Composite sodium supplement, positive electrode sheet, preparation method thereof, and electric device

Abstract

The present application relates to the technical field of energy storage devices, and particularly relates to a sodium supplement, a positive plate, a preparation method of the positive plate and an electric device. The composite sodium supplement is located in the positive plate of a sodium ion energy storage device, and the composite sodium supplement comprises: a first sodium supplement and a second sodium supplement, the first sodium supplement has a first oxidation potential, the second sodium supplement has a second oxidation potential, the first oxidation potential is less than 3.9V, and the second oxidation potential is 3.9V-4.4V. Since the composite sodium supplement is arranged in the positive plate, the composite sodium supplement has the advantages of easy operation and processing, reduced processing procedures, no harsh processing conditions and the like, and can realize industrial application. In addition, the composite sodium supplement has a relatively comprehensive sodium supplement function, can form a certain oxidation potential gradient, and realizes the effect of gradient sodium supplement. The sodium ion energy storage device can realize full-stage sodium supplement from the initialization stage to the subsequent cycle charging and discharging stage, and then the electrochemical performance of the sodium ion energy storage device is improved from the entire process of formation to cycle charging and discharging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage devices, in particular to a composite sodium supplementing agent, a positive electrode sheet, a preparation method thereof and an electric device. BACKGROUND

[0002] Since the positive electrode sheet of the sodium ion energy storage device has the problem of sodium loss, the lost sodium can be supplemented through the sodium supplementing technology. However, the current sodium supplementing technology is difficult to be industrialized, or the sodium supplementing function is relatively single, and the sodium ion energy storage device is difficult to supplement sodium in the whole stage from the initialization stage to the subsequent cycle charging and discharging stage, thereby being difficult to improve the electrochemical performance of the sodium ion energy storage device from the whole process of the initialization to the cycle charging and discharging. SUMMARY

[0003] The embodiments of the present application disclose a composite sodium supplementing agent, a positive electrode sheet, a preparation method thereof and an electric device. The composite sodium supplementing agent can be industrialized and can realize gradient sodium supplementing, and can supplement sodium in the whole stage from the initialization stage to the subsequent cycle charging and discharging stage, thereby being capable of improving the electrochemical performance of the sodium ion energy storage device from the whole process of the initialization to the cycle charging and discharging.

[0004] In order to achieve the above-mentioned purpose, in a first aspect, the present application discloses a composite sodium supplementing agent, which is arranged in a positive electrode sheet of a sodium ion energy storage device, and the composite sodium supplementing agent comprises: a first sodium supplementing agent and a second sodium supplementing agent, the first sodium supplementing agent has a first oxidation potential, the second sodium supplementing agent has a second oxidation potential, the first oxidation potential is less than 3.9V, and the second oxidation potential is 3.9V-4.4V.

[0005] As an optional implementation, in the embodiments of the present application, the first oxidation potential is less than or equal to 3.8V, and / or the second oxidation potential is 3.9V-4.1V.

[0006] As an optional implementation, in the embodiments of the present application, the first sodium supplementing agent comprises a mixture of one or more of NaNiO2, NaCrO2, Na2MnO2, NaFeO2, Na x Fe (1-y) Al y O2, Na x Fe (1-y) Ti y O2(0.8≤x≤2, y≧0), and / or the second sodium supplementing agent comprises a mixture of one or more of Na2O2, Na2O, Na3P, Na2C2O2, Na2C2O4.

[0007] As an optional implementation, in the embodiment of the present application, the molar ratio of the first sodium supplementing agent to the second sodium supplementing agent is (2-5):1.

[0008] In a second aspect, the present application discloses a positive electrode sheet of a sodium ion energy storage device, wherein the working voltage of the sodium ion energy storage device is 1.5-4.1 V, and the positive electrode sheet comprises the composite sodium supplementing agent according to the first aspect.

[0009] As an optional implementation, in the embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector, and a positive electrode active material layer and a sodium supplementing layer arranged on the positive electrode current collector, wherein the positive electrode active material layer comprises the second sodium supplementing agent, and the sodium supplementing layer comprises the first sodium supplementing agent.

[0010] As an optional implementation, in the embodiment of the present application, the sodium supplementing layer further comprises a first conductive agent and a first solvent, wherein the mass ratio of the first sodium supplementing agent, the first conductive agent and the first solvent is 80:(10-15):150.

[0011] As an optional implementation, in the embodiment of the present application, the positive electrode active material layer further comprises a positive electrode active substance, a second conductive agent and a second solvent, wherein the mass ratio of the second sodium supplementing agent and the positive electrode active substance is (1-5):100.

[0012] As an optional implementation, in the embodiment of the present application, the sodium supplementing layer further comprises the second sodium supplementing agent, and / or the positive electrode active material layer further comprises the first sodium supplementing agent.

[0013] As an optional implementation, in the embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector, and a positive electrode active material layer arranged on the positive electrode current collector, wherein the positive electrode active material layer comprises the first sodium supplementing agent and the second sodium supplementing agent.

[0014] As an optional implementation, in the embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector, and a positive electrode active material layer and a sodium supplementing layer arranged on the positive electrode current collector in sequence, wherein the sodium supplementing layer comprises the first sodium supplementing agent and the second sodium supplementing agent.

[0015] In a third aspect, the present application discloses a preparation method of the positive electrode sheet according to the second aspect, and the preparation method comprises the following steps:

[0016] providing a positive electrode current collector;

[0017] mixing and coating the second sodium supplementing agent, a positive electrode active substance, a second conductive agent and a second solvent on the positive electrode current collector and drying to obtain a positive electrode active material layer;

[0018] The first sodium supplement agent, the first conductive agent and the first solvent are mixed and processed to the surface of the positive active material layer to obtain a sodium supplement layer.

[0019] As an optional embodiment, in the embodiment of the present application, in the step of mixing and processing the first sodium supplement agent, the first conductive agent and the first solvent to the positive electrode sheet substrate and drying to obtain the sodium supplement layer, electrostatic spraying or electrostatic spinning is used for processing.

