Double-layer interface coated positive electrode material and preparation method thereof, lithium ion battery and electric equipment

Abstract

The invention provides a double-layer interface coated positive electrode material and a preparation method thereof, a lithium ion battery and electric equipment, and relates to the field of lithium ion batteries. The double-layer interface coated positive electrode material comprises an inner core, and a first coating layer and a second coating layer which are sequentially stacked on the surface of the inner core, wherein the first coating layer comprises metal sulfide; the second coating layer comprises a metal nitride; the chemical general formula of the inner core is LiCoxY (1-x) O2, Y comprises at least one of Ni, Mn and Al, and x is more than or equal to 0.03 and less than or equal to 1. The double coating layers are subjected to targeted interface improvement, the ionic conductivity and low-temperature dynamic performance of the material are improved, the initial impedance of the material is reduced, an ion-electron double high-conductivity network is constructed through internal-external cooperation, the defect of single crystallization of the positive electrode material is overcome, and the electrochemical kinetics, cycling stability and other performance of the positive electrode material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a double-layer interface-coated positive electrode material, a preparation method thereof, a lithium ion battery and an electric device. BACKGROUND

[0002] In order to meet the deep demand of the market for energy density, positive electrode materials such as LiCoO2, lithium-rich manganese-based positive electrode materials and ternary positive electrode materials are gradually applied to a higher voltage direction (≥4.5V). In order to balance the conditions of high voltage resistance, cycle performance, energy density requirements and the like, the above-mentioned positive electrode materials all adopt single crystallization to improve voltage resistance and cycle performance. Correspondingly, the primary particles of the material after single crystallization are increased from nanocrystallization to micrization. After the Li ion transmission path is improved, the electrical conductivity increases in a geometric progression. The above-mentioned problems gradually restrict the development of the technical route of the positive electrode material.

[0003] Therefore, there is an urgent need to provide a positive electrode material to solve the above-mentioned problems. SUMMARY

[0004] The purpose of the present application is to provide a double-layer interface-coated positive electrode material, a preparation method thereof, a lithium ion battery and an electric device to solve the above-mentioned problems.

[0005] To achieve the above purpose, the first aspect of the present application provides a double-layer interface-coated positive electrode material, comprising a core and a first coating layer and a second coating layer which are sequentially stacked on the surface of the core. The first coating layer comprises a metal sulfide. The second coating layer comprises a metal nitride. The chemical formula of the core is LiCo x Y 1-x O2, wherein Y comprises at least one of Ni, Mn and Al, 0.03≤x≤1.

[0006] Optionally, the metal sulfide comprises a sulfide of D, and D comprises at least one of Fe, Bi, La, Gd, Cr, Er and Sb. And / or, the metal nitride comprises a nitride of E, and E comprises at least one of In, Sr, V, Ta, Mo, Ga and Nb.

[0007] Optionally, D in the metal sulfide comprises La and / or Gd. And / or, E in the metal nitride comprises Ga and / or Ta.

[0008] Optionally, the thickness of the first coating layer is 1-10nm. And / or, the thickness of the second coating layer is 1-10nm. And / or, the particle size of the double-layer interface-coated positive electrode material is 2.0-5.0 μm.

[0009] Optionally, the BET of the double-layer interface-coated positive electrode material is 1.0-2.0 m 2 / g; And / or, the TD of the double-layer interface-coated positive electrode material is 1.0-2.5 g / cm 3 .

[0010] The second aspect of the present application provides a preparation method of the double-layer interface-coated positive electrode material, comprising: mixing the precursor and the lithium source under an oxygen-containing atmosphere to obtain a mixture; and sintering the mixture to obtain a single-crystal positive electrode material; mixing the single-crystal positive electrode material and a D source under a hydrogen sulfide atmosphere, and sintering to obtain a coated material; mixing the coated material and an E source under an ammonia-containing atmosphere, and sintering to obtain the double-layer interface-coated positive electrode material.

