Battery and electric device

Abstract

The invention discloses a battery and a power utilization device, and belongs to the technical field of secondary batteries. The battery comprises a positive plate, the positive plate comprises a positive current collector and a positive active material layer, the positive active material layer comprises a positive active material and a lithium supplement agent, and the lithium supplement agent comprises an iron-containing lithium supplement agent; the ratio (set as a) of the characteristic peak area of Fe < 3 + > to the peak area of O1s in the hollow electric state in the XPS spectrum of the positive plate, the ratio (set as b) of the negative electrode discharge capacity to the positive electrode discharge capacity of the battery and the discharge curve end potential (set as cV) of the negative plate are adjusted, so that a * b * c is controlled within a suitable range, the gram capacity of the positive plate can be effectively improved, and the battery performance is improved. And meanwhile, the cycle performance of the battery is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a battery and a power utilization device. BACKGROUND

[0002] Lithium ion batteries have been widely used in electric vehicles, medical devices, consumer electronics, aerospace, etc. due to their high energy density, long cycle life, no memory effect, low self-discharge rate, good charge-discharge capability and low self-discharge.

[0003] At present, the existing batteries have the problem that high capacity and long cycle life are difficult to be balanced. For example, the existing technology usually introduces a positive electrode lithium supplement agent (such as Li5FeO4) into the positive electrode sheet to improve the cycle performance of the battery. However, the introduction of the positive electrode lithium supplement agent makes the positive electrode sheet have poor conductivity, the charge transfer is hindered, and the battery capacity is attenuated.

[0004] Therefore, it is necessary to provide a technical solution to solve the above problems. SUMMARY

[0005] Based on the defects of the prior art, the purpose of the present application is to provide a battery and a power utilization device.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: The first aspect of the present application provides a battery, comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprises a positive electrode current collector, at least one side surface of the positive electrode current collector is provided with a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material and a lithium supplement agent, and the lithium supplement agent comprises an iron-containing lithium supplement agent; In the XPS spectrum of the positive electrode sheet, the ratio of the characteristic peak area of Fe 3+ to the peak area of O1s under empty state is a, the unit of the peak area is CPS.eV, and the XPS spectrum of the positive electrode sheet refers to the XPS spectrum measured after etching the positive electrode active material layer to a depth of 210nm; The ratio of the negative electrode discharge capacity to the positive electrode discharge capacity of the battery measured at 0.33C rate is set as b, and the unit of the negative electrode discharge capacity and the unit of the positive electrode discharge capacity are both mAh; The end potential of the discharge curve of the negative electrode sheet is cV, and the end potential of the discharge curve of the negative electrode sheet refers to the voltage corresponding to the end in the negative electrode discharge curve obtained when the battery is discharged to the lower limit voltage; The battery satisfies: 0.11≤a×b×c≤1.

[0007] The second aspect of the present application provides a power utilization device, comprising the battery provided by the first aspect of the present application.

[0008] Compared with the prior art, the beneficial effects of this application are as follows: The battery provided in this application includes a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material includes a lithium supplement agent, which includes an iron-containing lithium supplement agent. This application adjusts the Fe content in the XPS spectrum of the positive electrode sheet... 3+ The ratio of the characteristic peak area to the peak area of ​​O1s (set as a), the ratio of the negative electrode discharge capacity to the positive electrode discharge capacity measured at a rate of 0.33C (set as b), and the potential at the end of the discharge curve of the negative electrode (set as cV) are used to control a×b×c within an appropriate range, which can effectively improve the battery capacity while ensuring the battery's cycle performance. Detailed Implementation

[0009] To better illustrate the purpose, technical solution, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application.

[0010] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0011] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0012] In the description of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0013] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0014] In this application, the terms "battery", "lithium battery" and "lithium-ion battery" have the same meaning and refer to lithium-ion batteries, which typically include electrode components (such as positive electrode plates, negative electrode plates and separators), a container (such as a housing) that houses the electrode components, and an electrolyte.

[0015] The first aspect of this application provides a battery including a positive electrode sheet, the positive electrode sheet including a positive current collector, a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer including a positive active material and a lithium supplement agent, the lithium supplement agent including an iron-containing lithium supplement agent; In the XPS spectrum of the positive electrode, Fe in the uncharged state 3+ The ratio of the characteristic peak area to the peak area of ​​O1s is a, and the unit of the peak area is CPS.eV. The XPS spectrum of the positive electrode refers to the XPS spectrum measured after the positive electrode active material layer is etched to a depth of 210nm. The ratio of the negative electrode discharge capacity to the positive electrode discharge capacity measured at a rate of 0.33C is set as b, and the units of the negative electrode discharge capacity and the positive electrode discharge capacity are both mAh. The discharge curve end potential of the negative electrode is cV. The discharge curve end potential of the negative electrode refers to the voltage corresponding to the end of the negative electrode discharge curve obtained by discharging the battery to the lower limit voltage. The battery satisfies: 0.11≤a×b×c≤1.

[0016] The inventors discovered through research that in iron-containing lithium supplements (such as Li4FeO4), Fe is in the +4 oxidation state. During the lithium supplementation process, some Fe... 4+ Converted to Fe 3+ Release Li + And oxygen, thereby achieving lithium replenishment. This application will show Fe in the XPS spectrum of the said positive electrode. 3+ The ratio of the characteristic peak area to the O1s peak area is set as a, where Fe 3+The characteristic peaks are located at 710.5–711.5 eV, and the O1s peak is located at 530–531 eV. The O1s peak refers to the oxygen element peak. In XPS analysis, choosing O element as the benchmark to calculate the M / O ratio has the main advantage of effectively eliminating systematic errors of the instrument and sample through the role of "internal standard", thereby improving the reliability and repeatability of data analysis.

[0017] This ratio 'a' is related to the lithium supplement content in the positive electrode. This application controls the Fe content... 3+ The ratio 'a' of the characteristic peak area to the peak area of ​​O1s replenishes the active lithium consumed during charging, discharging, and cycling, improving battery cycle performance while avoiding impact on battery capacity. This application selects the Fe content measured after etching the positive electrode active material layer to a depth of 210 nm. 3+ The ratio 'a' of the characteristic peak area to the peak area of ​​O1s is mainly considered in light of the presence of an interface protective film on the surface of the positive electrode active material layer. By controlling the etching depth of the positive electrode active material layer to 210 nm, the detected 'a' can better reflect the content of lithium replenishing agent in the positive electrode active material layer.

[0018] The inventors discovered through research that the end potential of the discharge curve of the negative electrode sheet can be used to reflect the delithiation depth of the negative electrode material in the negative electrode sheet at the end of discharge. The greater the delithiation depth, the more thorough the delithiation of the negative electrode material. By adjusting the end potential of the discharge curve of the negative electrode sheet, the degree of delithiation of the negative electrode material can be improved, thereby increasing the battery capacity.

[0019] This application modifies the Fe content in the XPS spectrum of the positive electrode. 3+ The ratio of the characteristic peak area to the peak area of ​​O1s (set as a), the ratio of the negative electrode discharge capacity to the positive electrode discharge capacity (set as b), and the potential at the end of the discharge curve of the negative electrode (set as c) are used to control a×b×c within an appropriate range, which can effectively improve the specific capacity of the positive electrode, thereby improving the battery capacity, while ensuring the cycle performance of the battery.

[0020] This application relates to Fe 3+ The method for adjusting the ratio of the characteristic peak area to the peak area of ​​O1s (set as a) is not limited. Specifically, the ratio a can be controlled by changing the mass ratio of the lithium supplement to the positive electrode active material. The mass ratio of the lithium supplement to the positive electrode active material is (0.5~8):100.

