A battery and an electric device

Abstract

The present disclosure relates to the technical field of lithium ion batteries, and provides a battery and a power utilization device, wherein the battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode material, the positive electrode material comprises LiFeO2 particles, the surface elements of the LiFeO2 particles comprise Al, the mass content of Al elements in the positive electrode material is a%, the powder conductivity of the positive electrode material is b S / m, the length ratio of the long axis to the short axis of the LiFeO2 particles is c1, and the deviation rate of the long axis to the short axis is c=c1-1; wherein the relationship of a, b and c is a / (b×c), and the range of a / (b×c) is 0.01-0.3; the battery provided in the present application has excellent cycle performance and rate performance by controlling the range of a / (b×c).

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery technology, and more particularly to a battery and an electrical device. Background Technology

[0002] Lithium replenishment agents are key functional materials for lithium-ion batteries. They are used for pre-lithiation to compensate for the loss of active lithium during the first charge and discharge cycle, thereby significantly improving the battery's initial efficiency, energy density, and cycle life.

[0003] In the actual production and use of lithium-ion batteries, trace amounts of water and oxygen are inevitably introduced into the electrolyte. Lithium replenishment agent Li5FeO4, as a lithium-rich sacrificial material, releases active lithium ions through electrochemical delithiation during battery charging to achieve lithium replenishment. Its product after lithium replenishment is LiFeO2. However, lithium replenishment agent Li5FeO4 is prone to decomposition reaction under the action of water and / or oxygen in the electrolyte, resulting in a reduction in lithium replenishment effect. Summary of the Invention

[0004] The technical problem solved by this disclosure is to provide a battery with excellent cycle life and rate performance.

[0005] In view of this, this application provides a battery including a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material including LiFeO2 particles, the surface element of the LiFeO2 particles including Al, the mass content of Al element in the positive electrode material being a%, the powder conductivity of the positive electrode material being bS / m, the length ratio of the major axis to the minor axis of the LiFeO2 particles being c1, and the deviation rate between the major axis and the minor axis being c=c1-1;

[0006] The relationship between a, b, and c is a / (b×c), and the range of a / (b×c) is 0.01~0.3.

[0007] This application also provides an electrical device, including the battery described in the above-described scheme.

[0008] This disclosure provides a battery in which the positive electrode includes a positive electrode material. LiFeO2 particles, the product of the lithium replenisher Li5FeO4 after delithiation, are present in the positive electrode. The Al element on the surface of the LiFeO2 particles indirectly reflects that the surface of the lithium replenisher Li5FeO4 contains Al elements. The surface element Al of the LiFeO2 particles can reduce the decomposition reaction between the lithium replenisher and water and oxygen in the electrolyte, thus improving lithium replenishment performance. However, an excessively high Al mass content (a%) in the positive electrode material leads to increased surface resistivity, affecting rate performance. Simultaneously, controlling the powder conductivity (bS / m) of the positive electrode material can improve the battery's rate performance, but an excessively high powder conductivity (bS / m) on the positive electrode surface... Excessive electronic active sites can catalyze irreversible oxidative decomposition of the electrolyte, increasing gas production and affecting battery cycle life. Controlling the deviation rate c between the long and short axes of LiFeO2 particles reduces gas production and improves battery cycle life. Furthermore, by comprehensively regulating the range of a / (b×c) of the Al mass content (a%), the conductivity (bS / m) of the cathode material powder, and the deviation rate c between the long and short axes of LiFeO2 particles, both cycle life and rate performance are simultaneously improved. If the range of a / (b×c) is too large, the rate performance of the battery is poor; if the range of a / (b×c) is too small, the cycle life of the battery is poor. Attached Figure Description

[0009] Figure 1 The image shows a line scan of LiFeO2 particles obtained by field emission scanning electron microscopy (CP-SEM) combined with energy dispersive spectroscopy (EDS) in Example 1 of this disclosure.

[0010] Figure 2 This is a field emission scanning electron microscope (CP-SEM) image of LiFeO2 particles in Example 1 of this disclosure. Detailed Implementation

[0011] To further understand this disclosure, preferred embodiments of this disclosure are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this disclosure and are not intended to limit the scope of the claims of this disclosure.

[0012] Given the problem that the lithium replenishment effect of existing lithium replenishment agents is not significant, thus affecting the cycle life and rate performance of batteries, this disclosure provides a battery in which the lithium replenishment agent is Li5FeO4 with Al elements on its surface. After the lithium replenishment agent Li5FeO4 is delithiated, the product LiFeO2 remains in the positive electrode. The Al elements on its surface can effectively reduce the decomposition reaction of the lithium replenishment agent with water and oxygen in the electrolyte during use, thereby improving the lithium replenishment performance. However, if the Al mass content a% in the positive electrode material is too high, the surface resistivity will increase, affecting the rate performance. The rate performance of the battery can be improved by controlling the powder conductivity bS / m of the positive electrode material. If the powder conductivity bS / m is too high, the positive electrode material will have a high surface resistivity. Excessive active sites on the electrode surface can catalyze irreversible oxidative decomposition of the electrolyte, increasing gas production and affecting the battery's cycle life. Simultaneously, controlling the deviation rate (c) between the long and short axes of LiFeO2 particles reduces gas production in the cathode material, thereby improving battery cycle life. Furthermore, adjusting the range of a / (b×c) of the Al mass content (a%), the cathode material powder conductivity (bS / m), and the deviation rate (c) between the long and short axes of LiFeO2 particles achieves a simultaneous improvement in both cycle life and rate performance. If the range of a / (b×c) is too large, the battery's rate performance is poor; if the range of a / (b×c) is too small, the battery's cycle life is poor. Specifically, this disclosure provides a battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material comprising LiFeO2 particles, the surface element of the LiFeO2 particles comprising Al, the mass content of Al in the positive electrode material being a%, the powder conductivity of the positive electrode material being bS / m, the length ratio of the major axis to the minor axis of the LiFeO2 particles being c1, and the deviation rate between the major axis and the minor axis being c=c1-1;

[0013] The relationship between a, b, and c is a / (b×c), and the range of a / (b×c) is 0.01~0.3.

