Sodium-ion battery positive electrode material and preparation method therefor, positive electrode sheet, sodium secondary battery, and electrical device

Abstract

A sodium-ion battery positive electrode material and a preparation method therefor, a sodium secondary battery, and an electrical device. The sodium-ion battery positive electrode material comprises a positive electrode material matrix and a coating layer located on at least part of the surface of the positive electrode material matrix, and the effective internal friction angle of the sodium-ion battery positive electrode material is less than 30°. The sodium-ion battery positive electrode material has higher powder compaction density, and can improve the energy density of the battery.

Description

Sodium battery positive electrode material and preparation method thereof, positive electrode sheet, sodium secondary battery and power-consuming device Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a sodium battery positive electrode material and a preparation method thereof, a positive electrode sheet, a sodium secondary battery, and an electrical device. Background Art

[0002] Secondary batteries, represented by sodium batteries, have been applied in many fields, including electric vehicles, energy storage power systems (such as hydropower, thermal power, wind power, and solar power stations). Compared with lithium batteries, sodium batteries have significant advantages in raw material costs, especially for cathode materials, which account for a large proportion of the cost. The reserves of sodium salts, which are the main components of sodium cathode materials, are more abundant, making the cost of sodium cathode materials lower than that of lithium batteries. However, the poor electrochemical performance of sodium batteries in terms of capacity and stability has limited their practical application. Summary of the Invention

[0003] In response to the above-mentioned problems, the purpose of this application is to provide a sodium battery positive electrode material and its preparation method, a positive electrode sheet, a battery and an electrical device. The sodium battery positive electrode material has a high powder compaction density and can improve the energy density of the battery.

[0004] In a first aspect, the present application provides a sodium-based positive electrode material, comprising a positive electrode material matrix and a coating layer located on at least a portion of the surface of the positive electrode material matrix, wherein the effective internal friction angle of the sodium-based positive electrode material is less than 30°.

[0005] The sodium battery positive electrode material provided in the present application introduces a coating layer on the positive electrode material matrix and controls the effective internal friction angle of the material to be relatively small, which can reduce the surface friction between the positive electrode material particles, increase the sliding between the material particles during the powder pressing process, and reduce the pores formed by the overlap between the particles. The provided sodium battery positive electrode material has a higher powder compaction density and can improve the energy density of the battery.

[0006] In some embodiments of the present application, the coating layer comprises at least one of nanoparticles or polymers; wherein the nanoparticles comprise nanoinorganic and / or nanoorganic materials; and the polymer comprises one or more of the following groups: carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups, cycloalkyl groups, and heterocycloalkyl groups. As a result, the coating layer can act as a "molecular pulley," increasing the sliding motion between the sodium battery cathode materials. This sliding action facilitates close stacking of the cathode materials, thereby increasing the compaction density.

[0007] In some embodiments of the present application, the coating layer includes the nanoparticles. The nanoscale particles are evenly distributed on the surface of the positive electrode material matrix, forming a dense coating layer. This coating layer can effectively reduce the roughness of the material surface and alleviate the generation of residual alkali, thereby increasing the specific capacity.

[0008] Optionally, the nano-inorganic material includes nano-oxide.

[0009] Furthermore, the nano-oxide includes at least one of Al2O3, ZrO2, CaO, MgO or TiO2.

[0010] In some embodiments of the present application, the polymer includes at least one of polyacrylic acid, polyrotaxane, or polyurethane. The long polymer chains are bent and entangled, which helps to enhance the coating effect on the surface of the positive electrode material matrix, forming a dense coating layer, reducing the surface roughness of the material, and inhibiting capacity degradation.

[0011] In some embodiments of the present application, the residual Na + The content is lower than 1300ppm. Thus, the surface roughness of the sodium battery positive electrode material can be further reduced, the powder compaction density can be increased, and the battery can have higher cycle stability.

[0012] In some embodiments of the present application, the sodium cathode material comprises flaky single crystal particles. Compared to polycrystalline particles, single crystal particles can reduce problems such as particle fragmentation during excessive pressure. Flaky single crystals are more easily stacked tightly under sliding action to increase powder compaction density.

[0013] In some embodiments of the present application, the sheet thickness ratio γ of the sodium battery cathode material is 1 to 10. Alternatively, the sheet thickness ratio γ of the sodium battery cathode material is 2 to 6.5.

[0014] In some embodiments of the present application, the median particle size d of the sodium-ion cathode material is 2 μm to 15 μm. Alternatively, the median particle size d of the sodium-ion cathode material is 3 μm to 10 μm.

