Battery cell, secondary battery and electric equipment

Abstract

The invention provides a battery cell, a secondary battery and electric equipment. The battery cell comprises a plurality of positive electrode units, a plurality of negative electrode units and diaphragms, the positive electrode units and the negative electrode units are sequentially arranged in an overlapped mode, the diaphragms are located between the positive electrode units and the negative electrode units, and each positive electrode unit comprises a positive electrode current collector, a non-sodium-supplementing positive electrode active layer and a sodium-supplementing positive electrode active layer, the negative electrode unit comprises a negative electrode current collector, a first negative electrode plate and a second negative electrode plate which are respectively arranged on two side surfaces of the negative electrode current collector, and a negative electrode sodium supplementing layer, the negative electrode sodium supplementing layer is positioned on one side, far away from the negative electrode current collector, of the first negative electrode plate, and the negative electrode sodium supplementing layer is arranged towards the non-sodium-supplementing positive electrode active layer in the positive electrode unit; and the sodium-supplementing positive electrode active layer is arranged towards the second negative electrode plate in the negative electrode unit. The overall performance of the battery cell and the battery is improved through the sodium supplementing mode.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery cell, a secondary battery and an electrical device. Background Art

[0002] The abundant reserves of sodium make sodium-ion batteries an environmentally friendly and relatively low-cost battery technology. Sodium supplementation is considered to be a key technology to improve the energy density and life of batteries. By supplementing sodium, the active sodium consumption of the initial film formation of the negative electrode can be compensated, which significantly improves the energy density of the battery. At the same time, since the excess active sodium is pre-existing in the negative electrode, it can compensate for the continuous loss of active sodium during the cycle, thereby effectively improving the cycle and storage life of the battery.

[0003] Although the operation of positive electrode sodium supplementation is simple and highly compatible with the current production line, positive electrode sodium supplementation materials such as sodium chromate (NaCrO2), sodium nickelate (Na2NiO2), and sodium oxalate (Na2C2O4) have disadvantages such as low specific capacity (about 200-400mAh / g), decomposition and obvious gas production during subsequent cycles. For hard carbon systems with low initial efficiency and high specific capacity, conventional positive electrode sodium supplementation methods require the addition of a relatively high proportion (generally greater than 5%) of sodium supplement to compensate for the active sodium consumed in the first film formation, and there is basically no pre-existing sodium in the negative electrode. Therefore, simply supplementing the positive electrode with sodium cannot effectively supplement the hard carbon negative electrode system with sodium and improve the cycle life of the hard carbon negative electrode. In addition, due to the large number of added portions, it brings about problems of residual sodium supplement and gas production. Although the sodium powder and sodium foil of the negative electrode have high specific capacity (the specific capacity of metallic sodium is as high as 1166mAh / g) and adjustable surface density, and can be applied to various systems such as soft carbon, hard carbon and graphite, the process of sodium supplementation of the negative electrode is complex and the safety risk is high. When the double-sided negative electrode of the carbon negative electrode is supplemented with sodium, the solid phase embedding of sodium will make the pole piece brittle and hard and generate obvious heat, and the pole piece flatness is poor. As the amount of sodium supplementation increases, this problem becomes more serious, which poses a serious challenge to the safe circulation of the pole piece and the subsequent process. Therefore, the conventional pre-sodiumization technology has the obvious disadvantages of limited application range and difficulty in mass production. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one object of the present invention is to provide a battery cell that can effectively meet the sodium supplementation demand and has a long service life.

[0005] In one aspect of the present invention, the present invention provides a battery cell. According to an embodiment of the present invention, the battery cell includes a plurality of positive electrode units and negative electrode units that are sequentially overlapped and a separator between the positive electrode units and the negative electrode units, the positive electrode unit includes a positive electrode current collector and a non-sodium-supplemented positive electrode active layer and a sodium-supplemented positive electrode active layer that are respectively arranged on both sides of the positive electrode current collector, the negative electrode unit includes a negative electrode current collector, a first negative electrode sheet and a second negative electrode sheet that are respectively arranged on both sides of the negative electrode current collector, and a negative electrode sodium-supplemented layer, the negative electrode sodium-supplemented layer is located on a side of the first negative electrode sheet away from the negative electrode current collector, wherein the negative electrode sodium-supplemented layer is arranged toward the non-sodium-supplemented positive electrode active layer in the positive electrode unit, and the sodium-supplemented positive electrode active layer is arranged toward the second negative electrode sheet in the negative electrode unit. In the battery cell of the above structure, only one side of the positive electrode unit and the negative electrode unit is provided with sodium supplement material, and one side of the first negative electrode sheet with the negative electrode sodium supplement layer corresponds to the side of the non-sodium supplemented positive electrode active layer, and one side of the second negative electrode sheet without the sodium supplement layer corresponds to the side of the sodium supplemented positive electrode active layer, and the sheets are stacked or wound to form a sodium supplemented battery cell. The above sodium supplementation method overcomes the problems of low sodium supplementation capacity and large addition amount when sodium is supplemented on both sides of the positive electrode alone. Sodium supplementation on one side of the positive electrode can achieve the same sodium supplementation dosage while only supplementing half the mass of the positive electrode active layer, thereby increasing the proportion of sodium supplement agent without changing the mass and achieving a higher sodium supplementation demand, which not only compensates for the active sodium consumed in the first film formation of the negative electrode, but also improves the cycle life of the battery due to the additional active sodium pre-existing in the negative electrode; at the same time, it can overcome the shortcomings of obvious heating of the negative electrode sheet after sodium supplementation on both sides of the negative electrode, poor flatness of the negative electrode sheet and brittleness, which make it impossible to mass produce. It can be seen that the above-mentioned positive and negative electrode cation sodium supplementation method of the present invention fully utilizes the respective advantages of positive and negative electrode sodium supplementation and can achieve mass production, which has practical significance for the realization of high energy density and long life batteries.

[0006] According to an embodiment of the present invention, only one layer of sodium-supplementing structure is included between two adjacent positive electrode current collectors and negative electrode current collectors, and the sodium-supplementing structure is the sodium-supplementing positive electrode active layer or the negative electrode sodium-supplementing layer.

[0007] According to an embodiment of the present invention, the sodium supplement agent in the sodium supplement positive electrode active layer includes Na2NiO2, NaC r At least one of Na2O2, Na2C2O4, Na3N, Na2S, Na3P, Na2CO3, NaNO2, Na2C4O4, Na2C6O6, and Na2C6H2O6, and the negative electrode sodium supplement layer is sodium foil and / or sodium powder.