[0020] In a fourth aspect, the present application further discloses a power consumption device, which comprises a power consumption device body and a sodium ion energy storage device arranged in the power consumption device body, wherein the sodium ion energy storage device comprises the positive electrode sheet according to the second aspect, and the sodium ion energy storage device is used to supply power to the power consumption device body.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The composite sodium supplement agent provided by the embodiment of the present application forms a certain oxidation potential gradient through the first sodium supplement agent and the second sodium supplement agent with different oxidation potentials, and can realize the gradient sodium supplement effect of the sodium ion energy storage device. Moreover, since the composite sodium supplement agent is arranged in the positive electrode sheet of the sodium ion energy storage device, it has the advantages of easy operation and processing, reduced processing procedures, no harsh processing conditions, etc., and is suitable for industrial application. The first oxidation potential of the first sodium supplement agent is less than or equal to 3.9V, and the second oxidation potential of the second sodium supplement agent is 3.9V-4.4V.

[0023] The charging voltage in the initialization stage (English name: Formation, which refers to the first charging of the sodium ion energy storage device after high-temperature aging, used to activate the battery, and the initialization stage will form a SEI film (Solidelectrolyteinter Face, solid electrolyte interphase film) on the surface of the negative electrode sheet) of the sodium ion energy storage device is relatively low, generally not higher than 3.9V, and the SOC (State of Charge, state of charge) is within 60%. The first sodium supplement agent has a relatively low first oxidation potential of less than 3.9V, and can compensate sodium before the second sodium supplement agent, so as to compensate the sodium loss caused by the formation of the SEI film in the formation stage, and improve the first charge and discharge efficiency of the sodium ion energy storage device. The oxidation potential in the subsequent cycle stage of the sodium ion energy storage device is relatively high, and the second sodium supplement agent with a second oxidation potential of 3.9V-4.4V is arranged. Since the oxidation potential is relatively high, it can compensate the sodium loss in the charge and discharge cycle process, so as to improve the cycle performance of sodium ions. Therefore, the sodium ion energy storage device can realize sodium supplement in the whole stage from the initialization stage to the subsequent cycle charge and discharge stage, so as to improve the electrochemical performance of the sodium ion energy storage device in the whole process from the formation stage to the cycle charge and discharge. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet disclosed in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of another positive electrode structure disclosed in an embodiment of the present invention;

[0027] Figure 3 This is a flowchart of the preparation method of the positive electrode sheet disclosed in the embodiments of the present invention.

[0028] Figure reference numerals: 100, positive electrode sheet; 1, positive electrode current collector; 2, positive electrode active material layer; 3, sodium replenishment layer. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In this invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation.

[0031] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0032] In addition, the terms "mounting", "arrangement", "provided with", "connected", "linked" should be understood broadly. For example, it can be fixed connection, detachable connection, or integral structure; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, or internal communication between two devices, elements or components. The specific meaning of the above terms in the present application can be understood according to the specific circumstances by those skilled in the art.

[0033] In addition, the terms "first", "second" and the like are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not intended to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise stated, the meaning of "multiple" is two or more.

[0034] The technical solutions of the present application will be further described below in combination with embodiments and drawings.

[0035] Since the positive electrode sheet of the sodium ion energy storage device has the problem of sodium loss, the lost sodium can be supplemented by sodium supplement technology. Some sodium supplement technologies cannot take into account the factors of cost, environmental protection, safety and stability, and are difficult to realize industrial application. Specifically, physical pre-sodium operation is simple and convenient, but it is difficult to ensure safety; electrochemical pre-sodium can obtain a stable SEI film, but the process flow is complicated; chemical reaction pre-sodium can also form a uniform and dense SEI film, but it has certain requirements for atmosphere, and the solvent is expensive; setting a sodium supplement agent on the separator increases the process of separator treatment, and the operation difficulty increases. Some sodium supplement technologies are single in function, and it is difficult for the sodium ion energy storage device to realize sodium supplement in the whole stage from the initialization stage to the subsequent cycle charging and discharging stage, and further to improve the electrochemical performance of the sodium ion energy storage device from the whole process of the initialization stage to the cycle charging and discharging.

[0036] The present application proposes the following technical solutions in view of the problems existing in the above-mentioned existing sodium supplement technology.

[0037] In a first aspect, the present application provides a composite sodium supplement agent, the composite sodium supplement agent being located at a positive electrode sheet of a sodium ion energy storage device, and the composite sodium supplement agent comprising: a first sodium supplement agent and a second sodium supplement agent, the first sodium supplement agent having a first oxidation potential, and the second sodium supplement agent having a second oxidation potential, the first oxidation potential being less than 3.9 V, and the second oxidation potential being 3.9 V to 4.4 V. The composite sodium supplement agent is directly arranged at the positive electrode sheet, which is simple to operate, does not need to set special reaction conditions and use expensive solvents, has no harsh processing conditions, can reduce processing procedures, and can realize industrial application. The use of the composite sodium supplement agent can compensate for the single-function disadvantage of existing sodium supplement technologies. Specifically, the composite sodium supplement agent has a certain oxidation potential gradient, can realize gradient sodium supplement during the operation of the sodium ion energy storage device, can realize sodium supplement in the entire stage from the initialization stage to the subsequent cycle charging and discharging stage, and can improve the electrochemical performance of the sodium ion energy storage device in the entire charging and discharging process.

[0038] It can be understood that the first sodium supplement agent and the second sodium supplement agent (as well as the positive electrode active material) themselves have an oxidation potential range. When the working voltage of the sodium ion energy storage device reaches the oxidation potential range of the first sodium supplement agent and the second sodium supplement agent, the first sodium supplement agent and the second sodium supplement agent will undergo oxidation reaction to release sodium ions and electrons, and the released sodium ions serve as the sodium supplement agent.

