Secondary battery and electric equipment

Abstract

The invention belongs to the technical field of battery preparation, and particularly relates to a secondary battery and electric equipment. The secondary battery comprises a negative pole piece, wherein the negative pole piece comprises a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector; the negative active material layer comprises a main body region and a thinned region arranged at the edge of the main body region, and the thickness of the thinned region is smaller than that of the main body region; the negative pole piece further comprises an ionic conductive composite material, the ionic conductive composite material makes contact with the thinned area, and the ionic conductive composite material comprises ionic liquid and at least one of a conductive polymer and a sodium ion manganese-based layered oxide. According to the invention, the ionic conductive composite material is added into the negative electrode plate and is in contact with the thinned region, so that the effect of protecting the electrode plate is achieved, the sodium ion conductivity and capacity of the thinned region can be improved, polarization and negative electrode side potential drop in the circulation process can be slowed down, sodium precipitation and side reaction are inhibited, the loss of active sodium is reduced, and the service life of the battery is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery preparation, and particularly relates to a secondary battery and an electric device. BACKGROUND

[0002] At present, lithium ion batteries are widely used in various electronic products and electric vehicles due to their excellent energy density and electrical performance. However, lithium ion batteries have some shortcomings, such as poor cycle stability, obvious long cycle capacity attenuation, poor low-temperature performance, poor safety performance, and easy occurrence of fire and combustion accidents. Compared with lithium ion batteries, sodium ion batteries have a larger cost advantage, better low-temperature and cycle performance, and can make up for the shortcomings of lithium ion batteries.

[0003] The negative electrode sheet of the sodium ion battery is provided with a thinning area, which can improve the battery performance through local structure optimization, but the thinning area is prone to local sodium precipitation due to kinetic problems during charging and discharging, resulting in irreversible loss of active sodium, affecting the safety and service life of the battery. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defects in the prior art that the thinning area provided on the negative electrode sheet of the sodium ion battery can improve the battery performance, but is prone to local sodium precipitation after the charging and discharging process, resulting in irreversible loss of active sodium, reducing the safety and service life of the battery, and thus providing a secondary battery and an electric device.

[0005] To this end, the present application provides the following technical solutions.

[0006] The first aspect of the present application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector;

[0007] The negative electrode active material layer comprises a main body area and a thinning area provided at the edge of the main body area, and the thickness of the thinning area is less than the thickness of the main body area.

[0008] The negative electrode sheet further comprises an ion-conducting composite material, the ion-conducting composite material being in contact with the thinning area, and the ion-conducting composite material comprising an ionic liquid, and at least one of a conductive polymer and a sodium ion manganese-based layered oxide.

[0009] In an embodiment, the ion-conducting composite material is provided on the surface and / or inside the thinning area.

[0010] In an embodiment, the ion-conducting composite material is provided at the edge of the thinning area away from the main body area and in contact with the thinning area.

[0011] In an embodiment, the ionically conductive composite accounts for ≤5 wt% of the mass of the negative electrode tab.

[0012] In an embodiment, the ionically conductive composite comprises an ionic liquid, a conductive polymer, and a sodium-ion manganese-based layered oxide.

[0013] In an embodiment, the mass ratio of the ionic liquid, the conductive polymer, and the sodium-ion manganese-based layered oxide is 1:(2-4):(5-7).

[0014] In an embodiment, the sodium-ion manganese-based layered oxide has a general structure of Na x M1 y M2 z Mn u O2, wherein 0 < x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 < u < 1, y and z cannot be 0 at the same time, and M1 and M2 are independently selected from Li, Al, Ni, Co, Fe, Cu, or Zn;

[0015] The conductive polymer comprises at least one of polyacetylene, polyaniline, polypyrrole, polythiophene, polyphenylene, and fluorene-based conductive polymer.

[0016] The ionic liquid comprises at least one of imidazole-based ionic liquid, pyridine-based ionic liquid, quaternary ammonium salt-based ionic liquid, pyridine alkyl ketone-based ionic liquid, and piperidine-based ionic liquid.

[0017] In an embodiment, the negative electrode active material layer contains a negative electrode active material, the particle Dv50 of the negative electrode active material is 5-10 μm, and the particle Dv50 of the ionically conductive composite is 1-3 μm.

[0018] In an embodiment, the negative electrode active material layer has a compaction density of 0.8-1.2 g / cc.

