A composite battery cell suitable for sodium-ion batteries and a sodium-ion battery using the same

Abstract

The present invention provides a composite battery cell applicable to sodium-ion batteries: It includes a positive electrode sheet, and the number of types of the positive electrode sheet is greater than 1. Among the positive electrode sheets, the positive active material components contained in at least two positive electrode sheets are different from each other; the positive electrode sheet includes at least one of a first positive electrode sheet and a second positive electrode sheet; the first positive electrode sheet contains one positive active material; the second positive electrode sheet includes at least two positive active materials. The composite battery cell of the sodium-ion battery provided by the present invention integrates at least two positive active materials, and can select the types of the positive active materials used and adjust the amounts of different types of positive active materials, so that the composite battery cell can flexibly meet various different product requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular, relates to a composite battery cell suitable for sodium ion batteries and a sodium ion battery using the composite battery cell. Background Art

[0002] Mainstream sodium-ion battery positive electrode materials include layered transition metal oxides, polyanion compounds, and Prussian blue (white) compounds. Among them, layered transition metal oxide materials have high specific capacity, but poor cycle performance, polyanion compound materials have high redox potential and good cycle stability, but low capacity and poor conductivity, and Prussian blue (white) compound materials have excellent rate performance and low cost, but low capacity and poor cycle performance. It can be seen that there are differences in the performance of mainstream sodium-ion battery positive electrode materials, and with the diversification of user needs, a single sodium-ion battery positive electrode material is difficult to meet the needs.

[0003] However, due to the different material properties of different types of active materials, even if they are integrated into the same battery cell, they often cannot fully exert their material advantages due to uneven material mixing and unreasonable material matching. Based on this, how to integrate different active materials in the same battery cell and give full play to the synergistic advantages of the above active materials is still a difficult problem that the industry needs to solve urgently. Summary of the invention

[0004] The present invention provides a composite battery cell suitable for sodium ion batteries and a sodium ion battery using the composite battery cell, so that mainstream sodium ion positive electrode active materials can be flexibly matched to meet various product requirements.

[0005] According to one aspect of the present invention, a composite cell suitable for sodium ion batteries is provided: the composite cell includes a positive electrode sheet, the number of types of positive electrode sheets is greater than 1, and in the positive electrode sheets, at least two positive electrode sheets contain different positive electrode active material components; the positive electrode sheet includes at least one of a first positive electrode sheet and a second positive electrode sheet; the first positive electrode sheet contains only one positive electrode active material; the second positive electrode sheet includes at least two positive electrode active materials; the composite cell also includes a negative electrode sheet and a separator, and in the composite cell, the positive electrode sheet and the negative electrode sheet are arranged at intervals, and a separator is also provided between the positive electrode sheet and the negative electrode sheet. The composite cell of the sodium ion battery provided by the present invention integrates at least two positive electrode active materials, and can flexibly adapt the composite cell to various different product requirements by selecting the types of positive electrode active materials used and adjusting the amounts of different types of positive electrode active materials.

[0006] Preferably, the positive active materials contained in the composite battery cell include at least two of layered transition metal oxide-based positive active materials, polyanion compound-based positive active materials, Prussian blue compound-based positive active materials, and Prussian white compound-based positive active materials. The positive active materials are used to construct the positive active coating of the positive electrode plate.

[0007] Preferably, the structural general formula of the above-mentioned layered transition metal oxide-based positive active material is Na x MO2, and the M element in the general formula includes at least one of Fe element, Co element, Ni element, Mn element, Cr element, Ti element, V element, and Zn element. Preferably, the above-mentioned polyanion compound-based positive active materials include those with the structural general formula of Na x M y (X a O b )Z w compounds, where M is at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Ca, Mg, Al, and Nb, X is at least one of Si, S, P, As, B, Mo, W, and Ge, and Z is at least one of F and OH.

[0008] Preferably, the above-mentioned polyanion compound-based positive active materials include at least one of olivine-type polyanion compounds, NASICON-type polyanion compounds, and fluorophosphate-type polyanion compounds.

[0009] Preferably, in the composite battery cell, the ratio K1 of the total capacity per unit area of any positive electrode plate to the total capacity per unit area of any other positive electrode plate is 0.9 to 1.1. The total capacity per unit area of each positive electrode plate is represented by formula I: In formula I, Sn represents the surface density of any positive active coating included in the positive electrode plate. In this positive active coating, Cm represents the gram capacity of any positive active material, Wm represents the mass percentage of this positive active material in this positive active coating, i represents the number of types of positive active materials included in each positive active coating, i is an integer greater than or equal to 1, k represents the number of positive active coatings included in each positive electrode plate, and k is an integer greater than or equal to 1. In the above composite battery cell, different positive electrode plates satisfy a specific K1 value range. Thus, different positive electrode plates basically reach a state of capacity balance, thereby being able to effectively alleviate other deterioration effects such as impedance generated between different types of positive active materials integrated in the composite battery cell. Based on this, the composite battery cell can give full play to the synergistic advantages of different positive active materials, making the energy density, rate performance, and cycle performance of the above composite battery cell be improved as a whole compared with the battery cell using a single positive active material.