[0014] The battery disclosed herein includes a positive electrode sheet, which comprises a positive electrode material. The positive electrode material includes a lithium replenishing agent, which is Li5FeO4 with Al elements on its surface. In some specific embodiments, the Li5FeO4 surface has a coating layer containing Al elements. During battery use, after the lithium replenishing agent Li5FeO4 undergoes delithiation, LiFeO2 particles are generated and exist in the positive electrode material. The Al elements on the surface of the LiFeO2 particles indirectly reflect that the surface of the lithium replenishing agent Li5FeO4 contains Al elements. Al elements can effectively reduce the decomposition reaction of the lithium replenishing agent with water and oxygen in the electrolyte during use, improving lithium replenishment performance. However, excessive Al content in the positive electrode material leads to increased sheet resistance of the positive electrode sheet, affecting the battery's rate performance. In this disclosure, the mass content of Al elements in the positive electrode material... The content of Al is a%, where a ranges from 0.1% to 0.4%, indicating that the Al element on the surface of the LiFeO2 particles accounts for 0.1% to 0.4% of the mass of the cathode material. Specifically, a ranges from 0.2% to 0.3%. In some specific embodiments, the mass content of Al element in the cathode material is 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, and 0.39%.

[0015] In some specific embodiments, the surface elements of the LiFeO2 particles also include one or more of Ce, C, Zr, Ti, F, and S, which are doped in trace amounts with a content of <0.2%; that is, the coating layer on the surface of Li5FeO4 may also include one or more of the above elements. Among them, CeO2 is an ion-electron hybrid conductor, which is beneficial to charge transport and improves rate performance; the presence of C element in the above coating layer can reduce the contact between the lithium supplement and water and oxygen, reduce gas production, and C is beneficial to improve the conductivity of the cathode material, thereby improving the rate performance of the battery; the presence of F element in the coating layer optimizes ionic conductivity and structural stability, and improves cycle life.

[0016] In some specific embodiments, the LiFeO2 particles contain Al, indicating that the lithium supplement Li5FeO4 contains Al. The presence of Al is beneficial to the lattice stability of Li5FeO4, reducing the gas production of the cathode material and improving the cycle life of the battery. The Al content is 1% to 4% of the mass of the Li5FeO4 (LFO) particles. Content above 4% reduces LFO delithiation, resulting in poor lithium supplementation, deteriorated kinetics, and worsened cycle life. Content below 1% has a poor effect on gas production suppression. The LiFeO2 particles also contain one or more of Zr, P, and Ce; these elements can stabilize the lattice of the lithium supplement and improve the cycle life of the battery.

[0017] In some specific embodiments, the average particle size of the LiFeO2 particles is 3μm to 10μm, specifically 6μm to 10μm, more specifically 8μm to 9μm, and even more specifically, 8μm. The average particle size of the LiFeO2 particles affects the gas generation reaction between the lithium replenishing agent and the electrolyte, thereby affecting the cycle life of the battery.

[0018] In some specific embodiments, cracks exist on the surface and / or inside the LiFeO2 particles. The presence of cracks increases the risk of gas generation during the reaction of the lithium supplement with water. In this disclosure, the width of the cracks is 0.1 μm to 1.5 μm to reduce the risk of gas generation during the reaction of the lithium supplement with water, which is beneficial to ensuring the lithium supplementation effect. In some specific embodiments, the width of the cracks is 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, or 1.4 μm.

[0019] In some specific embodiments, the surface of the LiFeO2 particles has a carbon layer with a thickness of 5 nm to 20 nm; in some specific embodiments, the thickness of the carbon layer is 8 nm to 15 nm; in some specific embodiments, the thickness of the carbon layer is 10 nm to 13 nm. The carbon layer is beneficial for improving the conductivity of the cathode material. The outer surface of the carbon layer contains Al, or the carbon layer contains Al, or both the outer surface of the carbon layer and the carbon layer contain Al.

[0020] In this disclosure, the LiFeO2 particles are LiFeO2 particles with a coating layer, which includes a coating layer and LiFeO2 main particles, wherein the surface of the LiFeO2 particles is the coating layer, and the interior of the LiFeO2 particles is the LiFeO2 main particles (with LiFeO2 as the main structural framework); for example, the surface of the LiFeO2 particles includes Al elements, indicating that the coating layer of the LiFeO2 particles includes Al elements, and the interior of the LiFeO2 particles includes Al elements, indicating that the LiFeO2 main particles include Al elements.

[0021] In some specific embodiments, the major axis of the LiFeO2 particles is 6μm~10μm, and the minor axis is 4μm~8μm. In this disclosure, the major axis of the LiFeO2 particles represents the longest straight-line distance of the particle in a two-dimensional projection, and the minor axis represents the shortest straight-line distance perpendicular to the major axis in the same projection. According to the above definitions of major and minor axes, the size of the major axis in this disclosure should be greater than the size of the minor axis. In some specific embodiments, the major axis of the LiFeO2 particles is 7μm, 8μm, 9μm, or 10μm, and the minor axis is 5μm, 6μm, or 7μm. The ratio of the length of the major axis to the minor axis of the LiFeO2 particles is c1, and the deviation rate between the major axis and the minor axis is c = c1 - 1; the range of c is 0.1~0.8, specifically, the range of c is 0.2~0.4; in some specific embodiments, the value of c is 0.3, 0.5, 0.6, or 0.7. The control of c is used to reduce gas production and improve the cycle life of the battery.

