Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, the secondary battery comprises a positive pole piece, the positive pole piece comprises a positive pole active material layer, the single-side coating weight G1 of the positive pole active material layer is greater than or equal to 360 mg / 1540.25 mm < 2 > and less than or equal to 550 mg / 1540.25 mm < 2 >, and the compaction density rho1 of the positive pole piece is greater than or equal to 2.4 g / cm < 3 > and less than or equal to 2.9 g / cm < 3 >; the positive pole piece meets the following conditions: the positive pole piece and the lithium metal sheet are prepared into a button cell, the button cell is subjected to constant-current discharge to 3.2 V at the rate of 1C, and the obtained discharge gram capacity is C1; carrying out constant-current discharge on the button cell to 2V at the rate of 1C to obtain discharge gram capacity C2; wherein r = C1 / C2, and r is more than or equal to 80% and less than or equal to 98%. The secondary battery provided by the invention still has relatively high power performance under the conditions of thick coating and high pressure density.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, as the application scope of secondary batteries represented by lithium-ion batteries has become more and more extensive, secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and power performance. Summary of the invention

[0004] 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 density.

[0005] In order to achieve the above object, the first aspect of 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: 2.4 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 resulting discharge capacity in grams is C1; the button battery is discharged at a constant current of 1C to 2V, and the resulting discharge capacity in grams is C2; wherein, r = C1 / C2, and r satisfies: 80%≤r≤98%.

[0006] 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 satisfies 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 within the above range, that is, the battery is under relatively thick coating and relatively high compression conditions.

[0007] In some embodiments of the present application, the r satisfies: 85%≤r≤95%.

[0008] 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.

[0009] In some embodiments of the present application, at least one of the following conditions is met:

[0010] (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 ;

[0011] (2) The compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm 3 ≤ρ1≤2.9g / cm 3 .

[0012] 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.

[0013] The single-sided coating weight of the positive electrode active material layer is within the above range, which enables the positive electrode plate to be coated relatively thickly; such relatively thick coating of the positive electrode plate is beneficial to improving the capacity performance of the battery.

[0014] 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:

[0015] (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 ;

[0016] (2) The mass proportion ω of the positive electrode active material in the positive electrode active material layer satisfies: 95%≤ω≤98.5%;

[0017] (3) The positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a modified compound thereof.

[0018] The compaction density of the positive electrode active material is within the above range, which can improve the compaction density of the positive electrode plate, so that the positive electrode plate 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.

[0019] In some embodiments of the present application, the lithium-containing phosphate satisfies at least one of the following conditions:

[0020] (1) The lithium-containing phosphate satisfies the molecular formula LiFe 1-x-y Mn x M y PO 4 , 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;

[0021] 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;

[0022] (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.

[0023] 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 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 compression), and the power performance can still be maintained at a relatively high level.

[0024] In some embodiments of the present application, the secondary battery further includes an electrolyte, and the conductivity σ of the electrolyte satisfies: σ≥14 mS / cm, and can be optionally 14 mS / cm≤σ≤21 mS / cm.

[0025] 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.

[0026] In some embodiments of the present application, 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 , optional: 160mg / 1540.25mm 2 ≤G2≤200mg / 1540.25mm 2 .

[0027] When the single-sided coating weight of the negative electrode active material layer is within the above range, it can cooperate with the aforementioned setting of the positive electrode sheet, enabling the battery to achieve the aforementioned relatively thick coating and relatively high compaction density. Under the condition of satisfying the aforementioned r, it promotes the improvement of the battery power performance.

[0028] In some embodiments of the present application, the negative electrode sheet satisfies at least one of the following conditions:

[0029] (1) The compaction density ρ2 of the negative electrode sheet satisfies: 1.5 g / cm 3 ≤ρ2≤2 g / cm 3 , and optionally 1.6 g / cm 3 ≤ρ2≤2 g / cm 3 ;

[0030] (2) The porosity P of the negative electrode sheet satisfies: 0 < P ≤ 50%, and optionally 0 < P ≤ 35%.

[0031] When the compaction density of the negative electrode sheet is within the above range, it is beneficial to further improve the energy density of the battery; when the porosity of the negative electrode sheet is within the above range, it is beneficial to increase the transmission channels of active ions (such as lithium ions), promote the transmission of active ions, and further improve the power performance of the battery.

