Secondary batteries and electrical appliances

Abstract

This application discloses a secondary battery and an electrical appliance. The secondary battery includes a positive electrode sheet and a negative electrode sheet, and the secondary battery satisfies 0.258≦CB / PD≦0.700. This application appropriately controls the ranges of the CB value and the PD value to improve the cycle life and storage life of the secondary battery, improve the energy efficiency of the secondary battery, and reduce the energy loss during charging and discharging.

Description

[Technical Field]

[0001] This application claims priority from a Chinese patent application bearing application number 202211328888.2 and entitled "Secondary Battery and Electrical Appliance" filed with the China Patent Office on October 27, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of battery technology, and more particularly to secondary batteries and electrical appliances. [Background technology]

[0003] Although lithium-ion batteries have significant advantages in the field of energy storage, several challenges remain in their practical applications. For example, the service life of a lithium iron phosphate battery is 4,000–6,000 cycles, making it difficult to meet the 20–30-year service life (>10,000 cycles) required for energy storage projects with high lifespan requirements. Loss of active lithium is a major factor in the lifespan degradation of lithium-ion energy storage batteries. During the lithium desorption / sorption cycle, factors such as graphite expansion and contraction and positive electrode transition metal leaching can cause the SEI (solid electrolyte interphase) to fracture and form, increasing the area and thickness of the SEI film. This consumes the battery system's limited active lithium, ultimately shortening the battery's service life. Reducing and replenishing the loss of active lithium during the battery degradation process is a key challenge for improving the lifespan of lithium iron phosphate batteries.

[0004] To address these issues, a common approach is to "refill" the negative electrode with lithium. This method can be divided into physical refilling and electrochemical refilling. However, physical refilling can easily cause lithium deposition in the battery during subsequent cycles, leading to short circuits and safety hazards. While electrochemical refilling can address the shortcomings of physical refilling, current methods lack significant effectiveness, are complex, and expensive, making them unsuitable for widespread use in actual production.

[0005] Therefore, there is a demand for the development of a secondary battery that has a long cycle life, excellent electrochemical properties, is easy to process and manufacture, and is inexpensive to use. Summary of the Invention [Problem to be solved by the invention]

[0006] The present application aims to provide a secondary battery that has improved cycle life and storage life by adjusting the relationship between the CB value of the battery and the compressed density of the positive electrode sheet. [Means for solving the problem]

[0007] In a first aspect, an embodiment of the present application provides a secondary battery, the secondary battery including a positive electrode sheet and a negative electrode sheet, wherein the secondary battery satisfies 0.258≦CB / PD≦0.700, where CB is a ratio of the capacity of the negative electrode sheet per unit area to the capacity of the positive electrode sheet per unit area, and PD is a compressed density of the positive electrode sheet, expressed in g / cm. 3 is.

[0008] In some embodiments, 0.275≦CB / PD≦0.55.

[0009] In some embodiments, 0.31≦CB / PD≦0.48.

[0010] In some embodiments, 0.8≦CB≦1.1.

[0011] In some embodiments, 0.8≦CB≦1.05.

[0012] In some embodiments, the compressed density PD of the positive electrode sheet is 1.5≦PD≦3.1 (g / cm 3 ) is satisfied.

[0013] The positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer including a positive electrode active material, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer including a negative electrode active material, and the positive electrode active material and the negative electrode active material satisfy 2≦Dv50′ / Dv50≦25, where Dv50′ is the particle size, expressed in μm, corresponding to when the cumulative volume percentage of the negative electrode active material reaches 50%, and Dv50 is the particle size, also expressed in μm, corresponding to when the cumulative volume percentage of the positive electrode active material reaches 50%.

[0014] In some embodiments, the particle size of the negative electrode active material satisfies 5≦Dv50′≦25.

[0015] In some embodiments, the particle size of the positive electrode active material satisfies 0.3≦Dv50≦3.5.

[0016] In some embodiments, the particle size of the negative electrode active material satisfies 0.5≦Dv10′≦10, 2.5≦Dv90′≦45, Dv99′≦50, Dn10′≦4, 0.5≦Dn50′≦10.5, 1.5≦Dn90′≦25, Dn99′≦40, and the unit of particle size is μm.

[0017] In some embodiments, the particle size of the positive electrode active material satisfies 0.1≦Dv10≦1, 0.5≦Dv90≦6.5, 3.5≦Dv99≦20, 0.05≦Dn10≦1, 0.1≦Dn50≦2.5, 0.5≦Dn90≦3.5, 1.5≦Dn99≦10, and the unit of particle size is μm.

[0018] In some embodiments, the positive electrode active material layer and the negative electrode active material layer satisfy 0≦(H1-H2) / H2≦0.9, where H1 is the thickness of the positive electrode active material layer on one side, with the unit of μm, and H2 is the thickness of the negative electrode active material layer on one side, with the unit of μm.

[0019] In some embodiments, 40≦H1≦160 and 30≦H2≦120 are satisfied.

[0020] In some embodiments, the chemical formula of the positive electrode active material is Li y A x Fe (1-x) PO4, where 0.8≦y≦1.2, 0<x<1, and the element A includes at least one of Ni, Co, Mn, Mg, Ca, Ba, Ti, and V.

[0021] In some embodiments, the element A accounts for 0% to 36% of the weight of the positive electrode active material.

[0022] The secondary battery includes an electrolyte, the electrolyte includes a first additive, and the first additive includes at least one of vinylene carbonate and vinyl ethylene carbonate.

[0023] The electrolyte includes a second additive, and the second additive includes at least one of LiFSI, LiODFB, LiPO2F2, LiBF4, and LiBOB.

