Secondary battery and electrical apparatus

Abstract

The present application relates to a secondary battery and an electrical apparatus. The secondary battery comprises a positive electrode piece; the positive electrode piece comprises a positive electrode active material layer, the single-sided coating weight G1 of the positive electrode active material layer satisfying: 360 mg / 1540.25 mm2≤G1≤550 mg / 1540.25 mm2; the compaction density ρ1 of the positive electrode piece satisfies: 2.4 g / cm3≤ρ1≤2.9 g / cm3; the positive electrode piece satisfies: when the positive electrode piece and a lithium metal piece are manufactured into a button cell, and the button cell is subjected to constant-current discharging to 3.2 V at the 1C rate, the obtained discharge capacity per gram is C1, and when the button cell is subjected to constant-current discharging to 2 V at the 1C rate, the obtained discharge capacity per gram is C2, where r=C1 / C2, and r satisfies: 80%≤r≤98%.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311416459.5, filed on October 30, 2023, entitled “Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] In recent years, the application of secondary batteries, represented by lithium-ion batteries, has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved significant development, higher requirements have been placed on their energy density, cycle performance, and power performance.

[0006] Summary of the Invention

[0007] The present application provides a secondary battery and an electrical device, which can enable the secondary battery to still have high power performance under conditions of thick coating and high pressure sealing.

[0008] In order to achieve the above object, the first aspect of the present application provides a secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode active material layer, and the single-side coating weight G1 of the positive electrode active material layer satisfies: 360 mg / 1540.25 square millimeters (mg / 1540.25mm 2 )≤G1≤550mg / 1540.25mm 2 The compaction density ρ1 of the positive electrode sheet satisfies: 2.4 g / cm3 (g / cm 3 )≤ρ1≤2.9g / cm 3 ; The positive electrode plate satisfies: the positive electrode plate and the lithium metal plate are prepared into a button battery, the button battery is discharged at a constant current rate of 1C to 3.2V, and the resulting discharge capacity in grams is C1; the button battery is discharged at a constant current rate of 1C to 2V, and the resulting discharge capacity in grams is C2; wherein, r = C1 / C2, and r satisfies: 80%≤r≤98%.

[0009] The positive electrode plate and the lithium metal plate are prepared into a button battery, and when the gram capacity ratio r of the button battery measured under the above two test conditions meets the above range, the power performance of the battery can be improved; the battery can maintain relatively high power performance under the application conditions where G1 and ρ1 are in the above range, that is, the battery is under the application conditions of relatively thick coating and relatively high compaction.

[0010] In some embodiments of the present application, the r satisfies: 85%≤r≤95%.

[0011] When r is within the above range, the power performance of the battery can be further improved under thick coating and high-pressure density application conditions.

[0012] In some embodiments of the present application, at least one of the following conditions is met:

[0013] (1) The single-sided coating weight G1 of the positive electrode active material layer satisfies: 400 mg / 1540.25 mm 2 ≤G1≤550mg / 1540.25mm 2 ;

[0014] (2) The compaction density ρ1 of the positive electrode sheet satisfies: 2.5g / cm 3 ≤ρ1≤2.9g / cm 3 .

[0015] In some embodiments of the present application, the SOC power of the secondary battery at 25° C. satisfies: 0.95×r≤(10%×SOC power) / (50%×SOC power)≤r, r≤(20%×SOC power) / (50%×SOC power)≤1.05×r.

[0016] The single-sided coating weight of the positive electrode active material layer is within the above range, which enables the positive electrode sheet to be coated relatively thickly; such a relatively thick coating of the positive electrode sheet is beneficial to improving the capacity performance of the battery.

[0017] In some embodiments of the present application, the positive electrode active material layer contains a positive electrode active material, and the positive electrode active material satisfies at least one of the following conditions:

[0018] (1) The compaction density ρ' of the positive electrode active material under 3 tons of pressure satisfies: 2.45 g / cm 3 ≤ρ'≤2.7g / cm 3 ;

[0019] (2) The mass proportion ω of the positive electrode active material in the positive electrode active material layer satisfies: 95%≤ω≤98.5%;

[0020] (3) The positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a modified compound thereof.

[0021] The compaction density of the positive electrode active material is within the above range, which can improve the compaction density of the positive electrode sheet, so that the positive electrode sheet has a relatively high compaction, thereby improving the energy density of the battery; the mass proportion of the positive electrode active material in the positive electrode active material layer is within the above range, which is beneficial to improving the capacity performance of the battery.