[0019] The second aspect of the present application provides a use electric device comprising the secondary battery.

[0020] The technical solution of the present application has the following advantages:

[0021] 1. A secondary battery provided by the present application, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector; the negative electrode active material layer comprising a main body region and a thinned region provided at the edge of the main body region, the thickness of the thinned region being less than the thickness of the main body region; the negative electrode sheet further comprising an ionically conductive composite material, the ionically conductive composite material being in contact with the thinned region, the ionically conductive composite material comprising an ionic liquid, and at least one of a conductive polymer and a sodium ion manganese-based layered oxide. The present application adds an ionically conductive composite material to the negative electrode sheet and contacts it with the thinned region, which plays a role in protecting the electrode sheet, can improve the sodium ion conductivity and capacity of the thinned region, the ionically conductive composite material can improve the sodium intercalation kinetics on the negative electrode side, improve the sodium intercalation speed and sodium intercalation capacity, slow down the polarization and the decrease of the potential on the negative electrode side during the cycle, thereby inhibiting the sodium precipitation and side reactions, reducing the loss of active sodium, improving the battery life, and further improving the problem that the prior art negative electrode side cannot accept active sodium from the positive electrode in time and the potential on the negative electrode side decreases to the potential at which active sodium is reduced to elemental sodium during the cycle, resulting in a decrease in the level of kinetics and a decrease in sodium ion conductivity, resulting in sodium precipitation. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the description of the specific embodiments or prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0023] Figure 1 is a structural schematic diagram of the positive electrode sheet in Example 1 of the present application;

[0024] Figure 2 is a structural schematic diagram of the positive electrode sheet in Example 2 of the present application;

[0025] Figure 3 is a structural schematic diagram of the positive electrode sheet in Example 3 of the present application;

[0026] Reference signs:

[0027] 1 - conductive region; 2 - main body region; 3 - thinned region; 4 - current collector; 5 - composite thinned region. DETAILED DESCRIPTION

[0028] The following examples are provided to better enable those skilled in the art to further understand the application, and are not intended to limit the content and protection scope of the application, and do not constitute a limitation on the content and protection scope of the application, and any person who obtains any product identical or similar to the application under the enlightenment of the application or combines the application with other prior art features falls within the protection scope of the application.

[0029] If the specific experimental steps or conditions are not indicated in the examples, the operation or conditions can be carried out according to the conventional experimental steps described in the literature in the art. If the reagents or instruments used are not indicated by the manufacturer, they are conventional reagent products that can be obtained by purchase.

[0030] A thinning area is provided in the negative electrode sheet of the sodium ion battery, which improves the battery performance through local structure optimization. The thinning area can reduce the influence of edge effect on the battery performance, improve the cycle life and energy density, avoid excessive spreading of the middle coating to both sides during rolling, and ensure the uniformity of the transverse thickness of the sheet. The thinning area as a transition buffer area can reduce the problem of poor laser cutting caused by differences in material properties. However, during charging and discharging, the thinning area is prone to local sodium precipitation due to kinetic problems, leading to irreversible loss of active sodium in the battery, affecting the safety and life of the battery. In order to solve these problems, the application provides a secondary battery and an electric device.

[0031] The application provides a secondary battery, which comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector;

[0032] The negative electrode active material layer comprises a main body area and a thinning area provided at the edge of the main body area, and the thickness of the thinning area is less than that of the main body area.

[0033] The negative electrode sheet further comprises an ion-conducting composite material, which is in contact with the thinning area. The ion-conducting composite material comprises an ionic liquid, and at least one of a conductive polymer and a sodium ion manganese-based layered oxide.

[0034] The application adds an ion-conducting composite material to the negative electrode sheet, which is in contact with the thinning area, and plays a protective role for the sheet. The ion-conducting composite material can improve the sodium ion conductivity and capacity of the thinning area, improve the sodium intercalation kinetics on the negative electrode side, improve the sodium intercalation speed and capacity, slow down the polarization and potential drop on the negative electrode side during the cycle process, thereby inhibiting sodium precipitation and side reactions, reducing the loss of active sodium, improving the battery life, and further improving the problems of the prior art, such as the inability of the negative electrode side to accept active sodium from the positive electrode, the potential drop on the negative electrode side during the cycle process to the potential of reducing active sodium to elemental sodium, the decrease in the kinetic level, the deterioration of the sodium ion conductivity, and the sodium precipitation.