[0021] This application does not limit the means of adjusting the negative electrode potential c. Specifically, it can be adjusted by changing the particle size of the positive electrode active material, the particle size of the negative electrode active material, the content of the positive electrode active lithium supplement, the amount of carbon coating on the surface of the lithium supplement, and the particle size of the negative electrode.

[0022] This application does not limit the means of adjusting b. Specifically, b can be controlled by comprehensively adjusting the selection of positive electrode active material, the particle size of positive electrode active material, the type and content of doping elements in positive electrode active material, etc.

[0023] By introducing iron-containing lithium supplements, such as Li5FeO, into the positive electrode active material layer, these supplements undergo an irreversible oxidation reaction during the first charge of the battery, releasing lithium ions and electrons to compensate for the active lithium ions consumed during processes such as SEI film formation, thus improving the battery's cycle performance. However, after the addition of iron-containing lithium supplements, their electronic conductivity is typically low (e.g., the room temperature conductivity of Li5FeO4 is approximately 10). -6 ~10 -8 S / cm), due to its transition metal ions (such as Fe) 3+ The 3d electron localization of lithium ions makes it difficult to form effective electron migration pathways. Furthermore, some iron-containing lithium supplements have wide band gaps (e.g., the band gap of Li5FeO4 is >3 eV), resulting in extremely low thermally excited carrier concentrations and difficulty in electron conduction. Additionally, the narrow or tortuous lithium-ion diffusion channels in the crystal structure of some iron-containing lithium supplements (e.g., the high energy barrier of lithium sites in layered or spinel structures) lead to... + Low mobility (diffusion coefficient < 10) -12 cm 2 The factors mentioned above all affect the transport of lithium ions and electrons, resulting in a decrease in battery capacity. By adjusting the capacity ratio of the negative electrode and the positive electrode, the positive electrode can fully utilize its capacity; by adjusting the discharge curve end potential of the negative electrode, the voltage window of the negative electrode can be widened, prompting more lithium ions to be extracted and inserted back into the positive electrode, thereby increasing battery capacity. This application achieves a balance between battery capacity by controlling the ratio of the negative electrode discharge capacity to the positive electrode discharge capacity, as well as the discharge curve end potential of the negative electrode.

[0024] For example, a×b×c can be 0.11, 0.12, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two sets of values.

[0025] In some implementations, the battery satisfies: 0.4 ≤ a ≤ 1. For example, a can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two sets of values ​​therein.

[0026] In some implementations, the battery satisfies: 1 ≤ b ≤ 1.2. For example, b can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, or a range consisting of any two sets of values.

[0027] In some implementations, the battery satisfies: 0.2V ≤ cV ≤ 1V. For example, c can be 0.2V, 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1V, or a range of any two sets of values ​​therein.

[0028] In some embodiments, the battery satisfies the condition: 0.5 ≤ a × b × c ≤ 0.9. When a × b × c is in the range of 0.5 to 0.9, the overall performance of the battery is better.

[0029] In some embodiments, the battery satisfies the following conditions: 0.6 ≤ a ≤ 0.9, 1.05 ≤ b ≤ 1.18, and 0.6V ≤ cV ≤ 0.9V. When the battery meets these conditions, its overall performance is better.

[0030] In some embodiments, the particle size Dn50 of the lithium replenishing agent is 0.5 to 30 μm.

[0031] Research has shown that by controlling the particle size of the lithium replenishing agent, it can be more evenly dispersed in the positive electrode active material layer, better replenishing the active lithium consumed during the charging and discharging process, improving the lithium replenishment effect, enhancing the cycle performance of the battery, and at the same time avoiding the introduction of the lithium replenishing agent from having a significant impact on the conductivity of the positive electrode sheet.

[0032] In some embodiments, at least a portion of the lithium replenishing agent has a first coating layer on its particle surface, the first coating layer being a carbon coating layer, and the thickness of the first coating layer being 10–100 nm.

[0033] For example, the thickness of the first carbon coating layer can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or any two of these values.

[0034] This application reduces side reactions between the electrolyte and the lithium replenishing agent by setting a first coating layer on the surface of the lithium replenishing agent particles, thereby improving the cycle performance of the battery.

[0035] In some embodiments, the preparation method of the iron-containing lithium supplement includes, but is not limited to, the following steps: According to the stoichiometric ratio in the general chemical formula of the iron-containing lithium supplement, the lithium source and iron source are added and mixed in batches and multiple times. After multiple sintering treatments, the mixture is crushed, then a carbon source is added and coated and sintered. After demagnetization, the iron-containing lithium supplement is obtained. The lithium source includes at least one of lithium hydroxide and lithium oxide; the iron source includes at least one of iron hydroxide and ferric oxide; and the carbon source includes at least one of glucose, sucrose, and graphite. The sintering temperature is not lower than 600℃, and more preferably, the sintering temperature is 700-1000℃, and the sintering time is 10-15h; after adding the carbon source, the coating sintering temperature is not higher than 200℃, specifically 120-200℃.

[0036] It should be noted that the particle size of the iron-containing lithium supplement can be adjusted by regulating the number of sintering processes and the temperature and time of each sintering process.

[0037] In some embodiments, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and ternary materials, wherein the ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0038] In some embodiments, the ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet is 0.001 to 0.15 (μm·g) / mAh.

[0039] For example, the ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet can be 0.001 (μm·g) / mAh, 0.002 (μm·g) / mAh, 0.003 (μm·g) / mAh, 0.004 (μm·g) / mAh, 0.005 (μm·g) / mAh, 0.006 (μm·g) / mAh, 0.007 (μm·g) / mAh, 0.008 (μm·g) / mAh, 0.009 (μm·g) / mAh, 0.01 (μm·g) / mAh, or 0.02 (μm·g) / mA. h, 0.03(μm·g) / mAh, 0.04(μm·g) / mAh, 0.05(μm·g) / mAh, 0.06(μm·g) / mAh, 0.07(μm·g) / mAh, 0.08(μm·g) / mAh, 0.09(μm·g) / mAh, 0.1(μm·g) / mAh, 0.11(μm·g) / mAh, 0.12(μm·g) / mAh, 0.13(μm·g) / mAh, 0.14(μm·g) / mAh, 0.15(μm·g) / mAh, or a range consisting of any two of these values.

[0040] Research has revealed two main issues. First, when this ratio is too small, although the specific capacity of the cathode sheet is improved, resulting in better lithium replenishment, the particle size (Dn50) of the cathode active material is too small, leading to an increase in the specific surface area of ​​the cathode and thus an increase in side reactions between the cathode and the electrolyte. Second, when this ratio is too large, the lithium replenishment effect is poor, the specific capacity of the cathode sheet is low, and the particle size (Dn50) of the cathode active material is too large. This results in inconsistent diffusion rates between the lithium replenishing agent and Li within the cathode active material, which can lead to... + Lithium buildup on particle surfaces can lead to localized over-lithiation (even forming inert layers like Li2CO3), while the interior of the particles remains lithium-deficient, thus reducing the utilization rate of the lithium replenishment agent. This application addresses this by controlling the ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet, thereby balancing lithium replenishment performance, improving cycle performance, and maintaining battery capacity. On the one hand, this ratio should not be too small. Although the specific capacity of the positive electrode sheet is improved, which can achieve a better lithium replenishment effect, if the particle size Dn50 of the positive electrode active material is too small, it will easily increase the specific surface area with the positive electrode, resulting in an increase in side reactions with the electrolyte. On the other hand, this ratio should not be too large. On the one hand, the lithium replenishment effect will be poor and the specific capacity of the positive electrode will be low. On the other hand, if the particle size D50 of the positive electrode active material is too large, the diffusion rate of the lithium replenishing agent and Li in the positive electrode active material will be inconsistent. This will lead to the accumulation of Li on the particle surface, which may cause local over-lithiation on the particle surface (or even the formation of inert layers such as Li2CO3), while the inside of the particle is still deficient in lithium, thereby reducing the utilization rate of the lithium replenishing agent.

