing M′, M′ replaces O in the phosphorus-containing substance-coated cathode material, and M′ has good binding ability with Co, inhibiting the release of O, and greatly improving the phase transformation resistance of the phosphorus-containing substance-coated cathode material.

[0044] 3. M″ c PO z reacts with lithium in the phosphorus-containing substance-coated cathode material to form lithium cobalt phosphate compounds. The nanosized lithium cobalt phosphate compounds delay or inhibit the oxygen reduction reaction between the electrolyte and the surface of the cathode material, reduce Co dissolution, improve the surface structural stability of the phosphorus-containing substance-coated cathode material at high voltages, and improve the cycling, storage, and gas generation performance of the phosphorus-containing substance-coated cathode material.

[0045] 4. In the phosphorus-containing substance-coated cathode material of the present invention, M′ doping occupies the O position, forming O vacancies, improving the conductivity of the phosphorus-containing substance-coated cathode material. M doping occupies the Co position, enhancing the ionization of the Co-O-P bond, making it easier for lithium ions to migrate. M″ is coated on the surface layer to stabilize the interface structure. The nanosized lithium-containing M″ c PO z has good lithium ion transmission rate, coats the cathode material lithium cobaltate, and improves the structural stability of the de-lithiated lithium cobaltate.

[0046] 5. The introduction of M, M′, and M″ c PO z can inhibit the generation of microcracks on the surface of the phosphorus-containing substance-coated cathode material, thereby improving the electrical performance of the phosphorus-containing substance-coated cathode material under high voltage.

[0047] 6. The operation process of the present invention is simple, the raw material cost is low, and it is easy to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is the scanning electron microscope image of the phosphorus-containing substance-coated cathode material of Example 1 of the present invention;

[0049] Figure 2 is the scanning electron microscope image of the phosphorus-containing substance-coated cathode material of Example 3 of the present invention;

[0050] Figure 3 is the scanning electron microscope image of the phosphorus-containing substance-coated cathode material of Example 5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0051] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings.

[0052] Example 1

[0053] This example is used to illustrate the phosphorus-containing substance-coated cathode material of the present invention and its preparation method.

[0054] This example provides a preparation method for a phosphorus-containing substance-coated cathode material, comprising the following steps:

[0055] Prepare modified lithium cobaltate powder:

[0056] Mix lithium carbonate, cobalt tetroxide, titanium dioxide, and aluminum oxide evenly, then sinter at 1020 °C for 10 hours. After the obtained product is crushed, it is stirred evenly with selenium powder to obtain modified lithium cobaltate powder; wherein the amounts of substance of lithium carbonate, cobalt tetroxide, titanium dioxide, aluminum oxide, and selenium powder are 0.5 mol, 0.33 mol, 0.007 mol, 0.01 mol, and 0.001 mol in sequence;

[0057] Prepare a phosphorus-containing substance suspension:

[0058] S1: Mix lithium carbonate, aluminum metaphosphate, and magnesium carbonate, wherein the total mass of magnesium carbonate and aluminum metaphosphate accounts for 0.04% of the mass of modified lithium cobaltate, and the molar ratio of magnesium:aluminum = 1:1, and the mass of lithium carbonate accounts for 0.03% of the mass of modified lithium cobaltate. Sinter at 500 °C for 5 hours, then crush to obtain aluminum metaphosphate compound particles; place the aluminum metaphosphate compound particles in a micro-nano crusher, add ethanol, and then crush at a power of 200 W for 10 min to obtain aluminum metaphosphate compound powder, and the particle size of the aluminum metaphosphate compound powder is 100 nm;

[0059] S2: Add the aluminum metaphosphate compound powder obtained in S1 to deionized water, and the mass ratio of the aluminum metaphosphate compound powder to deionized water is 1:5, and stir evenly to obtain a phosphorus-containing substance suspension;

[0060] Prepare a phosphorus-containing substance-coated cathode material:

[0061] Spray the phosphorus-containing substance suspension into the modified lithium cobaltate powder at a rotation speed of 1500 r / min, mix for 9 min, then place the mixture in a box furnace, sinter at 450 °C for 7 h, crush the obtained block product, and sieve it through a 400-mesh sieve to obtain a phosphorus-containing substance-coated cathode material, and its structural formula is: 0.966Li 1.002 Co 0.95 Ti 0.007 Al 0.01 (O 1.999 Se 0.001 )·0.0337(LiMgAl(PO3)6).

