A secondary battery, preparation method and electrical equipment

Abstract

The present application discloses a secondary battery, a preparation method and an electrical device. The secondary battery of the present application comprises a positive electrode plate, a separator, a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a lithium metal plate and a modified layer arranged on at least one surface of the lithium metal plate, wherein the modified layer comprises a phosphate and a lithium metal alloy. The secondary battery of the present application is provided with a modified layer on the surface of the lithium metal plate, wherein the modified layer can effectively conduct lithium ions, and the lithium metal alloy can achieve uniform deposition of lithium ions, avoid the growth of lithium dendrites, and improve the electrochemical performance and safety performance of the battery.

Description

Technical Field

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

[0002] As a highly efficient energy storage device for the mutual conversion of electrical energy and chemical energy, lithium-ion batteries have been successfully used in 3C electronic devices due to their high energy density, long life, stable performance, and environmental friendliness. As the market continues to expand, the demand for batteries with higher energy density and longer cycle life is continuing to grow. The current battery system with graphite (372mAh / g) as the negative electrode cannot meet the development requirements of the industry due to its low energy density. Lithium metal has a very high theoretical specific capacity (3860mAh / g), ultra-low potential (-3.04V) and ultra-low density (0.534g / cm 3 ), making the application of higher energy batteries possible. However, lithium metal is much more active than other negative electrode materials. Whether in liquid batteries or solid-state batteries, it is very easy to react with electrolytes. In addition, during the charging process, the uneven deposition of lithium leads to the growth of lithium dendrites, which can pierce the diaphragm or solid electrolyte, causing short circuits and even battery explosions. Summary of the invention

[0003] The purpose of the present application is to provide a secondary battery, a preparation method and an electrical device. The secondary battery of the present application has a modified layer on the surface of the lithium metal sheet, which can effectively conduct lithium ions during charging, avoid the growth of lithium dendrites, and help improve the electrochemical performance and safety performance of the battery.

[0004] An embodiment of the present application provides a secondary battery, including a positive electrode plate, a separator, a negative electrode plate and an electrolyte, wherein the negative electrode plate includes a lithium metal plate and a modified layer arranged on at least one surface of the lithium metal plate, wherein the modified layer includes phosphate and a lithium metal alloy.

[0005] In some embodiments, the modification layer includes an organic compound, and the organic compound includes one or more groups selected from the group consisting of a carbon-carbon double bond, an epoxy group, and a benzene ring.

[0006] In some embodiments, based on the mass of the modified layer, the mass of the organic compound accounts for 1% to 30%.

[0007] In some embodiments, the lithium metal alloy includes an A element selected from one or more of Sb, Zn, Mg, Al, Sn, Zr, Bi, Ag, In, Se, B, and Si.

[0008] In some embodiments, the lithium metal alloy includes Li 3 / xA, where x ranges from 0.5 to 3.

[0009] In some embodiments, the molar ratio of the lithium element in the modification layer to the lithium element in the lithium metal sheet is: (0.01-0.2):1.

[0010] In some embodiments, the modification layer has a thickness of 500 nm to 10 μm.

[0011] Accordingly, an embodiment of the present application provides a method for preparing a secondary battery, comprising the following steps:

[0012] Assembling a positive electrode plate, a separator and a lithium metal plate coated with phosphate on the surface into a battery; the particle size of the phosphate is 50-500nm;

[0013] The battery is formed to obtain the secondary battery having the negative electrode plate, wherein the negative electrode plate includes phosphate and lithium alloy.

[0014] In some embodiments, the mass percentage concentration of phosphate in the dispersion is 5%-80%.

[0015] Accordingly, an embodiment of the present application provides an electrical device, including the above-mentioned secondary battery or the secondary battery prepared by the above-mentioned preparation method.

[0016] The beneficial effects of the present application are as follows: the secondary battery of the present application comprises a positive electrode plate, a separator, a negative electrode plate and an electrolyte, the negative electrode plate comprises a lithium metal plate and a modified layer arranged on at least one surface of the lithium metal plate, the modified layer comprises a phosphate and a lithium metal alloy. The secondary battery of the present application is provided with a modified layer on the surface of the lithium metal plate, the modified layer can effectively conduct lithium ions, the lithium metal alloy can achieve uniform deposition of lithium ions and avoid the growth of lithium dendrites, the introduction of organic compounds can improve the stability of the modified layer and improve the wettability of the plate, and effectively improve the electrochemical performance and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 The charging cycle process of the prior art lithium metal sheet as the negative electrode;

[0019] Figure 2 This is the charging cycle process of the negative electrode plate of this application. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only 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 those skilled in the art without creative work are within the scope of protection of the present application. In addition, in the description of the present application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used only as markings, and no numerical requirements or order are imposed. Various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and simplicity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values ​​within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the numbered range, such as 1, 2, 3, 4, 5 and 6, which are applicable regardless of the range. Additionally, whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range.