[0008] According to an embodiment of the present invention, with respect to the total mass of the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer, the content of the sodium-supplementing agent in the sodium-supplemented positive electrode active layer is less than or equal to 40% by mass.

[0009] According to an embodiment of the present invention, with respect to the total mass of the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer, the content of the sodium-supplemented agent in the sodium-supplemented positive electrode active layer is 1.5-10% by mass.

[0010] According to an embodiment of the present invention, for the sodium-supplemented positive electrode active layer, the surface density of the sodium-supplementing agent is 1 g / m 2 ~18g / m 2 .

[0011] According to an embodiment of the present invention, for the sodium-supplemented positive electrode active layer, the surface density of the sodium-supplementing agent is 4 g / m 2 ~16g / m 2 .

[0012] According to an embodiment of the present invention, the surface density of the negative electrode sodium supplement layer is 0.5 g / m 2 ~10g / m 2 .

[0013] According to an embodiment of the present invention, the surface density of the negative electrode sodium supplement layer is 1g / m 2 ~6g / m 2 .

[0014] According to an embodiment of the present invention, the effective active materials in the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer are transition metal oxides Na e MO2, Prussian blue compounds Na f M1[M2(CN)6] and polyanionic compound Na d M g (X a O b ) c Z h At least one of, wherein M, M1 and M2 are respectively one or more transition metal atoms, X is one or more Si, S, P, As, B, Mo, W, Ge elements, and Z is one or more F and OH; the effective active materials of the first negative electrode sheet and the second negative electrode sheet are respectively at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nanocarbon, carbon fiber, silicon negative electrode material and sodium embedded alloy.

[0015] In another aspect of the present invention, the present invention provides a secondary battery. According to an embodiment of the present invention, the secondary battery includes the battery cell described above. As a result, the service life of the secondary battery is long. It can be understood by those skilled in the art that the electrical device has all the features and advantages of the battery cell described above, and no further elaboration is given here.

[0016] In another aspect of the present invention, the present invention provides an electric device. According to an embodiment of the present invention, the electric device includes the secondary battery described above. As a result, the service life of the electric device is long. It can be understood by those skilled in the art that the electric device has all the features and advantages of the secondary battery described above, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0018] Figure 1 It is a schematic diagram of the structure of a battery cell in one embodiment of the present invention. DETAILED DESCRIPTION

[0019] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0020] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0021] In one aspect of the present invention, the present invention provides a secondary battery. Figure 1The secondary battery comprises a plurality of positive electrode units 10 and negative electrode units 20 which are sequentially overlapped and a separator 30 located between the positive electrode units 10 and the negative electrode units 20. The positive electrode unit 10 comprises a positive electrode current collector 13 and a non-sodium-supplemented positive electrode active layer 12 and a sodium-supplemented positive electrode active layer 11 which are respectively arranged on both sides of the positive electrode current collector 13. The negative electrode unit 20 comprises a negative electrode current collector 23, a first negative electrode sheet 21 and a second negative electrode sheet 22 which are respectively arranged on both sides of the negative electrode current collector 23, and a negative electrode sodium-supplementing layer 24. The negative electrode sodium-supplementing layer 24 is located on a side of the first negative electrode sheet 21 away from the negative electrode current collector 23. In the stacked structure of the positive electrode unit and the negative electrode unit, the negative electrode sodium-supplementing layer The layer 24 is arranged toward the side of the non-sodium-supplemented positive electrode active layer 12 in the positive electrode unit 10, and the sodium-supplemented positive electrode active layer 11 is arranged toward the side of the second negative electrode sheet 22 in the negative electrode unit 20, that is, only one side of the positive electrode unit and the negative electrode unit is provided with sodium-supplementing material, and the sodium-supplemented positive electrode active layer 11 in the positive electrode unit 10 is arranged opposite to the negative electrode sodium-supplementing layer 24 in the negative electrode unit 20, or in other words, one side of the first negative electrode sheet 21 with the negative electrode sodium-supplementing layer 24 corresponds to one side of the non-sodium-supplemented positive electrode active layer 12, and one side of the second negative electrode sheet 22 without the negative electrode sodium-supplementing layer 24 corresponds to one side of the sodium-supplemented positive electrode active layer 11, and the sheets are stacked or wound to form a sodium-supplemented secondary battery.

[0022] According to an embodiment of the present invention, referring to Figure 1 There is only one layer of sodium supplement structure between two adjacent positive electrode current collectors 13 and negative electrode current collectors 23 , and the sodium supplement structure is the sodium supplement positive electrode active layer 11 or the negative electrode sodium supplement layer 24 .

[0023] Those skilled in the art can understand that the non-sodium-supplemented positive electrode active layer 12 means that the positive electrode active layer does not contain a sodium supplement agent, and the sodium-supplemented positive electrode active layer 11 means that the positive electrode active layer contains a sodium supplement agent; in the negative electrode unit, a negative electrode sodium-supplementing layer is provided on one side of the negative electrode current collector where the first negative electrode sheet is arranged, while a negative electrode sodium-supplementing layer is not provided on the side where the second negative electrode sheet is arranged.

[0024] According to an embodiment of the present invention, the above-mentioned sodium supplementation structure has at least the following technical effects:

[0025] First, compared with the design of sodium supplementation on both sides of the positive electrode active material layer, this type of sodium supplementation on one side of the positive electrode active material layer can achieve a larger proportion of sodium supplementation dosage without affecting other properties (such as energy density, gas production and other electrochemical properties), thereby broadening the applicability of the positive electrode sodium supplementation scheme. Due to the specific capacity of the positive electrode sodium supplement (the common sodium supplementation specific capacity of Na2NiO2 is about 386mAh / g, the sodium supplementation specific capacity of Na2CrO2 is about 230mAh / g, and the sodium supplementation specific capacity of Na2C2O4 is about 38 0mAh / g) and the addition amount is limited. Conventional double-sided sodium supplementation of positive electrode active materials is generally used in combination with high first-efficiency negative electrodes such as graphite, which limits its application in combination with negative electrode materials with high specific capacity and low first efficiency (such as hard carbon, etc.). In the present invention, single-sided sodium supplementation of positive electrode active materials is used. Since the proportion of sodium supplementation agent in single-sided active materials is increased, it can be combined with various negative electrode systems such as hard carbon, silicon carbon, and sodium-embedded alloys to realize sodium supplementation design. At the same time, due to single-sided sodium supplementation, the gas production during the battery cycle can be significantly reduced;

