Secondary battery and electric device
Patent Information
- Application Number
- PCT/CN2026/086128
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-04-15
- Filing Date
- 2026-03-26
- Publication Date
- 2026-10-22
Smart Images
Figure PCTCN2026086128-FTAPPB-I100001 
Figure PCTCN2026086128-FTAPPB-I100002 
Figure PCTCN2026086128-FTAPPB-I100003
Abstract
Description
Secondary batteries and electrical devices
[0001] Cross-references to related applications
[0002] This application claims priority to Chinese Patent Application No. 202510473396.X, filed on April 15, 2025, the entire contents of which are incorporated herein by reference. Technical Field
[0003] This application relates to the field of battery technology, specifically to a secondary battery and an electrical device. Background Technology
[0004] Due to their high energy density and long cycle life, rechargeable batteries have become the main power source for electric vehicles. Novel high-performance cathode active materials, a key component of rechargeable batteries, have received extensive research attention.
[0005] Lithium nickel oxide (LiNiO) has become the mainstream cathode active material for high-performance electric vehicles due to its superior specific capacity, high voltage plateau, and high solid density. To further improve the energy density of LiNiO, the Ni content needs to be increased. However, with increasing Ni content, Ni located at the octahedral center tends to enter Li sites in the crystal lattice, leading to a decrease in electrochemical activity. LiNiO is typically charged to high voltages to achieve high energy density, but this simultaneously triggers various structural failure mechanisms, such as cracking due to lattice collapse, gas release, and structural reconstruction (or surface densification). These interconnected degradation phenomena may occur synergistically, resulting in deterioration of battery cycle performance and continuous voltage plateau decay.
[0006] Therefore, this application is submitted. Summary of the Invention
[0007] The purpose of this application is to overcome the shortcomings of the existing technology and provide a secondary battery and power device to improve the cycle performance and rate performance of the secondary battery.
[0008] To achieve the above objectives, a first aspect of this application provides a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising a positive active material comprising secondary particles. The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer comprising a negative active material.
[0009] The secondary battery satisfies: 1≤H≤40, H=(n1 / n2)·D v50 •(C1 / C2);
[0010] Among them, n1 are 0.01mm 2 The area of the positive electrode active material in the positive electrode active material layer is 0.01 mm in the scanning electron microscope (SEM) image. 2 The number of secondary particles with an area diameter ≥ 8 μm;
[0011] n2 pieces / 0.01mm 2 The area of the positive electrode active material in the positive electrode active material layer is 0.01 mm in the SEM image. 2 The number of secondary particles with an area diameter < 8 μm;
[0012] D v50 μm is the volume average particle size of the negative electrode active material;
[0013] C1 mAh / g is the discharge specific capacity of the positive electrode active material tested in the voltage range of 2.8V to 4.3V;
[0014] C2 mAh / g is the discharge specific capacity of the negative electrode active material tested in the voltage range of 0.01V to 2V.
[0015] In some embodiments of this application, the secondary battery satisfies at least one of the following (a) to (e):
[0016] (a) 8 ≤ n1 ≤ 42;
[0017] (b) 6 ≤ n² ≤ 35;
[0018] (c)5≤D v50 ≤16;
[0019] (d)204≤C1≤222;
[0020] (e)364≤C2≤655.
[0021] In some embodiments of this application, the secondary battery satisfies: 0.2≤n1 / n2≤7.
[0022] In some embodiments of this application, the positive electrode active material includes lithium nickel oxide, and the lithium nickel oxide includes materials with the chemical formula Li 1+a [Ni x Co y Mn z M bAt least one of the compounds of O2, wherein M includes at least one of Ti, Zr, Sr, Sb, Nb, Y, Ta, Ru, Nd, V, Ce, Mo, 0.5≤x<1, 0≤y<0.3, 0≤z<0.3, -0.1≤a<0.2, 0≤b<0.3, and x+y+z+b=1.
[0023] In some embodiments of this application, the positive electrode active material further includes a lithium phosphate, wherein the lithium phosphate comprises a lithium-containing phosphate with the chemical formula Li. n Mn t Fe u A s At least one of the compounds of PO4, wherein A includes one or more of Al, Ni, Co, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y, 0.95 <n<1.15,t+u+s=1,0≤t<1,0<u≤1,0≤s≤0.02。
[0024] In some embodiments of this application, the lithium phosphate accounts for 5% to 30% of the mass percentage of the positive electrode active material.
[0025] In some embodiments of this application, the electrolyte includes a fluorinated additive, and the secondary battery satisfies: 0.5 ≤ m2 / m1 ≤ 5;
[0026] Wherein, m1% is the mass percentage content of element M in the lithium nickel oxide;
[0027] m2% is the percentage of the fluorinated additive in the electrolyte by mass.
[0028] In some embodiments of this application, the secondary battery satisfies at least one of the following (f) to (h):
[0029] (f) 0.5 ≤ m1 ≤ 3;
[0030] (g) 1 ≤ m2 ≤ 5;
[0031] (h) The fluorinated additives include one or more of hexafluoroglutaric anhydride, fluoroethylene carbonate, difluoroethylene carbonate, and diethylfluoromalonate.
[0032] In some embodiments of this application, the negative electrode active material includes graphite and silicon oxide materials, wherein the silicon oxide materials account for 1% to 30% of the mass percentage of the negative electrode active material.
[0033] In some embodiments of this application, the porosity of the positive electrode sheet is 20% to 30%; and / or
[0034] The porosity of the negative electrode sheet is 30% to 45%.