[0062] Example 2

[0063] This example is used to illustrate the phosphorus-containing substance-coated cathode material of the present invention and its preparation method.

[0064] This example provides a preparation method for a phosphorus-containing substance-coated cathode material, including the following steps:

[0065] Prepare modified lithium cobaltate powder:

[0066] Mix lithium carbonate, nickel cobalt manganese hydroxide, titanium dioxide, and aluminum oxide evenly, and then sinter at 950 °C for 8 hours. After the obtained product is crushed, it is stirred evenly with selenium dioxide to obtain modified lithium cobaltate powder; where the chemical formula of nickel cobalt manganese hydroxide is Ni 0.6 Mn 0.2 Co 0.2 (OH)2; where the amounts of substances of lithium carbonate, nickel cobalt manganese hydroxide, titanium dioxide, aluminum oxide, and selenium dioxide are 0.5 mol, 0.5 mol, 0.003 mol, 0.005 mol, and 0.001 mol in sequence;

[0067] Prepare a phosphorus-containing substance suspension:

[0068] S1: Mix lithium carbonate, aluminum phosphate, and basic magnesium carbonate evenly. The total mass of basic magnesium carbonate and aluminum phosphate accounts for 0.04% of the mass of the modified lithium cobaltate powder, and the molar ratio of magnesium to aluminum = 1:1. The mass of lithium carbonate accounts for 0.03% of the mass of the modified lithium cobaltate powder. Sinter at 700 °C for 3 hours, and then crush to obtain phosphate compound particles; place the phosphate compound particles in a micro-nano grinder, add ethanol, and then crush at a power of 200 W for 10 min to obtain phosphate compound powder. The particle size of the phosphate compound powder is 200 nm;

[0069] S2: Add the phosphate compound powder obtained in S1 to deionized water. The mass ratio of the phosphate compound powder to deionized water is 1:15, and stir evenly to obtain a phosphorus-containing substance suspension;

[0070] Prepare a phosphorus-containing substance-coated cathode material:

[0071] Spray the phosphorus-containing substance suspension into the modified lithium cobaltate powder at a rotation speed of 1500 r / min, mix for 9 min, and then place the mixture in a box furnace and sinter at 300 °C for 8 h. After the obtained massive product is crushed, it is sieved through a 400-mesh sieve to obtain a phosphorus-containing substance-coated cathode material, and its structural formula is: 0.993Li 1.002 Ni 0.595 Co 0.198 Mn 0.198 Ti 0.003 Al 0.005(Se 0.001 O 1.999 )·0.007(LiMgAl(PO4)2).

[0072] Example 3

[0073] This example is used to illustrate the phosphorus-containing substance-coated cathode material of the present invention and its preparation method.

[0074] This example provides a preparation method of a phosphorus-containing substance-coated cathode material, including the following steps:

[0075] Prepare modified lithium cobaltate powder:

[0076] Mix lithium carbonate, cobalt tetroxide, titanium dioxide, aluminum oxide, and selenium dioxide evenly, and then sinter at 800 °C for 12 hours. After the obtained product is crushed, modified lithium cobaltate powder is obtained, where the amounts of substance of lithium carbonate, cobalt tetroxide, titanium dioxide, aluminum oxide, and selenium dioxide are 0.5 mol, 0.33 mol, 0.004 mol, 0.008 mol, and 0.0015 mol in sequence;

[0077] Prepare a phosphorus-containing substance suspension:

[0078] S1: Mix lithium carbonate, aluminum phosphate, and basic magnesium carbonate evenly, where the total mass of basic magnesium carbonate and aluminum phosphate accounts for 0.04% of the mass of the modified lithium cobaltate powder, and the molar ratio of magnesium to aluminum = 2:1, and the mass of lithium carbonate accounts for 0.03% of the mass of the modified lithium cobaltate powder; sinter at 600 °C for 5 hours, and then crush to obtain phosphoric acid compound particles; place the phosphoric acid compound particles in a micro-nano crusher, add ethanol, and then crush at a power of 200 W for 10 min to obtain phosphoric acid compound powder, and the particle size of the phosphoric acid compound powder is 500 nm;

