Positive electrode material and preparation method therefor, and lithium ion battery

Abstract

The present invention provides a positive electrode material and a preparation method therefor, and a lithium ion battery. The positive electrode material comprises an inner core, an oxygen absorption layer, and a passivation layer from inside to outside; the inner core comprises an oxide composed of Ni, Li, a metallic element M, and a non-metallic element Q; the metallic element M comprises at least one of Mg, Al, Zr, Ca, Ti, Sr, Y, Nb, Mo, W, Ta, or Ce; the non-metallic element Q comprises at least one of F, B, P, or Si; the oxygen absorption layer is an unsaturated oxide comprising a cladding element L; the cladding element L comprises at least one of V, Ga, In, Sn, Bi, Ce, Pr, or Sb; the passivation layer is a compound comprising an element F. According to the present invention, by means of functional design of different layered structures for the positive electrode material, the effect of suppressing oxygen precipitation can be achieved.

Description

Positive electrode material and preparation method thereof, and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on August 15, 2023, with application number 202311020334.0 and application name “A positive electrode material, its preparation method, and lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode material and a preparation method thereof, and a lithium ion battery. Background Art

[0003] The positive electrode material, serving as the lithium source for lithium batteries, releases lithium electrons during charging, which are then embedded in the structure of the negative electrode material. During discharge, the lithium electrons are released from the negative electrode material and reform into compounds, releasing electrical energy. Generally speaking, positive electrode materials are layered lithium nickel cobalt manganese oxide composites, which can be categorized into different types based on the ratio of the various elements in the material.

[0004] During the charge and discharge process of the cathode material, highly active lattice oxygen easily produces O2, which accelerates the decomposition of the electrolyte, causing increased interfacial impedance, the formation of microcracks, and irreversible phase transitions. Therefore, how to inhibit the evolution of oxygen is an urgent problem that needs to be solved.

[0005] Application Contents

[0006] In the related art, due to the high activity of lattice oxygen in the positive electrode material during the charge-discharge cycle, oxygen gas is easily released. How to suppress the release of oxygen gas is one of the technical problems that the present invention aims to solve.

[0007] To solve the above problems, the present invention provides a positive electrode material, which includes, from the inside to the outside, a core, an oxygen absorption layer, and a passivation layer; the core includes an oxide composed of Ni, Li, a metal element M and a non-metallic element Q; the metal element M includes at least one of Mg, Al, Zr, Ca, Ti, Sr, Y, Nb, Mo, W, Ta, and Ce; the non-metallic element Q includes at least one of F, B, P, and Si; the oxygen absorption layer is an unsaturated oxide containing a coating element L; the coating element L includes at least one of V, Ga, In, Sn, Bi, Ce, Pr, and Sb; and the passivation layer is a compound containing the element F.

[0008] In this technical solution, the positive electrode material includes a three-layer structure, which is composed of a core, an oxygen absorption layer, and a passivation layer from the inside to the outside. The core introduces metal elements M and non-metallic elements Q to achieve positive and negative ion doping; the metal element M is doped into the core as a positive ion, and the bond energy between the metal element M and the oxygen element is greater than the bond energy between the transition metal element and the oxygen element, so the metal element M can fix the oxygen element in the core. The non-metallic element Q is doped into the core as a negative ion, wherein boron, phosphorus, silicon, and oxygen form a stable polyanion structure. This structure is more stable, so it can play a role in fixing oxygen atoms and, to a certain extent, prevent the precipitation of oxygen; fluorine replaces lattice oxygen, and since the bond energy between fluorine and transition metal elements is greater than the bond energy between transition metal elements and oxygen elements, the material is more stable.

[0009] Furthermore, an oxygen-absorbing layer is provided on the outer surface of the inner core, which includes an unsaturated oxide of the coating element L. The coating element L is selected from an element with multiple valence states and is easily variable in valence. Therefore, in the oxide of the coating element L, the coating element L can present different valence states. When it contains a low-valence oxide, it has a certain reduction and valence-changing ability, so it is called an unsaturated oxide; that is, in this technical solution, the highest-valence oxide of the coating element L is considered to be a saturated oxide, and vice versa. It is an unsaturated oxide. During the charge and discharge process of the positive electrode material, since the oxygen-absorbing layer is an unsaturated oxide, it will undergo an oxidation-reduction reaction, and the valence state of the coating element L will change from low to high, which can effectively prevent the lattice oxygen from being oxidized to produce oxygen. The passivation layer includes a fluorine-containing compound, which can inhibit and slow down the corrosion power of HF in the electrolyte on the passivation layer, thereby making the passivation layer of the positive electrode material of the present invention more resistant to electrolyte corrosion than the ordinary oxide passivation layer.