[0039] In some embodiments, the working voltage of the sodium ion energy storage device is 1.5 V to 4.1 V, and the charging voltage of the sodium ion energy storage device in the initialization stage is generally not higher than 3.9 V. The first sodium supplement agent has a relatively low first oxidation potential of less than 3.9 V, can undergo oxidation reaction in the initialization stage, can perform sodium compensation prior to the second sodium supplement agent to release sodium ions, and thus can compensate for the sodium loss caused by the formation of the SEI film in the formation stage, and improve the first charging and discharging efficiency of the sodium ion energy storage device.

[0040] The working potential of the sodium ion energy storage device in the subsequent cycle stage is generally higher than 3.9 V, and the second sodium supplement agent having a second oxidation potential of 3.9 V to 4.4 V is arranged, can undergo oxidation reaction to release sodium ions in the cycle stage, can supplement the sodium loss in the cycle process, and thus can improve the cycle performance of the sodium ion energy storage device. The second sodium supplement agent can also achieve sodium compensation by increasing the cut-off voltage of the sodium ion energy storage device in the cycle stage, that is, increasing the cut-off voltage in the required time period to perform sodium compensation, which can achieve the effect of intermittent sodium supplement. Therefore, the sodium ion energy storage device can realize sodium supplement in the entire stage from the initialization stage to the subsequent cycle charging and discharging stage, and thus the electrochemical performance of the sodium ion energy storage device can be improved in the entire process from the formation stage to the cycle charging and discharging.

[0041] If the first oxidation potential of the first sodium supplement exceeds 3.9V, the working potential range of the initialization stage of the sodium ion energy storage device is not met, the oxidative decomposition of the sodium supplement cannot be achieved in the initialization stage, and a large amount of the first sodium supplement will remain on the surface of the positive electrode sheet, resulting in an increase in the impedance of the positive electrode sheet and affecting the electrochemical performance of the sodium ion energy storage device. If the second oxidation potential of the second sodium supplement exceeds 4.4V, the working voltage of the sodium ion energy storage device in the cycle stage is not met, and the sodium supplement cannot be achieved in the cycle stage; if the second oxidation potential is lower than 3.9V, the second sodium supplement is consumed in the initialization stage, and the sodium supplement cannot be achieved in the cycle stage, and cannot play a role in gradient sodium supplement.

[0042] In some embodiments, the working voltage of the sodium ion energy storage device is 1.5V-4.1V. If the working voltage is lower than 1.5V, the positive electrode active material on the positive electrode sheet cannot undergo redox reaction, and the sodium ion battery cannot work normally. If the working voltage is higher than 4.1V, the electrolyte in the sodium ion energy storage device may be decomposed at high voltage, and the structure of the positive electrode sheet may also be damaged at high voltage, affecting the cycle life.

[0043] Exemplarily, the first oxidation potential can be any value within the range of less than or equal to 3.9V, including but not limited to 0.2V, 0.5V, 0.7V, 1V, 1.2V, 1.5V, 1.7V, 2V, 2.1V, 2.2V, 2.3V, 2.4V, 2.5V, 2.6V, 2.7V, 2.8V, 2.9V, 3V, 3.1V, 3.2V, 3.3V, 3.4V, 3.5V, 3.6V, 3.7V, 3.8V, 3.9V, etc., and the second oxidation potential is any value within the range of 3.9V-4.4V, including but not limited to 3.9V, 3.92V, 3.94V, 3.96V, 3.98V, 4.0V, 4.02V, 4.04V, 4.06V, 4.08V, 4.1V, 4.12V, 4.14V, 4.16V, 4.18V, 4.2V, 4.22V, 4.24V, 4.26V, 4.28V, 4.3V, 4.32V, 4.34V, 4.36V, 4.38V, 4.4V, etc. The working voltage of the sodium ion energy storage device can be any value within the above range, for example, it can be 1.5V, 2V, 2.5V, 3V, 3.5V, 4.0V, 4.1V, etc.

[0044] Preferably, in some embodiments, the first oxidation potential is less than or equal to 3.8 V, and / or the second oxidation potential is 3.9 V to 4.1 V, and / or the state of charge (SOC) of the sodium-ion energy storage device is less than or equal to 60%, which can be more matched with the working voltage of the sodium-ion energy storage device in the initialization stage and the subsequent cycle stage. In the formation stage, the voltage of the sodium-ion energy storage device first rapidly rises to a peak value, and then gradually decreases to an equilibrium state; in the cycle stage, the voltage of the sodium-ion energy storage device is also constantly changing. The use of the first oxidation potential and the second oxidation potential in the preferred range can more match the dynamically changing voltage window of the sodium-ion energy storage device in the formation stage and the cycle stage. The first sodium supplement agent and the second sodium supplement agent can more accurately stage the oxidation reaction to release sodium ions and electrons and perform gradient sodium supplementation. The second sodium supplement agent can more accurately cooperate with the dynamically changing voltage to achieve intermittent sodium supplementation. It can be understood that the SOC of the sodium-ion energy storage device refers to the available charge in the energy storage device, i.e., the ratio between the stored electric quantity and the rated capacity of the energy storage device. Matching the voltage and SOC of the sodium-ion energy storage device in different stages can keep the SOC of the sodium-ion energy storage device less than or equal to 60%, which can make the first sodium supplement agent and the second sodium supplement agent better play the role of gradient sodium supplementation to full-stage sodium supplementation.

[0045] Regarding the material selection of the first sodium supplement agent and the second sodium supplement agent, there are mainly the following types of sodium compounds: organic sodium salt, organic sodium salt complex, inorganic sodium salt, metal sodium salt, sodium oxide, etc. Organic sodium salt has poor conductivity; inorganic sodium salt is highly toxic and explosive; metal sodium salt has low capacity release efficiency; and sodium oxide is difficult to effectively cooperate with other sodium compounds.