[0010] Taking the first positive electrode plate and the second positive electrode plate as examples respectively, the operation modes of different formula Ⅰ are illustrated. Formula Ⅰ, For example, only one type of positive electrode active material is used in the first positive electrode plate. Using this positive electrode active material, a positive electrode active coating is provided on each side of the positive electrode current collector. The two positive electrode active coatings located on the two layers of the positive electrode current collector are symmetrically arranged. Taking the mass content of the positive electrode active material in one of the positive electrode active coatings as W1, the specific capacity of this positive electrode active material as C1, and the areal density of this positive electrode active coating as S1, the capacity of this positive electrode active coating is S1×W1×C1. Correspondingly, the capacity of the other positive electrode active coating is also calculated in the above manner. Since the two positive electrode active coatings are symmetrically arranged, the total capacity of the first positive electrode plate is 2×S1×W1×C1. For example, a first alternative implementation of the second positive electrode plate (arrangement of positive electrode active coatings: single-sided layered coating on the current collector, symmetrically arranged on both sides): The second positive electrode plate uses two types of positive electrode active materials, labeled as the first positive electrode active material and the second positive electrode active material. On one side of the positive electrode current collector, a first positive electrode active coating containing only the first positive electrode active material and a second positive electrode active coating containing only the second positive electrode active material are sequentially provided. Then, on the other side of the positive electrode current collector, positive electrode active coatings symmetric to the first positive electrode active coating and the second positive electrode active coating are correspondingly provided; on either side of the positive electrode current collector, taking the mass content of the first positive electrode active material in the first positive electrode active coating as W1, the specific capacity of this first positive electrode active material as C1, and the areal density of the first positive electrode active coating as S1, the capacity of the first positive electrode active coating is S1×W1×C1. Taking the mass content of the second positive electrode active material in the second positive electrode active coating as W2, the specific capacity of this second positive electrode active material as C2, and the areal density of the second positive electrode active coating as S2, the capacity of the second positive electrode active coating is S2×W2×C2. Correspondingly, the capacity of the positive electrode active coating on this side is (S1×W1×C1 + S2×W2×C2). In addition, the capacity of the positive electrode active coating located on the other side of the positive electrode current collector is also calculated in the above manner. Since the positive electrode active coatings provided on the other side of the positive electrode current collector are symmetric to the first positive electrode active coating and the second positive electrode active coating respectively, the total capacity of the first positive electrode plate is 2×(S1×W1×C1 + S2×W2×C2).For example, the second alternative embodiment of the second positive electrode plate (setting of the positive electrode active coating: single-sided layer coating or single-layer coating on the current collector, asymmetric setting on both sides): The second positive electrode plate uses three positive electrode active materials, labeled as the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material. On one side of the positive electrode current collector, a first positive electrode active coating containing only the first positive electrode active material and a second positive electrode active coating containing only the second positive electrode active material are sequentially arranged, and then a third positive electrode active coating containing only the third positive electrode active material is arranged on the other side of the positive electrode current collector; on the side of the positive electrode current collector where a double-layer positive electrode active coating is arranged, if the mass content of the first positive electrode active material in the first positive electrode active coating is W1, the specific capacity of the first positive electrode active material is C1, and the areal density of the first positive electrode active coating is S1, then the capacity of the first positive electrode active coating is S1×W1×C1. If the mass content of the second positive electrode active material in the second positive electrode active coating is W2, the specific capacity of the second positive electrode active material is C2, and the areal density of the second positive electrode active coating is S2, then the capacity of the second positive electrode active coating is S2×W2×C2. Correspondingly, the capacity of the positive electrode active coating on this side is (S1×W1×C1 + S2×W2×C2); on the side of the positive electrode current collector where a single-layer positive electrode active coating is arranged, if the mass content of the third positive electrode active material in the third positive electrode active coating is W3, the specific capacity of the third positive electrode active material is C3, and the areal density of the third positive electrode active coating is S3, then the capacity of the first positive electrode active coating is S3×W3×C3; then the total capacity of the first positive electrode plate is (S1×W1×C1 + S2×W2×C2 + S3×W3×C3). For example, the third alternative embodiment of the second positive electrode plate (setting of the positive electrode active coating: single-sided single-layer coating on the current collector, symmetric setting on both sides): The second positive electrode plate uses two positive electrode active materials, labeled as the first positive electrode active material and the second positive electrode active material. A positive electrode active coating is arranged on each of the two sides of the positive electrode current collector using a slurry composed of a blend of the first positive electrode active material and the second positive electrode active material. The two positive electrode active coatings located on the two layers of the positive electrode current collector are symmetrically arranged. In one of the positive electrode active coatings, the mass content of the first positive electrode active material is W1, the specific capacity of the first positive electrode active material is C1, the mass content of the second positive electrode active material is W2, the specific capacity of the second positive electrode active material is C2, and the areal density of this positive electrode active coating is S1, then the capacity of this positive electrode active coating is S1×(W1×C1 + W2×C2). Correspondingly, the capacity of the other positive electrode active coating is also calculated in the above manner. Since the two positive electrode active coatings are symmetrically arranged, the total capacity of the second positive electrode plate is 2×(S1×(W1×C1 + W2×C2)).For example, the fourth optional embodiment of the second positive electrode sheet (arrangement of the positive electrode active coating: single-sided single-layer coating on the current collector, asymmetric arrangement on both sides): A first positive electrode active coating is provided on one side of the positive electrode active coating using a slurry composed of a blend of a first positive electrode active material and a second positive electrode active material, and then a second positive electrode active coating containing only the second positive electrode active material, a single positive electrode active material, is provided on the other side of the positive electrode current collector; in the first positive electrode active coating, the mass content of the first positive electrode active material is W1, the specific capacity of the first positive electrode active material is C1, the mass content of the second positive electrode active material is W2, the specific capacity of the second positive electrode active material is C2, the areal density of the first positive electrode active coating is S1, and the capacity of the first positive electrode active coating is S1×(W1×C1 + W2×C2); in the second positive electrode active coating, the mass content of the second positive electrode active material is W3, the specific capacity of the second positive electrode active material is C3, the areal density of the second positive electrode active coating is S2, and the capacity per unit area of the second positive electrode active coating is S2×W3×C3; the total capacity per unit area of this second positive electrode sheet is (S1×(W1×C1 + W2×C2) + S2×W3×C3).

[0011] Preferably, in the second positive electrode sheet, the positive electrode active coatings constructed using different types of positive electrode active materials are laminated and / or are respectively provided on both sides of the current collector of the first positive electrode sheet. Each layer of the positive electrode active coating of the second positive electrode sheet uses only one type of positive electrode active material, excluding the positive electrode active coating in which different types of positive electrode active materials are mixed with each other. Therefore, the situation where different types of positive electrode active materials are unevenly mixed due to differences in material properties, surface tension, etc. will not occur, thereby avoiding the deterioration effect caused by the uneven distribution of the positive electrode active materials in the same positive electrode active coating. When it is necessary to integrate two or more types of positive electrode active materials on the same positive electrode sheet, the method of laminating different types of positive electrode active materials on the same side or separately providing different types of positive electrode active materials on both sides of the current collector can achieve the effect of preventing different types of positive electrode active materials from mixing with each other.

[0012] Preferably, the composite battery cell includes two types of first positive electrode sheets. The first positive electrode sheet includes a polyanion compound type positive electrode sheet and a layered transition metal oxide type positive electrode sheet. The positive electrode active material contained in the polyanion compound type positive electrode sheet is a polyanion compound type positive electrode active material, and the positive electrode active material contained in the layered transition metal oxide type positive electrode sheet is a layered transition metal oxide type positive electrode active material.

[0013] Preferably, in the composite battery cell, A1 represents the number (sheets) of the polyanion compound type positive electrode sheets, A2 represents the number (sheets) of the layered transition metal oxide type positive electrode sheets, and A1 / A2 = 0.005 - 200.

[0014] Preferably, A1 / A2 = 0.01 - 100.

[0015] In the above composite battery cell, a positive electrode sheet containing only a single positive electrode active material of polyanion compound type positive electrode active material is used, and a positive electrode sheet containing only a single positive electrode active material of layered transition metal oxide type positive electrode active material is used, so that the advantages of polyanion compound type positive electrode active material and layered transition metal oxide type positive electrode active material are integrated in the battery cell. By using the advantage that the polyanion electrode sheet has low requirements for environmental humidity, the humidity sensitivity of the positive electrode sheet integrated with the layered transition metal oxide type positive electrode active material is reduced, thereby improving the working stability and safety of the positive electrode sheet integrated with the layered transition metal oxide type positive electrode active material, and also enabling the charge and discharge of the battery cell containing the above two positive electrode active materials respectively, making full use of the advantages of the two materials to form complementary advantages. Moreover, using a positive electrode sheet with only one positive electrode active material is beneficial to the batch production of the positive electrode sheet and improves production efficiency.