[0010] Furthermore, the elemental composition of the core is shown in formula (I):

[0011] Li y Ni a Co b Mn c M d Q α O2 (Ⅰ)

[0012] Among them, the values ​​of y, a, b, c, d, and α are as follows: 0.98≤y≤1.20, 0.5≤a≤0.9, 0≤b≤0.4, 0≤c≤0.4, 0<d<0.1, 0<α<0.1.

[0013] In this technical solution, the core of the positive electrode material is generally composed of a nickel-cobalt-manganese ternary material as a matrix, but in specific implementations, cobalt and / or manganese elements may not be included. Different ratios of nickel-cobalt-manganese materials can exhibit different properties. For example, increasing the nickel content can increase battery capacity; increasing the cobalt content can reduce cation mixing and enhance battery cycle performance; and increasing the manganese content can enhance battery safety. In the present invention, the nickel-cobalt-manganese content is shown in formula (I); the positive electrode material with this ratio has a higher energy density and better safety and stability.

[0014] Furthermore, in the core, the non-metallic element Q includes F; the elemental composition of the core is shown in formula (III):

[0015] Li y Ni a Co b Mn c M d Q1 α1 F α2 O 2-α2 (III)

[0016] Wherein, the element Q1 includes at least one of B, P, and Si;

[0017] The values ​​of y, a, b, c, d, α1, and α2 are as follows: 0.98≤y≤1.20, 0.5≤a≤0.9, 0≤b≤0.4, 0≤c≤0.4, 0<d<0.1, 0≤α1<0.05, 0<α2<0.05.

[0018] In this technical solution, fluorine can partially replace oxygen. Fluorine is doped into the core as a negatively charged ion. The highly electronegative fluorine atoms can replace some oxygen atoms, reducing the unstable lattice oxygen content. The bond energy between fluorine atoms and transition metal ions is greater than the bond energy between oxygen atoms and transition metal ions. Therefore, fluorine doping can also inhibit the dissolution of transition metal elements. Here, α2 is used to represent the substitution of fluorine for lattice oxygen.

[0019] The non-metallic element Q may comprise only fluorine, or may include at least one of boron, phosphorus, and silicon. B, P, and Si, as non-metallic ions, are doped into the core and can form a polyanionic structure with oxygen. Because their bond energy is greater than the bond energy between oxygen and transition metal elements, they can inhibit lattice oxygen precipitation and achieve the fixation of oxygen elements (oxygen atoms).

[0020] Furthermore, the elemental composition of the oxygen absorbing layer is shown in formula (II):

[0021] L e O 2-β (Ⅱ)

[0022] Among them, the values ​​of e and β are as follows: 0.8≤e≤4, 0.1<β<1.0.

[0023] In this technical solution, the oxygen absorbing layer is an unsaturated oxide, and the valence state of the coating element L in the layer presents various situations, so the value range of its subscript e is between 0.8-4. β is used to indicate the degree of unsaturation of the coating element L in the oxygen absorbing layer, reflecting the proportion of oxides of elements with different valence states (low valence states). The coating element L preferably has multiple valence states and is easy to change valence, such as V, Ga, In, Sn, Bi, Ce, Pr, Sb, etc. Preferably, the coating element L is Ce element, which has a 4f orbital that is not filled with electrons. Under oxidation or reduction conditions, Ce 3+ and Ce 4+ There is a rapid conversion between them, which acts as an electron "storage" to prevent the lattice oxygen from being oxidized.

[0024] Furthermore, the elemental composition of the passivation layer is shown in formula (IV):

[0025] X f O 2-γ F γ (IV)

[0026] The values ​​of f and γ are as follows: 0.6<f<4, 0.05<γ<0.3; the X element includes at least one of Li, Mg, Al, Zr, Ti, and W.