[0021] In order to solve the problem of lithium dendrites generated during the use of lithium metal sheets as negative electrode materials, the present application provides a secondary battery, including a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, the negative electrode sheet includes a lithium metal sheet and a modified layer arranged on at least one surface of the lithium metal sheet, the modified layer includes phosphate and a lithium metal alloy.

[0022] In this embodiment, the phosphate includes lithium phosphate. The lithium phosphate in the modified layer of the present application is a fast ion conductor and can effectively conduct lithium ions. The lithium metal alloy in the modified layer of the present application undergoes alloying / de-alloying reaction during the battery cycle. During the alloying process, it can induce uniform deposition of lithium ions and avoid the growth of lithium dendrites, which helps to improve the electrochemical performance and safety performance of the battery.

[0023] In some embodiments, the lithium metal alloy includes element A, and element A is selected from one or more of Sb, Zn, Mg, Al, Sn, Zr, Bi, Ag, In, Se, B and Si. The alloy formed by the above elements and lithium can make the lithium ion deintercalation process more uniform during the battery cycle, inhibit the growth of lithium dendrites, and further improve the battery safety performance.

[0024] In some embodiments, the modification layer includes an organic compound, and the organic compound includes one or more groups selected from the group consisting of carbon-carbon double bonds, epoxy groups, and benzene rings. In some embodiments, the organic compound is selected from one or more selected from the group consisting of polyethylene, polystyrene, and polyethylene oxide (PEO).

[0025] In the modified layer of the present application, the stability of the modified layer can be improved by introducing functional groups of organic compounds. At the same time, since the above-mentioned organic compounds contain groups such as carbon-carbon double bonds, epoxy groups, and benzene rings, the above-mentioned groups are polar groups and interact with the organic functional groups in the electrolyte, thereby improving the wetting performance of the negative electrode plate and effectively improving the electrochemical performance and safety performance of the battery.

[0026] In some embodiments, the mass proportion of the organic compound is 1% to 30% based on the mass of the modified layer. For example, the mass proportion of the organic compound is 1 to 10%, 1 to 20%, 10 to 20%. In some embodiments, the mass proportion (%) of the organic compound is any value of 1, 2, 3, 5, 10, 15, 20, 25, 30 or a range consisting of any two values ​​based on the mass of the modified layer.

[0027] The content of organic compounds directly affects the stability and wettability of the modified layer. When the organic compounds are within the above range, the performance of the modified layer can be further optimized, the stability and wettability of the modified layer can be improved, and the influence on the lithium ion migration efficiency of the modified layer can be avoided, so that the performance of the battery is further optimized. In the battery system, when the electrode has poor wettability to the electrolyte, the ion transmission path becomes longer, which hinders the shuttle of lithium ions between the positive and negative electrodes. The electrode that is not in contact with the electrolyte cannot participate in the electrochemical reaction of the battery. At the same time, the interface impedance of the battery increases, which affects the rate performance, discharge capacity and service life of the lithium battery.

[0028] In some embodiments, the lithium metal alloy includes Li 3 / x A, where x ranges from 0.5 to 3.

[0029] In some embodiments, the value of x is any value of 0.5, 1.5, 2, 2.5, 3, or a range consisting of any two values.

[0030] Li in the modified layer of this application 3 / x A can achieve uniform lithium ion deposition and avoid the growth of lithium dendrites. 3 / x The presence of A reduces the activity of lithium metal sheets and increases the interfacial stability.

[0031] In some embodiments, the molar ratio of lithium phosphate to lithium metal alloy is 1:(0.5-3).

[0032] In some embodiments, the molar ratio of lithium phosphate to lithium metal alloy is any value of 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, or a range of any two values.

[0033] In some embodiments, the molar ratio of lithium in the modification layer to lithium in the lithium metal sheet is:

[0034] (0.01-0.2): 1. For example, the molar ratio of the lithium element in the modified layer to the lithium element in the lithium metal sheet is any value among 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.12:1, 0.14:1, 0.15:1, 0.2:1, or a range consisting of any two values.