[0046] In some embodiments, the first sodium supplement agent includes a mixture of one or more of NaNiO2, NaCrO2, Na2MnO2, NaFeO2, Na x Fe (1-y) Al y O2, Na x Fe (1-y) Ti y O2 (0.8≤x≤2, y≧0), and / or the second sodium supplement agent includes a mixture of one or more of Na2O2, Na2O, Na3P, Na2C2O2, Na2C2O4. Na x Fe (1-y) Al y O2, Na x Fe (1-y) Ti yO2 (0.8≤x≤2, y≧0) is used as the first sodium replenisher. It does not generate gas and can reduce the accumulation of impurity byproducts, thus not deteriorating electrochemical performance. The first sodium replenisher has a low initial oxidation potential, making it suitable as a sodium replenisher during the formation stage to compensate for sodium losses during SEI film formation and improve the initial charge-discharge efficiency of the sodium-ion energy storage device. The second sodium replenisher has a high sodium content, high replenishment efficiency, and a high oxidation potential. It can replenish sodium losses during cycling, improve cycle performance, and does not generate gas during sodium ion operation.

[0047] In some embodiments, the molar ratio of the first sodium supplement to the second sodium supplement is (2-5):1. The amount of the first sodium supplement added is mainly determined based on the formation loss of the sodium-ion energy storage device, while the amount of the second sodium supplement added is mainly determined based on the cycle target. A molar ratio below this range results in an excessive amount of the second sodium supplement and an insufficient amount of the first sodium supplement. Excessive second sodium supplement reduces the content of other active materials in the positive electrode, lowers the energy density, increases the polarization of the energy storage device, and accelerates cycle decay; insufficient first sodium supplement fails to achieve the goal of improving capacity and initial charge / discharge efficiency. A molar ratio exceeding this range results in an excessive amount of the first sodium supplement and an insufficient amount of the second sodium supplement. Excessive first sodium supplement increases the impedance of the sodium-ion energy storage device, accumulates a large amount of byproducts, and deteriorates cell performance; insufficient second sodium supplement results in insufficient sodium source supply, failing to achieve the goal of improving cycle performance.

[0048] For example, the molar ratio of the first sodium supplement and the second sodium supplement can be any ratio within the above range, including but not limited to: 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, 5:1, etc.

[0049] Preferably, the ratio of sodium supplement 1 to sodium supplement 2 is controlled within the range of (2-3):1, which can provide sufficient sodium source for the cycle stage and improve the cycle capacity retention rate of the sodium ion energy storage device.

[0050] In a second aspect, the application provides a positive electrode sheet of a sodium-ion energy storage device, which comprises the composite sodium supplementing agent of the first aspect. The first and second sodium supplementing agents are arranged on the positive electrode sheet, which can directly supplement sodium for the positive electrode sheet and is highly compatible with the manufacturing process of the positive electrode sheet of the sodium-ion energy storage device. The process is simple, has low requirements for the environment, and the total cost depends on the cost of the first and second sodium supplementing agents themselves. The amount of the first and second sodium supplementing agents can be determined according to the formation loss and the cycle target of the sodium-ion energy storage device to control the degree of sodium supplementation. The operation is simple and safe, and the cost, environmental protection, safety and stability factors can be considered to achieve industrial application. The first and second sodium supplementing agents have the following arrangement modes, but are not limited to:

[0051] Please refer to Figure 1 In some embodiments, the positive electrode sheet comprises a positive electrode current collector, and a positive electrode active material layer and a sodium supplementing layer arranged on the positive electrode current collector in sequence. The positive electrode active material layer comprises the second sodium supplementing agent, and the sodium supplementing layer comprises the first sodium supplementing agent. The first and second sodium supplementing agents of the application have the following arrangement modes that can realize gradient sodium supplementation:

[0052] The first mode: the positive electrode active material layer 2 has the second sodium supplementing agent but not the first sodium supplementing agent, and the sodium supplementing layer 3 has the first sodium supplementing agent but not the second sodium supplementing agent.

[0053] In some embodiments, please continue to refer to Figure 1 The positive electrode sheet 100 comprises a positive electrode current collector 1, and a positive electrode active material layer 2 and a sodium supplementing layer 3 arranged on the positive electrode current collector 1 in sequence. The sodium supplementing layer 3 comprises the first and second sodium supplementing agents. It should be noted that in this arrangement mode, the positive electrode active material layer 2 does not have the first and second sodium supplementing agents.

[0054] Further, in some embodiments, please refer to Figure 2 The positive electrode sheet 100 is composed of a positive electrode current collector 1 and a positive electrode active material layer 2 arranged on the positive electrode current collector 1. The positive electrode active material layer 2 comprises the first and second sodium supplementing agents.

[0055] Preferably, the first arrangement is adopted, i.e., the positive electrode sheet 100 comprises the positive electrode current collector 1, and the positive electrode active material layer 2 and the sodium supplement layer 3 are sequentially stacked on the positive electrode current collector 1, the positive electrode active material layer 2 only has the second sodium supplement agent, and the sodium supplement layer 3 only has the first sodium supplement agent. In this way, the sodium supplement layer 3 is directly formed on the positive electrode active material layer 2, and the first sodium supplement agent and the second sodium supplement agent are arranged in different layers. The sodium supplement layer 3 is close to the negative electrode side, and the sodium source generated by the first sodium supplement agent can be moved to the negative electrode side the fastest to supplement the sodium consumed by the formation of the SEI film. The first sodium supplement agent is continuously consumed by the redox reaction, so that the sodium supplement layer 3 is gradually consumed in the formation stage. When the cycle stage is performed, the sodium supplement layer 3 has been completely consumed and cannot cover the surface of the positive electrode active material layer 2 to increase the polarization and affect the cycle stage.

