High-stability positive electrode lithium supplement agent, preparation method thereof, lithium ion battery and positive electrode plate of lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a high-stability positive lithium supplement agent, a preparation method thereof, a lithium ion battery and a lithium ion battery positive pole piece. The lithium supplement agent innovatively adopts a core-shell structure design, Li2O1-x (F2) x is taken as a core, and high lithium supplement capacity is provided by utilizing the characteristics of the Li2O1-x (F2) x; the shell is a spinel type Co3-yAlyO4 composite material and has a mesoporous structure, so that the conductivity and the structural stability are improved, and the lithium ion transmission efficiency is improved. The preparation process is realized through a solvothermal method, the effect of uniform dispersion can be achieved, and high crystallinity can be obtained. Compared with an unmodified traditional binary positive electrode lithium supplement agent Li2O, the high-stability positive electrode lithium supplement agent Li2O1-x (F2) x (at) Co3-yAlyO4 prepared by the invention has the advantages that the air stability and the lithium supplement efficiency can be effectively improved, and the cycling stability of a lithium ion battery is further enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a high-stability cathode lithium supplement agent, a preparation method thereof, a lithium-ion battery, and a lithium-ion battery cathode electrode sheet. Background Art

[0002] With the growth of the demand for high-energy-density lithium-ion batteries, cathode lithium supplement agents, as key materials for compensating for lithium loss in the first cycle, have attracted much attention. Li2O and the like are considered candidates for cathode lithium supplement agents. Li2O has the characteristics of low cost, high safety, good compatibility with polar solvents (such as NMP), and high theoretical capacity. However, due to its poor conductivity and low electrochemical activity, it has significant defects in practical applications: on the one hand, the highly active lithium component is prone to side reactions with the electrolyte, resulting in gas generation and swelling and an increase in interfacial impedance; on the other hand, the structure of the material collapses severely during long cycling, especially the capacity decay accelerates under low-temperature or high-rate conditions. In addition, most of the existing core-shell structure lithium supplement agents use a single metal oxide coating layer (such as CoO2), which has insufficient electronic conductivity and is difficult to effectively inhibit the irreversible dissolution of lithium ions, resulting in a sharp decline in the lithium supplement efficiency with the increase in the number of cycles. Summary of the Invention

[0003] To solve the problems of the prior art, the present invention provides a high-stability cathode lithium supplement agent, a preparation method thereof, a lithium-ion battery, and a lithium-ion battery cathode electrode sheet.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] In view of the above problems, the present invention develops a new type of lithium supplement agent with both high capacity, long-cycle stability, and wide-temperature-range adaptability. By introducing Li2O 1-x (F2) x composite core, the lithium storage density and the reversibility of the interfacial reaction can be synergistically improved; while the design of the Co 3-y Al y O4 composite material shell utilizes the doping effect of Al to reduce the oxidation state of Co, enhance the overall conductivity of the material, and at the same time its porous structure provides a fast channel for lithium-ion diffusion. Thus, the balance between lithium supplement capacity and structural stability is achieved at the molecular scale, providing key technical support for the development of high-safe and long-life lithium-ion batteries.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present application provides a high-stability cathode lithium supplement agent. Its core is Li2O 1-x (F2) x , and the shell is Co 3-y Al yO4 composite material, and Co 3-y Al y The O4 composite material shell has a mesoporous structure with a pore size of 3 - 20 nm.

[0008] Preferably, for the Li2O 1-x (F2) x In the core, the value range of x is 0.1 ≤ x ≤ 0.3. The high stability of the Li - F bond is used to inhibit lithium loss. At the same time, Li2O 1-x (F2) x The core provides a high specific capacity of > 700 mAh / g.

[0009] Preferably, for the Co 3-y Al y In the CoAlO4 composite material shell, Al 3+ completely or partially replaces the crystal lattice site of Co 3+ where the value range of y is 0.1 ≤ y < 1. Al doping reduces the oxidation state of Co to improve electronic conductivity. The Co 3-y Al y O4 composite material shell has a mesoporous structure with a pore size of 3 - 20 nm, accelerating lithium ion transport.