[0041] In some embodiments, the positive electrode active material comprises lithium iron phosphate, which contains doping elements, including at least one selected from Co, Mg, Zn, Ca, Ti, V, Ni, and Cr. By introducing the above-mentioned doping elements into the lithium iron phosphate, the conductivity of the positive electrode can be improved, and the influence of lithium supplementation agents on the conductivity of the positive electrode can be reduced.

[0042] The lithium iron phosphate (LFP) is a positive electrode active material with an olivine-type crystal structure, possessing advantages such as low cost and high safety. The general chemical formula of lithium iron phosphate can be LiFe. 1-x M x PO4, where x≤0.1, M is a dopant element with a mass content of 100ppm~10000ppm.

[0043] In some embodiments, when the positive electrode active material comprises lithium iron phosphate, the ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet is 0.005 to 0.012 (μm·g) / mAh. For batteries with lithium iron phosphate as the positive electrode active material, a ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet in the range of 0.005 to 0.012 (μm·g) / mAh results in better overall battery performance.

[0044] In some embodiments, at least a portion of the lithium iron phosphate particles have a second coating layer on their surface, the second coating layer being a carbon coating layer, and the thickness of the second coating layer being 3 to 10 nm.

[0045] This application improves the battery's cycle performance by setting a second coating layer on the surface of lithium iron phosphate particles, thereby reducing side reactions between the electrolyte and lithium iron phosphate.

[0046] In some embodiments, the method for preparing lithium iron phosphate includes, but is not limited to, at least one of the following: high-temperature solid-state method, carbothermal reduction method, hydrothermal method, and coprecipitation method.

[0047] In some embodiments, the positive electrode active material includes a ternary material.

[0048] In some embodiments, the ternary material includes a dopant element, which may include at least one selected from B, Zr, Ti, Si, Mo, La, Ce, Te, Nb, Ta, Si, Al, W, Sr, V, Y, Mg, Co, and Li. By introducing the above-mentioned dopant elements into the ternary material, the conductivity of the cathode can be improved, and the influence of the lithium supplement on the conductivity of the cathode can be reduced.

[0049] The ternary material satisfies the general formula: Li a Ni b Co c M1 d M2 e O2, wherein 0.75≤a≤1.2, 0<b<1, 0<c<1, 0<d<1, 0≤e≤0.2, b+c+d=1; M1 can be Mn or Al, M2 is the dopant element in the ternary material, and the mass content of M2 is 100pp~10000ppm; R includes, but is not limited to, at least one of N, F, S, and Cl.

[0050] In some embodiments, when the positive electrode active material comprises a ternary material, the ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet is 0.01 to 0.092 (μm·g) / mAh. For batteries where the positive electrode active material comprises a ternary material, a ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet in the range of 0.01 to 0.092 (μm·g) / mAh results in better overall battery performance.

[0051] In some embodiments, at least a portion of the particles in the ternary material have a third coating layer on their surface, the material of which includes at least one of aluminum oxide, lithium lanthanum oxyzirconium, lithium phosphate, tungsten trioxide, titanium dioxide, lanthanum titanate, calcium titanate, and boron trioxide.

[0052] This application reduces side reactions between the electrolyte and the ternary material by setting a third coating layer on the surface of the ternary material particles, thereby improving the cycle performance of the battery.

[0053] In this application, the lithium nickel manganese oxide (LNMO) is a positive electrode active material with a spinel structure, which has the advantage of high voltage characteristics. The lithium nickel manganese oxide satisfies the general formula: Li 1+x Ni y M z Mn 2-x-y-z O 4-k -0.1≤x≤0.2, 0.4≤y≤0.6, 0≤z≤0.2, 0≤k≤0.1, M is a doping element, M includes but is not limited to at least one of Cr, Mo, Nb, Ru, P, S, Ta, W, Tl and Ti.

[0054] The lithium manganese iron phosphate is a positive electrode active material with an olivine structure and a hexagonal close-packed structure. The chemical formula of lithium manganese iron phosphate is: Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R nIn the formula, a is 0.9–1.1, b is 0–0.1, x is 0.001–0.999, y is 0.001–0.999, 1-xy is 0–0.1, m is 0–0.1, and n is 0–0.1. In the formula, M represents the doping element at the manganese and / or iron sites of lithium manganese iron phosphate, and M includes, but is not limited to, at least one of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr; N represents the doping element at the lithium site of lithium manganese iron phosphate, and N includes, but is not limited to, at least one of Zn, Al, Na, K, Mg, Nb, Mo, and W; Q represents the doping element at the phosphorus site of lithium manganese iron phosphate, and Q includes, but is not limited to, at least one of B, S, Si, and N; R represents the doping element at the oxygen site of lithium manganese iron phosphate, and R includes, but is not limited to, at least one of S, F, Cl, and Br.

[0055] In some embodiments, the positive electrode active material includes a first particle and a second particle, wherein the particle size of the first particle is 0.9 to 1.8 μm; the particle size of the second particle is less than 0.9 μm, preferably 0.2 to 0.8 μm; and based on the sum of the masses of the first particle and the second particle, the mass percentage of the first particle is 20 to 40%, and the mass percentage of the second particle is 60 to 80%.

[0056] This application combines two positive electrode active materials with different particle sizes. The smaller particle size first particle fully fills the spaces between the larger particle size second particle, improving the electronic contact between particles and enhancing the electron transport performance of the positive electrode. This compensates for the poor conductivity of the lithium supplement on the positive electrode, increases the tolerance of the positive electrode to the lithium supplement, and thus improves the cycle performance of the battery while also considering the battery capacity.

[0057] In some embodiments, the first particle is lithium iron phosphate, and the preparation method of the first particle includes, but is not limited to, the following steps: The carbon source, iron source, phosphorus source, lithium source and dopant source (if any) are mixed in a solvent according to the target molar ratio. The resulting mixture is ground and then spray-dried. The resulting powder particles are calcined, impurities are removed, and the powder is pulverized to obtain the first particle. The solvent may include water; The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate. The phosphorus source includes at least one of ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and ammonium phosphate; the phosphorus source and the lithium source can be the same, such as lithium dihydrogen phosphate; The iron source includes at least one of ferrous oxalate, ferric hydroxide, ferrous hydroxide, ferric phosphate, ferrous phosphate, ferric acetate, ferrous acetate, ferric carbonate, ferrous carbonate, ferric oxide, ferric oxide, and ferric oxalate. The doping source includes at least one of the following: carbonate of the doping element, oxide of the doping element, nitrate of the doping element, oxalate of the doping element, phosphate of the doping element, citrate of the doping element, and acetate of the doping element. The carbon source includes at least one of glucose, sucrose, microcrystalline sugar, and organic polymer; the mass of the carbon source accounts for 1 to 20% of the theoretical mass of lithium iron phosphate produced. The grinding process takes 1.5 to 3 hours and the rotation speed is 400 to 600 r / min. The spray drying pressure is 0.4–0.7 MPa, the inlet temperature is 200–290°C, and the outlet temperature is 80–120°C. The calcination conditions are: heating rate of 3–5°C / min, calcination temperature of 720–850°C, and calcination time of 4–12 h.