[0056] In some embodiments, the sodium supplement layer further comprises the first conductive agent and the first solvent, and the mass ratio of the first sodium supplement agent, the first conductive agent and the first solvent is 80:(10-15):150. If the mass ratio is lower than this range, the content of the first sodium supplement agent is low, and the content of the first binder and the first conductive agent remaining on the surface after the first sodium supplement agent is decomposed is high, which is not conducive to the improvement of the energy density of the sodium ion energy storage device, and at the same time, the content of the non-active substance remaining on the surface of the positive electrode active material layer is high, which increases the polarization of the surface of the positive electrode sheet. If the mass ratio is higher than this range, the content of the first sodium supplement agent is high, and the content of the first binder is low, which is easy to cause the sodium supplement layer to fall off. The sodium supplement layer further comprises the first binder, and the mass ratio of the first sodium supplement agent, the first conductive agent, the first binder and the first solvent is 80:(10-15):(5-10):150.

[0057] For example, the mass ratio of the first sodium supplement agent, the first conductive agent, the first binder and the first solvent can be any value within the above range, including but not limited to 80:10:10:150, 80:11:9:150, 80:12:8:150, 80:13:7:150, 80:14:6:150, 80:15:5:150, etc.

[0058] In some embodiments, the positive electrode active material layer further comprises the positive electrode active substance, the second conductive agent and the second solvent, and the mass ratio of the second sodium supplement agent and the positive electrode active substance is (1-5):100. If the mass ratio is lower than this range, the content of the second sodium supplement agent is low, and it is difficult to supplement sodium in the cycle stage. If the mass ratio is higher than this range, the content of the second sodium supplement agent is high, which increases the resistance of the positive electrode sheet, reduces the sodium ion kinetics, increases the polarization, and is not conducive to the performance of the battery cell. The positive electrode active material layer further comprises the second binder.

[0059] For example, the mass ratio of the second sodium supplement agent and the positive electrode active substance can be any value within the above range, including but not limited to 1:100, 2:100, 3:100, 4:100, 5:100, etc.

[0060] The positive electrode active material can be a transition metal oxide / layered oxide, for example, can be: Na x MO2(M = Co, Fe, Mn, Ni, and a mixture thereof), for example, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, can also be a Prussian compound, for example, can be: Na x MA[MB(CN)6]·zH2O (MA and MB are transition metal ions), polyanion materials, amorphous materials, etc.

[0061] The first binder is a mixture of one or more of styrene butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylonitrile, polyacrylic acid, polyacrylate, carboxymethyl cellulose, sodium alginate, etc., and / or the first conductive agent is a mixture of one or more of acetylene black, Super-P (conductive carbon black), CNTs (carbon nanotubes), carbon fibers, graphene, etc., and / or the second binder is a mixture of one or more of styrene butadiene rubber, PVDF (polyvinylidene fluoride), polytetrafluoroethylene, polyvinyl alcohol, polyacrylonitrile, polyacrylic acid, polyacrylate, carboxymethyl cellulose, sodium alginate, etc., and / or the second conductive agent is a mixture of one or more of acetylene black, Super-P, carbon nanotubes, carbon fibers, graphene, etc., and / or the first solvent and the second solvent can be NMP (N-methyl pyrrolidone).

[0062] In a third aspect, the present application provides a preparation method of the positive electrode sheet as described in the second aspect, the preparation method comprising the following steps:

[0063] providing a positive electrode current collector;

[0064] forming a film layer with a composite sodium supplement agent on the positive electrode current collector to form the positive electrode sheet.

[0065] The positive electrode current collector can be an aluminum foil prepared from metallic aluminum.

[0066] In some embodiments, the step of forming a film layer with a composite sodium supplement agent on the positive electrode current collector to form the positive electrode sheet is:

[0067] mixing and coating the second sodium supplement agent, the positive electrode active material, the second conductive agent, the second binder, and the second solvent onto the positive electrode current collector and drying to obtain a positive electrode active material layer;

[0068] processing the first sodium supplement agent, the first conductive agent, the second binder, and the first solvent to the surface of the positive electrode active material layer to obtain a sodium supplement layer.

[0069] In the step of preparing the sodium supplement layer, the sodium supplement layer is prepared by electrostatic spraying or electrospinning. Preferably, the sodium supplement layer can be prepared by electrospinning technology. The electrospun nanofiber prepared by electrospinning has the characteristics of large specific surface area and high porosity. The micro / nano particles in the first sodium supplement agent, the first conductive agent, and the second binder can be distributed more uniformly, preventing the micro / nano particles from agglomerating, facilitating the release of sodium in the first sodium supplement agent, improving the sodium supplement efficiency of the first sodium supplement agent per unit volume or per unit mass, enabling the sodium supplement layer to supplement more sodium, and thus improving the capacity and the first charge-discharge efficiency of the sodium ion energy storage device.

[0070] In a fourth aspect, the present application also provides a power utilization device, which comprises a power utilization device body and a sodium ion energy storage device according to the fourth aspect arranged in the power utilization device body and used for supplying power to the device body. The power utilization device body comprises a device positive electrode and a device negative electrode, the positive electrode tab of the secondary energy storage device is electrically connected to the device positive electrode, and the negative electrode tab is electrically connected to the device negative electrode. The power utilization device includes a grid-level large-scale energy storage system, an uninterruptible power supply (UPS) device, an energy storage base station, an electric vehicle, and the like.

[0071] The technical solutions of the present application will be further explained and described below in combination with specific examples and experimental data.

[0072] Example 1

[0073] The present embodiment provides a sodium ion energy storage device, which is a sodium ion battery.

[0074] The sodium ion battery comprises a positive electrode tab, a negative electrode tab, an electrolyte, and a separator arranged between the positive electrode tab and the negative electrode tab.

[0075] The positive electrode tab comprises a current collector, a positive active material layer, and a sodium supplement layer arranged in sequence on the current collector. The sodium supplement layer comprises NaNiO2 as a first sodium supplement agent, PVDF as a first binder, Super P and CNTs as first conductive agents, and NMP as a first solvent, and the mass ratio of the first sodium supplement agent, the first binder, the first conductive agent, and the first solvent is 80:10:10:150.