[0032] The second aspect of the present application provides an electrical device, including the secondary battery of the first aspect of the present application.

[0033] 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.

[0034] The 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

[0035] To better describe and illustrate the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed application, the currently described embodiments or examples, and the currently understood best mode of these applications. Moreover, in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0036] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0037] Figure 2 is Figure 1 the exploded view of the battery cell according to an embodiment of the present application shown in

[0038] Figure 3 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0039] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application.

[0040] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0041] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0042] Description of reference numerals:

[0043] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0044] Below, some embodiments of the secondary battery and the electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are 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.

[0045] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0046] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0048] Reference to "embodiments" herein means 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 the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0049] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean 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 internal logic. If there is no special explanation, all steps of the present application can 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 also include step (c), indicating that step (c) can 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.

[0050] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions 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 the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present 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.

[0051] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0052] At present, with the development of secondary batteries, higher requirements are put forward for their capacity, energy density and power performance. In order to improve the capacity and energy density of the battery, the pole piece is usually thickly coated and high-pressure densely designed. However, thick coating of the pole piece will extend the transmission path of the active ions, while high-pressure densely packed will reduce the transmission channel of the active ions, resulting in greater impedance of solid phase diffusion and deterioration of the power performance of the battery.

[0053] 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 plate under different test conditions, the secondary battery can still have relatively high power performance under thick coating and high pressure density application conditions.

[0054] Secondary battery

[0055] 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: 2.4 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 resulting discharge capacity in grams is C1; the button battery is discharged at a constant current of 1C to 2V, and the resulting discharge capacity in grams is C2; wherein, r = C1 / C2, and r satisfies: 80%≤r≤98%.

[0056] It can be 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.

[0057] It is understood that the preparation process of the button cell can refer to national standards or industry specifications. For example, the positive electrode active material can be prepared into the electrode containing the positive electrode active material layer by combining the positive electrode active material with the binder and the conductive agent commonly used in the industry, and then the button cell can be prepared by using a lithium metal disc as the counter electrode and adding the electrolyte commonly used in the industry.

[0058] As a non-limiting example, a button cell may be prepared as follows:

[0059] 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. Then, a lithium metal disc is used as a counter electrode, and an electrolyte is added to assemble 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, and a fully dried lithium salt LiPF is added. 6 Dissolve in an organic solvent, then add fluoroethylene carbonate (FEC), mix well to obtain an electrolyte solution, in which LiPF 6 The concentration is 1 mol / L, and the mass percentage of FEC in the electrolyte is 6%.

[0060] It can be understood that the above-mentioned discharge capacity C1 can be obtained by testing in the following way: let the prepared button battery stand at 25°C for 30 minutes, charge to 3.75V at a constant current of 0.1C, until the cut-off current is 0.05mA; then let it stand for 10 minutes, discharge to 2V at a constant current of 0.33C, and calibrate the capacity at this time as C0; then let it stand at 25°C for 10 minutes again, charge to 3.75V at a constant current of 0.1×C0, until the cut-off current is 0.05mA; then let it stand for another 10 minutes, discharge to 3.2V at a constant current of C0, and obtain the discharge capacity C1', then C1=C1' / mass of the positive electrode active material in the positive electrode sheet.

[0061] 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.

[0062] Without intending to be limited by any theory, the positive electrode plate and the lithium metal plate are prepared into a button cell, and when the gram capacity ratio r measured by 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 basically all at the nanometer level, and there is no micron-sized large particle size or the number of micron-sized large particles is very small (ratio <0.1%). The nano-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 improving the power performance of the battery, so that the battery can maintain a relatively high power performance under the application conditions where G1 and ρ1 are within the above range, that is, the battery is under relatively thick coating and relatively high compaction application conditions.

[0063] In some embodiments, the r satisfies: 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 under thick coating and high pressure density application conditions can be further improved.

[0064] In some embodiments, the single-sided coating weight G1 of the positive electrode active material layer satisfies: 360 mg / 1540.25 mm 2 ≤G1≤550mg / 1540.25mm 2For 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.

[0065] In some embodiments, 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 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.

[0066] 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 surfaces of the positive electrode plate.

[0067] The single-sided coating weight of the positive electrode active material layer 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 taken, and the thickness of the positive electrode sheets was measured by a micrometer, 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, recorded as m (mg), which is the positive electrode active material layer 1540.25mm 2 Weight on area.

