Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. According to the secondary battery provided by the invention, the lithium supplement agent is introduced into the positive electrode active material layer and the negative electrode binder containing the alkali metal ions is selected; the non-Faraday capacitance of the positive pole piece, the mass percentage of alkali metal ions in the negative pole binder, the particle dispersity of the lithium supplement agent and the corresponding particle size when the accumulative volume percentage of the lithium supplement agent reaches 99% are reasonably controlled, so that the secondary battery meets the specific relational expression: 100 * Cdl * (A + 0.5) / N * (Dv99-7) is greater than or equal to 0.3; therefore, the rate capability and the cycle performance of the secondary battery can be effectively improved, and the lithium precipitation risk of the obtained secondary battery is low, namely, the safety performance is excellent.

Description

Technical Field

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

[0002] Under the current background of global energy transformation and low-carbon economy, the development of new energy technology has increasingly become the focus of national strategy and scientific and technological innovation. Among them, lithium-ion batteries have shown great application potential in the field of new energy, especially in electric vehicles, large-scale energy storage systems and portable electronic devices due to their high energy density, long life and good environmental compatibility.

[0003] In order to further improve the cycle life of lithium-ion batteries, the existing technology usually chooses to add lithium supplements to the positive electrode active material layer. However, how to avoid the defects of the lithium supplement itself and when compounding with other components while introducing the lithium supplement to achieve excellent cycle performance of secondary batteries remains to be studied. Summary of the invention

[0004] The purpose of the present application is to solve the problem in the prior art that the rate performance and cycle performance of secondary batteries cannot be improved simultaneously by introducing lithium supplements, and to provide a secondary battery and an electrical device with excellent rate performance, excellent cycle performance and high safety.

[0005] To achieve the above-mentioned object, in a first aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the positive electrode active material layer comprises a positive electrode active material and a lithium supplement, the negative electrode active material layer comprises a negative electrode active material and a negative electrode binder, and the negative electrode binder comprises alkali metal ions;

[0006] The secondary battery satisfies: Y≥0.3;

[0007] Wherein, Y = 100 × Cdl × (A + 0.5) / N × (Dv99-7);

[0008] Cdl nF is the non-Faraday capacitance of the positive electrode;

[0009] A% is the mass percentage of alkali metal ions in the negative electrode binder;

[0010] N is the particle dispersion of the lithium supplement;

[0011] Dv99μm is the particle size corresponding to when the cumulative volume percentage of the lithium supplement reaches 99%.

[0012] As an embodiment of the present application, the mass percentage A% of alkali metal ions in the negative electrode binder is 0.11% to 2%.

[0013] As an implementation scheme of the present application, the non-Faraday capacitance Cdl nF of the positive electrode plate is 0.4nF to 1.6nF.

[0014] As an embodiment of the present application, the particle dispersion degree of the lithium supplement agent is 11-16.

[0015] As an implementation scheme of the present application, when the cumulative volume percentage of the lithium supplement reaches 99%, the corresponding particle size Dv99μm is 10μm to 30μm.

[0016] As an embodiment of the present application, the mass percentage of the negative electrode binder in the negative electrode active material layer is 1.5% to 3%.

[0017] As an embodiment of the present application, the negative electrode binder includes a first negative electrode binder, and the first negative electrode binder includes at least one of lithium polyacrylate, lithium alginate, and lithium carboxymethyl cellulose.

[0018] As an embodiment of the present application, the weight average molecular weight of the first negative electrode binder is 10,000 to 3,000,000.

[0019] As an embodiment of the present application, the electrolyte includes an additive, and the additive includes lithium bismalonate borate or a derivative thereof, and the mass percentage of the lithium bismalonate borate or a derivative thereof in the electrolyte is 0.5% to 2%.

[0020] As an embodiment of the present application, the mass percentage of the lithium supplement agent in the positive electrode active material layer is 0.5% to 2%.

[0021] As an embodiment of the present application, the lithium supplement includes at least one of Li5FeO5, Li6CoO4, and Li2NiO2.

[0022] In a second aspect of the present application, an electrical device is provided, comprising the secondary battery described above.