[0058] The pulverization method is airflow pulverization.

[0059] It should be noted that, in this application, the particle size of the first particle can be controlled by the aforementioned characteristic parameters such as calcination temperature, heating rate, and calcination time.

[0060] In some embodiments, the second particle is lithium iron phosphate, and the preparation method of the second particle includes, but is not limited to, the following steps: According to the target molar ratio, phosphorus source and lithium source are mixed and reacted in solvent. The resulting product, iron source and dopant source are mixed, reducing agent is added, and nitrogen or argon gas is continuously introduced to remove air. Then, a hydrothermal reaction is carried out. After cooling, centrifugation and drying, lithium iron phosphate particles are obtained. The lithium iron phosphate particles are mixed with carbon source and calcined under inert atmosphere. Then, after grinding, spray drying, impurity removal and pulverization, a second particle coated with carbon layer is obtained. The solvent may include water; The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate. The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and ammonium phosphate; the phosphorus source and the lithium source can be the same, such as lithium dihydrogen phosphate. The iron source includes at least one of ferrous sulfate and ferrous chloride; The doping source includes at least one of the following: carbonate of the doping element, hydroxide of the doping element, nitrate of the doping element, oxalate of the doping element, phosphate of the doping element, citrate of the doping element, and acetate of the doping element. The reducing agent may be ascorbic acid; The carbon source includes at least one of glucose, sucrose, microcrystalline sugar, and organic polymer; the mass of the carbon source accounts for 1 to 20% of the mass of the lithium iron phosphate particles.

[0061] The hydrothermal reaction conditions are: pressure 1.5–2.5 MPa, temperature 180–220 °C, time 0.2–1 h, and system pH 5–7. The calcination conditions are: temperature of 600–720℃ and time of 2–4 hours.

[0062] The grinding time is 1 to 3 hours, and the rotation speed is 400 to 500 r / min.

[0063] The spray drying pressure is 0.4-0.7 MPa, the inlet temperature is 200-290°C, and the outlet temperature is 80-120°C. The pulverization method can be airflow pulverization.

[0064] It should be noted that, in this application, the particle size of the second particle can be controlled by the characteristic parameters such as the pressure of the hydrothermal reaction, the temperature of the hydrothermal reaction, the time of the hydrothermal reaction, the calcination temperature, the heating rate, and the calcination time.

[0065] In some embodiments, the thickness of the positive electrode active material layer is not less than 100 μm, and the battery satisfies: 0.5V ≤ cV ≤ 1V. The inventors have found that for batteries with a thicker positive electrode active material layer, the lithium-ion transport path within the positive electrode active material layer is relatively long. The introduction of lithium replenishing agents further affects the efficiency of lithium-ion transport. This application adjusts the cV to the above-mentioned range, which can reduce the impact of the thickness of the positive electrode active material layer on the battery capacity.

[0066] In some embodiments, the areal density of the positive electrode active material layer is 300–600 g / m³. 2 .

[0067] In some embodiments, the compaction density of the positive electrode active material layer is 2.4–2.7 g / cm³. 3 .

[0068] This application regulates the areal density of the positive electrode active material layer to a suitable range, which can improve the battery capacity; by regulating the compaction density of the positive electrode active material layer to a suitable range, this application can take into account the electrical contact between particles and reduce the impact of lithium supplementation on the conductivity of the positive electrode sheet.

[0069] In some alternative embodiments, the positive electrode active material layer further includes a positive electrode conductive agent and a positive electrode binder.

[0070] Based on the total mass of the positive electrode active material layer, the sum of the mass percentages of the positive electrode active material and the lithium supplement is 94.5% to 98.5%, the mass percentage of the positive electrode conductive agent is 1.3% to 3.2%, and the mass percentage of the positive electrode binder is 0.5% to 1.8%.

[0071] The positive electrode conductive agent may include conductive agents conventionally used in the art. For example, the positive electrode conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, acetylene black, Ketjen black, conductive graphite, graphene, and conductive carbon fiber.

[0072] The positive electrode binder may include positive electrode binders conventionally used in the art. For example, the positive electrode binder includes at least one selected from polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyacrylonitrile, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyimide, and polyamide-imide.

[0073] The positive current collector may include positive current collectors conventionally used in the art. For example, the positive current collector may include aluminum foil.

[0074] In some embodiments, a carbon layer is disposed on the surface of the positive electrode current collector, which can improve the electron transport efficiency between the positive electrode active material layer and the positive electrode current collector, improve the overall conductivity of the positive electrode sheet, and thus improve the specific capacity of the battery while taking into account the battery cycle performance; specifically, the carbon layer can be an SP conductive coating.

[0075] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the preparation method of the positive electrode sheet includes the following steps: mixing positive electrode active material, positive electrode conductive agent, positive electrode binder and solvent to obtain positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, drying and then rolling and cutting to obtain the positive electrode sheet.

[0076] In some embodiments, the electrolyte includes a solvent, a lithium salt, and additives.

[0077] Furthermore, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, phosphate ester solvents, ether solvents, nitrile solvents, and sulfone solvents.

[0078] Furthermore, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium dioxarate borate, lithium difluorooxarate borate, lithium trifluoromethanesulfonate, lithium difluorodioxarate phosphate, lithium tetrafluorooxarate phosphate, lithium difluoromethanesulfonylimide, and lithium ditrifluoromethanesulfonylimide.

[0079] Furthermore, the additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate (TMSB), lithium difluorophosphate (LiDFOP), trimethyl phosphate (TMP), triphenyl phosphate (TPP), propylene sulfite (PS), vinyl ethylene carbonate (VEC), and 1,3-propanesulfonate lactone (1,3-PS).

[0080] Furthermore, based on the mass of the electrolyte, the mass percentage of the additive is 0.5% to 2.5%. Introducing the additive into the electrolyte can improve the film-forming properties of the electrolyte on the negative electrode, reduce the side reactions between the negative electrode active material and the electrolyte, and thus reduce the amount of lithium supplementer required, thereby reducing the impact of its poor conductivity on the conductivity of the positive electrode.

[0081] In some embodiments, the negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode active material.

[0082] Furthermore, the areal density of the negative electrode active material layer is 150–200 g / m³. 2 .

[0083] Furthermore, the compaction density of the negative electrode active material layer is 1.5–1.8 g / cm³. 3 .

[0084] Furthermore, the negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, mesophase carbon microspheres, elemental silicon, silicon suboxide, silicon-carbon composite material, and lithium titanate.

[0085] Furthermore, the particle size Dv50 of the negative electrode active material is 5–25 μm. For example, the particle size Dv50 of the negative electrode active material can be 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, or a range consisting of any two sets of values ​​therein.

[0086] Furthermore, the negative electrode active material layer also includes a negative electrode conductive agent and a negative electrode binder.

[0087] Optionally, based on the total mass of the negative electrode active material layer, the mass percentage of the negative electrode active material is 90-99%, the mass percentage of the negative electrode conductive agent is 1-5%, and the mass percentage of the negative electrode binder is 0.5%-5%.

[0088] The negative electrode conductive agent may include conductive agents conventionally used in the art. For example, the negative electrode conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, acetylene black, Ketjen black, conductive graphite, graphene, and conductive carbon fiber.

[0089] The negative electrode binder may include binders conventionally used in the art. For example, the negative electrode binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyacrylonitrile, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyimide, and polyamide-imide.

[0090] Furthermore, the negative electrode sheet includes a negative electrode current collector, and the negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector.

[0091] The negative electrode current collector may include negative electrode current collectors conventionally used in the art. For example, the negative electrode current collector includes at least one of copper foil, chromium foil, nickel foil, and titanium foil.