[0026] Second, compared with the sodium supplementation on both sides of the negative electrode active material, due to the high activity of sodium metal, the negative electrode sheet will have obvious heat after pre-sodium. The heat of the negative electrode sheet after pre-sodium (i.e. sodium supplementation) leads to safety risks. Secondly, the double-sided pre-sodium usually encounters a large difference in the surface density of the sodium supplementation on both sides. This may not only make the actual state of the negative electrode sheet inconsistent with the theoretical design, leading to possible adverse risks such as uneven surface density and sodium precipitation, but also the unevenness of the negative electrode sheet due to the inconsistent expansion stress of the embedded sodium on both sides, which brings risks to the subsequent assembly. In addition, the high pre-sodium negative electrode sheet will become brittle and hard due to the accumulation of expansion stress due to the embedded sodium, which also brings huge challenges to the subsequent die-cutting assembly. The pre-sodiumization of the active material on one side of the negative electrode current collector of the present invention can significantly reduce the heat generation phenomenon after the pre-sodiumization of the negative electrode sheet (compared with the sodium supplementation on both sides of the negative electrode sheet), while avoiding the phenomenon of inconsistent surface density of the pre-sodiumization on both sides, and improving the consistency of the surface density of the negative electrode sodium supplementation layer. At the same time, since one side is not pre-sodiumized, the phenomenon of the negative electrode sheet becoming brittle and hard is significantly alleviated, thereby significantly reducing the safety risk and the assembly capacity of the later stage.

[0027] Third, the sodium supplementation scheme of the present invention not only combines the respective advantages of positive and negative electrode sodium supplementation to achieve a better sodium supplementation effect, but also overcomes the respective disadvantages of the above two sodium supplementation methods (sodium supplementation on both sides of the positive electrode active material layer and sodium supplementation on both sides of the negative electrode active material), significantly improving the yield and feasibility of the battery cell and secondary battery process, while helping to broaden the application scope of positive and negative electrode sodium supplementation and improve the performance and safety of the battery cell.

[0028] Fourth, the above-mentioned sodium supplementation method overcomes the problems of low sodium supplementation capacity and large addition amount when sodium is supplemented on both sides of the positive electrode alone. Sodium supplementation on a single positive electrode can achieve the same sodium supplementation dosage and only supplements sodium to half the mass of the positive electrode active layer, thereby increasing the proportion of sodium supplementation agent while maintaining the same mass, and achieving a higher sodium supplementation demand, which not only compensates for the active sodium consumed by the first film formation of the negative electrode, but also improves the cycle life of the battery due to the additional active sodium pre-existing in the negative electrode; at the same time, it can overcome the shortcomings of obvious heating of the negative electrode sheet after sodium supplementation on both sides of the negative electrode, poor flatness of the negative electrode sheet, and brittleness, which leads to the inability to mass produce. It can be seen from this that the above-mentioned positive and negative electrode yin and yang sodium supplementation method of the present invention fully utilizes the advantages of the positive and negative electrode sodium supplementation and can achieve mass production, which is of practical significance for the realization of high energy density and long-life batteries.

[0029] In the embodiments of the present invention, there is no special requirement for the specific stacking number of positive electrode units and negative electrode units in the above-mentioned battery cells, and those skilled in the art can flexibly select according to the actual conditions such as battery cell size and battery cell design. According to some specific embodiments, the positive electrode unit and the negative electrode unit can both have 120 layers.

[0030] According to some embodiments of the present invention, the sodium supplement agent in the sodium supplement positive electrode active layer includes Na2NiO2, NaC r At least one of O2, Na2C2O4, Na3N, Na2S, Na3P, Na2CO3, NaNO2, Na2C4O4, Na2C6O6, and Na2C6H2O6. The above-mentioned sodium supplement has a better specific capacity, can effectively supplement sodium to the battery core, the material is easy to purchase, and will not have adverse chemical reactions with the effective active substances in the positive electrode active layer. In some preferred embodiments, the sodium supplement in the positive electrode active layer that can supplement sodium includes sodium nickelate (Na2NiO2) and sodium oxalate (Na2C2O4), and the specific capacity of the sodium supplement is relatively high (the sodium supplement specific capacity of Na2NiO2 is about 285mAh / g, and the sodium supplement specific capacity of Na2C2O4 is about 380mAh / g), which can enable the battery core to achieve a better sodium supplement effect and better improve the battery energy density and service life.

[0031] According to an embodiment of the present invention, for the total mass of the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer, the content of the sodium-supplementing agent in the sodium-supplemented positive electrode active layer is less than or equal to 40%, such as 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 1%, 0.5%, 0.1%, etc. The above-mentioned content of the sodium-supplementing agent can not only effectively and uniformly achieve a good sodium-supplementing effect, but also will not affect the positive electrode performance of the positive electrode active layer. According to some specific embodiments of the present invention, for the total mass of the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer, the content of the sodium-supplementing agent in the sodium-supplemented positive electrode active layer is 1.5-10%, such as 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. The sodium supplement within the above content range can make the battery have better comprehensive performance. For example, while ensuring a good sodium supplement effect, it can also ensure the good performance of its positive electrode and improve the battery's cycle performance, battery capacity and other properties.

[0032] According to an embodiment of the present invention, for the sodium-supplemented positive electrode active layer, the surface density of the sodium-supplementing agent is 1 g / m 2 ~18g / m 2 For example, the surface density of the sodium supplement is 1g / m 2 , 3g / m 2 , 5g / m 2 , 8g / m 2 , 10g / m 2 , 12g / m 2 , 15g / m 2 , 18g / m 2 The sodium supplement agent with the above surface density can not only effectively and evenly achieve a good sodium supplement effect, but also will not affect the positive electrode performance of the positive electrode active layer, thereby ensuring good cycle performance and capacity of the battery. According to some specific embodiments of the present invention, for the sodium supplement positive electrode active layer, the surface density of the sodium supplement agent is 4g / m 2 ~16g / m 2 The sodium supplement within the above-mentioned surface density range can make the battery have better comprehensive performance. For example, while ensuring a good sodium supplement effect, it can also ensure the good performance of its positive electrode and improve the battery's cycle performance, battery capacity and other properties.

[0033] According to some embodiments of the present invention, the negative electrode sodium supplement layer is sodium foil and / or sodium powder. Metallic sodium has high activity, and using metallic sodium for sodium supplementation can achieve a better sodium supplementation effect. In some specific embodiments, the negative electrode sodium supplement layer is sodium powder, and the powdered sodium supplement can better and more conveniently adjust the amount of sodium supplementation, which helps to improve the uniformity of sodium supplementation dispersion.