[0023] Compared with the prior art, the beneficial effects of this application are:

[0024] In the secondary battery provided by the present application, by introducing a lithium supplement agent into the positive electrode active material layer and selecting a negative electrode binder containing alkali metal ions, and reasonably controlling the non-Faraday capacitance of the positive electrode plate, the mass percentage of alkali metal ions in the negative electrode binder, the particle dispersion of the lithium supplement agent, and the particle size corresponding to when the cumulative volume percentage of the lithium supplement agent reaches 99%, the secondary battery satisfies a specific relationship: 100×Cdl×(A+0.5) / N×(Dv99-7)≥0.3, thereby being able to comprehensively improve the comprehensive performance of the secondary battery and achieve excellent cycle performance, rate performance and safety performance. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0026] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0028] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0029] In one embodiment of the present application, the present application proposes a secondary battery, including a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet includes a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector, the negative electrode sheet includes a negative electrode collector and a negative electrode active material layer disposed on at least one surface of the negative electrode collector, the positive electrode active material layer includes a positive electrode active material and a lithium supplement, the negative electrode active material layer includes a negative electrode active material and a negative electrode binder, and the negative electrode binder includes alkali metal ions;

[0030] The secondary battery satisfies: Y≥0.3;

[0031] Wherein, Y = 100 × Cdl × (A + 0.5) / N × (Dv99-7);

[0032] Cdl nF is the non-Faraday capacitance of the positive electrode;

[0033] A% is the mass percentage of alkali metal ions in the negative electrode binder;

[0034] N is the particle dispersion of the lithium supplement;

[0035] Dv99μm is the particle size corresponding to when the cumulative volume percentage of the lithium supplement reaches 99%.

[0036] The research of this application found that the non-Faraday capacitance of the positive electrode plate, the mass percentage of alkali metal ions in the negative electrode binder, the particle dispersion of the lithium supplement, and the particle size corresponding to when the cumulative volume percentage of the lithium supplement reaches 99% will have a significant impact on the comprehensive performance of the secondary battery. This application can comprehensively improve the comprehensive performance of the secondary battery and achieve excellent cycle performance, rate performance and safety performance by making the secondary battery satisfy a specific relationship: 100×Cdl×(A+0.5) / N×(Dv99-7)≥0.3.

[0037] Specifically, the present application controls the secondary battery to satisfy a specific relationship. On the one hand, it can increase the surface area and effective tap density of the electrode, and can optimize the electronic / ionic conductive network of the secondary battery, so that the secondary battery can have a higher density while avoiding the overvoltage phenomenon caused by excessive density, thereby improving the rate performance of the secondary battery. On the second hand, it can reduce the mechanical stress experienced by the electrode during hot pressing, reduce the reaction area between the electrode and the electrolyte, effectively improve the electrode's liquid retention performance and the infiltration effect on the electrolyte, and improve the rate performance and cycle performance of the secondary battery. On the third hand, during the formation stage of the secondary battery, the lithium supplement can release lithium ions more fully, thereby reducing the gas production of the secondary battery during the cycle, reducing the lithium precipitation of the negative electrode of the secondary battery, and then improving the cycle performance and safety performance of the secondary battery.

[0038] Exemplarily, the secondary battery satisfies: Y ≥ 0.3, wherein Y can be any point value or any two point range values ​​of Y ≥ 0.3, such as 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 4.0, 6.0, 8.0, 10.0 or any two range values. In one embodiment, the secondary battery satisfies: 0.30 ≤ Y ≤ 3.21.

[0039] In one embodiment, the secondary battery satisfies: 0.53≤Y≤1.38. For example, Y can be 0.53, 0.55, 0.58, 0.60, 0.63, 0.65, 0.68, 0.70, 0.72, 0.75, 0.78, 0.80, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, 0.98, 1.0, 1.1, 1.2, 1.3, 1.32, 1.34, 1.36, 1.38, or any two of the range values. The present application has found that when the secondary battery is further selected to meet the above range, the comprehensive performance of the secondary battery obtained is better.

[0040] In one embodiment, the mass percentage A of alkali metal ions in the negative electrode binder is 0.11% to 2%.

[0041] It should be noted that the test method for the mass percentage of alkali metal ions in the negative electrode binder is: after the secondary battery is fully discharged, the negative electrode sheet is peeled off, and then it is added into an organic solvent (tetrahydrofuran) to dissolve, followed by filtering, collecting the filtrate and concentrating to obtain the negative electrode binder; taking a certain mass m1 of the negative electrode binder sample, and using the inductively coupled plasma emission spectroscopy (ICP) method to quantitatively test the mass m2 of the alkali metal element, then the mass percentage of the alkali metal element in the negative electrode binder is A=m2 / m1×100%.

[0042] Exemplarily, the mass percentage A% of alkali metal ions in the negative electrode binder may be any point value between 0.11% and 2% or any two point range values, for example, A may be 0.11%, 0.13%, 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% or any two of the range values.