[0016] Preferably, the battery cell assembly includes at least two different types of the first positive electrode sheets. In the composite battery cell, the first positive electrode sheet, the separator, and the negative electrode sheet are arranged in sequence, and different first positive electrode sheets are connected through tabs and are arranged in parallel.

[0017] Preferably, the composite battery cell includes a first positive electrode sheet A or a first positive electrode sheet B and a second positive electrode sheet, wherein the second positive electrode sheet is a layered oxide-polyanion composite positive electrode sheet; the positive electrode active material constituting the first positive electrode sheet is only a polyanion compound type positive electrode active material or only a layered transition metal oxide type positive electrode active material; the positive electrode active material contained in the layered oxide-polyanion composite positive electrode sheet includes a layered transition metal oxide type positive electrode active material and a polyanion compound type positive electrode active material.

[0018] Preferably, the layered oxide-polyanion composite positive electrode sheet includes a positive electrode active coating containing only a layered metal oxide as the positive electrode active material and a positive electrode active coating containing only a polyanion compound type as the positive electrode active material; on the same side of the current collector of the layered oxide-polyanion composite positive electrode sheet, in the direction away from the surface of the current collector, the positive electrode active coating containing the layered transition metal oxide type positive electrode active material and the positive electrode coating containing the polyanion compound type positive electrode active material are arranged in sequence.

[0019] Preferably, the battery cell assembly is composed of at least one electrode combination unit. Each electrode combination unit includes at least one first positive electrode tab A or first positive electrode tab B, one layered oxide-polyanion composite positive electrode tab, and one negative electrode tab. In the electrode combination unit, the first positive electrode tab A or first positive electrode tab B, separator, negative electrode tab, separator, and layered oxide-polyanion composite positive electrode tab are arranged in sequence. In the battery cell assembly, the first positive electrode tab A or first positive electrode tab B and the layered oxide-polyanion composite positive electrode tab are connected by a tab and are arranged in parallel.

[0020] Preferably, in the composite battery cell, let A1 represent the number (pieces) of the first positive electrode tabs, and A3 represent the number (pieces) of the layered oxide-polyanion composite positive electrode tabs, and A1 / A3 = 0.001 - 2000.

[0021] Preferably, A1 / A3 = 0.005 - 200.

[0022] Preferably, A1 / A3 = 0.01 - 100.

[0023] Preferably, the positive electrode active material used for the first positive electrode tab is a polyanion compound type positive electrode active material. In the above composite battery cell, the layered oxide-polyanion composite positive electrode tab and the polyanion compound type positive electrode tab are used in combination, so as to be able to expand the surface density range of the positive electrode tab containing the layered transition metal oxide type positive electrode active material. It can also realize the charge and discharge of the two positive electrode active materials respectively, give full play to the cycle advantages of the polyanion compound type positive electrode tab, and efficiently utilize the advantages of the two materials to form complementary advantages.

[0024] Preferably, the positive electrode active material used for the first positive electrode tab is the layered transition metal oxide type positive electrode active material. In the above composite battery cell, the layered oxide-polyanion composite positive electrode tab and the layered transition metal oxide type positive electrode tab are used in combination. Based on the advantage of the high safety performance of the polyanion complex, the composite battery cell using the layered transition metal oxide type positive electrode active material can have the advantages of high energy density and good safety at the same time.

[0025] Preferably, the current collector of the positive electrode tab includes two opposite side surfaces, and the positive electrode active coating is provided on each of the side surfaces. The ratio K2 of the total capacity per unit area of the positive electrode active coating provided on any one of the side surfaces to the total capacity per unit area of the positive electrode active coating provided on the other side surface is 0.9 - 1.1. The total capacity per unit area of the positive electrode active coating provided on the same side surface is determined according to formula II. Sn, Cm, Wm, and i included in Formula II have the same meanings as their respective meanings in Formula I. h included in Formula II represents the number of layers of the positive electrode active coating provided on the same side, and h is an integer greater than or equal to 1. In the above positive electrode sheet, a specific K2 value range is satisfied between the positive electrode active coatings located on different sides of the current collector. Thus, the two sides of the current collector of the positive electrode sheet are basically in a state of capacity balance, so that the positive electrode sheet can simultaneously have good energy density, rate performance, and cycle performance.

[0026] Preferably, the mass content of the positive electrode active material in the positive electrode active coating containing the same is 80-98%.

[0027] Preferably, the specific capacity of the layered transition metal oxide-based positive electrode active material is 80-300 mAh / g, the specific capacity of the polyanion compound-based positive electrode active material is 50-200 mAh / g, and the specific capacity of the Prussian blue compound-based positive electrode active material is 50-280 mAh / g.

[0028] Preferably, the areal density of each layer of the positive electrode active layer is 40-500 g / m 2 .

[0029] Preferably, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based negative electrode active material, a titanium-based negative electrode active material, an alloy-based negative electrode active material, a carbonyl compound-based negative electrode active material, a Schiff base compound-based negative electrode active material, an organic radical compound-based negative electrode active material, and an organic sulfide-based negative electrode active material.

[0030] Preferably, the carbon-based negative electrode active material includes at least one of hard carbon, soft carbon, graphene, and carbon nanotubes.

[0031] Preferably, the titanium-based negative electrode active material includes at least one of an oxide-based titanium-based material and a polyanion-based titanium-based material. Preferably, the oxide-based titanium-based material includes at least one of Na2Ti3O7, Na 0.6 (Cr 0.6 Ti 0.4 )O2, and Li4Ti5O 12 , and the polyanion-based titanium-based material includes at least one of NaTiOPO4 and NaTi2(PO4)3.

[0032] Preferably, the alloy-based negative electrode active material includes at least one of an Sn-based alloy, an Sb-based alloy, an In-based alloy, a Si-based alloy, and a Ge-based alloy.

[0033] According to a second aspect of the present invention, a sodium-ion battery is provided, which includes the composite battery cell as described above. The sodium-ion battery provided by the present invention has both good energy density, rate performance and cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of a single-component positive electrode tab in the first positive electrode tab;

[0035] Figure 2 is a schematic diagram of the first feasible structure in the second positive electrode tab;

[0036] Figure 3 is a schematic diagram of the second feasible structure in the second positive electrode tab;

[0037] Figure 4 is a schematic diagram of the third feasible structure in the second positive electrode tab;

[0038] Figure 5 is a schematic diagram of the fourth feasible structure in the second positive electrode tab;

[0039] Figure 6 is a schematic structural diagram of a single combined battery cell;

[0040] Figure 7 is a schematic structural diagram of a composite battery cell. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0042] Embodiment 1

[0043] In this embodiment, different layered transition metal oxide-based positive electrode active materials, polyanion compound-based positive electrode active materials, Prussian blue compound-based positive electrode active materials, and Prussian white compound-based positive electrode active materials are used to construct positive electrode tabs with different positive electrode active coating compositions. Among them, the positive electrode tab containing only a single positive electrode active material in all the positive electrode active coatings is used as the first positive electrode tab, and the positive electrode tab with a positive electrode active coating containing at least two positive electrode active materials is used as the second positive electrode tab.