[0035] Ionic liquids in ion-conducting composite materials possess excellent ionic conductivity and good solubility, serving as excellent solvents for other substances and improving slurry stability. Ionic liquids also have the advantages of being non-flammable and non-explosive, acting as flame retardants in batteries and enhancing battery safety. Conductive polymers can increase the active sites in ion-conducting composite materials, improving the electrode's sodium storage capacity, accelerating the insertion of sodium from the positive electrode onto the negative electrode side, and exhibiting structural stability and strong conductivity. This enhances the sodium ion conduction capacity in the thinned region, improves sodium insertion kinetics, suppresses sodium deposition and side reactions, and mitigates the increased polarization caused by sodium deposition, thus improving battery cycle life. Sodium-manganese-based layered oxides help improve capacity. By contacting the ion-conducting composite material with the thinned region, sodium-manganese-based layered oxides can compensate for irreversible active sodium loss due to edge effects, mitigate the increased polarization caused by sodium deposition during cycling, and suppress the decrease in negative electrode potential. In this application, the testing methods for ionic liquids, conductive polymers, and sodium-manganese ion-based crystalline oxides are as follows: the negative electrode is obtained by disassembling the battery, and powder containing the ionic conductive composite material is scraped off and sent for testing. Ionic liquids can be detected by reverse detection methods such as HNMR, chromatography, spectrophotometry, or electrochemical quantitative methods; conductive polymers can be detected by reverse detection methods such as infrared spectroscopy, thermogravimetric analysis, or DSC; and sodium-manganese ion-based crystalline oxides can be detected by reverse detection methods such as XRD, XPS, SEM, and TEM.

[0036] As an optional implementation, the ion-conducting composite material is disposed on the surface and / or inside the thinned region.

[0037] The ion-conducting composite material is placed on the surface of the thinned area to form a conductive area and is in contact with the thinned area. This arrangement allows the conductive area to accept sodium ions before the negative electrode, quickly accept sodium ions and conduct them to the negative electrode, further improving sodium conductivity, improving sodium deposition and cycle performance, and acting as a buffer during high-rate charge and discharge processes to reduce polarization internal resistance caused by slow diffusion of sodium ions, reduce polarization heat generation and temperature rise, and improve battery energy retention and fast charging performance.

[0038] The ion-conducting composite material is placed inside the thinning zone. This method involves thoroughly mixing the ion-conducting composite material with the negative electrode active material and coating it onto the surface of the negative electrode current collector to form the thinning zone. The ion-conducting composite material is uniformly distributed as a dispersed phase inside the thinning zone. This method can quickly respond to the deintercalation and intercalation of sodium ions, improve sodium deposition, enhance ion conductivity, reduce edge sodium deposition and irreversible active sodium loss, and help improve battery cycle performance and safety performance.

[0039] As an optional implementation, the ion-conducting composite material is disposed at the edge of the thinned region away from the main region and in contact with the thinned region. The ion-conducting composite material, disposed at the edge of the thinned region away from the main region, forms a conductive region. As the cycling process progresses, the battery polarization gradually increases, and the risk of sodium deposition on the negative electrode side increases. Because the coating weight of the thinned region is less than that of the main region, it receives less sodium from the positive electrode and is more prone to sodium deposition. When the thinned region is on the verge of sodium deposition, sodium ions can diffuse into this conductive region, serving as a "temporary storage point" for sodium ions, alleviating the sodium intercalation pressure in the thinned region, reducing the risk of sodium deposition, and improving battery safety, cycle performance, and lifespan.

[0040] As an optional implementation, the width of the conductive area accounts for ≤4% of the width of the negative electrode sheet. A larger conductive area width affects the coating effect of the main body area, thereby affecting the processing performance of the electrode sheet. It reduces the electrode sheet peel strength and cohesion, easily generates dust particles in subsequent processing, reduces battery yield, and poses a risk of powder shedding during cycling, affecting battery life and safety. Preferably, the ratio of the conductive area width to the width of the negative electrode sheet is ≥1.5%, further improving the sodium deposition suppression effect, improving the coating effect of the conductive area, and improving processing performance. For example, the percentage of the conductive area width to the width of the negative electrode sheet is 1.5%, 1.8%, 2%, 2.2%, 24%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, etc.

