POSITIVE ELECTRODE MATERIAL AND PREPARATION METHOD THEREOF, AND LITHIUM-ION BATTERY

Abstract

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

Claims

1. A positive electrode material, comprising a core, an oxygen-absorbing layer, and a passivation layer in sequence from inside to outside, wherein: 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, or Ce; the non-metal element Q comprises at least one of F, B, P, or Si; the oxygen-absorbing layer is an unsaturated oxide containing a coating element L; the coating element L comprises at least one of V, Ga, In, Sn, Bi, Ce, Pr, or Sb; the passivation layer is a compound containing element F.

2. The positive electrode material according to claim 1, wherein the core has an element composition as shown in Formula (I): ##STR00005## wherein values of y, a, b, c, d, and are as follows: $0.98y\underset{}{<}1.2,0.5a0.9,0b0\text{.4},$ $0c0.4,0<d<0.1,0<<0.1.$

3. The positive electrode material according to claim 1, wherein in the core, the non-metal element Q comprises F; the core has an element composition as shown in Formula (III): ##STR00006## wherein element Q1 comprises at least one of B, P, or Si; values of y, a, b, c, d, 1, and 2 are as follows: $0.98y\underset{}{<}1.2,0.5a0.9,0b0\text{.4},$ $0c0.4,0<d<0.1,01<0.05,0<2<0.05.$

4. The positive electrode material according to claim 1, wherein the oxygen-absorbing layer has an element composition as shown in Formula (II): ##STR00007## wherein, values of e and are as follows: 0.8e4, 0.1<<1.0.

5. The positive electrode material according to claim 1, wherein the passivation layer has an element composition shown in Formula (IV): ##STR00008## wherein, values of f and are as follows: 0.6<f<4, 0.05<<0.3; element X comprises at least one of Li, Mg, Al, Zr, Ti, or W.

6. The positive electrode material according to claim 1, wherein the core has a particle size of 0.5 m-20 m.

7. The positive electrode material according to claim 1, wherein the oxygen-absorbing layer has a thickness of 0.01 m-0.1 m.

8. The positive electrode material according to claim 1, wherein the passivation layer has a thickness of 0.01 m-0.1 m.

9. A method for preparing the positive electrode material according to claim 1, comprising the following steps: S10: obtaining a precursor, a lithium source and a dopant, mixing them evenly, and performing a primary sintering under an oxygen atmosphere or an air atmosphere to obtain a first oxide; S20: mixing the first oxide with a first coating agent, and performing a secondary sintering under a reducing atmosphere or an inert atmosphere to obtain a second oxide; S30: mixing the second oxide with a second coating agent, and performing a tertiary sintering under the reducing atmosphere or the inert atmosphere to obtain the positive electrode material; wherein, the dopant comprises the metal element M and the non-metal element Q; the first coating agent comprises the coating element L; and the second coating agent comprises the element F.

10. The method according to claim 9, wherein the primary sintering has a temperature of 500 C.-1000 C., and a holding duration of 8 h-15 h.

11. The method according to claim 9, wherein the secondary sintering has a temperature of 300 C.-600 C., and a holding duration of 8 h-15 h.

12. The method according to claim 9, wherein the tertiary sintering has a temperature of 300 C.-600 C., and a holding duration of 8 h-15 h.

13. The method according to claim 9, wherein the precursor, the lithium source and the dopant have a mixing molar ratio of 1:(1.04-1.20):(0.01-0.2).

14. The method according to claim 9, wherein the first oxide and the first coating agent have a mixing molar ratio of 1:(0.005-0.02).

15. The method according to claim 9, wherein the second oxide and the second coating agent have a mixing molar ratio of 1:(0.005-0.02).

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

17. The method according to claim 9, wherein the dopant comprises at least one of LiF, MgF.sub.2AlF.sub.3, CeF.sub.3, or ZrF.sub.4.

18. A lithium-ion battery, comprising the positive electrode material according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] The above and/or additional aspects and advantages of the present disclosure will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings.

[0040] FIG. 1 is a microscopic morphology image of a positive electrode material provided by an embodiment of the present disclosure.