[0011] Optionally, the precursor comprises at least one of hydroxides, oxides and carbonates of Co and / or Y; And / or, the D source comprises at least one of chloride salts of Fe, Bi, La, Gd, Cr, Er and Sb; And / or, the E source comprises at least one of chloride salts and / or organometallic compounds of In, Sr, V, Ta, Mo, Ga and Nb; And / or, the molar ratio of the precursor to lithium in the lithium source is 1:1-1.2; And / or, the mass ratio of the D source to the single-crystal positive electrode material is 0.002-0.005:1; And / or, the mass ratio of the E source to the single-crystal positive electrode material is 0.001-0.003:1; And / or, the heating rate of the first sintering is 5-10 ℃ / min, the end temperature is 700-1000 ℃, the constant temperature time is 12-18 h, and the oxygen concentration is greater than or equal to 80%; And / or, the rotation speed of the second mixing is 300-600 r / min, and the time is 30-60 min; And / or, the heating rate of the second sintering is 10-20 ℃ / min, the end temperature is 300-700 ℃, the constant temperature time is 1-3 h, and the H2S flow rate is 10-15 L / h; And / or, the heating rate of the third sintering is 5-10 ℃ / min, the end temperature is 200-500 ℃, and the constant temperature time is 3-5 h.

[0012] Optionally, the oxygen-containing atmosphere comprises air and / or oxygen, and the flow rate of the oxygen-containing atmosphere is 20-60 L / min during the first sintering; Optionally, the second sintering is performed by CVD treatment, and an inert gas is introduced before and during the CVD treatment, and the flow rate of the inert gas is 100-150 L / h, and the time for introducing the inert gas before the CVD treatment is 15-30 min; The inert gas comprises one or more of N2, He, Ne and Ar; Optionally, the third sintering is performed by ALD deposition treatment, and the time for introducing an ammonia-containing atmosphere before the ALD deposition treatment is 10-20 min, and the flow rate of the E source is 5-20 L / h; Optionally, after the third sintering, an inert gas is further introduced for purging, and the purging time is 30-60 s.

[0013] The third aspect of the present application provides a lithium ion battery comprising the double-layer interfacial coated positive electrode material.

[0014] The third aspect of the present application provides a use-electric device comprising the lithium ion battery.

[0015] Compared with the prior art, the present application has the following beneficial effects: The double-layer interfacial coated positive electrode material provided by the present application has an ionic conductivity of the first coating layer of 10 -3 S / cm, which can serve as a "fast channel" for lithium ions from the bulk phase to the electrolyte, reduces the interface ion transmission resistance, inhibits the precipitation of surface oxygen and the formation of rock salt phase, maintains the surface in a high ionic conductivity state, and further improves the intrinsic electrochemical kinetics of the material; the second coating layer utilizes its excellent electronic conductivity to form a conductive coating layer on the surface of the positive electrode particles, improving the electrical contact between particles and between particles and conductive agents, reducing the interface charge transfer impedance, and significantly improving the rate performance and utilization rate of active substances; finally, the excellent mechanical strength and thermal stability of the metal nitride inhibit the micro-cracks generated by the volume expansion / contraction of the positive electrode particles during the cycle process, improve the thermal stability of the material, delay the thermal runaway reaction of the positive electrode material and the electrolyte when the battery overheats, and improve the safety; the double-layer coating layer improves the material ion conductivity and low-temperature kinetic performance, reduces the initial impedance of the material, and through the internal-external synergy, constructs an ion-electron double-high-conductivity network, improves the defects of the positive electrode material single crystal, and improves the electrochemical kinetics, cycle stability and other performances of the positive electrode material.

[0016] The preparation method of the double-layer interfacial coated positive electrode material provided by the present application is simple to operate and the raw materials are easy to obtain.

[0017] The lithium ion battery and the electric device provided by the application have good cycle performance and excellent rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as limiting the scope of the application.

[0019] Figure 1 The EIS exchange impedance test comparison chart of the positive electrode material provided for Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0020] Firstly, the scheme provided by the application is explained in more detail, as follows: The first aspect of the application provides a double-layer interface-coated positive electrode material, which comprises a core and a first coating layer and a second coating layer sequentially stacked on the surface of the core. The first coating layer comprises a metal sulfide. The second coating layer comprises a metal nitride. The chemical formula of the core is LiCo x Y 1-x O2, wherein Y comprises at least one of Ni, Mn and Al, and 0.03≤x≤1.

[0021] Optionally, x can be 0.03, 0.1, 0.5, 1 or any value between 0.03 and 1.

[0022] In some embodiments, the metal sulfide comprises a sulfide of D, and D comprises at least one of Fe, Bi, La, Gd, Cr, Er and Sb. And / or, the metal nitride comprises a nitride of E, and E comprises at least one of In, Sr, V, Ta, Mo, Ga and Nb.