[0027] In this technical solution, the passivation layer contains fluoride, which acts as a physical barrier to protect the positive electrode material and slow the corrosion dynamics of the electrolyte. Furthermore, the fluorine in the passivation layer can partially replace oxygen, thereby reducing the content of unstable lattice oxygen. This achieves the same effect as the fluorine in the core, which will not be elaborated here.

[0028] Furthermore, the particle size of the core is 0.5 μm-20 μm; and / or the thickness of the oxygen absorption layer is 0.01 μm-0.1 μm; and / or the thickness of the passivation layer is 0.01 μm-0.1 μm.

[0029] In this technical solution, the inner core is generally spherical in shape, and the primary particles refer to irregular small particles, also called single crystals; the secondary particles are obtained by stacking the primary particles, also called polycrystals. The formation of primary particles and secondary particles is closely related to the sintering process; in the technical solution provided by the present invention, the inner core can be either a single crystal or a polycrystal, or a combination of single crystals and polycrystals. Preferably, the particle size range of the primary particles is between 0.5μm-10μm, and the particle size range of the secondary particles is between 1μm-20μm; therefore, the particle size of the inner core is between 0.5μm-20μm. The thickness of the oxygen absorption layer and the passivation layer is related to the diffusion rate of lithium ions. Preferably, the thickness of the oxygen absorption layer is 0.02μm-0.08μm; the thickness of the passivation layer is 0.03μm-0.08μm.

[0030] The present invention also provides a method for preparing the above-mentioned positive electrode material, comprising the following steps:

[0031] S10: obtaining a precursor, a lithium source, and a dopant, mixing them evenly, and sintering them once in an oxygen or air atmosphere to obtain a first oxide;

[0032] S20: mixing the first oxide and the first coating agent, and performing secondary sintering under a reducing atmosphere or an inert atmosphere to obtain a second oxide;

[0033] S30: mixing the second oxide and the second coating agent, and sintering them three times in a reducing atmosphere or an inert atmosphere to obtain a positive electrode material;

[0034] The dopant includes a metal element M and a non-metal element Q; the first coating agent includes a coating element L; and the second coating agent includes an F element.

[0035] In this technical solution, a precursor, lithium source, and dopant are sintered once to produce a first oxide, or core. This is then mixed with a first coating agent and sintered a second time to form an oxygen-absorbing layer on the core's surface. Furthermore, this is mixed with a second coating agent and sintered a third time to form a passivation layer on the oxygen-absorbing layer. Because the oxygen-absorbing layer is an unsaturated oxide, the second sintering atmosphere is either inert or reducing, preferably in a reducing atmosphere. Specifically, the reducing atmosphere can be at least one of hydrogen, nitrogen, or carbon monoxide.

[0036] In a specific implementation, between S10 and S20, the first oxide is crushed. The crushing can be performed by air flow or mechanical pulverization, and the D50 of the crushed first oxide is controlled to be 1-20 μm. The crushing process can further enhance mixing between the first oxide and the first coating agent, thereby facilitating more uniform coating of the oxygen-absorbing layer in the positive electrode material.

[0037] Furthermore, the temperature of the first sintering is 500℃-1000℃, and the holding time is 8h-15h; and / or the temperature of the second sintering is 300℃-600℃, and the holding time is 8h-15h; and / or the temperature of the third sintering is 300℃-600℃, and the holding time is 8h-15h; and / or the mixing molar ratio of the precursor, the lithium source and the dopant is 1:(1.04-1.20):(0.01-0.2); and / or the mixing molar ratio of the first oxide and the first coating agent is 1:(0.001-0.02); and / or the mixing molar ratio of the second oxide and the second coating agent is 1:(0.001-0.02).

[0038] Preferably, the temperature of the first sintering is 600℃-800℃, and the holding time is 10h-12h; the temperature of the second sintering is 400℃-500℃, and the holding time is 10h-12h; the temperature of the third sintering is 400℃-500℃, and the holding time is 10h-12h; the mixing molar ratio of the precursor, the lithium source and the dopant is 1:(1.1-1.15):(0.05-0.16); the mixing molar ratio of the first oxide and the first coating agent is 1:(0.008-0.015); and the mixing molar ratio of the second oxide and the second coating agent is 1:(0.008-0.015).