[0041] FIG. 2 is a microscopic morphology image of another positive electrode material provided by an embodiment of the present disclosure.

[0042] FIG. 3 is a microscopic morphology image of another positive electrode material provided by an embodiment of the present disclosure.

[0043] FIG. 4 shows volume growth rates of different samples of embodiments of the present disclosure under a storage condition of 70 C.

DESCRIPTION OF EMBODIMENTS

[0044] In order to make the above-mentioned purposes, features and advantages of the present disclosure more obvious and comprehensible, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Obviously, the described embodiments are merely part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without making creative work shall fall within the scope of protection of the present disclosure.

[0045] During the charge-discharge cycling process of the positive electrode material, when the majority of transition-metal ions have been fully oxidized after the first cycle of charging, the high activity of lattice oxygen causes the oxygen ions to start to participate in the oxidation process, forming gaseous oxygen and thereby generating oxygen vacancies. The energy required for the initial formation of oxygen vacancies is approximately 0.5-0.6 eV. Due to the slow migration of oxygen, oxygen vacancies are mainly formed in the surface and sub-surface regions within the top 5-6 atomic layers. When oxygen vacancies diffuse along specific crystallographic directions, they accumulate on the surface, causing significant volume contraction and changes in the c/a ratio, generating mechanical stress. This easily leads to lattice mismatch and the occurrence of micro-cracks in single-crystal positive electrode material. Oxygen vacancies and oxygen loss caused by the oxidation of lattice oxygen may induce phase transition, changes in electronic structure and the formation of defects, resulting in material dead zones.

[0046] Therefore, for the above problems, the present disclosure provides a positive electrode material. The positive electrode material includes a core, an oxygen-absorbing layer, and a passivation layer in sequence from inside to outside. The core includes an oxide composed of Ni, Li, a metal element M and a non-metal element Q. The metal element M includes at least one of Mg, Al, Zr, Ca, Ti, Sr, Y, Nb, Mo, W, Ta, or Ce. The non-metal element (includes at least one of F, B, P, or 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, or Sb. The passivation layer is a compound containing element F.

[0047] In this technical solution, the positive electrode material includes a three-layer structure, consisting of a core, an oxygen-absorbing layer and a passivation layer in sequence from inside to outside. Where, the metal element M and the non-metal element Q are introduced into the core to achieve the doping of positive and negative ions. The metal element M is doped into the core as a positive-valent ion, with a bond energy between the metal element M and element oxygen being greater than a bond energy between the transition-metal element and element oxygen, thus the metal element M can immobilize element oxygen in the core. The non-metal element Q is doped into the core as a negative-valent ion, where element boron, element phosphorus, element silicon, and element oxygen form a stable polyanion structure; and element fluorine replaces the lattice oxygen; and since the bond energy between the element fluorine and the transition-metal element is greater than the bond energy between the transition-metal element and oxygen element, the material is more stable.

[0048] Further, an oxygen-absorbing layer is arranged on an outer surface of the core, and is an unsaturated oxide containing the coating element L. The coating element L is selected from elements having multiple valence states and a tendency to valence change. 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 itself, and the valence state of the coating element L changes from low to high, which can effectively prevent the lattice oxygen from being oxidized to generate gaseous oxygen. The passivation layer includes a fluorine-containing compound, which can inhibit and slow down the corrosion kinetics of HF in the electrolyte toward the passivation layer, so that the passivation layer of the positive electrode material of the present disclosure exhibits better resistance to the electrolyte corrosion than ordinary oxide passivation layers.

[0049] The present disclosure can achieve the effect of inhibiting gaseous oxygen evolution by the functional design of different layered structures of the positive electrode material. Further, the above-mentioned positive electrode material is prepared by the following method.

[0050] S10: obtaining a precursor, a lithium source and a dopant, mixing them evenly, and performing a primary sintering under an oxygen atmosphere or an air atmosphere to obtain a first oxide.

[0051] S20: mixing the first oxide and a first coating agent, and performing a secondary sintering under a reducing atmosphere or an inert atmosphere to obtain a second oxide.

