Secondary batteries and electrical appliances

Abstract

This application relates to a secondary battery and an electrical device, belonging to the field of battery technology. The secondary battery of this application includes a positive electrode sheet, which includes a positive current collector and a positive electrode material located on at least one surface of the positive current collector. The positive electrode material comprises a positive active material, which includes lithium nickel manganese oxide particles. By controlling the constant current ratio b at 45°C and 1C rate and the sum c of the dissolution rates of nickel and manganese ions after the positive electrode material is stored in hydrofluoric acid solution at 70°C for 72 hours to satisfy 6 ≤ b × c ≤ 45, a balance between the stability of the positive electrode interface and the kinetic performance of the battery can be achieved, ensuring that the battery has both excellent cycle performance and fast charging performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a secondary battery and an electrical device. Background Technology

[0002] In the field of new energy, the application of lithium-ion power batteries is becoming increasingly widespread, and the market is placing higher demands on their energy density and output power. This has prompted researchers to shift their research focus to the development of high-voltage cathode materials. Spinel-type lithium nickel manganese oxide (LNMO) materials stand out due to their unique crystal structure, which provides a three-dimensional lithium-ion transport channel, endowing the material with good ionic conductivity and enabling it to achieve 4.7V (vs Li / Li). + The high-voltage platform has a theoretical specific capacity of 147mAh / g, showing great application potential in the field of high-voltage cathode materials.

[0003] However, in high-voltage applications, LNMO materials exhibit the following problems: Positive electrode metal ions easily dissolve and deposit on the negative electrode surface, reducing the stability of the positive electrode structure and affecting the negative electrode. This leads to poor integrity of the SEI film on the negative electrode, consumption of active lithium, severely impacting battery cycle performance and shortening battery life. Furthermore, lithium nickel manganese oxide has relatively poor electronic conductivity, which severely limits its fast-charging capability, making it difficult for the battery to be charged quickly in a short time.

[0004] Therefore, there is an urgent need to develop a technology that can balance the stability of the cathode interface and the kinetic performance of LNMO batteries, so that LNMO batteries can take into account both cycle performance and fast charging performance. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the prior art and provide a secondary battery and an electrical device, which has both excellent cycle performance and fast charging performance.

[0006] To achieve the above objectives, in a first aspect, this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode material located on at least one surface of the positive current collector, the positive electrode material comprising a positive active material, the positive active material including lithium nickel manganese oxide particles;

[0007] The secondary battery satisfies: 6≤b×c≤45;

[0008] Where b is the constant current ratio for charging at 45℃ and 1C rate, in percentage terms.

[0009] c represents the sum of the dissolution rates of nickel and manganese ions of the cathode material after storage in hydrofluoric acid solution at 70°C for 72 hours, expressed in units of _____.

[0010] Secondly, this application provides an electrical device including the aforementioned secondary battery.

[0011] Compared with the prior art, the beneficial effects of this application are as follows: By controlling the constant current ratio of charging at 45°C and 1C rate (b) and the sum of the dissolution rates of nickel ions and manganese ions of the cathode material after being stored in hydrofluoric acid solution at 70°C for 72 hours (c) to satisfy a specific relationship, this application can achieve a balance between the stability of the cathode interface and the dynamic performance of the LNMO battery, ensuring that the LNMO battery has both excellent cycle performance and fast charging performance. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] 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.

[0014] 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.

[0015] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0016] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0017] In this application, expressions such as "first time" and "second time" are not used to limit the number of operations, processes, or events; their sole purpose is to distinguish different operations, processes, or events.

[0018] Secondary batteries

[0019] This application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode material located on at least one surface of the positive current collector, the positive electrode material including a positive active material, the positive active material including lithium nickel manganese oxide particles;

[0020] The secondary battery satisfies: 6≤b×c≤45;

[0021] Where b is the constant current ratio for charging at 45℃ and 1C rate, in percentage terms.

[0022] c represents the sum of the dissolution rates of nickel and manganese ions of the cathode material after storage in hydrofluoric acid solution at 70°C for 72 hours, expressed in units of _____.

[0023] The constant current ratio (b) at 45℃ and 1C rate is obtained by charging and discharging the battery at 45℃ and 1C rate for two cycles, and calculating the ratio of the constant current charging capacity to the total charging capacity in the second cycle. The 45℃ test condition avoids performance degradation of the secondary battery while accelerating its kinetics, making it easy to observe the differences in the constant current ratio at 1C rate among different secondary batteries. A higher constant current ratio (b) at 45℃ and 1C rate indicates smoother lithium-ion insertion / extraction and better short-term fast charging performance. However, it also subjects the electrode material to greater stress during lithium-ion insertion / extraction, leading to a gradual decrease in the structural stability of the electrode material and a reduction in the battery's cycle performance. The constant current ratio (b) at 45℃ and 1C rate can be adjusted by modifying the electrolyte conductivity, the size of the lithium nickel manganese oxide particles, the structure of the lithium nickel manganese oxide particles, or the thickness of the surface coating layer of the lithium nickel manganese oxide particles (if a coating layer is present).