[0022] In some embodiments of the present application, the lithium-containing phosphate satisfies at least one of the following conditions:

[0023] (1) The lithium-containing phosphate satisfies the molecular formula LiFe 1-x-y Mn x M y PO4, 0≤x≤1, 0≤y<1, wherein M includes one or more transition metal elements other than Fe and Mn and non-transition metal elements;

[0024] Optionally, M includes one or more of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn and Pb;

[0025] (2) The lithium-containing phosphate includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0026] The positive electrode active materials include lithium-containing phosphates and their respective modified compounds. By selecting and regulating the lithium-containing phosphates and their respective modified compounds, the capacity ratio r of the battery can be made to meet the aforementioned range (80% ≤ r ≤ 98%). As a result, the battery can achieve an improvement in power performance under the aforementioned application conditions (relatively thick coating and relatively high compaction) and maintain the power performance at a relatively high level.

[0027] In some embodiments of the present application, the secondary battery further includes an electrolyte, and the conductivity σ of the electrolyte satisfies: σ≥14 millisiemens / cm (mS / cm), and can be optionally 14 mS / cm≤σ≤21 mS / cm.

[0028] The conductivity of the electrolyte is within the above range, which is conducive to promoting the transmission of active ions, reducing the liquid phase transmission impedance and liquid phase concentration polarization of active ions, reducing the DCR (direct current internal resistance) of the battery, and improving power performance.

[0029] In some embodiments of the present application, the secondary battery further includes a negative electrode plate, and the negative electrode plate includes a negative electrode active material layer, and the single-sided coating weight G2 of the negative electrode active material layer satisfies: 140 mg / 1540.25 mm 2 ≤G2≤200 mg / 1540.25 mm 2 , optionally 160 mg / 1540.25 mm 2 ≤G2≤200 mg / 1540.25 mm 2 .

[0030] When the single-sided coating weight of the negative electrode active material layer is within the above range, it can cooperate with the foregoing setting of the positive electrode plate to enable the battery to achieve the relatively thick coating and relatively high compaction density as described above, and promote the improvement of the battery power performance under the condition of satisfying the foregoing r.

[0031] In some embodiments of the present application, the negative electrode plate satisfies at least one of the following conditions:

[0032] (1) The compaction density ρ2 of the negative electrode plate satisfies: 1.5 g / cm 3 ≤ρ2≤2 g / cm 3 , optionally 1.6 g / cm 3 ≤ρ2≤2 g / cm 3 ;

[0033] (2) The porosity P of the negative electrode plate satisfies: 0 < P ≤ 50%, optionally 0 < P ≤ 35%.

[0034] When the compaction density of the negative electrode plate is within the above range, it is beneficial to further improve the energy density of the battery; when the porosity of the negative electrode plate is within the above range, it is beneficial to increase the transmission channels of active ions (such as lithium ions) and promote the transmission of active ions to further improve the power performance of the battery.

[0035] The second aspect of the present application provides an electrical device including the secondary battery of the first aspect of the present application.

[0036] The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0037] Details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive work. In the drawings:

[0039] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0040] FIG. 2 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG. 1 .

[0041] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0042] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0043] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application.

[0044] FIG6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0045] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0046] Below, some embodiments of the secondary battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0047] " range " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be including end value or excluding end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the scope of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are also listed, then the following range can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range " a to b " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2 to 10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0048] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0051] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0052] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both a closed feature or solution consisting of the listed members and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both a feature or solution that "A consists of a1, a2, and a3" and a feature or solution that "A not only includes a1, a2, and a3, but also includes other members". In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0053] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0054] The development of secondary batteries is driving higher demands on their capacity, energy density, and power performance. To improve battery capacity and energy density, thick coatings and high-density designs are often employed on the pole pieces. However, thick coatings extend the transport path for active ions, while high-density designs reduce these channels, increasing the impedance of solid-phase diffusion and degrading the battery's power performance.

[0055] In order to solve the above technical problems, the present application provides a secondary battery. By designing and regulating the discharge gram capacity ratio r of the positive electrode under different test conditions, the secondary battery can still have relatively high power performance under thick coating and high pressure density application conditions.

[0056] secondary batteries

[0057] In a first aspect, the present application provides a secondary battery comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material layer, and the single-side coating weight G1 of the positive electrode active material layer satisfies: 360 mg / 1540.25 mm 2 ≤G1≤550mg / 1540.25mm 2 The compaction density ρ1 of the positive electrode sheet satisfies: 2.4g / cm 3 ≤ρ1≤2.9g / cm 3 ; The positive electrode plate satisfies: the positive electrode plate and the lithium metal plate are prepared into a button battery, the button battery is discharged at a constant current rate of 1C to 3.2 volts (V), and the resulting discharge capacity in grams is C1; the button battery is discharged at a constant current rate of 1C to 2V, and the resulting discharge capacity in grams is C2; wherein, r = C1 / C2, and the r satisfies: 80%≤r≤98%.