[0034] According to some embodiments of the present invention, the surface density of the negative electrode sodium supplement layer is 0.5 g / m 2~10g / m 2 For example, the surface density of the sodium supplement is 0.5g / m 2 , 1g / m 2 , 2g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , 10g / m 2 The negative electrode sodium supplement layer with the above surface density can well supplement sodium for the battery cell, compensate for the consumption of active sodium in the initial film formation of the negative electrode, significantly improve the energy density of the battery, and well compensate for the continuous loss of active sodium during the cycle process, thereby effectively improving the cycle and storage life of the battery, while ensuring the good negative electrode function of the negative electrode unit. According to some specific embodiments of the present invention, the surface density of the negative electrode sodium supplement layer is 1g / m 2 ~6g / m 2 Therefore, while the sodium replenishment effect on the battery is good, the good cycle and energy density of the battery are further guaranteed.

[0035] According to an embodiment of the present invention, the effective active materials in the non-sodium supplemented positive electrode active layer and the sodium supplemented positive electrode active layer are transition metal oxides Na e MO2, Prussian blue compounds Na f M1[M2(CN)6] and polyanionic compound Na d M g (X a O b ) c Z h At least one of, wherein M, M1 and M2 are respectively one or more transition metal atoms, X is one or more of Si, S, P, As, B, Mo, W, Ge elements, and Z is one or more of F and OH, wherein M, M1 and M2 can be the same element or different elements.

[0036] In some embodiments, in addition to the effective active materials, the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer further include a conductive agent (the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers), a binder (the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin), etc., wherein there are no special requirements for the ratio of each raw material, and those skilled in the art can flexibly adjust it according to actual needs.

[0037] In some embodiments of the present invention, the effective active material of the first negative electrode sheet and the second negative electrode sheet is at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nanocarbon, carbon fiber, silicon negative electrode material and sodium embedded alloy. It can be seen that the above-mentioned sodium supplementation technical solution of the present invention can be applied to various sodium ion battery systems.

[0038] In some embodiments, in addition to the above-mentioned effective active materials, the first negative electrode sheet and the second negative electrode sheet further include a conductive agent (the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers), a binder (the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS)), and other ingredients, wherein there are no special requirements for the ratio of the raw materials, and those skilled in the art can flexibly adjust it according to actual needs.

[0039] According to some embodiments of the present invention, there are no special requirements for the specific materials of the positive electrode current collector and the negative electrode current collector, and those skilled in the art can flexibly select them according to existing technical means. For example, the positive electrode current collector can be aluminum foil, and the negative electrode current collector can be copper foil.

[0040] According to the embodiments of the present invention, there are no special requirements for the specific materials of the above-mentioned diaphragm, and those skilled in the art can flexibly select according to actual needs. The material of the diaphragm can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film without special restrictions. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different without special restrictions.

[0041] In another aspect of the present invention, the present invention provides a secondary battery. According to an embodiment of the present invention, the secondary battery includes the battery cell described above. As a result, the service life of the secondary battery is long. It can be understood by those skilled in the art that the electrical device has all the features and advantages of the battery cell described above, and no further elaboration is given here.

[0042] According to an embodiment of the present invention, the battery may be a laminated battery or a wound battery.

[0043] According to an embodiment of the present invention, the secondary battery further comprises a shell, and the shell may be an aluminum shell, a steel shell, a soft pack, or the like.

[0044] In another aspect of the present invention, the present invention provides an electric device. According to an embodiment of the present invention, the electric device includes the secondary battery described above. As a result, the service life of the electric device is long. It can be understood by those skilled in the art that the electric device has all the features and advantages of the secondary battery described above, which will not be described in detail here.

[0045] According to the embodiments of the present invention, there are no special requirements for the specific type of the electrical equipment, and those skilled in the art can flexibly select according to actual needs. For example, it can be a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but not limited thereto.

[0046] Example

[0047] Example 1

[0048] The method for preparing a secondary battery comprises:

[0049] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0050] 2) Preparation of sodium-supplemented positive electrode active layer: 97.8 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2.2 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing the sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density p of the applied active material (including the sodium supplement) was 184 g / m2 , among which, the surface density of the sodium supplement is 4.0g / m 2 , the effective active material surface density is 180g / m 2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0051] 3) Positive electrode sheet roll die cutting: n Layer and P p The positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the proportion of the surface density of the sodium supplement agent to the total effective active material (i.e. the content of the sodium supplement agent in the sodium supplement positive electrode active layer) is x=4.0 / 184*100%=2.2%.

[0052] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 95.8 g / m 2 The surface density of the double-sided active material is 191.6g / m 2 .

[0053] 5) Sodium supplementation on one side of the negative electrode sheet: Sodium powder or sodium foil is added to one side of the negative electrode sheet after rolling. The surface density of the negative electrode sodium supplementation layer is 1.5g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0054] 6) Negative electrode die cutting: Die the negative electrode sheet coated with N n and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0055] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit n The positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed in an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1527mAh.

[0056] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0057] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0058] Example 2

[0059] The method for preparing a secondary battery comprises:

[0060] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0061] 2) Preparation of sodium-supplemented positive electrode active layer: 96.8 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 3.2 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density of the applied active material (including sodium supplement) p was 185.9 g / m 2 Among them, the surface density of the sodium supplement is 5.9g / m 2 , the effective active material surface density is 180g / m 2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0062] 3) Positive electrode sheet roll die cutting: n Layer and P p The positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the proportion of the surface density of the sodium supplement agent to the total effective active material (i.e. the content of the sodium supplement agent in the sodium supplement positive electrode active layer) is x=5.9 / 185.9*100%=3.2%.

[0063] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 96.9 g / m 2 The surface density of the double-sided active material is 193.8g / m 2 .

[0064] 5) Sodium supplementation on one side of the negative electrode sheet: Sodium powder or sodium foil is added to one side of the negative electrode sheet after rolling. The surface density s of the negative electrode sodium supplementation layer is 2.3g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0065] 6) Negative electrode die cutting: Die the negative electrode sheet coated with N n and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0066] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit n The positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed into an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1578mAh.

[0067] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0068] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0069] Example 3

[0070] The method for preparing a secondary battery comprises:

[0071] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0072] 2) Preparation of sodium-supplemented positive electrode active layer: 95.8 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 4.2 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density of the applied active material (including sodium supplement) p was 187.9 g / m 2 Among them, the surface density of the sodium supplement is 7.9g / m 2 , the effective active material surface density is 180g / m 2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0073] 3) Positive electrode sheet roll die cutting: n Layer and P p The positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the proportion of the surface density of the sodium supplement agent to the total effective active material (i.e. the content of the sodium supplement agent in the sodium supplement positive electrode active layer) is x=7.9 / 187.9*100%=4.2%.