[0010] Preferably, the mass ratio of the core - shell structure is: the core Li2O 1-X (F2) x accounts for 65 wt% - 75 wt%, and the shell Co 3-y Al y O4 accounts for 25 wt% - 35 wt%.

[0011] Preferably, the particle size of the lithium supplement agent shows a monodisperse distribution and D50 is 100 - 200 nm.

[0012] Preferably, the first - de - lithium efficiency of the lithium supplement agent at 0.2C > 90%.

[0013] In the second aspect, the present application provides a method for preparing a high - stability cathode lithium supplement agent, including:

[0014] S1. Dissolve the lithium source and fluorine source in a specific solvent, and perform a solvothermal reaction at 180 - 220 °C for 6 - 12 hours to generate the Li2O 1-X (F2) x core;

[0015] S2. Add cobalt salt and aluminum salt to the reaction system, adjust the pH to 8 - 10, continue the solvothermal reaction for 12 - 24 hours, and capture the residual lithium during heating to form a fast - ion conductor layer, forming the Co 3-y Al y O4 composite material shell, and remove the solvent;

[0016] S3. Perform gradient annealing treatment in an Ar / H2 atmosphere. First, heat it to 300 °C at a rate of 2 °C / min and hold for 2 h, then heat it to 600 °C at a rate of 5 °C / min and hold for 5 h. Naturally cool to room temperature to obtain the final Li2O 1-X (F2) x @Co 3-y Al y O4 composite material.

[0017] Furthermore, in the step S1, the lithium source is one or a mixture of lithium hydroxide, lithium carbonate, lithium oxide, lithium peroxide, lithium nitrate, lithium sulfate, lithium citrate, lithium oxalate, lithium ethoxide.

[0018] Furthermore, in the step S1, the fluorine source is one or a mixture of ammonium fluoride, ammonium bifluoride, sodium fluoride.

[0019] Furthermore, in the step S2, the cobalt salt is one or a mixture of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt carbonate, ammonium cobalt nitrate, cobalt acetate, cobalt fluoride.

[0020] Furthermore, in the step S2, the aluminum salt is one or a mixture of aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum acetate, aluminum fluoride, aluminum isopropoxide, aluminum acetylacetonate.

[0021] Furthermore, the solvothermal method includes a lithium source, a fluorine source, a cobalt salt, an aluminum salt and a solvent. After the reaction, the solvent is removed to obtain the cathode lithium supplement composite material with a core-shell structure.

[0022] In the present invention, the solvent exemplarily includes any one or a combination of two or more of N-methylpyrrolidone, ethanol, ethylene glycol, isopropanol, N,N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide or acetone, etc. As long as the solvent used can dissolve the above materials, the present invention does not limit this.

[0023] In the present invention, the method for removing the solvent exemplarily includes drying treatment. The drying treatment method includes vacuum drying treatment or spray drying treatment. The temperature of the spray drying treatment is 60 - 150 °C, and the gas is dry air or an inert atmosphere.

[0024] In a third aspect, the present invention provides a cathode pole piece, which includes a cathode lithium supplement agent, a cathode active material, N-methylpyrrolidone and a current collector. The lithium supplement agent includes the cathode lithium supplement composite material with a core-shell structure according to the first aspect.

[0025] Preferably, the mass percentage content of the lithium supplement agent is 1 wt% - 5 wt%. By regulating the mass percentage of the lithium supplement agent, the secondary battery prepared has a longer cycle life.

[0026] Preferably, the compaction density of the positive electrode sheet > 3.0 g / cm 3 .