[0044] 1. The first positive electrode tab

[0045] The first positive electrode tab involved in this embodiment refers to a positive electrode tab including only one positive electrode active material. The structural schematic diagram of the first-phase positive electrode tab is as Figure 1As shown, a positive electrode active coating containing only one kind of positive electrode active material is symmetrically arranged on two sides of the positive electrode current collector, and is respectively marked as the first positive electrode active coating 1-1 and the second positive electrode active coating 1-2.

[0046] (1) Preparation of polyanion compound type positive electrode plate

[0047] 1) Preparation of olivine type first positive electrode plate: Using the polyanion compound NaFePO4 with an olivine structure and a specific capacity of 100 mAh / g as the positive electrode active material, a positive electrode coating slurry is prepared by uniformly mixing NaFePO4, binder PVDF, and conductive agent acetylene black according to a mass ratio of 90:5:5. Then, the above positive electrode coating slurry is respectively coated on two opposite sides of the positive electrode current collector, and dried, so as to form symmetrically arranged first positive electrode active coating 1-1 and second positive electrode active coating 1-2 on two sides of the positive electrode current collector. The positive electrode active material contained in the first positive electrode active coating 1-1 and the second positive electrode active coating 1-2 is only NaFePO4. The polyanion compound type positive electrode plate thus obtained is marked as the olivine type first positive electrode plate. In the prepared olivine type first positive electrode plate, the positive electrode active coating surface density included is 300 g / m 2 of the positive electrode plate is marked as olivine type first positive electrode plate I, and the positive electrode plate with a positive electrode active coating surface density of 200 g / m 2 is marked as olivine type first positive electrode plate II.

[0048] 2) Preparation of NASICON type first positive electrode plate: Using the polyanion compound NASICON with a specific capacity of 120 mAh / g as the positive electrode active material, a positive electrode coating slurry is prepared by uniformly mixing NASICON, binder PVDF, and conductive agent acetylene black according to a mass ratio of 90:5:5. Then, the above positive electrode coating slurry is respectively coated on two opposite sides of the positive electrode current collector, and dried, so as to form symmetrically arranged first positive electrode active coating 1-1 and second positive electrode active coating 1-2 on two sides of the positive electrode current collector. The positive electrode active material contained in the first positive electrode active coating 1-1 and the second positive electrode active coating 1-2 is only NASICON. The polyanion compound type positive electrode plate thus obtained is marked as NASICON type first positive electrode plate. In the prepared NASICON type first positive electrode plate, the positive electrode active coating surface density included is 120 g / m 2 of the positive electrode plate is marked as NASICON type first positive electrode plate I, and the positive electrode plate with a positive electrode active coating surface density of 100 g / m 2 is marked as NASICON type first positive electrode plate II.

[0049] The structural schematic diagrams of the olivine-type first positive electrode plate and the NASICON-type first positive electrode plate prepared above are as Figure 1 shown.

[0050] (2) Layered transition metal oxide-type positive electrode plate

[0051] Preparation of NaMnO₂ first positive electrode plate: Using the layered transition metal oxide NaMnO₂ with a specific capacity of 180 mAh / g as the positive electrode active material, a positive electrode coating slurry is prepared by uniformly mixing NaMnO₂, binder PVDF, and conductive agent acetylene black in a mass ratio of 80:10:10. Then, the above positive electrode coating slurry is respectively coated on two opposite side surfaces of the positive electrode current collector, and dried, so as to form symmetrically arranged first positive electrode active coating 1-1 and second positive electrode active coating 1-2 on the two side surfaces of the positive electrode current collector. The positive electrode active material contained in the first positive electrode active coating 1-1 and the second positive electrode active coating 1-2 is only NaMnO₂. The layered transition metal oxide-type positive electrode plate thus prepared is marked as the NaMnO₂ first positive electrode plate. In the prepared NaMnO₂ first positive electrode plate, the positive electrode plate with a positive electrode active coating surface density of 200 g / m 2 is marked as NaMnO₂ first positive electrode plate Ⅰ, and the positive electrode plate with a positive electrode active coating surface density of 300 g / m 2 is marked as NaMnO₂ first positive electrode plate Ⅱ.

[0052] The structural schematic diagram of the above-prepared NaMnO₂ first positive electrode plate is as Figure 1 shown.

[0053] (3) Prussian blue compound-type positive electrode plate

[0054] Using the Prussian blue compound Na₂Fe[Fe(CN)₆] with a specific capacity of 150 mAh / g as the positive electrode active material, a positive electrode coating slurry is prepared by uniformly mixing Na₂Fe[Fe(CN)₆], binder PVDF, and conductive agent acetylene black in a mass ratio of 90:5:5. Then, the above positive electrode coating slurry is respectively coated on two opposite side surfaces of the positive electrode current collector, and dried, so as to form symmetrically arranged first positive electrode active coating 1-1 and second positive electrode active coating 1-2 on the two side surfaces of the positive electrode current collector. The positive electrode active material contained in the first positive electrode active coating 1-1 and the second positive electrode active coating 1-2 is only Na₂Fe[Fe(CN)₆]. The Prussian blue compound-type positive electrode plate thus prepared is marked as the Na₂Fe[Fe(CN)₆] first positive electrode plate. In the prepared Na₂Fe[Fe(CN)₆] first positive electrode plate, the positive electrode plate with a positive electrode active coating surface density of 100 g / m 2The positive electrode plate is marked as the first positive electrode plate I of Na2Fe[Fe(CN)6], and the positive electrode active coating surface density it includes is 120 g / m 2 The positive electrode plate is marked as the first positive electrode plate II of Na2Fe[Fe(CN)6].

[0055] The structural schematic diagram of the first positive electrode plate of Na2Fe[Fe(CN)6] prepared above is as Figure 1 shown.