[0041] And / or, the width of the thinned region accounts for ≤5% of the width of the negative electrode sheet. For example, the percentage of the width of the thinned region to the width of the negative electrode sheet is 0.5%, 1.5%, 2%, 2.2%, 24%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.5%, 5%, etc.

[0042] As an optional implementation, the thinning region gradually thins along the main body region toward the edge of the electrode, and the difference between the maximum and minimum thickness of the thinning region is 5μm-12μm. For example, the difference between the maximum and minimum thickness of the thinning region is 5μm, 6.5μm, 8μm, 9μm, 10μm, 12μm, etc.

[0043] As an optional implementation, the difference between the thickness of the conductive region and the minimum thickness of the thinned region is 5μm-10μm. When the difference between the thickness of the conductive region and the minimum thickness of the thinned region is within this range, excessive extension of the conductive region towards the edge is avoided during rolling, improving thickness consistency. For example, the difference between the thickness of the conductive region and the minimum thickness of the thinned region can be 5μm, 6.5μm, 8μm, 9μm, 10μm, etc.

[0044] As an optional embodiment, the mass ratio of the ion-conductive composite material in the negative electrode sheet is ≤5 wt%, which can improve the kinetic level in the thinning area, is beneficial to suppressing sodium deposition, and further improves the safety performance and electrical performance of the battery. Excessive use of the ion-conductive composite material will increase costs, increase processing difficulty, and affect the capacity.

[0045] As an optional embodiment, the ion-conductive composite material includes an ionic liquid, a conductive polymer, and a sodium manganese-based layered oxide. The ionic liquid can act as a good solvent during the slurry mixing process, making the slurry evenly dispersed and improving the slurry stability. The conductive polymer can also improve the conductivity of the manganese-based layered oxide. After the three are mixed, they can better play the role of sodium conduction and reduce the loss of active sodium.

[0046] As an optional embodiment, the mass ratio of the ionic liquid, the conductive polymer, and the sodium manganese-based layered oxide is 1:(2 - 4):(5 - 7). When the ionic liquid, the conductive polymer, and the sodium manganese-based layered oxide in the present application satisfy the above mass ratio, it can ensure that the electrode sheet has good processing performance, improve the problem of powder falling off at the edge and conduction area of the electrode sheet, increase the peel strength and cohesion of the electrode sheet, and reduce the internal resistance of the membrane sheet. Exemplarily, the mass ratio of the ionic liquid, the conductive polymer, and the sodium manganese-based layered oxide is 1:2:5, 1:3:7, 1:4:5, 1:3:6, 1:2.5:5.5, 1:3.5:6.5, etc.

[0047] As an optional embodiment, the sodium manganese-based layered oxide has a structural general formula Na x M1 y M2 z Mn u O2, where 0 < x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 < u < 1, y and z are not both 0, and M1 and M2 are each independently selected from Li, Al, Ni, Co, Fe, Cu, or Zn; optionally, 0 < x < 2 / 3, 0 ≤ y < 1 / 3, 0 ≤ z < 1 / 3, 0 < u < 2 / 3; the layered oxide satisfying the above general formula is beneficial to further improving the sodium conduction ability and safety.

[0048] The conductive polymer includes at least one of polyacetylene, polyaniline, polypyrrole, polythiophene, polyphenylene, and fluorene-based conductive polymers; optionally, the conductive polymer includes at least one of polyacetylene, polyaniline, polypyridine, polythiophene, polyphenylene, and fluorene-based conductive polymers.

[0049] The ionic liquid includes at least one of imidazole ionic liquids, pyridine ionic liquids, quaternary ammonium salt ionic liquids, pyridinone ionic liquids, and piperidine ionic liquids; for example, the ionic liquid includes one or more of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, N-butylpyridine tetrafluoroborate, N-hexyl-4-methylpyridine hexafluorophosphate, triethylmethylammonium chloride, tetrabutylammonium bromide, N-methyl-N-ethylpyrrolidine bis(trifluoromethanesulfonyl)imide, N-methyl-N-butylpyrrolidine tetrafluoroborate, and N-ethyl-N-methylpiperidine tetrafluoroborate.

