Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The negative pole piece in the secondary battery comprises a first coating arranged on the surface of at least one side of a current collector and a second coating arranged on the first coating, the first coating comprises a first silicon negative electrode active material, and the second coating comprises a second silicon negative electrode active material; the first silicon negative electrode active material and the second silicon negative electrode active material comprise modified elements, and the modified elements comprise an element P, an element Al and an element K; the following relations are met: the content of the modified element satisfies P1lt; p2, Al < 1gt >; al2, K1gt; k2. The elements P, Al and K are introduced into the silicon negative electrode active material, the three modified elements are used together, and meanwhile, the element distribution in the silicon negative electrode active material is specifically designed, so that lithium precipitation of the secondary battery can be inhibited, and the service life of the secondary battery is prolonged.

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] Silicon negative electrodes are prone to defects such as lithium deposition and rapid capacity decay during the cycle process. By disassembling and analyzing silicon negative electrode cycle batteries, lithium deposition interfaces generally appear after 800 to 1200 cycles. At present, the above problems are mainly solved by reducing the compaction density of the negative electrode, using soft carbon or hard carbon coating to improve the kinetic performance of the negative electrode, and optimizing the electrolyte formula. However, the batteries obtained by the above modification methods gradually increase the polarization of the battery as the cycle progresses, and the overpotential between the positive and negative electrodes gradually increases. The capacity retention rate of the battery decreases significantly, which greatly shortens the service life of the secondary battery. Summary of the invention

[0003] The purpose of the present application is to improve the negative electrode plate in order to further increase the service life of the secondary battery and to provide a secondary battery with a longer service life.

[0004] To achieve the above-mentioned object, in a first aspect of the present application, a secondary battery is provided, comprising a negative electrode plate, wherein the negative electrode plate comprises:

[0005] A current collector; a first coating disposed on at least one side of the current collector, and a second coating coated on the first coating;

[0006] The first coating layer includes a first silicon negative electrode active material, and the second coating layer includes a second silicon negative electrode active material;

[0007] The first silicon negative electrode active material and the second silicon negative electrode active material contain a modifying element, wherein the modifying element contains an element P, an element Al and an element K; and the following relationship is satisfied:

[0008] The content of the modifying element meets: P1<P2,Al1> Al2, K1>K2,

[0009] Among them, P1, Al1 and K1 respectively represent the contents of element P, element Al and element K in the first silicon negative electrode active material, and P2, Al2 and K2 respectively represent the contents of element P, element Al and element K in the second silicon negative electrode active material.

[0010] As an implementation scheme of the present application, the negative electrode plate in the secondary battery satisfies: 1000ppm≤P2-P1≤2000ppm.

[0011] As an implementation scheme of the present application, the negative electrode plate in the secondary battery satisfies: 50ppm≤Al1-Al2≤1000ppm.

[0012] As an implementation scheme of the present application, the negative electrode plate in the secondary battery satisfies: 50ppm≤K1-K2≤600ppm.

[0013] As an implementation scheme of the present application, the negative electrode plate in the secondary battery satisfies: K1 is 500-700 ppm.

[0014] As an implementation scheme of the present application, the negative electrode plate in the secondary battery satisfies: K2 is 50 to 500 ppm.

[0015] As an embodiment of the present application, the modifying element is distributed on the surface and / or inside of the first silicon negative electrode active material or the second silicon negative electrode active material.

[0016] As an implementation scheme of the present application, the negative electrode sheet satisfies: 10 mAh / g≤C2-C1≤21 mAh / g; wherein C1 mAh / g represents the gram capacity of the first silicon negative electrode active material; and C2 mAh / g represents the gram capacity of the second silicon negative electrode active material.

[0017] As an embodiment of the present application, the particle size D of the first silicon negative electrode active material is V50 is 4.0 to 7.0 μm, and the particle size D of the second silicon negative electrode active material is V50 is 4.0 to 7.0 μm; wherein the particle size D V50 It indicates the particle size corresponding to when the volume accumulation of material particles reaches 50%, in μm.