[0052] S30: mixing the second oxide and a second coating agent, and performing a tertiary sintering under the reducing atmosphere or the inert atmosphere to obtain a positive electrode material.

[0053] Where, 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 element F.

[0054] In this technical solution, the precursor, lithium source and dopant are subjected to the primary sintering to obtain the first oxide, i.e., the core. Further, the first oxide is mixed with the first coating agent for the secondary sintering to form an oxygen-absorbing layer on a surface of the core. And further, the second oxide is mixed with the second coating agent for the tertiary sintering to form the passivation layer on a surface of the oxygen-absorbing layer. Since the oxygen-absorbing layer is an unsaturated oxide, the atmosphere of the secondary sintering is the inert atmosphere or reducing atmosphere. Specifically, the reducing atmosphere may be composed of one or more of hydrogen, methane or carbon monoxide.

Example 1

[0055] This example provides a method for preparing a positive electrode material, including the following steps.

[0056] 1. NCM811 precursor, LiOH, AlF.sub.3, and H.sub.3BO.sub.4 are mixed in a molar ratio of 1:1.05:0.001:0.001, added into a high-speed mixer for blending, and subjected to a primary sintering under an oxygen atmosphere to obtain a first oxide.

[0057] Where, a speed for blending is 800 rpm/min and a duration for blending is 30 min.

[0058] The primary sintering has a sintering process as follows: heating to 860 C. at a rate of 15 C./min and then maintaining for 12 h.

[0059] 2. The first oxide is crushed and then mixed with CeO.sub.2 in a molar ratio of 1:0.005, and subjected to a secondary sintering under a hydrogen atmosphere to obtain a second oxide.

[0060] Where, the secondary sintering has a sintering process as follows: heating to 600 C. at a rate of 15 C./min and then maintaining for 10 h. The first oxide after being crushed has a particle size controlled at D50-3.5 m.

[0061] 3. The second oxide and AlF.sub.3 are mixed in a molar ratio of 1:0.005, and subjected to a tertiary sintering under a nitrogen atmosphere to obtain a positive electrode material.

[0062] Where, the tertiary sintering has a sintering process as follows: heating to 450 C. at a rate of 15 C./min and then maintaining for 10 h.

[0063] The positive electrode material prepared in this example has a single-crystal morphology, and its microscopic structure is shown in FIG. 1.

Example 2

[0064] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, with the difference of mixing NCM811 precursor, LiOH, LiF, Al.sub.2O.sub.3, and H.sub.3BO.sub.4 according to a molar ratio of 1:1.10:0.05:0.0005:0.001.

Example 3

[0065] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, with the difference of replacing CeO.sub.2 with V.sub.2O.sub.5.

Example 4

[0066] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, with the difference of replacing AlF.sub.3 with MgF.

Example 5

[0067] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, except that the primary sintering has a sintering process as follows: heating to 800 C. at a rate of 15 C./min and then maintaining for 12 h.

[0068] The positive electrode material obtained by the sintering in this example has a polycrystal morphology, as shown in FIG. 2 and FIG. 3, which are electron microscope images of the positive electrode material in this example at different magnifications.

Comparative Example 1

[0069] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, with the difference of replacing AlF.sub.3 with Al.sub.2O.sub.3 in step 1.

Comparative Example 2

[0070] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, with the difference of no addition of H.sub.3BO.sub.4.

Comparative Example 3

[0071] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, except that the secondary sintering is performed under an oxygen atmosphere.

Comparative Example 4

[0072] This example provides a method for preparing a positive electrode material. The specific steps are as shown in Example 1, with the difference of replacing AlF.sub.3 with Al.sub.2O.sub.3 in step 3.

[0073] Performance tests are conducted on the positive electrode materials prepared in the above-mentioned Examples 1-5 and Comparative examples 1-4. Each of the positive electrode materials of the Examples and Comparative examples is fabricated into a battery, and volume growth rates of different samples under a storage condition of 70 C. are tested.

