Sodium ion secondary battery

Abstract

The invention discloses a sodium ion secondary battery, and belongs to the technical field of batteries. According to the sodium ion secondary battery disclosed by the invention, the current collector with a special structure and the composite active material layer with gradient active material content are constructed in the negative pole piece, so that the volume expansion problem of the tin-based material in the pole piece in the sodium deintercalation process of the sodium ion secondary battery is obviously relieved; the mechanical stability and the electric contact property of the pole piece are improved, and the sodium ion secondary battery has high sodium storage activity and high cycle stability.

Description

Technical Field

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

[0002] Due to the size limitation of the intercalated and deintercalated ions, sodium-ion secondary batteries have technical bottlenecks in terms of capacity, rate performance, and cycle stability that need to be overcome. At present, the common negative electrode active materials for sodium-ion secondary batteries are carbon-based materials such as hard carbon materials. These materials have high electrochemical stability but low sodium storage capacity. In contrast, metal-based materials have higher sodium storage capacity when used as negative electrode active materials for sodium-ion secondary batteries. For example, the theoretical sodium storage capacity of metallic tin is as high as 847 mAh / g. However, tin-based materials actually have serious volume expansion problems during sodium intercalation and deintercalation, which may cause the pole piece material to pulverize, fail, and fall off, ultimately leading to a sharp decline in battery capacity. Summary of the invention

[0003] The purpose of the present application is to overcome the shortcomings of the prior art and provide a sodium ion secondary battery. By constructing a current collector with a special structure and a composite active material layer with a gradient active material content in the negative electrode plate, the volume expansion problem of the tin-based material in the plate during the sodium insertion and extraction process of the sodium ion secondary battery is significantly alleviated, the mechanical stability and electrical contact of the plate are improved, and the sodium ion secondary battery has high sodium storage activity and high cycle stability.

[0004] To achieve the above-mentioned object, in a first aspect of the present application, the present application provides a sodium ion secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a current collector, a grid groove arranged on the current collector, and a conductive coating arranged on the surface of the current collector and around the grid groove;

[0005] The grid groove is filled with a first active material layer, and a second active material layer is arranged on a side of the first active material layer away from the grid groove; the first active material layer and the second active material layer contain tin-based materials;

[0006] The negative electrode sheet satisfies: L 1 >L 2 ;

[0007] Where L 1 % is the mass percentage of the tin-based material in the first active material layer;

[0008] Where L 2 % is the mass percentage of the tin-based material in the second active material layer.

[0009] As an embodiment of the present application, the single area of ​​the grid groove is 0.25 to 16 cm 2 .

[0010] As an implementation scheme of the present application, the thickness of the grid groove is 5 to 10 μm.

[0011] As an implementation scheme of the present application, the height of the grid groove is 50 to 200 μm.

[0012] As an embodiment of the present application, the thickness of the conductive coating is 1 to 5 μm.

[0013] Further preferably, the conductive coating contains at least one of graphene, carbon nanotubes, metallic copper and metallic silver.

[0014] As an embodiment of the present application, the tin-based material includes at least one of elemental tin, tin oxide, and tin sulfide.

[0015] As an embodiment of the present application, in the sodium ion secondary battery, L 1 =96~98%.

[0016] As an embodiment of the present application, in the sodium ion secondary battery, L 2 =80~90%.

[0017] As an embodiment of the present application, the sodium ion secondary battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer contains a positive electrode active material.

[0018] Further preferably, the sodium ion secondary battery satisfies: (M 3 ×L 3 ×C 3 ) / (M 1 ×L 1 ×C 1 )=0.99~1.01;

[0019] Further preferably, the sodium ion secondary battery satisfies: (M 2 ×L 2 ) / (M 1 ×L 1 )=0.1~0.2;

[0020] Among them, M 3 mg / cm 2 is the mass per unit area of ​​the positive electrode active material layer in the positive electrode sheet;

[0021] L 3 % is the mass percentage of the positive electrode active material in the positive electrode active material layer;

[0022] C 3 mAh / g is the reversible capacity of the positive electrode active material at 25°C;

[0023] M 1 mg / cm 2 is the mass per unit area of ​​the first active material layer in the negative electrode sheet;

[0024] C 1 mAh / g is the reversible capacity of the tin-based material in the negative electrode at 25°C;

[0025] M 2 mg / cm 2 It is the mass per unit area of ​​the second active material layer in the negative electrode sheet.

[0026] More preferably, M 3 =80~350mg / cm 2 ;

[0027] More preferably, L 3 =95~97%;

[0028] More preferably, C 3 =130~160mAh / g;

[0029] More preferably, M 1 =20~100mg / cm 2 ;

[0030] More preferably, C 1 =450~800mAh / g;

[0031] More preferably, M 2 =4~17mg / cm 2 .

[0032] As an embodiment of the present application, at least one of the first active material layer and the second active material layer further comprises a conductive agent and / or a binder;

[0033] Further preferably, the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers;

[0034] Further preferably, the binder includes at least one of styrene-butadiene rubber, water-based acrylic resin, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0035] As an implementation scheme of the present application, the peeling force of the negative electrode sheet is 8 to 20 N / m, and the resistance is 0.75 to 1.15 mΩ.