[0018] As an embodiment of the present application, the negative electrode sheet satisfies: 0.94≤PD2 / PD1≤1.07, PD1 g / cm 3 Indicates the compaction density of the first coating in the negative electrode sheet, PD2 g / cm 3 It represents the compaction density of the second coating layer in the negative electrode sheet.

[0019] A second aspect of the present application provides an electrical device, wherein the electrical device comprises the secondary battery described in the first aspect of the present application.

[0020] Compared with the prior art, the beneficial effects of this application are:

[0021] The present application introduces P, Al and K elements into the silicon negative electrode active material, and uses the three modifying elements together. At the same time, by specifically designing the element distribution in the silicon negative electrode active material, the gram capacity and structural stability of the silicon negative electrode material are improved, and the polarization is reduced, thereby improving the capacity retention rate of the silicon negative electrode cycle, improving the negative electrode cycle lithium deposition interface, and improving the service life of the secondary battery prepared therefrom. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the negative electrode plate of Example 1. DETAILED DESCRIPTION

[0023] To better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific examples and accompanying drawings, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in the present application are commercially available.

[0024] An embodiment of the present application provides a secondary battery, including a negative electrode plate, wherein the negative electrode plate includes:

[0025] A current collector; a first coating disposed on at least one side of the current collector, and a second coating disposed on the first coating;

[0026] The first coating layer includes a first silicon negative electrode active material, and the second coating layer includes a second silicon negative electrode active material;

[0027] The first silicon negative electrode active material and the second silicon negative electrode active material contain a modifying element, wherein the modifying element contains an element P, an element Al and an element K; and the following relationship is satisfied:

[0028] The content of the modifying element meets: P1<P2,Al1> Al2, K1>K2,

[0029] Among them, P1, Al1 and K1 respectively represent the contents of element P, element Al and element K in the first silicon negative electrode active material, and P2, Al2 and K2 respectively represent the contents of element P, element Al and element K in the second silicon negative electrode active material.

[0030] The negative electrode plate of the present application introduces P, Al and K elements into the silicon negative electrode active material, which can increase the interlayer spacing of the silicon negative electrode active material, increase the lithium ion diffusion coefficient, and reduce polarization; the P element can increase the gram capacity of the silicon negative electrode active material, and the K and Al elements can improve the structural stability of the silicon negative electrode active material and reduce the free energy of lithium insertion. The three modifying elements are used together, and at the same time, by specifically designing the element distribution in the silicon negative electrode active material, the gram capacity and structural stability of the silicon negative electrode material are increased, and the polarization is reduced, thereby increasing the capacity retention rate of the silicon negative electrode cycle, improving the negative electrode cycle lithium precipitation interface, and increasing the service life of the secondary battery prepared therefrom.

[0031] In the present application, the modifying element may be distributed on the surface of the first silicon negative electrode active material or the second silicon negative electrode active material, or may be distributed inside the first silicon negative electrode active material or the second silicon negative electrode active material. When the modifying element is distributed on the surface and inside the negative electrode active material, the stability of the negative electrode active material can be optimized, and the negative electrode material can have more electrochemical active sites.

[0032] In the first silicon negative electrode active material and the second silicon negative electrode active material in some embodiments of the present application, K and Al elements can improve the structural stability of the material and reduce the free energy of lithium insertion. At the same time, K and Al elements loaded into the silicon material can also work together with P element to improve the crystallization performance of the material, thereby significantly improving the cycle stability of the battery and extending the service life of the battery.

[0033] In some embodiments, the condition is satisfied: 1000ppm≤P2-P1≤2000ppm, and illustratively, the value of P2-P1 can be any one of 1000ppm, 1500ppm, 2000ppm, or a range between any two values. When the above conditions are met, the initial discharge capacity and cycle performance of the battery can be further improved.