[0076] The positive active material layer comprises Na2O2 as a second sodium supplement agent, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as a positive active material, PVDF as a second binder, Super P and CNTs as second conductive agents, and NMP as a second solvent, and the mass ratio of the second sodium supplement agent, the positive active material, the second binder, the second conductive agent, and the second solvent is 1:100:2.66:2.66:71.

[0077] The molar ratio of the first sodium supplement agent and the second sodium supplement agent is 3:1.

[0078] The present embodiment also provides a preparation method of the positive electrode sheet, and the preparation method comprises:

[0079] The positive electrode current collector is provided, and the positive electrode current collector is an aluminum foil.

[0080] 1 part of the second sodium supplement agent Na2O2, 100 parts of the positive electrode active material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, 2.66 parts of the second conductive agent Super P and CNTs, 2.66 parts of the second binder PVDF, and 71 parts of the second solvent NMP are mixed to be coated on the positive electrode current collector aluminum foil and dried to obtain a positive electrode active material layer.

[0081] 3 parts of the first sodium supplement agent NaNiO2, 0.375 parts of the first conductive agent Super P and CNTs, 0.375 parts of the second binder PVDF, and 5.625 parts of the first solvent NMP are mixed to be electrostatically sprayed on the surface of the positive electrode active material layer to obtain a sodium supplement layer.

[0082] The present embodiment also provides a preparation method of the sodium ion battery, and the preparation method comprises:

[0083] The positive electrode sheet with the sodium supplement layer is prepared.

[0084] The negative electrode sheet of the sodium ion battery is prepared: 95 parts of hard carbon, 2.5 parts of Super P, 2.5 parts of CMC (carboxymethyl cellulose) and SBR (styrene butadiene rubber), 80 parts of deionized water are uniformly mixed, coated on the negative electrode current collector copper foil, and then dried to obtain a dry negative electrode sheet.

[0085] The sodium ion battery is assembled: the prepared positive electrode sheet with the sodium supplement layer is used as the positive electrode, the negative electrode sheet is used as the negative electrode, the porous glass fiber is used as the separator, 1 mol / L of NaPF6 (sodium hexafluorophosphate) (ethylene carbonate EC: propylene carbonate PC: dimethyl carbonate DMC = 1:1:1, and 5% fluoroethylene carbonate FEC) is used as the electrolyte, and the button-type sodium ion battery is assembled in an argon glove box with a water oxygen value lower than 0.1 ppm.

[0086] Example Two

[0087] The difference between Example Two and Example One is that the molar ratio of the first sodium supplement agent and the second sodium supplement agent in Example Two is 2:1.

[0088] Example Three

[0089] The difference between Example Three and Example One is that the molar ratio of the first sodium supplement agent and the second sodium supplement agent in Example Three is 4:1.

[0090] Example Four

[0091] Example Four and Example One differ only in that the molar ratio of the first sodium supplement agent and the second sodium supplement agent in Example Four is 5:1.

[0092] Example Five

[0093] Example Five and Example One differ only in that the mass ratio of the second sodium supplement agent and the positive electrode active material in Example Five is 2:100.

[0094] Example Six

[0095] Example Six and Example One differ only in that the mass ratio of the second sodium supplement agent and the positive electrode active material in Example Six is 3:100.

[0096] Example Seven

[0097] Example Seven and Example One differ only in that the mass ratio of the second sodium supplement agent and the positive electrode active material in Example Seven is 4:100.

[0098] Example Eight

[0099] Example Eight and Example One differ only in that the mass ratio of the second sodium supplement agent and the positive electrode active material in Example Eight is 5:100.

[0100] Example Nine

[0101] Example Nine and Example One differ only in that the sodium supplement layer in Example Nine is prepared by electrospinning.

[0102] Example Ten

[0103] Example Ten and Example One differ only in that the first sodium supplement agent in Example Ten is NaCrO2.

[0104] Example Eleven

[0105] Example Eleven and Example One differ only in that the first sodium supplement agent in Example Eleven is NaFeO2.

[0106] Example Twelve

[0107] Example Twelve and Example One differ only in that the second sodium supplement agent in Example Twelve is Na2C2O4.

[0108] Example Thirteen

[0109] Example Thirteen and Example One differ only in that no sodium supplement layer is provided, and the first sodium supplement agent and the second sodium supplement agent are both mixed in the positive electrode active material layer.

[0110] Example Fourteen

[0111] The difference between Example 14 and Example 1 is only that the first sodium supplement agent and the second sodium supplement agent are mixed in the sodium supplement layer.

[0112] Comparative Example 1

[0113] The difference between Comparative Example 1 and Example 1 is only that the first sodium supplement agent and the second sodium supplement agent are not arranged.

[0114] Comparative Example 2

[0115] The difference between Comparative Example 2 and Example 1 is only that the second sodium supplement agent is not arranged.

[0116] Comparative Example 3

[0117] The difference between Comparative Example 3 and Example 1 is only that the first sodium supplement agent is not arranged.

[0118] Comparative Example 4

[0119] The difference between Comparative Example 1 and Example 1 is only that the first sodium supplement agent of Comparative Example 1 is Na2O2 and the second sodium supplement agent is NaNiO2.

[0120] Table 1: Related data of examples and comparative examples

[0121]

[0122]

[0123] Experimental test

[0124] The sodium ion batteries in the above examples and comparative examples were subjected to electrochemical performance test. The sodium ion batteries were subjected to constant current charge-discharge test on an energy storage device measuring device, and the test voltage was 4.0V-1.5V (vs Na / Na + ). The cyclic voltammetry test was performed on a battery tester, and the test voltage was 4.0V-1.5V (vs Na / Na + ). The test results are as follows:

[0125] Table 2: Electrochemical performance test results of examples and comparative examples

[0126]

[0127]

[0128] From the description in Table 1 and Table 2, the first circle discharge capacity, the first charge-discharge efficiency and the capacity retention rate of Examples 1 to 14 are all higher than those of Comparative Example 1 which does not arrange the first sodium supplement agent and the second sodium supplement agent. It can be seen that arranging the first sodium supplement agent and the second sodium supplement agent in the positive electrode sheet can obviously improve the electrochemical performance of the sodium ion battery.