[0058] It is understood that the above r can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 98% or within a range consisting of any of the above values.

[0059] It is understood that the preparation process of the aforementioned button-type battery can refer to national standards or industry specifications. For example, the positive electrode active material can be prepared with a conventional binder and conductive agent to form the aforementioned electrode comprising the positive electrode active material layer. A conventional electrolyte solution can then be added to a lithium metal disc as a counter electrode to prepare the button-type battery.

[0060] As a non-limiting example, a button cell may be prepared as follows:

[0061] The selected positive electrode active material, conductive agent, and binder are dispersed in a solvent (such as water) in a certain mass ratio to form a positive electrode slurry, which is then coated on a copper foil, dried to remove the solvent, cut into pieces, and pressed to form a circular electrode sheet containing the above-mentioned positive electrode active material layer. A small lithium metal disc is then used as a counter electrode, and an electrolyte is added to assemble it into a button battery in a glove box. The electrolyte can be an organic solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, dissolving fully dried lithium salt LiPF6 in the organic solvent, and then adding fluoroethylene carbonate (FEC). After mixing evenly, an electrolyte is obtained, wherein the concentration of LiPF6 is 1 mol / L (mol / L) and the mass percentage of FEC in the electrolyte is 6%.

[0062] It can be understood that the above-mentioned discharge capacity C1 can be obtained by testing as follows: the prepared button battery is allowed to stand at 25 degrees Celsius (℃) for 30 minutes (min), and charged to 3.75V at a constant current of 0.1C until the cut-off current is 0.05 milliamperes (mA); then allowed to stand for 10 minutes, discharged to 2V at a constant current of 0.33C, and the capacity at this time is calibrated as C0; then allowed to stand again at 25℃ for 10 minutes, charged to 3.75V at a constant current of 0.1×C0 until the cut-off current is 0.05mA; then allowed to stand for another 10 minutes, discharged to 3.2V at a constant current of C0, and the discharge capacity C1' is obtained, then C1 = C1' / the mass of the positive electrode active material in the positive electrode sheet.

[0063] It can be understood that the above-mentioned discharge capacity C2 can be obtained by testing as follows: the prepared button battery is allowed to stand at 25°C for 30 minutes, charged to 3.75V at a constant current of 0.1C, until the cut-off current is 0.05mA; then allowed to stand for 10 minutes, discharged to 2V at a constant current of 0.33C, and the capacity at this time is calibrated as C0; then allowed to stand at 25°C for 10 minutes again, charged to 3.75V at a constant current of 0.1×C0, until the cut-off current is 0.05mA; then allowed to stand for another 10 minutes, discharged to 2V at a constant current of C0, and the discharge capacity C2' is obtained, then C2 = C2' / the mass of the positive electrode active material in the positive electrode sheet.

[0064] Without intending to be bound by any theory, when the positive electrode sheet and the lithium metal sheet are prepared into a button cell, and the gram capacity ratio r measured for the button cell under the above two test conditions satisfies the above range, the particle size distribution of the positive electrode active material is uniform and essentially all at the nanometer level, with no micron-sized particles or a very small number of micron-sized particles (ratio <0.1%). The nanometer-scale uniform particle size of the positive electrode active material can significantly reduce the solid-phase diffusion impedance and reduce the DCR (direct current internal resistance) during high-rate discharge, thereby improving the low SOC power performance and enhancing the power performance of the battery, so that the battery can maintain relatively high power performance under the application conditions where G1 and ρ1 are within the above range, that is, under the application conditions where the battery is relatively thickly coated and relatively highly compacted.

[0065] In some embodiments, r satisfies the following: 85% ≤ r ≤ 95%. For example, r can be 85%, 87%, 89%, 91%, 93%, 95%, or any range thereof. When r is within the above range, the power performance of the battery can be further improved under thick coating and high pressure density application conditions.

[0066] In some embodiments, the single-side coating weight G1 of the positive electrode active material layer satisfies: 360 mg / 1540.25 mm 2 ≤G1≤550mg / 1540.25mm2 For example, G1 can be 360mg / 1540.25mm 2 , 390mg / 1540.25mm 2 , 420mg / 1540.25mm 2 , 450mg / 1540.25mm 2 , 480mg / 1540.25mm 2 , 510mg / 1540.25mm 2 , 540mg / 1540.25mm 2 , 550mg / 1540.25mm 2 or within a range consisting of any of the above values.