[0022] In this disclosure, the powder conductivity of the positive electrode material is bS / m, where b ranges from 10 to 30. By controlling the powder conductivity of the positive electrode material, the rate performance of the battery can be improved. If the value of b is too high, there will be too many electronic active sites on the surface of the positive electrode, which will catalyze irreversible oxidative decomposition of the electrolyte, increase gas production, and affect the cycle life of the battery. Specifically, b ranges from 15 to 20; in some specific embodiments, b is 11, 12, 13, 14, 16, 17, 18, 19, 21, 22, 23, 24, 25, 26, 27, 28, or 29.

[0023] Furthermore, in this disclosure, the relationship between the mass content of Al element a% in the cathode material, the powder conductivity bS / m of the cathode material, and the deviation rate c between the long axis and short axis of LiFeO2 particles is controlled: a / (b×c), where a / (b×c) ranges from 0.01 to 0.3. The control of the above relationship is to improve the cycle life and rate performance of the battery. If a / (b×c) is too large, the rate performance of the battery is poor; if a / (b×c) is too small, the cycle life of the battery is poor. a / (b×c) is specifically 0.025~0.1; in some specific embodiments, a / (b×c) is 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29.

[0024] In this disclosure, the above-mentioned relationship is a calculation of the values ​​of a, b, and c, for example, calculated according to the specific values ​​provided in the embodiments, without including the units.

[0025] In this disclosure, the specific method for preparing the lithium supplement is as follows:

[0026] The lithium source and iron source are mixed and sintered in an inert atmosphere. After cooling, the intermediate product is obtained by crushing.

[0027] The intermediate product and additives were mixed and sintered again, and then cooled to obtain the initial positive electrode lithium replenishment material.

[0028] The initial positive electrode lithium replenishment material is placed in a CVD reaction chamber, and the aluminum source is vaporized and introduced into the reaction chamber to carry out a gas-solid phase chemical reaction, thereby obtaining a Li5FeO4 lithium replenishment agent whose surface coating layer includes Al elements.

[0029] In the above-mentioned lithium supplement preparation process, the lithium source may include at least one of an inorganic salt containing Li, a hydroxide containing Li, and an oxide containing Li; the iron source may include at least one of an inorganic salt containing Fe, a hydroxide containing Fe, and an oxide containing Fe; in some specific embodiments, the lithium source is selected from LiOH and Li₂O, and the iron source is selected from Fe₂O₃. The sintering temperature is 600℃~850℃, the sintering time is 12h~24h, and the sintering is carried out under an inert atmosphere, specifically, under a nitrogen atmosphere. During the preparation of the intermediate product, the deviation rate c is controlled by the sintering temperature and sintering time; the higher the sintering temperature and the longer the sintering time, the smaller c is, and vice versa.

[0030] In the step of obtaining the initial cathode lithium supplementation material, the additive is selected from one or more of artificial graphite, hard carbon, soft carbon, and silicon carbide. The re-sintering temperature is 500℃~800℃, and the time is 2h~12h. In some specific embodiments, the re-sintering temperature is 600℃~700℃, and the time is 4h~8h. The mass percentage of the additive is 2%~4% of the intermediate product. In some specific embodiments, the mass percentage of the additive is 2.5%~3.5% of the intermediate product. The sintering temperature and the mass percentage of the additive affect the powder conductivity bS / m of the cathode material. If the mass percentage of the additive is too high, it will cause carbon agglomeration and deterioration of bS / m, resulting in an excessively large b; if the sintering temperature is too high, it will deteriorate the LFO structure, resulting in an excessively large b. Therefore, in the disclosure, the sintering temperature and the mass percentage of the additive are controlled to ensure the powder conductivity bS / m of the cathode material.

[0031] In the step of obtaining the Li5FeO4 lithium supplement agent whose surface coating includes Al, the aluminum source includes one or both of trimethylaluminum and triisobutylaluminum. The vaporization temperature is 200℃~300℃, in some specific embodiments 220℃~270℃, and in some specific embodiments 240℃~260℃. The gas-solid phase chemical reaction temperature is 300℃~700℃, in some specific embodiments 350℃~650℃, in some specific embodiments 400℃~600℃, and in some specific embodiments 460℃~550℃. The gas-solid phase chemical reaction time is 2h~4h, and in some specific embodiments 2.5h~3.5h. The mass ratio of the initial positive electrode lithium replenishment material to the vaporized aluminum source is 1:0.005 to 1:0.015. In some specific embodiments, the mass ratio is 1:0.008 to 1:0.012. The flow rate of the initial positive electrode lithium replenishment material is 0.15 m / s to 0.4 m / s. In some specific embodiments, the flow rate is 0.2 m / s to 0.3 m / s. In the gas-solid phase chemical reaction, the mass ratio of the initial positive electrode lithium replenishment material to the vaporized aluminum source, the flow rate, and the time of the gas-solid phase chemical reaction jointly determine the thickness and uniformity of the Al2O3 film, which in turn affects the mass content a% of the surface element of the LiFeO2 particles. Specifically, the longer the gas-solid phase chemical reaction time, the greater the mass content a%, and the smaller the mass ratio of the initial positive electrode lithium replenishment material to the vaporized aluminum source, or the smaller the flow rate, the greater the mass content a%. In this disclosure, the range of the mass content a% is ensured by controlling the time of the gas-solid phase chemical reaction, the mass ratio of the initial positive electrode lithium replenishment material to the vaporized aluminum source, and the flow rate of the initial positive electrode lithium replenishment material.