[0056] 2. The second positive electrode plate

[0057] The second positive electrode plate involved in this embodiment refers to a positive electrode plate including at least two positive electrode active materials. The first feasible structural form of the second positive electrode plate is as Figure 2 shown. The first positive electrode active coating 2-1 and the second positive electrode active coating 2-2 which are mutually composite are symmetrically arranged on two sides of the positive electrode current collector. The positive electrode active material contained in the first positive electrode active coating 2-1 is only one kind of the first positive electrode active material, and the positive electrode active material contained in the second positive electrode active coating 2-2 is only one kind of the second positive electrode active material, and the first positive electrode active material and the second positive electrode active material are different from each other. The second feasible structural form of the second positive electrode plate is as Figure 3 shown. The first positive electrode active coating 3-1 and the second positive electrode active coating 3-2 which are mutually composite are arranged on one side of the positive electrode current collector, and the third positive electrode active coating 3-3 is arranged on the other side of the positive electrode current collector. The positive electrode active material contained in the first positive electrode active coating 3-1 is only one kind of the first positive electrode active material, the positive electrode active material contained in the second positive electrode active coating 3-2 is only one kind of the second positive electrode active material, and the positive electrode active material contained in the third positive electrode active coating 3-3 is only one kind of the third positive electrode active material, and the third positive electrode active material is different from at least one of the first positive electrode active material and the second positive electrode active material. The third feasible structural form of the second positive electrode plate is as Figure 4 shown. The blended positive electrode active coatings 4-1 are symmetrically arranged on both sides of the positive electrode current collector, and the blended positive electrode active coating 4-1 contains two different kinds of positive electrode active materials (the first positive electrode active material and the second positive electrode active material). The fourth feasible structural form of the second positive electrode plate is as Figure 5 shown. The blended positive electrode active coating 5-1 is arranged on one side of the positive electrode current collector, and the blended positive electrode active coating 5-1 contains two different kinds of positive electrode active materials (the first positive electrode active material and the second positive electrode active material), and the single-phase positive electrode active coating 5-2 using only one kind of positive electrode active material is arranged on the other side of the positive electrode current collector.

[0058] (1) Symmetrically layered coated second positive electrode plate

[0059] The layered transition metal oxide NaMnO2 with a specific capacity of 180 mAh / g is used as the positive electrode active material. The first positive electrode coating slurry is prepared by uniformly mixing NaMnO2, binder PVDF, and conductive agent acetylene black in a mass ratio of 80:10:10. The polyanion compound NaFePO4 with an olivine structure and a specific capacity of 100 mAh / g is used as the positive electrode active material. The second positive electrode coating slurry is prepared by uniformly mixing NaFePO4, binder PVDF, and conductive agent acetylene black in a mass ratio of 90:5:5. The first positive electrode coating slurry is coated on one side of the positive electrode current collector, dried, and a first positive electrode active coating 2-1 is formed. Then, the second positive electrode coating slurry is coated on the surface of the first positive electrode active coating 2-1, dried, and a second positive electrode active coating 2-2 is formed. Then, the above operations are repeated on the other side of the positive electrode current collector to symmetrically arrange the mutually composite first positive electrode active coating 2-1 (using the layered transition metal oxide NaMnO2 as the positive electrode active material) and the second positive electrode active coating 2-2 (using the polyanion compound NaFePO4 as the positive electrode active material) on both sides of the positive electrode current collector. The surface density of the first positive electrode active coating 2-1 is 80 g / m 2 , and the surface density of the second positive electrode active coating 2-2 is 150 g / m 2 . The symmetrically layered-coated second positive electrode sheet thus prepared is marked as a layered oxide-polyanion layered-coated positive electrode sheet.

[0060] The structural schematic diagram of the above-prepared layered oxide-polyanion layered-coated positive electrode sheet is as shown in Figure 2 the figure.

[0061] (2) Symmetrically co-doped second positive electrode sheet

[0062] The polyanion compound NaFePO4 with an olivine structure and a specific capacity of 100 mAh / g and the layered transition metal oxide NaMnO2 with a specific capacity of 180 mAh / g are used as the positive electrode active materials. The above NaFePO4 and NaMnO2 are mixed in a mass ratio of 90:80, and then the obtained blended positive electrode active material, binder PVDF, and conductive agent acetylene black are uniformly mixed in a mass ratio of 90:5:5 to prepare a positive electrode coating slurry. Then, the positive electrode coating slurry is respectively coated on two opposite sides of the positive electrode current collector, dried, so as to form two symmetrically arranged blended positive electrode active coatings 4-1 on both sides of the positive electrode current collector. The positive electrode active material contained in each blended positive electrode active coating 4-1 is the blended NaFePO4 and NaMnO2, and the surface density of each blended positive electrode active coating 4-1 is 220 g / m 2 . The layered transition metal oxide type positive electrode sheet thus prepared is marked as a symmetrically co-doped second positive electrode sheet.

[0063] The structural schematic diagram of the symmetrically co-doped second positive electrode plate prepared above is as shown in Figure 4 the figure.

[0064] (2) Asymmetric second positive electrode plate

[0065] Using the polyanion compound NaFePO4 with an olivine structure and a specific capacity of 100 mAh / g and the layered transition metal oxide NaMnO2 with a specific capacity of 180 mAh / g as the positive electrode active materials. Mix the above-mentioned NaFePO4 and NaMnO2 in a mass ratio of 90:80, and then uniformly mix the resulting blended positive electrode active material, binder PVDF, and conductive agent acetylene black in a mass ratio of 90:5:5 to prepare the first positive electrode coating slurry. Mix the polyanion compound NaFePO4, binder PVDF, and conductive agent acetylene black in a mass ratio of 90:5:5 uniformly to prepare the second positive electrode coating slurry. Coat the first positive electrode coating slurry on one side of the positive electrode current collector, dry it to form a blended positive electrode active coating 5-1, and then coat the second positive electrode coating slurry on the other side of the positive electrode current collector, dry it to form a single-phase positive electrode active coating 5-2. The areal density of the blended positive electrode active coating 5-1 is 200 g / m 2 , and the areal density of the single-phase positive electrode active coating 5-2 is 300 g / m 2 . Mark the resulting layered transition metal oxide type positive electrode plate as the asymmetric second positive electrode plate.

[0066] The structural schematic diagram of the asymmetric second positive electrode plate prepared above is as shown in Figure 5 the figure.

[0067] According to Equation Ⅰ Calculate the total capacity per unit area of the above positive electrode plate prepared in this example; in Equation Ⅰ, Sn represents the areal density of any positive electrode active coating included in the positive electrode plate. In this positive electrode active coating, Cm represents the specific capacity of any positive electrode active material, Wm represents the mass percentage of this positive electrode active material in this positive electrode active coating, i represents the number of types of positive electrode active materials included in each positive electrode active coating, i is an integer greater than or equal to 1, k represents the number of positive electrode active coatings included in each positive electrode plate, and k is an integer greater than or equal to 1. K1 involved in Table 1 is the ratio of the total capacity per unit area of positive electrode plate A to the total capacity per unit area of positive electrode plate B. In Equation Ⅰ, represents the capacity level per unit area of a certain positive electrode active coating in the positive electrode plate. After calculating the capacity per unit area of each positive electrode active coating separately, sum up the calculation results, that is, calculate according to to finally obtain the capacity level per unit area of the entire positive electrode plate.