[0034] In some embodiments, P1 is in the range of 800 ppm to 1200 ppm. For example, the value of P1 can be any one of 800 ppm, 1000 ppm, 1200 ppm, or a range between any two values.

[0035] In some embodiments, P2 is in the range of 1800 ppm to 3200 ppm. For example, the value of P2 can be any one of 1800 ppm, 2000 ppm, 2900 ppm, 3000 ppm, 3200 ppm or a range between any two values.

[0036] In some embodiments, the following is satisfied: 50ppm≤Al1-Al2≤1000ppm; illustratively, the value of Al1-Al2 may be any one of 50ppm, 300ppm, 400ppm, 500ppm, 700ppm, 950ppm, or a range between any two values. When the above conditions are met, the cycle capacity retention rate of the battery can be further improved.

[0037] In some embodiments, Al1 is in the range of 1000 ppm to 1200 ppm. For example, the value of Al1 can be any one of 1000 ppm, 1050 ppm, 1200 ppm, or a range between any two values.

[0038] In some embodiments, Al2 is in the range of 100 ppm to 950 ppm. For example, the value of Al2 can be any one of 100 ppm, 300 ppm, 500 ppm, 700 ppm, 800 ppm, 950 ppm or a range between any two values.

[0039] In some embodiments, 50ppm≤K1-K2≤600ppm is satisfied. For example, the value of K1-K2 may be any one of 50ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, or a range between any two values. When the above conditions are met, the cycle capacity retention rate of the battery can be improved.

[0040] In some embodiments, K1 is in the range of 500 ppm to 700 ppm. For example, the value of K1 can be any one of 500 ppm, 550 ppm, and 700 ppm, or a range between any two values.

[0041] In some embodiments, K2 is in the range of 50 ppm to 500 ppm. For example, the value of K2 can be any one of 50 ppm, 100 ppm, 200 ppm, 300 ppm, 450 ppm or a range between any two values.

[0042] In some embodiments, the negative electrode plate satisfies: 0.94≤PD2 / PD1≤1.07, and more preferably 1.0≤PD2 / PD1≤1.07. For example, the value of PD2 / PD1 can be any one of 0.94, 0.97, 1.00, 1.03, 1.07, or a range between any two values. PD1 g / cm 3 Indicates the compaction density of the first coating in the negative electrode sheet, PD2 g / cm 3 It represents the compaction density of the second coating in the negative electrode plate. When PD2 / PD1 is within the above range, the cycle capacity retention rate of the battery can be improved.

[0043] In some embodiments, PD1 is 1.5 g / cm 3 ~1.6g / cm 3 In the range, for example, the value of PD1 can be 1.5 g / cm 3 , 1.6g / cm 3 Any value or a range of values ​​between any two values.

[0044] In some embodiments, PD2 is 1.5 g / cm 3 ~1.6g / cm 3 In the range, PD2 can be 1.5 g / cm 3, 1.55g / cm 3 , 1.6g / cm 3 Any value or a range of values ​​between any two values.

[0045] In some embodiments, PD1 is 1.5 g / cm 3 , PD2 is 1.55g / cm 3 , which can improve the battery's cycle capacity retention rate.

[0046] In some embodiments, the negative electrode sheet satisfies: 10mAh / g≤C2-C1≤21mAh / g; further preferably 15mAh / g≤C2-C1≤20mAh / g. Exemplarily, the value of C2-C1 can be any one of 10mAh / g, 11mAh / g, 14mAh / g, 15mAh / g, 20mAh / g, 21mAh / g, or a range between any two values. Wherein, C1 mAh / g represents the gram capacity of the first silicon negative electrode active material; C2 mAh / g represents the gram capacity of the second silicon negative electrode active material. When the above conditions are met, the cycle capacity retention rate of the battery can be improved.

[0047] In some embodiments, C1 is in the range of 1400mAh / g to 1415mAh / g. Exemplarily, the value of C1 can be any one of 1408mAh / g, 1409mAh / g, 1410mAh / g, 1412mAh / g, 1413mAh / g, 1415mAh / g, or a range value between any two values.