[0092] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the preparation method of the negative electrode sheet includes the following steps: mixing a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and a solvent to obtain a negative electrode slurry; coating the negative electrode slurry onto at least one side surface of a negative electrode current collector, drying it, rolling it and cutting it to obtain a negative electrode sheet.

[0093] In this application, the separator is located between the positive electrode and the negative electrode.

[0094] In some embodiments, the diaphragm includes a base membrane.

[0095] For example, the base film may be made of at least one of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride, and the polyolefin may include at least one of polypropylene and polyethylene.

[0096] The base film may also have a coating on at least one side surface. The coating may be an inorganic coating and an organic coating. The inorganic coating material includes at least one of alumina, silicon oxide, titanium oxide, magnesium oxide, zirconium oxide and boehmite. The organic coating includes at least one of aramid coating and polyvinylidene fluoride (PVDF) coating.

[0097] The second aspect of this application provides an electrical device, which includes the battery provided in the first aspect of this application.

[0098] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments.

[0099] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this application are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0100] Example 1 An embodiment of the lithium-ion battery described in this application includes a method for preparing the lithium-ion battery comprising the following steps: S1. Preparation of positive electrode active material: S11, Preparation of the first particle: According to the stoichiometric ratio in the general chemical formula of lithium iron phosphate and the percentage of glucose in the theoretical mass of lithium iron phosphate, a mixture of lithium dihydrogen phosphate, ferrous oxalate, oxides of doped elements, glucose and polyethylene glycol was mixed in water. Then, it was wet-milled at 450 r / min for 2 h to a suitable particle size and then atomized in a spray drying device (pressure 0.6 MPa, inlet temperature 200℃, outlet temperature 100℃). The spray-dried particles were transferred to a tube furnace and heated to 750℃ at a rate of 5℃ / min under nitrogen atmosphere protection and held for calcination for 8 h. After demagnetization, airflow crushing was performed to obtain the first particles. S12, Preparation of the second particle: According to the stoichiometric ratio in the general chemical formula of lithium iron phosphate, lithium hydroxide and phosphoric acid are mixed and reacted in deionized water. The resulting reaction product, ferrous sulfate, and oxides of doped elements are mixed, and ascorbic acid, a reducing agent, is added. Nitrogen or argon gas is continuously introduced to remove air. Then, a hydrothermal reaction is carried out at 200℃ and 2MPa for 0.5h to obtain lithium iron phosphate particles. Subsequently, glucose (10% of the mass of lithium iron phosphate particles) is added, and the particles are ground at 500r / min for 2h to a suitable particle size. Then, the particles are spray-dried (pressure 0.5MPa, inlet temperature 290℃, outlet temperature 100℃). The spray-dried material is transferred to a tube furnace and heated to 700℃ at a rate of 5℃ / min under nitrogen protection. The temperature is held for calcination for 3h, and after demagnetization, the particles are pulverized by airflow to obtain the second particle. S13. Mix the first particle and the second particle according to the mass ratio shown in Table 1 to obtain the positive electrode active material.

[0101] S2, Preparation of lithium supplement: According to the stoichiometric ratio in the general chemical formula of the iron-containing lithium supplement, lithium hydroxide (lithium source) and iron hydroxide (iron source) are added in batches and mixed in multiple batches. After sintering, the mixture is crushed. The sintering process includes the following stages: primary sintering stage: sintering at 700℃ for 10 hours; secondary sintering stage: sintering at 820℃ for 12.5 hours; tertiary sintering stage: sintering at 850℃ for 13 hours; then, graphite carbon sheets (carbon source) are introduced and mixed, and the mixture is sintered and coated under nitrogen. The mass of carbon source added is 20% of the theoretical mass of the iron-containing lithium supplement. After demagnetization, the iron-containing lithium supplement Li5FeO4 (LFO) is obtained.

[0102] S3, Preparation of the positive electrode: The positive electrode active material, lithium supplement, conductive carbon black SP, and binder polyvinylidene fluoride (PVDF) were mixed, with the mass ratio of the sum of the positive electrode active material and lithium supplement, the mass of conductive carbon black SP, and the mass of PVDF being 96:2:2. The mass ratios of the positive electrode active material and lithium supplement are shown in Table 1. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until the system was homogeneous to obtain the positive electrode slurry. The positive electrode slurry was then prepared at a ratio of 400 g / m³. 2 The areal density is uniformly coated on two opposing surfaces of the positive electrode current collector aluminum foil along its thickness direction. After air drying at room temperature, it is transferred to an oven for further drying, and then rolled to form a compacted density of 2.6 g / cm³ on the aluminum foil. 3 The positive electrode active material layer is cut to obtain the positive electrode sheet.

[0103] S4. Preparation of the negative electrode: The negative electrode active material was ball-milled. The negative electrode active material, conductive agent acetylene black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of negative electrode active material:acetylene black:CMC:SBR = 96.4:1:1.2:1.4. Deionized water was added, and the mixture was stirred under vacuum until homogeneous, yielding the negative electrode slurry. This negative electrode slurry was then prepared at a concentration of 160 g / m³. 2 The areal density is coated onto one side surface of the copper foil, dried at room temperature, then transferred to an oven for further drying, and finally rolled to form a compacted density of 1.7 g / cm³ on the copper foil. 3 The negative electrode active material layer is cut to obtain the negative electrode sheet.

[0104] S5. Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of EC:EMC:DEC = 1:1:1:1. Ethylene carbonate (VC) was added as an additive, and fully dried lithium salt LiPF6 was added to prepare an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L and the mass percentage of VC was 1%.

[0105] S6. Preparation of the diaphragm: Polypropylene film is selected as the base film, and an alumina coating is prepared by dip coating on the two opposite surfaces of the base film; S7, the above-obtained positive electrode, separator and negative electrode are stacked in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation, and then wound to obtain a bare cell; the bare cell is placed in the outer packaging shell, dried and injected with electrolyte, and after vacuum sealing, standing, formation and shaping processes, a lithium-ion battery is obtained.

[0106] Examples 2-4 The difference between Examples 2-4 and Example 1 is that Examples 2-4 changed the calcination temperature and calcination time in step S11, and also changed the sintering conditions in step S13. Examples 2-4 also changed the ball milling time of the negative electrode active material in step S4, which changed the particle size of the negative electrode active material in the battery, as shown in Table 1.

[0107] Examples 5-22 and Comparative Examples 1-4 The differences between Examples 5-22 and Comparative Examples 1-4 and Example 1 are as follows: Examples 5-22 and Comparative Examples 1-4 changed the calcination temperature and calcination time in step S11, and did not perform steps S12 and S13. In step S3, the product obtained in step S11 was used as the positive electrode active material, as shown in Table 1. Examples 5-22 and Comparative Examples 1-4 also changed the sintering conditions in step S2 when preparing the iron-containing lithium supplement, as shown in Table 2. Examples 5-22 and Comparative Examples 1-4 also changed the ball milling time of the negative electrode active material in step S4, which changed the particle size of the negative electrode active material in the battery, as shown in Table 2. Examples 15 and 20 also changed the doping elements in step S11, as shown in Table 1; Examples 21-22 also changed the areal density in step S2 to 520 g / m³. 2 This alters the thickness of the positive electrode active material layer and also changes the stacking thickness of the battery cell, as shown in Table 2.