[0035] A second aspect of this application provides an electrical device comprising the aforementioned secondary battery.
[0036] The beneficial effects of this application are as follows: This application controls the number of secondary particles of the positive electrode active material in the SEM image (i.e., controls the diameter of the secondary particles in the SEM image), the volume average particle size of the negative electrode active material, and the discharge specific capacity of the positive and negative electrode active materials to satisfy the following relationship: 1≤H≤40, H=(n1 / n2)·D v50 • (C1 / C2); The particle size distribution of the positive electrode active material exhibits a multi-level gradation, maximizing the filling of the particle pores. This effectively improves the compaction density and specific capacity of the positive electrode active material, enhances the wettability of the electrolyte to the secondary particles, thereby effectively reducing interfacial side reactions, minimizing gas generation in the secondary battery, improving the lithium-ion diffusion path, and enhancing the stability of both the positive and negative electrode active material particles, thus increasing the particles' resistance to breakage. Simultaneously, the discharge specific capacity of the positive and negative electrode active materials exhibits good compatibility, effectively improving the cycle performance and rate performance of the secondary battery. Detailed Implementation
[0037] 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, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.
[0038] 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.
[0039] 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 a numerical range refers to an integer, 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, these multiple ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.
[0040] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.
[0041] The inventors of this application have discovered that there are currently two common cathode active material designs on the market. One cathode active material design consists of one or a very small number of primary particles, i.e., single-crystal materials. Single-crystal cathode materials do not contain small grains, therefore there are no grain boundaries, and no intergranular cracks occur. Moreover, their relatively low surface-to-volume ratio minimizes interfacial side reactions, such as gas escape, transition metal dissolution, and side reactions with the electrolyte, thus exhibiting excellent thermal stability. However, in the case of using single-crystal cathode materials, their micron-sized structure leads to longer Li... + The diffusion path leads to poor reaction kinetics and low capacity. Although single-crystal cathode materials have high mechanical strength, their low compaction density is detrimental to improving the energy density of the battery system. Another cathode active material design uses secondary particles composed of many primary particles as the cathode active material. This material also has many problems. For example, in secondary particles of the same size, a large number of primary particles means that the particle size of the primary particles is too small, resulting in a large specific surface area. This can cause severe side reactions between the primary particles and the electrolyte, leading to severe gas production. Moreover, such secondary particles are easily broken during the pressing process, resulting in poor cycle performance, poor thermal stability, and poor safety. In addition, the inventors of this application have also considered different aspects in the particle size design of the secondary particles, because the particle size of the cathode active material has a significant impact on the overall electrochemical performance of the battery. Specifically, small particles have better material kinetics and can be matched with battery systems that have high requirements for fast charging performance, but small particles are not pressure resistant and are easily broken during cycling; large particles can have higher compaction capacity, thereby significantly improving the particle's resistance to breakage, but large particles have poor kinetic performance.
[0042] Therefore, based on the above-mentioned problems, this application provides a secondary battery and an electrical device. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, which includes secondary particles. The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer includes a negative active material.
[0043] The secondary battery satisfies: 1≤H≤40, H=(n1 / n2)·D v50 •(C1 / C2);
[0044] Among them, n1 are 0.01mm 2 The area of the positive electrode active material in the positive electrode active material layer is 0.01 mm in the SEM image.2 The number of secondary particles with an area diameter ≥ 8 μm;
[0045] n2 pieces / 0.01mm 2 The area of the positive electrode active material in the positive electrode active material layer is 0.01 mm in the SEM image. 2 The number of secondary particles with an area diameter < 8 μm;
[0046] D v50 μm is the volume average particle size of the negative electrode active material;
[0047] C1 mAh / g is the discharge specific capacity of the positive electrode active material tested in the voltage range of 2.8V to 4.3V;
[0048] C2 mAh / g is the discharge specific capacity of the negative electrode active material tested in the voltage range of 0.01V to 2V.
[0049] The inventors of this application have discovered that controlling the diameter of the secondary particles in the SEM image of the positive electrode active material, the volume average particle size of the negative electrode active material, and the discharge specific capacity of the positive and negative electrode active materials can affect the performance of the secondary battery. This application controls the diameter of the secondary particles in the SEM image, the volume average particle size of the negative electrode active material, and the discharge specific capacity of the positive and negative electrode active materials to satisfy the following relationship: 1 ≤ H ≤ 40, H = (n1 / n2)·D v50 • (C1 / C2); The particle size distribution of the positive electrode active material exhibits a multi-level gradation, maximizing the filling of the particle pores. This effectively improves the compaction density and specific capacity of the positive electrode active material, enhances the wettability of the electrolyte to the secondary particles, thereby effectively reducing interfacial side reactions, minimizing gas generation in the secondary battery, improving the lithium-ion diffusion path, and enhancing the stability of both the positive and negative electrode active material particles, thus increasing the particles' resistance to breakage. Simultaneously, the discharge specific capacity of the positive and negative electrode active materials exhibits good compatibility, effectively improving the cycle performance and rate performance of the secondary battery.
[0050] In one implementation, 4 ≤ H ≤ 20. Controlling H within this range can further improve cycling performance and rate performance. For example, H can also be a range of one or both of 4, 8, 10, 13, 19, and 20.