[0027] In a fourth aspect, the present invention provides a high-stability lithium-ion battery, which includes a positive electrode, a negative electrode, and an electrolyte, and the positive electrode includes the positive electrode according to the third aspect.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention provides a positive electrode lithium supplement composite material with a core-shell structure. On the one hand, the present invention dopes F into the positive electrode lithium supplement material Li2O, uses the high stability of the Li-F bond to inhibit lithium loss, improves the structural stability of Li2O, and performs Co-Al-O coating treatment. Finally, a coating layer with good chemical stability can be formed on the surface of the positive electrode lithium supplement material, thereby preventing water molecules and corrosive substances from directly contacting the positive electrode lithium supplement material, and improving the chemical stability and electrochemical stability of the positive electrode lithium supplement composite material. Compared with the traditional solid-phase method coating, it is thinner and more uniform, so the conductivity is higher. Specifically, the positive electrode lithium supplement composite material with a core-shell structure provided by the present invention has more excellent cycle stability after being placed for 10 days compared with the uncoated positive electrode lithium supplement material. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more obvious.

[0031] Figure 1 SEM diagram of the Li2O 1-X (F2) x @Co 3-y Al y O4 lithium supplement composite material in Example 1;

[0032] Figure 2 Comparison chart of the full battery capacity retention rates of the positive electrode lithium supplement composite materials provided by Example 1, Example 2, and Comparative Example 1 in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following further describes the present invention in detail through examples. The examples are only used to illustrate the present invention and do not limit the scope of the present invention.

[0034] The present invention focuses on a high-stability positive electrode lithium supplement agent and its preparation method. The lithium supplement agent innovatively adopts a core-shell structure design with Li2O 1-x (F2) xAs the core, its characteristics are utilized to provide a high lithium supplement capacity; the shell is a spinel-type Co 3-y Al y O4 composite material with a mesoporous structure, which improves electrical conductivity, structural stability, and lithium ion transport efficiency. The preparation process is realized by the solvothermal method, which can achieve a uniform dispersion effect and obtain high crystallinity. The high-stability cathode lithium supplement agent Li2O 1-x (F2) x @Co 3-y Al y O4 prepared by the present invention can effectively improve air stability and lithium supplement efficiency compared with the unmodified traditional binary cathode lithium supplement agent Li2O, thereby enhancing the cycle stability of lithium ion batteries.

[0035] A high-stability cathode lithium supplement agent, with the core being Li2O 1-X (F2) x and the shell being a spinel-type Co 3-y Al y O4, having a mesoporous structure.

[0036] In the Li2O 1-X (F2) x core, the value range of x is 0.1 ≤ x ≤ 0.3; in the Co 3-y Al y O4 shell, Al 3+ partially replaces the crystal lattice site of Co 3+ , where the value range of y is 0.01 ≤ y < 1.

[0037] The mass ratio of the core-shell structure is: the core Li2O 1-x (F2) x accounts for 60wt% - 75wt%, and the shell Co 3-y Al y O4 accounts for 25wt% - 40wt%, and the shell has a mesoporous structure with a pore size of 3 - 20nm.

[0038] The high-stability cathode lithium supplement agent has a specific capacity > 700mAh / g (0.2C, 2.8 - 4.4V), and the initial de-lithiation efficiency ≥ 90%.

[0039] The high-stability cathode lithium supplement agent has a monodisperse particle size distribution and a D50 of 100 - 200nm.

[0040] A lithium ion battery cathode plate includes the high-stability cathode lithium supplement agent described in claims 1 - 5, and also includes a cathode active material, N-methylpyrrolidone, and a current collector. The mass ratio of the lithium supplement agent is 1wt% - 10wt%.

[0041] The positive electrode plate of the lithium-ion battery, the compaction density of the positive electrode plate of the lithium-ion battery ≥ 3.0 g / cm 3 .

[0042] The preparation method of the high-stability positive electrode lithium supplement agent includes the following steps:

[0043] S1. Prepare Li2O 1-X (F2) x core matrix material;

[0044] S2. Further coat the surface of the Li2O 1-X (F2) x core matrix material with metal oxide Co 3- y Al y O4 through solvothermal method, and capture residual lithium during the heating process to form a fast ion conductor layer, obtaining a pre-coated matrix;

[0045] S3. Place the pre-coated matrix in a tube furnace for gradient annealing treatment.