[0035] When the ratio of the molar content of lithium in the modified layer to the molar content of lithium in the metal sheet is within the above range, the migration efficiency of the modified layer for lithium ions can be ensured, the impedance value can be reduced, the growth of lithium dendrites can be avoided, and the cycle performance and rate performance of the battery can be improved.

[0036] In some embodiments, the thickness of the modification layer is 500 nm to 10 μm.

[0037] In this embodiment, the thickness of the modified layer refers to the thickness of the modified layer on one side of the negative electrode sheet. If the modified layer is disposed on both sides of the negative electrode sheet, the thickness of each side is between 500nm and 10μm. When the thickness of the modified layer is within the above range, the impedance value of the negative electrode sheet can be ensured to be within a suitable range, while taking into account the migration rate of lithium ions, further optimizing the electrochemical performance of the battery.

[0038] In some embodiments, the thickness of the modification layer is any value of 500 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range of any two values.

[0039] The embodiment of the present application also provides a method for preparing the secondary battery, comprising the following steps:

[0040] (S1) The positive electrode sheet, the separator and the surface coated with phosphate A x PO 4 The lithium metal sheets are assembled into a battery; the particle size of the phosphate is 50-500nm;

[0041] (S2) The battery is formed to obtain a secondary battery having a negative electrode plate.

[0042] In some embodiments, step (S1) comprises:

[0043] An organic compound and a phosphate salt are placed in an organic solvent to obtain the dispersion, wherein the organic compound includes one or more of polyethylene, polystyrene, and polyethylene oxide; the dispersion is sprayed or coated on the surface of a lithium metal sheet, or the lithium metal sheet is immersed in the dispersion, and a modified lithium metal negative electrode is obtained after drying. In this embodiment, the particle size of the phosphate is controlled at 50 to 500 nm, which is conducive to the uniform dispersion of the phosphate and improves the uniformity of the modified layer.

[0044] This application A x PO 4 During the first charge, decomposition occurs to generate lithium phosphate and A, and alloying / de-alloying reactions occur in subsequent cycles, i.e., Li 3 / x A Formation and decomposition of alloy.

[0045] The reaction process is: A x PO4+3Li + +3e - →xA+Li 3 PO 4 ;

[0046]

[0047] In some embodiments, the coating amount of the dispersion on the lithium metal sheet is: 10-100 μL / cm 2 .

[0048] In some embodiments, the coating amount (μL / cm 2 ) is: any value among 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range of any two values.

[0049] In some embodiments, the mass percentage concentration of phosphate in the dispersion is 5%-80%.

[0050] In some embodiments, the mass percent concentration (%) of phosphate in the dispersion is any value of 5, 15, 25, 35, 45, 55, 65, 75, 80, or a range of any two values.

[0051] In some embodiments, the organic solvent is selected from one or more of xylene, p-xylene, o-xylene, n-hexane, cyclopentane, cyclopentane, tetrahydrofuran, ethyl acetate, butyl acetate, acetonitrile, and acetone.

[0052] In some embodiments, the phosphate is in the form of nanoparticles. Preferably, the nanoparticles have a particle size of 50 nm to 500 nm.

[0053] In some embodiments, the particle size (nm) of the nanoparticles is any value among 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, or a range between any two values.

[0054] In some embodiments, the drying temperature is 50-100° C., the drying time is 30 min-10 h, and the drying needs to be performed under an inert atmosphere.

[0055] In some embodiments, the lithium metal sheet coated with phosphate is fabricated in a glove box filled with argon gas with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm.

[0056] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material covered on the positive current collector, a binder and a conductive agent, and the type and content of the conductive agent and the binder are not specifically limited and can be selected according to actual needs. In some embodiments, the conductive agent may include conductive carbon black, carbon nanotubes, graphene, etc., and the binder may include polyvinylidene fluoride.

[0057] In some embodiments, the preparation of the positive electrode sheet includes: dispersing the positive electrode active material, the conductive agent, and the binder in N-methylpyrrolidone (NMP) in a certain proportion, coating the obtained slurry on an aluminum foil, drying it, and then cold pressing and slitting it to obtain the positive electrode sheet.

[0058] In some embodiments, the main components of the electrolyte include a lithium salt, an organic solvent, and an additive. The types and compositions of the lithium salt and the organic solvent are not particularly limited and can be selected according to actual needs. The lithium salt may include lithium hexafluorophosphate, and the solvent may include one or more of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propyl propionate.