[0074] The volume of gas expansion is calculated using a drainage method. Batteries with different degrees of gas expansion are placed into a water tank (a recharge process is required, and the tab should be well protected). Their drainage weights are measured using an electronic density tester, and then a volume conversion is performed to obtain the amount of volume expansion.

[0075] Specific steps are as follows: [0076] 1. Preparing a battery with each of the positive electrode materials of the Examples and Comparative Examples, protecting the tab of battery under a fully charged state, and slowly placing the battery into a 70 C. water tank; waiting for 30 s, then measuring the weight of water drained from the water tank, and dividing the weight by a medium density to obtain an initial volume V.sub.0 of the battery; [0077] 2. Drying the battery and placing it into an incubator for storage at a high temperature of 70 C. for 7 days; [0078] 3. Protecting the tab of battery well after high-temperature storage, and slowly placing the battery into the 70 C. water tank; waiting for 30 s, then measuring the weight of water drained from the water tank, and dividing the weight by the medium density to obtain a volume V.sub.7 of the battery; and calculating a volume growth rate at Day 7 by the formula: (V.sub.7V.sub.0)/V.sub.0100%; [0079] 4. After drying the battery, fully charging the battery at 4.35V and placing the battery into the incubator for storage at a high temperature of 70 C. for another 7 days; [0080] 5. Repeating steps 3-4 to obtain the volume growth rates under different days of high-temperature storage.

[0081] The volume growth rates of different samples under a storage condition of 70 C. are shown in Table 1. A line chart obtained by plotting the data in Table 1 is shown in FIG. 4.

TABLE-US-00001 TABLE 1 Day Day Day Day Day Day Day Day Sample 0 7 14 21 28 35 42 Example 1 0 0.7 7.3 12.5 15.3 20 28.1 Example 2 0 0.9 9.4 14.3 17.7 21 29.3 Example 3 0 1.1 11.3 15.7 18.5 21.8 30.5 Example 4 0 1.3 11.9 16.4 20.1 23.1 32.7 Example 5 0 1.5 13.7 17.8 23.6 25.6 34.8 Comparative 0 1.9 14.6 20.2 27.3 29.7 38.6 Example 1 Comparative 0 2.2 15.8 21.7 28.8 32.8 40.5 Example 2 Comparative 0 3.4 17.3 23.3 30.1 34.9 42.8 Example 3 Comparative 0 4.8 18.4 25.8 33.3 37.8 45.7 Example 4

[0082] The experimental results show the following.

[0083] In the comparison between Example 2 and Example 1, it is illustrated that the F-ion doping of the core can be achieved by replacing AlF.sub.3 with LiF and Al.sub.2O.sub.3.

[0084] In the comparison between Example 3 and Example 1, it is illustrated that V.sub.2O.sub.5 can also achieve the effect of an oxygen-absorbing layer.

[0085] In the comparison between Example 4 and Example 1, it is illustrated that MgF can replace AlF.sub.3.

[0086] In the comparison between Example 2 and Example 1, it is illustrated that polycrystal materials can also achieve performance improvement.

[0087] In the comparison between Comparative example 1 and Example 1, it is illustrated that addition of appropriate F ions into the core is beneficial for improving gas production performance.

[0088] In the comparison between Comparative example 2 and Example 1, it is illustrated that addition of appropriate B ions into the core is beneficial for improving gas production performance. In the comparison between Comparative example 3 and Example 1, it is illustrated that

[0089] sintering in an oxygen atmosphere causes element Ce to be in its highest valence state of Ce.sup.4+, resulting in failure of the oxygen-absorbing layer, which is not conducive to improving gas production performance.

[0090] In the comparison between Comparative example 4 and Example 1, it is illustrated that addition of appropriate F ions into the passivation layer is beneficial for suppressing electrolyte corrosion and reducing gas generation.

Example 6

[0091] This example provides a positive electrode material including a core, an oxygen-absorbing layer, and a passivation layer in sequence from inside to outside; where the core has a chemical formula of Li.sub.0.98Ni.sub.0.88Co.sub.0.1Mg.sub.0.02F.sub.0.012O.sub.1.988, and a particle size of 1 m-3 m; the oxygen-absorbing layer has a chemical formula of Ga.sub.3.6O.sub.1.1, and a thickness of 0.02 m; and the passivation layer has a chemical formula of Al.sub.0.67W.sub.0.33O.sub.1.72F.sub.0.28, and a thickness of 0.02 m.