[0024] In some embodiments, the first additive accounts for a% of the total weight of the electrolyte, where a, CB, and PD satisfy 0.2≦a×CB / PD≦3.

[0025] In some embodiments, the second additive accounts for b% of the total weight of the electrolyte. a and b satisfy at least one of the following characteristics. (I) 0.1≦a + b≦5; (II) 0.1≦a / b≦10.

[0026] In some embodiments, the secondary battery satisfies 1.1≦CB′≦1.3, where CB′ is the ratio of the reversible capacity of the negative electrode sheet per unit area to the actual capacity of the positive electrode sheet per unit area.

[0027] In a second aspect, the present invention further provides an electrical appliance including a secondary battery, the secondary battery being used as a power supply for the electrical appliance. [Effects of the Invention]

[0028] Compared with the prior art, the secondary battery of the present application includes a positive electrode sheet and a negative electrode sheet, and the secondary battery satisfies 0.258≦CB / PD≦0.700. By controlling the ratio of the battery design CB value and the positive electrode sheet PD value, the present application improves the cycle and storage life of the secondary battery, improves the energy efficiency of the secondary battery, and reduces energy loss during charging and discharging. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present application provides a secondary battery and an electrical appliance. In order to make the purpose, technical solution, and technical effects of the present application clearer and more explicit, the present application will be described in more detail below through examples. It should be understood that the specific examples described in this specification are for the purpose of illustrating the present application only and are not intended to limit the present application.

[0030] secondary battery

[0031] The present application provides a secondary battery, which includes a positive electrode sheet and a negative electrode sheet, and satisfies 0.258≦CB / PD≦0.700, where CB is the ratio of the capacity of the negative electrode sheet per unit area to the capacity of the positive electrode sheet per unit area, and PD is the compressed density (g / cm ) of the positive electrode sheet. 3 )

[0032] To calculate the CB value, the unit area of ​​the positive and negative electrode sheets must be kept equal, and the CB value is the reversible capacity of the negative electrode sheet / the reversible capacity of the positive electrode sheet. By limiting the CB / PD ratio, the present application balances the lithium ion absorption and desorption rates of the positive and negative electrode materials, thereby improving the cycle and storage life of the secondary battery.

[0033] In some examples, the CB value is obtained by the following test method:

[0034] The capacity of the negative electrode sheet per unit area is obtained by the following method: leaving one side of the active material on a unit area of ​​the negative electrode sheet, combining it with lithium chips, a separator, and an electrolyte to form a button battery, discharging it at 0.1 C to 0.005 V, discharging it at 0.05 mA to 0.005 V, discharging it at 0.02 mA to 0.005 V, and charging it at 0.1 C to 2 V. The resulting charge capacity is the capacity of the negative electrode sheet per unit area.

[0035] The capacity of the positive electrode sheet per unit area is obtained by the following method: leaving one side of the active material on a unit area of ​​the positive electrode sheet, combining it with lithium chips, a separator, and an electrolyte to form a button battery, charging it to 3.7 V at 0.1 C, applying a constant voltage of 50 μA, and discharging it to 2.0 V at 0.1 C, and the resulting discharge capacity is the capacity of the positive electrode sheet per unit area.

[0036] In some embodiments, the compressed density is calculated according to the following formula:

[0037] Compressed density = areal density / (thickness of sheet after rolling - thickness of current collector), unit: g / cm 3 is.

[0038] In some embodiments, the compressed density of the positive electrode sheet can be calculated using the following formula:

[0039] Compressed density of positive electrode sheet = areal density of positive electrode sheet / (thickness of positive electrode sheet after being rolled - thickness of positive electrode current collector), unit: g / cm 3 is.

[0040] In some embodiments, the compressed density is tested by a compressed density meter, and the test procedure can refer to the international standard GB / T24533-2019.

[0041] In some embodiments, the value of CB / PD may be any one of the following, or a range consisting of any two of the following values: 0.258, 0.28, 0.30, 0.32, 0.33, 0.341, 0.35, 0.353, 0.36, 0.367, 0.37, 0.38, 0.383, 0.39, 0.40, 0.41, 0.43, 0.45, 0.458, 0.47, 0.48, 0.50, 0.52, 0.54, 0.55, 0.57, 0.59, 0.60, 0.62, 0.64, 0.65, 0.67, 0.69, 0.70.

[0042] In some embodiments, the value of CB may be any one of the following values, or a range consisting of any two of the following values: 0.8, 0.81, 0.82, 0.821, 0.83, 0.845, 0.846, 0.85, 0.852, 0.86, 0.87, 0.88, 0.89, 0.896, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.952, 0.958, 0.96, 0.97, 0.98, 0.99, 1.0, 1.05, 1.10.

[0043] The present application increases the reversible capacity of the battery positive electrode sheet by designing a surplus positive electrode sheet, and uses a constant capacity method through charge test control during the battery operation process to make the positive electrode sheet release only a portion of the lithium ions, and uses the surplus lithium ions as reserve to make up for the loss of active lithium during the operation of the secondary battery, thereby keeping the active lithium within an appropriate range at all times and improving the recovery rate of storage capacity and energy efficiency.

[0044] In some embodiments, PD (g / cm 3 ) may be any one of 1.5, 1.6, 1.8, 1.9, 2.0, 2.2, 2.4, 2.5, 2.7, 2.8, 2.9, 3.0, and 3.1, or may be a range consisting of any two of these values.