[0023] It should be noted that the first coating layer will undergo the following reaction during high-voltage long cycle: S 2-The lithium is oxidized to elemental sulfur (S8, solid), and reduced to soluble long-chain lithium polysulfides (mainly Li2S8) at the start of discharge. Li2S8 is further reduced in the electrolyte to generate a series of soluble polysulfides. The soluble polysulfides generated in the positive electrode region (such as Li2S4 and Li2S6) diffuse from the positive electrode through the electrolyte and membrane to the negative electrode due to the concentration gradient, simultaneously consuming Li and being reduced to insoluble short-chain sulfides (such as Li2S2 or Li2S). The shorter-chain polysulfides generated at the negative electrode (or partially oxidized polysulfides) diffuse back to the positive electrode, where they are oxidized to long-chain polysulfides. At the end of the charge, soluble polysulfides are eventually reduced to insoluble, insulating lithium sulfide (Li₂S) and lithium disulfide (Li₂S₂), which deposit on the electrode surface. The slow redox kinetics of these reactions lead to charging difficulties and increased voltage polarization; this process, known as the shuttle effect, continuously consumes active lithium and electrolyte, increasing battery internal resistance and shortening battery life. To address the shuttle effect caused by the dissolution of lithium polysulfides in the first coating layer, a second coating layer is applied to modify the first coating layer. This second coating layer uses metal nitrides for synergistic coating. The second coating layer can be chemically anchored, i.e., by cations on the surface of the metal nitride (exemplarily, cations are M). n+ ) and nitrogen anion (N 3- ) Forming polar bonds, S in metal sulfides n 2- With M n+ Strong coordination occurs, and nitrogen anions can adsorb Li through hydrogen bonding or electrostatic interactions. + This forms a stable MS-Li-N interface structure, fixing it to the electrode surface and preventing dissolution and diffusion (shuttle effect); or it captures persulfides through physical adsorption, i.e., high specific surface area and porous structure, reducing their migration in the electrolyte, while providing sufficient active sites for electrochemical reactions. The two coating layers work synergistically, with the second coating layer improving the shuttle effect of the first coating layer.

[0024] It should also be noted that the metal elements selected in metal sulfides and metal nitrides should have specific electronic structures, ionic radii, electronegativity, and bonding capabilities, so that they can form sulfide and nitride coatings with special band gaps, two-dimensional layered structures, and good thermal or chemical stability, so that the coated cathode material has good kinetic characteristics and thermal and chemical stability.

[0025] In some embodiments, D in the metal sulfide includes La and / or Ga; It should be noted that La and Ga are rare earth elements with special electronic arrangement, and the metal sulfide coating layer formed by La and Ga contains a specific band gap, and has good ion conductivity. The use of such a coating layer can have good ion conductivity, and the unique layered structure of the sulfide can further stabilize the surface structure of the positive electrode material by capturing the precipitation of surface oxygen. And / or, E in the metal nitride includes Ta and / or Ga.

[0026] It should be noted that the nitride formed by Ta and Ga is a semiconductor and conductive ceramic with excellent conductivity. This coating can greatly improve the electron transport on the surface of the positive electrode material particles, reduce the interface charge transfer impedance, and help improve the rate performance and electrochemical polarization of the single-crystal positive electrode material. Its good mechanical strength and thermal stability inhibit the micro-cracks generated by the volume expansion / contraction of the positive electrode particles during the cycle process, improve the thermal stability of the material, delay the thermal runaway reaction of the positive electrode material and the electrolyte when the battery overheats, and improve the safety.

[0027] In some embodiments, the thickness of the first coating layer is 1-10 nm; Optionally, the thickness of the first coating layer can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any value between 1-10 nm; And / or, the thickness of the second coating layer is 1-10 nm; Optionally, the thickness of the second coating layer can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any value between 1-10 nm; And / or, the particle size of the double-layer interface-coated positive electrode material is 2.0-5.0 μm.

[0028] Optionally, the particle size of the double-layer interface-coated positive electrode material can be 2 μm, 3 μm, 4 μm, 5 μm, or any value between 2-5 μm.

[0029] In some embodiments, the BET of the double-layer interface-coated positive electrode material is 1.0-2.0 m 2 / g; Optionally, the BET of the double-layer interface-coated positive electrode material can be 1 m 2 / g, 1.5 m 2 / g, 2 m 2 / g, or any value between 1-2 m 2 / g; And / or, the TD of the double-layer interface-coated positive electrode material is 1.0-2.5 g / cm 3.