[0079] S2: Add the phosphoric acid compound powder obtained in S1 to deionized water, and the mass ratio of the phosphoric acid compound powder to deionized water is 1:50, and stir evenly to obtain a phosphorus-containing substance suspension;

[0080] Prepare a phosphorus-containing substance-coated cathode material:

[0081] Spray the phosphorus-containing substance suspension onto the bulk material at a rotation speed of 1300 r / min, mix for 12 min, and then place the mixture in a box furnace and sinter at 800 °C for 3 h. After the obtained massive product is crushed, it is sieved through a 400-mesh sieve to obtain a phosphorus-containing substance-coated cathode material, and its structural formula is:

[0082] 0.98Li 1.002 Co 0.988 Ti 0.004 Al 0.008 (Se 0.0015 O1.9985 )·0.02(Li2Mg2Al(PO4)3).

[0083] Example 4

[0084] This example is used to illustrate the phosphorus-containing substance-coated cathode material of the present invention and its preparation method.

[0085] This example provides a preparation method for a lithium cobaltate cathode material modified by coating with nano-magnesium aluminum phosphate lithium, including the following steps:

[0086] Prepare the modified lithium cobaltate powder:

[0087] Mix lithium carbonate, cobalt tetroxide, titanium dioxide, aluminum oxide, and lithium fluoride evenly, and then sinter at 1020 °C for 10 hours. After the obtained product is crushed, the modified lithium cobaltate powder is obtained, where the amounts of substances of lithium carbonate, cobalt tetroxide, titanium dioxide, aluminum oxide, and lithium fluoride are 0.5 mol, 0.334 mol, 0.006 mol, 0.012 mol, and 0.003 mol in sequence;

[0088] Prepare the phosphorus-containing substance suspension:

[0089] S1: Mix lithium carbonate, aluminum metaphosphate, and basic magnesium carbonate evenly. The total mass of basic magnesium carbonate and aluminum metaphosphate accounts for 0.04% of the mass of the modified lithium cobaltate powder, and the molar ratio of magnesium to aluminum = 1:3. The mass of lithium carbonate accounts for 0.05% of the mass of the modified lithium cobaltate powder. Sinter at 500 °C for 5 hours, and then crush to obtain aluminum metaphosphate compound particles; Place the aluminum metaphosphate compound particles in a micro-nano mill, add ethanol, and then crush at a power of 200 W for 10 min to obtain aluminum metaphosphate compound powder, and the particle size of the aluminum metaphosphate compound powder is 200 nm;

[0090] S2: Add the aluminum metaphosphate compound powder obtained in S1 to deionized water, and the mass ratio of the aluminum metaphosphate compound powder to deionized water is 1:5. Stir evenly to obtain the phosphorus-containing substance suspension;

[0091] Prepare the phosphorus-containing substance-coated cathode material:

[0092] Spray the phosphorus-containing substance suspension into the modified lithium cobaltate powder at a rotation speed of 1500 r / min, mix for 9 min, and then place the mixture in a box furnace and sinter at 450 °C for 7 h. After the obtained massive product is crushed and passed through a 400-mesh sieve, the phosphorus-containing substance-coated cathode material is obtained, and its structural formula is: 0.998Li 1.005 Co 0.982 Ti 0.006 Al 0.012 (F 0.003 O 1.997 )·0.002(LiMgAl3(PO3)12 )。

[0093] Example 5

[0094] This example is used to illustrate the phosphorus-containing substance-coated cathode material of the present invention and its preparation method.