[0024] This application does not limit the method for detecting the charging constant current ratio (b) at 45℃ and 1C rate. Those skilled in the art can detect the charging constant current ratio (b) at 45℃ and 1C rate using conventional techniques. For example, the charging constant current ratio (b) at 45℃ and 1C rate can be detected using the following method:

[0025] At 45℃, an empty battery is cycled for 2 cycles at a charge / discharge rate of 1C. The ratio of the constant current charging capacity in the second cycle to the total charging capacity is calculated. The result is the constant current ratio (b) at 45℃ and 1C rate. The voltage range is 3.5~4.8V. During charging, the battery is first charged at 1C constant current to the upper limit voltage of 4.8V, and then charged at constant voltage until the current is less than or equal to 0.05C. During discharging, the battery is discharged at 1C to 3.5V.

[0026] The sum of nickel and manganese ion dissolution rates (c) of the cathode material after storage in hydrofluoric acid solution at 70℃ for 72 hours was calculated by storing the cathode material at 70℃ in hydrofluoric acid solution with HF mass content of 30% for 72 hours, and then calculating the proportion of nickel and manganese dissolution mass to the total mass (i.e., total nickel and manganese mass). At a storage temperature of 70℃, the difference in the sum of nickel and manganese ion dissolution rates of different cathode materials can be observed significantly within a short period. A smaller value of the sum of nickel and manganese ion dissolution rates (c) after storage in hydrofluoric acid solution at 70℃ for 72 hours indicates higher stability of the cathode interface. This value can also reflect the passivation degree of the cathode material to some extent. By controlling the nickel and manganese ion dissolution rate and adjusting the passivation degree, the oxidative properties of the cathode active material can be reduced, thus protecting the cathode sheet, reducing manganese dissolution, improving electron and ion diffusion performance, and enhancing the battery's fast-charging capability. The sum of the dissolution rates (c) of nickel and manganese ions after the cathode material is stored in hydrofluoric acid solution at 70°C for 72 hours can be adjusted by changing the diameter of lithium nickel manganese oxide particles and the thickness of the coating layer of lithium nickel manganese oxide particles (if there is a coating layer).

[0027] This application does not limit the method for detecting the sum of the dissolution rates (c) of nickel and manganese ions of the cathode material after storage in hydrofluoric acid solution at 70°C for 72 hours. Those skilled in the art can detect the sum of the dissolution rates (c) of nickel and manganese ions of the cathode material after storage in hydrofluoric acid solution at 70°C for 72 hours using conventional techniques. For example, the sum of the dissolution rates (c) of nickel and manganese ions of the cathode material after storage in hydrofluoric acid solution at 70°C for 72 hours can be detected using the following method:

[0028] Disassemble the empty battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and dry it at room temperature with humidity ≤15%. Scrape off the positive electrode material on the surface of the current collector and digest it to obtain a sample solution. Then, use ICP (inductively coupled plasma) to determine the content of Ni and Mn in the sample solution. Calculate the mass percentage of Ni and Mn in the positive electrode material accordingly. Measure three parallel samples according to this method and calculate the average value M1 of the mass percentage of Ni and Mn in the positive electrode material.

[0029] The empty battery was disassembled and the positive electrode material was obtained by the above method. The obtained positive electrode material was added to an HF solution with a mass percentage of 30% at a material-to-liquid ratio of 1g:5mL. The solution was stored at a constant temperature of 70℃ for 72h, then centrifuged. The supernatant was taken and the contents of Ni and Mn were determined by ICP method. The mass percentage of Ni and Mn dissolved in the positive electrode material was calculated accordingly. Three parallel samples were measured according to the method and the average mass percentage of Ni and Mn dissolved in the positive electrode material, M2, was calculated.

[0030] The sum of the dissolution rates (c) of nickel and manganese ions of the cathode material after being stored in hydrofluoric acid solution at 70℃ for 72 hours was calculated using the formula c=M2 / M1×100%.

[0031] The digestion methods are as follows: disperse the positive electrode material in 20 mL of water, add 10 mL of nitric acid (HNO3 mass percentage is 66%), disperse and heat until the positive electrode material is completely dissolved, dilute with water to 100 mL to obtain the test solution, and perform ICP test on the test solution;

[0032] The ICP instrument can be the Thermo Fisher Scientific ICAP7400, set to 1150W RF power and 0.5L / min carrier gas flow rate.

[0033] The constant current ratio at 45℃ and 1C rate (b) and the sum of the dissolution rates of nickel and manganese ions of the cathode material after 72 hours of storage in hydrofluoric acid solution at 70℃ (c) both affect the fast charging capability and cycle performance of lithium-ion secondary batteries to varying degrees. Moreover, the dissolution of nickel and manganese ions will cause the cathode structure to deteriorate, collapse, and increase the internal impedance of the battery, thus affecting the constant current ratio. At the same time, the improvement of the latter (i.e., the sum of the dissolution rates of nickel and manganese ions of the cathode material after 72 hours of storage in hydrofluoric acid solution at 70℃ (c)) will affect the fast charging performance to some extent. In order to improve the dissolution rate of transition ions, it is possible to set a coating layer, change the particle diameter, etc., which will affect the lithium ion transport and thus affect the former (i.e., the constant current ratio at 45℃ and 1C rate (b)). b and c have mutual influence, and it is difficult to achieve both excellent fast charging capability and cycle performance by controlling a single variable. This application achieves a balance between the cathode interface stability and kinetic performance of LNMO batteries by controlling the constant current ratio at 45°C and 1C rate (b) and the sum of the dissolution rates of nickel and manganese ions after the cathode material is stored in hydrofluoric acid solution at 70°C for 72 hours (c) to satisfy the above specific relationship, thus ensuring that LNMO batteries have both excellent cycle performance and fast charging performance.