[0030] Optionally, the TD of the double-layer interfacial coated positive electrode material can be any value between 1 g / cm 3 , 1.5 g / cm 3 , 2 g / cm 3 , 2.5 g / cm 3 or 1-2.5 g / cm 3 .

[0031] The second aspect of the present application provides a preparation method of the double-layer interfacial coated positive electrode material, comprising: mixing the precursor and the lithium source under an oxygen-containing atmosphere to obtain a mixture; and first sintering the mixture to obtain a single-crystal positive electrode material; second mixing and second sintering the single-crystal positive electrode material and the D source under a hydrogen sulfide atmosphere to obtain a coated material; third mixing and third sintering the coated material and the E source under an ammonia-containing atmosphere to obtain the double-layer interfacial coated positive electrode material.

[0032] In some embodiments, the precursor comprises at least one of a hydroxide, an oxide or a carbonate of Co and / or Y; and / or, the D source comprises at least one of a chloride salt of Fe, Bi, La, Gd, Cr, Er and Sb; and / or, the E source comprises at least one of a chloride salt and / or an organic metal compound of In, Sr, V, Ta, Mo, Ga and Nb; and / or, the molar ratio of the precursor to lithium in the lithium source is 1:1-1.2; Optionally, the molar ratio of the precursor to lithium in the lithium source can be 1:1, 1:1.1, 1:1.2 or any value between 1:1-1.2; Optionally, the molar ratio of the precursor to lithium in the lithium source can be 1:1, 1:1.1, 1:1.2 or any value between 1:1-1.2; and / or, the mass ratio of the D source to the single-crystal positive electrode material is 0.002-0.005:1; Optionally, the mass ratio of the D source to the single-crystal positive electrode material can be 0.002:1, 0.003:1, 0.004:1, 0.005:1 or any value between 0.002-0.005:1; and / or, the mass ratio of the E source to the single-crystal positive electrode material is 0.001-0.003:1; Optionally, the mass ratio of the E source and the single-crystal positive electrode material can be 0.001:1, 0.002:1, 0.003:1, or any value between 0.001-0.003:1. And / or, the temperature rising rate of the first sintering is 5-10℃ / min, the end point temperature is 700-1000℃, the constant temperature time is 12-18h, and the oxygen concentration is greater than or equal to 80%; Optionally, the temperature rising rate of the first sintering can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or any value between 5-10℃ / min, the end point temperature can be 700℃, 800℃, 900℃, 1000℃, or any value between 700-1000℃, the constant temperature time can be 12h, 14h, 16h, 18h, or any value between 12-18h, and the oxygen concentration can be 80%, 85%, 90%, 95%, or any value greater than or equal to 80%; And / or, the rotation speed of the second mixing is 300-600r / min, and the time is 30-60min; Optionally, the rotation speed of the second mixing can be 300 r / min, 400 r / min, 500 r / min, 600 r / min, or any value between 300-600 r / min, and the time can be 30min, 40min, 50min, 60min, or any value between 30-60min; And / or, the temperature rising rate of the second sintering is 10-20℃ / min, the end point temperature is 300-700℃, the constant temperature time is 1-3h, and the input rate of H2S is 10-15L / h; Optionally, the temperature rising rate of the second sintering can be 10℃ / min, 15℃ / min, 20℃ / min, or any value between 10-20℃ / min, the end point temperature can be 300℃, 400℃, 500℃, 600℃, 700℃, or any value between 300-700℃, the constant temperature time can be 1h, 2h, 3h, or any value between 1-3h, and the input rate of H2S can be 10L / h, 11 L / h, 12 L / h, 13 L / h, 14 L / h, 15 L / h, or any value between 10-15 L / h; And / or, the temperature rising rate of the third sintering is 5-10℃ / min, the end point temperature is 200-500℃, and the constant temperature time is 3-5h.

[0033] Optionally, the heating rate of the third sintering can be any value between 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min or 5-10℃ / min, the final temperature can be any value between 200℃, 300℃, 400℃, 500℃ or 200-500℃, and the isothermal time can be any value between 3h, 4h, 5h or 3-5h.