[0095] This example provides a preparation method of a phosphorus-containing substance-coated cathode material, including the following steps:

[0096] Prepare modified lithium cobaltate powder:

[0097] Mix lithium carbonate, cobalt tetroxide, titanium dioxide, aluminum oxide, and lithium fluoride evenly, and then sinter at 1020 °C for 10 hours. After the obtained product is crushed, modified lithium cobaltate powder is obtained, where the amounts of substances of lithium carbonate, cobalt tetroxide, titanium dioxide, aluminum oxide, and selenium dioxide are 0.5 mol, 0.2 mol, 0.005 mol, 0.01 mol, and 0.002 mol in sequence;

[0098] Prepare a phosphorus-containing substance suspension:

[0099] S1: Mix lithium carbonate, phosphorus pentoxide, and aluminum oxide evenly. The total mass of phosphorus pentoxide and aluminum oxide accounts for 0.03% of the mass of the modified lithium cobaltate powder, and the mass of lithium carbonate accounts for 0.05% of the mass of the modified lithium cobaltate powder. Sinter at 500 °C for 5 hours, and then crush to obtain phosphoric acid compound particles; Place the phosphoric acid compound particles in a micro-nano grinder, add ethanol, and then crush at a power of 200 W for 10 min to obtain phosphoric acid compound powder with a particle size of 300 nm;

[0100] S2: Add the phosphoric acid compound powder obtained in S1 to deionized water, and the mass ratio of the phosphoric acid compound powder to deionized water is 1:5. Stir evenly to obtain a phosphorus-containing substance suspension;

[0101] Prepare a phosphorus-containing substance-coated cathode material:

[0102] Spray the phosphorus-containing substance suspension into the modified lithium cobaltate powder at a rotation speed of 1500 r / min, mix for 9 min, and then place the mixture in a box furnace and sinter at 450 °C for 7 h. After the obtained massive product is crushed and passed through a 400-mesh sieve, a phosphorus-containing substance-coated cathode material is obtained, and its structural formula is: 0.997Li 1.008 Co 0.985 Ti 0.005 Al 0.01 (F 0.002 O 1.998 )·0.003(Li3Al(PO4)2).

[0103] Example 6

[0104] The only difference between this embodiment and Embodiment 5 is that lithium fluoride is replaced by elemental sulfur in the preparation of the modified lithium cobaltate cathode material.

[0105] Embodiment 7

[0106] The only difference between this embodiment and Embodiment 5 is that phosphorus pentoxide and alumina are replaced by aluminum phosphate in the preparation of the phosphorus-containing substance suspension.

[0107] Comparative Example 1

[0108] The only difference between this comparative example and Embodiment 1 is that selenium powder is not added in the preparation of the modified lithium cobaltate cathode material.

[0109] Comparative Example 2

[0110] The only difference between this comparative example and Embodiment 3 is that basic magnesium carbonate is not added in the preparation of the phosphorus-containing substance suspension.

[0111] Comparative Example 3

[0112] The only difference between this comparative example and Embodiment 1 is that titanium oxide and alumina are not added in the preparation of the modified lithium cobaltate cathode material.

[0113] Comparative Example 4

[0114] The only difference between this comparative example and Embodiment 1 is that aluminum metaphosphate is replaced by alumina in the preparation of the phosphorus-containing substance suspension.

[0115] Comparative Example 5

[0116] The only difference between this comparative example and Embodiment 2 is that aluminum phosphate is replaced by alumina in the preparation of the phosphorus-containing substance suspension.

[0117] Effect Example 1

[0118] This embodiment provides a lithium battery. The phosphorus-containing substance-coated cathode materials obtained in Embodiments 1-2 and Comparative Examples 1-5 are respectively made into lithium batteries. The preparation method of the lithium battery is as follows: The phosphorus-containing substance-coated cathode material, polyvinylidene fluoride, and conductive carbon black are mixed evenly, and the mass ratio of the phosphorus-containing substance-coated cathode material, polyvinylidene fluoride, and conductive carbon black is phosphorus-containing substance-coated cathode material: polyvinylidene fluoride: conductive carbon black = 90:5:5. The obtained mixture is added with NMP (N-methylpyrrolidone), stirred to form a slurry, coated on aluminum foil, and dried at 80 °C to make a positive electrode plate. Using the prepared positive electrode plate, graphite, electrolyte, and separator as raw materials, a soft-pack battery is made by winding.