[0032] In this disclosure, the positive electrode material of the positive electrode sheet includes a positive electrode active material, which includes lithium iron phosphate (LiFePO4) and lithium manganese iron phosphate (LiFePO4). 1-x Mn x PO4), lithium nickel cobalt manganese oxide (LiNi) x Co y Mn 1-x-yThe positive electrode active material is selected from one or more of lithium iron manganese phosphate (Li2O4), lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), and lithium nickel oxide (LiNiO2). Specifically, the positive electrode active material is selected from one or more of lithium iron manganese phosphate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel oxide. In some specific embodiments, the positive electrode active material is selected from lithium iron phosphate. In some specific embodiments, the surface of the positive electrode active material has a coating layer, which includes one or more of carbon, phosphate, magnesium oxide, aluminum oxide, and zirconium oxide. In some specific embodiments, the coating layer is selected from one of carbon, phosphate, magnesium oxide, aluminum oxide, and zirconium oxide. The above-mentioned coating layer suppresses the gas-generating side reaction between the positive electrode and the electrolyte, thereby improving the cycle life of the battery.

[0033] In this disclosure, the particle size Dv50 of the positive electrode material is 0.5 μm to 1.5 μm, specifically, 0.7 μm to 1.1 μm, and more specifically, 0.8 μm to 1.0 μm. The particle size Dv50 represents the particle size value corresponding to a cumulative volume distribution of 50% of the particles. The particle size of the positive electrode material affects the battery capacity and the oxidation-gas production reaction between the positive electrode and the electrolyte. A particle size within the aforementioned range is beneficial for improving battery capacity, reducing the oxidation-gas production reaction between the positive electrode and the electrolyte, and improving the battery's cycle life.

[0034] In this disclosure, the mass content of carbon in the cathode material affects the powder conductivity of the cathode material, thereby affecting the rate performance of the battery. The mass content of carbon in the cathode material is 1% to 2%, which is sufficient to ensure the powder conductivity of the cathode material, thus ensuring the rate performance of the battery. In some specific embodiments, the mass content of carbon in the cathode material is 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, or 1.9%.

[0035] In a battery, besides the positive electrode, there is also a negative electrode. The particle size of the negative electrode material affects the contact area between the negative electrode material and the electrolyte, thus affecting the amount of gas generated inside the battery and consequently its cycle life. In this disclosure, the particle size Dv50 of the negative electrode material is 11μm~14μm, specifically 12μm~13μm. The specific surface area of ​​the negative electrode material affects the amount of gas generated by the electrolyte on the negative electrode side, thus affecting the cycle life of the battery. In this disclosure, the specific surface area of ​​the negative electrode material is 1m². 2 / g~2m 2 / g, specifically, the specific surface area of ​​the negative electrode material is 1.1m². 2 / g, 1.2m 2 / g, 1.3m2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g. To improve battery capacity and reduce battery gas production, the negative electrode material includes a negative electrode active material, which includes natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, elemental silicon, and SiO2. x In some specific embodiments, the negative electrode active material is selected from one or more of silicon and carbon, including natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, elemental silicon, and SiO2. x One of silicon and carbon; the selection of the above-mentioned negative electrode active material is beneficial to improving the battery capacity, reducing the battery gas production, and thus improving the battery cycle life.

[0036] The battery also includes an electrolyte. In some specific embodiments, the electrolyte includes one or more of phosphate esters, sulfate esters, phosphites, nitrs, lithium bis(oxalato)borate, and fluorophosphates. Specifically, the electrolyte is selected from one of phosphate esters, sulfate esters, phosphites, nitrs, lithium bis(oxalato)borate, and fluorophosphates. The selection of the electrolyte can suppress the oxidation of the electrolyte by the positive electrode and improve the cycle life of the battery.

[0037] Furthermore, this disclosure also provides an electrical device that includes the battery described in the above-described scheme.

[0038] To further understand this disclosure, the battery provided in this disclosure will be described in detail below with reference to the embodiments. The scope of protection of this disclosure is not limited to the following embodiments.

[0039] Example 1

[0040] 1) Preparation of lithium supplement

[0041] According to the molar ratio of Li to Fe of 5.5:1 and the mass ratio of LiOH to Li2O of 3:7, Fe2O3, LiOH and Li2O were weighed, mixed and kept at 500℃ for 6h, and ball milled for 60min to obtain the precursor. The precursor was transferred to a sintering furnace, argon gas was introduced, and after the air in the furnace was exhausted, the temperature was raised to 800℃ and kept at 24h for sintering. After cooling, the intermediate product was obtained by air jet crushing.

[0042] Artificial graphite, an additive for forming a coating layer, was added to the intermediate product and sintered again in a nitrogen atmosphere at a temperature of 500°C for 4 hours. The mass of artificial graphite accounted for 3% of the mass of the intermediate product. After natural cooling, the initial positive electrode lithium replenishing agent LFO powder was obtained.

[0043] The initial positive electrode lithium supplement LFO powder was placed in a CVD reaction chamber with a fluidized bed to effectively disperse and fluidize the powder. Trimethylaluminum was vaporized at 240°C and introduced into the reaction chamber through nitrogen gas. A gas-solid phase chemical reaction occurred on the surface of the heated LFO powder, and an Al2O3 film was gradually deposited at 550°C for 2.5 h to obtain the lithium supplement. In this process, the mass ratio of the initial positive electrode lithium supplement LFO to the vaporized trimethylaluminum was 1:0.012, and the flow rate of the initial positive electrode lithium supplement LFO was 0.3 m / s.