[0015] In some embodiments of the present application, the chemical formula of the positive electrode material matrix is ​​Na a [Ni b Mn c M d ]O2, wherein 0.65≤a≤1.1, 0.1≤b≤0.4, 0.1≤c≤0.5, 0.1≤d≤0.5, b+c+d=1, and M is selected from one or more of Fe, Cu, Zn, Ti, Zr, Mg, La, Y, Ca, Sb or Sn. As a result, the sodium battery positive electrode material has high structural stability, enabling the battery to achieve high capacity while improving cycle stability.

[0016] In some embodiments of the present application, the BET specific surface area of ​​the sodium cathode material is ≤0.6 g / m 2 The roughness of the sodium cathode material is reduced, the surface of the material is smoother, and it has a lower specific surface area, which is beneficial to improving the powder compaction density.

[0017] In some embodiments of the present application, the effective internal friction angle of the sodium cathode material is 10° to 25°. A smaller effective internal friction angle can further promote sliding between materials and increase compaction density.

[0018] In some embodiments of the present application, the powder compaction density of the sodium cathode material at 3T pressure is greater than 3.12 g / cm 3 .

[0019] In a second aspect, the present application provides a method for preparing a sodium battery positive electrode material, comprising: mixing a positive electrode material matrix and a coating layer raw material in the presence of a solvent, and sintering to form a coating layer on at least a portion of the surface of the positive electrode material matrix.

[0020] In this application, a wet coating process is used to treat the positive electrode material matrix. On the one hand, by selecting a coating layer material with a "molecular pulley" effect, the sliding between the single crystal materials is increased. On the other hand, a large amount of impurities such as residual sodium on the surface can be removed, further reducing the surface friction of the material, thereby improving the powder and electrode compaction density of the material.

[0021] In some embodiments of the present application, the coating layer raw material includes at least one of nano-scale particles or polymers, wherein the nano-scale particles include nano-inorganic matter and / or nano-organic matter; the polymer includes one or more of the following groups: carboxyl group, sulfonic acid group, phenolic hydroxyl group, cycloalkyl group, and heterocycloalkyl group.

[0022] In some embodiments of the present application, the nano-inorganic material includes nano-oxide.

[0023] Optionally, the nano-inorganic material includes at least one of Al2O3, ZrO2, CaO, MgO or TiO2.

[0024] In some embodiments of the present application, the polymer includes at least one of polyacrylic acid, polyrotaxane or polyurethane.

[0025] In some embodiments of the present application, the sintering temperature is 150°C to 450°C. Thus, sintering is performed at a relatively low temperature. Compared to high-temperature sintering, low-temperature sintering can, on the one hand, promote the adhesion of the coating raw material to the surface of the positive electrode material substrate without excessive fusion with the positive electrode material substrate, and on the other hand, can make the coating layer formed on the surface have higher mechanical rigidity, further promoting inter-particle sliding during the powder compaction process.

[0026] In some embodiments of the present application, the sintering time is 3 hours to 12 hours.

[0027] In some embodiments of the present application, the coating layer raw material includes the nano-inorganic material, and the sintering temperature is 300° C. to 420° C. This not only promotes proper adhesion between the coating raw material and the positive electrode material matrix, but also ensures that the formed coating layer has high mechanical rigidity, further promoting inter-particle sliding.

[0028] Optionally, the coating layer raw material includes the nano-inorganic substance, and the sintering time is 3 hours to 7 hours.

[0029] In some embodiments of the present application, the coating layer raw material includes the polymer, and the sintering temperature is 180° C. to 220° C. Thus, the polymer is attached to the surface of the positive electrode material substrate while suppressing thermal decomposition of the polymer.

[0030] Optionally, the coating layer raw material includes the polymer, and the sintering time is 3 hours to 6 hours.

[0031] In some embodiments of the present application, the solvent includes at least one of water or alcohol.

[0032] In some embodiments of the present application, the amount of the solvent used is 0.4 L to 1 L relative to 1 kg of the positive electrode material matrix. This can improve the uniformity of raw material dispersion while promoting the adhesion of the coating layer raw material to the surface of the positive electrode material matrix.

[0033] In some embodiments of the present application, the mixing method includes: first dispersing the coating layer raw material in the solvent, then adding the positive electrode material matrix to perform a second dispersion; the first dispersion is performed at a first temperature T1 under stirring conditions, and the stirring speed of the first dispersion is P1; the second dispersion is performed at a second temperature T2 under stirring conditions, and the stirring speed of the second dispersion is P2; wherein T1≤T2, P1>P2. The higher stirring speed in the first stage can improve the uniformity of the dispersion of the coating layer raw material in the solvent, and the lower stirring speed in the second stage can cause the coating layer raw material to fall back to the surface of the positive electrode material matrix to improve the coating efficiency.