[0046] A lithium-ion battery, which is assembled by a positive electrode plate, a high-capacity graphite-doped silicon negative electrode plate, an electrolyte, and a separator.

[0047] Example 1

[0048] S1. Weigh lithium acetate (LiCH3COO) and ammonium fluoride (NH4F) according to the molar ratio of Li:F = 1:0.5, dissolve them in a mixed solvent of ethylene glycol - isopropyl alcohol (volume ratio 3:1), and the total solvent volume is 70% of the reaction kettle volume. Transfer the mixture to a stainless steel reaction kettle with a polytetrafluoroethylene lining, seal it and place it in a forced-air drying oven. Heat it to 190 °C at a rate of 3 °C / min and keep it at a constant temperature for 6 hours to generate Li2O 1-X (F2) x nanocrystalline nuclei.

[0049] After the reaction, naturally cool it to below 60 °C, open the kettle and centrifuge (8000 rpm, 10 minutes) to collect the precipitate. Wash it 3 times with absolute ethanol, ultrasonically disperse it for 5 minutes each time to remove residual organic matter and ions. After drying, obtain white Li2O 1-x (F2) x powder.

[0050] S2. Take the Li2O obtained in S1 1-x (F2) xThe powder was redispersed in a mixed solvent of ethylene glycol - isopropyl alcohol (volume ratio 3:1), and ultrasonic treatment was carried out for 30 minutes to form a uniform suspension. Cobalt nitrate (Co(NO3)2·6H2O) and aluminum sulfate (Al2(SO4)3·18H2O) were added in a molar ratio of Co:Al = 1:1.2, stirred for 2 hours, the pH was adjusted to 9, and stirring was continued for 30 minutes to uniformly adsorb metal ions.

[0051] The mixed solution was transferred to a reaction kettle and reacted at 190 °C for 12 hours to form a core - shell structure of Li2O 1-x (F2) x @Co 3-y Al y O4. The product was separated by centrifugation and washed with absolute ethanol. After drying, the precursor powder was obtained.

[0052] S3. The precursor powder was placed in a tubular furnace, and a mixed gas of Ar / H2 (95:5) (flow rate 50 sccm) was introduced and pre - purged for 30 minutes. First - stage annealing: heated to 300 °C at a rate of 2 °C / min and held for 2 hours to promote the decomposition of organic matter and the densification of the structure. Second - stage annealing: heated to 600 °C at a rate of 5 °C / min and held for 5 hours to induce the conversion of the Co 3-y Al y O4 shell into a spinel - type oxide. It was naturally cooled to room temperature to obtain the final Li2O 1-x (F2) x @Co 3-y Al y O4 composite material.

[0053] The cathode lithium - supplementing composite material with a core - shell structure and mesoporous structure in the shell prepared in this example is as Figure 1 shown.

[0054] Example 2

[0055] The difference between this example and Example 1 is that the prepared Li2O 1-X (F2) x powder was not subjected to coating treatment.

[0056] Comparative Example

[0057] This comparative example provides a Li2O cathode lithium - supplementing material without coating treatment.

[0058] The cathode lithium - supplementing materials provided in the examples and the comparative example were divided into two groups. One group was directly assembled into batteries as follows, and the other group of lithium - supplementing agent powders were stored in air with an environmental humidity of 40% for 10 days and then assembled into batteries and tested for performance.