[0043] The present application has found that controlling the content of alkali metal ions in the negative electrode binder within a specific range has a significant effect on achieving an excellent comprehensive effect of the secondary battery; specifically, on the first hand, the negative electrode binder containing alkali metal ions can combine the negative electrode active material, the conductive agent and the negative electrode current collector to form a stable electrode sheet structure, and the stability of the structure will directly affect the mechanical strength and energy density of the electrode sheet; on the second hand, the alkali metal ions in the negative electrode binder can also serve as an alkali metal ion source, wherein the alkali metal ions can be dissociated in the electrolyte, providing active ions for the secondary battery, and helping to improve the rate performance of the secondary battery; on the third hand, the alkali metal ions in the negative electrode binder can promote the electrolyte to infiltrate the negative electrode sheet and improve the liquid retention capacity of the negative electrode sheet through solvation interaction with the electrolyte, thereby improving the cycle performance of the secondary battery.

[0044] In one embodiment, the mass percentage A% of alkali metal ions in the negative electrode binder is 0.9% to 1.5%. For example, A% can be a range of one or any two of 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%. The present application has found that when the mass percentage A of alkali metal ions in the negative electrode binder is further selected to be 0.9% to 1.5%, the comprehensive performance of the secondary battery obtained is better.

[0045] In one embodiment, the non-Faraday capacitance Cdl nF of the positive electrode plate is 0.4 nF to 1.6 nF.

[0046] It should be noted that the test method of the non-Faraday capacitance Cdl of the positive electrode plate includes the following steps:

[0047] S1: Clean the surface of the positive electrode with electrolyte to remove surface impurities, dry, cut into discs, transfer to a vacuum oven after weighing, dry at 90-105°C for 6h, and assemble symmetrical batteries in a glove box;

[0048] S2: The assembled battery is tested by cyclic voltammetry (CV) to obtain the non-Faraday potential interval of the corresponding battery. The test voltage range is 0.05-3.0V, and the scan rate is 0.1-1mV / s;

[0049] S3: Select the flat potential interval in the second step to perform cyclic voltammetry (CV) test and collect voltage-current curves, wherein the potential range is 2.5-2.7 V and the scan rate is 1-20 mV / s;

[0050] S4: Obtain the median U of the potential interval of five specific scan rates V1 in the third step (the specific scan rate can be 0.1mV / s, 1mV / s, 5mV / s, 10mV / s and 20mV / s, etc.), and obtain the corresponding current value, obtain a scan rate-current scatter plot, and fit a linear function. The slope of the linear function is the non-Faraday capacitance Cdl of the positive electrode plate.

[0051] Non-Faradaic capacitance refers to the ability of an electrode material to store charge in an electrolyte by physical adsorption of charge or intercalation of ions. This application study found that in a secondary battery, the size of the non-Faradaic capacitance will affect the instantaneous charging rate and instantaneous power output of the secondary battery. By selecting the non-Faradaic capacitance of the positive electrode to be 0.4nF to 1.6nF, the cycle performance and rate performance of the secondary battery can be effectively improved.

[0052] Exemplarily, the Cdl nF may be any point value or any two point range values ​​between 0.4nF and 1.6nF. For example, Cdl nF may be one or any two range values ​​of 0.4nF, 0.5nF, 0.6nF, 0.7nF, 0.8nF, 0.9nF, 1.0nF, 1.1nF, 1.2nF, 1.3nF, 1.4nF, 1.5nF, and 1.6nF.

[0053] In one embodiment, the non-Faraday capacitance Cdl nF of the positive electrode plate is 0.9nF to 1.4nF. For example, Cdl can be 0.9nF, 0.93nF, 0.95nF, 0.98nF, 1nF, 1.03nF, 1.05nF, 1.08nF, 1.1nF, 1.13nF, 1.15nF, 1.18nF, 1.2nF, 1.23nF, 1.25nF, 1.28nF, 1.3nF, 1.33nF, 1.35nF, 1.38nF, 1.4nF, or any two of them. The present application has found that when the non-Faraday capacitance Cdl nF of the positive electrode plate is further selected to be 0.9nF to 1.4nF, the rate performance and cycle performance of the secondary battery obtained are better.

[0054] In one embodiment, the particle dispersion N of the lithium supplement agent is 11-16.

[0055] It should be noted that the particle dispersion N of the lithium supplement agent is obtained by testing with a laser particle size analyzer; the dispersion of the lithium supplement agent in the electrode is separated by the density difference between the decomposition products of the lithium supplement agent and other components, and the dispersion of the lithium supplement agent is obtained by testing the dispersion of the decomposition products of the lithium supplement agent.