[0034] In some embodiments of the present application, the coating layer raw material includes a nano-inorganic material, T1 is 5°C to 15°C, P1 is 800 rpm to 1000 rpm, T2 is 5°C to 15°C, and P2 is 300 rpm to 500 rpm. At lower temperatures, molecular thermal motion is slower, and Na in the lattice is less likely to escape, reducing the impact on material properties.

[0035] In some embodiments of the present application, the coating layer raw material includes a polymer, T1 is 5°C to 15°C, P1 is 600rpm to 800rpm, T2 is 20°C to 35°C, and P2 is 300rpm to 500rpm. Wherein, T2>T1, and T2 is near room temperature, thereby inhibiting the release of Na from the lattice while promoting the wrapping and coating of the polymer on the positive electrode material matrix.

[0036] In some embodiments of the present application, the second dispersion time is 1 min to 10 min.

[0037] In some embodiments of the present application, based on the mass of the positive electrode material matrix, the mass proportion of the coating layer raw material is 2000ppm to 30000ppm.

[0038] Optionally, based on the mass of the positive electrode material matrix, the mass proportion of the coating layer raw material is 5000ppm to 20000ppm. Thus, while improving the surface roughness of the positive electrode material matrix, the battery can also have higher electrochemical performance.

[0039] In some embodiments of the present application, the chemical formula of the positive electrode material matrix is ​​Na a [Ni b Mn c M d ]O2, wherein 0.65≤a≤1.1, 0.1≤b≤0.5, 0.1≤c≤0.5, 0.1≤d≤0.5, b+c+d=1, and M is selected from one or more of Fe, Cu, Zn, Ti, Zr, Mg, La, Y, Ca, Sb, or Sn. Thus, the prepared sodium battery positive electrode material can have high structural stability, allowing the battery to achieve high capacity while improving the battery's cycle stability.

[0040] In some embodiments of the present application, the cathode material matrix includes flaky single crystal particles, and the thickness ratio γ0 of the flaky single crystal particles is 1 to 10. Optionally, the thickness ratio γ0 of the flaky single crystal particles is 2 to 5.

[0041] In some embodiments of the present application, the median particle size d0 of the flaky single crystal particles is 2 μm to 15 μm. Alternatively, the median particle size d0 of the flaky single crystal particles is 3 μm to 10 μm.

[0042] In a third aspect, the present application provides a positive electrode plate, comprising the sodium battery positive electrode material described in the first aspect of the present application or the sodium battery positive electrode material prepared by the preparation method described in the second aspect of the present application.

[0043] In a fourth aspect, the present application provides a sodium secondary battery, comprising the positive electrode sheet described in the third aspect of the present application.

[0044] In a fifth aspect, the present application provides an electrical device comprising the sodium secondary battery described in the fourth aspect of the present application.

[0045] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiment below. The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present application. In the accompanying drawings:

[0047] FIG1 is a SEM image of the sodium cathode material of Example 1;

[0048] FIG2 is a SEM image of the single crystal sodium oxide of Comparative Example 1;

[0049] FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0050] FIG4 is an exploded view of the battery cell according to an embodiment of the present application shown in FIG3 ;

[0051] FIG5 is a schematic diagram of a battery module according to an embodiment of the present application;

[0052] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0053] FIG7 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG6 ;

[0054] FIG8 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0055] Explanation of reference numerals: 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: housing; 52: electrode assembly; 53: top cover assembly. DETAILED DESCRIPTION

[0056] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0057] In this application, references to "embodiments" mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor do they represent independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0058] " Scope " disclosed in the present application is limited in the form of lower limit and / or upper limit, and given range is limited by selecting a lower limit and / or an upper limit, and the selected lower limit and / or the rear upper limit define the boundary of special range. The scope limited in this way generally includes end value, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope that is not clearly recorded, and any lower limit can be combined with other lower limits to form a scope that is not clearly recorded, and any upper limit can be combined with any other upper limit to form a scope that is not clearly recorded. In addition, each separately disclosed point or single numerical value itself can be combined with any other point or single numerical value as a lower limit or upper limit or form a scope that is not clearly recorded with other lower limits or upper limits.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0060] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0061] In this application, the terms "plurality," "multiple," and "at least one" refer to more than two. "Above" and "below" are inclusive. For example, "two or more" includes two itself, such as two, three, four, or more.