[0068] The single-sided coating weight of the positive electrode active material layer is within the above range, which enables the positive electrode plate to be coated relatively thickly; such relatively thick coating of the positive electrode plate is beneficial to improving the capacity performance of the battery.

[0069] 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.

[0070] 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.

[0071] The compaction density of the positive electrode sheet is well known in the art and can be measured by methods known in the art. For example, the area of ​​the dried positive electrode sheet cut to 1540.25 mm 2 Take 5 pieces of electrode sheets, measure the thickness of each positive electrode sheet with a micrometer, record it as d0cm, scrape off the positive electrode active material layer in the positive electrode sheet with a scraper, weigh the mass of the positive electrode active material layer with a balance, record it as m (mg). Measure the thickness of the positive current collector after removing the positive electrode active material layer with a micrometer, record it as dcm, and calculate the compaction density of the positive electrode active material layer according to the following formula: compaction density = m / [154.025×(d0-d)]. The compaction density ρ1 of the positive electrode sheet is the average compaction density of the positive electrode active material layer in the 5 positive electrode sheets cut as above.

[0072] The compaction density of the positive electrode sheet is within the above range, which enables the positive electrode sheet to achieve relatively high compaction; such relatively high compaction of the positive electrode sheet is beneficial to improving the energy density of the battery.

[0073] 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.

[0074] The SOC power of a secondary battery at 25°C can be measured using the following method:

[0075] The prepared secondary battery was left at rest for 30 min at 25°C, and charged to 3.8 V at a constant current of 0.33C until the cut-off current was 0.05C; then left at rest for 30 min, and 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, and charged to 3.8 V at a constant current of 0.33×C0 until the cut-off current was 0.05×C0; then left at rest for another 30 min, and discharged to 2 V at a constant current of 0.33C, and the capacity at this time was calibrated as C0; ×C0 constant current discharge for 90min, make the secondary battery at 50% SOC, stand for 120min and read the static voltage of 50% SOC as V1, use 4×C0 constant current discharge for 30s, record the voltage at the end of discharge as V2, this step of discharge DCR1 = (V1-V2) / (4×C0), at this time 50% SOC power = ((V1-2) / DCR1)×2; and so on, obtain the power of 20% SOC and 10% SOC respectively.

[0076] 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.

[0077] In some embodiments, the positive electrode active material layer includes a positive electrode active material.

[0078] 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.

[0079] The compaction density of the positive electrode active material is well known in the art and can be measured by methods known in the art. For example, it can be measured by an electronic pressure tester, such as the UTM7305 electronic pressure tester, with reference to GB / T24533-2009 standard. Accurately weigh about 1g of the sample and add a bottom area of ​​1.327cm 2In the mold, a pressure device is used to apply 3 tons of pressure to the sample and keep it at this pressure for 30 seconds before removing the pressure. Then the height of the sample is measured and the compaction density of the material can be obtained by the formula ρ'=m / (1.327×h). In the formula, ρ' represents the compaction density of the material, m represents the mass of the sample, and h represents the height of the sample after 3 tons of pressure is applied and kept at this pressure for 30 seconds before removing the pressure.

[0080] The compaction density of the positive electrode active material is within the above range, which can improve the compaction density of the positive electrode plate, so that the positive electrode plate has a relatively high compaction, thereby improving the energy density of the battery.

[0081] In some embodiments, the mass proportion ω of the positive electrode active material in the positive electrode active material layer satisfies: 95%≤ω≤98.5%. For example, ω can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5% or within a range consisting of any of the above values.

[0082] 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.

[0083] In some embodiments, the positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a modified compound thereof.

[0084] It can be understood that the modified compound of the lithium-containing phosphate with an olivine structure is not limited to a specific type, and can include a modified compound of the lithium-containing phosphate modified by coating, and a modified compound of the lithium-containing phosphate modified by doping, etc. Among them, the types of modified substances for coating modification and doping modification are not limited, and can be selected according to actual needs.

[0085] In some embodiments, the lithium-containing phosphate satisfies the molecular formula LiFe 1-x-y Mn x M y PO 4 , 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.

[0086] 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.

[0087] 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.

[0088] 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 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 compression), and the power performance can still be maintained at a relatively high level.