[0056] The dispersion of lithium supplement agent particles refers to the spatial distribution between lithium supplement agent particles. The more concentrated the particle size, the higher the dispersion. The research in this application found that the dispersion of lithium supplement agent particles has an important influence on the performance of secondary batteries. The lithium supplement agent within the appropriate particle dispersion range can not only effectively reduce the internal resistance of the secondary battery and improve the rate performance of the secondary battery, but also effectively reduce the gas production of the secondary battery and improve the cycle performance and safety performance of the secondary battery.

[0057] Exemplarily, the particle dispersion N of the lithium supplement may be any point value or any two point range values ​​between 11 and 16, for example, N may be one of 11, 12, 13, 14, 15, 16 or any two range values.

[0058] In one embodiment, the particle dispersion N of the lithium supplement agent is 14 to 15. For example, N can be a range of one or any two of 14.1, 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.8, 14.9, and 15. The present application has found that when the particle dispersion N of the lithium supplement agent is further selected to be 14 to 15, the cycle performance, safety performance, and rate performance of the secondary battery obtained are all better.

[0059] In one embodiment, when the cumulative volume percentage of the lithium supplement reaches 99%, the corresponding particle size Dv99 is 10 μm to 30 μm.

[0060] It should be noted that the Dv99 of the lithium supplement is obtained by testing with a dynamic image particle analyzer.

[0061] Exemplarily, the particle size Dv99 corresponding to the cumulative volume percentage of the lithium supplement reaching 99% can be any point value or any two point range values ​​between 10μm and 30μm, for example, it can be one of 10μm, 13μm, 15μm, 18μm, 20μm, 23μm, 25μm, 28μm, 30μm or any two range values.

[0062] The present application study found that a lithium supplementer within a suitable Dv99 range can provide a larger surface area for contact with the electrolyte, improve the charge and discharge characteristics of the lithium supplementer and the release of lithium ions, thereby improving the energy density, and can also avoid the recrystallization phenomenon caused by the lithium supplementer particles being too small, thereby improving the cycle performance and safety performance of the secondary battery.

[0063] In the present application, the lithium supplement with a specific Dv99 range and a specific particle dispersion range can be obtained by pulverizing and then screening.

[0064] In one embodiment, the Dv99μm of the lithium supplement is 14μm to 25μm. For example, Dv99μm can be a range of one or any two of 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, and 25μm. The present application has found that when the Dv99 of the lithium supplement is further selected to be 14μm to 25μm, the comprehensive performance of the secondary battery obtained is better.

[0065] In one embodiment, the mass percentage of the negative electrode binder in the negative electrode active material layer is 1.5% to 3%.

[0066] It should be noted that the testing method for the mass percentage of the negative electrode binder in the negative electrode active material layer is: scrape a certain mass m3 of the negative electrode material layer from the negative electrode plate of the secondary battery, and test the mass of the alkali metal element therein by the ICP method as m4, and the mass percentage of the alkali metal element in the binder is A%. Based on the mass of the electrode active material layer, the mass percentage of the binder containing alkali metal ions = m4 / (A%) / m3.

[0067] Exemplarily, the mass percentage of the negative electrode binder in the negative electrode active material layer may be any point value or any two point range values ​​between 1.5% and 3%, such as one of 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3% or any two range values.

[0068] The present application study found that the mass percentage of the negative electrode binder in the negative electrode active material layer will not only affect the solvation interaction between the negative electrode binder and the electrolyte, thereby affecting the wetting effect of the electrolyte on the negative electrode sheet and the liquid retention capacity of the negative electrode sheet, but also affect the energy density of the negative electrode sheet. When the mass percentage of the negative electrode binder in the negative electrode active material layer is further selected to be 1.5% to 3%, the rate performance, cycle performance and safety performance of the secondary battery obtained are better.

[0069] In one embodiment, the negative electrode binder includes a first negative electrode binder and a second negative electrode binder.

[0070] In one embodiment, the first negative electrode binder includes a binder containing lithium or a binder containing sodium.

[0071] In one embodiment, the first negative electrode binder includes at least one of lithium polyacrylate, lithium alginate, and lithium carboxymethyl cellulose. The present application has found that when the first negative electrode binder is further of the above substances, the rate performance, cycle performance, and safety performance of the secondary battery obtained are better.

[0072] In one embodiment, the weight average molecular weight of the first negative electrode binder is 10,000 to 3,000,000.

[0073] It should be noted that the weight average molecular weight of the first negative electrode binder is obtained through gel permeation chromatography testing.

[0074] Exemplarily, the weight-average molecular weight of the first negative electrode binder may be any point value or any two point range values ​​between 10,000 and 3,000,000, such as 10,000, 100,000, 200,000, 400,000, 600,000, 800,000, 1,000,000, 1,200,000, 1,400,000, 1,600,000, 1,800,000, 2,000,000, 2,200,000, 2,400,000, 2,600,000, 2,800,000, and 3,000,000, or any two range values.