[0050] As an optional implementation, the negative electrode active material layer contains a negative electrode active material with a particle size Dv50 of 5μm-10μm, and the ion-conducting composite material has a particle size Dv50 of 1μm-3μm. The particle size of the ion-conducting composite material in this application is smaller than that of the negative electrode active material, allowing for better distribution of the ion-conducting composite material within the electrode, providing more active sites, improving sodium intercalation capability, and enhancing battery cycle performance. Smaller particle sizes also provide more active sites, shorten the sodium ion diffusion path, and improve sodium ion conductivity. Optionally, the particle size Dv99 of the negative electrode active material is 10μm-15μm, and the particle size Dv99 of the ion-conducting composite material is 5μm-8μm. Excessively small particle sizes affect compaction density and increase side reactions, leading to gas production. For example, the particle Dv50 of the negative electrode active material is 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm; the particle Dv50 of the ion-conducting composite material is 1μm, 2μm, or 3μm, etc.

[0051] As an optional implementation, the compaction density of the negative electrode active material layer is 0.8 g / cc-1.2 g / cc. An ion-conducting composite material is disposed on the surface of the thinned area, forming a conductive zone with a compaction density of 2 g / cc-2.5 g / cc. The ion-conducting composite material is also disposed at the edge of the thinned area away from the main body area, forming a conductive zone with a compaction density of 2 g / cc-2.5 g / cc. In this application, the compaction density of the conductive zone formed by the ion-conducting composite material is higher than that of the negative electrode active material layer. Since the thickness of the conductive zone is slightly thinner than that of the thinned area, adjusting the compaction density of the conductive zone results in a smaller thickness of the conductive zone under the same rolling pressure. When the conductive zone is disposed at the edge of the thinned area away from the main body area, it can improve problems such as bulging at the electrode edge due to differences in material ductility.

[0052] As an optional implementation, the negative electrode sheet is prepared using a method known in the art. Exemplarily, it includes: preparing a negative electrode active material slurry with a viscosity range of 4000-7000 cp for later use; mixing an ionic liquid with a conductive polymer and / or a sodium-manganese base oxide to obtain an ion-conducting composite slurry with a viscosity range of 3000-8000 cp for later use. First, the negative electrode active material slurry is coated onto the negative electrode current collector to form a main body region and a thinned region. Then, the ion-conducting composite slurry is coated onto the surface of the thinned region or its edge away from the main body region, and dried to obtain the negative electrode sheet; or, first, a portion of the negative electrode active material slurry is coated onto the negative electrode current collector to form a main body region, and then the remaining negative electrode active material slurry is mixed with the ion-conducting composite slurry and coated onto the negative electrode current collector to form a thinned region.

[0053] This application provides an electrical device including the aforementioned secondary battery.

[0054] Example 1

[0055] This embodiment provides a secondary battery, including:

[0056] Negative electrode plate: The structure of the negative electrode plate is as follows Figure 1 As shown; hard carbon, conductive agent acetylene black, and binder (SBR and CMC in a mass ratio of 1.5:1) were added to water at a ratio of 95.5:3:1.5 and thoroughly mixed using a high-speed mixer to form a negative electrode slurry with a viscosity of 4000-5500 cp. Sodium ion manganese-based layered oxide (Na... 2 / 3 Ni 1 / 3 Mn 2 / 3 O2), conductive polymer polyacetylene, ionic liquid (triethylmethylammonium chloride) are thoroughly mixed with water, PAA (polyacrylic acid), and auxiliary materials (SBR, conductive carbon black, and CMC) at a mass ratio of 1:3:6 to obtain an ion-conductive composite slurry. The slurry contains 45 wt% water, 2 wt% PAA, and 6 wt% auxiliary materials. The negative electrode slurry is coated onto one surface of copper foil 4, and the coating thickness is controlled to form a negative electrode active material layer with a thinned region. This layer includes a main region 2 and a thinned region 3 located at the edge of the main region 2. The width of the thinned region 3 accounts for 5% of the width of the negative electrode sheet, and the interface thickness (maximum thickness) between the thinned region 3 and the main region 2 is 185 μm. The ion-conductive composite slurry is then coated onto the edge of the thinned region 3 away from the main region 2 through an auxiliary channel to form a conductive region 1. (See schematic diagram). Figure 1The electrode is then placed in contact with the thinned region 3, where the thickness (minimum thickness) of the thinned region 3 is 175 μm. The width of the conductive region 1 accounts for 2% of the width of the negative electrode sheet, and the thickness of the conductive region 1 is 165 μm. The electrode is then dried in a multi-section series oven using a gradient drying method to avoid cracking and bulging of the coated dry film. After drying, the electrode sheet is rolled to obtain an electrode sheet with a certain compaction density. The compaction density of the negative electrode active material layer is 0.95 g / cc, and the compaction density of the conductive region 1 is 2.2 g / cc.