[0034] In this application, 6 ≤ b × c ≤ 45. The value of b × c can be selected from 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45 or any two of the above values ​​forming an interval range.

[0035] In one preferred embodiment, the secondary battery satisfies: 13 ≤ b × c ≤ 28. Controlling the value of b × c within this specific range helps to improve the balance between positive electrode interface stability and kinetic performance, thereby optimizing the coordination between the battery's fast charging capability and cycle performance.

[0036] In some embodiments, the range of b is 60% ≤ b ≤ 93%, for example, b is 60%, 62%, 65%, 67%, 70%, 72%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 93%, or any interval formed by any two of the above values. In some embodiments, the range of b is 60% ≤ b ≤ 90%. In one preferred embodiment, the range of b is 75% ≤ b ≤ 85%.

[0037] When the constant current ratio (b) of the charging at 45℃ and 1C rate is in the range of 60%~90%, especially in the range of 75%~85%, the lithium-ion insertion and extraction are smoother, and the electrode material is subjected to lower stress during the lithium-ion insertion and extraction process. The electrode material has good stability, which is conducive to optimizing the coordination between the battery's fast charging capability and cycle performance.

[0038] In some embodiments, the range of c is 0.07% ≤ c ≤ 0.65%, for example, c is 0.07%, 0.08%, 0.09%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, or an interval formed by any two of the above values. In some embodiments, the range of c is 0.08% ≤ c ≤ 0.60%. In one preferred embodiment, the range of c is 0.15% ≤ c ≤ 0.35%.

[0039] When the sum of the dissolution rates (c) of nickel ions and manganese ions of the cathode material after being stored in hydrofluoric acid solution at 70°C for 72 hours is in the range of 0.08% to 0.60%, especially in the range of 0.15% to 0.35%, not only is the stability of the cathode interface better, but the degree of "passivation" of the cathode surface is also low, and the diffusion of electrons and ions is good, which is conducive to optimizing the coordination between the fast charging capability and cycle performance of the battery.

[0040] In some embodiments, the diameter of the lithium nickel manganese oxide particles ranges from 3 to 8 μm. This application does not limit the method for detecting the diameter of the lithium nickel manganese oxide particles; those skilled in the art can detect the diameter of the lithium nickel manganese oxide particles using conventional techniques. For example, the diameter of the lithium nickel manganese oxide particles can be detected using the following method:

[0041] Take a sample and place it in a sample tube, add anhydrous ethanol, and sonicate at 25°C for 40 min to obtain a suspension;

[0042] Use a pipette to drop the suspension onto a copper grid and place it in a vacuum drying oven to dry completely.

[0043] The dried sample was placed on the test stage and transferred to the cavity. The particle diameter was measured using TEM. 100 particles were selected and the average particle diameter was calculated to obtain the diameter of the lithium nickel manganese oxide particles.

[0044] The lithium nickel manganese oxide particles are spinel type with the chemical formula LiNi. x Mn 2-x O4, where x > 0, such as 0.1, 0.2, 0.3, 0.4, 0.5, or any range formed by two of the above values. The lithium nickel manganese oxide particles may or may not contain doped elements. This application does not limit the type of doped element in the lithium nickel manganese oxide; for example, it may be at least one of Al, P, Mg, Zr, etc. The surface of the lithium nickel manganese oxide particles may or may not have a coating layer.

[0045] In some embodiments, the surface of the lithium nickel manganese oxide particles is further provided with a coating layer, which may be disposed on part or all of the surface of the lithium nickel manganese oxide particles. The material of the coating layer may be selected from at least one of alumina, tungsten oxide, and zirconium oxide, but is not limited thereto. By coating the lithium nickel manganese oxide particles as described above, side reactions between the positive electrode and the electrolyte can be suppressed, thereby improving the cycle performance of the battery.

[0046] In some embodiments, the ratio of the thickness of the coating layer to the diameter of the lithium nickel manganese oxide particle ranges from 0.5 to 4.5 nm / μm, for example, this ratio is 0.5 nm / μm, 0.8 nm / μm, 1 nm / μm, 1.5 nm / μm, 2 nm / μm, 2.5 nm / μm, 3 nm / μm, 3.5 nm / μm, 4 nm / μm, 4.5 nm / μm, or any range formed by two of the above values. In one embodiment, the ratio of the thickness of the coating layer to the diameter of the lithium nickel manganese oxide particle ranges from 0.5 to 4.5 nm / μm.

[0047] When the ratio of the thickness of the coating layer to the diameter of the lithium nickel manganese oxide particles is controlled within the range of 0.5~4.5 nm / μm, the lithium nickel manganese oxide particles can have both high strength and kinetic properties, while the coating layer can better suppress the side reactions between the positive electrode and the electrolyte, and also has moderate resistance to ion and electron transport.