[0067] In some embodiments, the single-side coating weight G1 of the positive electrode active material layer satisfies: 400 mg / 1540.25 mm 2 ≤G1≤550mg / 1540.25mm 2 For example, G1 can be 400mg / 1540.25mm 2 , 430mg / 1540.25mm 2 , 460mg / 1540.25mm 2 , 490mg / 1540.25mm 2 , 520mg / 1540.25mm 2 , 550mg / 1540.25mm 2 or within a range consisting of any of the above values.

[0068] It can be understood that the single-sided coating weight of the positive electrode active material layer refers to the coating weight of the positive electrode active material layer on any one of the two oppositely disposed sides of the positive electrode plate.

[0069] The coating weight of the positive electrode active material layer on one side can be measured by methods known in the art. For example, the dried positive electrode sheet is cut into an area of ​​1540.25 mm. 2 5 pieces of electrode sheets were measured respectively by using a micrometer to measure the thickness of the positive electrode sheets, which was recorded as d0cm. The positive electrode active material layer in the positive electrode sheet was scraped off with a scraper, and the weight of the positive electrode active material layer was weighed by a balance, which was recorded as m (mg), which is the positive electrode active material layer 1540.25mm 2 Weight on area.

[0070] The single-sided coating weight of the positive electrode active material layer is within the above range, which enables the positive electrode sheet to be coated relatively thickly; such a relatively thick coating of the positive electrode sheet is beneficial to improving the capacity performance of the battery.

[0071] In some embodiments, the compaction density ρ1 of the positive electrode sheet satisfies: 2.4 g / cm 3 ≤ρ1≤2.9g / cm 3 For example, ρ1 can be 2.4 g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 or within a range consisting of any of the above values.

[0072] In some embodiments, the compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm 3 ≤ρ1≤2.9g / cm 3 For example, ρ1 can be 2.5 g / cm 3 , 2.55g / cm 3 , 2.65g / cm 3 , 2.75g / cm 3 , 2.85g / cm 3 , 2.9g / cm 3 or within a range consisting of any of the above values.

[0073] The compaction density of the positive electrode sheet is well known in the art and can be measured using methods known in the art. For example, a dried positive electrode sheet is cut into an area of ​​1540.25 mm 2 Five electrode sheets were cut. The thickness of each positive electrode sheet was measured using a caliper (d0 cm). The positive electrode active material layer was scraped off the positive electrode sheet using a scraper and the mass of the positive electrode active material layer was weighed using a balance (m (mg)). The thickness of the positive electrode current collector without the positive electrode active material layer was measured using a caliper (d cm). The compacted density of the positive electrode active material layer was calculated according to the following formula: Compacted density = m / [154.025 × (d0 - d0)]. The compacted density of the positive electrode sheet, ρ1, is the average of the compacted densities of the positive electrode active material layer in the five positive electrode sheets cut above.

[0074] The compaction density of the positive electrode sheet is within the above range, which enables the positive electrode sheet to achieve relatively high compaction; this relatively high compaction of the positive electrode sheet is beneficial to improving the energy density of the battery.

[0075] In some embodiments, the SOC power of the secondary battery at 25° C. satisfies: 0.95×r≤10% SOC power / 50% SOC power≤r, r≤20% SOC power / 50% SOC power≤1.05×r.

[0076] The SOC power of a secondary battery at 25°C can be measured using the following method:

[0077] The prepared secondary battery was placed at 25°C for 30 minutes, charged to 3.8V at a constant current of 0.33C until the cutoff current reached 0.05C; then placed at rest for 30 minutes, discharged to 2V at a constant current of 0.33C, and the capacity at this time was calibrated as C0; then placed at 25°C for another 30 minutes, charged to 3.8V at a constant current of 0.33×C0 until the cutoff current reached 0.05×C0; then placed at rest for another 30 minutes, discharged to 2V at a constant current of 0.33C, and the capacity at this time was calibrated as C0; Discharge at a constant current of C0 for 90 minutes to bring the secondary battery to 50% SOC. Let it stand for 120 minutes and read the static voltage of 50% SOC as V1. Discharge at a constant current of 4×C0 for 30 seconds and record the voltage at the end of discharge as V2. In this step of discharge, DCR1 = (V1-V2) / (4×C0). At this time, the power at 50% SOC = ((V1-V2) / DCR1)×2. Similarly, the power at 20% SOC and 10% SOC are obtained respectively.

[0078] The SOC power of the secondary battery at 25°C meets the above conditions, which enables the battery to still have relatively high power performance under relatively thick coating and relatively high compaction conditions.

[0079] In some embodiments, the positive electrode active material layer comprises a positive electrode active material.