[0034] In some embodiments, the oxygen-containing atmosphere includes air and / or oxygen, and the flow rate of the oxygen-containing atmosphere is 20-60 L / min during the first sintering. Optionally, the ventilation flow rate of the oxygen-containing atmosphere can be any value between 20 L / min, 30 L / min, 40 L / min, 50 L / min, 60 L / min, or 20-60 L / min; And / or, the second sintering is performed by CVD treatment. Before and during the CVD treatment, an inert gas is introduced. The inert gas flow rate is 100-150 L / h, and the inert gas is introduced for 15-30 min before the CVD treatment. Optionally, the inert gas flow rate can be any value between 100 L / h, 110 L / h, 120 L / h, 130 L / h, 140 L / h, 150 L / h or 100-150 L / h, and the inert gas introduction time before CVD treatment can be any value between 15 min, 20 min, 25 min, 30 min or 15-30 min. It should be noted that CVD vapor deposition forms metal sulfides, which have excellent ionic conductivity and can greatly improve the shortcomings of single-crystal cathode materials in terms of kinetic performance. However, under high voltage conditions, the metal sulfide coating layer is prone to dissolution to generate lithium polysulfides, which causes a shuttle effect and increases the impedance of the material during cycling. The inert gas includes one or more of N2, He, Ne, and Ar; And / or, the third sintering is performed using ALD deposition treatment. Before performing the ALD deposition treatment, the ammonia-containing atmosphere is introduced for 10-20 min, and the E source is introduced at a rate of 5-20 L / h. Optionally, before performing ALD deposition, the ammonia atmosphere can be introduced for any time between 10 min, 15 min, 20 min, or 10-20 min, and the E source can be introduced at any rate between 5 L / h, 10 L / h, 15 L / h, 20 L / h, or 5-20 L / h. It should be noted that by using the ALD deposition method to deposit a metal nitride coating layer with excellent electronic conductivity outside the first coating layer, the shielding effect of the coating layer can be used to isolate the shuttle effect of lithium polysulfide generated by the first coating layer during cycling. At the same time, the synergistic effect of the excellent ion-electron dual conductivity of the double-layer interface coating layer can reduce the influence of insufficient kinetic performance of the single-crystal cathode material and improve the problem of large impedance growth rate during cycling. And / or, after the third sintering is completed, an inert gas is introduced for purging, and the purging time is 30-60 seconds.

[0035] Optionally, the purging time can be any value between 30s, 40s, 50s, 60s, or 30-60s.

[0036] A third aspect of this application provides a lithium-ion battery, including the aforementioned dual-layer interface-coated positive electrode material.

[0037] A third aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0038] It should be noted that electrical equipment may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; among them, mobile devices may include, but are not limited to, at least one of mobile phones, laptops, etc.; electric vehicles may include, but are not limited to, at least one of pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0039] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0040] Example 1 The first aspect of this embodiment provides a dual-layer interface-coated cathode material, including a core and a first coating layer and a second coating layer sequentially stacked on the surface of the core; The kernel is LiNi 0.68 Co 0.10 Mn 0.22 O2; The first coating layer is La2S3; The second coating layer is InN.

[0041] The second aspect of this embodiment provides a method for preparing a bilayer interface-coated cathode material, the specific steps of which are as follows: S1: Weigh out the ternary precursor Ni hydroxide at a molar ratio of 1:1.035. 0.68 Co 0.10 Mn 0.22 (OH)2 and LiOH·H2O were mixed at high speed and then placed in a box furnace for one sintering. The one sintering procedure was as follows: the temperature was raised to 910℃ at 5℃ / min, held at the temperature for 15h and then cooled naturally. Oxygen was introduced at a flow rate of 50L / min during the sintering process. After the one sintering was completed, the material was subjected to air jet pulverization to obtain material A. S2: Take material A from the above steps and 0.25wt% of LaCl3, mix them in a ball mill at a rate of 500r / min for 30min. After mixing, take it out and spread it inside a tube furnace. First, introduce N2 into the furnace for 20min to replace it. After replacement, set the N2 introduction rate to 150L / h and the H2S introduction rate to 15L / h. At the same time, set the heating rate to 15℃ / min and the target temperature to 450℃. After reaching the reaction temperature, react for 2h and cool naturally to obtain the first interface coated modified single crystal cathode material B. S3: Take material B from the above steps and add it to the deposition reaction chamber. Weigh 0.2wt% of the corresponding mass of InCl3 and add it to the gasification chamber. First, introduce NH3 into the reaction chamber for 10 minutes of gas replacement. After the replacement is completed, set the heating rate to 5℃ / min, the reaction temperature to 400℃, the gasification chamber temperature to 200℃, and control the gas flow rate in the gasification chamber to 10L / h. After the InCl3 is completely introduced, continue the reaction for 3 hours. After the reaction is completed, allow it to cool naturally. Finally, purge with N2 for 30 seconds to obtain the double-layer interface coated cathode material.