[0039] In the above scheme, after each sintering, it is naturally cooled to room temperature before proceeding to the next step. The heating rate of the first sintering, the second sintering and the third sintering is preferably 10℃ / h-150℃ / h; more preferably 50℃ / h-110℃ / h.

[0040] Furthermore, the lithium source comprises LiF; and / or the dopant comprises at least one of LiF, MgF2, AlF3, ZrF4, and CeF3.

[0041] In this technical solution, LiF is preferably doped into the lithium source, thereby directly completing the doping of fluorine. The dopant comprises a metal element M and a non-metallic element Q, specifically at least one of Al2O3, Al(OH)3, SrO, TiO2, ZrO2, MgO, CaCO3, Ca(OH)2, Y2O3, Nb2O5, CeO2, MoO3, WO3, H2WO4, LiF, NH4F, MgF2, AlF3, ZrF4, CeF3, B2O3, H3BO3, TiB2, (NH4)3PO4, AlPO4, MgHPO4, H2SiO3, and Al2SiO5. The first coating agent comprises a coating element L, specifically at least one of V2O3, Ga2O3, In2O3, SnO2, Bi2O5, CeO2, PrO2, and Sb2O3. The second coating agent contains F element, and specifically can be selected from at least one of LiF, NH4F, MgF2, AlF3, and ZrF4; the second coating agent can also include at least one of Al2O3, TiO2, ZrO2, MgO, WO3, and H2WO4.

[0042] Preferably, the dopant includes at least one of LiF, MgF2, AlF3, CeF3, and ZrF4; the cations in the above dopants can replace transition metal elements, and the formed AO bond energy is greater than TM-O; the AF bond energy is greater than TM-F; wherein A represents Mg, Al, and Zr elements; TM represents a transition metal element; therefore, the overflow of unstable lattice oxygen can be suppressed.

[0043] The present invention further provides a lithium-ion battery comprising the positive electrode material provided by any of the above-mentioned solutions, which thus includes the effects of any of the above-mentioned solutions and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0045] FIG1 is a microscopic morphology of a cathode material provided by an embodiment of the present invention;

[0046] FIG2 is a microscopic morphology of another cathode material provided by an embodiment of the present invention;

[0047] FIG3 is a microscopic morphology diagram of another cathode material provided by an embodiment of the present invention;

[0048] FIG4 shows the volume growth rates of different samples stored at 70° C. according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0050] During the charge-discharge cycle of the cathode material, due to the high activity of lattice oxygen, after the first charge cycle, when most transition metal ions are completely oxidized, oxygen ions begin to participate in the oxidation process, forming oxygen gas and, in turn, generating oxygen vacancies. The onset energy of oxygen vacancies is approximately 0.5-0.6 eV. Due to the slow migration of oxygen, oxygen vacancies primarily form on the surface and subsurface regions within the top 5-6 atomic layers. When oxygen vacancies diffuse along specific crystal directions, they accumulate on the surface, causing significant volume shrinkage and changes in the c / a ratio, generating mechanical stress. This can easily lead to lattice mismatch and the appearance of microcracks in single-crystal cathode materials. Oxygen vacancies and oxygen loss caused by the oxidation of lattice oxygen can lead to phase transitions, changes in electronic structure, and the formation of defects, resulting in material dead zones.

[0051] Therefore, in response to the above problems, the present invention provides a positive electrode material, which includes, from the inside to the outside, a core, an oxygen absorption layer, and a passivation layer; the core includes an oxide composed of Ni, Li, a metal element M and a non-metallic element Q; the metal element M includes at least one of Mg, Al, Zr, Ca, Ti, Sr, Y, Nb, Mo, W, Ta, and Ce; the non-metallic element Q includes at least one of F, B, P, and Si; the oxygen absorption layer includes an unsaturated oxide of a coating element L; the coating element L includes at least one of V, Ga, In, Sn, Bi, Ce, Pr, and Sb; and the passivation layer includes a compound of the element F.