[0036] In a second aspect of the present application, the present application provides an electrical device, comprising the sodium ion secondary battery, wherein the sodium ion secondary battery serves as a power supply for the electrical device.

[0037] The beneficial effects of this application are:

[0038] The present application provides a sodium ion secondary battery, a sodium ion secondary battery, which significantly alleviates the volume expansion problem of the tin-based material in the electrode during the sodium insertion and extraction process of the sodium ion secondary battery by constructing a current collector with a special structure and a composite active material layer with a gradient active material content in the negative electrode electrode, and improves the mechanical stability and electrical contact of the electrode. The sodium ion secondary battery has high sodium storage activity and high cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the structure of the negative electrode plate of the sodium ion secondary battery described in this application. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0041] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0042] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0043] The present application is further described below with specific embodiments:

[0044] The embodiment of the present application provides a sodium ion secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a current collector, a grid groove arranged on the current collector, and a conductive coating arranged on the surface of the current collector and around the grid groove;

[0045] The grid groove is filled with a first active material layer, and a second active material layer is arranged on a side of the first active material layer away from the grid groove; the first active material layer and the second active material layer contain tin-based materials;

[0046] The negative electrode sheet satisfies: L 1 >L 2 ;

[0047] Where L 1 % is the mass percentage of the tin-based material in the first active material layer;

[0048] Where L 2 % is the mass percentage of the tin-based material in the second active material layer.

[0049] When tin-based materials are used as negative electrode active materials for sodium ion secondary batteries, severe volume expansion occurs during the sodium deintercalation process, which leads to pulverization of the electrode material and even electrical contact failure. For this reason, in the sodium ion secondary battery described in the present application, a mesh-shaped groove is arranged on the current collector during construction and filled with a first active material layer containing a high mass content of tin-based materials. Due to the high strength characteristics of the current collector and the grid restriction, the volume expansion phenomenon of the tin-based material in the first active material layer during sodium deintercalation is effectively alleviated, and since the relative contact area between this part of the material layer and the current collector is increased, its electrical contact activity is also improved; on the other hand, a second active material layer containing a low mass content of tin-based materials is further arranged on the first active material layer, which can be in close contact with and connected to the first active material layer, thereby enhancing the structural stability of the overall electrode, while improving the overall conductivity of the electrode and reducing the charge transfer internal resistance in the system, improving the sodium storage capacity of the overall active material layer, and thus achieving higher conductivity and long-term sodium deintercalation stability, and finally the sodium ion secondary battery has good cycle stability.

[0050] In some embodiments, the single area of ​​the grid groove is 0.25 to 16 cm 2 .

[0051] Further preferably, the single area of ​​the grid groove is 0.25 cm 2 、0.5cm 2 、0.8cm 2 , 1cm 2 , 2m 2 、4cm 2 、8cm 2 , 10cm 2 、12cm 2 、14cm 2 、16cm 2 The range value of one or both of them.

[0052] Since the grid grooves are filled with the first active material layer, the area of ​​a single grid groove will affect the degree to which the grid groove structure alleviates the volume expansion effect of the first active material layer during sodium deintercalation, as well as the overall contact area between the grid groove and the active material layer, thereby affecting the peeling force of the electrode sheet. It will also affect the connectivity between the two active material layers. When the single area size of the grid groove of the current collector on the negative electrode sheet described in the present application is set within the above-mentioned preferred range, the negative electrode sheet can have both higher peeling strength and conductivity, and the sodium ion secondary battery has higher cycle stability.

[0053] In some embodiments, the thickness of the grid grooves is 5 to 10 μm.

[0054] Further preferably, the thickness of the grid groove is in a range of one or any two of 5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0055] On the one hand, the thickness of the grid groove will affect the mechanical strength of the overall current collector, and thus the degree of inhibition and relief of the volume expansion of the tin-based material will also be different; on the other hand, the thickness of the grid groove will also affect the contact area of ​​the filled active material layer, and thus the overall connectivity of the pole piece structure will be different, and the pole piece resistance will also be different. When the thickness of the grid groove on the pole piece described in the present application is set within the above-mentioned preferred range, the product can have both better mechanical strength and electrochemical activity.

[0056] In some embodiments, the height of the grid grooves is 50-200 μm.

[0057] Further preferably, the height of the grid grooves is in the range of one or any two of 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, and 300 μm.

[0058] As the height of the grid groove increases, the contact area between the grid groove and the active material layer becomes larger, and the peeling force of the entire electrode sheet will increase, but the relative electrode sheet resistance will also increase. When the height of the grid groove is preferably within the above range, the electrode sheet can have both better electrode sheet peeling force and electrode sheet conductivity.

[0059] In some embodiments, the conductive coating has a thickness of 1 to 5 μm.

[0060] Further preferably, the thickness of the conductive coating is in a range of one or any two of 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 4.5 μm, and 5 μm.