[0062] Unless otherwise specified, the term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0063] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and any variations thereof are intended to cover non-exclusive inclusions. Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0064] The effective internal friction angle of a material can reflect the friction characteristics and shear strength between bulk materials. In this application, the effective internal friction angle of a powder can reflect the mechanical properties of the powder particles when they slide against each other.

[0065] The current types of sodium-ion positive electrode materials include sodium-ion oxides. Most of the sodium-ion oxide positive electrode material particles are single crystal particles (sodium-ion single crystal oxides), and the morphology of the single crystal particles is relatively irregular. During the powder pressing process, the overlapping support between the particles with irregular morphology will increase the pores between the particles, resulting in the sodium-ion oxide positive electrode material powder compaction density and the prepared electrode compaction density being low, which is not conducive to improving the energy density of sodium-ion battery systems. In addition, the sodium-ion oxide positive electrode material has a large amount of impurities (such as residual alkali) on the surface, and the impurities are distributed in the form of particles on the surface of the material particles, which also leads to a large friction force between the particles and is not easy to slide relative to each other. Therefore, the pore structure formed during the pressing process is difficult to be destroyed, affecting the compaction density.

[0066] Accordingly, the first aspect of the present application provides a sodium-based positive electrode material, comprising a positive electrode material matrix and a coating layer located on at least a portion of the surface of the positive electrode material matrix, wherein the effective internal friction angle of the sodium-based positive electrode material is less than 30°.

[0067] The sodium battery positive electrode material provided in the present application introduces a coating layer on the positive electrode material matrix and controls the effective internal friction angle of the material to be relatively small, which can reduce the surface friction between the positive electrode material particles. During the powder pressing process, it can increase the sliding between the material particles and reduce the pores formed by the overlap between the particles. Therefore, the provided sodium battery positive electrode material has a higher powder compaction density, which can subsequently increase the energy density of the battery.

[0068] In the present application, the nano-scale particles can be nano-scale inorganic substances or nano-scale organic substances. In some embodiments, the average particle size of the nano-scale particles can be 5 nm to 100 nm, for example, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 80 nm, etc.

[0069] In some embodiments, the coating layer comprises at least one of nanoparticles or polymers; the nanoparticles comprise nanoinorganic and / or nanoorganic materials; and the polymer comprises one or more of the following groups: carboxyl, sulfonic, phenolic, cycloalkyl, and heterocycloalkyl. As a result, the coating layer acts as a "molecular pulley," increasing the sliding motion between the sodium cathode materials. This sliding action facilitates close stacking of the materials, thereby increasing the compaction density.

[0070] As some specific embodiments, the coating layer includes the nano-scale particles. The nano-scale particles are distributed on the surface of the positive electrode material matrix, which can effectively reduce the roughness of the material surface and increase the specific capacity.

[0071] Optionally, the nano-inorganic material includes nano-oxide.

[0072] Furthermore, the nano-oxide includes at least one of Al2O3, ZrO2, CaO, MgO or TiO2.

[0073] In some specific embodiments, the coating layer includes the polymer. The polymer can form a coating layer around the surface of the positive electrode substrate by wrapping long molecular chains. This coating layer helps improve the coating effect on the surface of the positive electrode material substrate, forming a dense coating layer, reducing surface roughness of the material, and suppressing capacity degradation.

[0074] Optionally, the polymer comprises at least one of polyacrylic acid, polyrotaxane or polyurethane.

[0075] Optionally, the polymer includes polyacrylic acid. The molecular chain of polyacrylic acid has carboxyl groups, which, as active functional groups, can neutralize residual alkali on the surface of the positive electrode material matrix, thereby improving the reliability between the coating layer and the positive electrode material matrix.

[0076] As some examples, the viscosity average molecular weight (Mv) of the polyacrylic acid may be 2 million to 4 million, for example, 2 million, 2.5 million, 3 million, 4 million, etc.

[0077] Alternatively, the polymer comprises at least one of polyrotaxane or polyurethane. The molecular chains of such polymers may include cycloalkyl and / or heterocycloalkyl groups, and such cyclic groups may promote relative slippage between polymer molecular chains.

[0078] As some examples, the polyrotaxane may include a cyclodextrin polyrotaxane, such as a polyrotaxane formed by intercalating β-cyclodextrin into a guest polymer chain (such as polyethylene glycol).

[0079] As some examples, the polyurethane may include a polyurethane formed by reacting an isocyanate having a cycloalkyl group (such as IPDI) with a polyamine.