[0057] Positive electrode plate: Positive active material NaFe 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, conductive agent Super P, and binder PVDF are mixed in a mass ratio of 95.5:2.1:2.4, and solvent NMP is added. The mixture is kneaded for 1 hour to prepare a positive electrode slurry with a viscosity of 4000-7000 cp. The slurry is coated onto one side of an aluminum foil by extrusion coating and dried. The same positive electrode slurry is then coated onto the other side of the aluminum foil and dried to obtain a double-coated positive electrode sheet.

[0058] Electrolyte: consists of MC:DMC:PC in a volume ratio of 1:1:1; the concentration of NaPF6 in the electrolyte is 1 mol / L.

[0059] Separator: a PE base film with a thickness of 12μm and a PVDF coating layer with a thickness of 5μm on one surface of the base film, and an alumina ceramic layer with a thickness of 3μm on the other surface of the base film.

[0060] A battery is obtained by sequentially stacking the positive electrode, the separator, and the negative electrode, and then injecting electrolyte.

[0061] Example 2

[0062] This embodiment provides a secondary battery, which is basically the same as that in Embodiment 1, except that: an ion-conducting composite slurry is coated on the surface of the thinned region (denoted as the longitudinal direction), such as... Figure 2 As shown, all other parameters are the same.

[0063] Example 3

[0064] This embodiment provides a secondary battery, which is basically the same as that in Embodiment 1, except that: the ion-conducting composite slurry is mixed with the negative electrode slurry, so that the ion-conducting composite material is uniformly dispersed as a dispersed phase inside the thinned region. The composition of these two slurries is the same as that in Embodiment 1, such as... Figure 3 As shown, the negative electrode sheet includes copper foil 4, main body region 2, and composite thinning region 5.

[0065] Examples 4-6

[0066] This embodiment provides a secondary battery, which is basically the same as that in Embodiment 1, except that the mass ratio of the ion-conducting composite material to the negative electrode sheet is different.

[0067] Examples 7-10

[0068] This embodiment provides a secondary battery that is basically the same as that in Embodiment 1, except that the mass ratio of ionic liquid, conductive polymer and sodium ion manganese base oxide is different.

[0069] Examples 11-14

[0070] This embodiment provides a secondary battery, which is basically the same as that in Embodiment 1, except that: in Embodiments 11-14, the sodium-manganese base oxide is NaFe. 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, the types of ionic liquids and conductive polymers in Examples 11-14 are shown in Table 1.

[0071] Examples 15-16

[0072] This embodiment provides a secondary battery that is basically the same as that in Embodiment 1, except that the particle Dv50 of the negative electrode active material is different.

[0073] Examples 17-18

[0074] This embodiment provides a secondary battery, which is basically the same as that in Embodiment 1, except that the particle Dv50 of the ion-conducting composite material is different.

[0075] Examples 19-20

[0076] This embodiment provides a secondary battery that is basically the same as that in Embodiment 1, except that the compaction density of the negative electrode active material layer is different.

[0077] Example 21

[0078] This embodiment provides a secondary battery that is basically the same as that in Embodiment 1, except that polyacetylene is not added during the preparation of the negative electrode sheet.

[0079] Example 22

[0080] This embodiment provides a secondary battery, which is basically the same as that in Embodiment 1, except that layered oxide Na is not added during the preparation of the negative electrode sheet. 2 / 3 Ni 1 / 3 Mn 2 / 3 O2.

[0081] Comparative Example 1

[0082] This comparative example provides a secondary battery that is basically the same as that in Example 1, except that the negative electrode does not contain ion-conducting composite material.