[0045] This application further limits the compaction density of the positive electrode sheet, thereby increasing the usable capacity of the battery and improving its cycle life. During the manufacturing process of lithium-ion batteries, compaction density has a significant impact on battery performance. Experiments have proven that compaction density is closely related to specific capacity, efficiency, internal resistance, and battery cycle performance, so compaction density is also considered a reference index for material energy density.

[0046] In some embodiments, the positive electrode active material particles Dv50 (unit: μm) and the negative electrode active material particles Dv50′ (unit: μm) of the present application satisfy 2≦Dv50′ / Dv50≦25.

[0047] In some embodiments, 5≦Dv50′ / Dv50≦25 is satisfied.

[0048] In some embodiments, 10≦Dv50′ / Dv50≦25.

[0049] In some embodiments, 14≦Dv50′ / Dv50≦25 is satisfied.

[0050] In some embodiments, Dv50' / Dv50 is 5.0, 5.5, 5.9, 6.0, 6.3, 6.5, 6.8, 7.0, 7.3, 7.8, 8.0, 8.3, 8.5, 8.8, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13.0, 13.1, 13.2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 14.0, 14.1, 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.8, 14.9, 15.0, 15.1, 15.2, 15.3, 15.4, 15.5, 15.6, 15.7, 15.8, 15.9, 16.1, 16.2, 16. The value may be any one of 2.3, 12.5, 12.7, 13.0, 13.3, 13.5, 13.7, 13.9, 14.0, 14.3, 14.5, 14.8, 15.0, 15.3, 15.5, 15.7, 16.0, 16.3, 16.5, 16.7, 17.0, 17.3, 17.5, 17.7, 18.0, 18.3, 18.5, 18.7, 19.0, 19.3, 19.5, 19.9, 20.0, 20.5, 21.0, 21.5, 22.0, 23.0, 24.0, and 25.0, or a range consisting of any two of these values.

[0051] The present invention further optimizes the particles of the positive electrode active material and the particles of the negative electrode active material to improve the matching of the lithium ion absorption and desorption rates of the positive and negative electrode active materials, thereby improving the cycle life of the secondary battery.

[0052] In some embodiments, the particle size of the positive electrode active material satisfies 0.3≦Dv50≦3.5, 0.1≦Dv10≦1.0, 0.5≦Dv90≦6.5, 3.5≦Dv99≦20, 0.1≦Dn50≦2.5, 0.05≦Dn10≦1.0, 0.5≦Dn90≦3.5, 1.5≦Dn99≦10, and the unit of particle size is μm.

[0053] In some embodiments, the particle size Dv50 (μm) of the positive electrode active material may be any one of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, and 3.5, or a range consisting of any two of these values.

[0054] In some embodiments, the particle size of the negative electrode active material satisfies 5.0≦Dv50′≦25.0, 0.5≦Dv10′≦10.0, 2.5≦Dv90′≦45.0, Dv99′≦50.0, 0.5≦Dn50′≦10.5, Dn10′≦4.0, 1.5≦Dn90′≦25.0, Dn99′≦40.0, and the unit of particle size is μm.

[0055] In some embodiments, the particle size Dv50′ (μm) of the negative electrode active material is 5.0, 5.5, 6.0, 6.3, 6.5, 6.7, 7.0, 7.3, 7.5, 7.8, 8.0, 8.3, 8.5, 8.8, 9.0, 9.3, 9.5, 9.8, 10.0, 10.3, 10.5, 10.8, 11.0, 11.3, 11.5, 11.8, 12.0, 12.3, 12.5, 12.8, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 29.0, 30.0, 31.0, 32.0, 33.0, 34.0, 35.0, 36.0, 37.0, 38.0, 39.0, 40.0, 41.0, 42.0, 43.0, 44.0, 45.0, 46.0, 47.0, 48.0, 49.0, 50.0, 51.0, 52.0, 53.0, 54.0, 55.0, 56.0, 57.0, 58.0, 59.0, 60.0, 61.0, 62.0, 63.0, 64.0, 65.0, 66.0, 6 The value may be any one of 3.3, 13.5, 13.8, 14.0, 14.3, 14.5, 14.8, 15.0, 15.3, 15.5, 15.8, 16.0, 16.3, 16.5, 16.8, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, 20.0, 21.0, 22.0, 23.0, 24.0, and 25.0, or a range consisting of any two of these values.

[0056] The definitions of the particle size of the positive electrode material and the particle size of the negative electrode material in this application have the meanings well known in the technical field. Dv10' is the particle size corresponding to the cumulative volume percentage of the negative electrode active material particles reaching 10%. Dv50' is the particle size corresponding to the cumulative volume percentage of the negative electrode active material particles reaching 50%. Dv90' is the particle size corresponding to the cumulative volume percentage of the negative electrode active material particles reaching 90%. Dv99' is the particle size corresponding to the cumulative volume percentage of the negative electrode active material particles reaching 99%. Dn10' is the particle size corresponding to the distribution number of the negative electrode active material particles reaching 10%. Dn50' is the particle size corresponding to the distribution number of the negative electrode active material particles reaching 50%. Dn99' is the particle size corresponding to the distribution number of the negative electrode active material particles reaching 99%.

[0057] Dv10 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material particles reaching 10%. Dv50 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material particles reaching 50%. Dv90 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material particles reaching 90%. Dv99 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material particles reaching 99%. Dn10 is the particle size corresponding to the distribution number of the positive electrode active material particles reaching 10%. Dn50 is the particle size corresponding to the distribution number of the positive electrode active material particles reaching 50%. Dn99 is the particle size corresponding to the distribution number of the positive electrode active material particles reaching 99%.