[0129] Further, compared with Comparative Example 2, Comparative Example 2 does not dispose the second sodium supplement agent in the positive active material layer, the capacity retention rate of Example 1 is 95.4% after 500 cycles, while the capacity retention rate of Comparative Example 2 is 86%, the capacity retention rate in the cycle stage is nearly 10% lower than that of Example 1. It shows that in the cycle stage, the second sodium supplement agent can effectively realize gradient sodium supplement, thereby improving the cycle capacity retention rate of the sodium ion battery.

[0130] Further, compared with Comparative Example 3, Comparative Example 3 does not dispose the sodium supplement layer and the first sodium supplement agent. The first cycle discharge capacity of Example 1 is 128.9 mAh / g, the first charge-discharge efficiency is 98.2%, and the capacity retention rate after 500 cycles is 95.4%. The first cycle discharge capacity of Comparative Example 3 decreases to 125.4 mAh / g, which decreases by 3.5 mAh / g, the first charge-discharge efficiency decreases to 88.8%, which decreases by 9.4%, and the capacity retention rate after 500 cycles is 88.0%, which decreases by 7.4%. It can be seen that the first sodium supplement agent is not disposed, which affects the sodium supplement in the first charge-discharge formation stage, and further affects the electrochemical performance in the subsequent cycle stage.

[0131] Compared with Comparative Example 4, the first sodium supplement agent of Example 1 is the second sodium supplement agent of Comparative Example 4, and the second sodium supplement agent of Example 1 is the first sodium supplement agent of Comparative Example 4, that is, in Comparative Example 4, Na2O2 with a high oxidation potential is disposed in the sodium supplement layer, and NaNiO2 with a low oxidation potential is disposed in the positive active material layer. The first cycle discharge capacity of Comparative Example 4 decreases to 124.6 mAh / g, which decreases by 4.3 mAh / g, the first charge-discharge efficiency is 88.2%, which decreases by 10%, and the capacity retention rate after 500 cycles is 85.7%, which decreases by 9.7%. In each of the comparative examples, the performance data of Comparative Example 4 decreases most obviously. It can be seen that the sodium supplement agent with a higher oxidation potential disposed in the sodium supplement layer not only cannot supplement sodium, but also increases the impedance of the positive plate, reduces the conductivity of ions and electrons. The sodium supplement agent with a lower oxidation potential disposed in the positive active material layer is consumed in the formation stage, and a large amount of by-products are easily accumulated in the positive active material layer under the blockage of the sodium supplement layer, which deteriorates the performance of the sodium ion battery.

[0132] In Example 1 to Example 4, the molar ratio of the first sodium supplement agent and the second sodium supplement agent is appropriately reduced, that is, the amount of the second sodium supplement agent is appropriately increased, which is more conducive to compensating sodium in the cycle stage and improving the capacity retention rate of the sodium ion battery after 500 cycles.

[0133] In Embodiment One and Embodiments Five to Eight, the mass ratio of the second sodium supplement agent and the positive active material is appropriately reduced, which is also beneficial to improve the capacity retention rate of the sodium ion battery after 500 cycles. Therefore, the amount of the second sodium supplement agent needs to be considered and balanced with the amount of the first sodium supplement agent and the positive active material, and too much or too little will lead to a decrease in the capacity retention rate of the sodium ion battery after 500 cycles.

[0134] In various embodiments, Embodiment Nine uses the electrostatic spinning process to prepare the sodium supplement layer, and the electrochemical performance of the sodium ion battery is improved most significantly. The first cycle discharge capacity of the sodium ion battery of Embodiment Nine is 129.5 mAh / g, the first charge-discharge efficiency is 99.3%, and the capacity retention rate after 500 cycles is 96.4%. Compared with Comparative Example One (corresponding to 125.6 mAh / g, 88.4%, and 82.5%), the discharge capacity is increased by 3.9 mAh / g, the first charge-discharge efficiency is increased by nearly 10%, and the capacity retention rate is increased by 13.9%. It can be seen that the electrostatic spinning process for preparing the sodium supplement layer can significantly improve the performance of the sodium ion battery compared with the electrostatic spraying process.

[0135] In Embodiment One, Embodiment Ten, and Embodiment Eleven, the first sodium supplement agent of Embodiment One is NaNiO2, the first sodium supplement agent of Embodiment Ten is NaCrO2, and the first sodium supplement agent of Embodiment Eleven is NaFeO2. According to the molecular weight of Ni, Cr, and Fe, the efficiency of sodium supplement in the formation stage is in the order of NaCrO2> NaFeO2> NaNiO2. Therefore, the first charge-discharge efficiency of Embodiments Ten and Eleven is slightly higher than that of Embodiment One. In order to balance the first cycle discharge capacity and the capacity retention rate after 500 cycles, it is preferred that the first sodium supplement agent is NaNiO2.

[0136] Compared with Embodiment One and Comparative Example One, the second sodium supplement agent of Embodiment One is Na2O2, and the second sodium supplement agent of Embodiment Twelve is Na2C2O4. Embodiment Twelve can also improve the sodium ion electrochemical performance, but the improvement effect is not as good as that of Embodiment One. The Na content in Na2O2 is high, the sodium supplement efficiency is better than that of Na2C2O4, and no gas is generated in the cycle stage.

[0137] Compared with Embodiment One and Comparative Example One, the first sodium supplement agent of Embodiment One is arranged in the sodium supplement layer, and the second sodium supplement agent is arranged in the positive active material layer. The first sodium supplement agent and the second sodium supplement agent of Embodiment Thirteen are both arranged in the positive active material layer. The first sodium supplement agent and the second sodium supplement agent of Embodiment Thirteen can also significantly improve the sodium supplement effect in the formation stage, increase the first charge-discharge efficiency and the first cycle discharge capacity, and slightly improve the capacity retention rate, but the improvement effect is not as good as that of Embodiment One.