[0052] In this technical solution, the positive electrode material includes a three-layer structure, which is composed of a core, an oxygen absorption layer, and a passivation layer from the inside to the outside. The core introduces metal elements M and non-metallic elements Q to achieve positive and negative ion doping; the metal element M is doped into the core as a positive ion, and the bond energy between the metal element M and the oxygen element is greater than the bond energy between the transition metal element and the oxygen element, so the metal element M can fix the oxygen element in the core. The non-metallic element Q is doped into the core as a negative ion, wherein boron, phosphorus, silicon, and oxygen form a stable polyanion structure, and fluorine replaces lattice oxygen. Since the bond energy between fluorine and transition metal elements is greater than the bond energy between transition metal elements and oxygen elements, the material is more stable.

[0053] Furthermore, an oxygen-absorbing layer is provided on the outer surface of the inner core, comprising an unsaturated oxide of a coating element L. The coating element L is selected from an element having multiple valence states and easily changing valence. Therefore, during the charge and discharge process of the positive electrode material, since the oxygen-absorbing layer is an unsaturated oxide, it undergoes a redox reaction, and the valence state of the coating element L changes from low to high, which can effectively prevent the oxidation of lattice oxygen to produce oxygen. The passivation layer comprises a fluorine-containing compound, which can inhibit and slow the corrosion dynamics of HF in the electrolyte on the passivation layer, thereby making the passivation layer of the positive electrode material of the present invention more resistant to electrolyte corrosion than ordinary oxide passivation layers.

[0054] The present invention can achieve the effect of inhibiting oxygen evolution by designing the functions of different layered structures of the positive electrode material. Furthermore, the positive electrode material is prepared by the following method:

[0055] S10: obtaining a precursor, a lithium source, and a dopant, mixing them evenly, and sintering them once in an oxygen or air atmosphere to obtain a first oxide;

[0056] S20: mixing the first oxide and the first coating agent, and performing secondary sintering under a reducing atmosphere or an inert atmosphere to obtain a second oxide;

[0057] S30: mixing the second oxide and the second coating agent, and sintering them three times in a reducing atmosphere or an inert atmosphere to obtain a positive electrode material;

[0058] The dopant includes a metal element M and a non-metal element Q; the first coating agent includes a coating element L; and the second coating agent includes an F element.

[0059] In this technical solution, the precursor, lithium source, and dopant are sintered once to produce a first oxide, or core. This is then mixed with a first coating agent and sintered a second time to form an oxygen-absorbing layer on the core's surface. Furthermore, this is mixed with a second coating agent and sintered a third time to form a passivation layer on the oxygen-absorbing layer. Because the oxygen-absorbing layer is an unsaturated oxide, the secondary sintering atmosphere can be either inert or reducing. Specifically, the reducing atmosphere can be composed of one or more of hydrogen, methane, or carbon monoxide.

[0060] Example 1:

[0061] This embodiment provides a method for preparing a positive electrode material, comprising the following steps:

[0062] 1. Mix NCM811 precursor, LiOH, AlF3, and H3BO4 in a molar ratio of 1:1.05:0.001:0.001, add the mixture to a high-speed mixer, and sinter once in an oxygen atmosphere to obtain the first oxide.

[0063] The mixing speed is 800 rpm / min and the mixing time is 30 min.

[0064] The sintering process of the primary sintering was as follows: heating to 860°C at 15°C / min and then maintaining for 12 h.

[0065] 2. After the first oxide is crushed, it is mixed with CeO2 in a molar ratio of 1:0.005, and secondary sintering is performed under a hydrogen atmosphere to obtain the second oxide.

[0066] The secondary sintering process is as follows: heating to 600° C. at a rate of 15° C. / min and then maintaining the temperature for 10 hours. The particle size of the first oxide after pulverization is controlled to be D50=3.5 μm.

[0067] 3. The second oxide and AlF3 were mixed in a molar ratio of 1:0.005 and sintered three times under a nitrogen atmosphere to obtain a positive electrode material.

[0068] The sintering process of the three-stage sintering is as follows: heating to 450°C at a rate of 15°C / min and then maintaining for 10 hours.

[0069] The positive electrode material prepared in this embodiment has a single crystal morphology, and its periscopic structure is shown in FIG1 .

[0070] Example 2:

[0071] This embodiment provides a method for preparing a positive electrode material. The specific steps are similar to those in Example 1, except that an NCM811 precursor, LiOH, LiF, Al2O3, and H3BO4 are mixed in a molar ratio of 1:1.10:0.05:0.0005:0.001.