Example 7

[0092] This example provides a positive electrode material including a core, an oxygen-absorbing layer, and a passivation layer in sequence from inside to outside; where the core has a chemical formula of Li.sub.1Ni.sub.0.5Mn.sub.0.4Al.sub.0.06B.sub.0.02F.sub.0.02O.sub.1.98, and a particle size of 5 m-8 m; the oxygen-absorbing layer has a chemical formula of Sn.sub.1.8O.sub.1.6, and a thickness of 0.04 m; and the passivation layer has a chemical formula of MgO.sub.1.92F.sub.0.08, and a thickness of 0.04 m.

Example 8

[0093] This example provides a positive electrode material, including a core, an oxygen-absorbing layer, and a passivation layer in sequence from inside to outside; where the core has a chemical formula of Li.sub.1.1Ni.sub.0.843Co.sub.0.05Mn.sub.0.1Mo.sub.0.005P.sub.0.002O.sub.2, and a particle size of 12 m-13 m; the oxygen-absorbing layer has a chemical formula of Bi.sub.0.9O.sub.1.2, and a thickness of 0.06 m; and the passivation layer has a chemical formula of Al.sub.1.32O.sub.1.94F.sub.0.06, and a thickness of 0.06 m.

Example 9

[0094] This example provides a positive electrode material, including a core, an oxygen-absorbing layer, and a passivation layer in sequence from inside to outside; where the core has a chemical formula of Li.sub.1.2Ni.sub.0.64Mn.sub.0.35Zr.sub.0.007Si.sub.0.003O.sub.2, and a particle size of 18 m-20 m; the oxygen-absorbing layer has a chemical formula of Pr.sub.1.1O.sub.1.8, and a thickness of 0.08 m; and the passivation layer has a chemical formula of Zr.sub.0.94O.sub.1.72F.sub.0.28, and a thickness of 0.08 m.

Example 10

[0095] This example provides a method for preparing a positive electrode material, which may be used for preparing the positive electrode material of any one of Examples 6-9, and the specific process thereof is as follows: [0096] 1. Obtaining respective raw materials according to the composition proportion of the target positive electrode material; [0097] 2. Mixing a precursor, a lithium source and a dopant evenly and performing a primary sintering under an oxygen atmosphere to obtain a first oxide, where the primary sintering has a temperature of 500 C. and a holding duration of 15 h; [0098] 3. Mixing the first oxide with a first coating agent, and performing a secondary sintering under a reducing atmosphere to obtain a second oxide, where the secondary sintering has a temperature of 600 C. and a holding duration of 8 h; [0099] 4. Mixing the second oxide with a second coating agent, and performing a tertiary sintering under an inert atmosphere to obtain a positive electrode material, where the tertiary sintering has a temperature of 600 C. and a holding duration of 8 h.

Example 11

[0100] This example provides a method for preparing a positive electrode material, which may be used for preparing the positive electrode material of any one of Examples 6-9, and the specific process thereof is as shown in Example 10, except that the primary sintering has a temperature of 1000 C., and a holding duration of 8 h.

Example 12

[0101] This example provides a method for preparing a positive electrode material, which may be used for preparing the positive electrode material of any one of Examples 6-9, and the specific process thereof is as shown in Example 10, except that the secondary sintering has a temperature of 300 C., and a holding duration of 15 h.

Example 13

[0102] This example provides a method for preparing a positive electrode material, which may be used for preparing the positive electrode material of any one of Examples 6-9, and the specific process thereof is as shown in Example 10, except that the tertiary sintering has a temperature of 300 C., and a holding duration of 15 h.

[0103] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned examples, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned examples, or make equivalent replacements for some of the technical features therein. However, such modifications or replacements do not make the essence of corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various examples of the present disclosure.