[0051] The positive electrode active material in the positive electrode sheet is 0.01 mm thick. 2 The number (n1) of the secondary particles with an area diameter ≥ 8 μm and 0.01 mm 2The number (n2) of secondary particles with an inner diameter < 8 μm can be obtained by the following method: A sample containing the positive electrode active material layer is prepared using a cross-sectional polisher (such as the JEOL IB-09010CP argon ion cross-sectional polisher). After scanning electron microscopy (SEM) testing of the sample, a cross-sectional SEM image of the positive electrode active material particles in the positive electrode active material layer is obtained. A specific area (0.01 mm²) of the obtained sample is then analyzed using the testing software or other tools with measurement capabilities (such as Nanomeature). 2 The diameter of the secondary particles in the sample was measured, and the values were statistically analyzed to be 0.01 mm at a magnification of 1 k. 2 The values of n1 and n2 are obtained by determining the number of secondary particles with a diameter ≥ 8 μm and the number of secondary particles with a diameter < 8 μm within the area.
[0052] The specific testing method for the discharge specific capacity of the positive electrode active material in the voltage range of 2.8V to 4.3V is as follows: The positive electrode active material, conductive agent (carbon black), and binder (polyvinylidene fluoride) are mixed according to the formula ratio of positive electrode active material: conductive agent: binder = 90:5:5. After stirring, a slurry is prepared. After coating, rolling and other processes, a positive electrode sheet is obtained. A lithium sheet is used as the negative electrode, PP polypropylene is used as the separator, and the electrolyte is a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) (according to EC:PC:DMC = 30:30:40 by mass). The positive electrode active material was tested after assembling a coin cell with LiPF6 at a concentration of 1 mol / L in a mixture of proportions. The specific test method was as follows: the assembled coin cell was charged at a constant current of 0.1C to the upper limit voltage of 4.3V, allowed to stand for 5 minutes, charged at the upper limit voltage to the current ≤0.05mA, allowed to stand for 5 minutes, and discharged at a constant current of 0.1C to the lower limit voltage of 2.8V. The discharge specific capacity (unit: mAh / g) was calculated, where the discharge specific capacity = (discharge current × discharge time) / mass of the positive electrode active material, and C is the theoretical capacity of the battery.
[0053] The specific testing method for the discharge specific capacity of the negative electrode active material in the voltage range of 0.01V to 2V is as follows: The negative electrode active material, conductive agent, and binder are mixed according to the formula ratio of negative electrode active material: conductive agent (carbon black): binder (sodium carboxymethyl cellulose) = 90:5:5. After stirring, a slurry is prepared. After coating, rolling and other processes, a negative electrode sheet is obtained. A lithium sheet is used as the reference negative electrode, PP polypropylene is used as the separator, and the electrolyte is a mixed solvent (EC:PC) dissolved in ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC). The coin cells were assembled with 1 mol / L LiPF6 in a 30:30:40 mass ratio of DMC to 1 mol / L and then tested to obtain the discharge specific capacity of the negative electrode active material. The specific testing method was as follows: the assembled coin cells were discharged at a constant current of 0.05C to 0.01V, then discharged at a constant current of 40μA to 0.005V, and finally discharged at a constant current of 10μA to 0.005V. The discharge specific capacity of the negative electrode active material was calculated, where discharge specific capacity = total discharge capacity / mass of negative electrode active material, in mAh / g. The total discharge capacity is the sum of the discharge capacities of the three discharge processes, and the discharge capacity of each discharge process = discharge current × discharge time.
[0054] In one embodiment, 8 ≤ n1 ≤ 42, for example, it can be a range of 8, 10, 12, 14, 16, 22, 26, 30, 34, 38, 42, or any two of these values. By controlling n1 within this range, interfacial side reactions can be effectively reduced, the stability of the positive electrode active material during the tableting process can be effectively improved, and the particle's resistance to breakage can be significantly enhanced, thereby improving the cycle performance and rate performance of the secondary battery.
[0055] In one embodiment, 6 ≤ n2 ≤ 35, for example, it can be a range of 6, 8, 10, 12, 14, 20, 24, 28, 31, 35, or any two of these values. By controlling n2 within this range, the diffusion distance of lithium ions in the secondary particles can be effectively reduced, the lithium ion insertion / extraction rate can be improved, the contact area between the positive electrode active material and the electrolyte can be increased, and the electrochemical reactivity of the secondary battery can be improved, thereby improving the cycle performance and rate performance of the secondary battery.
[0056] In one implementation, 5≤D v50The value is ≤16, for example, it can be a range of 5, 6, 8, 10, 12, 14, 15, 16, or any two of these values. By controlling the volume average particle size of the negative electrode active material within this range, the insertion and extraction of lithium ions are further promoted, allowing for more thorough contact between the negative electrode active material and the electrolyte, forming more active sites, alleviating volume expansion and mechanical stress caused by lithium ion insertion and extraction, and reducing the risk of particle cracking. Simultaneously, the discharge specific capacity of the positive and negative electrode active materials has good compatibility, thereby effectively improving the cycle performance and rate performance of the secondary battery.
[0057] The volume average particle size D of the negative electrode active material v50 As is known in the art, it represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the material. The D-value of the negative electrode active material can be obtained by particle size analysis using a Malvern laser particle size analyzer. v50 The reference standard for particle size analysis is GB-T19077-2016. The specific method includes: obtaining the negative electrode sheet of a secondary battery and placing it in a beaker, adding pure water and ultrasonically dissolving the binder for 1 hour, discarding the upper liquid, and repeating the ultrasonic dissolution step 2-3 times; removing the current collector and filtering to obtain a solid powder sample, drying the powder sample, transferring it to a box furnace, and calcining it at 450℃ for 3-5 hours to obtain the calcined powder sample. The particle size of the calcined powder sample is then analyzed using a Malvern laser particle size analyzer to obtain the D-value of the negative electrode active material in the negative electrode sheet. v50 .