[0058] In some embodiments, the thickness of the positive electrode active material layer (the thickness of the active material on one side, H1, in μm) and the thickness of the negative electrode active material layer (the thickness of the active material on one side, H2, in μm) satisfy 0≦(H1−H2) / H2≦0.9. When the thicknesses of the positive electrode active material layer and the negative electrode active material layer are within this range, the matching of the lithium ion absorption and desorption rates of the positive and negative electrode materials is improved, and the cycle life of the secondary battery is improved.

[0059] In some embodiments, (H1 - H2) / H2 may be any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or a range consisting of any two of these values.

[0060] In some embodiments, 40 ≤ H1 ≤ 160 is satisfied.

[0061] In some embodiments, H1 (unit: μm) may be any one of 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, or a range consisting of any two of these values.

[0062] In some embodiments, 30 ≤ H2 ≤ 120 is satisfied.

[0063] In some embodiments, H2 (unit: μm) may be any one of 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, or a range consisting of any two of these values.

[0064] In some embodiments, the chemical formula of the positive electrode active material is Li y A x Fe (1-x) contains PO4, 0.8 ≤ y ≤ 1.2, 0 < x < 1, and the element A contains at least one of Ni, Co, Mn, Mg, Ca, Ba, Ti, V.

[0065] In some embodiments, the content of element A in the lithium-containing compound of the positive electrode active material is appropriate, whereby high energy density and stability can be imparted to the positive electrode active material particles, and the electrical equipment can have better overall performance.

[0066] In some embodiments, element A accounts for 0% - 36% of the weight of the positive electrode active material.

[0067] In some examples, element A may comprise 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36% by weight of the cathode active material, or a range consisting of any two of these values.

[0068] In the present invention, by adding element A to the positive electrode active material and limiting the content of element A, the operating voltage platform of the secondary battery is improved, the energy density is increased, and the kinetics of the positive electrode material is improved, thereby improving the cycle life and energy efficiency of the secondary battery.

[0069] In some embodiments, a secondary battery includes an electrolyte solution, the electrolyte solution including a first additive, the first additive including at least one of vinylene carbonate and vinyl ethylene carbonate, and a content of the first additive of a % based on a total weight of the electrolyte solution.

[0070] In some embodiments, the electrolyte includes a second additive, the second additive including at least one of LiFSI, LiODFB, LiPO2F2, LiBF4, and LiBOB, and the content of the second additive is b% based on the total weight of the electrolyte.

[0071] In some embodiments, 0.2≦a*CB / PD≦3.

[0072] In some embodiments, 0.1≦a+b≦5.

[0073] In some embodiments, 0.1≦a / b≦10.

[0074] In some embodiments, the value of a*CB / PD may be any one of the following values, or a range consisting of any two of the following values: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0.

[0075] In some embodiments, the value of a+b may be any of the following values: 0.1, 0.5, 0.8, 1.0, 1.3, 1.5, 1.8, 2.0, 2.3, 2.5, 2.8, 3.0, 3.3, 3.5, 3.8, 4.0, 4.3, 4.5, 4.8, 5.0, or a range consisting of any two of these values.

[0076] In some embodiments, the value of a / b may be any of the following, or a range consisting of any two of the following values: 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.3, 1.5, 1.7, 2.0, 2.3, 2.5, 2.8, 3.0, 3.3, 3.5, 3.7, 4.0, 4.3, 4.5, 4.8, 5.0, 5.3, 5.5, 5.8, 6.0, 6.3, 6.5, 7.0, 7.3, 7.5, 7.8, 8.0, 8.3, 8.5, 8.8, 9.0, 9.3, 9.5, 9.7, 10.0.

[0077] In the present invention, by ensuring sufficient amounts of the first additive and the second additive throughout the entire life cycle of the secondary battery, the acceleration of capacity decay due to an insufficient amount of additive is not brought about.

[0078] In some embodiments, due to the relatively excessive positive electrode capacity, a constant capacity charging method is used during the operation of the secondary battery to prevent lithium deposition on the negative electrode during the charging process from affecting the life and safety performance of the secondary battery.

[0079] In some embodiments, the secondary battery is charged at n1 / n2 (unit: A) for n2 hours during charging in the pre-cycle period, where n2≧0.5, where n1 is the nominal capacity of the secondary battery, i.e., the actual used capacity, in Ah, and n2 is the charging time of the secondary battery, in h.

[0080] The nominal capacity is the standard capacity determined at the time of battery shipment.

[0081] In some embodiments, the secondary battery satisfies 1.10≦n4 / n1≦1.3, 0.8≦n4 / n3≦1.1, where n3 is the positive electrode reversible capacity of the secondary battery, in Ah, and n4 is the negative electrode reversible capacity of the secondary battery, in Ah.

[0082] In some embodiments, actual use C B value is 1.10≦C B≦ 1.30, that is, the reversible capacity of the negative electrode of the battery / the actual capacity of the positive electrode of the battery is 1.10 to 1.30.

[0083] In some embodiments, the CB' value may be any one of the following, or a range consisting of any two of the following values: 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.30.

[0084] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector.

[0085] In some embodiments, the active cathode material can be one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, or lithium manganese oxide.

[0086] In some embodiments, the cathode active material is lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, and the manufacturing method thereof may be a high-temperature solid-state method, a carbothermal reduction method, a spray-drying method, a template method, or a hydrothermal synthesis method.

[0087] Specifically, lithium iron phosphate, which is a positive electrode active material, can be prepared by the following method: A lithium source (Li2CO3), an iron source (FePO4), and a carbon source are mixed and pre-treated at 300 to 500°C, and then sintered at 600 to 850°C to prepare lithium iron phosphate, which is used as a positive electrode active material.