[0048] In some embodiments, C2 is in the range of 1415mAh / g to 1432mAh / g. Exemplarily, the value of C2 can be any one of 1418mAh / g, 1420mAh / g, 1423mAh / g, 1424mAh / g, 1425mAh / g, 1430mAh / g, 1432mAh / g, or a range value between any two values.

[0049] In some embodiments, C1 is 1420 mAh / g, and C2 is 1425 mAh / g, which can improve the lithium deposition of the negative electrode, thereby further improving the cycle capacity retention rate of the battery. In some embodiments, the particle size D of the first silicon negative electrode active material is V50 For example, the particle size D of the first silicon negative electrode active material is 4.0 to 7.0 μm. V50 It can take any value among 4μm, 5μm, 6μm, 7μm or a range value between any two values.

[0050] In some embodiments, the particle size D of the second silicon negative electrode active material V50For example, the particle size D of the second silicon negative electrode active material is 4.0 to 7.0 μm. V50 It can take any value among 4μm, 5μm, 6μm, 7μm or a range value between any two values.

[0051] In this application, the particle size D V50 It indicates the particle size corresponding to when the volume accumulation of material particles reaches 50%, in μm.

[0052] When the particle size of the silicon negative electrode active material is within the above range, the compaction density of the coating can be further improved, thereby increasing the capacity of the battery. At the same time, when the particle size ratio of the two silicon negative electrode active materials is within the above range, a good ion channel can be formed on the basis of a higher compaction density, thereby improving the ion transmission performance and further improving the battery's cycle capacity retention rate.

[0053] In some embodiments, the active material in the first silicon negative electrode active material and the second silicon negative electrode active material includes at least one of silicon oxide (SiOx, x=1 or 2), Si alloy, and Si-C. It should be noted that in the present application, the silicon negative electrode active material includes active materials and modifying elements.

[0054] In some embodiments, the first coating layer and the second coating layer, in addition to the silicon negative electrode active material, also contain a conductive agent, a binder, and a thickener.

[0055] In the present application, the secondary battery further includes a positive electrode plate, an electrolyte, and a separator.

[0056] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active coating disposed on at least one side of the positive electrode current collector; the positive electrode active coating includes a positive electrode active material, and the positive electrode active material includes but is not limited to at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium iron phosphate.

[0057] In some embodiments, the positive electrode plate may further include a conductive agent, a binder, and a thickener.

[0058] The conductive agent includes but is not limited to at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0059] The binder includes but is not limited to at least one of styrene-butadiene rubber, styrene-acrylic emulsion, polyacrylic acid, and sodium alginate.

[0060] The thickener includes but is not limited to at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0061] The present application also protects an electric device including the secondary battery.

[0062] The following are specific embodiments of the present application, and the technical scheme of the present application is further described in conjunction with the embodiments, but the present application is not limited to these embodiments. The reagents, methods and equipment used in the present application, unless otherwise specified, are conventional reagents, methods and equipment in the art.

[0063] Example 1

[0064] This embodiment provides a secondary battery, and the preparation method includes the following steps:

[0065] Negative electrode preparation

[0066] A negative electrode active material (a mixture of a first silicon negative electrode active material and graphite in a mass ratio of 10:90), a conductive agent (conductive carbon black and carbon nanotubes in a weight ratio of 1:1), a thickener sodium carboxymethyl cellulose, and a binder polyacrylic acid in a mass ratio of 96:1.5:0.5:2 are mixed, deionized water is added, and a first negative electrode slurry is obtained under the action of a vacuum mixer;

[0067] The negative electrode active material (a mixture of the second silicon negative electrode active material and graphite in a mass ratio of 10:90), the conductive agent (conductive carbon black and carbon nanotubes mixed in a weight ratio of 1:1), the thickener sodium carboxymethyl cellulose, and the binder polyacrylic acid in a mass ratio of 96:1.5:0.5:2 were mixed, deionized water was added, and a second negative electrode slurry was obtained under the action of a vacuum mixer;

[0068] The first negative electrode slurry is evenly coated on both sides of the negative electrode current collector copper foil to form a first coating on both sides; then the second negative electrode slurry is coated on the first coating to form a second coating; then the coated electrode sheet is transferred to an oven for drying, and then cold pressed and cut to obtain a negative electrode sheet. The structural schematic diagram of the negative electrode sheet is shown in FIG. Figure 1 shown.