[0089] In some embodiments, the secondary battery further comprises an electrolyte, and 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 of any of the above values. Optionally, 14 mS / cm ≤ σ ≤ 21 mS / cm.

[0090] The conductivity of the electrolyte is well known in the art and can be measured by 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 keep it at a constant temperature to the temperature to be tested and the standard solution at a constant temperature to 25°C (deviation ±0.1°C); then, test the two standard solutions at 25°C to calibrate the instrument. After the calibration is completed and the electrodes are cleaned, place the test sample electrode vertically into the electrolyte to be tested, start the test using a conductivity meter, and record the test results after the data is stable for more than 10 seconds to obtain the conductivity of the electrolyte.

[0091] 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 the power performance; at the same time, by cooperating with the aforementioned capacity ratio r (85% ≤ r ≤ 95%), the battery can be relatively thickly coated (360mg / 1540.25mm 2 ≤G1≤550mg / 1540.25mm 2 ) and relatively high compaction (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 a relatively high power performance.

[0092] As a specific example, when r is 80% to 98% and σ ≥ 14 mS / cm, at least G1 of 360 mg / 1540.25 mm 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: 0.95×r≤(10%×SOC power) / (50%×SOC power)≤r, r≤(20%×SOC power) / (50%×SOC power)≤1.05×r.

[0093] As a specific example, when r is 85% to 98% and σ ≥ 16 mS / cm, at least G1 of 360 mg / 1540.25 mm 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: 0.95×r≤(10%×SOC power) / (50%×SOC power)≤r, r≤(20%×SOC power) / (50%×SOC power)≤1.05×r.

[0094] 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.

[0095] Optionally, G2 meets: 160mg / 1540.25mm 2 ≤G2≤200mg / 1540.25mm 2 .

[0096] 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 surfaces of the negative electrode plate.

[0097] The single-sided 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 taken, and 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, and 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.

[0098] The single-sided coating weight of the negative electrode active material layer is within the above range, which can cooperate with the above arrangement of the positive electrode sheet to enable the battery to achieve the aforementioned relatively thick coating and relatively high compaction, and promote the improvement of battery power performance under the condition of satisfying the above r. At the same time, the single-sided coating weight of the negative electrode active material layer is within the above range, which is also conducive to further improving the battery capacity performance.

[0099] 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 .

[0100] The compaction density of the negative electrode sheet is well known in the art and can be measured by methods known in the art. For example, the area of ​​the dried negative electrode sheet cut to 1540.25 mm 2 Take 5 electrode sheets, measure the thickness of each negative electrode sheet with a micrometer, record it as d0cm, scrape off the negative electrode active material layer in the negative electrode sheet with a scraper, weigh the mass of the negative electrode active material layer with a balance, record it as m (mg). Measure the thickness of the negative current collector after removing the negative electrode active material layer with a micrometer, record it as dcm, and calculate the compaction density of the negative electrode active material layer according to the following formula: compaction density = m / [154.025×(d0-d)]. The compaction density ρ2 of the negative electrode sheet is the average compaction density of the negative electrode active material layer in the 5 negative electrode sheets cut as above.

[0101] The compaction density of the negative electrode sheet is within the above range, and can also cooperate with the above arrangement of the positive electrode sheet, so that the battery can better achieve the aforementioned relatively thick coating and relatively high compaction, and promote the improvement of battery power performance under the condition of satisfying the above r. At the same time, the compaction density of the negative electrode sheet is within the above range, which is also conducive to further improving the battery energy density.

[0102] 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, P is 0 < P ≤ 35%.

[0103] 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 circular pieces 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.

[0104] 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.

[0105] In addition, the secondary battery and the electrical device of the present application will be described below with appropriate reference to the drawings.

[0106] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging 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.

[0107] Positive electrode sheet

[0108] 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.

[0109] 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 either or both of the two opposite surfaces of the positive electrode current collector.

[0110] In some of the 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.

[0111] In some of the embodiments, the positive electrode active material may include at least one of the olivine-structured lithium-containing phosphates and their respective modified compounds as described above in the present application.

[0112] In some of these embodiments, the positive electrode active material may also include positive electrode active materials for batteries that are well 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), one or more of 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 modified compounds thereof. Non-limiting examples of lithium phosphates containing 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 LiCoO 2 Non-limiting examples of lithium nickel oxides may include LiNiO 2 Non-limiting examples of lithium manganese oxides may include LiMnO 2 、LiMn 2 O 4 etc.; Non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (Also referred to as NCM 333 )、LiNi 0.5 Co0.2 Mn 0.3 O 2 (Also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (Also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.15 Al 0.05 O 2 .