[0059] In some embodiments, the type of the isolation film is not particularly limited and can be selected according to actual needs. The isolation film can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride, a spandex film, an aramid film, or a multi-layer composite film modified by a coating.

[0060] In some embodiments, the preparation of a secondary battery includes: stacking the positive electrode sheet, the isolation membrane, and the negative electrode sheet in order, so that the isolation membrane is between the positive and negative electrode sheets to play an isolating role, and then winding them into a square core, and then hot and cold pressing them, and loading them into a battery casing, and then baking them at 65 to 95°C to remove water, injecting electrolyte, sealing, and after standing, forming, and capacity separation processes, a secondary battery is obtained.

[0061] In some embodiments, the secondary battery in the present application may be a liquid lithium battery, a semi-solid lithium battery, a solid lithium battery, a lithium-sulfur battery, or a lithium-air battery.

[0062] The present application also provides an electrical device, and the electrical device of the present application includes the above-mentioned secondary battery. The electrical device includes but is not limited to backup power supplies, motors, electric vehicles, electric motorcycles, power-assisted bicycles, bicycles, power tools, large household batteries, etc.

[0063] The present application has been tested many times, and some of the test results are now cited as references to further describe the present application in detail, and the following is a detailed description in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0064] Embodiment 1:

[0065] Preparation of negative electrode: In a glove box filled with argon, phosphate (zinc phosphate) with an average particle size of 100 nm was dispersed in an organic solvent xylene to prepare a phosphate dispersion with a concentration of 10%. The dispersion was coated on both sides of the lithium metal negative electrode with a coating amount of 50 μL / cm 2 After drying at 60°C for 4 h, the modified lithium metal negative electrode was obtained as the negative electrode sheet.

[0066] Preparation of positive electrode sheets: lithium nickel cobalt manganese oxide, conductive carbon black and PVDF in a weight ratio of 90:5:5 are mixed and dissolved in NMP. After mixing evenly, they are double-sided coated on carbon-coated aluminum foil (double-sided coating, 14μm), and then the sheets are dried, rolled, slit and cut to obtain positive electrode sheets.

[0067] Diaphragm: polyethylene film;

[0068] Electrolyte: LiPF 6 Soluble in V EC :V DMC :V DEC =1:1:1 mixed solvent to obtain electrolyte, LiPF 6 The concentration is 1 mol / L.

[0069] The positive electrode sheet and the negative electrode sheet prepared in the present application are separated by a diaphragm, wound into corresponding winding cores, and subjected to processes such as shaping, welding, assembly, baking, liquid injection, formation, and capacity division to obtain a soft-pack lithium-ion battery.

[0070] The battery formation parameters are: charging at a current of 0.05C for 20 hours, during which a modified layer is formed on the surface of the negative electrode.

[0071] Example 2 to Example 11: The preparation method is the same as Example 1, except that the type of phosphate and the concentration of the phosphate dispersion are changed to obtain modified layers containing different types of lithium alloys and different ratios of lithium phosphate to lithium alloy, see Table 1 for details.

[0072] Example 12 to Example 19: The preparation method is the same as that of Example 1, except that the proportion of lithium element in the modification layer and the thickness of the modification layer are controlled by adjusting the coating amount of the dispersion. The specific parameters are shown in Table 1.

[0073] Example 20 to Example 26: The preparation method is the same as that of Example 1, except that an organic compound is added to the dispersion. The rest of the preparation method is the same as that of Example 1.

[0074] Comparative Example 1: The preparation method is the same as that of Example 1, except that there is no preparation and coating process of the phosphate dispersion in the preparation of the negative electrode plate, and there is no modification layer in the prepared battery.

[0075] Comparative Example 2: The preparation method is the same as that of Example 1, except that zinc phosphate is replaced by zinc chloride. The specific parameters are shown in Table 1.

[0076] Performance parameter testing:

[0077] Cycle capacity retention rate: Under 25±5℃ environment, the battery is subjected to room temperature cycle test: 0.5C constant current charge to 4.35V, 4.35V constant voltage charge to cut-off current 0.05C, and then constant current 1C discharge to 2.8V. Cycle test until the capacity retention rate is less than 80%, and record the number of cycles at the end point. The test is completed.