[0108] Examples 23-26 and Comparative Example 5 The difference between Examples 23-26 and Comparative Example 5 and Example 1 is that step S1 in Examples 23-26 and Comparative Example 5 is as follows: Li2CO3, NiCO3, MnO2 and oxides of doping elements are added to a ball mill according to the stoichiometric ratio in the general chemical formula of ternary materials, and the mixture is ball-milled at a speed of 2000 r / min for 10 h. Then, sintering is performed in an air atmosphere to obtain ternary material particles. Subsequently, an ALD atomic deposition instrument is used to deposit the coating layer raw material powder on the surface of the ternary material particles with a deposition pressure of 10 Pa and a deposition cycle of 200 cycles to obtain ternary materials. The sintering process and the types of doping elements are shown in Table 1. In Examples 23-26 and Comparative Example 5, step S3 uses the ternary material obtained in step S1 as the positive electrode active material, as shown in Table 1. Examples 23-26 and Comparative Example 5 also changed the ball milling time of the negative electrode active material in step S4, which changed the particle size of the negative electrode active material in the battery, as shown in Table 2.

[0109] Using the batteries provided in the above embodiments and comparative examples as test objects, the following tests were conducted: 1. Fe in the positive electrode plate 3+ Relative content: The battery was discharged to 2.5V at 0.33C. The empty battery was removed, the positive electrode was disassembled, and the positive electrode was soaked in dimethyl carbonate (DMC) solution for 4 hours and then dried. The positive electrode was cut into small pieces with an area of ​​5×5mm in a glove box. The sample is fixed in a suitable position, such as on conductive tape on a copper sheet, and then sent into the analysis chamber through a rapid sample introduction chamber. A 120W monochromatic Al Kα X-ray source is used; the energy resolution is ≤0.48eV; the test beam spot is 400μm, and the instrument automatically supplements the test pass range according to the element to be measured; etching conditions: Ar ions are used for etching, and the etching depth is controlled by adjusting the etching rate or etching time, etc. In this application, the etching depth is 210nm. After the test, the data was processed by peak separation to obtain the Fe spectrum in the XPS image. 3+ The area of ​​the characteristic peak (i.e., the binding energy range of the 2p3 / 2 peak of Fe3+ is approximately 710.5–711.5 eV) and the area of ​​the O1s peak (located at 530–531 eV) are used to calculate the Fe content in the cathode using the following formula. 3+ The relative content a: a = Fe 3+ Characteristic peak area / O1s peak area, Fe 3+ The units for the characteristic peak area and the O1s peak area are both CPS.eV, and the test results are shown in Table 3.

[0110] 2. N / P: The battery was discharged at 0.33C to the lower limit voltage of 2.5V, and then disassembled to remove the positive and negative electrode plates. Cut the positive electrode sheet into a 75mm×60mm square (with tabs retained), and cut the negative electrode sheet into a 77mm×62mm square (with tabs retained); then soak it in the inert solvent dimethyl carbonate (DMC) in a glove box for 2 hours to remove soluble electrolyte residue, and then vacuum dry it. The dried positive and negative electrode sheets were assembled with lithium sheets to form a half cell. The assembled half cell was then packaged, welded and injected with electrolyte. After standing for 24 hours, the capacity was tested. A charge-discharge test is performed on the half-cell. The battery rate can be 0.33C. The half-cell is charged at 0.33C to the upper limit voltage (3.65V when the positive electrode active material is lithium iron phosphate; 4.25V when the positive electrode active material is ternary material), with a cutoff current of 0.05C. Then it is discharged at 0.33C to the lower limit voltage of 2.5V. This constitutes one cycle, and three charge-discharge cycles are performed. The discharge capacity of the third cycle is taken as the fixed capacity. The discharge capacity of the positive electrode half-cell is denoted as C. 正 The discharge capacity of the negative electrode half-cell is denoted as C. 负 ; Calculate N / P using the following formula: N / P = C 负 / C 正 N / P is the ratio of the negative electrode discharge capacity to the positive electrode discharge capacity, denoted as b. The test results are shown in Table 3.

[0111] 3. Negative electrode potential: The battery was discharged at 0.33C to the lower limit voltage of 2.5V, then disassembled, the negative electrode was removed, and the negative electrode was cut into a square of 77mm×62mm (the tabs must be retained); then it was soaked in the inert solvent dimethyl carbonate (DMC) in a glove box for 2 hours to remove soluble electrolyte residue, and then vacuum dried. The dried negative electrode sheet and lithium sheet are assembled into a half cell. The assembled half cell is then packaged, welded and injected with electrolyte. After standing for 24 hours, the capacity is tested. The half-cell was charged and discharged. The battery rate can be 0.1C. The battery was charged at 0.1C to the upper limit voltage (3.65V when the positive electrode active material is lithium iron phosphate; 4.25V when the positive electrode active material is ternary material), with a cutoff current of 0.05C. Then it was discharged at 0.1C to the lower limit voltage of 2.5V. The potential at the end of the discharge is the negative electrode terminal potential. The potential at the end of the discharge is the negative electrode terminal potential, denoted as cV. The c in the test results is shown in Table 3.

[0112] 4. Specific capacity of the positive electrode: Disassemble the battery in a depleted state, remove the positive electrode, and cut the positive electrode into a 75mm×60mm square (the tabs must be retained); then soak it in the inert solvent dimethyl carbonate (DMC) in a glove box for 2 hours to remove soluble electrolyte residue, and then vacuum dry it; The dried positive electrode sheet and lithium sheet are assembled into a half cell. Then the half cell is packaged, welded and injected with electrolyte. After standing for 24 hours, the capacity is tested. The battery was subjected to charge-discharge tests. The test procedure was as follows: the battery was charged at 0.1C to the upper limit voltage (3.65V when the positive electrode active material is lithium iron phosphate; 4.25V when the positive electrode active material is ternary material), with a cutoff current of 0.05C. Then, it was discharged at 0.1C to the lower limit voltage of 2.5V. This was repeated as one cycle, for a total of 3 charge-discharge cycles. The discharge capacity of the third cycle was taken as the C value. 负放 ; The specific capacity of the positive electrode is calculated using the following formula: Specific capacity of the positive electrode = C 负放 / (mass of positive electrode sheet - mass of aluminum foil) × mass percentage of positive electrode active material in the positive electrode active material layer; the test results are shown in Table 2.

[0113] The mass percentage of the positive electrode active material in the positive electrode active material layer was tested using the following method: The battery was discharged at 0.33C to the lower limit voltage of 2.5V. In the empty state, the positive electrode sheet was disassembled; the total mass of the beaker and filter membrane was weighed and recorded as m0; the mass of the blank aluminum foil was weighed and recorded as m1; n positive electrode sheets were weighed, with a mass of m2, and placed in a conical flask; 30mL of concentrated hydrochloric acid solution (concentration 28wt%) was added to the flask, and the mixture was heated at 180℃ for 20min to digest the solution, yielding approximately 2mL of digestion solution 1, which was then cooled; the digestion solution 1 was vacuum filtered using a filter membrane to obtain filter residue 1, which was then rinsed with 200mL of pure water; the filter residue 1 was then removed and mixed with a 37wt% acid solution. The acid solution was prepared at a mass ratio of 1:5 and subjected to a second heating digestion at 250℃ for 5 minutes to obtain 5 mL of digestion solution 2. Digestion solution 2 was then filtered through a filter membrane, and the filter residue was rinsed with 200 mL of pure water until the filtrate was colorless and transparent to obtain filter residue 2. Filter residue 2 was dried at 85℃ for 5 hours, weighed, and placed in a dry beaker for 30 hours. Finally, the total mass of the beaker, filter residue 2, and filter membrane was weighed as m3. Based on the total mass of the beaker and filter membrane m0, the mass of the blank aluminum foil m1, the total mass of the positive electrode sheet m2, and the total mass of the beaker, filter residue 2, and filter membrane m3, the mass percentage of the positive electrode active material in the positive electrode active material layer was calculated using the following formula: w=[1-(m3-m0) / (m2-n×m1)]×100%.