[0058] In one embodiment, 204 ≤ C1 ≤ 222, for example, it can be a range of 204, 208, 210, 215, 220, 222, or any two of these values. By controlling C1 within this range, the amount of lithium removed from the positive electrode active material and the structural stability of the positive electrode active material can be improved, enabling the secondary battery to have both high energy density and long lifespan performance, thereby meeting the requirements of long range and slow degradation for electric vehicles.
[0059] In one implementation, 208 ≤ C1 ≤ 218.
[0060] In one embodiment, 210≤C1≤215.
[0061] In one embodiment, 364 ≤ C2 ≤ 655, for example, it can be a range of 364, 380, 400, 420, 450, 460, 480, 500, 520, 550, 580, 600, 620, 640, 650, 655, or any two of these values. By controlling C2 within this range, the secondary battery can possess both high energy density and long lifespan performance, thereby meeting the requirements of long driving range and slow degradation for electric vehicles.
[0062] In one implementation, 380≤C2≤560.
[0063] In one embodiment, the following condition is satisfied: 0.2 ≤ n1 / n2 ≤ 7, for example, it can be 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, or any two of these values. By controlling the ratio of n1 / n2 within the above range, the filling effect of the particle pores of the positive electrode active material is further optimized, effectively improving the compaction density and specific capacity of the positive electrode active material, increasing the wettability of the electrolyte to the secondary particles, effectively reducing interfacial side reactions, and reducing gas production in the secondary battery.
[0064] In one embodiment, the positive electrode active material comprises lithium nickel oxide, wherein the lithium nickel oxide comprises a material with the chemical formula Li 1+a [Ni x Co y Mn z M b The active cathode material comprises at least one compound of O2, wherein M includes at least one of Ti, Zr, Sr, Sb, Nb, Y, Ta, Ru, Nd, V, Ce, and Mo, with 0.5 ≤ x < 1, 0 ≤ y < 0.3, 0 ≤ z < 0.3, -0.1 ≤ a < 0.2, 0 ≤ b < 0.3, and x + y + z + b = 1. In this embodiment, the lithium nickel oxide is a secondary particle formed by the agglomeration of primary lithium nickel oxide particles. When the positive electrode active material includes the aforementioned lithium nickel oxide containing M, the doping element can widen the lithium interlayer spacing, promote lithium ion transport, inhibit nickel ion migration to the lithium layer, reduce cation mixing, and thus improve the structural stability of the positive electrode active material. Simultaneously, the doping element can strengthen the transition metal-oxygen bond, suppress harmful phase transitions during cycling, and inhibit oxygen release. Therefore, the secondary battery composed of the aforementioned positive electrode active material has superior rate performance and cycle performance.
[0065] In one embodiment, the element M in the lithium nickel oxide may include at least one of Zr, Sr, Ti, Sb, Nb, Y, and Mo. The selection of the above elements for M can effectively suppress lattice distortion of the lithium nickel oxide during charge and discharge processes, enhance the structural stability of the material, reduce the capacity loss of the material caused by volume change and structural degradation during long-term cycling, prolong the cycle life of the battery, improve the electronic conductivity of the material and the transport rate of lithium ions, and improve the charge-discharge efficiency and power performance of the secondary battery.
[0066] In one embodiment, the element M in the lithium nickel oxide may include Zr and Sr. On the one hand, Zr and Sr can suppress Ni at the transition metal sites of the lithium nickel oxide 2+ migration, effectively reduce the degree of cation mixing, and promote the transport of lithium ions. On the other hand, Zr and Sr form Zr-O bonds and Sr-O bonds with high bond energy by bonding with lattice oxygen, which effectively suppresses the lattice distortion of the material during charge and discharge processes and enhances the structural stability of the material.
[0067] In one embodiment, the element M in the lithium nickel oxide may include Nb and Y. Nb and Y can improve the electrical conductivity of the lithium nickel oxide, and at the same time expand the lattice parameters, widen the lithium ion migration path, reduce the lithium ion migration energy barrier, thereby accelerating the migration of lithium ions; Nb and Y can also alleviate anisotropic mechanical strain, inhibit the formation and propagation of microcracks, suppress the erosion of the electrolyte, and reduce the occurrence of side reactions.
[0068] In one embodiment, the positive electrode active material further includes a lithium-containing phosphate, and the lithium-containing phosphate includes a compound having the chemical formula Li n Mn t Fe u A s PO4. In the compound, A includes one or more of Al, Ni, Co, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y, 0.95<n<1.15, t+u+s=1, 0≤t<1, 0<u≤1, 0≤s≤0.02. In this embodiment, the lithium-containing phosphate is primary particles. In one embodiment, the element A in the above lithium-containing phosphate includes one or more of Ti and Al. Ti doping can improve the thermal stability and cycle performance of the material, and Al doping can improve the electronic conductivity of the material and optimize the comprehensive performance of the lithium-containing phosphate.
[0069] In one embodiment, the lithium phosphate comprises 5% to 30% of the positive electrode active material by mass, for example, 5%, 6%, 8%, 10%, 12%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, or any two of these values. This application, by using a combination of lithium nickel oxide and lithium phosphate as the positive electrode active material, benefits from improved electronic conductivity and ion diffusion, mitigates polarization during charging / discharging, enhances power performance under low state of charge (SOC) conditions, improves battery safety, reduces cost, and maintains high energy density.