[0061] The conductive coating provided on the current collector can improve the conductivity of the entire electrode system and reduce the electrode resistance. Under the premise of not affecting the electrode design and the grid groove effect, when the thickness of the conductive coating is selected within the above preferred range, the negative electrode has a higher peeling force and better conductivity, and the cycle stability of the sodium ion secondary battery is better.

[0062] In some embodiments, the conductive coating contains at least one of graphene, carbon nanotubes, metallic copper, and metallic silver.

[0063] When the above preferred types of conductive materials are selected to construct the conductive coating, higher system adaptability and electrode stability can be achieved.

[0064] In some embodiments, the current collector comprises an aluminum current collector.

[0065] Further preferably, the current collector and the grid grooves arranged on the current collector are made of the same material.

[0066] In some embodiments, the tin-based material includes at least one of elemental tin, tin oxide, and tin sulfide.

[0067] The sodium ion secondary battery described in the present application is constructed based on the functionality of the negative electrode plate, and can not only use single metal tin as the negative electrode active material, but is also adaptable to other tin-based materials.

[0068] In some embodiments, the L 1 =96~98%.

[0069] More preferably, the L 1 = at least one of 96%, 96.5%, 97%, 97.5%, 98%.

[0070] In some embodiments, the L 2 =80~90%.

[0071] More preferably, the L 2 = at least one of 80%, 82%, 84%, 86%, 88%, 90%.

[0072] By designing a gradient mass percentage of the tin-based material in the two active material layers and setting the mass percentage within the above-mentioned preferred range, the ion / electron conduction of the entire electrode system can be effectively coordinated, the sodium deintercalation efficiency can be improved, and the stability of sodium ions when they are deintercalated in different structural layers can also be ensured.

[0073] The L 1 and L 2The test method is as follows: the sodium ion secondary battery is disassembled and the negative electrode sheet is taken out, and then the first active material layer in the grid groove and the surface layer of the second active material layer on the grid groove are scraped and collected respectively, and the initial weight is recorded, and then placed in a thermogravimetric-mass spectrometry coupling tester, helium is introduced and heated, with a maximum temperature of 800°C, and the secondary weight of the remaining sample is recorded, and then the remaining sample material is soaked and dissolved in dilute hydrochloric acid for 2 hours, and then washed and dried with water, and the final weight of the sample is weighed and recorded. The weight of the active material in the active material layer is the initial weight-secondary weight-final weight, and L 1 and L 2 That is, 100% in the active material layer x weight of active material / initial weight.

[0074] In some embodiments, the sodium ion secondary battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer contains a positive electrode active material.

[0075] Further preferably, the sodium ion secondary battery satisfies at least one of the following conditions:

[0076] (1)(M 3 ×L 3 ×C 3 ) / (M 1 ×L 1 ×C 1 )=0.99~1.01;

[0077] (2)(M 2 ×L 2 ) / (M 1 ×L 1 )=0.1~0.2;

[0078] Among them, M 3 mg / cm 2 is the mass per unit area of ​​the positive electrode active material layer in the positive electrode sheet;

[0079] L 3 % is the mass percentage of the positive electrode active material in the positive electrode active material layer;

[0080] C 3 mAh / g is the reversible capacity of the positive electrode active material at 25°C;

[0081] M 1 mg / cm 2 is the mass per unit area of ​​the first active material layer in the negative electrode sheet;

[0082] C 1 mAh / g is the reversible capacity of the tin-based material in the negative electrode at 25°C;

[0083] M 2 mg / cm 2 It is the mass per unit area of ​​the second active material layer in the negative electrode sheet.

[0084] By the preferred setting of the above relationship, there is better adaptability between the positive electrode active material and the negative electrode active material, and between the active materials in the first active material layer and the second active material layer, and the sodium ion secondary battery has a lower risk of sodium precipitation during charging and discharging.

[0085] It should be noted that the above conditions can be adjusted by adjusting different material types when setting C 1 and C 3 The L can be adjusted by adjusting the active material slurry formula during the preparation of the electrode. 1 , L 2 and L 3 , M can be adjusted by adjusting the coating thickness of the active material layer 1 、M 2 and M 3 .

[0086] In some embodiments, the M 3 =80~350mg / cm 2 ;

[0087] Further preferably, the M 3 =80mg / cm 2 、85mg / cm 2 、85.4mg / cm 2 、88mg / cm 2 、90mg / cm 2 、100mg / cm 2 、120mg / cm 2 、150mg / cm 2 、170mg / cm 2 、170.7mg / cm 2 , 200mg / cm 2 、250mg / cm 2 、300mg / cm 2 、340mg / cm 2 、350mg / cm 2 The range value of one or both of them.

[0088] In some embodiments, the L 3 =95~97%;

[0089] More preferably, the L 3=A range value of one or any two of 95%, 95.5%, 96%, 96.5%, 97%.