[0059] Button cell assembly:

[0060] The above positive electrode lithium supplement materials are respectively mixed with Super P and PVDF according to a mass ratio of 80:10:10, and then dispersed in NMP solvent to obtain a positive electrode slurry. The slurry is coated on an aluminum foil current collector at a surface density of 2 mg / cm2, dried, rolled, and punched to obtain a positive electrode sheet. A button cell case, the positive electrode sheet, a PE separator, and a lithium metal sheet are stacked in sequence, and after adding electrolyte dropwise, a button cell is obtained. Among them, the electrolyte includes a solvent and a lithium salt. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide with a concentration of 1 mol / L, and the solvent is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate with a volume ratio of 1:1:1.

[0061] Button cell test:

[0062] At 25 °C, the button cell is charged and discharged at a charge-discharge rate of 0.2C within a cut-off voltage range of 2.8 - 4.4V. Record the charging capacity and the first-cycle discharge capacity of the battery. The first-cycle irreversible capacity of the battery is obtained by subtracting the first-cycle discharge capacity from the first-cycle charging capacity. The first-cycle efficiency = first-cycle discharge specific capacity / first-cycle charging specific capacity × 100%. The test results are shown in Table 1, and Table 1 shows the button cell test data of the fresh lithium supplement agent and the lithium supplement agent stored in air for 10 days.

[0063]

[0064] Table 1

[0065] It can be seen from Table 1 that the positive electrode lithium supplement materials prepared in Example 1 and Example 2 of the present invention still have a relatively high first-cycle charging specific capacity after being left standing in air with an environmental humidity of 40% for 10 days. It shows that by doping an appropriate amount of F element, the crystal structure of Li2O changes, thereby inhibiting its decomposition in air and significantly improving its air stability and having excellent storage capacity. By coating a Co - Al - O shell, a coating layer with good chemical stability can be formed on the surface of the positive electrode lithium supplement agent material, improving the electronic conductivity of the lithium supplement agent, preventing water molecules and electrolyte from directly contacting the positive electrode lithium supplement agent material, and improving the stability of the positive electrode lithium supplement composite material. In the comparative example, Li2O is extremely easy to react with air and is rapidly decomposed, resulting in a sharp drop in the actual specific capacity and seriously affecting its lithium supplement performance.

[0066] Full cell assembly:

[0067] Preparation of the positive electrode sheet: The above positive electrode lithium supplement materials, the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, the conductive agent Super P, and the binder PVDF are mixed according to a mass ratio of 5:89:3:3, and then dispersed in NMP solvent to obtain a positive electrode slurry. The slurry is at 16 mg / cm 2The single-sided areal density is coated on the aluminum foil current collector, dried, punched, and rolled to obtain the positive electrode sheet.

[0068] Preparation of the negative electrode sheet: A high-capacity graphite-silicon-doped negative electrode, conductive agent Super P, binder CMC, and dispersant SBR are mixed in a mass ratio of 94.6:1.4:1.55:2.45, and then dispersed in deionized water to obtain a negative electrode slurry. The slurry is coated on a carbon-coated copper foil current collector at a single-sided areal density of 8 mg / cm2, dried, punched, and rolled to obtain the negative electrode sheet;

[0069] Assembly of the lithium-ion battery: After stacking the positive electrode sheet, PE separator, and negative electrode sheet in a laminated manner, the battery cell is placed in an aluminum-plastic film packaging bag, injected with electrolyte, and sealed to obtain the lithium-ion battery;

[0070] Full battery test:

[0071] The following performance tests are carried out on the fully assembled battery above:

[0072] Formation first-cycle Coulombic efficiency: At 45 °C, the full battery is charged and discharged within a cut-off voltage range of 2.8 - 4.4 V, and the first-cycle charge specific capacity and first-cycle discharge specific capacity of the battery are recorded. The first-cycle efficiency = first-cycle discharge specific capacity / first-cycle charge specific capacity × 100%.

[0073] Capacity retention rate: At 25 °C, the full battery is charged and discharged cyclically at a charge-discharge rate of 0.5C within a cut-off voltage range of 2.8 - 4.4 V, and the capacity retention rate of the battery after 100 cycles is recorded. The test results are shown in Table 2.