[0074] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 99.0 g / m 2 The surface density of the double-sided active material is 197.9g / m 2 .

[0075] 5) Sodium supplementation on one side of the negative electrode sheet: Sodium powder or sodium foil is added to one side of the negative electrode sheet after rolling. The surface density of the negative electrode sodium supplementation layer is 3.1g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0076] 6) Negative electrode die cutting: Die the negative electrode sheet coated with N n and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0077] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit nThe positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed in an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1587mAh.

[0078] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0079] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0080] Example 4

[0081] The method for preparing a secondary battery comprises:

[0082] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0083] 2) Preparation of sodium-supplemented positive electrode active layer: 94.3 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 5.7 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density of the applied active material (including sodium supplement) p was 191.0 g / m 2 , among which, the surface density of the sodium supplement is 11.0g / m 2 , the effective active material surface density is 180g / m 2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0084] 3) Positive electrode sheet roll die cutting: n Layer and P pThe positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the proportion of the surface density of the sodium supplement agent to the total effective active material (i.e. the content of the sodium supplement agent in the sodium supplement positive electrode active layer) is x=11.0 / 191*100%=5.8%.

[0085] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 102.1 g / m 2 The surface density of the double-sided active material is 204.2g / m 2 .

[0086] 5) Sodium supplementation on one side of the negative electrode sheet: Sodium powder or sodium foil is added to one side of the negative electrode sheet after rolling. The surface density s of the negative electrode sodium supplementation layer is 4.2g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0087] 6) Negative electrode die cutting: Die the negative electrode sheet coated with N n and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0088] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit n The positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed in an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1595mAh.

[0089] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0090] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0091] Example 5

[0092] The method for preparing a secondary battery comprises:

[0093] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0094] 2) Preparation of sodium-supplemented positive electrode active layer: 93.3 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 6.7 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density of the applied active material (including sodium supplement) p was 193 g / m 2 , among which, the surface density of the sodium supplement is 13.0g / m 2 , the effective active material surface density is 180g / m 2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0095] 3) Positive electrode sheet roll die cutting: n Layer and P p The positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the proportion of the surface density of the sodium supplement agent to the total effective active material (i.e. the content of the sodium supplement agent in the sodium supplement positive electrode active layer) is x=13.0 / 193*100%=6.7%.

[0096] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 104.2 g / m 2 The surface density of the double-sided active material is 208.4g / m 2 .

[0097] 5) Sodium supplementation on one side of the negative electrode sheet: Sodium powder or sodium foil is added to one side of the negative electrode sheet after rolling. The surface density s of the negative electrode sodium supplementation layer is 5.0g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0098] 6) Negative electrode die cutting: Die the negative electrode sheet coated with Nn and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0099] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit n The positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed in an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1604mAh.

[0100] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0101] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0102] Example 6

[0103] The method for preparing a secondary battery comprises:

[0104] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0105] 2) Preparation of sodium-supplemented positive electrode active layer: 91.8 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 8.2 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density of the applied active material (including sodium supplement) p was 196 g / m 2 , among which, the surface density of the sodium supplement is 16.0g / m 2 , the effective active material surface density is 180g / m2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0106] 3) Positive electrode sheet roll die cutting: n Layer and P p The positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the proportion of the surface density of the sodium supplement agent to the total effective active material (i.e. the content of the sodium supplement agent in the sodium supplement positive electrode active layer) is x=16.0 / 196*100%=8.2%.

[0107] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 108.3 g / m 2 The surface density of the double-sided active material is 216.6g / m 2 .

[0108] 5) Sodium supplementation on one side of the negative electrode sheet: After rolling, sodium powder or sodium foil is added to one side of the negative electrode sheet. The surface density s of the negative electrode sodium supplementation layer is 6.2g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0109] 6) Negative electrode die cutting: Die the negative electrode sheet coated with N n and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0110] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit n The positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed in an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1613mAh.

[0111] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0112] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0113] Example 7

[0114] The method for preparing a secondary battery comprises:

[0115] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0116] 2) Preparation of sodium-supplemented positive electrode active layer: 90.9 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 9.1 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density of the applied active material (including sodium supplement) p was 198 g / m 2 , among which, the surface density of the sodium supplement is 18.0g / m 2 , the effective active material surface density is 180g / m 2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0117] 3) Positive electrode sheet roll die cutting: n Layer and P p The positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the proportion of the surface density of the sodium supplement agent to the total effective active material (i.e. the content of the sodium supplement agent in the sodium supplement positive electrode active layer) is x=18.0 / 198*100%=9.1%.

[0118] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was applied on copper foil. The surface density of the coated single-sided active material was 110.4 g / m 2 The surface density of the double-sided active material is 220.8g / m 2 .

[0119] 5) Sodium supplementation on one side of the negative electrode sheet: Sodium powder or sodium foil is added to one side of the negative electrode sheet after rolling. The surface density of the negative electrode sodium supplementation layer is 7.0g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0120] 6) Negative electrode die cutting: Die the negative electrode sheet coated with N n and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0121] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit n The positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed in an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1630mAh.

[0122] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0123] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0124] Example 8

[0125] The method for preparing a secondary battery comprises:

[0126] 1) Preparation of non-sodium supplemented positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare a positive electrode slurry without sodium supplementation agent, and the slurry was coated on aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The non-sodium-supplemented positive electrode active layer on this side is denoted as P n layer (without pre-sodiumization);

[0127] 2) Preparation of sodium-supplemented positive electrode active layer: 99.4 parts by mass of iron-based Prussian white (Na2Fe[Fe(CN)6]), 0.6 parts by mass of Na2NiO2 sodium supplement, 2 parts by mass of conductive agent and 2.2 parts by mass of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on the other side of the aluminum foil. The surface density of the applied active material (including sodium supplement) p was 181.1 g / m 2 , among which, the surface density of the sodium supplement is 1.1g / m 2 , the effective active material surface density is 180g / m 2 The sodium-supplemented positive electrode active layer on this side is denoted as P p layer (pre-sodiumization);

[0128] 3) Positive electrode sheet roll die cutting: n Layer and P p The positive electrode sheet of the layer is rolled and die-cut to form a positive electrode unit with single-side sodium supplementation, wherein the surface density of the sodium supplement agent accounts for a proportion of x=1.1 / 181.1*100%=0.6% of the total effective active material.