[0069] The first silicon negative electrode active material and the second silicon negative electrode active material are obtained by mixing, grinding and sintering silicon dioxide (or Si-C material) and metal salts of modifying elements, such as AlPO4 and K3PO4.

[0070] Other parameters of the negative electrode sheet and the silicon negative electrode active material are shown in Tables 1 and 2.

[0071] Positive electrode preparation

[0072] The positive electrode active material (high nickel ternary material, chemical formula LiNi 0.9 Co 0.05 Mn 0.05O2), binder polyvinylidene fluoride (PVDF), and conductive agent (conductive carbon black and carbon nanotubes are mixed in a weight ratio of 1:1) in a mass ratio of 97:1.5:1.5, and solvent N-methylpyrrolidone is added; then the mixture is transferred into a vacuum mixer and stirred until the system becomes uniform to obtain positive electrode slurry; the positive electrode slurry is evenly coated on both sides of the positive electrode collector (carbon-coated aluminum foil); the coated electrode sheet is dried in an oven, and then cold pressed and cut to obtain the positive electrode sheet.

[0073] Preparation of electrolyte

[0074] The organic solvent is a mixed solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC and DEC is 20:20:60. In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium salt lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) (mixed in a molar ratio of 1:1), and additives (fluoroethylene carbonate (FEC), tris(trimethylsilyl) phosphate (TMSP), and vinyl sulfate (DTD) mixed in a mass ratio of 1:1:1) are dissolved in the organic solvent and mixed evenly to obtain an electrolyte; in the electrolyte of this embodiment, the concentration of the lithium salt is 1.2mol / L, and the concentration of the additive is 5wt%.

[0075] Secondary battery assembly

[0076] The positive electrode sheet, separator (PE base film + [ceramic & PVDF coating]), and negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound into a square bare battery cell, loaded into a shell, and then baked at 100°C to remove water, and then the electrolyte is injected and sealed. After standing, hot and cold pressing, formation, capacity division and other processes, a secondary battery can be obtained.

[0077] Examples 2-23, Comparative Examples 1-4

[0078] A series of secondary batteries are provided, which are prepared according to the method of Example 1, and the negative electrode sheets are slightly different from those of Example 1. The differences are detailed in the parameters in Table 1 and Table 2. In the silicon negative electrode active material of Comparative Example 4, the first silicon negative electrode material and the second silicon negative electrode material are not doped with modifying elements.

[0079] Table 1

[0080]

[0081] Table 2

[0082]

[0083]

[0084] Note: In the table, P1 represents the content of element P in the first silicon negative electrode active material; P2 represents the content of element P in the second silicon negative electrode active material; Al1 represents the content of element Al in the first silicon negative electrode active material; Al2 represents the content of element Al in the second silicon negative electrode active material; K1 represents the content of element K in the first silicon negative electrode active material; K2 represents the content of element K in the second silicon negative electrode active material.

[0085] Performance Testing

[0086] The performance of the secondary batteries obtained in the above embodiments and comparative examples was tested, which specifically includes the following steps:

[0087] ⑴Stand at 45℃ for 30 minutes; ⑵Discharge at 0.02C constant current to 2.5V; ⑶Stand at 30 minutes; ⑷Charge at 0.02C constant current to 4.2V, and charge at constant voltage to a current of 0.05C; ⑸Stand at 30 minutes; ⑹Discharge at 0.02C constant current to 2.5V; ⑺Stand at 45℃ for 180 minutes; ⑻Charge at 1C constant current to 4.25V, and charge at constant voltage to a current of 0.05C; ⑼Stand at 60 minutes; ⑽Discharge at 1C constant current to 2.5V; ⑾Stand at 120 minutes; record the discharge capacity in grams at this time, which is the initial discharge capacity in grams; ⑿Repeat steps ⑻ to ⑾ 1500 times, stop the test, and record the discharge capacity in grams at this time.