[0044] 2) Preparation of positive electrode sheet:

[0045] Lithium iron phosphate (LFP) positive electrode active material, the lithium supplement agent prepared in step 1), conductive carbon black SP, polyvinylidene fluoride (PVDF) binder, and polyvinylpyrrolidone (PVP) were mixed in a mass ratio of 94.2:2.8:0.5:2:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until the system was homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on two opposing surfaces of the positive electrode current collector aluminum foil along its thickness direction. After drying at room temperature, it was transferred to an oven for further drying. Then, it was rolled to form a positive electrode active material layer on the aluminum foil. The foil was then cut to obtain a positive electrode sheet with an areal density of 395 g / m³. 2 The compacted density is 2.6 g / cm³. 3 ;

[0046] 3) Negative electrode preparation:

[0047] Artificial graphite was sand-milled for 30 minutes. The sand-milled artificial graphite, conductive carbon black (SP), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and binder (water-based polyacrylic acid (PAA) binder LA134D) were mixed at a mass ratio of 96.8:0.6:0.6:1:1. Deionized water was added, and the mixture was stirred under vacuum until homogeneous, yielding a negative electrode slurry. This negative electrode slurry was coated onto two opposing surfaces of a copper foil with a thickness of 112 μm. After air-drying at room temperature, it was transferred to an oven for further drying. Then, it was rolled to form a negative electrode active material layer on the copper foil. The coated material was then cut to obtain a negative electrode sheet with an areal density of 180 g / m³. 2 The compacted density is 1.6 g / cm³. 3 ;

[0048] 4) Preparation of electrolyte

[0049] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 1:1:2 to obtain an organic solvent. Fully dried lithium hexafluorophosphate (LiPF6) was then dissolved in the organic solvent and allowed to stand in a refrigerator for 0.5 hours. Ethylene carbonate (VC) and fluoroethylene carbonate (FEC) were then added to the resulting mixed solution to obtain an electrolyte with a LiPF6 concentration of 1 mol / L. The mass percentages of VC and FEC added were 0.5% of the total mass of the mixed solution.

[0050] 5) Preparation of the separating membrane

[0051] 9μm PE was selected as the base membrane, with a porosity of 40%. A 2μm thick adhesive layer was set on one side of the base membrane, and a 3μm thick coating and a 2μm thick adhesive layer were set on the other side. That is, the membrane specification is 2+9+3+2 (adhesive layer + base membrane + coating + adhesive layer, μm).

[0052] 6) Assembly and formation

[0053] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0054] Example 2

[0055] The preparation method of the lithium replenishing agent is basically the same as that in Example 1, except that: in the step of obtaining the intermediate product, the sintering temperature is 750℃ and the sintering time is 18h; in the step of obtaining the initial positive electrode lithium replenishing material, the mass ratio of artificial graphite is 2.5% and the sintering temperature is 550℃; in the step of obtaining the Li5FeO4 lithium replenishing agent with Al element in the surface coating layer, the mass ratio of the initial positive electrode lithium replenishing agent LFO to the gasified trimethylaluminum is 1:0.014, the flow rate of the initial positive electrode lithium replenishing agent LFO is 0.3m / s, and the gas-solidification chemical reaction time is 3h.

[0056] The mass content of Al in the cathode material (a%), the powder conductivity of the cathode material (bS / m), and the deviation rate of the long axis and short axis of LiFeO2 particles (c) were detected. The results are shown in Table 1.

[0057] The performance of the lithium-ion battery prepared in this embodiment was tested, and the results are shown in Table 1.

[0058] Example 3

[0059] The preparation method of the lithium replenishing agent is basically the same as that in Example 1, except that: in the step of obtaining the intermediate product, the sintering temperature is 700℃ and the sintering time is 16h; in the step of obtaining the initial positive electrode lithium replenishing material, the mass ratio of artificial graphite is 2.8% and the sintering temperature is 550℃; in the step of obtaining the Li5FeO4 lithium replenishing agent with Al element in the surface coating layer, the mass ratio of the initial positive electrode lithium replenishing agent LFO to the gasified trimethylaluminum is 1:0.008, the flow rate of the initial positive electrode lithium replenishing agent LFO is 0.3m / s, and the gas-solidification chemical reaction time is 3h.

[0060] The mass content of Al in the cathode material (a%), the powder conductivity of the cathode material (bS / m), and the deviation rate of the long axis and short axis of LiFeO2 particles (c) were detected. The results are shown in Table 1.

[0061] The performance of the lithium-ion battery prepared in this embodiment was tested, and the results are shown in Table 1.

[0062] Example 4

[0063] The preparation method of the lithium replenishing agent is basically the same as that in Example 1, except that: in the step of obtaining the intermediate product, the sintering temperature is 800℃ and the sintering time is 24h; in the step of obtaining the initial positive electrode lithium replenishing material, the mass ratio of artificial graphite is 4% and the sintering temperature is 700℃; in the step of obtaining the Li5FeO4 lithium replenishing agent with Al element in the surface coating layer, the mass ratio of the initial positive electrode lithium replenishing agent LFO to the gasified trimethylaluminum is 1:0.015, the flow rate of the initial positive electrode lithium replenishing agent LFO is 0.2m / s, and the gas-solidification chemical reaction time is 4h.

[0064] The mass content of Al in the cathode material (a%), the powder conductivity of the cathode material (bS / m), and the deviation rate of the long axis and short axis of LiFeO2 particles (c) were detected. The results are shown in Table 1.

[0065] The performance of the lithium-ion battery prepared in this embodiment was tested, and the results are shown in Table 1.

[0066] Example 5

[0067] The preparation method of the lithium replenishing agent is basically the same as that in Example 1, except that: in the step of obtaining the intermediate product, the sintering temperature is 800℃ and the sintering time is 24h; in the step of obtaining the initial positive electrode lithium replenishing material, the mass ratio of artificial graphite is 3% and the sintering temperature is 620℃; in the step of obtaining the Li5FeO4 lithium replenishing agent with Al element in the surface coating layer, the mass ratio of the initial positive electrode lithium replenishing agent LFO to the gasified trimethylaluminum is 1:0.012, the flow rate of the initial positive electrode lithium replenishing agent LFO is 0.3m / s, and the gas-solidification chemical reaction time is 2.5h.

[0068] The mass content of Al in the cathode material (a%), the powder conductivity of the cathode material (bS / m), and the deviation rate of the long axis and short axis of LiFeO2 particles (c) were detected. The results are shown in Table 1.

[0069] The performance of the lithium-ion battery prepared in this embodiment was tested, and the results are shown in Table 1.