[0083] Table 1 Parameters of each embodiment

[0084]

[0085]

[0086] Test case

[0087] This test case provides performance tests of the secondary batteries provided in various embodiments and comparative examples, as detailed below:

[0088] Test method for sodium deposition performance: Disassemble the battery after 1000 cycles (EOL battery), observe the interface of the negative electrode for sodium deposition points, and judge the degree of sodium deposition based on the proportion A of sodium deposition to the entire electrode: No sodium deposition: 0% ≤ A < 2%; Slight sodium deposition: 2% ≤ A < 5%; Localized sodium deposition: 5% ≤ A < 10%; Large-area sodium deposition: 10% ≤ A < 100%.

[0089] Cyclic performance test method: (1) Charging: 1C constant current and constant voltage charging to the upper voltage limit of 3.95V, cutoff current is 0.05C; (2) Resting: rest for 30 minutes; (3) Discharging: 1C constant current discharge to the lower voltage limit of 2V; (4) Resting: rest for 30 minutes; (5) Cycle steps 1-4 1000 times, the cycle test ends. The capacity retention rate is used to characterize the cycle performance. The capacity retention rate = battery discharge capacity in the 1000th cycle / battery discharge capacity in the 1st cycle × 100%.

[0090] DCR growth rate test method: (1) Charging: 0.33C n (1) Charge with constant current and constant voltage to the upper voltage limit of 3.95V, with a cutoff current of 0.05C; (2) Let stand: stand for 30 minutes; (3) Discharge: 0.33C n (3) Constant current discharge for 90 minutes (adjust to 50% SOC); (4) Rest: let stand for 30 minutes; (5) Discharge: 3C0 constant current discharge for 10 seconds; (6) Rest: let stand for 30 minutes. Among them, C0 and C n The capacitance values ​​are divided into round 0 and round 1000; the end voltage value of step 4 in round 1000 is V1 and the end voltage value of step 5 is V2, and the end current value of constant current discharge in step 5 is I. The formula for calculating the DCR growth rate is as follows:

[0091] DCR growth rate = 100% × (V1 - V2) / I.

[0092] Table 2 Test Results

[0093]

[0094]

[0095] Based on the above results, the addition of ion-conducting composite material to the negative electrode in this application plays a protective role for the electrode, which can improve sodium deposition, reduce active sodium loss and polarization, and improve battery life.

[0096] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A secondary battery, characterized in that, The negative electrode includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; The negative electrode active material layer includes a main region and a thinned region disposed at the edge of the main region, wherein the thickness of the thinned region is less than the thickness of the main region; The negative electrode sheet further comprises an ion-conducting composite material, which is in contact with the thinned region. The ion-conducting composite material comprises an ionic liquid and at least one of a conductive polymer and a sodium ion manganese-based crystalline oxide.

2. The secondary battery according to claim 1, characterized in that, The ion-conducting composite material is disposed on the surface and / or inside the thinned region.

3. The secondary battery according to claim 1, characterized in that, The ion-conducting composite material is disposed at the edge of the thinned region away from the main region and is in contact with the thinned region.

4. The secondary battery according to claim 1, characterized in that, The ion-conducting composite material accounts for ≤5 wt% of the mass of the negative electrode sheet.

5. The secondary battery according to claim 1, characterized in that, The ion-conducting composite material comprises an ionic liquid, a conductive polymer, and a sodium ion manganese base oxide.

6. The secondary battery according to claim 5, characterized in that, The mass ratio of the ionic liquid, the conductive polymer, and the sodium ion manganese base oxide is 1:(2-4):(5-7).

7. The secondary battery according to any one of claims 1-6, characterized in that, The sodium-ion manganese-based layered oxide has a structural general formula Na x M1 y M2 z Mn u O2, where 0 < x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 < u < 1, y and z are not simultaneously 0, and the M1 and M2 are each independently selected from Li, Al, Ni, Co, Fe, Cu or Zn; The conductive polymer includes at least one of polyacetylene, polyaniline, polypyrrole, polythiophene, polyphenylene and fluorene-based conductive polymers; The ionic liquid includes at least one of imidazole ionic liquids, pyridine ionic liquids, quaternary ammonium salt ionic liquids, pyridinone ionic liquids, and piperidine ionic liquids.

8. The secondary battery according to claim 1, characterized in that, The negative electrode active material layer contains a negative electrode active material, the particle size of which is 5μm-10μm, and the particle size of the ion-conducting composite material is 1μm-3μm.

9. The secondary battery according to claim 1, characterized in that, The compaction density of the negative electrode active material layer is 0.8 g / cc-1.2 g / cc.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-9.

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