[0075] The present application study found that the weight-average molecular weight of the first negative electrode binder affects the bonding performance of the negative electrode active material, the conductive agent and the negative electrode current collector, thereby affecting the mechanical properties and energy density of the negative electrode plate. At the same time, it also affects the interaction between the negative electrode plate and the electrolyte, that is, it affects the liquid retention and wetting ability of the negative electrode plate to the electrolyte. When the weight-average molecular weight of the first negative electrode binder is further selected to be 10,000 to 3 million, the comprehensive performance of the secondary battery obtained is better.

[0076] In one embodiment, the weight average molecular weight of the first negative electrode binder is 1 million to 2 million. For example, it can be 1 million, 1.1 million, 1.2 million, 1.3 million, 1.4 million, 1.5 million, 1.6 million, 1.7 million, 1.8 million, 1.9 million, 2 million, or any two of them. The present application found that when the weight average molecular weight of the first negative electrode binder is further selected to be 1 million to 2 million, the rate performance and cycle performance of the secondary battery obtained are better.

[0077] In the present application, the first negative electrode binder can be purchased from conventional markets or made by oneself, wherein the homemade preparation method comprises: first, preparing the polymerization reaction raw materials acrylic acid (AA), alkali metal source lithium carbonate (Li2CO3), and initiator potassium persulfate (K2S2O8). AA and the lithium source are mixed in deionized water in a molar ratio, and a lithium acrylic acid (AA-Li) solution precursor is obtained by stirring evenly. The solution is heated to 80-90°C, and potassium persulfate is added to initiate the polymerization reaction, and the reaction time is usually 4-6 hours. After the reaction, the solution is cooled and washed with ethanol precipitation to remove unreacted monomers and by-products. The product is dried to obtain pure PAA-Li powder; by controlling the parameters in the preparation process, the polymerization degree of the first negative electrode binder can be changed to achieve a change in the weight average molecular weight of the first negative electrode binder; at the same time, by controlling the parameters in the preparation process, the content of alkali metal ions in the first negative electrode binder can also be changed, thereby achieving a change in the mass percentage of alkali metal ions in the negative electrode binder.

[0078] In one embodiment, the second negative electrode binder includes styrene-butadiene rubber (SBR).

[0079] In one embodiment, the electrolyte includes an additive, and the additive includes a boron-containing lithium salt. In one embodiment, the boron-containing lithium salt includes at least one of lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium bisethyl malonate borate (LiBMB-A), lithium bis-n-butyl malonate borate (LiBMB-B), lithium bis-n-octyl malonate borate (LiBMB-C), and lithium bis-1-methylpropyl malonate borate (LiBMB-D).

[0080] In one embodiment, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the positive electrode active material layer comprises a positive electrode active material and a lithium supplement, the negative electrode active material layer comprises a negative electrode active material and a negative electrode binder, the negative electrode binder comprises an alkali metal ion, the electrolyte comprises an additive, the additive comprises lithium bismalonate borate or a derivative thereof, and the mass percentage of the lithium bismalonate borate or a derivative thereof in the electrolyte is 0.5% to 2%;

[0081] The secondary battery satisfies: Y≥0.3;

[0082] Wherein, Y = 100 × Cdl × (A + 0.5) / N × (Dv99-7);

[0083] Cdl nF is the non-Faraday capacitance of the positive electrode;

[0084] A% is the mass percentage of alkali metal ions in the negative electrode binder;

[0085] N is the particle dispersion of the lithium supplement;

[0086] Dv99μm is the particle size corresponding to when the cumulative volume percentage of the lithium supplement reaches 99%.

[0087] It should be noted that the mass percentage of the lithium bis(malonate borate) or its derivatives in the electrolyte is obtained through chromatographic testing.

[0088] Exemplarily, the mass percentage of the lithium bis(malonate borate) or its derivatives in the electrolyte can be any point value between 0.5% and 2% or any two point range values, such as 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2% or any two range values.

[0089] Exemplarily, the lithium bismalonate borate derivative includes any one of lithium bisethylmalonate borate (LiBMB-A), lithium bis-n-butylmalonate borate (LiBMB-B), lithium bis-n-octylmalonate borate (LiBMB-C), and lithium bis-1-methylpropylmalonate borate (LiBMB-D).

