Secondary battery and battery pack

Abstract

Provided are a secondary battery and a battery pack, and the secondary battery meets the following relationship: (6000 / V)-P / 2-(2×C) / (10×E)=Z, wherein Z is a set comparison value, V is the volumetric energy density of the secondary battery, with the unit of Wh / L, P is the compaction density of a positive electrode sheet, with the unit of g / cm3, C is the surface density of the positive electrode sheet, with the unit of mg / cm2, and E is the electrolyte filling coefficient of the battery, with the unit of Ah / g. The volumetric energy density of the secondary battery, the compaction density of the positive electrode sheet, the surface density of the positive electrode sheet and the electrolyte filling coefficient of the battery meet a specific relationship, thereby remarkably improving the volumetric energy density of the battery, and enabling the battery to have relatively high energy density and relatively good cycle performance at the same time.

Description

Secondary battery and battery pack

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on March 26, 2024, with application number CN202410352800.3 and invention name “A Secondary Battery and Battery Pack”, the entire contents of which are incorporated herein by reference. Technical Field The present application belongs to the field of battery technology and relates to a secondary battery, and in particular to a secondary battery and a battery pack. Background Art Range concerns for new energy vehicles (NEVs) have become a significant constraint on their development. Currently, mainstream power batteries are primarily ternary (TC) and lithium iron phosphate (LFP) batteries. Ternary batteries offer high energy density but relatively low economic and safety considerations. LFP batteries, on the other hand, have lower energy density but lower manufacturing costs, higher safety, and an exceptionally long cycle life. Improving the energy density of LFP batteries is a straightforward and feasible approach to addressing NEV range concerns. LFP cathode materials have a relatively low theoretical capacity of only ~170 mAh / g, a correspondingly low operating voltage of approximately 3.4V, and a true density of only 3.6 g / cm³. These three limitations result in a relatively low volumetric energy density, typically below 420 Wh / L. This creates a bottleneck for the application of LFP-based lithium batteries in the energy-dense power battery market. Because the specific capacity of the LFP cathode active material is relatively fixed, increasing its energy density is crucial. The secondary batteries disclosed in the prior art have certain defects, such as the relatively high volume density of the battery. The low energy density makes it difficult to make the battery have both high energy density and good cycle performance. Therefore, it is very important to develop and design a new type of secondary battery and vehicle. Summary of the Invention In response to the shortcomings of the existing technology, the purpose of this application is to provide a secondary battery and a battery pack. In this application, the volume energy density of the secondary battery, the compaction density of the positive electrode sheet, the surface density of the positive electrode sheet and the filling coefficient of the battery satisfy a specific relationship, which significantly improves the volume energy density of the battery and enables the battery to have both higher energy density and better cycle performance. To achieve this goal, this application adopts the following technical solutions: In a first aspect, the present application provides a secondary battery, wherein the secondary battery satisfies the following relationship: Wherein, Z is a set comparison value; V is the volume energy density of the secondary battery, in Wh / L; P is the compaction density of the positive electrode sheet of the secondary battery, in g / cm3; C is the surface density of the positive electrode sheet, in mg / cm2; E is the injection coefficient of the secondary battery, in Ah / g. At present, we are starting from the direction of material system. Lithium manganese iron phosphate is based on lithium iron phosphate with manganese added. The new positive electrode material obtained by adding manganese elements makes up for the low energy density caused by the low voltage of lithium iron phosphate by increasing the voltage of the material system. However, the electrical conductivity and lithium ion diffusion coefficient of lithium manganese iron phosphate are both low. Because manganese ions are easily dissolved and deposited on the surface of the negative electrode during the battery cycle, it will greatly reduce the life of the battery. Therefore, improving the positive electrode material system is not a mature technical solution at present. The volume energy density of the secondary battery in this application, the compaction density of the positive electrode sheet, the positive electrode sheet The surface density and the battery's filling coefficient satisfy a specific relationship, which significantly improves the battery's volume energy density and enables the battery to have both higher energy density and better cycle performance. In this application, Z is a set comparison value, 9≤Z≤13, and the value of Z can be, for example, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or 13, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the