[0068] For the first positive electrode plate, the calculation method of the total capacity is as follows: Taking the mass content of the positive electrode active material used in it in the first positive electrode active coating 1-1 as W1, the specific capacity of this positive electrode active material as C1, and the areal density of the first positive electrode active coating 1-1 as S1, then the capacity per unit area of the first positive electrode active coating 1-1 is S1×W1×C1. Correspondingly, the capacity of the second positive electrode active coating 1-2 is also calculated in the above manner. Since the first positive electrode active coating 1-1 and the second positive electrode active coating 1-2 are symmetrically arranged, the total capacity per unit area of this first positive electrode plate is 2×S1×W1×C1.

[0069] For the symmetrically layered-coated second positive electrode plate, the calculation method of its total capacity is as follows: On either side of the positive electrode current collector, taking the mass content of the positive electrode active material in the first positive electrode active coating 2-1 as W1, the specific capacity of this positive electrode active material as C1, and the areal density of the first positive electrode active coating 2-1 as S1, then the capacity per unit area of the first positive electrode active coating 2-1 is S1×W1×C1. Taking the mass content of the positive electrode active material in the second positive electrode active coating 2-2 as W2, the specific capacity of this positive electrode active material as C2, and the areal density of the second positive electrode active coating 2-2 as S2, then the capacity per unit area of the second positive electrode active coating 2-2 is S2×W2×C2. And, correspondingly, the capacity per unit area of the positive electrode active coating on this side is (S1×W1×C1 + S2×W2×C2). In addition, the capacity of the positive electrode active coating located on the other side of the positive electrode current collector is also calculated in the above manner. Since the positive electrode active coatings arranged on the other side of the positive electrode current collector are symmetric to the first positive electrode active coating 2-1 and the second positive electrode active coating 2-2 respectively, the total capacity per unit area of this first positive electrode plate is 2×(S1×W1×C1 + S2×W2×C2).

[0070] For the symmetrically co-doped second positive electrode plate, the calculation method of its total capacity is as follows: In one layer of the blended positive electrode active coating 4-1, the mass content of one kind of positive electrode active substance (the polyanion compound NaFePO4) is W1, the specific capacity of this positive electrode active substance is C1, the mass content of another kind of positive electrode active substance (the layered transition metal oxide NaMnO2) is W2, the specific capacity of this positive electrode active substance is C2, and the areal density of this layer of blended positive electrode active coating 4-1 is S1, then the capacity per unit area of this layer of blended positive electrode active coating 4-1 is S1×(W1×C1 + W2×C2). Correspondingly, the capacity of the other layer of blended positive electrode active coating 4-1 is also calculated in the above manner. Since the two layers of blended positive electrode active coatings 4-1 are symmetrically arranged, the total capacity per unit area of this second positive electrode plate is 2×(S1×(W1×C1 + W2×C2)).

[0071] For the asymmetric second positive electrode sheet, the calculation method of its total capacity is as follows: In the blended positive electrode active coating 5-1 containing multiple positive electrode active materials, the mass content of one positive electrode active substance (the polyanion compound NaFePO4) is W1, and its gram capacity is C1. The mass content of another positive electrode active substance (the layered transition metal oxide NaMnO2) is W2, and its gram capacity is C2. The areal density of the blended positive electrode active coating 5-1 is S1. Then, the capacity per unit area of the blended positive electrode active coating 5-1 is S1×(W1×C1 + W2×C2). In the single-phase positive electrode active coating 5-2 containing only one positive electrode active material, the mass content of the positive electrode active material (the polyanion compound NaFePO4) is W3, and the gram capacity of the third positive electrode active material is C3. The areal density of the single-phase positive electrode active coating 5-2 is S2. The capacity per unit area of the single-phase positive electrode active coating 5-2 is S2×W3×C3. The total capacity per unit area of this second positive electrode sheet is (S1×(W1×C1 + W2×C2) + S2×W3×C3).

[0072] Table 3. Calculation of the total capacity per unit area of each positive electrode sheet

[0073]

[0074]

[0075] Example 2

[0076] In this example, different sodium-ion battery cells were prepared by using the different positive electrode sheets obtained in Example 1, negative electrode sheets, and separators.

[0077] The negative electrode sheet used in this example was prepared as follows: Hard carbon was used as the negative electrode active material, and the hard carbon, conductive agent acetylene black, binder sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 94:1:2:3 to form a negative electrode coating slurry. Then, the above negative electrode coating slurry was respectively coated on two opposite side surfaces of the negative electrode current collector and dried, so as to form two symmetrically arranged layers of negative electrode active coatings on the two side surfaces of the negative electrode current collector.

[0078] The separator used in this example was a polyethylene film.

[0079] The positive electrode sheets prepared in Application Example 1 were combined with the above-mentioned negative electrode sheets prepared in this example in different combinations to construct sodium-ion battery cells, and the cells with different positive electrode sheet combinations were numbered. The specific grouping situations are shown in Table 2 and Table 3. Among them, the cells shown in Table 2 are single-combination cells that use only one type of positive electrode sheet, and the cells shown in Table 3 are composite cells that use two types of positive electrode sheets. Using the data shown in Table 1 for calculation, the capacity distribution per unit area of the positive electrode sheets of the composite cells with the positive electrode sheets combined is shown in Table 4. In Table 4, K1 is the ratio of the total capacity per unit area of positive electrode sheet A to the total capacity per unit area of positive electrode sheet B in the composite cell.

[0080] The sodium-ion battery using a single-combination cell was prepared as follows: 60 positive electrode sheets 6-1 and 61 negative electrode sheets 6-2 were used. The positive electrode sheets 6-1 and the negative electrode sheets 6-2 were arranged at intervals in turn, and each pair of electrode sheets was separated by a separator 6-3. A single-combination cell was obtained through a stacking or winding process. The structural schematic diagram of the single-combination cell is as Figure 6 shown; then the single-combination cell was placed in a battery case, and then the battery case was processed such as welding the electrode tabs and baking. After the moisture content was detected to be qualified, an appropriate amount of electrolyte was injected into the battery case, and it was encapsulated. Through aging, formation, and evacuation and encapsulation, a sodium-ion battery was prepared.

[0081] The sodium-ion battery using a composite cell was prepared as follows: 60 positive electrode sheets (among them, 30 positive electrode sheets A7-1 and 30 positive electrode sheets B7-2) and 61 negative electrode sheets 7-3 were used. According to the arrangement order of positive electrode sheet A7-1, negative electrode sheet 7-3, positive electrode sheet B7-2, negative electrode sheet 7-3, positive electrode sheet A7-1... the positive electrode sheet A7-1, negative electrode sheet 7-3, and positive electrode sheet B7-2 were arranged in a repeated order in turn. Each pair of adjacent electrode sheets was separated by a separator 7-4. A single-combination cell was obtained through a stacking or winding process. The structural schematic diagram of the composite cell is as Figure 7 shown; then the single-combination cell was placed in a battery case, and then the battery case was processed such as welding the electrode tabs and baking. After the moisture content was detected to be qualified, an appropriate amount of electrolyte was injected into the battery case, and it was encapsulated. Through aging, formation, and evacuation and encapsulation, a sodium-ion battery was prepared.