[0070] In one embodiment, the electrolyte includes a fluorinated additive, and the secondary battery satisfies: 0.5 ≤ m2 / m1 ≤ 5, where m1% is the mass percentage of element M in the lithium nickel oxide; and m2% is the mass percentage of the fluorinated additive in the electrolyte. For example, m2 / m1 can be a range of 0.5, 1, 2, 3, 4, 5, or any two of these values.
[0071] In one embodiment, the mass percentage (m2, %) of the fluorinated additive in the electrolyte is determined by a quantitative analysis method, specifically including sample pretreatment, quantitative detection of fluorinated components, and data calculation. Different pretreatments are performed on the sample depending on the chemical properties of the fluorinated additive and the testing objective. If soluble organic fluorinated additives (such as FEC) need to be measured, the electrolyte sample is weighed in an inert atmosphere, diluted with an anhydrous organic solvent (such as acetonitrile) to precipitate lithium salts, centrifuged, and the supernatant is filtered. Gas chromatography or liquid chromatography is used for determination, and the component content (m2) is calculated based on the electrolyte sample mass. If poorly soluble fluorinated components need to be measured, the residue is separated by centrifugation, washed to remove salt, dried, and then treated using an oxygen flask combustion method to convert organic fluorine into inorganic fluorine, which is then absorbed by the absorbent. Subsequently, according to the detection target, ion chromatography or fluoride ion selective electrode method is used to determine the fluoride ion concentration, and the component content (m2) is calculated based on the sample mass and conversion factor.
[0072] By controlling the value of m2 / m1 within the above range, this application can further improve the interfacial stability between the positive and negative electrodes and the electrolyte, form a stable and dense interfacial film, further improve the stability of the positive electrode active material, effectively inhibit the metal dissolution of the positive electrode active material and the decomposition of the electrolyte, maintain the integrity of the positive electrode sheet, alleviate the volume expansion of the negative electrode active material, and thus further improve the cycle performance and rate performance of the secondary battery.
[0073] The method for testing the type and content of element M is as follows: using energy dispersive X-ray spectroscopy (SEM-EDS) of scanning electron microscopy, surface / line analysis is performed on the cross-sectional composition of the secondary particles of different sizes, thereby determining the composition and content of element M in the polycrystalline secondary particles of different sizes.
[0074] In one implementation, 0.5 ≤ m1 ≤ 3, for example, it can be a range of 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3 or any two of these values.
[0075] In one implementation, 1 ≤ m2 ≤ 5, for example, it can be a range of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any two of these values.
[0076] In one embodiment, the fluorinated additive includes one or more of hexafluoroglutaric anhydride, fluoroethylene carbonate, difluoroethylene carbonate, and diethylfluoromalonate.
[0077] In one embodiment, the negative electrode active material comprises graphite and silicon-oxygen materials, and the silicon-oxygen material accounts for 1% to 30% of the mass percentage of the negative electrode active material, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 16%, 20%, 30%, or any two of these values. This application uses a negative electrode active material composed of graphite and silicon-oxygen materials, which has excellent compatibility with the positive electrode active material. While maintaining the stability of graphite, the high capacity of silicon-oxygen materials can be utilized to improve the capacity and energy density of the negative electrode active material, alleviate the pulverization of the negative electrode active material during repeated charge-discharge processes, provide a stable electron conduction path, and improve the stability of the negative electrode active material, thereby further improving the cycle performance and rate performance of the secondary battery.
[0078] In one embodiment, the porosity of the positive electrode sheet is 20% to 30%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or any two of these values. When the porosity of the positive electrode sheet is within this range, the wettability of the electrolyte is good, resulting in lower polarization and faster lithium-ion transport rate in the secondary battery. Therefore, the internal resistance of the secondary battery is lower, and the cycle performance of the battery is better. Moreover, when the porosity of the positive electrode sheet is within this range, the bonding tightness between the primary particles is moderate, which gives the secondary particles composed of primary particles higher compressive strength, making them more resistant to particle breakage. During long-term cycling, the particles are less likely to break, reducing side reactions between the active surface and the electrolyte, thereby improving the overall performance of the secondary battery.
[0079] In one embodiment, the porosity of the negative electrode sheet is 30% to 45%, for example, it can be a range of 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, or any two of these values. When the porosity of the negative electrode sheet is within this range, it can effectively reduce the expansion of the negative electrode active material during cycling and improve the battery's long cycle life, while maintaining low impedance and effectively improving the material's fast-charging performance. When the porosity of the negative electrode sheet does not meet the target range, it increases the contact and consumption between the negative electrode active material and the electrolyte, resulting in a thicker solid electrolyte interphase (SEI) film, reducing the amount of electrolyte wetting the negative electrode sheet, leading to a significant decrease in the material's cycle life and an increased electrode sheet expansion rate. Simultaneously, when the porosity of the negative electrode sheet does not meet the target range and has a large pore size, it may lead to a decrease in the mechanical stability of the electrode material, thereby affecting the battery's cycle life and safety.
[0080] In one embodiment, the porosity of the positive and negative electrode sheets is determined by the hexadecane absorption method. This method calculates the pore volume by measuring the amount of hexadecane absorbed by the electrode, and determines the porosity by combining the electrode mass and material density. Specifically, the dried electrode sheet is accurately weighed first, then completely immersed in hexadecane for at least 24 hours to ensure the pores are fully filled. Afterward, it is removed and any residual hexadecane on the surface is cleaned. It is then weighed again to calculate the absorbed hexadecane mass. The pore volume is calculated using the density of hexadecane, and the porosity is then calculated by combining this with the apparent volume of the electrode sheet (determined by dimensional measurement or mercury porosimetry), where porosity (%) = (pore volume / apparent volume) × 100%.