[0072] Example 3:

[0073] This embodiment provides a method for preparing a positive electrode material. The specific steps are similar to those in Example 1, except that CeO2 is replaced by V2O5.

[0074] Example 4:

[0075] This embodiment provides a method for preparing a positive electrode material. The specific steps are similar to those in Example 1, except that AlF3 is replaced by MgF.

[0076] Example 5:

[0077] This embodiment provides a method for preparing a positive electrode material. The specific steps are as follows: see Example 1, except that the sintering process of the primary sintering is as follows: heating to 800° C. at 15° C. / min and then maintaining for 12 hours.

[0078] The positive electrode material obtained by sintering in this embodiment has a polycrystalline morphology, as shown in FIG2 and FIG3 , which are electron microscope images of the positive electrode material in this embodiment at different magnifications.

[0079] Comparative Example 1:

[0080] This embodiment provides a method for preparing a positive electrode material. The specific steps are similar to those in Example 1, except that AlF3 in step 1 is replaced by Al2O3.

[0081] Comparative Example 2:

[0082] This embodiment provides a method for preparing a positive electrode material. The specific steps are similar to those in Example 1, except that H3BO4 is not added.

[0083] Comparative Example 3:

[0084] This embodiment provides a method for preparing a positive electrode material. The specific steps are similar to those in Example 1, except that the secondary sintering is performed in an oxygen atmosphere.

[0085] Comparative Example 4:

[0086] This embodiment provides a method for preparing a positive electrode material. The specific steps are similar to those in Example 1, except that AlF3 in step 3 is replaced by Al2O3.

[0087] The performance tests were conducted on the positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-4. Batteries were prepared from the positive electrode materials in the Examples and Comparative Examples, and the volume growth rates of the different samples were tested under storage conditions at 70°C.

[0088] The volume of inflation is calculated using the water displacement method; put the battery with no inflation into the water tank (there is a charging process, and the tabs must be well protected), measure its water displacement weight with an electronic density tester, and then convert the volume to get the volume expansion.

[0089] Specific steps:

[0090] 1. Prepare batteries with the positive electrode materials of the examples and comparative examples. Protect the battery tabs in the fully charged state and slowly place them in a 70°C water tank. After waiting for 30 seconds, measure the weight of the water discharged from the water tank and divide it by the medium density to obtain the initial volume V0 of the battery.

[0091] 2. After drying, place the battery in an insulated box and store it at 70°C for 7 days.

[0092] 3. Protect the battery tabs after high-temperature storage and slowly place them in a 70°C water tank. After 30 seconds, measure the weight of the water drained from the tank and divide it by the dielectric density to obtain the battery volume V7. The volume growth rate after 7 days is calculated as (V7 - V0) / V0 × 100%.

[0093] 4. After drying the battery, fully charge it at 4.35V and store it in an insulated box at 70℃ for another 7 days.

[0094] 5. Repeat steps 3-4 to obtain the volume growth rate under high temperature storage for different days.

[0095] The volume growth rates of different samples under 70°C storage conditions are shown in Table 1. The line graph obtained by plotting the data in Table 1 is shown in Figure 4.

[0096] Table 1

[0097] According to the experimental results, we can see that:

[0098] The comparison between Example 2 and Example 1 shows that the F ion doping of the core can be achieved by replacing AlF 3 with LiF and Al 2 O 3 .

[0099] The comparison between Example 3 and Example 1 shows that V2O5 can also act as an oxygen absorbing layer.

[0100] The comparison between Example 4 and Example 1 shows that MgF can replace AlF3.

[0101] The comparison between Example 2 and Example 1 shows that polycrystalline materials can also achieve performance improvements.

[0102] The comparison between Comparative Example 1 and Example 1 shows that adding appropriate F ions into the core is beneficial to improving the gas production performance.

[0103] The comparison between Comparative Example 2 and Example 1 shows that adding appropriate B ions to the core is beneficial to improving the gas production performance.

[0104] The comparison between Comparative Example 3 and Example 1 shows that the oxygen atmosphere sintering makes the Ce element in Ce 4+ The highest valence state causes the oxygen absorption layer to fail, which is not conducive to improving the gas production performance.

[0105] The comparison between Comparative Example 4 and Example 1 shows that adding appropriate F ions to the passivation layer is beneficial to inhibiting electrode liquid corrosion and reducing gas generation.