[0090] In some embodiments, the C 3 =130~160mAh / g;

[0091] Further preferably, the C 3 =A range value of one or any two of 130 mAh / g, 140 mAh / g, 145 mAh / g, 150 mAh / g, and 160 mAh / g.

[0092] By setting and selecting the positive electrode active material in the above-mentioned preferred positive electrode plate, the first active material layer with a high mass content of the negative electrode plate described in the present application can be better matched, so that the sodium deintercalation efficiency of the sodium ion secondary battery is higher and the long-cycle stability is better.

[0093] In some embodiments, the C 1 =450~800mAh / g;

[0094] Further preferably, the C 1 =A range value of one or any two of 450 mAh / g, 480 mAh / g, 500 mAh / g, 550 mAh / g, 600 mAh / g, 650 mAh / g, 700 mAh / g, 750 mAh / g, and 800 mAh / g.

[0095] In some embodiments, the M 1 =20~100mg / cm 2 ;

[0096] Further preferably, the M 1 =20mg / cm 2 , 23mg / cm 2 , 25mg / cm 2 、28mg / cm 2 、30mg / cm 2 、32mg / cm 2 、35mg / cm 2 , 40mg / cm 2 , 42mg / cm 2 , 45mg / cm 2 , 46mg / cm 2 、50mg / cm 2 、55mg / cm 2 、60mg / cm 2 、70mg / cm 2 、80mg / cm 2 、90mg / cm2 、92mg / cm 2 、95mg / cm 2 、100mg / cm 2 The range value of one or both of them.

[0097] In some embodiments, the M 2 =4~17mg / cm 2 ;

[0098] Further preferably, the M 2 =4mg / cm 2 , 4mg / cm 2 , 4.1mg / cm 2 , 4.5mg / cm 2 , 4.8mg / cm 2 , 5mg / cm 2 , 5.5mg / cm 2 , 6mg / cm 2 , 7mg / cm 2 、7.5mg / cm 2 、7.8mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 、14mg / cm 2 、15mg / cm 2 、16mg / cm 2 、16.2mg / cm 2 、17mg / cm 2 The range value of one or both of them.

[0099] In the negative electrode plate of the sodium ion secondary battery described in the present application, the first active material layer and the second active material layer are interconnected and play different roles. When there is a gradient in the mass content of the active materials of the two, further setting the mass per unit area of ​​the active materials within the above-mentioned preferred range can ensure lower resistance of the plate and lower volume expansion effect of the active material layer.

[0100] In some embodiments, at least one of the first active material layer and the second active material layer further comprises a conductive agent and / or a binder;

[0101] The conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers;

[0102] The binder includes at least one of styrene-butadiene rubber, water-based acrylic resin, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0103] Selecting the above-mentioned preferred conductive agent and binder to construct the active material layer can ensure better interlayer connectivity of the negative electrode plate, better electrical contact effect, and lower plate resistance.

[0104] In some embodiments, the negative electrode sheet has a peeling force of 8 to 20 N / m and a resistance of 0.75 to 1.15 mΩ.

[0105] Further preferably, the peeling force of the negative electrode sheet is 8N / m, 8.5N / m, 8.8N / m, 9N / m, 9.4N / m, 9.5N / m, 10N / m, 10.5N / m, 11N / m, 11.5N / m, 11.9N / m, 12N / m, 12.6N / m, 13N / m, 13.4N / m, 14N / m, 14.9N / m, 15.1N / m, 15.5N / m, 15.9N / m, 16.1N / m, 16.5N / m, 16.6N / m, 16.8N / m, 17N / m, 17.5N / m, 18N / m, 18.5N / m, 19N / m, 19.8N / m, 20N / m or any two of the range values.

[0106] Further preferably, the resistance of the negative electrode plate is in the range of one or any two of 0.75mΩ, 0.80mΩ, 0.85mΩ, 0.90mΩ, 0.91mΩ, 0.92mΩ, 0.93mΩ, 0.94mΩ, 0.98mΩ, 0.99mΩ, 1.01mΩ, 1.02mΩ, 1.06mΩ, 1.10mΩ, 1.13mΩ, and 1.15mΩ.

[0107] The negative electrode plate of the sodium ion secondary battery described in the present application is based on the design of the current collector and the active material layer, has a high peeling force, high mechanical strength, good conductivity, and low electrode resistance, and can achieve better electrochemical performance when used.

[0108] The present invention is further described below with specific examples, which are not to be construed as limiting the scope of the present invention:

[0109] Example 1

[0110] A sodium ion secondary battery, the preparation method comprising the following steps:

[0111] (1) Preparation of positive electrode sheet: Layered metal oxide Na 0.8 MnO 2As a positive electrode material, the reversible capacity is 160 mAh / g and the particle size is D v50 The thickness of the slurry is 10 μm, and then it is mixed with carbon nanotubes and PVDF in a mass ratio of 97:1.5:1.5, and NMP is used as a solvent to prepare a slurry, which is coated on an aluminum foil current collector, dried, and cut to obtain a positive electrode sheet with a thickness of 150 μm;