[0129] 4) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 95.8 g / m 2 The surface density of the double-sided active material is 191.6g / m 2 .

[0130] 5) Sodium supplementation on one side of the negative electrode sheet: Sodium powder or sodium foil is added to one side of the negative electrode sheet after rolling. The surface density s of the negative electrode sodium supplementation layer is 0.4g / m 2 , the side containing the sodium supplement layer is marked as N p Layer (pre-sodiumization), the side without sodium supplementation is marked as N n layer (without pre-sodiumization).

[0131] 6) Negative electrode die cutting: Die the negative electrode sheet coated with N n and N p The negative electrode sheets of the layers are die-cut to form negative electrode units with single-side sodium supplementation.

[0132] 7) Positive and negative electrode unit lamination assembly: Align the Pn layer of the positive electrode unit with the N layer of the negative electrode unit. p Layer, positive electrode unit P p The N layer corresponds to the negative electrode unit n The positive and negative electrode units are stacked in the form of 7+8 layers, and a separator is added between them to form a soft-pack small battery cell, which is then packed in an aluminum shell or aluminum-plastic film to form a secondary battery. After liquid injection, the battery is charged and discharged for the first time. The designed capacity is 1475mAh.

[0133] 9) Sodium-supplemented battery injection and decomposition: The battery after injection is formed by using 0.05C constant current charging for 2h and 0.2C constant current charging for 3h. After the SEI film is formed, the battery is further charged to 4.0V using 0.005C current to fully decompose and release sodium in the sodium-supplemented positive electrode active layer, and the negative electrode side without the sodium-supplemented layer is electrochemically supplemented with sodium;

[0134] 10) Sodium supplemented battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is 1 / 3C constant current and constant voltage charging to 4.0V, leaving it for 10 minutes, and 1 / 3C constant current discharge to 2.0V. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0135] Comparative Example 1

[0136] The preparation method of a secondary battery (neither the positive nor the negative electrode is sodium supplemented) comprises:

[0137] 1) Preparation of positive electrode active layer: 100 parts by weight of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts by weight of conductive agent and 2.2 parts by weight of binder were dissolved and mixed by NMP to prepare positive electrode slurry without sodium supplementation agent. The slurry was coated on both sides of aluminum foil. The effective active material surface density of the coating was 180 g / m 2 The effective active material surface density on both sides is 360g / m 2 ;

[0138] 2) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 95.8 g / m 2 The surface density of the double-sided active material is 191.6g / m 2 ;

[0139] 3) Positive and negative electrode die-cutting and lamination assembly: After die-cutting the positive and negative electrode sheets, they are laminated with the diaphragm to form 7+8 layers of soft-pack small cells, which are then packed into an aluminum shell or aluminum-plastic film outer packaging to form a battery. After liquid injection, the first charge and discharge are carried out. The battery design capacity is 1458mAh;

[0140] 4) Battery filling and formation: Use 0.05C constant current charging for 2h and 0.2C constant current charging for 3h to form the battery after filling;

[0141] 10) Battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is to charge to 4.0V with 1 / 3C constant current and constant voltage, leave it for 10 minutes, and discharge to 2.0V with 1 / 3C constant current. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0142] Comparative Example 2

[0143] The preparation method of a secondary battery (sodium is supplemented on both sides of the positive electrode and sodium is not supplemented on the negative electrode) comprises:

[0144] 1) Preparation of positive electrode sheet: 94.3 parts of iron-based Prussian white (Na2Fe[Fe(CN)6]), 5.7 parts of Na2NiO2 sodium supplement, 2 parts of conductive agent and 2.2 parts of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on both sides of the aluminum foil. The single surface density of the applied active material was 185.5 g / m 2 (including sodium supplement), wherein the surface density of the sodium supplement is 5.5g / m 2 , the effective active material surface density is 180g / m 2 ; Double-sided active material surface density is 371g / m 2 (including sodium supplement), the double-sided sodium supplement surface density is 11g / m 2 The effective active material surface density on both sides is 360g / m 2 ;

[0145] 2) Rolling and die-cutting of positive electrode plates: The positive electrode plates with sodium supplement added on both sides are rolled and die-cut to make positive electrode double-sided sodium supplemented plates, wherein the surface density of the sodium supplement accounts for the total effective active material (i.e., the content of the sodium supplement in the sodium supplement positive electrode active layer) x = 5.5 / 185.5*100% = 3.0%.

[0146] 3) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 102.1 g / m 2 The surface density of the double-sided active material is 204.2g / m 2 .

[0147] 5) Positive and negative electrode die-cutting and lamination assembly: After die-cutting the positive and negative electrode sheets, they are laminated with the diaphragm to form a 7+8-layer soft-pack small battery cell, which is then packed into an aluminum shell or aluminum-plastic film outer packaging to form a battery. After liquid injection, the first charge and discharge is performed. The battery design capacity is 1527mAh;

[0148] 6) Liquid injection and decomposition of positive sodium-supplemented battery: The battery after liquid injection is formed by charging at 0.05C constant current for 2h and 0.2C constant current for 3h. After the SEI film is formed, the battery is further charged to 4.0V using a current of 0.005C, so that the sodium-supplementing agent in the sodium-supplemented positive active layer is fully decomposed and sodium is released, and the battery is electrochemically supplemented with sodium;

[0149] 10) Battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is to charge to 4.0V with 1 / 3C constant current and constant voltage, leave it for 10 minutes, and discharge to 2.0V with 1 / 3C constant current. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0150] Comparative Example 3

[0151] The preparation method of a secondary battery (sodium is supplemented on both sides of the positive electrode and sodium is not supplemented on the negative electrode) comprises:

[0152] 1) Preparation of positive electrode sheet: 90.0 parts of iron-based Prussian white (Na2Fe[Fe(CN)6]), 10.0 parts of Na2NiO2 sodium supplement, 2 parts of conductive agent and 2.2 parts of binder were dissolved and mixed by NMP to prepare a positive electrode slurry containing sodium supplement. The slurry was applied on both sides of the aluminum foil. The single surface density of the applied active material was 190g / m 2 (including sodium supplement), wherein the surface density of the sodium supplement is 10.0 g / m 2 , the effective active material surface density is 180g / m 2 ; Double-sided active material surface density is 380g / m 2 (including sodium supplement), the double-sided sodium supplement surface density is 20g / m 2 The effective active material surface density on both sides is 360g / m 2 ;

[0153] 2) Rolling and die-cutting of positive electrode plates: The positive electrode plates with sodium supplement added on both sides are rolled and die-cut to make positive electrode double-sided sodium supplemented plates, in which the surface density of the sodium supplement accounts for the total effective active material (i.e., the content of the sodium supplement in the sodium supplement positive electrode active layer) x = 10 / 190*100% = 5.3%.