[0048] In some embodiments, the thickness of the coating layer ranges from 2 to 35 nm, for example, the thickness is 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 35 nm, or any range formed by two of the above values. In one embodiment, the thickness of the coating layer ranges from 2 to 20 nm.

[0049] This application does not limit the method for detecting the thickness of the coating layer and the ratio of the coating layer thickness to the diameter of the lithium nickel manganese oxide particles. Those skilled in the art can detect the thickness of the coating layer and the ratio of the coating layer thickness to the diameter of the lithium nickel manganese oxide particles using conventional techniques. For example, the thickness of the coating layer and the diameter of the lithium nickel manganese oxide particles can be detected using the following method:

[0050] Take a sample and place it in a sample tube, add anhydrous ethanol, and sonicate at 25°C for 40 min to obtain a suspension;

[0051] Use a pipette to drop the suspension onto a copper grid and place it in a vacuum drying oven to dry completely.

[0052] The dried sample was placed on the test stage and transferred into the cavity. The thickness of the coating layer and the diameter of the core were measured using TEM. Fifty particles were selected, and the average thickness of the coating layer of the particles was calculated to obtain the thickness of the coating layer. At the same time, the average diameter of the core of these particles was calculated to obtain the diameter of the lithium nickel manganese oxide particles.

[0053] This application does not limit the preparation method of the lithium nickel manganese oxide particles. Those skilled in the art can prepare the lithium nickel manganese oxide particles using conventional techniques. For example, the lithium nickel manganese oxide particles can be prepared using a method including the following steps:

[0054] Lithium nickel manganese oxide particles are obtained by mixing and dispersing lithium, nickel, and manganese sources, calcining, and cooling. The calcination conditions can be selected as follows: calcination temperature 600~900℃, calcination time 6~48h.

[0055] The lithium source includes, but is not limited to, at least one of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium acetate; and / or

[0056] Nickel sources include, but are not limited to, at least one of nickel hydroxide, nickel carbonate, and nickel nitrate; and / or

[0057] The manganese source includes, but is not limited to, at least one of manganese dioxide, manganese hydroxide, manganese oxide, and manganese sulfate.

[0058] The lithium nickel manganese oxide particles prepared by the above preparation method can also be coated as needed. For example, atomic layer deposition (ALD) technology can be used to coat the surface of the lithium nickel manganese oxide particles with a coating material. The coating material can be selected from at least one of alumina, tungsten oxide, zirconium oxide, etc. The number of ALD deposition layers can be selected from 20 to 350 layers, and the thickness of one ALD deposition layer can be selected from 0.1 to 0.3 nm.

[0059] When preparing lithium nickel manganese oxide particles, a certain amount of dopant element source (if any) can be mixed and dispersed together with lithium source, nickel source and manganese source to prepare lithium nickel manganese oxide particles. The dopant element source is at least one of Si, Mg, P, Co, Al, Cr, Nb, etc., to obtain lithium nickel manganese oxide particles containing a certain amount of dopant element.

[0060] In some embodiments, the compaction density of the positive electrode sheet ranges from 2.5 to 3.5 g / cm³. 3 For example, the compaction density is 2.5 g / cm³. 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 3.0g / cm 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 The range formed by any two of the above values ​​is not only beneficial for electrolyte wetting, but also for good contact between positive electrode material particles, which helps to improve lithium-ion transport efficiency and thus improve the fast charging performance of the battery.

[0061] This application does not limit the method for detecting the compaction density of the positive electrode sheet. Those skilled in the art can detect the compaction density of the positive electrode sheet using conventional techniques. For example, the compaction density of the positive electrode sheet can be detected using the following method:

[0062] Disassemble the empty battery to obtain the positive electrode. Soak the positive electrode in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode. Take it out and air dry it at room temperature with humidity ≤15%.

[0063] The pretreated positive electrode sheet is punched into circular pieces of a fixed area using a punching machine. The area is recorded as S0. To ensure the accuracy of the test, a piece is taken from the middle and flat position of the electrode sheet. Three circular pieces are taken as parallel samples. The mass of the three circular pieces is weighed using an electronic balance, and the average value is recorded as M1. The thickness of the three circular pieces is measured using a micrometer, and the average value is recorded as H. Finally, an appropriate amount of deionized water is dropped onto each of the three circular pieces. The coating on the circular pieces is gently wiped off with lint-free paper to expose the copper foil. The pieces are left to stand at room temperature (or dried) for 10 minutes. After the copper foil is dry, the mass of the three copper foil pieces is weighed, and the average value is recorded as M0. The coating compaction density A is calculated according to the following formula: A = (M1 - M0) / (H × S0).

[0064] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode material is 93% to 98%, such as 93%, 94%, 95%, 96%, 97%, 98%, or any range formed by any two of the above values.

[0065] In addition to the aforementioned positive electrode active material, the positive electrode material also includes a conductive agent and a binder.

[0066] The conductive agent in the cathode material is used to provide conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent in the cathode material includes, but is not limited to, at least one of carbon nanotubes (CNTs), carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon blacks are, for example, SP (Super P), acetylene black, and Ketjen black.