[0081] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.
[0082] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
[0083] The present application is further illustrated below with specific embodiments.
[0084] Example 1
[0085] A method for preparing a secondary battery includes the following steps:
[0086] (1) Preparation of positive electrode active material:
[0087] S1. Add nickel sulfate, manganese sulfate and cobalt sulfate to deionized water, mix well, and prepare a mixed solution. Then add the mixed solution to the first reaction vessel. The molar ratio of nickel, manganese and cobalt is Ni:Co:Mn=90:5:5. Then use a metering pump to introduce ammonia water (concentration of 0.4mol / L) and sodium hydroxide aqueous solution (concentration of 1mol / L) into the first reaction vessel, adjust the pH of the reaction system to 11.3, stir well, and obtain a mixed solution.
[0088] S2. Add Nb2O5 to a certain volume of ethanol solution to obtain mixture A. The amount of Nb2O5 added is such that the molar amount of Nb in the lithium nickel oxide is Nb:Me = 0.002:0.996 to the total molar amount of nickel, cobalt and manganese (denoted as Me).
[0089] S3. Add Y2O3 to a certain volume of ethanol solution to obtain mixture B. The amount of Y2O3 added is such that the molar amount of Y element in lithium nickel oxide is in the ratio of the total molar amount of nickel, cobalt and manganese elements to Y:Me = 0.002:0.996.
[0090] S4. Add the mixture A obtained in step 2 and the mixture B obtained in step 3 to the second reactor; then add the mixture obtained in step 1 to the second reactor and stir continuously to carry out a coprecipitation reaction; the coprecipitation reaction is divided into a first stage and a second stage. In the first stage, the stirring speed is 400 rpm, the pH value of the reaction solution is 12.5, the ammonia value is 14 g / L, and the reaction time is 2.5 h; in the second stage, the stirring speed is 500 rpm, the pH value of the reaction solution is 12.0, the ammonia value is 8 g / L, and at the same time, stop adding the mixtures obtained in steps 2 and 3, and react for 3 h to obtain a solid-liquid mixture;
[0091] S5. Filter the solid-liquid mixture obtained in step 4, and wash, dry, sieve, and demagnetize the resulting filter cake to obtain a ternary cathode active material precursor (Ni) with multiple particle size distributions and in-situ doping of oriented elements. 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 (OH)2.
[0092] S6. Add lithium salt Li2CO3 and positive electrode active material precursor (Ni) 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 (OH)₂ was mixed, and then mechanically mixed to obtain a mixture. The amount of lithium carbonate and the positive electrode active material precursor added was such that the molar ratio of lithium to the total molar ratio of nickel, cobalt, and manganese was Li:Me = 1.08:1, and Me = Ni + Co + Mn. The mixture was placed in a tube furnace and sintered at 750℃ for 13 hours in air at a programmed heating rate of 5℃ / min. Afterwards, it was cooled to room temperature with the furnace and crushed to obtain Li particles of different particle sizes. 1.08 (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 O2.
[0093] S7. The lithium nickel oxide Li obtained in step S6 1.08 (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 O2 and lithium phosphate (specifically LiMn) 0.6 Fe 0.4 PO4) is mixed evenly at a mass ratio of 80:20 to obtain the positive electrode active material.
[0094] (2) Preparation of positive electrode sheet
[0095] The positive electrode active material prepared in step (1) above, along with conductive carbon black and polyvinylidene fluoride binder, were added to a high-speed vacuum mixer at a mass ratio of 97.3:1.8:0.9 and mixed evenly. Then, N-methylpyrrolidone was added as a solvent, and the mixture was stirred for 12 hours to obtain a slurry. The slurry was then evenly coated onto the positive electrode current collector aluminum foil using a coating machine and dried in an oven at 110°C. Following rolling, cutting, and slitting processes, the positive electrode sheet was obtained. The designed compaction density of the positive electrode sheet was 3.5 g / cm³. 3 .
[0096] (3) Preparation of negative electrode sheet
[0097] D v50 =12.5μm graphite and D v50 SiO2 with a diameter of 8.5 μm was mixed uniformly at a mass ratio of 95:5 to obtain the negative electrode active material;
[0098] The negative electrode active material, conductive agent acetylene black, binder styrene-butadiene rubber, and negative electrode thickener sodium carboxymethyl cellulose were added to a high-speed vacuum mixer at a mass ratio of 96:2:1:1 and mixed evenly. Deionized water was then added as a solvent, and the mixture was stirred for 12 hours to obtain a slurry. This slurry was then evenly coated onto the negative electrode current collector copper foil using a coating machine and dried in an oven at 120°C. Following rolling, cutting, and slitting processes, the negative electrode sheet was obtained. The designed compaction density of the negative electrode sheet was 1.6 g / cm³. 3 .
[0099] (4) Preparation of the separating membrane
[0100] Polyethylene polymer film was selected as the separator.
[0101] (5) Preparation of electrolyte
[0102] Ethylene carbonate and dimethyl carbonate were mixed in a 1:1 volume ratio to obtain an organic solvent. Lithium hexafluorophosphate was then dissolved in the organic solvent. Hexafluoroglutaric anhydride at a mass percentage of 2.5% (relative to the total mass of the electrolyte) was added as a fluorine-containing additive to prepare the electrolyte, wherein the concentration of lithium hexafluorophosphate was 1 mol / L.