[0113] As the Li content in the positive electrode material changes, how to define the subscript of Li in the general formula:

[0114] For ternary materials:

[0115] Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y , x is 0.2-1.2;

[0116] Li x A a (Ni a Co b Mn c ) 1-d M d O 2-y A y , x+a is 0.2-1.2.

[0117] For lithium manganese iron phosphate materials:

[0118] Li a Mn 1-y B y P 1-z C z O 4-n D n , a is 0-1.1;

[0119] Li a A x Mn 1-y B y P 1-z C z O 4-n D n , a+x is 0-1.1.

[0120] The above definition of x includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2-5V).

[0121] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the enumeration of positive electrode materials in this application, unless otherwise specified, the content of Li 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 content of Li in the positive electrode material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li 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.

[0122] In the list of positive electrode materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0123] In some embodiments, the positive electrode active material may also include at least one of the following materials: one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. 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.

[0124] 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 include Na x MO 2 , where M may include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0125] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO 4 ) 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 (YO 4 ) n- valence state.

[0126] The polyanionic compound can also be a compound having sodium ions, transition metal ions, tetrahedral (YO 4 ) n- A class of compounds of 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 (YO 4 ) n- valence state; the halogen can be one or more of F, Cl and Br.

[0127] The polyanionic compound can also be a compound having sodium ions, tetrahedral (YO 4 ) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO 4 ) 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; m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0128] The polyanionic compound may include NaFePO 4 、Na 3 V 2 (PO 4 ) 3 (Sodium vanadium phosphate, referred to as NVP), Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ), NaM'PO 4 F and Na 3 (VO y ) 2 (PO4 ) 2 F 3-2y (0≤y≤1) or more. Among them, NaM'PO 4 M' in F may include one or more of V, Fe, Mn and Ni.

[0129] 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 Me b 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.

[0130] In some of these embodiments, the positive electrode active material layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0131] 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.

[0132] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: 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 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 collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode 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 25000mPa·s. When the positive electrode slurry is coated, the coating unit surface density on a dry weight basis (excluding the solvent) can be 15 to 35mg / cm 2The 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 .

[0133] Negative electrode

[0134] 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.

[0135] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0136] In some of the 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.

[0137] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries 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. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, 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.

[0138] 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).

[0139] 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.

[0140] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0141] In some of the 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 collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode 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 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75 to 220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0142] Electrolytes

[0143] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0144] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0145] In some embodiments, the electrolyte salt may include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ) lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO 2 F 2), one or more of lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0146] 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, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0147] In some embodiments, the electrolyte may further include additives, such as 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, additives that improve battery high or low temperature performance, etc.

[0148] 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.

[0149] Isolation film

[0150] 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 stability and mechanical stability can be selected.

[0151] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0152] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may be 12 to 20 μm.

[0153] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0154] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0155] 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 package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0156] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0157] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0158] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0159] In some of these embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate 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 form 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 infiltrated 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.

[0160] The secondary battery may be a battery module 4 or a battery pack 1 .

[0161] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0162] Figure 3 4 is an example of a battery module. Figure 3In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0163] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0164] In some of the 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 a suitable number according to the application and capacity of the battery pack.

[0165] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0166] In addition, the present application also provides an electrical device, which includes a secondary battery provided by 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 may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0167] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0168] Figure 6 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0169] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0170] Example

[0171] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0172] Example 1

[0173] (1) Preparation of positive electrode sheet

[0174] The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a weight ratio of 97:2:1, and then the solvent N-methylpyrrolidone (NMP) is added to adjust the viscosity, and the positive electrode slurry is prepared after stirring evenly; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried and cold pressed to obtain the positive electrode sheet. Among them, the single-sided coating weight of the positive electrode sheet is 420mg / 1540.25mm 2 , compacted density is 2.55g / cm 3 .

[0175] (2) Preparation of negative electrode sheet

[0176] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber and the thickener sodium carboxymethyl cellulose were mixed in a weight ratio of 96:1:2:1, and then the solvent deionized water was added and stirred evenly to obtain 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. Among them, the single-sided coating weight of the negative electrode sheet is 190mg / 1540.25mm 2 , compacted density is 1.6g / cm 3 , the porosity is 30%.