[0067] In some embodiments, the mass percentage of the conductive agent in the positive electrode material is 0.05% to 4%, such as 0.05%, 1%, 2%, 3%, 4%, or any range formed by any two of the above values.

[0068] The binder in the positive electrode material is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesion and does not significantly cause adverse chemical changes in the battery. For example, the binder in the positive electrode material layer includes, but is not limited to, fluorinated polyolefin binders, including but not limited to polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified derivatives (e.g., modified with carboxylic acids, acrylic acid, acrylonitrile, etc.).

[0069] In some of these embodiments, the mass percentage content of the binder in the positive electrode material is 0.5% to 3%, such as 0.5%, 1%, 2%, 3%, or the range formed by any two of the above values.

[0070] The positive electrode material can be located on one side of the positive electrode current collector or on both sides of the positive electrode current collector.

[0071] This application places no special restrictions on the positive electrode current collector, as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, aluminum, nickel, titanium, stainless steel, fired carbon can be used; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.

[0072] The positive electrode sheet of this application can be prepared according to conventional methods in the art. For example, the positive electrode active material, conductive agent, and binder are dispersed in a solvent to obtain a positive electrode slurry, and then the positive electrode slurry is coated on at least one side of the positive electrode current collector. After processes such as drying, cold pressing, and slitting, a positive electrode sheet is obtained. Among them, the solvents used to prepare the positive electrode slurry include but are not limited to at least one of N-methylpyrrolidone (NMP) and deionized water.

[0073] In some of these embodiments, the secondary battery further includes a negative electrode sheet.

[0074] The negative electrode sheet of this application includes a negative electrode current collector and a negative electrode material located on at least one surface of the negative electrode current collector, and the negative electrode material contains a negative electrode active material.

[0075] This application places no special restrictions on the negative electrode active material. Exemplarily, the negative electrode active material includes but is not limited to natural graphite, artificial graphite, hard carbon, soft carbon, mesocarbon microbeads (MCMB), silicon, SiO x (0 < x < 2, such as x = 1), silicon carbide, Li4Ti5O 12 and at least one of them.

[0076] In some of these embodiments, the mass percentage content of the negative electrode active material in the negative electrode material is 94% to 98%, such as 94%, 95%, 96.4%, 97%, 98%, or the range formed by any two of the above values.

[0077] The negative electrode material may further contain a conductive agent and / or a binder.

[0078] The conductive agent in the negative electrode material is used to provide conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent in the negative electrode material includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP, acetylene black, Ketjen black, etc.

[0079] In some embodiments, the mass percentage of the conductive agent in the negative electrode material is 0.5% to 2.5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, or any range formed by any two of the above values.

[0080] The binder in the negative electrode material is used to improve the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesion and does not significantly cause adverse chemical changes in the battery. For example, the binder in the negative electrode material includes, but is not limited to, at least one of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, and aqueous acrylic resin.

[0081] In some embodiments, the mass percentage of binder in the negative electrode material is 1% to 4%, such as 1%, 1.4%, 2%, 3%, 4%, or any range formed by any two of the above values.

[0082] As needed, the negative electrode material may also contain a thickener. The thickener in the negative electrode material is used to prevent the agglomeration and sedimentation of components such as the negative electrode active material and conductive agent in the slurry, ensuring good dispersion of each component in the slurry. Any thickener can be used without particular limitation, as long as it has suitable thickening properties and does not significantly cause adverse chemical changes in the battery. For example, the thickener in the negative electrode material includes, but is not limited to, at least one of carboxymethyl cellulose (CMC) and styrene-butadiene rubber.

[0083] In some embodiments, the mass percentage of thickener in the negative electrode material is 0.5% to 1.5%, such as 0.5%, 0.8%, 1%, 1.2%, 1.5%, or any range formed by any two of the above values.

[0084] The negative electrode material can be located on one side of the negative electrode current collector or on both sides of the negative electrode current collector.

[0085] This application does not impose any particular restrictions on the negative electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can use, for example: copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with at least one of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0086] In some embodiments, the secondary battery further includes an electrolyte.

[0087] The electrolyte used in this application can be any of the various electrolytes suitable for batteries in the art.

[0088] In some embodiments, the ionic conductivity of the electrolyte ranges from 2 to 6 mS / cm, for example, 2 mS / cm, 2.2 mS / cm, 2.4 mS / cm, 2.6 mS / cm, 2.8 mS / cm, 3 mS / cm, 3.2 mS / cm, 3.4 mS / cm, 3.6 mS / cm, 3.8 mS / cm, 4 mS / cm, 4.2 mS / cm, 4.4 mS / cm, 4.6 mS / cm, 4.8 mS / cm, 5 mS / cm, 5.2 mS / cm, 5.4 mS / cm, 5.6 mS / cm, 5.8 mS / cm, 6 mS / cm, or any range formed by two of the above values. In one embodiment, the ionic conductivity of the electrolyte ranges from 3 to 5 mS / cm. Controlling the ionic conductivity of the electrolyte to a range of 2~6 mS / cm, especially 3~5 mS / cm, not only enhances the electrolyte's own lithium-ion transport capacity, but also makes the electrolyte viscosity suitable, reducing the resistance of viscosity to lithium-ion diffusion. At the same time, it can also reduce the electrolyte's oxidation resistance and reduce its side reactions at the positive electrode interface, thereby improving the battery's fast charging capability and cycle performance.