[0119] Test the performance of the obtained soft-pack battery. The test method is as follows:

[0120] (1) 45°C Cycling Test: At 45°C, the soft-pack batteries prepared in Examples 1-2 and Comparative Examples 1-5 were charged with a constant current (CC) at a rate of 1C until the voltage reached 4.48 V (versus Li), and the current was cut off at a rate of 0.05C while maintaining the voltage at 4.48 V in constant voltage mode (CV). Then, the battery was discharged with a constant current (CC) at a rate of 1C until the discharge voltage reached 3.0 V (versus Li) and cycled in this way. The cycling capacity retention rate = (discharge capacity of the Nth cycle / discharge capacity of the first cycle) × 100%, and when the retention rate reached 80%, the test was stopped. During the entire charge / discharge cycle, a holding time of 5 min was set after each charge / discharge.

[0121] (2) Storage Capacity Retention Rate: At 25°C, the soft-pack batteries prepared in Examples 1-2 and Comparative Examples 1-5 were charged with a constant current (CC) at a rate of 1C until the voltage reached 4.48 V (versus Li), and the current was cut off at a rate of 0.05C while maintaining the voltage at 4.48 V in constant voltage mode (CV). Then, it was left standing for 5 min, and then the battery was discharged with a constant current (CC) at a rate of 1C until the discharge voltage reached 3.0 V (versus Li). It was cycled in this way. The cycling capacity retention rate = (discharge capacity of the Nth cycle / discharge capacity of the first cycle) × 100%, and when the retention rate reached 80%, the test was stopped. During the entire charge / discharge cycle, a holding time of 5 min was set after each charge / discharge.

[0122] Capacity retention rate (%) = [first discharge capacity after full charge storage / last discharge capacity before full charge storage] × 100.

[0123] (3) Gas Generation at 70°C: At 70°C, the soft-pack batteries prepared in Examples 1-2 and Comparative Examples 1-5 were charged with a constant current (CC) at a rate of 1C until the voltage reached 4.48 V (versus Li), and the current was cut off at a rate of 0.05C while maintaining the voltage at 4.48 V in constant voltage mode (CV). It was cycled in this way. During the entire charge / discharge cycle, a holding time of 5 min was set after each charge / discharge.

[0124] The test results are shown in Table 1.

[0125] Table 1

[0126]

[0127]

[0128] As analyzed in Table 1, the 45°C cycling performance, storage retention rate, and gas generation at 70°C of Comparative Example 1 are inferior to those of Example 1, indicating that Se doping can replace the position of oxygen in the cathode material, reduce gas generation during cycling, and improve structural stability; in Comparative Example 3, without adding aluminum oxide and titanium oxide, the 45°C cycling and gas generation deteriorate significantly, indicating that aluminum and titanium doping can stabilize the structure of the cathode material, inhibit phase transformation to a certain extent, reduce stress accumulation in the material, and reduce the generation of surface microcracks; in Comparative Example 4, changing the aluminum phosphate coating to an aluminum oxide coating results in basically unchanged 45°C cycling performance, improved storage, and deteriorated gas generation; the nanosized cobalt lithium phosphate compound delays or inhibits the oxygen reduction reaction between the electrolyte and the surface of the cathode material, reduces Co dissolution, improves the surface structural stability of the cathode material (such as lithium cobaltate) during long cycling at high voltages, and improves cycling, storage, and gas generation.

[0129] In Comparative Example 5, changing the aluminum phosphate to aluminum oxide results in comparable 45°C cycling and storage, but significantly deteriorated gas generation at 70°C; this indicates that the formation of Co-O-P on the particle surface improves gas generation.