[0080] In some embodiments, the compaction density ρ' of the positive electrode active material under 6 tons of pressure satisfies: 2.45 g / cm 3 ≤ρ'≤2.7g / cm 3 For example, ρ' can be 2.45 g / cm 3 , 2.5g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3 , 2.65g / cm 3 , 2.7g / cm 3 or within a range consisting of any of the above values.

[0081] The compaction density of the positive electrode active material is well known in the art and can be measured using methods known in the art. For example, it can be measured using an electronic pressure tester, such as the UTM7305 electronic pressure tester, with reference to GB / T24533-2009. Accurately weigh about 1 gram (g) of sample and add a bottom area of ​​1.327 square centimeters (cm 2) mold, a pressurizing device applies 3 tons of pressure to the sample, maintains this pressure for 30 seconds, and then removes the pressure. The sample's height is then measured, and the material's compacted density is calculated using the formula ρ' = m / (1.327 × h). Here, ρ' represents the material's compacted density, m represents the sample's mass, and h represents the sample's height after the 3 tons of pressure is applied, maintained for 30 seconds, and then removed.

[0082] The compaction density of the positive electrode active material is within the above range, which can improve the compaction density of the positive electrode sheet, so that the positive electrode sheet has a relatively high compaction, thereby improving the energy density of the battery.

[0083] In some embodiments, the mass percentage ω of the positive electrode active material in the positive electrode active material layer satisfies the following: 95%≤ω≤98.5%. For example, ω can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, or any range thereof.

[0084] The mass proportion of the positive electrode active material in the positive electrode active material layer is within the above range, which is beneficial to improving the capacity performance of the battery.

[0085] In some embodiments, the positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a modified compound thereof.

[0086] It is understood that the specific types of modified compounds of olivine-structured lithium-containing phosphates are not limited, and can include modified compounds of the lithium-containing phosphates that have been coated and modified, and modified compounds of the lithium-containing phosphates that have been doped. The types of modified substances for coating and doping are not limited and can be selected based on actual needs.

[0087] In some embodiments, the lithium-containing phosphate satisfies the molecular formula LiFe 1-x-y Mn x M y PO4, 0≤x≤1, 0≤y<1, wherein M includes one or more transition metal elements other than Fe and Mn and non-transition metal elements.

[0088] Optionally, M includes one or more of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn and Pb.

[0089] In some embodiments, the lithium-containing phosphate includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0090] The positive electrode active materials include lithium-containing phosphates and their respective modified compounds. By selecting and regulating the lithium-containing phosphates and their respective modified compounds, the capacity ratio r of the battery can be made to meet the aforementioned range (80% ≤ r ≤ 98%). As a result, the battery can achieve an improvement in power performance under the aforementioned application conditions (relatively thick coating and relatively high compaction), and the power performance can still be maintained at a relatively high level.

[0091] In some embodiments, the secondary battery further comprises an electrolyte, wherein the conductivity σ of the electrolyte satisfies: σ ≥ 14 mS / cm. For example, σ may be 14 mS / cm, 16 mS / cm, 18 mS / cm, 20 mS / cm, 21 mS / cm, 22 mS / cm, 24 mS / cm, or within a range thereof. Alternatively, 14 mS / cm ≤ σ ≤ 21 mS / cm.

[0092] The conductivity of an electrolyte is well known in the art and can be measured using methods known in the art. For example, the following method can be used for testing: First, pre-treat the electrolyte: Take the electrolyte to be tested and thermostat it to the temperature to be tested, and the standard solution and thermostat it to 25°C (with a deviation of ±0.1°C); then, calibrate the instrument with the two standard solutions at 25°C. After calibration is completed and the electrodes are cleaned, place the test sample electrode vertically into the electrolyte to be tested, and start testing using a conductivity meter. Wait for the data to stabilize for at least 10 seconds (s) to record the test results to obtain the conductivity of the electrolyte.

[0093] The conductivity of the electrolyte is within the above range, which is conducive to promoting the transmission of active ions, reducing the liquid phase transmission impedance and liquid phase concentration polarization of active ions, reducing the DCR (direct current internal resistance) of the battery, and improving power performance; at the same time, by cooperating with the aforementioned capacity ratio r (85% ≤ r ≤ 95%), the battery can be used in a relatively thick coating (360mg / 1540.25mm 2 ≤G1≤550mg / 1540.25mm 2 ) and relatively high density (2.4 g / cm 3 ≤ρ1≤2.9g / cm 3 ) conditions, its SOC power at 25°C satisfies the aforementioned relationship: 0.95×r≤(10%×SOC power) / (50%×SOC power)≤r, r≤(20%×SOC power) / (50%×SOC power)≤1.05×r, that is, the battery at this time still has relatively high power performance.