[0114] 5. Particle size Dn50 and thickness: 5.1 The particle size Dn50 of the first particle and the particle size Dn50 of the second particle: In Examples 1-4 and Comparative Examples 1-4, the positive electrode active material includes a first particle and a second particle. The particle size Dn50 of the first particle and the particle size Dn50 of the second particle were measured using the following method: The battery was discharged at 0.33C to the lower limit voltage of 2.5V. In the empty state, the positive electrode sheet was disassembled. The obtained positive electrode sheet was soaked in dimethyl carbonate (DMC) at room temperature (25°C) for 2 hours, dried, and the powder on the surface of the dried electrode sheet was scraped off with a scraper as a sample. The sample was fixed with conductive adhesive, CP argon ion polished, a conductive film was deposited, placed on a sample stage, and observed under a scanning electron microscope (SEM). The microscope was adjusted to 10Kx. At high magnification, three regions were photographed. Elemental data were collected in each region using EDS (Energy Dispersive X-ray Spectroscopy) spot scanning to confirm the positive electrode active material. Then, the first and second particles were identified by their diameters, with the first particle being larger and the second smaller. The particle size of all particles in each region was measured, and the statistical results of the first and second particles were categorized. The Dn50, representing the 50% distribution of the two particle types, was calculated. The average value of the results from the three regions was taken to obtain the particle size Dn50 of the first and second particles. The test results are shown in Table 1.

[0115] 5.2 Test procedure for particle size Dn50 of positive electrode active material: Following step ① above, the battery was discharged at 0.33C to the lower limit voltage of 2.5V. In the empty state, the positive electrode sheet was disassembled and soaked in dimethyl carbonate (DMC) at room temperature (25℃) for 2 hours. After drying, the powder on the surface of the dried electrode sheet was scraped off with a scraper as a sample. The sample was fixed with conductive adhesive and polished with CP argon ion, coated with a conductive film, placed on the sample stage, and observed under a scanning electron microscope (SEM). Elemental collection was performed by EDS (energy dispersive X-ray spectroscopy) spot scanning to confirm the positive electrode active material. Then, the particle size of the positive electrode active material was collected by the diagonal scribing method. The particle size of 100 positive electrode active materials in the magnified area was counted. The particle size of the positive electrode active material whose cumulative number of particles in the number baseline distribution reached 50% was counted to obtain the cumulative number distribution particle size Dn50 of the positive electrode active material. When lithium iron phosphate is used as the positive electrode active material, and it is a combination of the first particle and the second particle, Dn50 should be equal to the average value of the sum of the Dn50 of the first particle and the Dn50 of the second particle.

[0116] Based on the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet measured by the above method, the ratio between the positive electrode active material Dn50 and the specific capacity of the positive electrode sheet was calculated, and the calculation results are shown in Table 2.

[0117] 5.3 Particle size Dn50 of the positive electrode lithium replenishment agent: Following the steps described above, the battery was discharged at 0.33C to the lower limit voltage of 2.5V. In the empty state, the positive electrode was disassembled and soaked in dimethyl carbonate (DMC) at room temperature (25℃) for 2 hours. After drying, the powder on the surface of the dried electrode was scraped off with a scraper and used as a sample. The sample was fixed with conductive adhesive and polished with CP argon ion, coated with a conductive film, placed on the sample stage, and observed under a scanning electron microscope (SEM). Elemental collection was performed by EDS (energy dispersive X-ray spectroscopy) spot scanning to confirm the lithium replenishing agent (containing elements Fe and O). Then, the particle size of the lithium replenishing agent was collected by the diagonal scribing method. The particle size of 100 lithium replenishing agents in the magnified area was counted. The particle size of the lithium replenishing agent whose cumulative number of particles in the number baseline distribution reached 50% was counted to obtain the cumulative distribution particle size Dn50 of the lithium replenishing agent. The test results are shown in Table 2.

[0118] 5.4 Particle size Dv50 of the negative electrode active material: The negative electrode sheet was disassembled from the empty-charge secondary battery. The obtained positive electrode sheet was soaked in dimethyl carbonate (DMC) at room temperature (25℃) for 2 hours, dried, and the powder on the surface of the dried electrode sheet was scraped off with a scraper as a sample. The sample was fixed with conductive adhesive and polished with CP argon ion, coated with a conductive film, placed on the sample stage and observed under a scanning electron microscope (SEM). Three areas were selected and photographed at a magnification of 10Kx. After photographing, the particle size distribution was measured using a laser particle size distribution measuring instrument (Mastersizer 3000) according to the particle size distribution laser diffraction method (specific steps refer to GB / T19077-2016). The particle size corresponding to the cumulative particle size distribution percentage reaching 50% is the particle size Dv50 of the negative electrode active material. The test results are shown in Table 2.

[0119] 5.5 Thickness of the positive electrode active material layer: The positive electrode sheet was disassembled from the empty-charge secondary battery, and the cross-section was cut out using an ultrathin slicer. The cross-section was placed on the sample stage and observed and photographed under a scanning electron microscope (SEM). The thickness of the positive electrode active material layer at five different locations was directly measured on the photographed image, and the average value was taken to obtain the thickness of the positive electrode active material layer. The test results are shown in Table 2.

[0120] 6. Coating thickness: Discharge the battery to 2.5V at 0.33C, take the positive electrode sheet of the lithium-ion battery in the empty state, soak it in dimethyl carbonate (DMC) solution at room temperature for 4 hours, after soaking, take out the positive electrode sheet and dry it in a vacuum environment, and scrape off the powder on the surface of the positive electrode sheet with a ceramic knife. The scraped powder was uniformly dispersed in ethanol and subjected to TEM (transmission electron microscopy) testing. Elemental data were collected in the TEM field of view using EDS (energy-dispersive X-ray spectroscopy) spot scanning to confirm the lithium supplement (containing elements Fe and O). The thickness of the coating layer on the outer surface of the core was measured at three different locations on a single lithium supplement particle, and the average value was calculated to obtain the coating layer thickness of the particle. The test results are shown in Table 2.

[0121] 7. Specific capacity of lithium-ion batteries: After formation and capacitance, the batteries are charged at 25°C with a constant current of 0.33C to 3.65V, then charged with a constant voltage to the cutoff current of 0.05C, and then discharged at 0.33C to the lower limit voltage of 2.5V. This is one cycle, and three charge-discharge cycles are performed. The discharge capacity Q of the third cycle is taken as the discharge capacity Q of the battery. The specific capacity of the battery is calculated using the following formula: Specific capacity of battery = Discharge capacity of battery / Mass of positive electrode active material layer. The test results are shown in Table 3.

[0122] 8. Cycle performance of lithium-ion batteries: At 25°C, the lithium-ion battery was cycle-tested according to the following procedure: After formation, the battery is charged at 25°C with a constant current of 0.33C to the upper limit voltage, then charged with a constant voltage to the cutoff current of 0.05C, and then discharged at 0.33C to the lower limit voltage of 2.5V. This is one cycle, and the battery is charged and discharged 3 times. The discharge capacity of the third cycle is taken as the initial capacity of the battery. ① Charge at a constant current rate of 1C to the upper limit voltage, and then charge at a constant voltage until the current drops to 0.05C; this is one cycle, charge and discharge 3 times, and use the third cycle as the initial capacity; ② Let stand for 30 minutes; ③ Discharge the lithium-ion battery to 2.5V at a 1C rate, record the discharge time (t) and current (I), and calculate the capacity of the lithium-ion battery according to the following formula: Capacity = I / t; ④ Let stand for 30 minutes; Perform cyclic testing according to steps ① to ④ above until the capacity of the lithium-ion battery is ≤ 80% of the initial capacity, and record the number of cycles. In the above steps, when the positive electrode active material is lithium iron phosphate, the upper limit voltage is 3.65V; when the positive electrode active material is ternary material, the upper limit voltage is 4.25V. The test results are shown in Table 3.