[0112] (2) Preparation of negative electrode sheet: an aluminum foil current collector with uniformly arranged grid grooves on one side is provided, a conductive slurry prepared with carbon nanotubes is coated on the surface of the current collector and around the grid grooves, and a conductive coating is formed after drying. Subsequently, metal tin powder is used as the negative electrode active material, with a reversible capacity of 600 mAh / g and a particle size of D v50 The slurry is 3 μm, and then mixed with conductive graphite, CMC, and SBR in a mass ratio of 96:1.5:1:1.5, and the first active material layer slurry is prepared with water as a solvent and coated and filled in the grid groove; the metal tin powder is mixed with conductive graphite, CMC, and styrene-butadiene rubber SBR in a mass ratio of 85:6:3:6, and the second active material layer slurry is prepared with water as a solvent and coated on the grid groove, i.e., the first active material layer, and dried and cut to obtain a negative electrode sheet with a thickness of 120 μm; the structural schematic diagram of the negative electrode sheet is as shown in Figure 1 As shown;

[0113] (3) Assemble the positive electrode sheet, negative electrode sheet and separator (PP base film) into a soft-pack battery cell and inject 1M NaPF 6 The electrolyte prepared by dissolving in EC / DEC (1:1) and 5% FEC solvents is the sodium ion secondary battery.

[0114] The parameters of each sodium ion secondary battery are shown in Tables 1 and 2.

[0115] Embodiments 2 to 22

[0116] A sodium ion secondary battery is different from Example 1 only in that the parameters are set differently, as shown in Tables 1 and 2.

[0117] Embodiment 23

[0118] A sodium ion secondary battery, which differs from Example 1 only in that the layered metal oxide Na 0.8 MnO 2 Replaced by Na 0.74 CoO 2 , reversible capacity is 130mAh / g, particle size D v50 is 10μm.

[0119] Embodiment 24

[0120] A sodium ion secondary battery, which differs from Example 1 only in that the layered metal oxide Na0.8 MnO 2 Replaced by Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 ]O 2 , reversible capacity is 140 mAh / g, particle size D v50 is 10μm.

[0121] Embodiment 25

[0122] A sodium ion secondary battery, the difference from Example 1 is that the metal tin powder is replaced by SnSe 2 , reversible capacity is 450mAh / g, particle size D v50 3μm.

[0123] Embodiment 26

[0124] A sodium ion secondary battery, the difference from Example 1 is that the metal tin powder is replaced by SnS 2 , reversible capacity is 800mAh / g, particle size D v50 3μm.

[0125] Examples 27-28

[0126] A sodium ion secondary battery, which differs from Example 1 only in that parameter settings are different and the thickness of the negative electrode plate is different, as shown in Table 1.

[0127] Comparative Example 1

[0128] A sodium ion secondary battery, which differs from Example 1 only in that:

[0129] The preparation method of the negative electrode plate is as follows: a flat aluminum foil current collector with no surface structure is provided, and metal tin powder is used as the negative electrode active material, with a reversible capacity of 600 mAh / g and a particle size of D v50 The thickness of the negative electrode sheet is 3 μm, and then it is mixed with conductive graphite, CMC, and styrene-butadiene rubber SBR in a mass ratio of 96:1.5:1:1.5. The first active material layer slurry is prepared with water as the solvent and evenly coated on the surface of the current collector. After drying and cutting, a negative electrode sheet with a thickness of 100 μm is obtained.

[0130] Comparative Example 2

[0131] A sodium ion secondary battery, which differs from Example 1 only in that:

[0132] The preparation method of the negative electrode plate is as follows: a flat aluminum foil current collector with no structure on the surface is provided, a conductive slurry prepared by carbon nanotubes is coated on the surface of the current collector, and a conductive coating is formed after drying, and then metal tin powder is used as the negative electrode active material, with a reversible capacity of 600 mAh / g and a particle size of D v50The thickness of the slurry is 3 μm, and then it is mixed with conductive graphite, CMC, and SBR in a mass ratio of 96:1.5:1:1.5, and water is used as a solvent to prepare a first active material layer slurry and apply it on the current collector; the metal tin powder is mixed with the conductive graphite, CMC, and SBR in a mass ratio of 85:6:3:6, and water is used as a solvent to prepare a second active material layer slurry and apply it on the first active material layer, dry, and cut to obtain a negative electrode sheet with a thickness of 120 μm.

[0133] Comparative Example 3

[0134] A sodium ion secondary battery, which differs from Example 1 only in that:

[0135] The preparation method of the negative electrode plate is as follows: a flat aluminum foil current collector with no surface structure is provided, and metal tin powder is used as the negative electrode active material, with a reversible capacity of 600 mAh / g and a particle size of D v50 The thickness of the slurry is 3 μm, and then it is mixed with conductive graphite, CMC, and SBR in a mass ratio of 96:1.5:1:1.5, and water is used as a solvent to prepare a first active material layer slurry and apply it on the current collector; metal tin powder is mixed with conductive graphite, CMC, and styrene-butadiene rubber SBR in a mass ratio of 85:6:3:6, and water is used as a solvent to prepare a second active material layer slurry and apply it on the first active material layer, dry, and cut to obtain a negative electrode sheet with a thickness of 120 μm.