[0088] In some embodiments, the cathode active material is lithium cobalt oxide, and the manufacturing method may be conventional techniques such as high temperature solid state methods, sol-gel methods, and the like.

[0089] Specifically, lithium cobalt oxide, which is a positive electrode active material, can be prepared by the following method: a lithium source (Li2CO3), a cobalt source (Co3O4), and ethanol are mixed and ground, pre-treated at 300°C, fired at 600°C, and then subjected to a solid-state reaction at 800°C to obtain lithium cobalt oxide.

[0090] In some embodiments, to obtain a cathode active material having an optimized particle size distribution and specific surface area, an intermediate product obtained during the manufacturing process of the cathode active material is crushed and sieved. Here, the crushing method is not particularly limited and can be selected according to actual requirements, for example, using a particle crusher. The manufacturing method of the cathode active material of the present application is not limited to the above manufacturing method, and may be any method as long as the formed cathode active material has the characteristics described herein.

[0091] In some embodiments, the manufacturing process for the positive electrode sheet can include steps such as stirring, coating, drying, cold pressing, slitting, and sheeting.

[0092] In some embodiments, the positive electrode sheet further includes a conductive agent and a binder, and the types and contents of the conductive agent and the binder are not particularly limited and can be selected according to actual needs. In some embodiments, the conductive agent can include conductive carbon black, carbon nanotubes, graphene, etc., and the binder can include polyvinylidene fluoride.

[0093] In some embodiments, the method for producing a positive electrode sheet includes dispersing the positive electrode active material, the conductive agent, and the binder in specific ratios in N-methylpyrrolidone (NMP), coating the resulting slurry on an aluminum foil, drying, and then cold pressing and slitting to obtain a positive electrode sheet.

[0094] Negative electrode sheet

[0095] In some embodiments, the negative electrode sheet includes a negative electrode current collector, a negative electrode active material covering the negative electrode current collector, a binder, and a conductive agent. The types and contents of the negative electrode active material, the binder, and the conductive agent are not particularly limited and can be selected according to actual needs. In some embodiments, the negative electrode active material includes one or more of artificial graphite, natural graphite, mesocarbon microbeads, amorphous carbon, lithium titanate, or a silicon-carbon alloy. The negative electrode active material should also have characteristics such as high compaction density, high mass-specific capacitance, and high volume-specific capacitance.

[0096] electrolyte

[0097] In some embodiments, the main components of the electrolyte solution include a lithium salt, an organic solvent, and an additive. Here, the types and compositions of the lithium salt and the organic solvent are not particularly limited and can be selected according to actual needs. Here, the lithium salt can include lithium hexafluorophosphate, and the solvent can include ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, propyl propionate, etc.

[0098] Separator

[0099] In some embodiments, the type of separator is not particularly limited and can be selected according to actual requirements. The separator can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride film, a spandex film, an aramid film, or a multi-layer composite film after coating modification.

[0100] In some embodiments, the secondary battery is manufactured by sequentially stacking a positive electrode sheet, a separator, and a negative electrode sheet, with the separator positioned between the positive electrode sheet and the negative electrode sheet to provide insulation, then winding the stack around a square bare core, placing the stack in a battery housing, baking at 65°C to 95°C to remove water, then injecting an electrolyte, sealing, and undergoing processes such as standing, hot and cold pressing, chemical formation, clamping, and volume separation to obtain a secondary battery.

[0101] In some embodiments, fabricating a secondary battery includes the following steps. (1) Lithium iron phosphate, a positive electrode conductive agent, a positive electrode binder, and a positive electrode solvent are mixed to prepare a positive electrode slurry, and the positive electrode slurry is applied to the surface of a positive electrode current collector to obtain a positive electrode sheet. (2) Graphite, anode dispersant, anode conductive agent, anode binder, and anode solvent are mixed to prepare anode slurry, which is then applied to the surface of anode current collector to obtain anode sheet. (3) In the manufacturing process of a lithium-ion battery, the positive electrode sheet, negative electrode sheet, separator, and other battery components manufactured in the present application are assembled, and then subjected to processes such as shaping, firing, sealing, liquid injection, chemical formation, and capacity separation to obtain a long-life lithium iron phosphate lithium-ion battery, which includes battery types such as soft pack, cylindrical, and aluminum housing, where the design CB value of the battery satisfies 0.8≦CB≦1.10, i.e., the reversible capacity of the negative electrode sheet of the battery / the reversible capacity of the positive electrode sheet of the battery is 0.8-1.10, and also satisfies 0.258≦battery design CB / positive electrode sheet PD≦0.700, and 2.0≦negative electrode Dv50′ / positive electrode Dv50≦25.

[0102] In some embodiments, during the use of the battery, the charging rules of the battery are optimized and the charging capacity of the battery is strictly controlled, so that the actual use CB value of the battery is stable at 1.10 to 1.30, i.e., the reversible capacity of the negative electrode sheet of the battery / the actual capacity of the positive electrode sheet of the battery is 1.10 to 1.30.

[0103] In some embodiments, the secondary battery includes a lithium ion battery. Although only soft-pack lithium ion batteries have been cited above as examples, the present application is not limited to applications to soft-pack batteries, but also includes applications to common lithium ion battery configurations such as aluminum housing batteries, cylindrical batteries, etc.

[0104] Electrical appliances

[0105] In some embodiments, the present application provides an electric appliance, which includes the above-described secondary battery, and the electric appliance can be used in, but is not limited to, a backup power source, a motor, an electric vehicle, an electric motorcycle, an electric-assisted bicycle, a bicycle, an electric tool, a large-scale household battery, and the like.