[0042] Example 2 The difference from Example 1 is that in step S2, LaCl3 is replaced with BiCl3, and the target temperature for the second sintering is 550°C. In step S3, InCl3 is replaced with trimethylgallium (TMGa), the vaporization chamber temperature is set to 50°C, and the final temperature of the third sintering is set to 450°C.

[0043] Example 3 The difference from Example 1 is that in step S2, LaCl3 is replaced with GdCl3, and the target temperature for the second sintering is 400°C. In step S3, InCl3 is changed to TaCl5, the gasification chamber temperature is changed to 130℃, and the final temperature of the third sintering is changed to 300℃.

[0044] Example 4 The difference from Example 1 is that in step S2, LaCl3 is replaced with CrCl3, and the target temperature for the second sintering is 600°C. In step S3, InCl3 is replaced with vanadium triisopropoxy (VO(OiPr)3), the gasification chamber temperature is set to 100℃, and the final temperature of the third sintering is set to 200℃.

[0045] Example 5 The difference from Example 1 is that in step S2, LaCl3 is replaced with LaCl3 and GdCl3 in a mass ratio of 1:1; In step S3, InCl3 is replaced with trimethylgallium (TMGa) and TaCl5 in a mass ratio of 1:1.

[0046] Comparative Example 1 The difference from Example 1 is that steps S2 and S3 are not performed, that is, the first coating layer and the second coating layer are not set.

[0047] Comparative Example 2 The difference from Example 1 is that step S3 is not performed, that is, the second coating layer is not set.

[0048] Comparative Example 3 The difference from Example 1 is that step S2 is not performed, that is, the first coating layer is not set.

[0049] Comparative Example 4 The difference from Example 1 is that the order of steps S2 and S3 is changed, that is, the positions of the first coating layer and the second coating layer are changed.

[0050] Comparative Example 5 The difference from Example 1 is that in step S2, LaCl3 is replaced with ZnCl2.

[0051] Comparative Example 6 The difference from Example 1 is that in step S3, InCl3 is replaced with CuCl2.

[0052] The relevant product parameters of the cathode materials prepared in the above embodiments and comparative examples are shown in Table 1.

[0053] Table 1 Product Parameters

[0054] The cathode materials prepared in the above examples and comparative examples were assembled into CR2032 coin cells according to the national standard GB / T 37201-2018 and their electrochemical performance was tested. The electrochemical performance test items were: first charge-discharge test at room temperature (0.1C, 2.8-4.5V), capacity retention test at -20℃, DCR impedance test after 3C initial DCR followed by 1C / 1C room temperature cycling test followed by 3C cycling, and EIS AC impedance spectroscopy (10mHz~10KHz, 5mV perturbation) test. The specific test results are shown in Table 2.

[0055] Table 2 Electrochemical Performance Tests

[0056] In addition, EIS AC impedance tests were performed on the four groups of materials in Example 1 and Comparative Examples 1-3. The specific results are as follows: Figure 1 As shown.

[0057] analyze: As can be seen from the above test results, the different interface coating combinations provided in the embodiments can achieve similar improvement effects. The first discharge capacity of the embodiments is 212-213 mAh / g, the first discharge efficiency is about 92%, the initial impedance is about 14Ω, the 100-cycle retention rate is about 84%, the DCR growth rate after cycling is 26%, and the capacity retention rate at -20℃ is about 87%. Among them, the fifth group, based on the above four groups of embodiments, has carried out co-coating of the first and second interface coatings with dual metal elements. Based on the synergistic effect of the metal elements inside and between the two coating layers, the first discharge capacity, cycle impedance growth rate and other data of this embodiment have been further optimized.