[0082] Table 2. Positive electrode sheets corresponding to single-combination cells

[0083]

[0084] Table 3. Positive electrode sheet combination situations included in composite cells

[0085]

[0086] Table 4. Capacity distribution per unit area of the cathode electrode combination in the composite battery cell

[0087]

[0088]

[0089] Test example

[0090] 1. Test object

[0091] In this test example, the sodium-ion battery prepared in Example 2 was used as the test object to conduct relevant performance tests.

[0092] 2. Test content

[0093] (1) Energy density

[0094] The tested sodium-ion battery was charged at a constant current and constant voltage of 0.33C to 4.25V, cut off at 0.02C, and then discharged at 0.33C to 2.8V. Record the capacity, average voltage and battery cell mass. Calculate the energy density of the sodium-ion battery according to the following formula: Energy density = Capacity * Average voltage / Battery mass.

[0095] (2) DC impedance

[0096] The tested sodium-ion battery was charged at a constant current and constant voltage of 0.33C to 4.25V, cut off at 0.02C, and then discharged at 0.33C for 90 min and left standing for 10 min. Record the voltage V1 at the end of standing; then discharge at 2C (current I) for 10 s and record the voltage V2 at the end of discharge. Calculate the DC impedance of the sodium-ion battery according to the following formula: DC impedance = |V1 - V2| / I.

[0097] (3) Cycle performance

[0098] The tested sodium-ion battery was placed in a 45°C constant temperature oven, charged at a constant current and constant voltage of 1C, cut off at 0.02C, and then discharged at 1C until the 80% SOH was reached, and record the number of cycles.

[0099] 3. Test results

[0100] The test results of this test example are shown in Table 5. In order to analyze the test results more intuitively, the tested battery cells will be grouped and discussed below according to the types of cathode active materials included in the battery cells.

[0101] Among the tested composite battery cells, the positive active materials used in composite battery cells 1, 2, 5, 6, 7, 8, and 9 all include: the polyanion compound NaFePO4 with an olivine structure and a specific capacity of 100 mAh / g, and the layered transition metal oxide NaMnO2 with a specific capacity of 180 mAh / g. For single-combination battery cells, the positive active materials used in single-combination battery cells 1 and 2 are the polyanion compound NaFePO4 with an olivine structure and a specific capacity of 100 mAh / g, and the positive active materials used in single-combination battery cells 5 and 6 are both the layered transition metal oxide NaMnO2 with a specific capacity of 180 mAh / g. Therefore, taking single-combination battery cells 1, 2, 5, and 6 as references, the performance of composite battery cells 1, 2, 5, 6, 7, 8, and 9 was analyzed. Compared with the reference single-combination battery cells that each only use one type of positive active material, by integrating different types of positive active materials in the same battery cell, composite battery cells 1, 2, 5, 6, 7, 8, and 9 can make the obtained composite battery cells have better cycling characteristics than single-combination battery cells that only contain one type of positive active material. At the same time, the energy density and DC impedance value of these combined battery cells can be maintained at an applicable level, and there is no situation of a sharp drop in energy density or a sharp increase in DC impedance compared with single-combination battery cells. Among them, the battery cells used in composite battery cell 1 and composite battery cell 2 both belong to the first positive electrode plates where each plate only contains one type of positive active material. However, through the data shown in Table 4, composite battery cell 1 meets the condition that the ratio of the total capacity per unit area of any two positive electrode plates is within the range of 0.9 to 1.1, while composite battery cell 2 does not meet the above condition. And the data shown in Table 5 indicates that the comprehensive performance of composite battery cell 1 is better than that of composite battery cell 2. On the other hand, composite battery cells 5 to 9 all include the second positive electrode plates containing two types of positive active materials. Among these composite battery cells: the second positive electrode plates included in composite battery cells 5, 6, and 7 do not have a positive active coating containing a blend of multiple positive active materials. The second positive electrode plates used in these composite battery cells obtain the second positive electrode plates with different types of positive active materials distributed in different active coatings by means of co-lateral layer coating to construct the positive active coating or by separating the positive active coatings containing different positive active materials on both sides of the current collector. Among these positive electrode plates; while the second positive electrode plates included in composite battery cells 8 and 9 both have at least one positive active coating prepared by blending more than one positive active material. Different types of positive active materials have certain differences in material properties. For example, their surface stress conditions are inconsistent, which makes the dispersion uniformity of the system containing a blend of different types of positive active materials lower than that of the system only containing the same type of positive active material. And if there is uneven distribution between different positive active materials, it is easy to make the coating of the positive active paste difficult and will also have a certain adverse impact on the electrical properties of the formed positive active coating.By comparison, among the composite battery cells 5-9, the measured number of cycle times of the composite battery cells 5-7 is higher than that of the composite battery cells 8 and 9 respectively, which precisely illustrates the above problem.

[0102] Among the tested composite battery cells, the positive active materials used in the composite battery cells 3 and 4 both include: the polyanion compound NASICON with a specific capacity of 120 mAh / g and the Prussian blue compound Na2Fe[Fe(CN)6] with a specific capacity of 150 mAh / g. Regarding the single composite battery cells, the positive active material used in the single composite battery cells 3 and 4 is the polyanion compound NASICON with a specific capacity of 120 mAh / g, and the positive active materials used in the single composite battery cells 7 and 8 are both the Prussian blue compound Na2Fe[Fe(CN)6] with a specific capacity of 150 mAh / g. Therefore, taking the single composite battery cells 3, 4, 7, and 8 as references, the performance of the composite battery cells 3 and 4 is analyzed.

[0103] Compared with the reference single composite battery cells that only use one type of positive active material respectively, by integrating different types of positive active materials in the same battery cell, the composite battery cells 3 and 4 can endow the obtained composite battery cells with better cycle characteristics than the single composite battery cells that only contain one type of positive active material. At the same time, the energy density and DC impedance value of these composite battery cells can be maintained at an applicable level, without the situation of a sharp drop in energy density or a sharp increase in DC impedance compared with the single composite battery cells. The battery cells used in the composite battery cell 3 and the composite battery cell 4 both belong to the first positive electrode plate in which each piece only contains one type of positive active material. However, through the data shown in Table 4, the ratio of the total capacity per unit area of any two positive electrode plates of the composite battery cell 3 belongs to the range of 0.9-1.1, while the composite battery cell 4 does not meet the above conditions. And the data shown in Table 5 indicates that the comprehensive performance of the composite battery cell 3 is better than that of the composite battery cell 4.