[0089] This application does not limit the method for detecting the ionic conductivity of the electrolyte. Those skilled in the art can detect the ionic conductivity of the electrolyte using conventional techniques. For example, the ionic conductivity of the electrolyte can be tested according to the national standard GB / T 11007-2008.

[0090] The electrolyte comprises an electrolyte and a solvent, and the electrolyte may typically include a lithium salt.

[0091] For example, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be selected from 0.5 to 2 mol / L, such as 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or any range formed by two of the above values.

[0092] For example, the solvent includes, but is not limited to, at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The mass percentage of the solvent in the electrolyte can be selected from 70% to 98%, such as 70%, 75%, 80%, 85%, 90%, 95%, 98%, or any range formed by any two of the above values.

[0093] In some embodiments, the electrolyte contains a solvent, which includes an ester solvent. Adding an ester solvent can improve oxidation resistance while maintaining high ionic conductivity. In one preferred embodiment, the ester solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC).

[0094] Additives can be added to the electrolyte as needed. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery high-temperature performance, battery overcharge performance, and battery low-temperature performance.

[0095] In some embodiments, the secondary battery further includes a separator.

[0096] The separator is located between the positive and negative electrode plates, serving to separate them and prevent short circuits caused by contact. The separator can be any battery-grade separator material suitable for use in the art. For example, the separator includes, but is not limited to, at least one of polypropylene and polyethylene.

[0097] Electrical appliances

[0098] This application also provides an electrical device that includes the aforementioned secondary battery. The secondary battery serves as the power supply for the electrical device.

[0099] The term "electrical device" refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other energy forms, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, and e-cigarettes; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0100] The present application is further illustrated below with specific embodiments. It should be noted that, unless otherwise specified, the sintering is carried out in an air atmosphere:

[0101] Example 1

[0102] This embodiment provides a secondary battery, and the specific preparation method is as follows:

[0103] (1) Preparation of positive electrode

[0104] Li₂CO₃, NiCO₃, and MnO₂ were combined according to the chemical formula LiNi 0.5 Mn 1.5 The stoichiometric ratios of Li, Ni, and Mn in O4 were added to a ball mill and mixed and dispersed to obtain a mixture. This mixture was then placed in a muffle furnace and heated to 850℃ (the calcination temperature) for 12 hours. After cooling to room temperature, a bare lithium nickel manganese oxide sample was obtained. An alumina coating layer was then deposited on the surface of the bare lithium nickel manganese oxide sample using an ALD instrument, with 100 deposition cycles, each cycle having a thickness of 0.1 nm, resulting in alumina-coated LiNi. 0.5 Mn 1.5 O4;

[0105] The resulting alumina-coated LiNi 0.5 Mn 1.5 O4 was used as the positive electrode active material. The positive electrode active material, conductive agent CNTs, and binder PVDF were mixed at a mass ratio of 97:1:2. NMP solvent was added, and the mixture was stirred and dispersed under the action of a vacuum stirrer to obtain the positive electrode slurry.

[0106] The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, a compacted density of 2.8 g / cm³ was obtained. 3 The positive electrode plate.

[0107] (2) Preparation of the separating membrane

[0108] A polyethylene (PE) diaphragm with a thickness of 15 μm is used.

[0109] (3) Preparation of negative electrode sheet

[0110] The negative electrode active material graphite, conductive agent acetylene black, thickener CMC, and binder SBR were mixed in a mass ratio of 96.4:1:1.2:1.4, and deionized water was added as solvent. The mixture was stirred and dispersed under vacuum to obtain a negative electrode slurry.

[0111] The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the negative electrode sheet is obtained.

[0112] (4) Preparation of electrolyte

[0113] Ethylene carbonate (EC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) were mixed in a volume ratio of 5:3:2 to obtain a mixed organic solvent. Then, dried lithium salt LiPF6 was dissolved in the above mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0114] (5) Preparation of secondary batteries

[0115] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, a copper wire is inserted as a reference electrode, and the bare cell is obtained by winding.

[0116] The bare battery cell is placed in the outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, it is left to stand for 24 hours and then formed to obtain a secondary battery. The specific formation steps are as follows: using the LAND system, the battery is first charged to 4.5V at a constant current rate of 0.05C, then charged to 4.8V at a constant current and constant voltage rate of 0.33C, and then discharged to 3.5V at a constant current rate of 0.33C. After that, the above charge and discharge program is repeated for one cycle (i.e., a total of 2 cycles).

[0117] Examples 2-22 and Comparative Examples 1-2

[0118] These examples and comparative examples all provide a secondary battery, and the preparation method is similar to that of Example 1, except that:

[0119] (a) In step (1), the calcination temperature, type and number of ALD deposition materials, and compaction density of the positive electrode sheet are shown in Table 1;

[0120] (b) In step (4), the volume ratios of EC, DMC and FEC are shown in Table 1.