[0103] (6) Preparation of secondary batteries
[0104] The positive electrode sheet, separator, and negative electrode sheet prepared above are wound in sequence to prepare a bare cell. The bare cell is placed in an outer packaging aluminum-plastic film, baked to remove moisture, injected with a certain amount of electrolyte, and vacuum sealed to prepare a secondary battery.
[0105] The relevant parameters of the secondary battery in Example 1 are shown in Tables 1, 2 and 3.
[0106] Examples 2-5
[0107] The difference between the preparation methods of the secondary batteries in Examples 2-5 and Example 1 is that in Examples 2-5, the lithium nickel oxide Li in the preparation process of the positive electrode active material in step (1) is adjusted. 1.08 (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 O2 and lithium-containing phosphates (LiMn is selected as the lithium-containing phosphate) 0.6 Fe 0.38 Ti 0.01 Al 0.01 The mixing mass ratio of PO4 was adjusted to adjust the value of C1.
[0108] Examples 6-9
[0109] The difference between the preparation methods of the secondary battery in Examples 6-9 and Example 1 is that the C2 value was adjusted by adjusting the mass ratio of graphite and SiO2 in the preparation process of the negative electrode sheet in step (3).
[0110] Examples 10-13
[0111] The difference between the preparation method of the secondary battery in Examples 10-13 and that in Example 1 is that, by adjusting the types of doping sources added in S2 and S3 during the preparation of the positive electrode active material in step (1), positive electrode active materials with different types of M element doping were obtained in Examples 10-13.
[0112] Examples 14-17
[0113] The difference between the preparation methods of the secondary battery in Examples 14-17 and in Example 1 is that, in Examples 14-17, the reaction time of the first and second stages of the co-precipitation reaction in step S4 during the preparation of the positive electrode active material in step (1) is adjusted to obtain ternary positive electrode active material precursors with different particle size distributions.
[0114] Examples 18-20
[0115] The difference between Examples 18-20 and the preparation method of the secondary battery in Example 1 lies in the steps of the latter. Examples 18-20 adjust the D of the graphite and SiO2 negative electrode materials used in step (3) of the negative electrode preparation process. v50 , obtained different Dv50 The negative electrode active material.
[0116] Examples 21-23
[0117] The difference between the preparation method of the secondary battery in Examples 21-23 and that in Example 1 is that, in Examples 21-23, the proportion of doping sources added in S2 and S3 during the preparation of the positive electrode active material in step (1) was adjusted to obtain positive electrode active materials with different doping M element contents.
[0118] Examples 24-26
[0119] The difference between the preparation methods of the secondary battery in Examples 24-26 and in Example 1 is that, in Examples 24-26, the content of hexafluoroglutaric anhydride added during the preparation of the electrolyte in step (5) was adjusted to obtain electrolytes with different contents of fluorine additives.
[0120] Examples 27-28
[0121] The difference between the preparation method of the secondary battery in Examples 27-28 and that in Example 1 is that, by adjusting the types of fluorine-containing additives added in the preparation process of the electrolyte in step (5), electrolytes with different types of fluorine-containing additives were obtained in Examples 27-28.
[0122] Comparative Examples 1-2
[0123] The difference between Comparative Examples 1 and 2 and the preparation method of the secondary battery in Example 1 lies in the following steps: Comparative Examples 1 and 2 adjust the reaction time of the first and second stages of the co-precipitation reaction in step S4 of the positive electrode active material preparation process in step (1) to obtain ternary positive electrode active material precursors with different particle size distributions, or adjust the lithium nickel oxide Li in the positive electrode active material preparation process in step (1). 1.08 (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 O2 and LiMn 0.6 Fe 0.4 By adjusting the mixing mass ratio of PO4 (lithium manganese iron phosphate) or by adjusting the mixing mass ratio of graphite and SiO2 during the preparation of the negative electrode in step (3), secondary batteries with different H values were obtained.
[0124] Table 1
[0125] Table 2
[0126] Table 3
[0127] Performance testing
[0128] 1. Test method for specific capacity of secondary batteries at 1 / 3C (i.e., 0.33C)
[0129] The secondary battery was left to stand at a constant temperature of 25℃ for 2 hours. Then, it was charged at a constant current of 0.33C to 4.25V under a voltage range of 2.8V to 4.25V. Next, it was charged at a constant voltage of 4.25V until the current ≤0.05mA, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to 2.8V. The capacity of the secondary battery was recorded. Dividing this capacity test value by the mass of the positive electrode active material in the battery gives the 0.33C specific capacity of the secondary battery. The test results are shown in Table 4.
[0130] 2. Cycle performance test method for secondary batteries
[0131] Under constant temperature conditions of 45℃, the capacitor was charged at a constant current of 1C to 4.25V within a voltage range of 2.8V to 4.25V. Then, it was charged at a constant voltage of 4.25V until the current was ≤0.05mA. After resting for 5 minutes, it was discharged at a constant current of 1C to 2.8V. The capacitance is denoted as D. n (n=0,1,2,……), repeat the above charge and discharge process until the capacity decays to 80% of the initial capacity, and record the number of cycles of the lithium-ion secondary battery. The test results are shown in Table 4.