[0177] (3) Isolation film

[0178] A polyethylene (PE) film coated with nano-aluminum oxide with a thickness of 12 μm was used as the separator.

[0179] (4) Preparation of electrolyte

[0180] In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a mass ratio of 40:30:30 to obtain an organic solvent; 15% by mass of lithium hexafluorophosphate (LiPF 6 ) is lithium salt, which is stirred thoroughly until it is completely dissolved. After returning to room temperature, 3% vinylene carbonate and other additives are added, and the electrolyte is obtained after being fully mixed.

[0181] (5) Preparation of batteries

[0182] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain a wound electrode assembly; the electrode assembly is added to the outer packaging square aluminum shell, and the electrolyte is injected after drying, and the secondary battery is obtained through the processes of packaging, standing, formation, aging, secondary packaging, and capacity. The liquid retention coefficient of the secondary battery is 3.0g / Ah.

[0183] Examples 2 to 26 and Comparative Examples 1 to 4

[0184] The preparation of the electrode and the battery is similar to that in Example 1, except that the relevant parameters in the preparation process are adjusted, as shown in Table 1 below.

[0185] The relevant parameters of the pole pieces of the above-mentioned embodiments 1 to 26 and comparative examples 1 to 4 are shown in the following Table 1.

[0186] Table 1

[0187]

[0188] In addition, the batteries obtained in the above 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.

[0189] Test Section

[0190] (1) Power performance test

[0191] The prepared battery was left at 25°C for 30 min, charged to 3.8 V at 0.33C constant current until the cut-off current was 0.05C; then left at 30 min, discharged to 2 V at 0.33C constant current, and the capacity at this time was calibrated as C0; then left at 25°C for another 30 min, charged to 3.8 V at 0.33×C0 constant current until the cut-off current was 0.05×C0; then left at 30 min again, and discharged to 2 V at 0.33C constant current, and the capacity at this time was calibrated as C0; C0 constant current discharge for 90min, make the secondary battery at 50% SOC, stand for 120min, read the static voltage of 50% SOC as V1, use 4×C0 constant current discharge for 30s, record the voltage at the end of discharge as V2, this step of discharge DCR1 = (V1-V2) / (4×C0), at this time 50% SOC power = ((V1-2) / DCR1)×2; and so on, get the power of 20% SOC and 10% SOC respectively.

[0192] Table 2

[0193]

[0194] 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 the present 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 the present application).

[0195] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0196] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that: The positive electrode sheet includes 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 sheet satisfies the following: when the positive electrode sheet and a lithium metal sheet are fabricated into a button cell and the button cell is discharged at a constant current rate of 1C to 3.2V, the discharge capacity in grams obtained is C1; when the button cell is discharged at a constant current rate of 1C to 2V, the discharge capacity in grams obtained is C2; wherein, r = C1 / C2, and r satisfies: 80% ≤ r ≤ 98%.

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

3. The secondary battery according to claim 1, characterized in that: It satisfies 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, characterized in that: The SOC power of the secondary battery at 25°C satisfies: 0.95×r ≤ (10%×SOC power) / (50%×SOC power) ≤ r, and r ≤ (20%×SOC power) / (50%×SOC power) ≤ 1.05×r.

5. The secondary battery according to any one of claims 1 to 3, characterized in that: 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 ratio 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 olivine-structured lithium-containing phosphates and their modified compounds.

6. The secondary battery according to claim 5, characterized in that: 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; 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; (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 manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: It further includes an electrolyte, and the conductivity σ of the electrolyte satisfies: σ ≥ 14 mS / cm, and optionally 14 mS / cm ≤ σ ≤ 21 mS / cm.

8. The secondary battery according to any one of claims 1 to 6, characterized in that: 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 , optional: 160mg / 1540.25mm 2 ≤G2≤200mg / 1540.25mm 2 .

9. The secondary battery according to claim 8, characterized in that: 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 , optional 1.6g / cm 3 ≤ρ2≤2g / cm 3 ; (2) The porosity P of the negative electrode sheet satisfies: 0 < P ≤ 50%, and optionally 0 < P ≤ 35%.

10. An electrical device, characterized in that: It includes the secondary battery according to any one of claims 1-9.

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