[0058] Compared with Comparative Example 1, without any interface coating modification, the discharge capacity, first-efficiency, impedance and other performance indicators of the single-crystal cathode material are greatly degraded. This is attributed to the large particle size of the single-crystal cathode material, which results in poor Li kinetic performance. Especially at low temperatures, the charge migration rate is further weakened by temperature, thus further limiting the low-temperature kinetic performance of the material. Furthermore, since the primary particle surface is not treated in any way, it is subject to corrosion by harmful substances generated by electrolyte decomposition during cycling and surface structure deterioration caused by the dissolution of transition metal elements inside the material lattice. The cycling performance and cycling impedance growth are both poor. Moreover, the semicircle representing charge transfer impedance in the high-frequency region of its electrochemical AC impedance spectrum has a large radius, and the slope of the straight line representing the solid-phase diffusion rate of Li+ in the low-frequency region is low. All of these prove that the kinetic performance of the unmodified single-crystal cathode material is poor. Compared with Comparative Example 1 and Comparative Example 2, after the first interface coating modification, thanks to the sulfide coating layer uniformly deposited on the surface of the single-crystal cathode material by CVD, its excellent ionic conductivity to a certain extent compensates for the weak kinetic performance of the single-crystal cathode material. Therefore, Comparative Example 2 shows a certain degree of improvement in the initial discharge capacity and initial discharge efficiency, with the discharge capacity increasing by about 10 mAh / g, the initial efficiency increasing by 4%, the initial impedance decreasing by 40%, the cycle retention rate increasing by 10%, and the low-temperature retention rate increasing by 12%. The high-frequency value representing charge transfer impedance in the EIS impedance spectrum is also improved. The radius of the semicircle in the region was reduced by 10%; however, the overall data still showed a certain gap compared to Example 1. The main reason for the performance gap was that under high voltage conditions, the decomposition and oxidation of the sulfide coating during cycling produced lithium polysulfides, which underwent a shuttle effect. This effect continuously consumed the CEI, SEI film and active Li, resulting in irreversible capacity loss. Therefore, its cycle retention rate and the rate of increase in impedance after cycling were both higher than those of Example 1. In addition, although the sulfide improved the ion transport efficiency to some extent, the electron transport efficiency was not improved accordingly. Therefore, the low-temperature capacity retention rate was about 20% lower than that of Example 1. Compared with Comparative Example 1 and Comparative Example 3, after the second interface coating modification, the nitride coating layer deposited by ALD on the surface of the single-crystal cathode material has the following advantages: First, it isolates the harmful substances generated by electrolyte decomposition under high voltage from the surface of the single-crystal cathode material. At the same time, it further weakens the damage to the material interior caused by stress generated during cycling by its own excellent mechanical strength. On the other hand, its excellent electronic conductivity improves the poor kinetic characteristics of the single-crystal cathode material under low temperature conditions to a certain extent. According to the experimental data, the initial discharge capacity of Comparative Example 3 is 10 mAh / g higher than that of Comparative Example 1, the initial efficiency is improved by 5%, the initial impedance is reduced by about 39%, the cycle retention rate is improved by 16%, the low temperature retention rate is improved by 15%, and the semi-circle radius in the high-frequency region of the EIS impedance spectrum is reduced by 11%. Compared with Comparative Example 2, the cycle retention rate is improved by 5%, and the impedance growth rate after cycling is reduced by 17%. This is attributed to the good chemical stability of the nitride coating layer, which does not cause a large amount of metal elements to dissolve during cycling. At the same time, the active Li consumption rate is slow, so the impedance growth rate is also lower than that of Comparative Example 2. Based on the experimental results of Example 1, Comparative Example 2, and Comparative Example 3, by organically combining the two interface coating modification methods, the metal nitride coating layer can slow down the degradation rate of the sulfide coating layer during high voltage by utilizing its excellent mechanical and chemical stability, weaken the adverse effects of the sulfide coating layer shuttle effect, slow down the interface impedance growth rate while improving cycle stability, and organically unify the excellent ionic conductivity and electronic conductivity of the two interface coating layers, which greatly improves the initial kinetic performance and cycle stability of the single-crystal cathode material and reduces the interface impedance growth rate.

[0059] Comparing the experimental results of Example 1 and Comparative Example 4, after adjusting the order of the metal sulfide coating and the metal nitride coating, the short-term electrochemical kinetic characteristics such as discharge capacity, low-temperature retention rate, and initial DCR are at the same level as in Example 1. However, after long-term cycling, the shuttle effect of the metal sulfide coating cannot be effectively limited by the metal nitride coating. Therefore, the long-term data such as cycle retention rate and impedance growth rate are significantly different from those in Example 1. Thus, the coating order of the two coatings cannot be arbitrarily changed.