[0106] Example 1

[0107] Lithium iron phosphate, a positive electrode conductive agent, a positive electrode binder, and a positive electrode solvent are mixed to prepare a positive electrode slurry, which is then applied to the surface of a positive electrode current collector to obtain a positive electrode sheet.

[0108] The positive electrode sheet was manufactured as follows: Lithium iron phosphate, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97:0.7:2.3, then added to NMP and mixed thoroughly. After uniform mixing, the mixture was coated on both sides of a (12 + 1 + 1) μm carbon aluminum foil. The sheet was then dried, rolled, stripped, and cut into pieces to obtain a positive electrode sheet. The thickness of the positive electrode active material layer on one side was 81 μm, and the particle sizes of the lithium iron phosphate were Dv50 (0.67 μm), Dv10 (0.15 μm), Dv90 (5.5 μm), Dv99 (9.2 μm), Dn50 (0.33 μm), Dn10 (0.10 μm), Dn90 (1.15 μm), and Dn99 (3.20 μm).

[0109] Graphite, a negative electrode dispersant, a negative electrode conductive agent, a negative electrode binder, and a negative electrode solvent are mixed to prepare a negative electrode slurry, which is then applied to the surface of a negative electrode current collector to obtain a negative electrode sheet.

[0110] The negative electrode sheet was manufactured as follows: graphite, conductive carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.3:0.7:1.1:1.9, then thoroughly mixed in water until uniform. The mixture was then applied to two surfaces of 6 μm-thick copper foil. The sheet was then dried, rolled, slit, and cut to obtain a negative electrode sheet. The thickness of the negative electrode active material layer on one side was 65 μm, and the particle sizes of the negative electrode active material were Dv50' (16.3 μm), Dv10' (8.5 μm), Dv90' (30.2 μm), Dv99' (40.4 μm), Dn50' (8.2 μm), Dn10' (3.1 μm), Dn90' (15.2 μm), and Dn99' (25.3 μm).

[0111] The separator is a polyethylene film.

[0112] The method for producing the electrolyte is as follows. ethyleneCarbonate, methyl ethyl carbonate, and dimethyl carbonate are mixed in a mass ratio of 1:1:1, and then lithium hexafluorophosphate is added. The mixture is uniformly mixed and additives are added. The content of lithium hexafluorophosphate is 12% and the content of vinylene carbonate, an additive, is 0.5% based on the mass of the electrolyte.

[0113] In the manufacturing process of a lithium-ion battery, the positive electrode sheet, negative electrode sheet, separator, and other battery components manufactured in the present application are assembled, and then undergo processes such as shaping, firing, sealing, liquid injection, chemical formation, and capacity separation to obtain a lithium iron phosphate lithium-ion battery with a long life.

[0114] Examples 2 to 16 were produced as follows: the particle size of the active material was screened to obtain active material materials with different particle sizes, the coating weight of the active material on the positive electrode sheet and the negative electrode sheet was adjusted to control the design CB value, and the rolling thickness of the active material layer was adjusted to control the compressed density, and Examples 2 to 16 were produced by the method of Example 1, and the parameters of Examples 2 to 16 are shown in Table 1.

[0115] Battery performance testing

[0116] The cycle capacity retention rate is calculated as follows: The nominal capacity of the secondary battery is C1, and the battery is cycled at a specific temperature (25°C, 45°C, 60°C) at 1C / 1C for the corresponding number of cycles to obtain the discharge capacity C2, and the capacity retention rate is calculated as C2 / C1 × 100%.

[0117] Energy efficiency is the ratio of the energy output during discharge of a lithium-ion battery to the energy input during the previous charge.

[0118] The energy efficiency test method is as follows:

[0119] The secondary battery is charged to the nominal capacity of the battery at a constant current of 1C, and the charging energy is E1. It is then left for 30 minutes, and discharged to the lower voltage limit (2.5V) at a constant current of 1C, and the discharging energy is E2. The energy efficiency value of the secondary battery is E2 / E1.

[0120] The test method for the recovery rate of storage capacity is as follows.

[0121] At room temperature, charge the secondary battery at a constant current of 1C up to the battery's nominal capacity x 1Ah.

[0122] The secondary battery is transferred to a 60°C oven and stored for 400 days. At room temperature, the secondary battery is discharged to 2.5V at 1C and left for 30 minutes. Then, the secondary battery is charged to 3.65V at a 1C constant current and constant voltage, with a cutoff current of 0.05C. After leaving for 30 minutes, the secondary battery is discharged to 2.5V at a 1C constant current. The discharge capacity is X2Ah, and the capacity recovery rate of the secondary battery is X2 / X1×100%.

[0123] [Table 1]

[0124] Referring to the results in Table 1, when the battery design CB / positive electrode sheet PD is within the range of 0.258 to 0.700 and the Dv50' / Dv50 is within the range of 2 to 25, particularly when the Dv50' / Dv50 shown in Examples 1 to 16 is within the range of 14 to 25, the lithium ion desorption / desorption rates of the positive and negative electrode materials are matched, resulting in an improved cycle life of the secondary battery. When the battery design CB / positive electrode sheet PD is within the range of 0.258 to 0.700 and the Dv50' / Dv50 range is outside this range, the desorption / desorption rates of the positive and negative electrodes are inconsistent, resulting in an insufficient cycle life of the battery. When the Dv50' / Dv50 is within the range of 2.0 to 20 and the battery design CB / positive electrode sheet PD is outside the range of 0.258 to 0.700, the cycle and storage life of the secondary battery are not satisfactory, and the cycle life of the battery cannot be extended. The present invention limits the actual use CB value to a range of 1.1 to 1.3 to ensure that the negative electrode has an appropriate amount of lithium vacancies during operation. If the actual use CB value is greater than 1.3, the negative electrode will have excess lithium vacancies during operation, consuming excessive active lithium in the process of forming the SEI, which is detrimental to improving cycle life / storage life. If the actual use CB is less than 1.1, the negative electrode will have insufficient lithium vacancies during operation, causing lithium precipitation, increasing side reactions in the secondary battery and affecting cycle storage life.