[0080] In some embodiments, the residual Na + The content is less than 1300ppm, residual Na + For example, it is 200ppm, 230ppm, 250ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1200ppm, etc. Residual Na + The lower it is, the more conducive it is to reducing impurities on the surface of the material, thereby improving the surface roughness of the sodium battery positive electrode material and increasing the powder compaction density.

[0081] Optionally, the residual Na + The content is less than 900ppm.

[0082] In this application, residual Na + This refers to the residual sodium content of the positive electrode material, namely the sodium compounds such as oxides, hydroxides, and carbonates formed on the surface of the positive electrode material. It is expressed in % (w / w). These alkaline sodium compounds affect the material's moisture absorption and processing properties. This parameter is typically measured using an automatic potentiometric titrator and converted to residual sodium. For specific calculations, refer to the industry standard SJ / T 11794-2022, "Test Method for Free Lithium in Lithium-ion Battery Cathode Materials," using alcohol as the solvent.

[0083] In some embodiments, the sodium cathode material comprises flaky single crystal particles. Compared to polycrystalline particles, single crystal particles can reduce problems such as particle fragmentation during excessive pressure. Flaky single crystals are more easily stacked tightly under sliding action to increase powder compaction density.

[0084] In some embodiments, the sheet thickness ratio γ of the sodium cathode material is 1 to 10, for example, 1.2, 2, 2.7, 3, 4, 5, 5.4, 6, 7, 8, 9, 10, etc. The sheet thickness ratio is a parameter that can indicate the degree of irregularity of the flaky cathode material particles, generally being the ratio of the longest axis of the flaky material particle to the short axis (α) perpendicular thereto. A lower sheet thickness ratio indicates that the material tends to have a short rectangular or cubic particle morphology, while a higher sheet thickness ratio indicates that the material tends to have a larger, thinner flaky particle morphology.

[0085] Optionally, the sheet thickness ratio γ of the sodium cathode material is 2 to 6.5, thereby reducing the material synthesis cost while further promoting the relative slip degree of the material.

[0086] In the present application, a scanning electron microscope (SEM) can be used to obtain the sheet thickness ratio of the material, as specifically shown in the following examples.

[0087] In some embodiments, the median particle size d of the sodium cathode material is 2 μm to 15 μm. Alternatively, the median particle size d of the sodium cathode material is 3 μm to 10 μm, such as 3 μm, 5 μm, 5.5 μm, 7 μm, 8 μm, 8.5 μm, 10 μm, etc.

[0088] In some embodiments, the median particle size d and thickness α of the sodium cathode material satisfy the relationship: 6γ / π<(d / α) 3 <6γ 2 / π.

[0089] In this application, "median particle size" refers to Dv 50 .

[0090] In some embodiments, the cathode material matrix comprises a single crystal sodium oxide.

[0091] Optionally, the chemical formula of the positive electrode material matrix is ​​Na a [Ni b Mn c M d ]O2, wherein 0.65≤a≤1.1, 0.1≤b≤0.5, 0.1≤c≤0.5, 0.1≤d≤0.5, b+c+d=1, and M is selected from one or more of Fe, Cu, Zn, Ti, Zr, Mg, La, Y, Ca, Sb or Sn. As a result, the sodium battery positive electrode material has high structural stability, can exert high capacity while improving the cycle stability of the battery.

[0092] Optionally, 0.8≤a≤1.1, 0.2≤b≤0.4, 0.2≤c≤0.4, 0.2≤d≤0.4. Further, 0.88 <a<0.95。

[0093] Optionally, M includes one or more of Fe, Cu or Zn.

[0094] As some examples, the cathode material matrix may be Na 0.9 Ni 0.22 Mn 0.4 Fe 0.3 Zn 0.08 O2、Na 0.92 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2、Na 0.92 Ni 0.23 Mn 0.4 Fe 0.3 Zn0.04 Cu 0.03 One or more of O2.

[0095] In the present application, the effective internal friction angle of the sodium cathode material is less than 30°, for example, 8°, 10°, 12°, 15°, 17°, 20°, 21°, 25°, 26°, 28°, etc. The effective internal friction angle can characterize the ability of the powder material to slide. The smaller the effective internal friction angle, the stronger the sliding ability of the material. The effective internal friction angle can be measured using a triaxial test. Specific examples are shown below.

[0096] In some embodiments, the effective internal friction angle of the sodium cathode material is 10° to 25°. This allows the battery to have higher cycle stability while increasing the compaction density.

[0097] In some embodiments, the BET specific surface area of ​​the sodium cathode material is ≤0.6 g / m 2 , for example 0.2g / m 2 , 0.25g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.45g / m 2 , 0.5g / m 2 , 0.57g / m 2 , 0.6g / m 2 In the cathode material matrix with the same composition (ie, the same chemical formula), the smaller the BET specific surface area, the higher the smoothness of the material surface, thereby increasing the powder compaction density of the sodium battery cathode material.