[0106] Example 6

[0107] This embodiment provides a positive electrode material, which includes a core, an oxygen absorption layer, and a passivation layer from the inside to the outside. The chemical formula of the core is: Li 0.98 Ni 0.88 Co 0.1 Mg 0.02 F 0.012 O 1.988 , the particle size is 1μm-3μm; the chemical formula of the oxygen absorption layer is: Ga 3.6 O 1.1 , thickness is 0.02μm; the chemical formula of the passivation layer is: Al 0.67 W 0.33 O 1.72 F 0.28 , thickness is 0.02μm.

[0108] Example 7

[0109] This embodiment provides a positive electrode material, which includes a core, an oxygen absorption layer, and a passivation layer from the inside to the outside. The chemical formula of the core is: Li1Ni 0.5 Mn 0.4 Al 0.06 B 0.02 F 0.02 O 1.98 , the particle size is 5μm-8μm; the chemical formula of the oxygen absorbing layer is: Sn 1.8 O 1.6 , thickness is 0.04μm; the chemical formula of the passivation layer is: MgO 1.92 F 0.08 , thickness is 0.04μm.

[0110] Example 8

[0111] This embodiment provides a positive electrode material, which includes a core, an oxygen absorption layer, and a passivation layer from the inside to the outside. The chemical formula of the core is: Li 1.1 Ni 0.843 Co 0.05 Mn 0.1 Mo 0.005 P 0.002 O2, particle size is 12μm-13μm; the chemical formula of the oxygen absorbing layer is: Bi 0.9 O 1.2 , thickness is 0.06μm; the chemical formula of the passivation layer is: Al 1.32 O 1.94 F 0.06 , thickness is 0.06μm.

[0112] Example 9

[0113] This embodiment provides a positive electrode material, which includes a core, an oxygen absorption layer, and a passivation layer from the inside to the outside. The chemical formula of the core is: Li1.2 Ni 0.64 Mn 0.35 Zr 0.007 Si 0.003 O2, particle size is 18μm-20μm; the chemical formula of the oxygen absorbing layer is: Pr 1.1 O 1.8 , thickness is 0.08μm; the chemical formula of the passivation layer is: Zr 0.94 O 1.72 F 0.28 , thickness is 0.08μm.

[0114] Example 10

[0115] This embodiment provides a method for preparing a positive electrode material, which can be used to prepare the positive electrode material of any one of Examples 6-9. The specific process is as follows:

[0116] 1. Obtain various raw materials according to the composition ratio of the target positive electrode material.

[0117] 2. The precursor, lithium source, and dopant are mixed uniformly and sintered once in an oxygen atmosphere to obtain the first oxide. The primary sintering temperature is 500° C. and the holding time is 15 hours.

[0118] 3. Mix the first oxide and the first coating agent, and perform secondary sintering under a reducing atmosphere to obtain the second oxide, wherein the secondary sintering temperature is 600° C. and the holding time is 8 hours.

[0119] 3. Mix the second oxide and the second coating agent and sinter them three times under an inert atmosphere to obtain a positive electrode material. The temperature of the three sinterings is 600°C and the holding time is 8 hours.

[0120] Example 11

[0121] This embodiment provides a method for preparing a positive electrode material, which can be used to prepare the positive electrode material of any one of Examples 6-9. The specific process is shown in Example 10, except that the primary sintering temperature is 1000° C. and the holding time is 8 hours.

[0122] Example 12

[0123] This embodiment provides a method for preparing a positive electrode material, which can be used to prepare the positive electrode material of any one of Examples 6-9. The specific process is shown in Example 10, except that the secondary sintering temperature is 300° C. and the holding time is 15 hours.

[0124] Example 13

[0125] This embodiment provides a method for preparing a positive electrode material, which can be used to prepare the positive electrode material of any one of Examples 6-9. The specific process is shown in Example 10, except that the temperature of the three sinterings is 300° C. and the holding time is 15 hours.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A positive electrode material, wherein: The positive electrode material includes a core, an oxygen absorption layer, and a passivation layer from the inside to the outside; The core comprises an oxide composed of Ni, Li, a metal element M and a non-metal element Q; the metal element M comprises at least one of Mg, Al, Zr, Ca, Ti, Sr, Y, Nb, Mo, W, Ta, and Ce; the non-metal element Q comprises at least one of F, B, P, and Si; The oxygen absorbing layer is an unsaturated oxide containing a coating element L; the coating element L includes at least one of V, Ga, In, Sn, Bi, Ce, Pr, and Sb; The passivation layer is a compound containing F element.