[0136] Comparative Example 4

[0137] A sodium ion secondary battery, which differs from Example 1 only in that:

[0138] The preparation method of the negative electrode plate is as follows: an aluminum foil current collector with uniformly arranged grid grooves on one side is provided, and metal tin powder is used as the negative electrode active material, with a reversible capacity of 600 mAh / g and a particle size D v50 The thickness of the negative electrode sheet is 3 μm, and then it is mixed with conductive graphite, CMC, and SBR in a mass ratio of 96:1.5:1:1.5, and the first active material layer slurry is prepared with water as the solvent and coated on the current collector; dried and cut to obtain a negative electrode sheet with a thickness of 115 μm, that is, the second active material layer slurry coated on the first active material layer in Example 1 is replaced by the first active material layer slurry.

[0139] Comparative Example 5

[0140] A sodium ion secondary battery, which differs from Example 1 only in that:

[0141] The preparation method of the negative electrode plate is as follows: an aluminum foil current collector with uniformly arranged grid grooves on one side is provided, and metal tin powder is used as the negative electrode active material, with a reversible capacity of 600 mAh / g and a particle size D v50The thickness of the slurry is 3 μm, and then it is mixed with conductive graphite, CMC, and SBR in a mass ratio of 85:6:3:6, and water is used as a solvent to prepare a first active material layer slurry, and the slurry is coated and filled in the grid grooves; the metal tin powder is mixed with conductive graphite, CMC, and styrene-butadiene rubber SBR in a mass ratio of 96:1.5:1:1.5, and water is used as a solvent to prepare a second active material layer slurry, and the slurry is coated on the first active material layer, dried, and cut to obtain a negative electrode sheet with a thickness of 110 μm.

[0142] In Table 1 and Table 2, L 1 % is the mass percentage of tin powder in the first active material layer, L 2 % is the mass percentage of the tin-based material in the second active material layer, M 1 mg / cm 2 is the mass per unit area of ​​the first active material layer in the negative electrode sheet, M 2 mg / cm 2 is the mass per unit area of ​​the second active material layer in the negative electrode sheet, S cm 2 is the single area of ​​the grid groove, Rμm is the thickness of the grid groove, Hμm is the height of the grid groove, N nm is the thickness of the conductive coating in the negative electrode sheet, and L 3 % is the mass percentage of the positive electrode active material in the positive electrode active material layer of the positive electrode sheet, M 3 mg / cm 2 is the mass per unit area of ​​the positive electrode active material layer in the positive electrode sheet, A=(M 2 ×L 2 ) / (M 1 ×L 1 ), B=(M 3 ×L 3 ×C 3 ) / (M 1 ×L 1 ×C 1 ), where if no relevant parameters are set in the comparative example, they are marked as “ / ” in the table.

[0143] Table 1

[0144]

[0145]

[0146] Table 2

[0147] parameter <![CDATA[S(cm 2 )]]> R(μm) H(μm) N(nm) Example 1 0.25 5 100 1 Example 2 0.25 5 50 1 Example 3 0.25 5 80 1 Example 4 0.25 5 150 1 Example 5 0.25 5 200 1 Example 6 0.25 10 100 1 Example 7 0.25 9 100 1 Example 8 0.25 8 100 1 Example 9 0.25 6.5 100 1 Example 10 1 5 100 1 Embodiment 11 4 5 100 1 Example 12 8 5 100 1 Embodiment 13 12 5 100 1 Embodiment 14 16 5 100 1 Embodiment 15 0.25 5 100 2 Example 16 0.25 5 100 3 Embodiment 17 0.25 5 100 4 Embodiment 18 0.25 5 100 5 Embodiment 19 0.25 5 100 1 Embodiment 20 0.25 5 100 1 Embodiment 21 0.25 5 100 1 Embodiment 22 0.25 5 100 1 Embodiment 23 0.25 5 100 1 Embodiment 24 0.25 5 100 1 Embodiment 25 0.25 5 100 1 Embodiment 26 0.25 5 100 1 Embodiment 27 0.25 5 100 1 Embodiment 28 0.25 5 100 1 Comparative Example 1 / / / / Comparative Example 2 / / / 1 Comparative Example 3 / / / / Comparative Example 4 0.25 5 100 1 Comparative Example 5 0.25 5 100 1

[0148] Effect example

[0149] The sodium ion secondary batteries obtained in each embodiment and comparative example were tested as follows:

[0150] (1) Negative electrode peeling force test: stick a clean and foreign-free double-sided tape with a width of 25 mm on the steel plate to make the double-sided tape adhere to the steel plate, then stick the cut electrode on the steel plate with the double-sided tape, and roll the electrode back and forth 5 times with a clean roller to make the sample close to the steel plate and not easy to fall off and separate, and then test it with an electronic universal tensile testing machine AGS-X500N; install the fixture (select 50N sensor), screw the tensile connector to the sensor, insert the fixture, then insert the pin, fix the lower connector with bolts, turn the locking nut, adjust the hole position, and then insert the pin; move the crosshead of the testing machine to the installation position of the sample, adjust the GL gauge length, adjust the load and stroke to zero, clamp the sample on the upper fixture, and clamp the sample on the lower fixture; set the load: full scale 50N, load limit 40N; stroke limit 150mm.