[0125] Comparing the battery test results in the table above, the long-life lithium iron phosphate lithium-ion battery manufactured in this application is significantly superior to the conventional lithium iron phosphate lithium-ion battery without a redundant cathode design in terms of cycle capacity retention at 25°C 1C / 1C and 45°C 1C / 1C, storage capacity recovery rate at 60°C 100% SOC, and energy efficiency.

[0126] Examples 17 to 20 are produced by the following method.

[0127] Lithium iron phosphate, a positive electrode conductive agent, a positive electrode binder, and a positive electrode solvent are mixed to prepare a positive electrode slurry, which is then applied to the surface of a positive electrode current collector to obtain a positive electrode sheet.

[0128] The manufacturing method of the positive electrode sheet is as follows: Lithium iron phosphate, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96.7:0.9:2.4, then added to NMP and mixed thoroughly until uniform. After mixing, the mixture is coated on both sides of a (12+1+1) μm carbon aluminum foil, and then the sheet is dried, rolled, slit, and cut to obtain a positive electrode sheet. The thickness of the positive electrode active material layer on one side is 81 μm.

[0129] The negative electrode sheet is manufactured as follows: graphite, conductive carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96.1:0.7:1.1:2.1, then thoroughly mixed in water until uniform, and then coated on two surfaces of 6 μm copper foil. The sheet is then dried, rolled, slit, and cut to obtain a negative electrode sheet, with the negative electrode active material layer on one side being 65 μm thick.

[0130] The separator is a polyethylene film.

[0131] The production method was the same as in Example 1, except for the amount of vinylene carbonate shown in Table 2.

[0132] In the manufacturing process of a lithium ion battery, the positive electrode sheet, negative electrode sheet, separator, and other battery components manufactured in the present application are assembled, and then undergo processes such as shaping, firing, sealing, liquid injection, chemical formation, and capacity separation to obtain a lithium lithium ion battery.

[0133] [Table 2]

[0134] The a value in different embodiments can be obtained by adjusting the amount of the first additive in the electrolyte. The present application controls the relationship between the first additive a, CB, and PD in the electrolyte to ensure a*CB / PD within the range of 0.2 to 3, ensuring sufficient first additive content throughout the entire life cycle of the secondary battery and preventing accelerated capacity fade due to insufficient additive amount. If a*CB / PD is greater than 3, the negative electrode SEI film will be too thick, resulting in poor system dynamics of the secondary battery and an increased risk of lithium deposition during room temperature cycling, which is detrimental to room temperature cycle life. If a*CB / PD is less than 0.2, the negative electrode SEI film will be insufficiently thick, increasing the consumption of negative electrode active lithium during cycling and resulting in poor cycle performance. Therefore, the actual CB value range for use should be 1.10 to 1.30, ensuring adequate lithium vacancies in the negative electrode and improving battery life.

[0135] Comparing the battery test results in the above table, the long-life lithium iron phosphate lithium-ion battery manufactured according to the present application by controlling the values ​​of a, PD, and a*CB1 / PD based on the cathode redundancy design is significantly superior to the conventional lithium iron phosphate lithium-ion battery without a cathode redundancy design in terms of 25°C 1C / 1C, 45°C 1C / 1C cycle capacity retention, 60°C 100% SOC storage capacity recovery rate, and energy efficiency.

[0136] Examples 21 to 24 are all produced by the following method.

[0137] Lithium iron phosphate, a positive electrode conductive agent, a positive electrode binder, and a positive electrode solvent are mixed to prepare a positive electrode slurry, which is then applied to the surface of a positive electrode current collector to obtain a positive electrode sheet.

[0138] The manufacturing method of the positive electrode sheet is as follows: Lithium iron phosphate, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.3:0.5:2.2, then added to NMP and mixed thoroughly. After uniform mixing, the mixture is coated on both sides of a (12+1+1) μm carbon aluminum foil. The sheet is then dried, rolled, slit, and cut to obtain a positive electrode sheet. The thickness of the positive electrode active material layer on one side is 81 μm.

[0139] The negative electrode sheet is manufactured as follows: graphite, conductive carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96.5:0.5:1.2:1.8, then thoroughly mixed in water. After uniform mixing, the mixture is applied to two surfaces of 6 μm copper foil. The sheet is then dried, rolled, slit, and cut to obtain a negative electrode sheet. The negative electrode active material layer on one side is 65 μm thick.

[0140] Graphite, a negative electrode dispersant, a negative electrode conductive agent, a negative electrode binder, and a negative electrode solvent are mixed to prepare a negative electrode slurry, which is then applied to the surface of a negative electrode current collector to obtain a negative electrode sheet.

[0141] The method for producing the electrolyte is as follows. ethylene Carbonate, methyl ethyl carbonate, and propyl propionate were mixed in a mass ratio of 1:1:1, and then lithium hexafluorophosphate was added and mixed uniformly. The additives were added. The lithium hexafluorophosphate content was 12% by mass of the electrolyte, the first additive was vinylene carbonate, and the second additive was lithium bis(oxalato)borate. The contents of the first and second additives were as shown in Table 3.