[0121] Table 1

[0122]

[0123] The coated LiNi in each embodiment and comparative example was tested using the following method. 0.5 Mn 1.5 The following parameters were measured: the diameter (core diameter) and coating thickness of lithium nickel manganese oxide particles (O4, i.e., positive electrode active material); the compaction density of the positive electrode sheet; the ionic conductivity of the electrolyte; the constant current ratio of the secondary battery at 45℃ and 1C rate (b); and the sum of the dissolution rates of nickel and manganese ions of the positive electrode material after storage in hydrofluoric acid solution at 70℃ for 72 hours (c). The cycle performance and fast-charging performance of the secondary battery were also tested. Specific test methods are as follows:

[0124] (1) Coated LiNi 0.5 Mn 1.5 Detection of lithium nickel manganese oxide particle diameter and coating thickness in O4

[0125] Take a sample and place it in a sample tube, add anhydrous ethanol, and sonicate at 25°C for 40 min to obtain a suspension;

[0126] Use a pipette to drop the suspension onto a copper grid and place it in a vacuum drying oven to dry completely.

[0127] The dried sample was placed on the test stage and transferred into the cavity. The thickness of the coating layer and the diameter of the core were measured using TEM. Fifty particles were selected, and the average thickness of the coating layer of the particles was calculated to obtain the thickness of the coating layer. At the same time, the average diameter of the core of these particles was calculated to obtain the diameter of the lithium nickel manganese oxide particles.

[0128] (2) Test of compaction density of positive electrode sheet

[0129] Disassemble the empty battery to obtain the positive electrode. Soak the positive electrode in DMC (dimethyl carbonate) at room temperature (25℃) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode. Take it out and air dry it at room temperature with humidity ≤15%.

[0130] The pretreated positive electrode sheet is punched into circular pieces of a fixed area using a punching machine. The area is recorded as S0. To ensure the accuracy of the test, a piece is taken from the middle and flat position of the electrode sheet. Three circular pieces are taken as parallel samples. The mass of the three circular pieces is weighed using an electronic balance, and the average value is recorded as M1. The thickness of the three circular pieces is measured using a micrometer, and the average value is recorded as H. Finally, an appropriate amount of deionized water is dropped onto each of the three circular pieces. The coating on the circular pieces is gently wiped off with lint-free paper to expose the copper foil. The pieces are left to stand at room temperature (or dried) for 10 minutes. After the copper foil is dry, the mass of the three copper foil pieces is weighed, and the average value is recorded as M0. The coating compaction density A is calculated according to the following formula: A = (M1 - M0) / (H × S0).

[0131] (3) Detection of ionic conductivity of electrolyte

[0132] The test was conducted in accordance with the national standard GB / T 11007-2008.

[0133] (4) Detection of constant current ratio (b) at 45℃ and 1C rate

[0134] At 45℃, the battery is charged and discharged at a rate of 1C for 2 cycles in an empty state. The ratio of the constant current charging capacity to the total charging capacity in the second cycle is calculated. The result is the constant current ratio (b) at 45℃ and 1C rate. The voltage range is 3.5~4.8V. During charging, the battery is first charged at 1C constant current to the upper limit voltage of 4.8V, and then charged at constant voltage until the current is less than or equal to 0.05C. During discharging, the battery is discharged at 1C to 3.5V.

[0135] (5) Detection of the sum of the dissolution rates (c) of nickel and manganese ions of the cathode material after storage in hydrofluoric acid solution at 70°C for 72 h.

[0136] Disassemble the empty battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and dry it at room temperature with humidity ≤15%. Scrape off the positive electrode material on the surface of the current collector and digest it to obtain a sample solution. Then, use ICP (inductively coupled plasma) to determine the content of Ni and Mn in the sample solution. Calculate the mass percentage of Ni and Mn in the positive electrode material accordingly. Measure three parallel samples according to this method and calculate the average value M1 of the mass percentage of Ni and Mn in the positive electrode material.

[0137] The empty battery was disassembled and the positive electrode material was obtained by the above method. The obtained positive electrode material was added to an HF solution with a mass percentage of 30% at a material-to-liquid ratio of 1g:5mL. The solution was stored at a constant temperature of 70℃ for 72h, then centrifuged. The supernatant was taken and the contents of Ni and Mn were determined by ICP method. The mass percentage of Ni and Mn dissolved in the positive electrode material was calculated accordingly. Three parallel samples were measured according to the method and the average mass percentage of Ni and Mn dissolved in the positive electrode material, M2, was calculated.

[0138] The sum of the dissolution rates (c) of nickel and manganese ions of the cathode material after being stored in hydrofluoric acid solution at 70℃ for 72 hours was calculated using the formula c=M2 / M1×100%.

[0139] The digestion methods are as follows: disperse the positive electrode material in 20 mL of water, add 10 mL of nitric acid (HNO3 mass percentage is 66%), disperse and heat until the positive electrode material is completely dissolved, dilute with water to 100 mL to obtain the test solution, and perform ICP test on the test solution;

[0140] The ICP instrument can be the Thermo Fisher Scientific ICAP7400, set to 1150W RF power and 0.5L / min carrier gas flow rate.