[0154] 3) Preparation of negative electrode sheet: 100 parts by mass of hard carbon material, 1 part by mass of conductive agent and 5 parts by mass of binder were dissolved and mixed evenly in deionized water to prepare negative electrode slurry, which was coated on copper foil. The surface density of the coated single-sided active material was 112.5 g / m 2 The surface density of the active material on both sides is 225.0g / m 2 .

[0155] 5) Positive and negative electrode die-cutting and lamination assembly: After die-cutting the positive and negative electrode sheets, they are laminated with the diaphragm to form 7+8 layers of soft-pack small cells, which are then packed into an aluminum shell or aluminum-plastic film outer packaging to form a battery. After liquid injection, the first charge and discharge are carried out. The battery design capacity is 1595mAh;

[0156] 6) Liquid injection and decomposition of positive sodium-supplemented battery: The battery after liquid injection is formed by charging at 0.05C constant current for 2h and 0.2C constant current for 3h. After the SEI film is formed, the battery is further charged to 4.0V using a current of 0.005C, so that the sodium-supplementing agent in the sodium-supplemented positive active layer is fully decomposed and sodium is released, and the battery is electrochemically supplemented with sodium;

[0157] 10) Battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is to charge to 4.0V with 1 / 3C constant current and constant voltage, leave it for 10 minutes, and discharge to 2.0V with 1 / 3C constant current. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0158] Comparative Example 4

[0159] The preparation method of a secondary battery (the positive electrode is not supplemented with sodium, and both sides of the negative electrode are supplemented with sodium) comprises:

[0160] 1) Preparation of positive electrode sheet: 100 parts of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts of conductive agent and 2.2 parts of binder were dissolved and mixed by NMP to prepare positive electrode slurry, which was coated on aluminum foil. The single surface density of the coated active material was 180 g / m 2 , double-sided density is 360g / m 2 , after roller pressing and die cutting, the positive electrode sheet is made;

[0161] 2) Preparation of negative electrode sheet: 100 parts of hard carbon material, 1 part of conductive agent and 5 parts of binder were dissolved and mixed evenly in deionized water to make negative electrode slurry, which was coated on copper foil. The single surface density of the coated active material was 102.1 g / m 2 The surface density of the double-sided active material is 204.2g / m 2 .

[0162] 4) Sodium supplementation on both sides of the negative electrode: Sodium powder or sodium foil is added to both sides of the negative electrode after rolling, and the single-sided density of sodium supplementation is 4.2g / m 2 , double-sided total 8.4g / m 2 .

[0163] 5) Positive and negative electrode die-cutting and lamination assembly: After die-cutting the positive and negative electrode sheets, they are laminated with the diaphragm to form a 7+8-layer soft-pack small battery cell, which is then packed into an aluminum shell or aluminum-plastic film outer packaging to form a battery. After liquid injection, the first charge and discharge is performed. The battery design capacity is 1527mAh;

[0164] 6) Battery filling and formation: Use 0.05C constant current charging for 2h and 0.2C constant current charging for 3h to form the battery after filling;

[0165] 7) Battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is to charge to 4.0V with 1 / 3C constant current and constant voltage, leave it for 10 minutes, and discharge to 2.0V with 1 / 3C constant current. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0166] Comparative Example 5

[0167] The preparation method of a secondary battery (the positive electrode is not supplemented with sodium, and both sides of the negative electrode are supplemented with sodium) comprises:

[0168] 1) Preparation of positive electrode sheet: 100 parts of iron-based Prussian white (Na2Fe[Fe(CN)6]), 2 parts of conductive agent and 2.2 parts of binder were dissolved and mixed by NMP to prepare positive electrode slurry, which was coated on aluminum foil. The single surface density of the coated active material was 180 g / m 2 , double-sided density is 360g / m 2 , after roller pressing and die cutting, the positive electrode sheet is made;

[0169] 2) Preparation of negative electrode sheet: 100 parts of hard carbon material, 1 part of conductive agent and 5 parts of binder were dissolved and mixed evenly in deionized water to make negative electrode slurry, which was coated on copper foil. The single surface density of the coated active material was 112.5 g / m 2 The surface density of the active material on both sides is 225.0g / m 2 .

[0170] 4) Sodium supplementation on both sides of the negative electrode: Sodium powder or sodium foil is added to both sides of the negative electrode after rolling, and the single-sided density of sodium supplementation is 8.0g / m 2 , double-sided total 16.0g / m 2 .

[0171] 5) Positive and negative electrode die-cutting and lamination assembly: After die-cutting the positive and negative electrode sheets, they are laminated with the diaphragm to form 7+8 layers of soft-pack small cells, which are then packed into an aluminum shell or aluminum-plastic film outer packaging to form a battery. After liquid injection, the first charge and discharge are carried out. The battery design capacity is 1595mAh;

[0172] 6) Battery filling and formation: Use 0.05C constant current charging for 2h and 0.2C constant current charging for 3h to form the battery after filling;

[0173] 7) Battery sorting: The battery is evacuated, sealed and aged for 24 hours before capacity sorting. The capacity sorting process is to charge to 4.0V with 1 / 3C constant current and constant voltage, leave it for 10 minutes, and discharge to 2.0V with 1 / 3C constant current. The discharge capacity at this time is recorded as C0. After leaving it for 24 hours, the battery OCV is recorded.

[0174] The performance tests were performed on the batteries obtained in the above embodiments and comparative examples. The test results are shown in Table 1 below, where:

[0175] The method for determining the heat generation of the negative electrode piece is as follows: weigh a negative electrode piece with a diameter of 2 mm and then perform a DSC test on the heat generation. The test conditions are in an Ar atmosphere, from room temperature to 180°, with a heating rate of 5K / min, and calculate the unit heat generation Q of the negative electrode piece;

[0176] Cycle number: At room temperature of 25 degrees, the formed battery is cycled and tested. The test steps are as follows: 1) Stand for 10 minutes; 2) 0.5C CC-CV to 4.3V 0.05C cut-off; 3) Stand for 10 minutes; 4) 0.5C CC to 2.0V; 5) Cycle the above steps n times until the retention rate reaches 80%, and record the cycle number;

[0177] Gas production test method: Use the drainage method to test the gas production per unit Ah V (ml / Ah, 80% SOH) before and after the battery cycle;

[0178] Pre-stored sodium ratio: The pre-stored sodium ratio is a design value, which is equal to the ratio of the active sodium capacity of the negative electrode that has not been released after the discharge is completed to the complete discharge capacity of the positive electrode active layer.