Z satisfies 10<Z≤12, and the value of Z can be, for example, 10.1, 10.2, 10.4, 10.6, 10.8, 11, 11.2, 11.4, 11.6, 11.8 or 12, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the V≥420Wh / L, for example, it can be 420Wh / L, 425Wh / L, 430Wh / L, 435Wh / L, 440Wh / L, 445Wh / L, 450Wh / L, 455Wh / L, 460Wh / L, 465Wh / L, 470Wh / L or 480Wh / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. The volume energy density of a secondary battery in this application refers to the amount of electrical energy stored per unit volume. Volume energy density is one of the important indicators to measure battery performance. It determines how much electrical energy the battery can store in a limited volume. A higher volume energy density means that the battery can store more electrical energy in the same volume, thereby providing longer usage time or higher power output. The calculation method of the liquid filling coefficient E in the present invention is: the capacity of the battery divided by the mass of the liquid filling. Preferably, the P is ≥ 2.4 g / cm3, for example, it can be 2.4 g / cm3, 2.6 g / cm3, 2.8 g / cm3, 3g / cm3, 3.2g / cm3, 3.4g / cm3, 3.6g / cm3, 3.8g / cm3, 4g / cm3 or 4.5g / cm3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. The compaction density of the positive electrode sheet in this application refers to the density of the positive electrode active material layer during the battery manufacturing process. The density after compaction has a direct impact on battery performance. A higher compaction density can increase the specific surface area of ​​the positive electrode active material and increase the contact area between the electrolyte and the positive electrode, thereby improving the battery's reaction rate and power density. In addition, a high compaction density can also reduce the pores inside the secondary battery and improve the mechanical stability and cycle life of the secondary battery. Preferably, the C is ≥ 22 mg / cm2, for example, 22 mg / cm2, 23 mg / cm2, 24 mg / cm2, 25mg / cm2, 26mg / cm2, 27mg / cm2, 28mg / cm2, 29mg / cm2, 30mg / cm2, 32mg / cm2, 34mg / cm2, 36mg / cm2, 38mg / cm2 or 40mg / cm2, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. The surface density of the positive electrode sheet in this application refers to the surface density of the positive electrode active material layer on the positive electrode sheet. Preferably, the E≤3.6Ah / g, for example, 3.6Ah / g, 3.5Ah / g, 3.4Ah / g, 3.3Ah / g, 3.2Ah / g, 3.1Ah / g, 3.0Ah / g, 2.9Ah / g, 2.8Ah / g, 2.7Ah / g, 2.6Ah / g, 2.5Ah / g, 2.4Ah / g, 2.2Ah / g or 2Ah / g, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 2.9-3.6Ah / g. Preferably, the positive electrode sheet includes a positive electrode current collector and a positive electrode current collector surface covered with a positive electrode current collector. Active material layer. Preferably, the positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder and Dispersant. Preferably, the mass fraction of the positive electrode active material in the positive electrode active material layer is 92-99 wt %. For example, it can be 92wt%, 93wt%, 94wt%, 95wt%, 95wt%, 96wt%, 97wt%, 98wt% or 99wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the positive electrode active material includes lithium iron phosphate material. When the positive electrode active material in this application is lithium iron phosphate material, the secondary battery is lithium iron phosphate battery. Since lithium iron phosphate batteries are cheap and have high safety, the secondary battery in this application not only has high energy density and good cycle performance, but also has low production cost and high safety. Preferably, the positive electrode active material layer further contains doping elements, and the doping elements include Ti, Any one or a combination of at least two of Al, Mg, V, Ni or Mn elements, typical but non-limiting combinations include a combination of Ti and Al, a combination of Mg and V, a combination of Ni and Mn, or a combination of Ti, Al and Mg. Preferably, the content of each element in the doping element is not higher than 5000ppm, for example It is 5000ppm, 4500ppm, 4000ppm, 3500ppm, 3000ppm, 2500ppm, 2000ppm, 1500ppm, 1000ppm or 500ppm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the positive electrode current collector comprises copper foil, aluminum foil, copper alloy foil or aluminum alloy foil. Preferably, the positive electrode current collector is aluminum foil, and the thickness of the aluminum foil is 6 μm to 15 μm, for example It can be 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable; Or the positive electrode current collector includes a first substrate and a carbon layer, the first substrate is aluminum foil, the carbon The layer is located on the surface of the first substrate, and the thickness of the carbon layer is 0.2μm to 3μm, for example, it can be 0.2μm, 0.4μm, 0.6μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm or 3μm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable. Preferably, the secondary battery further comprises a negative electrode sheet, including a negative electrode current collector and the negative electrode current collector. The negative electrode active material layer covers the fluid surface. Preferably, the single-surface density of the negative electrode sheet is 8 to 15 mg / cm2, for example, 8 mg / cm2, 9mg / cm2, 10mg / cm2, 11mg / cm2, 