[0141] (6) 45℃ cyclic test

[0142] The LAND system was used to perform cycle performance testing on the secondary battery. The battery was cycled 100 times at 45°C with a 1C / 1C charge / discharge rate. It was charged at a constant current of 1C to 4.8V, with a cutoff current less than or equal to 0.05C, and then discharged at 1C to 3.5V, which was considered one cycle. After the cycle, the data was processed to obtain the capacity retention rate (capacity retention rate after n cycles = discharge capacity at week n / discharge capacity at week one × 100%), thus obtaining the capacity retention rate after 100 cycles.

[0143] (7) Fast charging time test at room temperature (i.e., 25℃) with 10%-80% SOC

[0144] At 25℃, using the LAND system, the battery was first cycled twice at a 0.33C rate within a voltage range of 3.5V to 4.8V. The final cycle's capacity was set as C1. First, the battery was charged at a constant current rate of 0.33C1 to 10% SOC. Then, it was sequentially charged at constant current rates of 4C1, 3C1, 2.5C1, 2C1, 1.2C1, and 0.8C1 to 4.80V. After each different constant current charge, constant voltage charging was performed until the cutoff current was ≤0.05C or the negative reference electrode potential was below 0 mV. Finally, it was charged again at a constant current and constant voltage rate of 0.33C1 to 4.80V, with a cutoff current of 0.05C. After the test, the time taken to charge the battery from 10% to 80% SOC was calculated; this is the fast charging time. (Starting from 4C1, the charging capacity is calculated cumulatively according to the charging rate of each segment. If the cumulative capacity is ≥80% SOC, the time consumed in these processes is added together.)

[0145] The test results are shown in Table 2.

[0146] Table 2

[0147]

[0148] As shown in Table 2, the batteries prepared in each embodiment of this application have a capacity retention rate of ≥82% after 100 cycles at 45℃, and a fast charging time of ≤33.2 min at room temperature from 10% to 80% SOC. It can be seen that the batteries of this application have both excellent cycle performance and fast charging performance.

[0149] Comparing Examples 1 and 4-5 with Examples 2-3 and 12, and Examples 6-7, 10-11, and 13-15 with Examples 8-9, it can be seen that when the constant current ratio (b) of charging at 45°C and 1C rate and the sum of the dissolution rates of nickel and manganese ions of the cathode material after being stored in hydrofluoric acid solution at 70°C for 72 hours (c) meet the preferred range described in this application, the balance between cycle performance and fast charging performance is better.

[0150] Comparing Examples 1 and 4-5 with Examples 8 and 9, and comparing Examples 2-3 and 12 with Examples 6-7, 10-11, and 13-15, it can be seen that when the secondary battery satisfies 13≤b×c≤28, the balance between cycle performance and fast charging performance is better.

[0151] According to Comparative Examples 1 and 2, even if the constant current ratio (b) at 45°C and 1C rate and the sum of the dissolution rates of nickel and manganese ions (c) of the cathode material after being stored in hydrofluoric acid solution at 70°C for 72 hours are within a suitable range, the cycle performance and fast charging performance of the battery are relatively poor when the value of b×c exceeds the range of 6 to 45.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. 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 article without departing from the essence and scope of the technical solutions of this article.

Claims

1. A secondary battery, characterized in that, The device includes a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material located on at least one surface of the positive current collector, the positive electrode material comprising a positive electrode active material, the positive electrode active material comprising lithium nickel manganese oxide particles; The secondary battery satisfies: 6≤b×c≤45; Where b is the constant current ratio for charging at 45℃ and 1C rate, in percentage terms. c represents the sum of the dissolution rates of nickel and manganese ions of the cathode material after storage in hydrofluoric acid solution at 70°C for 72 hours, expressed in units of _____.

2. The secondary battery as described in claim 1, characterized in that, The secondary battery satisfies: 13≤b×c≤28.

3. The secondary battery as described in claim 1 or 2, characterized in that, The range of b is 60% ≤ b ≤ 90%.

4. The secondary battery as described in claim 1 or 2, characterized in that, The range of c is 0.08% ≤ c ≤ 0.60%.

5. The secondary battery as described in claim 1 or 2, characterized in that, The surface of the lithium nickel manganese oxide particles is further provided with a coating layer, and the material of the coating layer is selected from at least one of alumina, tungsten oxide, and zirconium oxide.

6. The secondary battery as described in claim 5, characterized in that, The ratio of the thickness of the coating layer to the diameter of the lithium nickel manganese oxide particles ranges from 0.5 to 4.5 nm / μm; and / or The thickness of the coating layer ranges from 2 to 20 nm.

7. The secondary battery as described in claim 1 or 2, characterized in that, The diameter of the lithium nickel manganese oxide particles ranges from 3 to 8 μm.

8. The secondary battery as described in claim 1 or 2, characterized in that, The compaction density of the positive electrode sheet ranges from 2.5 to 3.5 g / cm³. 3 .

9. The secondary battery as described in claim 1 or 2, characterized in that, The secondary battery also includes an electrolyte, the electrolyte having an ionic conductivity range of 3~5 mS / cm.

10. The secondary battery as described in claim 1 or 2, characterized in that, The secondary battery also includes an electrolyte, which contains a solvent, and the solvent contains an ester solvent.

11. The secondary battery as described in claim 10, characterized in that, The ester solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 11.

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