[0088] The 1500-cycle capacity retention rate (%) = the discharge capacity in grams after 1500 cycles / the initial discharge capacity in grams*100%.

[0089] After 1500 cycles, the rechargeable battery was further disassembled to observe whether lithium was deposited on the negative electrode and calculate the lithium deposited area. The lithium deposited situation is shown in Table 3.

[0090] Table 3

[0091]

[0092] From the above results we can see that:

[0093] P, Al and K elements are introduced into the silicon negative electrode active material and the three modified elements are used together. At the same time, through the specific design of the element distribution in the silicon negative electrode active material, the capacity retention rate of the silicon negative electrode cycle can be significantly improved, the negative electrode cycle lithium deposition interface can be improved, and the service life of the secondary battery prepared therefrom can be significantly improved.

[0094] Finally, it should be noted that the above embodiments are only used 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, ordinary technicians in this field should understand that the technical solution of the present application can 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 negative electrode plate, It is characterized in that The negative electrode plate comprises: A current collector; a first coating disposed on at least one side of the current collector, and a second coating disposed on the first coating; The first coating layer includes a first silicon negative electrode active material, and the second coating layer includes a second silicon negative electrode active material; The first silicon negative electrode active material and the second silicon negative electrode active material contain a modifying element, wherein the modifying element contains an element P, an element Al and an element K; and the following relationship is satisfied: The content of the modifying element satisfies: P 1 <P 2 , Al 1 >Al 2 , K 1 >K 2 , Among them, P 1 、Al 1 and K 1 Respectively represent the contents of element P, element Al and element K in the first silicon negative electrode active material, P 2 、Al 2 and K 2 Respectively represent the contents of element P, element Al and element K in the second silicon negative electrode active material.

2. The secondary battery according to claim 1, It is characterized in that Meet: 1000ppm≤P 2 -P 1 ≤2000ppm.

3. The secondary battery according to claim 1, It is characterized in that Satisfy: 50ppm≤Al 1 -Al 2 ≤1000ppm.

4. The secondary battery according to claim 1, It is characterized in that Meet: 50ppm≤K 1 -K 2 ≤600ppm.

5. The secondary battery according to claim 1, It is characterized in that The modifying element is distributed on the surface and / or inside of the first silicon negative electrode active material or the second silicon negative electrode active material.

6. The secondary battery according to claim 1, It is characterized in that The negative electrode sheet meets the following requirements: 10 mAh / g≤C 2 -C 1 ≤21mAh / g; C 1 mAh / g represents the gram capacity of the first silicon negative electrode active material; C 2 mAh / g represents the gram capacity of the second silicon negative electrode active material.

7. The secondary battery according to claim 4, Features For K 1 500~700ppm, K 2 It is 50~500ppm.

8. The secondary battery according to claim 1, It is characterized in that The negative electrode plate satisfies: 0.94≤PD 2 / PD 1 ≤1.07, PD 1 g / cm 3 represents the compaction density of the first coating in the negative electrode sheet, PD 2 g / cm 3 It represents the compaction density of the second coating layer in the negative electrode sheet.

9. The secondary battery according to claim 1, It is characterized in that The particle size D of the first silicon negative electrode active material V50 is 4.0 to 7.0 μm, and the particle size D of the second silicon negative electrode active material is V50 4.0~7.0μm; Wherein, the particle size D V50 It indicates the particle size corresponding to when the volume accumulation of material particles reaches 50%, in μm.

10. An electrical device, It is characterized in that A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

Images