2. The positive electrode material according to claim 1, wherein The element composition of the core is shown in formula (I): Li y Ni a Co b Mr c M d Q α O2 (Ⅰ), Among them, the values ​​of y, a, b, c, d, and α are as follows: 0.98≤y≤1.20, 0.5≤a≤0.9, 0≤b≤0.4, 0≤c≤0.4, 0<d<0.1, 0<α<0.

1.

3. The positive electrode material according to claim 1, wherein In the core, the non-metallic element Q includes F; the element composition of the core is shown in formula (III): Li y Ni a Co b Mr c M d Q1 α1 F α2 O 2-α2 (Ⅲ), Wherein, the element Q1 includes at least one of B, P, and Si; The values ​​of y, a, b, c, d, α1, and α2 are as follows: 0.98≤y≤1.20, 0.5≤a≤0.9, 0≤b≤0.4, 0≤c≤0.4, 0<d<0.1, 0≤α1<0.05, 0<α2<0.

05.

4. The positive electrode material according to claim 1, wherein The element composition of the oxygen absorbing layer is shown in formula (II): IT e A 2-β (Ⅱ), Among them, the values ​​of e and β are as follows: 0.8≤e≤4, 0.1<β<1.

0.

5. The positive electrode material according to claim 1, wherein The element composition of the passivation layer is shown in formula (IV): X f O 2-γ F γ (IV), Among them, the values ​​of f and γ are as follows: 0.6<f<4, 0.05<γ<0.3; The X element includes at least one of Li, Mg, Al, Zr, Ti, and W.

6. The positive electrode material according to any one of claims 1 to 5, wherein The particle size of the core is 0.5 μm-20 μm.

7. The positive electrode material according to any one of claims 1 to 6, wherein The thickness of the oxygen absorbing layer is 0.01 μm-0.1 μm.

8. The positive electrode material according to any one of claims 1 to 7, wherein The thickness of the passivation layer is 0.01 μm-0.1 μm.

9. A method for preparing a positive electrode material according to any one of claims 1 to 8, wherein: The following steps are involved: S10: obtaining a precursor, a lithium source and a dopant, mixing them evenly, and sintering them once in an oxygen or air atmosphere to obtain a first oxide; S20: mixing the first oxide and the first coating agent, and performing secondary sintering in a reducing atmosphere or an inert atmosphere to obtain a second oxide; S30: mixing the second oxide and the second coating agent, and sintering them three times in a reducing atmosphere or an inert atmosphere to obtain the positive electrode material; Wherein, the dopant includes the metal element M and the non-metal element Q; the first coating agent includes the coating element L; and the second coating agent includes the F element.

10. The preparation method according to claim 9, wherein: The primary sintering temperature is 500° C.-1000° C., and the heat preservation time is 8 h-15 h.

11. The preparation method according to claim 9 or 10, wherein: The secondary sintering temperature is 300° C.-600° C., and the heat preservation time is 8h-15h.

12. The preparation method according to any one of claims 9 to 11, wherein: The temperature of the three sintering processes is 300° C.-600° C., and the heat preservation time is 8 h-15 h.

13. The preparation method according to any one of claims 9 to 12, wherein: The mixing molar ratio of the precursor, the lithium source and the dopant is 1:(1.04-1.20):(0.01-0.2).

14. The preparation method according to any one of claims 9 to 13, wherein: The mixing molar ratio of the first oxide to the first coating agent is 1:(0.005-0.02).

15. The preparation method according to any one of claims 9 to 14, wherein: The mixing molar ratio of the second oxide to the second coating agent is 1:(0.005-0.02).

16. The preparation method according to claim 9, wherein: The lithium source comprises LiF.

17. The preparation method according to claim 9 or 16, wherein: The dopant includes at least one of LiF, MgF2AlF3, CeF3, and ZrF4.

18. A lithium ion battery, wherein: Comprising the positive electrode material as described in any one of claims 1 to 8.

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