12mg / cm2, 13mg / cm2, 14mg / cm2 or 15mg / cm2, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder and Dispersant. Preferably, the mass fraction of the negative electrode active material in the negative electrode active material layer is 92-99 wt %. For example, it can be 92wt%, 93wt%, 94wt%, 95wt%, 95wt%, 96wt%, 97wt%, 98wt% or 99wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the negative electrode active material in the negative electrode active material layer is graphite. Graphite includes natural graphite and / or artificial graphite. Preferably, the thickness of the negative electrode current collector is 4 to 12 μm, for example, 4 μm, 5 μm, 6 μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the negative electrode current collector is copper foil or composite copper foil. Preferably, the secondary battery further comprises a separator, wherein the separator comprises a second substrate and a modified coating. The modified coating is attached to the surface of the second substrate; wherein the second substrate is selected from at least one of polypropylene and polyethylene, and the modified coating comprises a ceramic material; the thickness of the second substrate is 5 to 20 μm, and the thickness of the modified coating is 1 to 6 μm. The ceramic material in the present invention includes alumina. The thickness of the second substrate in the present invention is 5 to 20 μm, for example, 5 μm, 6 μm, 7 μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Preferably, the thickness of the modified coating is 1 to 6 μm, for example, 1 μm, 2 μm, 3 μm, 4μm, 5μm or 6μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. In a second aspect, the present application provides a battery pack, the battery pack comprising the battery pack described in the first aspect Secondary battery. Compared with the prior art, this application has the following beneficial effects: The volume energy density of the secondary battery in this application, the compaction density of the positive electrode sheet, the positive electrode sheet The surface density and the battery's filling coefficient satisfy a specific relationship, which significantly improves the battery's volume energy density and enables the battery to have both higher energy density and better cycle performance. DETAILED DESCRIPTION The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application. Example 1 This embodiment provides a secondary battery, which satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=11.66, preferably 10<Z≤12; V is the secondary battery Volume energy density, V = 420Wh / L; P is the compaction density of the positive electrode sheet, P = 2.45g / cm3; C is the surface density of the positive electrode sheet, C = 24.5mg / cm2; E is the battery filling coefficient, E = 3.5Ah / g. The positive electrode sheet includes a positive electrode current collector with a thickness of 13 μm and a positive electrode current collector surface covered with The positive electrode active material layer is covered; the positive electrode current collector is a carbon-coated aluminum foil; the positive electrode active material layer includes 92 to 99 wt% lithium iron phosphate by mass, and the remainder is a conductive agent, a binder and a dispersant; the positive electrode active material layer also contains doping elements, and the doping elements include any one or a combination of at least two of Ti, Al, Mg, V, Ni or Mn elements; the content of each element in the doping elements is not higher than 5000 ppm. The secondary battery further comprises a negative electrode sheet, including a negative electrode current collector with a thickness of 6 μm and the negative electrode A negative electrode active material layer covering the surface of the negative electrode current collector; the negative electrode current collector is copper foil; the single-side density of the negative electrode plate is 8 to 15 mg / cm2; the negative electrode active material layer includes graphite with a mass fraction of 92 to 99 wt%, and the remainder is a conductive agent, a binder and a dispersant. The secondary battery further comprises a separator, wherein the separator comprises PP and / or PE with a thickness of 5 to 20 μm. The substrate and the surface of the PP and / or PE substrate are covered with a diaphragm coating with a thickness of 1 to 6 μm; the diaphragm coating comprises aluminum oxide and a binder. Example 2 This embodiment provides a secondary battery, which satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=11.26; V is the volume energy density of the secondary battery, V = 430Wh / L; P is the compaction density of the positive electrode sheet, P = 2.55g / cm3; C is the surface density of the positive electrode sheet, C = 25.5mg / cm2; E is the liquid filling coefficient of the battery, E = 3.6Ah / g, and the rest are the same as in Example 1. Example 3 This embodiment provides a secondary battery, which satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=11.01, preferably 10<Z≤12; V is the secondary battery Volume energy density, V = 435Wh / L; P is the compaction density of the positive electrode sheet, P = 2.58g / cm3; C is the surface density of the positive electrode sheet, C = 26.5mg / cm2; E is the liquid filling coefficient of the battery, E = 3.57Ah / g, and the rest are the same as in Example 1. Example 4 This embodiment provides a secondary battery, which satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=10.76; V