[0094] As a specific example, when r is 80% to 98% and σ≥14mS / cm, at least G1 of 360mg / 1540.25mm can be achieved. 2~410mg / 1540.25mm 2 , and ρ1 is 2.4 g / cm 3 ~2.9g / cm 3 For a battery cell, its SOC power at 25°C satisfies the following: 0.95×r≤(10%×SOC power) / (50%×SOC power)≤r, r≤(20%×SOC power) / (50%×SOC power)≤1.05×r.

[0095] As a specific example, when r is 85% to 98% and σ≥16mS / cm, at least G1 of 360mg / 1540.25mm can be achieved. 2 ~550mg / 1540.25mm 2 , and ρ1 is 2.5 g / cm 3 ~2.9g / cm 3 For a battery cell, its SOC power at 25°C satisfies the following: 0.95×r≤(10%×SOC power) / (50%×SOC power)≤r, r≤(20%×SOC power) / (50%×SOC power)≤1.05×r.

[0096] In some embodiments, the secondary battery further comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode active material layer, and the single-side coating weight G2 of the negative electrode active material layer satisfies: 140 mg / 1540.25 mm 2 ≤G2≤200mg / 1540.25mm 2 For example, G2 can be 140mg / 1540.25mm 2 , 160mg / 1540.25mm 2 , 180mg / 1540.25mm 2 , 200mg / 1540.25mm 2 or within a range consisting of any of the above values.

[0097] Optionally, G2 meets: 160mg / 1540.25mm 2 ≤G2≤200mg / 1540.25mm 2 .

[0098] It can be understood that the single-sided coating weight of the negative electrode active material layer refers to the coating weight of the negative electrode active material layer on any one of the two oppositely disposed sides of the negative electrode plate.

[0099] The single-side coating weight of the negative electrode active material layer can be measured by methods known in the art. For example, the dried negative electrode sheet is cut into an area of ​​1540.25 mm. 25 pieces of electrode sheets were used. The thickness of the negative electrode sheets was measured by a micrometer, recorded as d0cm. The negative electrode active material layer in the negative electrode sheet was scraped off with a scraper. The weight of the negative electrode active material layer was weighed by a balance, recorded as m (mg), which is the negative electrode active material layer 1540.25mm 2 Weight on area.

[0100] The single-sided coating weight of the negative electrode active material layer within the aforementioned range can cooperate with the aforementioned arrangement of the positive electrode sheet to achieve the aforementioned relatively thick coating and relatively high compaction of the battery, thereby promoting improved battery power performance while meeting the aforementioned r condition. Furthermore, the single-sided coating weight of the negative electrode active material layer within the aforementioned range is also conducive to further improving battery capacity performance.

[0101] In some embodiments, the compaction density ρ2 of the negative electrode sheet satisfies: 1.5 g / cm 3 ≤ρ2≤2g / cm 3 For example, ρ2 can be 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2g / cm 3 Or within the range of any of the above values. Optionally, ρ2 is 1.6 g / cm 3 ≤ρ2≤2g / cm 3 .

[0102] The compaction density of the negative electrode sheet is well known in the art and can be measured using methods known in the art. For example, the area of ​​the dried negative electrode sheet is cut into 1540.25 mm 2 Take five electrode sheets and measure the thickness of each negative electrode sheet using a caliper (d0 cm). Use a scraper to scrape off the negative active material layer from the negative electrode sheet and weigh the mass of the negative active material layer using a balance (m (mg)). Measure the thickness of the negative current collector without the negative active material layer using a caliper (d cm). Calculate the compacted density of the negative active material layer using the following formula: Compacted density = m / [154.025 × (d0 - d)]. The compacted density of the negative electrode sheet, ρ2, is the average of the compacted densities of the negative active material layers in the five negative electrode sheets obtained above.

[0103] The compaction density of the negative electrode sheet within the above range can also cooperate with the aforementioned arrangement of the positive electrode sheet to better achieve the aforementioned relatively thick coating and relatively high compaction of the battery, promoting the improvement of battery power performance while meeting the aforementioned r condition. At the same time, the compaction density of the negative electrode sheet within the above range is also conducive to further improving the battery energy density.

[0104] In some embodiments, the porosity P of the negative electrode sheet satisfies: 0 < P ≤ 50%. For example, P can be 0.1%, 0.5%, 1%, 5%, 10%, 20%, 30%, 40%, 50% or within the range composed of any of the above values. Optionally, 0 < P ≤ 35%.