[0151] (2) Negative electrode resistance test: The ACCFilm membrane resistance tester is used to test the electrode resistance after confirming that the test probe is clean. That is, the resistance difference of the electrode is not more than 0.1 mΩ after three consecutive tests under no-load conditions. The pressure is 0.400t and the area is 154.025mm 2 The disc electrode is placed on the lower probe, and the pneumatic valve is rotated at a constant speed to lower the upper terminal. After 10 seconds, the computer automatically records the test results. Other parallel batches of electrodes are used to repeat the test for more than 10 times and the average value is taken.

[0152] (3) Cyclic test of sodium ion secondary battery: voltage range is 1.5~4.05V, standing time is 5min, current is 1C, charging stage is 1C charging to 4.05V, 4.05V constant voltage to 0.05C, and discharging stage is 1C discharging to 1.5V.

[0153] The test results are shown in Table 3.

[0154] Table 3

[0155]

[0156]

[0157] From Table 3, we can see that

[0158] (1) Due to the design of the grid grooves on the current collector in the negative electrode sheet and the arrangement of two active material layers with different active material mass percentages, the sodium ion secondary battery described in the present application has a high interlayer connection strength of the overall negative electrode sheet, a high peeling force that can reach 8.5N / m or more, good mechanical properties, and at the same time, the ion / electron transmission efficiency is improved, the conductivity is improved, and the sheet resistance is reduced to less than 1.15mΩ. The volume expansion effect of the tin-based active material during sodium ion deintercalation is effectively limited and alleviated. Therefore, the capacity retention rate of the sodium ion secondary battery can be maintained at 75% or more after 1000 cycles, and the cycle stability is excellent.

[0159] (2) It can be seen from Examples 1 to 14 that the grid grooves on the current collector are filled with the first active material layer with a high mass percentage of active material. Therefore, the height, thickness and single area of ​​the grid grooves will directly affect the relative contact area between the grid grooves and the active material layer. At the same time, the relative specific surface area of ​​the grid grooves will also change. On the one hand, it affects the physical connectivity between the active material layer and the grid grooves and the limiting effect on the active material layer, thereby affecting the peeling force of the negative electrode sheet and the degree of inhibition of the volume effect of the active material during the charge and discharge process. On the other hand, the degree of electrical contact between the materials is also different, thereby affecting the conductivity of the overall electrode system. When constructing the grid grooves on the current collector, selecting the appropriate size and parameter size can make the prepared electrode sheet have both mechanical properties and electrochemical properties, and at the same time can also well reflect the volume effect of the tin-based material, so that the sodium ion secondary battery has a more stable cycle performance.

[0160] (3) It can be seen from Example 1 and Examples 15 to 18 that, in addition to the grid groove arrangement on the current collector, the conductive coating contained therein actually also has a certain influence on the conductive properties and even the physical properties of the negative electrode sheet. It can be seen that as the thickness of the conductive coating increases, the resistance of the negative electrode sheet gradually decreases, and the peeling force also increases from 15.9 N / m to 16.8 N / m, and the comprehensive performance is improved. The corresponding cycle capacity retention rate of the sodium ion secondary battery also increases from 85% to 88%, and the electrochemical performance is improved.

[0161] (4) It can be seen from Examples 1 and 19 to 22 that when the mass percentage of the tin-based material in the first and second active material layers in the negative electrode sheet changes, in order to ensure the reasonable design of the positive and negative electrodes of the secondary battery, the sodium ions are completely deintercalated at the positive and negative electrodes with a stable and sufficient coulombic efficiency, and the risk of sodium precipitation is kept low, the mass per unit area of ​​the active material layer in the negative electrode sheet and even the corresponding parameters of the positive electrode sheet also need to be adjusted synchronously. When L is preferred 1 In the range of 96-98%, L 2In the range of 80 to 90%, when other parameters are adjusted so that coefficient A preferably satisfies the range of 0.1 to 0.2 and coefficient B preferably satisfies the range of 0.99 to 1.01, the negative electrode sheet can have higher peeling force and conductivity, and at the same time, the risk of sodium precipitation in the sodium ion secondary battery is lower and the cycle stability is better.

[0162] As can be seen from Examples 27 and 28, L of the second active material layer 2 and M 2 When a change occurs, the coefficient A related to the structural setting will also change. When the coefficient A changes alone and meets the above-mentioned preferred range, the sodium ion secondary battery can ensure higher charge and discharge performance.