[0098] In some embodiments, the powder compaction density of the sodium cathode material at 3T pressure is greater than 3.12 g / cm 3 .

[0099] In some embodiments, in the sodium battery cathode material, the mass ratio of the cathode material matrix to the coating layer is 100:(0.1-2). Thus, the coating layer can promote relative sliding between the materials while enabling the battery to have better electrochemical performance.

[0100] The second aspect of the present application provides a method for preparing a sodium battery positive electrode material, comprising: mixing a positive electrode material matrix and a coating layer raw material in the presence of a solvent, and sintering to form a coating layer on at least a portion of the surface of the positive electrode material matrix.

[0101] Conventional methods use dry coating or chemical precipitation to form a coating layer. The coated material has poor distribution uniformity and the surface is rough, resulting in high surface friction of the material. The present application uses a wet coating process to treat the positive electrode material matrix. On the one hand, by forming a coating layer with a "molecular pulley" effect, the sliding between single crystal materials is increased. On the other hand, a large amount of impurities such as residual sodium on the surface can be removed, further reducing the surface friction of the material, thereby improving the powder and electrode compaction density of the material. The preparation method of the present application can effectively reduce the effective internal friction angle of the matrix, and can make the effective internal friction angle of the prepared sodium positive electrode material less than 30°, and can further be selected to be no more than 25°.

[0102] In some embodiments, the coating layer material comprises at least one of nanoparticles or polymers; the nanoparticles comprise nanoinorganic and / or nanoorganic materials; and the polymer comprises one or more of the following groups: carboxyl, sulfonic, phenolic, cycloalkyl, and heterocycloalkyl. As a result, the coating layer acts as a "molecular pulley," enhancing the sliding motion between the positive electrode material particles. This sliding action facilitates close stacking of the material particles, thereby increasing the compaction density.

[0103] In some specific embodiments, the coating layer raw material includes the nanoparticles. In this case, the nanoparticles adhere to the cathode material substrate, forming a highly hard coating lubricating film that blocks direct contact between rough interfaces of the materials during the pressing process. Furthermore, the nanoparticles are smaller and more easily slideable, acting as solid lubricants to promote sliding between cathode materials, alleviate overlap between particles, reduce porosity, and increase powder compaction density.

[0104] Optionally, the average particle size of the nanoscale particles may be 5 nm to 100 nm, for example, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 80 nm, etc.

[0105] Optionally, the nano-inorganic material includes nano-oxide.

[0106] Furthermore, the nano-inorganic material includes at least one of Al2O3, ZrO2, CaO, MgO or TiO2.

[0107] As some specific embodiments, the coating layer raw material includes the polymer. The polymer can use its "flexible" long molecular chain to wrap around the surface of the positive electrode material matrix to form a smooth coating layer.

[0108] Optionally, the polymer comprises at least one of polyacrylic acid, polyrotaxane or polyurethane.

[0109] Optionally, the polymer includes polyacrylic acid. The molecular chain of polyacrylic acid has carboxyl groups, which, as active functional groups, can neutralize residual alkali on the surface of the single crystal sodium oxide, thereby improving the reliability between the coating layer and the positive electrode material matrix.

[0110] As some examples, the viscosity average molecular weight (Mv) of the polyacrylic acid may be 2 million to 4 million, such as 2 million, 2.5 million, 3 million, 3.5 million, etc.

[0111] Optionally, the polymer includes at least one of polyrotaxane or polyurethane. The molecular chains of such polymers may include cycloalkyl and / or heterocycloalkyl groups, which can promote relative slippage between polymer molecular chains.

[0112] As some examples, the polyrotaxane may include a cyclodextrin polyrotaxane, such as a polyrotaxane formed by intercalating β-cyclodextrin into a guest polymer chain (such as polyethylene glycol).

[0113] As some examples, the polyurethane may include a polyurethane formed by reacting an isocyanate having a cycloalkyl group (such as IPDI) with a polyamine.

[0114] In some embodiments, the positive electrode material matrix includes a single crystal sodium oxide. The single crystal particle morphology of the single crystal sodium oxide determines that the particles will overlap and support each other during the pressing process. Due to the large friction between the particles, the overlapping support between the edges and corners of the flaky particles during the pressing process will cause the pores to increase, resulting in a lower compaction density, which affects the energy density of the battery. The preparation method of the present application uses a wet coating process to treat the single crystal sodium oxide, which can remove a large amount of impurities such as residual sodium on the surface, and can also form a coating layer that can act as a "molecular pulley" to increase the compaction density of the single crystal sodium oxide.