[0123] Table 1 Table 2 Table 3 As can be seen from Tables 1-3, Examples 1-22 and Comparative Examples 1-4 used lithium iron phosphate as the positive electrode active material, and the Fe content in the XPS spectra of the positive electrode was adjusted. 3+ The ratio of the characteristic peak area to the peak area of ​​O1s (set as a), the ratio of the negative electrode discharge capacity to the positive electrode discharge capacity measured at a 0.33C rate (set as b), and the potential at the end of the discharge curve of the negative electrode (set as c) are used to control a×b×c within a suitable range. This effectively improves the battery capacity while ensuring the battery's cycle performance, ensuring that the battery can cycle at 25℃ to 80% SOH for no less than 5320 cycles, and the specific capacity of the battery is in the range of 113~159mAh / g. When 0.6≤a≤0.9, 1.05≤b≤1.18, 0.6V≤c≤0.9V, and 0.5≤a×b×c≤0.9, the battery capacity and cycle performance are better. In Comparative Example 1, a×b×c is too large, and the battery's cycle performance and specific capacity are significantly reduced. In Comparative Example 2, a×b×c is too small, and the battery's cycle performance is significantly reduced. In Comparative Example 3, when a×b×c is too large and c is also too large, the battery's cycle performance and specific capacity decrease significantly. In Comparative Example 4, when a×b×c is too small and a is also too small, the battery's cycle performance decreases significantly.

[0124] Examples 23-26 and Comparative Example 5 used ternary materials as positive electrode active materials. In Examples 23-26, a×b×c were within a suitable range, and the number of cycles when the battery was cycled to 80% SOH at 25°C was not less than 4000 cycles, and the specific capacity of the battery was in the range of 164-190 mAh / g. However, in Comparative Example 5, a×b×c was too small, and the cycle performance of the battery dropped sharply, causing the number of cycles when the battery was cycled to 80% SOH at 25°C to decrease to 3468 cycles, and the capacity of the battery also decreased.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A battery, characterized in that, It includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive current collector. At least one side surface of the positive current collector is provided with a positive active material layer. The positive active material layer contains a positive active material and a lithium supplement agent. The lithium supplement agent includes an iron-containing lithium supplement agent. In the XPS spectrum of the positive electrode, Fe in the uncharged state 3+ The ratio of the characteristic peak area to the peak area of ​​O1s is a, and the unit of the peak area is CPS.eV. The XPS spectrum of the positive electrode refers to the XPS spectrum measured after the positive electrode active material layer is etched to a depth of 210nm. The ratio of the negative electrode discharge capacity to the positive electrode discharge capacity measured at a rate of 0.33C is set as b, and the units of the negative electrode discharge capacity and the positive electrode discharge capacity are both mAh. The discharge curve of the negative electrode plate has a terminal potential of cV. The terminal potential of the discharge curve of the negative electrode plate refers to the voltage at the end of the negative electrode discharge curve obtained by discharging the battery to the lower limit voltage. The battery satisfies: 0.11≤a×b×c≤1.

2. The battery as described in claim 1, characterized in that, The battery satisfies at least one of the following conditions: (1)0.4≤a≤1； (2)1≤b≤1.2； (3) 0.2V≤cV≤1V.

3. The battery according to claim 1 or 2, characterized in that, The battery satisfies the following condition: 0.5 ≤ a × b × c ≤ 0.

9.

4. The battery according to claim 3, characterized in that, The battery satisfies at least one of the following conditions: (1)0.6≤a≤0.9； (2)1.05≤b≤1.18； (3) 0.2V≤cV≤1V.

5. The battery as described in claim 1, characterized in that, The lithium replenishing agent has a particle size Dn50 of 0.5–30 μm.

6. The battery as described in claim 1 or 5, characterized in that, At least some of the particles in the lithium replenishing agent have a first coating layer on their surface, the first coating layer including a carbon coating layer.

7. The battery as described in claim 6, characterized in that, The thickness of the first coating layer is 10–100 nm.

8. The battery as claimed in claim 1, characterized in that, The positive electrode active material layer includes LiFeO2.

9. The battery as claimed in claim 1, characterized in that, The positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and ternary materials.

10. The battery as claimed in claim 9, characterized in that, The ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet is 0.001 to 0.15 (μm·g) / mAh.

11. The battery as claimed in claim 10, characterized in that, The positive electrode active material includes lithium iron phosphate, and the ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet is 0.005 to 0.012 (μm·g) / mAh.

12. The battery as claimed in claim 11, characterized in that, At least a portion of the lithium iron phosphate particles have a second coating layer on their surface, the second coating layer including a carbon coating layer.

13. The battery as claimed in claim 11 or 12, characterized in that, The lithium iron phosphate contains doping elements, and the doping elements in the lithium iron phosphate include at least one of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

14. The battery as claimed in claim 9, characterized in that, The positive electrode active material includes ternary materials, and the ratio between the particle size Dn50 of the positive electrode active material and the specific capacity of the positive electrode sheet is 0.01 to 0.092 (μm·g) / mAh.

15. The battery as claimed in claim 14, characterized in that, At least some of the particles in the ternary material have a third coating layer on their surface, and the material of the third coating layer includes at least one of aluminum oxide, lithium lanthanum oxyzirconium, lithium phosphate, tungsten trioxide, titanium dioxide, lanthanum titanate, calcium titanate, and boron trioxide.

16. The battery as claimed in claim 14 or 15, characterized in that, The ternary material contains doping elements, and the doping elements in the ternary material include at least one of B, Zr, Ti, Si, Mo, La, Ce, Te, Nb, Ta, Si, Al, W, Sr, V, Y, Mg, Co, and Li.

17. The battery as claimed in claim 1, characterized in that, The positive electrode active material includes a first particle and a second particle, wherein the particle size of the first particle is 0.9 to 1.8 μm and the particle size of the second particle is less than 0.9 μm.

18. The battery as claimed in claim 1, characterized in that, The thickness of the positive electrode active material layer is not less than 100 μm, and 0.5V≤cV≤1V.

19. The battery as claimed in claim 18, characterized in that, The thickness of the positive electrode active material layer is 100–200 μm.

20. The battery as claimed in claim 1, characterized in that, The battery includes an electrolyte, which comprises an organic solvent, a lithium salt, and additives; The organic solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, phosphate ester solvents, ether solvents, nitrile solvents, and sulfone solvents, and / or the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, lithium difluoromethanesulfonylimide, and lithium ditrifluoromethanesulfonylimide, and / or the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluorooxalate borate, lithium dioxalate borate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, lithium difluorophosphate, trimethyl phosphate, triphenyl phosphate, propylene sulfite, vinyl vinyl carbonate, and 1,3-propanesulfonate lactone.

21. The battery as claimed in claim 1, wherein the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material; The negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, mesophase carbon microspheres, elemental silicon, silicon suboxide, silicon-carbon composite material, and lithium titanate. The particle size Dv50 of the negative electrode active material is 5–25 μm.

22. An electrical appliance, characterized in that, Includes the battery as described in any one of claims 1 to 21.

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