[0163] (5) In the design of the negative electrode plate of the sodium ion secondary battery described in Comparative Example 1, a planar current collector with a grid-free groove structure is adopted, and no conductive coating is provided. After the active material layer containing tin-based materials is constructed on the current collector, the current collector cannot provide assistance for the volume expansion problem of the tin-based materials, and the connectivity and electrical contact with the active material layer are low. Therefore, the peeling force and conductivity of the negative electrode plate are not ideal, and the corresponding sodium ion secondary battery cycle performance is also poor. Based on Comparative Example 1, Comparative Example 2 provides a conductive coating on the planar current collector, and the active material layer is provided with a first and a second active material layer similar to Example 1. This approach can improve the conductivity of the entire plate to a certain extent, and the presence of the second active material layer also has a certain mitigating effect on the volume expansion effect of the tin-based material in the first active material layer, but the degree is not high. Therefore, the performance of the negative electrode plate and the sodium ion secondary battery described in Comparative Example 2 is slightly improved compared with Comparative Example 1, but is far inferior to the product of the embodiment. The negative electrode plate of Comparative Example 3 removes the conductive coating on the basis of Comparative Example 2. It can be clearly seen that even if it is set on a planar current collector, the conductive coating will still improve the mechanical strength and conductivity of the negative electrode plate.

[0164] (6) From the comparison between Example 1 and Comparative Examples 4 to 5, it can be seen that the arrangement of the two active material layers in the negative electrode plate is very critical. Reasonable arrangement of the two active material layers with different active material contents at different positions can take into account the high sodium storage activity of the tin-based material, the plate stability and the electrical contact, so that the negative electrode plate has high-intensity and high electrochemical activity. If the arrangement is improper, even if a collector with a special structure is arranged, the expected effect cannot be achieved.

Claims

1. A sodium ion secondary battery, characterized in that: The negative electrode comprises a negative electrode plate, wherein the negative electrode plate comprises a current collector, a grid groove arranged on the current collector, and a conductive coating arranged on the surface of the current collector and around the grid groove; The grid groove is filled with a first active material layer, and a second active material layer is arranged on a side of the first active material layer away from the grid groove; the first active material layer and the second active material layer contain tin-based materials; The negative electrode sheet satisfies: L1>L2; Wherein L1% is the mass percentage of the tin-based material in the first active material layer; Wherein L2% is the mass percentage of the tin-based material in the second active material layer.

2. The sodium ion secondary battery according to claim 1, characterized in that: The sodium ion secondary battery satisfies at least one of the following conditions: (1) The single area of ​​the grid groove is 0.25 to 16 cm 2 ; (2) The thickness of the grid groove is 5 to 10 μm; (3) The height of the grid groove is 50 to 200 μm.

3. The sodium ion secondary battery according to claim 1, characterized in that: The thickness of the conductive coating is 1-5 μm, and / or the conductive coating contains at least one of graphene, carbon nanotubes, metal copper and metal silver.

4. The sodium ion secondary battery according to claim 1, characterized in that: The tin-based material includes at least one of elemental tin, tin oxide, and tin sulfide.

5. The sodium ion secondary battery according to claim 1, characterized in that: The sodium ion secondary battery satisfies at least one of the following conditions: (1)L1＝96～98％； (2)L2＝80～90％。 6. The sodium ion secondary battery according to claim 1, characterized in that: The sodium ion secondary battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the sodium ion secondary battery satisfies at least one of the following conditions: (1) (M3×L3×C3) / (M1×L1×C1)=0.99~1.01; (2) (M2×L2) / (M1×L1)=0.1-0.2; Where M3 mg / cm 2 is the mass per unit area of ​​the positive electrode active material layer in the positive electrode sheet; L3% is the mass percentage of the positive electrode active material in the positive electrode active material layer; C3 mAh / g is the reversible capacity of the positive electrode active material at 25°C; M1 mg / cm 2 is the mass per unit area of ​​the first active material layer in the negative electrode sheet; C1 mAh / g is the reversible capacity of the tin-based material in the negative electrode at 25°C; M2 mg / cm 2 It is the mass per unit area of ​​the second active material layer in the negative electrode sheet.

7. The sodium ion secondary battery according to claim 6, characterized in that: The sodium ion secondary battery satisfies at least one of the following conditions: <h2 style=";text-align:left;direction:ltr">(1)M3=80~350mg / cm<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> ; (2)L3＝95～97％； (3) C3 = 130-160 mAh / g; (4)M1=20~100mg / cm 2 ; (5) C1 = 450-800 mAh / g; (6)M2=4~17mg / cm 2 。 8. The sodium ion secondary battery according to claim 1, characterized in that: At least one of the first active material layer and the second active material layer further comprises a conductive agent and / or a binder; The conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; The binder includes at least one of styrene-butadiene rubber, water-based acrylic resin, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

9. The sodium ion secondary battery according to claim 1, characterized in that: The negative electrode sheet has a peeling force of 8 to 20 N / m and a resistance of 0.75 to 1.15 mΩ.

10. An electrical device, characterized in that: It comprises the sodium ion secondary battery according to any one of claims 1 to 9, wherein the sodium ion secondary battery is used as a power supply for the electrical device.

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