[0104] Table 5. Performance test results of sodium-ion batteries in this test example

[0105]

[0106]

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A composite battery cell applicable to sodium-ion batteries, characterized in that: The composite battery cell includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active coating; the number of types of the positive electrode sheets is greater than 1, and among the positive electrode sheets, the compositions of the positive electrode active material components contained in at least two of the positive electrode sheets are different from each other; The positive electrode sheet includes at least one of a first positive electrode sheet and a second positive electrode sheet; the first positive electrode sheet contains only one positive electrode active material; the second positive electrode sheet includes at least two positive electrode active materials; The composite battery cell further includes a negative electrode sheet and a separator. In the composite battery cell, the positive electrode sheets and the negative electrode sheets are arranged at intervals, and a separator is also provided between the positive electrode sheet and the negative electrode sheet; In the composite battery cell, the ratio K1 of the total capacity per unit area of any one of the positive electrode sheets to the total capacity per unit area of any other positive electrode sheet is 0.9 to 1.1, and the total capacity per unit area of each positive electrode sheet is expressed by formula I: In formula I, Sn represents the surface density of any one of the positive electrode active coatings included in the positive electrode sheet. In this layer of the positive electrode active coating, Cm represents the gram capacity of any one of the positive electrode active materials, Wm represents the mass percentage of this type of positive electrode active material in this layer of the positive electrode active coating, i represents the number of types of the positive electrode active materials included in each layer of the positive electrode active coating, i is an integer greater than or equal to 1, and k represents the number of layers of the positive electrode active coatings included in each positive electrode sheet, k is an integer greater than or equal to 1.

2. The composite battery cell applicable to sodium-ion batteries according to claim 1, wherein: The positive electrode active materials contained in the composite battery cell include at least two of layered transition metal oxide-based positive electrode active materials, polyanion compound-based positive electrode active materials, Prussian blue compound-based positive electrode active materials, and Prussian white compound-based positive electrode active materials. The positive electrode active materials are used to construct the positive electrode active coatings of the positive electrode sheets.

3. The composite battery cell applicable to sodium ion batteries according to claim 1, characterized in that: In the second positive electrode sheet, the positive electrode active coatings constructed by using different types of the positive electrode active materials are laminated and / or respectively arranged on both sides of the current collector of the first positive electrode sheet.

4. The composite battery cell applicable to a sodium ion battery according to claim 2, characterized in that: The first positive electrode sheet includes a polyanion compound type positive electrode sheet and a layered transition metal oxide type positive electrode sheet. The positive electrode active material contained in the polyanion compound type positive electrode sheet is a polyanion compound-based positive electrode active material, and the positive electrode active material contained in the layered transition metal oxide type positive electrode sheet is a layered transition metal oxide-based positive electrode active material.

5. The composite battery cell applicable to sodium ion batteries according to claim 4, wherein: In the composite battery cell, A1 represents the number of the polyanion compound type positive electrode sheets, A2 represents the number of the layered transition metal oxide type positive electrode sheets, and A1 / A2 = 0.005 to 200.

6. The composite battery cell applicable to sodium-ion batteries according to claim 1, wherein: The composite battery cell includes at least two different first positive electrode sheets. In the composite battery cell, the first positive electrode sheets, the separator, and the negative electrode sheet are arranged in sequence, and different first positive electrode sheets are connected by tabs and arranged in parallel.

7. The composite battery cell applicable to sodium-ion batteries according to claim 2, characterized in that: The composite battery cell includes the first positive electrode sheet and the second positive electrode sheet, wherein the second positive electrode sheet is a layered oxide-polyanion composite positive electrode sheet; The positive electrode active material constituting the first positive electrode sheet is only the polyanion compound type positive electrode active material or only the layered transition metal oxide type positive electrode active material; The positive electrode active material contained in the layered oxide-polyanion composite positive electrode sheet includes a layered transition metal oxide type positive electrode active material and a polyanion compound type positive electrode active material.

8. The composite battery cell applicable to a sodium ion battery according to claim 7, wherein: The layered oxide-polyanion composite positive electrode sheet includes a positive electrode active coating in which the positive electrode active material contained is only a layered metal oxide and a positive electrode active coating in which the positive electrode active material contained is only a polyanion compound type; on the same side of the current collector of the layered oxide-polyanion composite positive electrode sheet, in the direction away from the surface of the current collector, the positive electrode active coating containing the layered transition metal oxide type positive electrode active material and the positive electrode active coating containing the polyanion compound type positive electrode active material are arranged in sequence.

9. The composite battery cell applicable to a sodium ion battery according to claim 7, wherein: The composite battery cell includes at least two different first positive electrode sheets. In the composite battery cell, the first positive electrode sheet, the separator, the negative electrode sheet, the separator, and the layered oxide-polyanion composite positive electrode sheet are arranged in sequence, and different positive electrode sheets are connected by tabs and arranged in parallel.

10. The composite battery cell applicable to sodium ion batteries according to claim 7, wherein: In the composite battery cell, A1 represents the number of the first positive electrode sheets, A3 represents the number of the layered oxide-polyanion composite positive electrode sheets, and A1 / A3 = 0.005 to 200.

11. The composite battery cell applicable to sodium ion batteries according to claim 7, characterized in that: The positive electrode active material used for the first positive electrode sheet is the polyanion compound type positive electrode active material.

12. The composite battery cell applicable to sodium ion batteries according to claim 7, wherein: The positive electrode active material used for the first positive electrode sheet is the layered transition metal oxide type positive electrode active material.

13. The composite battery cell applicable to a sodium ion battery according to any one of claims 1 to 12, characterized in that: The current collector of the positive electrode sheet includes two side surfaces facing each other, and a positive electrode active coating is provided on each of the side surfaces. The ratio K2 of the total capacity per unit area of the positive electrode active coating provided on any one of the side surfaces to the total capacity per unit area of the positive electrode active coating provided on the other side surface is 0.9 to 1.

1. The total capacity per unit area of the positive electrode active coating provided on the same side surface is determined according to Formula II. In Formula II, Sn, Cm, Wm, and i included therein have the same meanings as those in Formula I respectively. h included in Formula II represents the number of layers of the positive electrode active coating provided on the same side surface, and h is an integer greater than or equal to 1.

14. The composite battery cell applicable to a sodium ion battery according to any one of claims 1 to 12, characterized in that: The mass content of the positive electrode active material in the positive electrode active coating containing it is 80 to 98%.

15. The composite battery cell applicable to sodium ion batteries according to claim 2, wherein: The specific capacity of the layered transition metal oxide type positive electrode active material is 80 to 300 mAh / g, the specific capacity of the polyanion compound type positive electrode active material is 50 to 200 mAh / g, and the specific capacity of the Prussian blue compound type positive electrode active material is 50 to 280 mAh / g.

16. The composite battery cell applicable to a sodium-ion battery according to any one of claims 1 to 12, characterized in that: The areal density of each layer of the positive electrode active coating is 40 to 500 g / m 2 .

17. A sodium-ion battery, characterized in that: Including the composite battery cell according to any one of claims 1 to 16.

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