[0138] Compared with Comparative Example 1, in Example 1, the first sodium supplement agent is arranged in the sodium supplement layer, and the second sodium supplement agent is arranged in the positive active material layer. In Example 14, the first sodium supplement agent and the second sodium supplement agent are both arranged in the sodium supplement layer. Example 14 can effectively supplement sodium in the formation stage, can obviously improve the first circle discharge capacity and the first charge-discharge efficiency, but the capacity retention rate after 500 cycles is less improved. It can be seen that arranging the first sodium supplement agent and the second sodium supplement agent in the sodium supplement layer and the positive active material layer respectively can effectively consider the sodium supplement in the formation stage and the cycle stage, so as to more comprehensively improve the electrochemical performance of the sodium ion battery.

[0139] The composite sodium supplement agent, the positive plate, the preparation method thereof and the electric equipment are described in detail above. The principle and implementation mode of the present application are described by applying specific examples. The above examples are only used to help understand the composite sodium supplement agent, the positive plate, the preparation method thereof and the electric equipment and the core idea thereof. Meanwhile, for the general skilled in the art, the specific implementation mode and application range will be changed according to the idea of the present application. In conclusion, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A positive electrode sheet of a sodium-ion energy storage device, characterized by, The positive electrode sheet comprises a composite sodium supplement agent; The composite sodium supplement agent comprises a first sodium supplement agent and a second sodium supplement agent, the first sodium supplement agent has a first oxidation potential, and the second sodium supplement agent has a second oxidation potential, the first oxidation potential is less than 3.9 V, and the second oxidation potential is 3.9 V-4.4 V; The positive electrode sheet comprises a positive electrode current collector, and a positive electrode active material layer and a sodium supplement layer arranged on the positive electrode current collector, the positive electrode active material layer comprises the second sodium supplement agent, and the sodium supplement layer comprises the first sodium supplement agent.

2. The positive electrode sheet according to claim 1, characterized by The first oxidation potential is less than or equal to 3.8 V, and / or the second oxidation potential is 3.9 V-4.1 V.

3. The positive electrode sheet according to claim 1, characterized by The first sodium supplement includes one or more of NaNiO2, NaCrO2, Na2MnO2, NaFeO2, Na x Fe （1-y） Al y O2, Na x Fe （1-y） Ti y O2, wherein the Na x Fe （1-y） Al y O2 and the Na x Fe （1-y） Ti y O2, wherein x and y are each: 0.8≤x≤2, y≥0; and the second sodium supplement includes one or more of Na2O2, Na2O, Na3P, Na2C2O4.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized by, The molar ratio of the first sodium supplement agent to the second sodium supplement agent is (2-5):

1.

5. The positive electrode sheet according to claim 1, characterized by The working voltage of the sodium ion energy storage device is 1.5 V-4.1 V.

6. The positive electrode sheet according to claim 1, characterized by The sodium supplement layer further comprises a first conductive agent and a first solvent, and the mass ratio of the first sodium supplement agent, the first conductive agent, and the first solvent is 80:(10-15):

150.

7. The positive electrode sheet according to claim 1, characterized by The positive electrode active material layer further comprises a positive electrode active material, a second conductive agent, and a second solvent, and the mass ratio of the second sodium supplement agent and the positive electrode active material is (1-5):

100.

8. A positive electrode sheet of a sodium-ion energy storage device, characterized by, The positive electrode sheet comprises a composite sodium supplement agent; The composite sodium supplement agent comprises a first sodium supplement agent and a second sodium supplement agent, the first sodium supplement agent has a first oxidation potential, and the second sodium supplement agent has a second oxidation potential, the first oxidation potential is less than 3.9 V, and the second oxidation potential is 3.9 V-4.4 V; The positive electrode sheet comprises a positive electrode current collector, and a positive electrode active material layer and a sodium supplement layer arranged on the positive electrode current collector, the positive electrode active material layer comprises the second sodium supplement agent, and the sodium supplement layer comprises the first sodium supplement agent.

9. A positive electrode sheet of a sodium-ion energy storage device, characterized by comprising: The positive electrode sheet comprises a composite sodium supplement agent; The composite sodium supplement agent comprises a first sodium supplement agent and a second sodium supplement agent, the first sodium supplement agent has a first oxidation potential, and the second sodium supplement agent has a second oxidation potential, the first oxidation potential is less than 3.9 V, and the second oxidation potential is 3.9 V-4.4 V; The positive electrode sheet comprises a positive electrode current collector, and a positive electrode active material layer and a sodium supplement layer arranged on the positive electrode current collector, the positive electrode active material layer comprises the second sodium supplement agent, and the sodium supplement layer comprises the first sodium supplement agent.

10. A method for producing the positive electrode sheet according to any one of claims 1 to 7, characterized by, The preparation method comprises the following steps: Providing a positive electrode current collector; Mixing and coating the second sodium supplement agent, a positive electrode active material, a second conductive agent, and a second solvent on the positive electrode current collector and drying to obtain a positive electrode active material layer; Mixing and processing the first sodium supplement agent, a first conductive agent, and a first solvent to the surface of the positive electrode active material layer to obtain a sodium supplement layer.

11. The method of claim 10, wherein, In the step of mixing and processing the first sodium supplement agent, a first conductive agent, and a first solvent on the positive electrode active material layer and drying to obtain the sodium supplement layer, electrostatic spraying or electrospinning is used for processing.

12. An electrical device, characterized by The electric device comprises an electric device body and a sodium ion energy storage device arranged in the electric device body, the sodium ion energy storage device comprises the positive electrode plate according to any one of claims 1 to 9, and the sodium ion energy storage device is used for supplying power for the electric device body.

Images