[0090] The present application study found that when lithium bismalonate borate or its derivatives are included as additives in the electrolyte, lithium bismalonate borate or its derivatives have higher molecular weight and excellent stability compared to lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bisoxalate borate, etc. At the same time, it synergizes with the first negative electrode binder and has a more excellent solvation interaction, thereby forming ion clusters with a weak solvation sheath, effectively reducing the energy barrier when active ions are embedded in and out of the negative electrode, and further improving the rate performance and cycle performance of the secondary battery.

[0091] In one embodiment, the mass percentage of the lithium supplement in the positive electrode active material layer is 0.5% to 2%.

[0092] It should be noted that the mass percentage of the lithium supplement in the positive electrode active material layer is obtained through inductively coupled plasma (ICP) testing.

[0093] Exemplarily, the mass percentage of the lithium supplement in the positive electrode active material layer may be any point value or any two point range values ​​between 0.5% and 2%, such as one of 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2% or any two range values.

[0094] The present application study found that the mass percentage of the lithium replenisher in the positive electrode active material layer not only affects the amount of active ions it provides, but also affects the liquid absorption capacity of the positive electrode plate, thereby affecting the rate performance and cycle performance. When the mass percentage of the lithium replenisher in the positive electrode active material layer is further selected to be 0.5% to 2%, the rate performance and safety performance of the secondary battery obtained are better.

[0095] In one embodiment, the lithium supplement includes at least one of Li5FeO5, Li6CoO4, and Li2NiO2.

[0096] In one embodiment, the positive electrode active material includes a lithium-containing phosphate having an olivine structure. In one embodiment, the lithium-containing phosphate includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0097] In one embodiment, the negative electrode active material includes at least one of graphite, silicon, silicon oxide, silicon-carbon composite material, and hard carbon. In one embodiment, the graphite includes artificial graphite and / or natural graphite.

[0098] In one embodiment, the positive electrode current collector may be made of a material with good electrical conductivity and mechanical strength to perform the functions of electrical conduction and current collection. In one embodiment, the positive electrode current collector may be made of a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector is made of aluminum foil or carbon-coated aluminum foil.

[0099] In one embodiment, the negative electrode current collector may be made of a material with good electrical conductivity and mechanical strength to perform the functions of conducting electricity and collecting current. In one embodiment, the negative electrode current collector may be made of a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector is made of copper foil.

[0100] In one embodiment, the electrolyte further comprises a lithium salt and an organic solvent. The present application has no limitation on the organic solvent and the lithium salt in the electrolyte, and any known organic solvent and lithium salt can be used.

[0101] Exemplarily, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl acetate, and ethyl propionate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0102] In one embodiment, the diaphragm includes at least one of a polyethylene film, a polypropylene film, a non-woven fabric film, a polyimide film, and a ceramic-coated diaphragm.

[0103] In one embodiment of the present application, the present application proposes an electrical device, and the electrical device includes the secondary battery described in the present application.

[0104] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0105] Example 1

[0106] The present invention provides a secondary battery, wherein a method for preparing the secondary battery comprises the following steps:

[0107] (1) Preparation of positive electrode sheet

[0108] Lithium iron phosphate, lithium supplement Li5FeO5 (particle dispersion N is 14, Dv99 is 20μm), conductive carbon black (SP), and PVDF are mixed in a weight ratio of 94:3:0.9:2.1, then added into NMP for thorough mixing, and after mixing evenly, coated on both sides on a (12+1+1)μm carbon-coated aluminum foil, and then the electrode is dried, rolled, slit, and cut to obtain a positive electrode;

[0109] Among them, the non-Faraday capacitance of the positive electrode is 0.9nF;

[0110] (2) Preparation of negative electrode sheet

[0111] Artificial graphite, conductive carbon black (SP), a first binder (lithium polyacrylate) and a second binder (styrene-butadiene rubber) are mixed evenly in a mass ratio of 96.9:1:1.1:1, and then water is added to the mixture in batches and continued to be fully mixed and stirred to prepare a negative electrode slurry, and then the homogeneous negative electrode slurry is evenly coated on both sides of a 6μm copper foil, and after drying, rolling, slitting and cutting, a negative electrode sheet is obtained;

[0112] (3) Preparation of electrolyte

[0113] Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate solvents are uniformly mixed in a mass ratio of 1:1:1, and then 0.9 mol / L lithium hexafluorophosphate and an appropriate amount of additives are added, wherein the additives include lithium bismalonate borate, and the mass of the lithium bismalonate borate accounts for 1wt% of the total mass of the electrolyte;

[0114] (4) Preparation of secondary batteries

[0115] The prepared positive electrode sheet, negative electrode sheet, separator (polypropylene, thickness of 14 μm) and other battery components are assembled, and a secondary battery is obtained through processes such as shaping, baking, packaging, liquid injection, formation, and capacity division.