[0142] In the manufacturing process of a lithium-ion battery, the positive electrode sheet, negative electrode sheet, separator, and other battery components manufactured in the present application are assembled, and then undergo processes such as shaping, firing, sealing, liquid injection, chemical formation, and capacity separation to obtain a lithium iron phosphate lithium-ion battery with a long life.

[0143] [Table 3]

[0144] As shown in Table 3, the values ​​of a and b can be obtained by adjusting the amounts of the first and second additives. When a + b is within this range, the amount of film-forming additive in the negative electrode is sufficient, ensuring satisfactory cycle life and storage life. At the same time, when a / b is within this range, the cycle life and storage life of the secondary battery can be improved and its energy efficiency can be ensured. Comparing the battery test results shown in the above table, the long-life lithium iron phosphate lithium-ion battery manufactured by controlling the values ​​of a, a + b, and a / b based on the positive electrode redundancy design of the present application is significantly superior to conventional lithium iron phosphate lithium-ion batteries without a positive electrode redundancy design in terms of 25°C 1C / 1C and 45°C 1C / 1C cycle capacity retention, 60°C 100% SOC storage capacity recovery rate, and energy efficiency.

[0145] In the above embodiments, the description of each embodiment has its own focus, and for the parts of the embodiments that are not described in detail, please refer to the related descriptions of other embodiments.

[0146] Although the secondary battery and the electrical appliance according to the embodiments of the present application have been described in detail above, the present application describes the principles and embodiments of the present application by applying specific examples, and the explanation of the above examples is intended to facilitate understanding of the method and core idea of ​​the present application. Furthermore, it should be understood that those skilled in the art may make modifications to the specific embodiments and application scope in light of the idea of ​​the present application, and the contents of the present application are not intended to limit the present application.

Claims

1. A secondary battery comprising: a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material; the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material; The chemical formula of the positive electrode active material is Li y A x Fe (1-x) PO 4 , where 0.8≦y≦1.2 and 0<x<1, and the element A includes at least one of Ni, Co, Mn, Mg, Ca, Ba, Ti, and V; the negative electrode active material comprises one or more of artificial graphite, natural graphite, mesocarbon microbeads, amorphous carbon, lithium titanate, or silicon carbon alloy; the secondary battery satisfies 0.258≦CB / PD≦0.65, Here, CB is the ratio of the capacity of the negative electrode sheet per unit area to the capacity of the positive electrode sheet per unit area, PD is the compressed density of the positive electrode sheet, and its unit is g / cm ３ and The CB satisfies 0.8≦CB≦0.99, the particle size of the negative electrode active material satisfies 5≦Dv50′≦25, and the particle size of the positive electrode active material satisfies 0.3≦Dv50≦3.5; Here, Dv50' is the particle size, expressed in μm, corresponding to the cumulative volume percentage of the negative electrode active material reaching 50%, and Dv50 is the particle size, expressed in μm, corresponding to the cumulative volume percentage of the positive electrode active material reaching 50%. Secondary battery.

2. 0.275≦CB / PD≦0.55 is satisfied, The secondary battery according to claim 1 .

3. 0.31≦CB / PD≦0.48 is satisfied; The secondary battery according to claim 1 .

4. 1.5≦PD≦3.1 is satisfied; The secondary battery according to claim 1 .

5. The positive electrode active material and the negative electrode active material satisfy 2≦Dv50′ / Dv50≦25. The secondary battery according to claim 1 .

6. The positive electrode active material layer and the negative electrode active material layer have a structure in which 0≦(H １ -H ２ ) / H ２ ≦0.9 is satisfied, Here, H １ is the thickness of the positive electrode active material layer on one side, expressed in μm, H ２ is the thickness of the negative electrode active material layer on one side, expressed in μm; The secondary battery according to claim 5 .

7. The secondary battery includes an electrolyte solution, the electrolyte solution includes a first additive, and the first additive includes at least one of vinylene carbonate and vinyl ethylene carbonate. The secondary battery according to claim 1 .

8. The electrolyte solution includes a second additive, and the second additive is LiFSI, LiODFB, LiPO ２ F ２ , LiBF ４ , LiBOB; The secondary battery according to claim 7 .

9. The first additive accounts for a% of the total weight of the electrolyte, where a, CB, and PD satisfy 0.2≦a×CB / PD≦3; The secondary battery according to claim 7 .

10. the second additive accounts for b% of the total weight of the electrolyte; a and b satisfy at least one of the following characteristics: (I) 0.1≦a+b≦5; (II) 0.1≦a / b≦10, The secondary battery according to claim 8.

11. The particle diameters of the negative electrode active material satisfy the following conditions: 0.5≦Dv10′≦10, 2.5≦Dv90′≦45, Dv99′≦50, Dn10′≦4, 0.5≦Dn50′≦10.5, 1.5≦Dn90′≦25, Dn99′≦40, and the unit of the particle diameter is μm. The secondary battery according to claim 5 .

12. The particle diameters of the positive electrode active material satisfy the following conditions: 0.1≦Dv10≦1, 0.5≦Dv90≦6.5, 3.5≦Dv99≦20, 0.05≦Dn10≦1, 0.1≦Dn50≦2.5, 0.5≦Dn90≦3.5, 1.5≦Dn99≦10, and the unit of the particle diameter is μm. The secondary battery according to claim 5 .

13. 40≦H １ ≦160, 30≦H ２ Satisfying ≦120, The secondary battery according to claim 6.

14. A secondary battery comprising the secondary battery according to any one of claims 1 to 13. Electrical appliances.

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