[0070] Example 6

[0071] The preparation method of the lithium replenishing agent is basically the same as that in Example 1, except that: in the step of obtaining the intermediate product, the sintering temperature is 700℃ and the sintering time is 24h; in the step of obtaining the initial positive electrode lithium replenishing material, the mass ratio of artificial graphite is 3% and the sintering temperature is 650℃; in the step of obtaining the Li5FeO4 lithium replenishing agent with Al element in the surface coating layer, the mass ratio of the initial positive electrode lithium replenishing agent LFO to the gasified trimethylaluminum is 1:0.018, the flow rate of the initial positive electrode lithium replenishing agent LFO is 0.4m / s, and the gas-solidification chemical reaction time is 5h.

[0072] The mass content of Al in the cathode material (a%), the powder conductivity of the cathode material (bS / m), and the deviation rate of the long axis and short axis of LiFeO2 particles (c) were detected. The results are shown in Table 1.

[0073] The performance of the lithium-ion battery prepared in this comparative example was tested, and the results are shown in Table 1.

[0074] Comparative Example 1

[0075] The preparation method of the lithium replenishing agent is basically the same as that in Example 1, except that: in the step of obtaining the intermediate product, the sintering temperature is 650℃ and the sintering time is 18h; in the step of obtaining the initial positive electrode lithium replenishing material, the mass ratio of artificial graphite is 1% and the sintering temperature is 600℃; in the step of obtaining the Li5FeO4 lithium replenishing agent with Al element in the surface coating layer, the mass ratio of the initial positive electrode lithium replenishing agent LFO to the gasified trimethylaluminum is 1:0.02, the flow rate of the initial positive electrode lithium replenishing agent LFO is 0.1m / s, and the gas-solidification chemical reaction time is 4h.

[0076] The mass content of Al in the cathode material (a%), the powder conductivity of the cathode material (bS / m), and the deviation rate of the long axis and short axis of LiFeO2 particles (c) were detected. The results are shown in Table 1.

[0077] The performance of the lithium-ion battery prepared in this comparative example was tested, and the results are shown in Table 1.

[0078] Comparative Example 2

[0079] The preparation method of the lithium replenishing agent is basically the same as that in Example 1, except that: in the step of obtaining the intermediate product, the sintering temperature is 750℃ and the sintering time is 24h; in the step of obtaining the initial positive electrode lithium replenishing material, the mass ratio of artificial graphite is 3% and the sintering temperature is 650℃; in the step of obtaining the Li5FeO4 lithium replenishing agent with Al element in the surface coating layer, the mass ratio of the initial positive electrode lithium replenishing agent LFO to the gasified trimethylaluminum is 1:0.004, the flow rate of the initial positive electrode lithium replenishing agent LFO is 1m / s, and the gas-solidification chemical reaction time is 0.5h.

[0080] The mass content of Al in the cathode material (a%), the powder conductivity of the cathode material (bS / m), and the deviation rate of the long axis and short axis of LiFeO2 particles (c) were detected. The results are shown in Table 1.

[0081] The performance of the lithium-ion battery prepared in this comparative example was tested, and the results are shown in Table 1.

[0082] The lithium-ion battery obtained above was characterized, and the specific process is as follows:

[0083] a) Perform initial treatment on the lithium-ion battery obtained above, take the positive electrode sheet for CP testing, and perform Al characterization by EDS line scan:

[0084] Preliminary treatment: The lithium-ion battery was discharged to the lower limit voltage of 2.5V at 0.33C. The positive electrode sheets in the central and edge regions were taken in the empty state and immersed in dimethyl carbonate (DMC) solution at room temperature for 4 hours. After immersion, the electrode sheets were removed and dried in a vacuum environment. A layer of conductive adhesive was first applied to the sample holder, and the sample was attached to the sample holder. CP argon ion polishing and slicing were performed, and a conductive film was deposited. The tools and sample stage were wiped with anhydrous ethanol, and a certain amount of the sample to be tested was placed on the sample stage.

[0085] The sample was observed under a scanning electron microscope (SEM). Three regions were randomly selected from the sample. Ten positive electrode lithium supplement particles of different diameters were taken from each region. Ten small particles of different diameters were taken from each positive electrode lithium supplement particle for EDS spot and line scanning to determine the surface elements of LiFeO2 and the variation trend of elements from the outside to the inside. Figure 1 As shown, the field emission scanning electron microscope (CP-SEM) combined with energy dispersive spectroscopy (EDS) line scanning technology was used to characterize LiFeO2 particles. The distribution characteristics of Al element (Al Kα-characteristic spectral line) along a specified path (approximately 8 μm in length) of the LiFeO2 particles were quantitatively characterized. From the EDS line scanning curve, it can be seen that Al element exhibits a non-uniform gradient distribution characteristic on the sample cross section: the Al element signal intensity in the sample surface area is significantly higher than that in the internal matrix, indicating that there is obvious Al element enrichment in the sample surface layer.

[0086] b) Deviation rate of the major and minor axes of LiFeO2 particles; c) Characterization of surface crack length:

[0087] Sample processing: Discharge the battery at 0.33C to the lower limit voltage of 2.5V. Take the positive electrode sheets from the central region and the edge region in the empty state, respectively, and soak them in dimethyl carbonate (DMC) solution at room temperature for 4 hours. After soaking, remove the electrode sheets and dry them in a vacuum environment. Use a ceramic knife to scrape off the active material powder on the surface of the electrode sheets to obtain the sample.