[0115] Optionally, the chemical formula of the positive electrode material matrix is ​​Na a [Ni b Mn c M d ]O2, wherein 0.65≤a≤1.1, 0.1≤b≤0.5, 0.1≤c≤0.5, 0.1≤d≤0.5, b+c+d=1, and M is selected from one or more of Fe, Cu, Zn, Ti, Zr, Mg, La, Y, Ca, Sb or Sn. Thus, the prepared sodium battery positive electrode material has high structural stability, which enables the battery to achieve high capacity while improving the cycle stability of the battery.

[0116] Optionally, 0.8≤a≤1.1, 0.2≤b≤0.4, 0.2≤c≤0.4, 0.2≤d≤0.4. Further, 0.88 <a<0.95。

[0117] Optionally, M includes one or more of Fe, Cu or Zn.

[0118] As some examples, the cathode material matrix may be Na 0.9 Ni 0.22 Mn 0.4 Fe 0.3 Zn 0.08 O2、Na 0.92 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2、Na 0.92 Ni 0.23 Mn 0.4 Fe 0.3 Zn 0.04 Cu 0.03 One or more of O2.

[0119] In some embodiments, the cathode material matrix includes flaky single crystal particles.

[0120] In some embodiments, the thickness ratio γ0 of the flaky single crystal particles is 1 to 10. Alternatively, the thickness ratio γ0 of the flaky single crystal particles is 2 to 6.5.

[0121] In some embodiments, the median particle size d0 of the flaky single crystal particles is 2 μm to 15 μm. Alternatively, the median particle size d0 of the flaky single crystal particles is 3 μm to 10 μm, such as 3 μm, 5 μm, 5.5 μm, 7 μm, 8 μm, 8.5 μm, 10 μm, etc.

[0122] In the present application, the sodium-ion single crystal oxide used as the matrix of the positive electrode material can be obtained commercially or prepared according to methods well known in the art.

[0123] As some examples, the sodium electric single crystal oxide can be prepared by a solid phase method. The specific process of the solid phase method may include: mixing a sodium source, a nickel source, a manganese source and an M source, and calcining to obtain the sodium electric single crystal oxide.

[0124] As other examples, the single crystal sodium oxide can be obtained by a liquid phase method. The specific process of the liquid phase method may include: in the presence of a first solvent (such as water), a nickel source, a manganese source and an M source are subjected to a co-precipitation reaction, and the obtained precursor is filtered and washed, mixed with a sodium source, and calcined to obtain a single crystal sodium oxide.

[0125] Optionally, the calcination temperature may be 700°C to 1000°C, for example, 700°C, 800°C, 850°C, 900°C, 950°C, 970°C, etc.

[0126] Optionally, the calcination time can be 8 h to 20 h, for example, 8 h, 10 h, 12 h, 15 h, 16 h, 18 h, 20 h, etc.

[0127] Alternatively, the calcination may be performed in an oxygen-containing atmosphere (eg, air, oxygen).

[0128] Optionally, the coprecipitation reaction is carried out in the presence of a precipitant and a complexing agent. Specific examples of the precipitant include, but are not limited to, one or more of sodium hydroxide, sodium carbonate, potassium carbonate, and potassium hydroxide. Specific examples of the complexing agent include, but are not limited to, one or more of ammonia water, ammonium chloride, ammonium sulfate, ammonium carbonate, ammonium bicarbonate, citric acid, and the like.

[0129] Alternatively, the sodium source, nickel source, manganese source, and M source may be selected from one or more of oxides, sulfates, carbonates, nitrates, oxalates, and chlorides of the respective metals.

[0130] In some embodiments, the solvent comprises at least one of water or alcohol, for example ethanol.

[0131] In some embodiments, the amount of the solvent used is 0.4 L to 1 L, for example, 0.4 L, 0.5 L, 0.7 L, 0.8 L, 1 L, etc., relative to 1 kg of the positive electrode material matrix. This improves the uniformity of raw material dispersion while promoting the coating raw material to adhere to the surface of the positive electrode material matrix to form a coating layer.

[0132] In some embodiments, based on the mass of the positive electrode material matrix, the mass proportion of the coating layer raw material is 2000ppm to 30000ppm, for example, 2000ppm, 4000ppm, 4500ppm, 6250ppm, 8000ppm, 15000ppm, 20000ppm, 25000ppm, etc.