[0179] The determination method of A in the table: The A value is the difference in the surface capacity of the positive electrode sodium supplement and the negative electrode sodium supplement, satisfying A = p*x*ab*s, where the total surface density of the positive electrode active material (including the sodium supplement) is p, the proportion of the single-sided sodium supplement is x, and the specific capacity of the sodium supplement is a (the specific capacity a of Na2NiO2 is 386mAh / g); the surface density of the negative electrode sodium supplement layer is s, and the specific capacity is b (the specific capacity b of Na is 1000mAh / g). This value is obtained by testing the specific capacity of the positive and negative electrode sodium supplements with a buckle test. The value between -100 and +100 indicates that the positive and negative electrode sodium supplements match each other and the battery cell design is reasonable.

[0180] Table 1

[0181]

[0182]

[0183] It can be seen from the data in the above table that the batteries in Examples 1 to 8 of the present invention have good battery capacity and cycle number, which means that the sodium supplementation method of the present invention will not have an adverse effect on the battery capacity and cycle number, and even a more suitable amount of sodium supplementation can also help to improve the battery capacity and cycle number, such as Examples 4 to 7; compared with the negative electrode double-sided sodium supplementation scheme in Comparative Examples 4 and 5, the sodium supplementation method of Examples 1 to 8 can significantly reduce the heat generation phenomenon after the negative electrode sheet is pre-sodiumized. By comparing Example 4 with Comparative Example 4, it can also be seen that the sodium supplementation scheme of the single-sided negative electrode of the present invention can well reduce the heat generation phenomenon after the negative electrode sheet is pre-sodiumized. In addition, since sodium supplementation is not provided on both sides of the negative electrode in Comparative Examples 1 to 3, there is almost no heat generation phenomenon after pre-sodiumization; compared with the double-sided positive electrode sodium supplementation scheme in Comparative Examples 2 and 3, the sodium supplementation method of Examples 1 to 8 can significantly alleviate the adverse phenomenon of "gas production during the cycle" caused by positive electrode sodium supplementation. In addition, since sodium supplementation is not provided on the positive electrode in Comparative Examples 4 and 5, the gas production is extremely low. Furthermore, from the data of the difference A in the surface capacity of the positive and negative electrodes in the above embodiments, it can be seen that the sodium replenishment amounts of the positive and negative electrodes of the present invention match each other; the pre-stored sodium ratio in the above embodiments is between 0% and 20%, which shows that the battery of the present invention has a more suitable pre-stored sodium ratio.

[0184] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0185] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0186] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A battery cell, characterized in that: The invention comprises a plurality of positive electrode units and negative electrode units which are sequentially overlapped and a separator between the positive electrode units and the negative electrode units, wherein the positive electrode unit comprises a positive electrode current collector and a non-sodium-supplemented positive electrode active layer and a sodium-supplemented positive electrode active layer which are respectively arranged on both sides of the positive electrode current collector, and the negative electrode unit comprises a negative electrode current collector, a first negative electrode sheet and a second negative electrode sheet which are respectively arranged on both sides of the negative electrode current collector, and a negative electrode sodium-supplemented layer, wherein the negative electrode sodium-supplemented layer is located on a side of the first negative electrode sheet away from the negative electrode current collector, Wherein, the negative electrode sodium supplement layer is arranged toward the non-sodium supplement positive electrode active layer in the positive electrode unit, and the sodium supplement positive electrode active layer is arranged toward the second negative electrode sheet in the negative electrode unit.

2. The battery cell according to claim 1, characterized in that: There is only one layer of sodium supplement structure between two adjacent positive electrode current collectors and negative electrode current collectors, and the sodium supplement structure is the sodium supplement positive electrode active layer or the negative electrode sodium supplement layer.

3. The battery cell according to claim 1, characterized in that: The sodium supplement agent in the sodium supplement positive electrode active layer includes Na2NiO2, NaC r At least one of O2, Na2C2O4, Na3N, Na2S, Na3P, Na2CO3, NaNO2, Na2C4O4, Na2C6O6, and Na2C6H2O6, The negative electrode sodium supplement layer is sodium foil and / or sodium powder.

4. The battery cell according to any one of claims 1 to 3, characterized in that: With respect to the total mass of the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer, the content of the sodium-supplemented agent in the sodium-supplemented positive electrode active layer is less than or equal to 40% by mass.

5. The battery cell according to claim 4, characterized in that: With respect to the total mass of the non-sodium-supplemented positive electrode active layer and the sodium-supplemented positive electrode active layer, the content of the sodium-supplemented agent in the sodium-supplemented positive electrode active layer is 1.5-10% by mass.

6. The battery cell according to claim 4, characterized in that: For the sodium-supplemented positive electrode active layer, the surface density of the sodium-supplementing agent is 1 g / m 2 ~18g / m 2 .

7. The battery cell according to claim 6, characterized in that: For the sodium-supplemented positive electrode active layer, the surface density of the sodium-supplementing agent is 4 g / m 2 ~16g / m 2 .

8. The battery cell according to any one of claims 1 to 3, characterized in that: The surface density of the negative electrode sodium supplement layer is 0.5g / m 2 ~10g / m 2 .

9. The battery cell according to claim 8, characterized in that: The surface density of the negative electrode sodium supplement layer is 1g / m 2 ~6g / m 2 .

10. The battery cell according to any one of claims 1 to 3, characterized in that: The effective active materials in the non-sodium supplemented positive electrode active layer and the sodium supplemented positive electrode active layer are transition metal oxides Na e MO2, Prussian blue compounds Na f M1[M2(CN)6] and polyanionic compound Na d M g (X a O b ) c Z h At least one of, wherein M, M1 and M2 are respectively one or more transition metal atoms, X is one or more Si, S, P, As, B, Mo, W, Ge elements, and Z is one or more F and OH; The effective active materials of the first negative electrode sheet and the second negative electrode sheet are at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nanocarbon, carbon fiber, silicon negative electrode material and sodium embedded alloy.

11. A secondary battery, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 10.

12. An electrical equipment, characterized in that: The secondary battery according to claim 11 is included.

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