[0088] First, apply a layer of conductive adhesive to the sample holder, then attach the sample to the sample holder. Perform CP argon ion polishing and sectioning, then deposit a conductive film. Wipe the tools and sample stage with anhydrous ethanol. Place a certain amount of the sample to be tested on the sample stage. Observe the sample to be tested using a scanning electron microscope (SEM) at a magnification of 5KX. Select three areas for photography. Take 5-10 positive electrode lithium supplement particles from each area according to different diameter ranges of large particles, measure the long axis / short axis lengths, and take the average value. Figure 2 As shown, Figure 2 Here is a CP-SEM image of the LiFeO2 particles in Example 1, based on... Figure 2 It can be seen that stress cracks appear on both the surface and inside of the LiFeO2 particles. Figure 2 (The yellow arrow in the right figure indicates a crack); measure the crack width and take the average value of 0.12 μm;

[0089] c) Characterization of the powder conductivity bS / m of the cathode material:

[0090] Pretreatment: The battery was discharged at 0.33C to the lower limit voltage of 2.5V. The electrode of the lithium-ion battery in the empty state was taken and soaked in dimethyl carbonate (DMC) solution at room temperature for 4 hours. After soaking, the electrode was taken out and dried in a vacuum environment. The powder on the surface of the electrode was scraped off with a ceramic knife. The scraped powder was gently ground with a mortar and pestle to remove the lumps in the powder. The powder was collected for testing.

[0091] Test: The collected powder samples were placed into the sample cell of the YK22-FT-300II powder conductivity meter to test the conductivity. The powder conductivity was obtained, and the results are shown in Table 1.

[0092] d) Characterization of Al mass content a% in the cathode material:

[0093] Pretreatment: Discharge the battery to the lower limit voltage of 2.5V at 0.33C, disassemble the empty lithium-ion battery, disassemble the lithium-ion battery to obtain the electrode sheets, immerse the positive or negative electrode sheets in DMC (dimethyl carbonate) at room temperature for 60 minutes, take them out, and air dry them at room temperature with humidity ≤15%; scrape off the positive electrode material from the surface of the positive electrode sheet;

[0094] Accurately weigh 0.2g of positive electrode material powder, disperse it in 20ml of water, add 10ml of nitric acid, mix well, and heat to dissolve the positive electrode material powder. Then, dilute the powder with water to 100mL to obtain the test solution. Perform ICP testing on the test solution. Before the test, a standard solution needs to be prepared. The linear correlation coefficient of the standard concentration should be above 0.999 to be used as a normal standard. Dilute the 1000mg / L standard solution with deionized water to different concentrations (generally 0, 1mg / 100mL, 2mg / 100mL, 3mg / 100mL), and select the element detection wavelength. Set the experimental conditions: According to the characteristics of the sample and the element to be detected, set the appropriate ICP instrument working conditions: gas flow rate 0.5L / min, power 1150W, and select element detection wavelengths such as Li 610.365nm, Fe 259.940nm, etc. The content of elements in the sample can be read by the self-analysis function of the ICP test software. The results are shown in Table 1.

[0095] e) Average particle size of LiFeO2 particles:

[0096] Sample preparation: The battery was discharged to 2.5V at 0.33C. Positive electrode sheets from the central and edge regions in the empty state were taken and immersed in dimethyl carbonate (DMC) solution at room temperature for 4 hours. After immersion, the electrode sheets were removed and dried in a vacuum environment. The active material powder on the surface of the electrode sheets was scraped off with a ceramic knife to obtain the sample. A layer of conductive adhesive was first applied to the sample holder, and the sample was adhered to the sample holder. CP argon ion polishing and slicing were performed, followed by the deposition of a conductive film. The tools and sample stage were wiped with anhydrous ethanol, and a certain amount of the sample to be tested was placed on the sample stage. The sample to be tested was observed using a scanning electron microscope (SEM) at a magnification of 5KX. Three regions were selected for photography, and 5-10 positive electrode lithium supplement particles were taken from each region according to different particle diameter ranges. The results showed that the average particle size of LiFeO2 particles was 8μm-9μm.

[0097] f) Thickness of the carbon layer:

[0098] The battery was discharged at 0.33C to the lower limit voltage of 2.5V. Positive electrode sheets from the central and edge regions in their empty state were taken and immersed in dimethyl carbonate (DMC) solution at room temperature for 4 hours. After immersion, the electrodes were removed and dried in a vacuum environment. Active material powder was scraped off the surface of the electrodes with a ceramic knife to obtain the sample. The carbon-coated LFO sample was characterized using transmission electron microscopy (TEM) at 200 kV. The sample was ultrasonically dispersed in ethanol and then drop-coated onto an ultrathin carbon film copper mesh. After natural drying, it was tested. The morphology of the carbon layer at the particle edge was observed under high-magnification TEM (400kx~600kx). The carbon layer thickness was vertically measured using DigitalMicrograph software. Statistical analysis was performed on at least 50 points, yielding an average carbon layer thickness of 10~11 nm.

[0099] g) Particle size Dv50 of the cathode material:

[0100] The particle size distribution of the sample was tested using a laser particle size analyzer. Water was used as the dispersion medium, and the sample was ultrasonically dispersed for 3 min. The particle size distribution was determined based on the Mie scattering theory to obtain D10, D50, D90 and the particle size distribution span. The Dv50 of the cathode material in Example 1 was found to be 0.9 μm to 1.0 μm.

[0101] h) Particle size Dv50 of the negative electrode material:

[0102] The particle size distribution of the sample was tested using a laser particle size analyzer. Water was used as the dispersion medium and the sample was ultrasonically dispersed for 3 min. The particle size distribution was determined based on the Mie scattering theory to obtain D10, D50, D90 and the particle size distribution span. The particle size Dv50 of the negative electrode material in Example 1 was found to be 12 μm to 13 μm.

[0103] 8) The lithium-ion batteries prepared above were subjected to performance tests, as detailed below:

[0104] a) DCR (DC internal resistance, characterizing rate performance) testing:

[0105] a1) The prepared lithium-ion battery was placed at room temperature (25°C) and left to stand for 4 hours until thermal equilibrium was reached.