[0078] Battery DC impedance test method: At 25±5℃, place the battery aside for 5 minutes, charge to 4.2V at 1C constant current, and then charge at constant voltage until the current is less than or equal to 0.05C. At this time, the battery's state of charge (SOC) is 100%. Then place the battery aside for 5 minutes, and then discharge at 1C constant current to adjust the battery's state of charge (SOC) to 50%. Place the battery with 50% SOC for another 10 minutes, and discharge at 4C constant current for 30 seconds. Record the voltage U1 at the last second of the placement, the voltage U2 at the last second of the 4C constant current discharge, and the current I of the 4C constant current discharge. The battery's DC impedance R = (U2-U1) / I at 25℃, 50% SOC, and 4C constant current discharge for 30s.

[0079] Table 1 Parameters and test results of Examples 1 to 26 and Comparative Examples 1 to 2

[0080]

[0081]

[0082] From the results in Table 1, it can be seen that: from the data of Examples 1 to 17, it can be seen that the cycle performance of the battery with the modified layer is better than that of Comparative Example 1, and different types of modified layers have different effects. Zinc, magnesium, antimony, silver, and boron have better effects, which may be because these elements have a stronger affinity with lithium and are easier to form lithium alloys; comparing Example 1 with Examples 12 to 17, it can be found that with the increase of the thickness of the modified layer, the cycle retention rate of the battery shows a trend of first increasing and then decreasing, which shows that it is very important to select a modified layer of appropriate thickness; comparing Example 1 with Comparative Example 2, it is found that the cycle performance of Example 1 is significantly better than that of Comparative Example 2, which is mainly due to the presence of the modified layer, such as Figures 1-2 As shown, the modified layer of the present application can protect the negative electrode during the cycle process, avoid the growth of lithium dendrites, and greatly improve the cycle capacity of the battery.

[0083] It can be seen from the data of Example 1 and Examples 16 to 26 that when there are organic compounds in the modification layer, the DC impedance of the battery can be reduced. This is because the presence of the organic compound can improve the wettability of the negative electrode plate, thereby reducing the internal resistance of the battery. When the content of the organic compound is within a certain range, the cycle life of the battery can be effectively improved. Although the higher the content of the organic compound, the smaller the internal resistance of the battery, when the content of the organic compound is too high, the proportion of phosphate and lithium alloy in the modification layer decreases, which easily deteriorates the battery cycle performance and reduces the battery cycle life. Therefore, the content of the organic compound should be controlled within a reasonable range.

[0084] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0085] The above is a detailed introduction to a secondary battery, a preparation method and an electrical device provided in the embodiments of the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A secondary battery, characterized in that: The invention comprises a positive electrode plate, a separator, a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a lithium metal plate and a modified layer arranged on at least one surface of the lithium metal plate, wherein the modified layer comprises a phosphate and a lithium metal alloy; The phosphate includes lithium phosphate, and the lithium phosphate has a chemical formula of A x The phosphate of PO4 reacts with the lithium metal sheet during the charge and discharge process, and the chemical formula of the lithium metal alloy is Li 3 / x A, wherein the A element includes one or more of Sb, Zn, Mg, Al, Sn, Zr, Bi, Ag, In, Se, B and Si, and the value of x is 0.5 to 3.

2. The secondary battery according to claim 1, characterized in that: The modification layer includes an organic compound, and the organic compound includes one or more groups selected from the group consisting of a carbon-carbon double bond, an epoxy group, and a benzene ring.

3. The secondary battery according to claim 2, characterized in that: Based on the mass of the modified layer, the mass proportion of the organic compound is 1% to 30%.

4. The secondary battery according to claim 1, characterized in that: The molar ratio of the lithium element in the modified layer to the lithium element in the lithium metal sheet is: (0.01-0.2):

1.

5. The secondary battery according to claim 1, characterized in that: The thickness of the modified layer is 500nm-10μm.

6. A method for preparing a secondary battery as claimed in claim 1, characterized in that: The following steps are involved: Assembling a positive electrode plate, a separator and a lithium metal plate coated with phosphate on the surface into a battery; the particle size of the phosphate is 50-500nm; The battery is formed to obtain the secondary battery having the negative electrode plate, wherein the negative electrode plate includes phosphate and lithium alloy.

7. The method for preparing a secondary battery according to claim 6, characterized in that: The preparation method of the lithium metal sheet coated with phosphate on the surface includes: Dispersing the phosphate and the organic compound in an organic solvent to prepare a dispersion; The dispersion is applied to the surface of the lithium metal sheet, and after drying, the lithium metal sheet with the surface coated with phosphate is obtained.

8. An electrical device, characterized in that: The invention comprises a secondary battery as claimed in any one of claims 1 to 5 or a secondary battery prepared by the preparation method as claimed in any one of claims 6 to 7.

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