[0116] Embodiments 2 to 4

[0117] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the non-Faraday capacitance of the positive electrode sheet is changed by adjusting the content ratio of the positive electrode active material in the positive electrode sheet, the particle size distribution of the positive electrode active material, the powder compaction density of the positive electrode material, and the porosity and compaction density of the positive electrode sheet, as well as the positive electrode formulation (such as the conductive agent content, the positive electrode active material content).

[0118] Embodiments 5 to 7

[0119] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of alkali metal ions in the negative electrode binder is changed by adjusting the lithium content in the negative electrode binder.

[0120] Embodiments 8 to 10

[0121] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the dispersion of the lithium supplement agent is changed by adjusting the preparation process of the lithium supplement agent.

[0122] Examples 11 to 14

[0123] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the change of the lithium supplement Dv99 is achieved by adjusting the preparation process of the lithium supplement.

[0124] Embodiments 15-16

[0125] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the negative electrode binder in the negative electrode active material layer is changed by adjusting the addition amount of the first negative electrode binder.

[0126] Examples 17 to 20

[0127] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the weight average molecular weight of the first negative electrode binder is changed by adjusting the degree of polymerization of the first negative electrode binder.

[0128] Embodiment 21

[0129] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the type of the first negative electrode binder is adjusted.

[0130] Embodiments 22-23

[0131] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the additive in the electrolyte is changed by adjusting the amount of the additive added in the electrolyte.

[0132] Embodiment 24

[0133] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the type of additive is adjusted.

[0134] Embodiments 25-26

[0135] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the lithium supplement agent in the positive electrode active material layer is changed by adjusting the addition amount of the lithium supplement agent.

[0136] Embodiment 27

[0137] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the type of lithium supplement agent is adjusted.

[0138] Comparative Example 1

[0139] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that the non-Faraday capacitance of the positive electrode sheet, the particle dispersion and Dv99 of the lithium supplement agent, and the mass percentage of alkali metal ions in the negative electrode binder are changed by adjusting the content ratio of the positive electrode active material in the positive electrode sheet, the particle size distribution of the positive electrode active material, the powder compaction density of the positive electrode material, and the porosity and compaction density of the positive electrode sheet, as well as the positive electrode formula (such as the conductive agent content, the positive electrode active material content), the type of the negative electrode binder, and the preparation process of the lithium supplement agent.

[0140] Comparative Example 2

[0141] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that the first negative electrode binder containing alkali metal ions is not added, and the non-Faraday capacitance of the positive electrode sheet is changed by adjusting the content ratio of the positive electrode active material in the positive electrode sheet, the particle size distribution of the positive electrode active material, the powder compaction density of the positive electrode material, the porosity and compaction density of the positive electrode sheet, and the positive electrode formulation (such as the conductive agent content, the positive electrode active material content).

[0142] Comparative Example 3

[0143] The comparative example of the present application provides a secondary battery, which is different from the embodiment 1 in that no lithium supplement agent is added.

[0144] The non-Faraday capacitance Cdl of the positive electrode sheet in the embodiment and the comparative example, the particle dispersion N of the lithium supplement, the particle size Dv99 corresponding to the cumulative volume percentage of the lithium supplement reaching 99%, the mass percentage A of the alkali metal ions in the negative electrode binder, the mass percentage B of the negative electrode binder in the negative electrode active material layer, the weight average molecular weight Mw of the first negative electrode binder, the type of the first negative electrode binder, the type of the additive in the electrolyte, the mass percentage C of the additive in the electrolyte, the type of the lithium supplement, and the mass percentage D of the lithium supplement in the positive electrode active material layer are shown in Table 1;

[0145] The first negative electrode binder A1 is lithium polyacrylate, the first negative electrode binder A2 is a mixture of sodium carboxymethyl cellulose and lithium polyacrylate in a mass ratio of 1:1; the first negative electrode binder A3 is polyacrylate;

[0146] Additive 1 is lithium bismalonate borate, and additive 2 is lithium bisethylmalonate borate;

[0147] Lithium supplement 1 is Li5FeO5, and lithium supplement 2 is Li2NiO4;

[0148] Table 1 Parameters of secondary batteries

[0149]

[0150]

[0151] The cycle performance, rate performance and lithium deposition of the secondary batteries prepared in the examples and comparative examples are shown in Table 2; wherein the test method comprises the following steps:

[0152] 1) Cycle capacity retention rate: The nominal capacity of the battery is C0. After 3000 cycles at 0.5C / 0.5C at 25°C, the discharge capacity C is obtained. The capacity retention rate = C / C0×100%;