is the volume energy density of the secondary battery, V=440Wh / L; P is the compaction density of the positive electrode sheet, P=2.6g / cm3; C is the surface density of the positive electrode sheet, C=27.5mg / cm2; E is the liquid filling coefficient of the battery, E=3.5Ah / g, and the rest are the same as in Example 1. Example 5 This embodiment provides a secondary battery, which satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=9.0; V is the volume energy density of the secondary battery, V=460Wh / L; P is the compaction density of the positive electrode sheet, P = 2.8 g / cm3; C is the surface density of the positive electrode sheet, C = 31.5 mg / cm2; E is the liquid filling coefficient of the battery, E = 2.6 Ah / g, and the rest are the same as in Example 1. Example 6 This embodiment provides a secondary battery, which satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=13; V is the volume energy density of the secondary battery, V=390Wh / L; P is the compaction density of the positive electrode sheet, P = 2.35 g / cm3; C is the surface density of the positive electrode sheet, C = 22 mg / cm2; E is the liquid injection coefficient of the battery, E = 3.75 Ah / g, and the rest are the same as in Example 1. Example 7 This embodiment provides a secondary battery, except that Z is a set comparison value, Z=12.03; V is a secondary The volume energy density of the battery is V = 415Wh / L; P is the compaction density of the positive electrode sheet, P = 2.4g / cm3; C is the surface density of the positive electrode sheet, C = 22mg / cm2; E is the liquid injection coefficient of the battery, E = 3.6Ah / g, and the rest are the same as in Example 1. Comparative Example 1 This embodiment provides a secondary battery, except that the secondary battery satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=8.80; V is the volume energy density of the secondary battery, V=470Wh / L; P is the compaction density of the positive electrode sheet, P=2.8g / cm3; C is the surface density of the positive electrode sheet, C=32mg / cm2; E is the liquid filling coefficient of the battery, E=2.5Ah / g, and the rest are the same as in Example 1. Comparative Example 2 This embodiment provides a secondary battery, except that the secondary battery satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Wherein, Z is the set comparison value, Z=14.13; V is the volume energy density of the secondary battery, V = 365Wh / L; P is the compaction density of the positive electrode sheet, P = 2.3g / cm3; C is the surface density of the positive electrode sheet, C = 22mg / cm2; E is the liquid filling coefficient of the battery, E = 3.8Ah / g, and the rest are the same as in Example 1. The secondary batteries in Examples 1 to 8 and Comparative Examples 1 and 2 were subjected to cycle stability tests. The stability test method is as follows: at 25°C, the secondary batteries corresponding to the embodiments and comparative examples are first charged at a constant current and constant voltage of 1C to a voltage of 3.65V, then charged at a constant voltage of 3.65V with a cut-off current of 0.05C. After standing for 30 minutes, the batteries are discharged at a constant current of 1C to a voltage of 2.5V. After 500 charge and discharge cycles, the ratio of the discharge capacity of the battery in the 500th cycle to the discharge capacity in the first cycle is calculated, and this is used as the capacity retention rate of the battery after 500 cycles. The capacity retention rates after 500 cycles are shown in Table 1. Table 1 As can be seen from Table 1, when the value of Z is 10-12, it can better balance the energy density and cycle Cycle life effectively increases the overall cell energy density (above 420Wh / L) and maintains a good cycle life. The secondary battery achieves both high energy density and good cycle performance. A more preferred Z value is 10.7-11.7. From Table 1, we can get: (1) The secondary batteries provided in Examples 1 to 6 of the present application also have a high volume energy density The secondary battery has both high energy density and good cycle performance. (2) By comparing Example 1 with Example 7, it can be seen that when the volume energy density of the secondary battery is When it is smaller, a higher capacity retention rate, that is, a higher cycle stability, can be guaranteed, but the secondary battery at this time does not take into account both higher energy density and better cycle performance. (3) By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that when the comparison value is set to be lower than 9, The capacity retention rate of the secondary battery is too low, and the secondary battery at this time does not take into account both higher energy density and better cycle performance; when the comparison value is set higher than 13, the volume energy density of the secondary battery is too low. This is because the secondary battery at this time also does not take into account both higher energy density and better cycle performance. In summary, the volume energy density of the secondary battery and the compaction density of the positive electrode sheet in this application are The surface density of the positive electrode sheet and the filling coefficient of the battery satisfy a specific relationship, which significantly improves the volume energy density of the battery and enables the battery to have both higher energy density and better cycle performance.