[0130] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A phosphorus-containing substance-coated cathode material, characterized in that, The chemical formula of the phosphorus-containing substance-coated cathode material is (1-x)Li 1+a (Ni (1-m-n) Co n Mn m ) 1-b M b M′ y O 2-y ·xM″ c PO z , Wherein M is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, S, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, Ca; Where 0≤a≤0.1, 0 < b≤0.1, 0 < c≤3, 0≤m≤1, 0≤n≤1, 3≤z≤4, 0.001≤x≤0.05; Wherein M′ is one or two of F, Se, S, and 0.0001≤y≤0.1; Wherein M″ is at least one of La, Al, Ti, Y, Zr, Co, Ni, Mn, Mg, B; The method for preparing the phosphorus-containing substance-coated cathode material includes the following steps: Preparing the bulk material: Mixing a lithium source, a precursor, a compound containing M, and a substance containing M′ evenly by stirring, then calcining and crushing to obtain the bulk material; Preparing the phosphorus-containing substance suspension: S1: Mixing a lithium source, a phosphorus source, and a substance containing M″ evenly, then calcining and crushing to obtain a phosphorus-containing substance powder; S2: Adding the phosphorus-containing substance powder obtained in S1 into deionized water and stirring evenly to obtain the phosphorus-containing substance suspension; Preparing the phosphorus-containing substance-coated cathode material: Spraying the phosphorus-containing substance suspension onto the bulk material under rotating conditions, mixing evenly, then sintering and pulverizing to obtain the phosphorus-containing substance-coated cathode material; The substance containing M″ is at least one of an oxide containing M″, a hydroxide containing M″, a carbonate containing M″, and a hydroxyoxide containing M″.

2. A preparation method of a phosphorus-containing substance-coated cathode material as described in claim 1, characterized in that, Including the following steps: Preparing the bulk material: Mixing a lithium source, a precursor, a compound containing M, and a substance containing M′ evenly by stirring, then calcining and crushing to obtain the bulk material; Preparing the phosphorus-containing substance suspension: S1: Mixing a lithium source, a phosphorus source, and a substance containing M″ evenly, then calcining and crushing to obtain a phosphorus-containing substance powder; S2: Adding the phosphorus-containing substance powder obtained in S1 into deionized water and stirring evenly to obtain the phosphorus-containing substance suspension; Preparing the phosphorus-containing substance-coated cathode material: Spraying the phosphorus-containing substance suspension onto the bulk material under rotating conditions, mixing evenly, then sintering and pulverizing to obtain the phosphorus-containing substance-coated cathode material; The substance containing M″ is at least one of an oxide containing M″, a hydroxide containing M″, a carbonate containing M″, and a hydroxyoxide containing M″, and M″ is at least one of La, Al, Ti, Y, Zr, Co, Ni, Mn, Mg, B.

3. The preparation method according to claim 2, wherein At least one of the following (a) to (d): (a) The lithium source is at least one of lithium hydroxide, lithium carbonate, and lithium oxalate; (b) The precursor is a compound containing at least one element of nickel, cobalt, and manganese, and the compound is an oxide, a hydroxide, a carbonate, or a hydroxyoxide; (c) The compound containing M is at least one of an oxide containing M, a hydroxide containing M, an acetate containing M, and a carbonate containing M; M is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, S, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, Ca; (d) The substance containing M' is at least one of an oxide containing M', a fluoride containing M', a lithium salt containing M', and M' in its elemental form; M' is one or two of F, Se, and S.

4. The preparation method according to claim 2, characterized in that, The calcination temperature for preparing the bulk material is 800 - 1100 °C, and the sintering time is 8 - 12 h.

5. The preparation method according to claim 2, wherein The calcination temperature for preparing the phosphorus-containing substance powder is 500 - 700 °C, and the sintering time is 3 - 6 h.

6. The preparation method according to claim 2, wherein The particle size of the phosphorus-containing substance powder is 10 - 500 nm.

7. The preparation method according to claim 2, characterized in that, The weight ratio of the phosphorus-containing substance powder to deionized water is 1:5 - 1:

50.

8. The preparation method according to claim 2, characterized in that, The sintering temperature for preparing the phosphorus-containing substance-coated cathode material is 300 - 800 °C, and the sintering time is 3 - 8 h.

9. A lithium battery, characterized in that, The lithium battery includes the phosphorus-containing substance-coated cathode material as claimed in claim 1.

10. An electrochemical energy storage device, characterized in that, The electrochemical energy storage device includes the phosphorus-containing substance-coated cathode material as claimed in claim 1 or the lithium battery as claimed in claim 9.

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