[0153] 2) 1C lithium deposition: At 25°C, the battery was disassembled after 3 cycles of charge and discharge at a rate of 0.5C and 10 cycles of charge and discharge at a rate of 1C to observe the lithium deposition at the interface of the negative electrode. According to the degree of lithium deposition, it was divided into four levels: no lithium deposition, slight lithium deposition, moderate lithium deposition and severe lithium deposition; among them, no lithium deposition means that the lithium deposition area is less than 2%, slight lithium deposition means 2-10%, moderate lithium deposition means 10-30%, and severe lithium deposition means more than 30%;

[0154] 3) 2C lithium deposition: At 25°C, the battery was disassembled after 3 cycles of charge and discharge at a rate of 0.5C and 10 cycles of charge and discharge at a rate of 2C to observe the lithium deposition at the interface of the negative electrode. According to the degree of lithium deposition, the battery was divided into four levels: no lithium deposition, slight lithium deposition, moderate lithium deposition and severe lithium deposition; among them, no lithium deposition means that the lithium deposition area is less than 5%, slight lithium deposition means 5-20%, moderate lithium deposition means 20-50%, and severe lithium deposition means more than 50%;

[0155] Table 2 Performance test table of secondary batteries

[0156]

[0157]

[0158] As can be seen from Table 2, when the secondary battery is controlled to satisfy 100×Cdl×(A+0.5) / N×(Dv99-7)≥0.3, the secondary battery obtained in the present application has good cycle performance, rate performance and safety performance; specifically, the obtained secondary battery has a cycle capacity retention rate of more than 88.98% after 6000 cycles at 0.5C / 0.5C at 25°C, and the 1C / 2C lithium precipitation tests both show no lithium precipitation.

[0159] The results of Examples 1 to 27 of the present application and Comparative Example 1 also show that when Y satisfies Y ≥ 0.3, it can ensure that the secondary battery has excellent cycle performance, rate performance and good lithium deposition; the results of Examples 1 to 27 of the present application and Comparative Example 2 also show that when the first negative electrode binder containing alkali metal ions is not introduced into the negative electrode active material layer, the obtained secondary battery cannot achieve the effect of the present application; the results of Examples 1 to 27 of the present application and Comparative Example 3 also show that when the lithium supplement agent is not introduced into the positive electrode active material layer, the comprehensive performance of the obtained secondary battery cannot achieve the purpose of the present application.

[0160] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, characterized in that: The positive electrode active material layer includes a positive electrode active material and a lithium supplement, the negative electrode active material layer includes a negative electrode active material and a negative electrode binder, and the negative electrode binder includes alkali metal ions; The secondary battery satisfies: Y≥0.3; Wherein, Y = 100 × Cdl × (A + 0.5) / N × (Dv99-7); Cdl nF is the non-Faraday capacitance of the positive electrode; A% is the mass percentage of alkali metal ions in the negative electrode binder; N is the particle dispersion of the lithium supplement; Dv99μm is the particle size corresponding to when the cumulative volume percentage of the lithium supplement reaches 99%.

2. The secondary battery according to claim 1, characterized in that: The mass percentage A% of alkali metal ions in the negative electrode binder is 0.11% to 2%.

3. The secondary battery according to claim 1, characterized in that: At least one of the following is met: a. The non-Faraday capacitance Cdl nF of the positive electrode plate is 0.4nF to 1.6nF; b. The particle dispersion of the lithium supplement agent is 11 to 16; c. When the cumulative volume percentage of the lithium supplement reaches 99%, the corresponding particle size Dv99μm is 10μm to 30μm.

4. The secondary battery according to claim 1, characterized in that: The mass percentage of the negative electrode binder in the negative electrode active material layer is 1.5% to 3%.

5. The secondary battery according to claim 1, characterized in that: The negative electrode binder includes a first negative electrode binder, and the first negative electrode binder includes at least one of lithium polyacrylate, lithium alginate, and lithium carboxymethyl cellulose.

6. The secondary battery according to claim 5, characterized in that: The weight average molecular weight of the first negative electrode binder is 10,000 to 3,000,000.

7. The secondary battery according to claim 1, characterized in that: The electrolyte includes an additive, wherein the additive comprises lithium bismalonate borate or its derivatives, and the mass percentage of the lithium bismalonate borate or its derivatives in the electrolyte is 0.5% to 2%.

8. The secondary battery according to claim 1, characterized in that: The mass percentage of the lithium supplement in the positive electrode active material layer is 0.5% to 2%.

9. The secondary battery according to claim 1, characterized in that: The lithium supplement includes at least one of Li5FeO5, Li6CoO4, and Li2NiO2.

10. An electrical device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 9.

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