[0132] 3. High-Temperature Gas Generation Test Method for Secondary Batteries
[0133] At room temperature, the initial volume of the secondary battery was measured by the water displacement method. The secondary battery was charged at a constant current of 1C to 4.25V, and then charged at a constant voltage until the current dropped to 0.05C (fully charged state). It was then placed in a 70℃ constant temperature chamber for 30 days. After cooling to room temperature, the volume of the secondary battery after 30 days of standing was measured by the water displacement method. The volume expansion rate of the secondary battery was calculated according to the following formula: Volume expansion rate of secondary battery (%) = (Volume after 30 days of standing / Initial volume - 1) × 100%.
[0134] Table 4
[0135] As can be seen from Table 1, this application controls the diameter of secondary particles in the SEM image, the volume average particle size of the negative electrode active material, and the discharge specific capacity of the positive and negative electrode active materials to satisfy the following relationship: 1≤H≤40, H=(n1 / n2)·D v50• (C1 / C2) can effectively improve the cycle performance and rate performance of secondary batteries.
[0136] Comparing Examples 17 and 14 with Examples 1-13, 15-16, and 18-28, it can be seen that by controlling 4≤H≤20, the cycle performance and rate performance of the secondary battery can be further improved.
[0137] 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.
Claims
1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising a positive active material comprising secondary particles; the negative electrode comprises a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer comprising a negative active material; The secondary battery satisfies: 1≤H≤40, H=(n1 / n2)·D v50 • (C1 / C2); wherein, n1 per 0.01 mm 2 the number of the secondary particles having a diameter of 8 μm or more within the area of the positive electrode active material in the positive electrode active material layer in an SEM image 2 the number of the secondary particles having a diameter of 8 μm or more within the area of the positive electrode active material in the positive electrode active material layer in an SEM image n2 per 0.01 mm 2 the number of the secondary particles having a diameter < 8 μm within the area of 0.01 mm 2 the number of the secondary particles having a diameter < 8 μm within the area of 0.01 mm D v50 μm is the volume average particle diameter of the negative electrode active material; C1mAh / g is the discharge specific capacity of the positive electrode active material tested in the voltage range of 2.8V to 4.3V; C2mAh / g is the discharge specific capacity of the negative electrode active material obtained by testing in the voltage range of 0.01V to 2V.
2. The secondary battery according to claim 1, wherein the secondary battery satisfies at least one of the following (a) to (e): (a) 8 ≤ n1 ≤ 42; (b) 6 ≤ n² ≤ 35; (c) 5 < D v50 ≤ 16 (d)204≤C1≤222; (e)364≤C2≤655.
3. The secondary battery according to claim 2, wherein 210 ≤ C1 ≤ 215; and / or 380≤C2≤560。 4. The secondary battery according to any one of claims 1-3, wherein the secondary battery satisfies: 0.2≤n1 / n2≤7.
5. The secondary battery according to any one of claims 1-4, wherein 4 ≤ H ≤ 20.
6. The secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material comprises a lithium nickel oxide comprising at least one of a compound of a chemical formula of Li 1+a [Ni x Co y Mn z M b ]O2, wherein M comprises at least one of Ti, Zr, Sr, Sb, Nb, Y, Ta, Ru, Nd, V, Ce, Mo, 0.5 < x < 1, 0 < y < 0.3, 0 < z < 0.3, -0.1 < a < 0.2, 0 < b < 0.3, and x + y + z + b = 1.
7. The secondary battery according to claim 6, wherein element M in the lithium nickel oxide includes at least one of Zr, Sr, Ti, Sb, Nb, Y, and Mo.
8. The secondary battery according to claim 7, wherein element M in the lithium nickel oxide includes Nb and Y.
9. The secondary battery according to any one of claims 1 to 8, wherein the positive electrode active material further comprises a lithium-containing phosphate, the lithium-containing phosphate comprising at least one of a compound of the formula Li n Mn t Fe u A s PO4, wherein, A includes one or more of Al, Ni, Co, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y, 0.95 <n<1.15,t+u+s=1,0≤t<1,0<u≤1,0≤s≤0.02。 10. The secondary battery according to claim 9, wherein the lithium phosphate is in the form of primary particles.
11. The secondary battery according to claim 9 or 10, wherein the element A containing lithium phosphate includes one or more of Ti and Al.
12. The secondary battery according to any one of claims 9-11, wherein the lithium phosphate comprises 5% to 30% by mass of the positive electrode active material.
13. The secondary battery according to any one of claims 6-12, wherein the electrolyte comprises a fluorine-containing additive, and the secondary battery satisfies: 0.5 ≤ m2 / m1 ≤ 5; wherein m1% is the mass percentage content of element M in the lithium nickel oxide; m2% is the percentage of the fluorinated additive in the electrolyte by mass.
14. The secondary battery according to claim 13, wherein the secondary battery satisfies at least one of the following (f) to (h): (f) 0.5 ≤ m1 ≤ 3; (g) 1 ≤ m2 ≤ 5; (h) The fluorinated additives include one or more of hexafluoroglutaric anhydride, fluoroethylene carbonate, difluoroethylene carbonate, and diethylfluoromalonate.
15. The secondary battery according to any one of claims 1 to 14, wherein the negative electrode active material comprises graphite and a silicon-oxygen material, the silicon-oxygen material being contained in a mass percentage of 1 to 30% of the negative electrode active material.
16. The secondary battery according to any one of claims 1 to 15, wherein the positive electrode sheet has a porosity of 20 to 30%; and / or the negative electrode sheet has a porosity of 30 to 45%.
17. An electric device comprising the secondary battery according to any one of claims 1 to 16.