[0106] a2) Perform 3 standard cycles at a current of 1 / 3C; record the standard capacity C of the battery. The standard cycle steps are: charge the lithium-ion battery at a constant current of 0.33C to the upper limit voltage of 3.65V, charge it at a constant voltage to 0.05C, and then discharge it at a constant current of 0.33C to the lower limit voltage of 2.5V to obtain the standard capacity C.

[0107] a3) Charge the battery to 50% SOC at a 1 / 3C discharge rate;

[0108] a4) Let it stand for 2 hours, record the voltage at the end of the standing period as U1, discharge at 1C rate for 18 seconds, record the starting current as I and the ending voltage as U2. Calculate the DC internal resistance R according to the formula R=(U2-U1) / I. The results are shown in Table 1.

[0109] b) Testing for capacity retention (characterizing battery cycle life):

[0110] b1) At 60℃, the lithium-ion battery is charged at a constant current of 0.33C to the upper limit voltage of 3.65V, charged at a constant voltage to the 0.05C cutoff charge, and discharged at a constant current of 0.33C to the lower limit voltage of 2.5V. The above steps are repeated for a total of 3 charge and discharge cycles to obtain the discharge capacity Q1 of the third charge and discharge cycle, which is taken as the fixed capacity. Then, the battery is charged at a constant current of 1C at a set rate to the upper limit voltage of 3.65V, charged at a constant voltage to the cutoff current of 0.05C, and then discharged at a set rate of 1C at a lower limit voltage of 2.5V. This is one cycle, and the cycle is repeated 600 times to obtain the discharge capacity Q2 of the battery in the 600th cycle. The capacity retention rate is Q2 / Q1*100%, and the results are shown in Table 1.

[0111] The Al mass content (a%), powder conductivity (b), and deviation rate (c) of the long and short axes of LiFeO2 particles in the cathode material were detected according to the method in Example 1. The results are shown in Table 1.

[0112] The performance of the lithium-ion battery prepared in this example was tested according to the method in Example 1, and the results are shown in Table 1.

[0113] Table 1. Relevant parameters and performance data for the examples and comparative examples.

[0114]

[0115] As shown in Table 1, in Examples 1 to 6, the value of a / (b×c) is within the range, and the battery has excellent cycle life and DCR, with a capacity retention rate ≥85% and DCR ≤410mΩ. Among them, Example 1 has the best cycle life and DCR, with a capacity retention rate of 95% and a DCR of 300mΩ. In Comparative Examples 1 and 2, the value of a / (b×c) is not within the range, and the cycle life and DCR are poor.

[0116] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this disclosure. It should be noted that those skilled in the art can make several improvements and modifications to this disclosure without departing from the principles of this disclosure, and these improvements and modifications also fall within the protection scope of the claims of this disclosure.

[0117] The above description of the disclosed embodiments enables those skilled in the art to make or use this disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A battery, characterized in that, The cathode material includes a positive electrode sheet, which in turn includes a positive electrode material. The positive electrode material includes LiFeO2 particles, and the surface element of the LiFeO2 particles includes Al. The mass content of Al in the positive electrode material is a%, the powder conductivity of the positive electrode material is bS / m, the ratio of the length of the major axis to the minor axis of the LiFeO2 particles is c1, and the deviation rate between the major axis and the minor axis is c=c1-1. The relationship between a, b, and c is a / (b×c), and the range of a / (b×c) is 0.01~0.

3.

2. The battery according to claim 1, characterized in that, The surface elements of the LiFeO2 particles also include one or more of Ce, C, Zr, Ti, F, and S.

3. The battery according to claim 1 or 2, characterized in that, The interior of the LiFeO2 particles contains the element Al.

4. The battery according to claim 3, characterized in that, The interior of the LiFeO2 particles also includes one or more of the elements Zr, P, and Ce.

5. The battery according to claim 1 or 4, characterized in that, The average particle size of the LiFeO2 particles is 3μm~10μm.

6. The battery according to claim 1, characterized in that, The range of a is 0.1 to 0.

4.

7. The battery according to claim 1 or 6, characterized in that, The range of b is 10 to 30.

8. The battery according to claim 7, characterized in that, The range of c is 0.1 to 0.

8.

9. The battery according to claim 5, characterized in that, The surface of the LiFeO2 particles has a carbon layer with a thickness of 5 nm to 20 nm.

10. The battery according to claim 1, characterized in that, The LiFeO2 particles have a major axis dimension of 6μm~10μm and a minor axis dimension of 4μm~8μm.

11. The battery according to claim 1, characterized in that, The LiFeO2 particles have cracks, and the width of the cracks is 0.1 μm to 1.5 μm.

12. The battery according to claim 1, characterized in that, The cathode material includes a cathode active material, which includes one or more of lithium manganese iron phosphate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel oxide.

13. The battery according to claim 1 or 12, characterized in that, The particle size Dv50 of the cathode material is 0.5μm~1.5μm.

14. The battery according to claim 12, characterized in that, The surface of the positive electrode active material has a coating layer, which includes one or more of carbon, phosphate, magnesium oxide, aluminum oxide and zirconium oxide.

15. The battery according to claim 1 or 14, characterized in that, The carbon content in the cathode material is 1% to 2% by mass.

16. The battery according to claim 1, 2, 4, 6, 8, 9, 10, 11, 12 or 14, characterized in that, The particle size Dv50 of the negative electrode material of the battery is 11μm~14μm.

17. The battery according to claim 16, characterized in that, The specific surface area of ​​the negative electrode material of the battery is 1m². 2 / g~2m 2 / g.

18. The battery according to claim 1 or 17, characterized in that, The negative electrode material of the battery includes negative electrode active materials, which include natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, elemental silicon, and SiO2. x And one or more of silicon and carbon.

19. The battery according to claim 18, characterized in that, The electrolyte of the battery includes one or more of the following: phosphate ester, sulfate ester, phosphite ester, nitrile, lithium bis(oxalato)borate, and fluorophosphate ester.

20. An electrical device comprising the battery as described in any one of claims 1 to 19.

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