Claims

1. A secondary battery, characterized in that: The secondary battery satisfies the following relationship: 9≤(6000 / V)-P / 2-(2×C) / (10×E)=Z≤13 Among them, Z is the set comparison value; V is the volume energy density of the secondary battery, in Wh / L; P is the compaction density of the positive electrode sheet of the secondary battery, in g / cm3; C is the surface density of the positive electrode sheet, in mg / cm2; E is the filling coefficient of the secondary battery, in Ah / g.

2. The secondary battery according to claim 1, wherein The Z satisfies 10<Z≤12.

3. The secondary battery according to claim 1 or 2, characterized in that The V≥420Wh / L.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The P≥2.4g / cm3.

5. The secondary battery according to any one of claims 1 to 4, characterized in that The C≥22mg / cm2.

6. The secondary battery according to any one of claims 1 to 5, characterized in that The E is ≤ 3.6 Ah / g, preferably 2.9 to 3.6 Ah / g.

7. The secondary battery according to any one of claims 1 to 6, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer covered on the surface of the positive electrode current collector; Preferably, the positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder and a dispersant; Preferably, the mass fraction of the positive electrode active material in the positive electrode active material layer is 92 to 99 wt%; Preferably, the positive electrode active material includes lithium iron phosphate material; Preferably, the positive electrode active material further contains a doping element, and the doping element includes any one or a combination of at least two of Ti, Al, Mg, V, Ni or Mn elements; Preferably, the content of each element in the doping element is not higher than 5000 ppm; Preferably, the positive electrode current collector is aluminum foil, and the thickness of the aluminum foil is 6 μm to 15 μm; Alternatively, the positive electrode current collector includes a first substrate and a carbon layer, the first substrate is aluminum foil, the carbon layer is located on the surface of the first substrate, and the thickness of the carbon layer is 0.2 μm-3 μm.

8. The secondary battery according to any one of claims 1 to 7, characterized in that The secondary battery further comprises a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer covering the surface of the negative electrode current collector; Preferably, the single-surface density of the negative electrode sheet is 8 to 15 mg / cm2; Preferably, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder and a dispersant; Preferably, the mass fraction of the negative electrode active material in the negative electrode active material layer is 92 to 99 wt%; Preferably, the negative electrode active material in the negative electrode active material layer is graphite; Preferably, the thickness of the negative electrode current collector ranges from 4 μm to 12 μm; Preferably, the negative electrode current collector is copper foil or composite copper foil.

9. The secondary battery according to any one of claims 1 to 8, characterized in that The secondary battery also includes a separator, which includes a second substrate and a modified coating, and the modified coating is attached to the surface of the second substrate; wherein the second substrate is selected from at least one of polypropylene and polyethylene, and the modified coating includes a ceramic material; the thickness of the second substrate is 5 to 20 μm, and the thickness of the modified coating is 1 to 6 μm.

10. A battery pack, characterized in that: The battery pack includes the secondary battery according to any one of claims 1 to 9.

Images