[0105] The porosity of the negative electrode sheet has the meaning well-known in the art and can be measured by methods known in the art. For example, after the reaction, the negative electrode sheet is cut into a circular piece with a diameter of 10 mm, and the gas replacement method is used to test the porosity of the negative electrode active material layer. The calculation formula for the porosity is: P = (V - V0) / V × 100%, where P is the porosity, V0 is the true volume of the electrode sheet coating, and V is the apparent volume of the electrode sheet coating.

[0106] When the porosity of the negative electrode sheet is within the above range, it is beneficial to increase the transport channels of active ions (such as lithium ions), promote the transport of active ions, and further improve the power performance of the battery.

[0107] In addition, the secondary battery and the electrical device of the present application will be described below with appropriate reference to the accompanying drawings.

[0108] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0109] Positive electrode sheet

[0110] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0111] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0112] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0113] In some embodiments, the positive electrode active material may include at least one of the aforementioned olivine-structured lithium-containing phosphates and their respective modified compounds.

[0114] In some embodiments, the positive electrode active material may also include positive electrode active materials for batteries known in the art. As non-limiting examples, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0115] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0116] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0117] In some embodiments, the positive electrode active material may also include at least one of the following materials: one or more of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0118] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of sodium transition metal oxides may be Na x MO2, wherein M may include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0119] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si; n represents (YO4) n- valence.

[0120] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si, and n represents (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0121] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0122] Polyanionic compounds may include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1) wherein M′ in NaM′PO4F may include one or more of V, Fe, Mn and Ni.

[0123] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of Prussian blue compounds may include Na a Meb Me' c (CN)6, wherein Me and Me' can each independently be one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0124] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0125] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 to 25000 milliPa·seconds (mPa·s). When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 to 35 mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0127] Negative electrode

[0128] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0129] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0130] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0131] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0132] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0133] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0134] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0135] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 to 10000 mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75 to 220 g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0136] electrolytes

[0137] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0138] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0139] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0140] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0141] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0142] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0143] Isolation film

[0144] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0145] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0146] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and optionally 12 to 20 μm.

[0147] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0148] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0149] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0150] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0151] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0152] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0153] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0154] The secondary battery may be a battery module 4 or a battery pack 1 .

[0155] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0156] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0157] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0158] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0159] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0160] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0161] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0162] Figure 6 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0163] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0164] Example

[0165] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0166] Example 1

[0167] (1) Preparation of positive electrode sheet

[0168] The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride, and the conductive agent acetylene black were mixed in a weight ratio of 97:2:1, and then the solvent N-methylpyrrolidone (NMP) was added to adjust the viscosity. After stirring evenly, the positive electrode slurry was prepared; the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, dried, and cold pressed to obtain the positive electrode sheet. The single-side coating weight of the positive electrode sheet is 420mg / 1540.25mm 2 , compacted density is 2.55g / cm 3 .

[0169] (2) Preparation of negative electrode sheet

[0170] The negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber and thickener sodium carboxymethyl cellulose were mixed in a weight ratio of 96:1:2:1, and then deionized water was added as a solvent and stirred evenly to prepare the negative electrode slurry; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil, dried and cold pressed to obtain the negative electrode sheet. The single-side coating weight of the negative electrode sheet is 190mg / 1540.25mm 2 , compacted density is 1.6g / cm 3 , the porosity is 30%.

[0171] (3) Isolation film

[0172] A polyethylene (PE) film coated with a nano-aluminum oxide coating and having a thickness of 12 μm was used as the separator.

[0173] (4) Preparation of electrolyte

[0174] In an argon-filled glove box with a water content of <10 parts per million (ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a 40:30:30 mass ratio to create an organic solvent. 15% by mass of lithium hexafluorophosphate (LiPF6) was slowly added as a lithium salt and stirred thoroughly until completely dissolved. After returning to room temperature, 3% vinylene carbonate and other additives were added and thoroughly mixed to create the electrolyte.

[0175] (5) Preparation of batteries

[0176] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to form a wound electrode assembly. The electrode assembly is placed in a square aluminum shell for outer packaging, dried, and then injected with electrolyte. The secondary battery is completed through a series of steps including packaging, standing, formation, aging, secondary packaging, and capacity measurement. The secondary battery has a liquid retention coefficient of 3.0 g / ampere-hour (g / Ah).

[0177] Examples 2 to 26 and Comparative Examples 1 to 4

[0178] The preparation of the electrode and the battery is similar to that of Example 1, except that the relevant parameters in the preparation process are adjusted, as shown in Table 1 below.

[0179] The relevant parameters of the electrode pieces of the above-mentioned Examples 1 to 26 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0180] Table 1

[0181] In addition, the batteries obtained in Examples 1 to 26 and Comparative Examples 1 to 4 were subjected to performance tests, and the test results are shown in Table 2 below.