[0074] According to the data in Table 2, when the fresh lithium supplement agent is added to the NCM811 positive electrode sheet at an addition amount of 5% and paired with a high-capacity graphite-silicon-doped negative electrode, the first-cycle charge specific capacity of the full battery of the comparative example of the present invention is slightly higher than that of Example 1 and Example 2, indicating that after modifying and coating Li2O, a part of the lithium supplement capacity will be lost. The 100-cycle capacity retention rate of Example 1 at 0.2C is higher, indicating that Li2O after doping and coating 1-x (F2) x @Co 3-y Al y O4 composite material added to the NCM811 full battery has more excellent cycle stability. After adding the lithium supplement agent stored in the air for 10 days to the NCM811 positive electrode at the same ratio, significant differences in the first-cycle charge specific capacity and 100-cycle capacity retention rate of the full batteries of Example 1-2 and the comparative example occurred. And by Figure 2It can be seen that the 100-cycle capacity retention rate of the full battery is significantly improved after the powder is placed for 10 days, which proves that the cathode lithium supplement composite material provided by the present invention has strong structural stability and good environmental stability. It can be seen from this that the present invention synthesizes and coats the cathode lithium supplement agent material by the solvothermal method, which has more advantages in stability in air, and then adds it to the battery system, so that the obtained lithium-ion battery has better cycling performance. Table 2 shows the full battery test data of the fresh lithium supplement agent and the lithium supplement agent stored in air for 10 days.

[0075]

[0076] Table 2

[0077] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0078] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cathode lithium supplement with high stability, characterized in that The core is Li2O 1-X (F2) x , and the shell is spinel-type Co 3- y Al y O4, with a mesoporous structure.

2. The high-stability cathode lithium supplement agent according to claim 1, wherein The Li2O described 1-X (F2) x The value range of x in the core is 0.1 ≤ x ≤ 0.3; the Co described 3-y Al y In the Al2O4 shell, Al 3+ Partially replaces the crystal lattice sites of Co 3+ where the value range of y is 0.01 ≤ y < 1.

3. The high-stability cathode lithium supplement agent according to claim 1, wherein The mass ratio of the core-shell structure is: the core is Li2O 1-x (F2) x with a proportion of 60 wt% to 75 wt%, and the shell is Co 3-y Al y O4 with a proportion of 25 wt% to 40 wt%, and the shell has a mesoporous structure with a pore size of 3 to 20 nm.

4. The high-stability cathode lithium supplement agent according to claim 1 has a specific capacity > 700 mAh / g and an initial de-lithiation efficiency ≥ 90%.

5. The high-stability cathode lithium supplement agent according to claim 1, wherein: The particle size shows a monodisperse distribution and the D50 is 100 - 200 nm.

6. A positive electrode sheet of a lithium-ion battery, characterized in that: It contains the high-stability cathode lithium supplement agent described in claims 1 - 5, and also includes a cathode active material, N-methylpyrrolidone, and a current collector, and the mass ratio of the lithium supplement agent is 1 wt% - 10 wt%.

7. The positive electrode sheet of the lithium-ion battery according to claim 6, characterized in that: The compaction density of the positive electrode plate of the lithium-ion battery is ≥ 3.0 g / cm 3 .

8. A method for preparing a cathode lithium supplement with high stability according to any one of claims 1-5, characterized in that, It includes the following steps: S1. Prepare Li2O by solvothermal method 1-X (F2) x Inner core matrix material S2. On Li2O 1-X (F2) x The surface of the core matrix material is further coated with metal oxides Co 3-y Al y O4 by solvothermal method, and residual lithium is captured during the heating process to form a fast ion conductor layer, obtaining a pre-coated matrix; S3. Place the pre-coated matrix in a tube furnace for gradient annealing treatment.

9. A lithium-ion battery, characterized in that, The lithium-ion battery is assembled from a cathode electrode sheet, a high-capacity graphite-silicon-doped anode electrode sheet, an electrolyte, and a separator.

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