[0060] Comparative examples 5 and 6 show that replacing the metal elements in the corresponding coatings outside the defined range does not necessarily result in sulfide or nitride coatings formed by arbitrary elements having a specific modification effect on the single-crystal cathode material. Some coatings may not be able to improve the existing problems of the single-crystal cathode material. Instead, the reactants generated by the side reactions during the electrochemical process may damage the cathode material itself, thus failing to achieve the corresponding beneficial effect.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0062] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A double-layer interface-coated cathode material, characterized in that, It includes a core and a first coating layer and a second coating layer that are sequentially stacked on the surface of the core; The first coating layer comprises a metal sulfide; The second coating layer comprises a metal nitride; The general chemical formula of the core is LiCo. x Y 1-x O2, wherein Y includes at least one of Ni, Mn and Al, and 0.03 ≤ x ≤ 1.

2. The dual-layer interface-coated cathode material according to claim 1, characterized in that, The metal sulfide includes a sulfide of D, where D includes at least one of Fe, Bi, La, Gd, Cr, Er, and Sb. And / or, the metal nitride includes a nitride of E, wherein E includes at least one of In, Sr, V, Ta, Mo, Ga, and Nb.

3. The double-layer interface-coated cathode material according to claim 2, characterized in that, The D in the metal sulfide includes La and / or Gd; And / or, E in metal nitrides includes Ga and / or Ta.

4. The double-layer interface-coated cathode material according to claim 1, characterized in that, The thickness of the first coating layer is 1-10 nm; And / or, the thickness of the second coating layer is 1-10 nm; And / or, the particle size of the double-layer interface-coated cathode material is 2.0-5.0 μm.

5. The dual-layer interface-coated cathode material according to claim 1, characterized in that, The BET of the dual-layer interface-coated cathode material is 1.0-2.0m. 2 / g; And / or, the TD of the dual-layer interface-coated cathode material is 1.0-2.5 g / cm³. 3 .

6. A method for preparing a bilayer interface-coated cathode material according to any one of claims 1-5, characterized in that, include: In an oxygen-containing atmosphere, the precursor and lithium source are first mixed to obtain a mixture; the mixture is then first sintered to obtain a single-crystal cathode material. Under a hydrogen sulfide atmosphere, the single-crystal cathode material and the D source are mixed and sintered a second time to obtain the coated material. Under an ammonia-containing atmosphere, the coated material and the E source are mixed and sintered for a third time to obtain a double-layer interface coated cathode material.

7. The method for preparing a double-layer interface-coated cathode material according to claim 6, characterized in that, The precursor includes at least one of the following: hydroxides, oxides, and carbonates of Co and / or Y; And / or, the D source includes at least one of the chloride salts of Fe, Bi, La, Gd, Cr, Er, and Sb; And / or, the E source includes at least one of the chloride salts of In, Sr, V, Ta, Mo, Ga, Nb and / or organometallic compounds; And / or, the molar ratio of the precursor to lithium in the lithium source is 1:1-1.2; And / or, the mass ratio of the D source to the single-crystal cathode material is 0.002-0.005:1; And / or, the mass ratio of the E source to the single-crystal cathode material is 0.001-0.003:1; And / or, the heating rate of the first sintering is 5-10℃ / min, the final temperature is 700-1000℃, the isothermal time is 12-18h, and the oxygen concentration is greater than or equal to 80%; And / or, the second mixing speed is 300-600 r / min, and the time is 30-60 min; And / or, the heating rate of the second sintering is 10-20℃ / min, the final temperature is 300-700℃, the isothermal time is 1-3h, and the H2S introduction rate is 10-15L / h. And / or, the heating rate of the third sintering is 5-10℃ / min, the final temperature is 200-500℃, and the holding time is 3-5h.

8. The method for preparing a double-layer interface-coated cathode material according to claim 6 or 7, characterized in that, The oxygen-containing atmosphere includes air and / or oxygen, and the flow rate of the oxygen-containing atmosphere is 20-60 L / min during the first sintering. And / or, the second sintering is performed by CVD treatment. Before and during the CVD treatment, an inert gas is introduced. The inert gas flow rate is 100-150 L / h, and the inert gas is introduced for 15-30 min before the CVD treatment. The inert gas includes one or more of N2, He, Ne, and Ar; And / or, the third sintering is performed using ALD deposition treatment. Before performing the ALD deposition treatment, the ammonia-containing atmosphere is introduced for 10-20 min, and the E source is introduced at a rate of 5-20 L / h. And / or, after the third sintering is completed, an inert gas is introduced for purging, and the purging time is 30-60 seconds.

9. A lithium-ion battery, characterized in that, Includes the double-layer interface coated cathode material as described in any one of claims 1-5.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

Images