[0182] Test section

[0183] (1) Power performance test

[0184] The prepared battery was left at rest for 30 min at 25°C, charged to 3.8 V at a constant current of 0.33C until the cutoff current reached 0.05C; then left at rest for 30 min, discharged to 2 V at a constant current of 0.33C, and the capacity at this time was calibrated as C0; then left at rest for another 30 min at 25°C, charged to 3.8 V at a constant current of 0.33×C0 until the cutoff current reached 0.05×C0; then left at rest for another 30 min, discharged to 2 V at a constant current of 0.33C, and the capacity at this time was calibrated as C0; 0 constant current discharge for 90 minutes to make the secondary battery at 50% SOC. Let it stand for 120 minutes and read the static voltage of 50% SOC as V1. Use 4×C0 constant current discharge for 30 seconds and record the voltage at the end of discharge as V2. In this step of discharge, DCR1 = (V1-V2) / (4×C0). At this time, the power of 50% SOC = ((V1-V2) / DCR1)×2; and so on, obtain the power of 20% SOC and 10% SOC respectively.

[0185] Table 2

[0186] In Table 2, by comparing the embodiments with the comparative examples, it can be seen that the power of the embodiments is higher than that of the comparative examples, indicating that under the premise that r meets the protection scope of this application, the battery can still maintain a relatively high power performance under the application conditions of relatively thick coating and relatively high compaction (that is, when G1 and ρ1 are both within the protection scope of this application).

[0187] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0188] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material layer, and the single-side coating weight G1 of the positive electrode active material layer satisfies: 360 mg / 1540.25 mm 2 ≤G1≤550mg / 1540.25mm 2 The compaction density ρ1 of the positive electrode sheet satisfies: 2.4 g / cm 3 ≤ρ1≤2.9g / cm 3 ; The positive electrode plate satisfies: the positive electrode plate and the lithium metal plate are prepared into a button battery, and the button battery is discharged at a constant current of 1C to 3.2V, and the obtained discharge capacity in grams is C1; the button battery is discharged at a constant current of 1C to 2V, and the obtained discharge capacity in grams is C2; in, r=C1 / C2, and r satisfies: 80%≤r≤98%.

2. The secondary battery according to claim 1, wherein The r satisfies: 85%≤r≤95%.

3. The secondary battery according to claim 1 or 2, wherein: Satisfy at least one of the following conditions: (1) The single-sided coating weight G1 of the positive electrode active material layer satisfies: 400 mg / 1540.25 mm 2 ≤G1≤550mg / 1540.25mm 2 ; (2) The compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm 3 ≤ρ1≤2.9g / cm 3 .

4. The secondary battery according to any one of claims 1 to 3, wherein: The SOC power of the secondary battery at 25° C. satisfies: 0.95×r≤(10%×SOC power) / (50%×SOC power)≤r, r≤(20%×SOC power) / (50%×SOC power)≤1.05×r.

5. The secondary battery according to any one of claims 1 to 4, wherein: The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material satisfies at least one of the following conditions: (1) The compaction density ρ' of the positive electrode active material under a pressure of 3 tons satisfies: 2.45 g / cm 3 ≤ρ'≤2.7g / cm 3 ; (2) The mass proportion ω of the positive electrode active material in the positive electrode active material layer satisfies: 95%≤ω≤98.5%; (3) The positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a modified compound thereof.

6. The secondary battery according to claim 5, wherein The lithium-containing phosphate satisfies at least one of the following conditions: (1) The lithium-containing phosphate satisfies the molecular formula LiFe 1-x-y Mn x M y PO4, 0≤x≤1, 0≤y<1, wherein M includes one or more transition metal elements other than Fe and Mn and non-transition metal elements; (2) The lithium-containing phosphate includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

7. The secondary battery according to any one of claims 1 to 6, wherein: The invention also includes an electrolyte, wherein the conductivity σ of the electrolyte satisfies: σ≥14 mS / cm.

8. The secondary battery according to claim 7, wherein 14mS / cm≤σ≤23mS / cm.

9. The secondary battery according to any one of claims 1 to 8, wherein: It also includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, and the single-side coating weight G2 of the negative electrode active material layer meets the following requirements: 140 mg / 1540.25 mm 2 ≤G2≤200mg / 1540.25mm 2 .

10. The secondary battery according to claim 9, wherein The negative electrode sheet satisfies at least one of the following conditions: (1) The compaction density ρ2 of the negative electrode sheet satisfies: 1.5 g / cm 3 ≤ρ2≤2g / cm 3 ; (2) The porosity P of the negative electrode sheet satisfies: 0 <P≤50%。 11. An electrical device comprising the secondary battery according to any one of claims 1 to 10.

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