[0133] Optionally, based on the mass of the positive electrode material matrix, the mass proportion of the coating layer raw material is 5000ppm to 20000ppm. Thus, while improving the surface roughness of the positive electrode material matrix, the battery can also have higher electrochemical performance.

[0134] In some embodiments, the mixing method includes: first dispersing the coating material in the solvent, then adding the positive electrode material matrix to perform a second dispersion; the first dispersion is performed at a first temperature T1 under stirring, and the stirring speed of the first dispersion is P1; the second dispersion is performed at a second temperature T2 under stirring, and the stirring speed of the second dispersion is P2; wherein T1 ≤ T2, P1 > P2. The higher stirring speed in the first stage can improve the uniformity of the coating material dispersion in the solvent, while the lower stirring speed in the second stage can encourage the coating material to fall back to the surface of the positive electrode material matrix to improve the coating efficiency.

[0135] In some embodiments, the second dispersion time (stirring time) is 1 min to 10 min, for example, 1 min, 2 min, 5 min, 10 min, etc.

[0136] Optionally, the second dispersion time is 1 min to 5 min. Thus, while promoting the coating layer raw material to adhere to the surface of the positive electrode material matrix, it also reduces the Na + The possibility of dissolution causing a decrease in the material's gram capacity.

[0137] In some embodiments, the sintering temperature is 150° C. to 450° C., for example, 150° C., 180° C., 200° C., 220° C., 250° C., 300° C., 330° C., 350° C., 400° C., 420° C., 450° C., etc. At this sintering temperature, on the one hand, the coating layer raw material can be allowed to adhere to the surface of the positive electrode material substrate without excessive fusion with the positive electrode material substrate, and on the other hand, the formed coating layer can have high mechanical rigidity, promoting inter-particle sliding during the pressing process.

[0138] In some embodiments, the sintering time is 3 hours to 12 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 11 hours, etc. In this way, the degree of adhesion of the coating layer to the positive electrode material substrate can be controlled, which, on the one hand, reduces the possibility of the coating layer falling off during the pressing process, and on the other hand, promotes the distribution of the coating layer on the surface of the positive electrode material substrate to play an effective sliding role.

[0139] In some embodiments, the sodium cathode material described in the first aspect of the present application can be prepared by the preparation method described in the second aspect.

[0140] According to the preparation method of the present application, in some embodiments, the mixing and sintering conditions can be selected according to the raw materials of the coating layer.

[0141] As some examples, the coating layer raw material includes the nano-inorganic material.

[0142] During the mixing process, the first dispersion temperature T1 is controlled to be 5°C to 15°C, the speed P1 is controlled to be 800 rpm to 1000 rpm, and the speed T2 is controlled to be 5°C to 15°C, and the speed P2 is controlled to be 300 rpm to 500 rpm. Controlling T1 and T2 below room temperature slows down molecular thermal motion, making it difficult for Na in the crystal lattice to escape, thereby reducing the impact on material properties.

[0143] During the sintering process, the sintering temperature is controlled to be 300° C. to 420° C. At this temperature, the nano-inorganic material and the positive electrode material matrix can maintain a suitable adhesion state, reducing the possibility of the nano-inorganic material being incorporated into the positive electrode material matrix or fusing with the positive electrode material matrix, so that the formed coating layer has both high mechanical rigidity and promotes inter-particle sliding.

[0144] During the sintering process, the sintering time is controlled to be 3 hours to 7 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, etc.

[0145] As some other examples, the coating layer material includes the polymer.

[0146] During the mixing process, the first dispersion temperature T1 is controlled to be 5°C to 15°C, P1 is controlled to be 800 rpm to 1000 rpm, T2 is controlled to be 20°C to 35°C, and P2 is controlled to be 300 rpm to 500 rpm. T2 is controlled to be greater than T1 and to be near room temperature, thereby suppressing the release of Na from the crystal lattice and promoting the wrapping of the polymer around the positive electrode material matrix.

[0147] During the sintering process, the sintering temperature is controlled to be 180° C. to 220° C. At this temperature, the nano-inorganic material and the positive electrode material matrix can be kept in a proper adhesion state, and the thermal decomposition of the polymer can be suppressed.

[0148] During the sintering process, the sintering time is controlled to be 3 hours to 6 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, etc.

[0149] In the present application, a coating layer formed on the surface of the sodium cathode material can be obtained by transmission electron microscopy (TEM), and the elemental composition of the coating layer can be obtained by energy dispersive spectroscopy (EDS).

[0150] The third aspect of the present application provides a positive electrode plate, comprising the sodium battery positive electrode material described in the first aspect of the present application or the sodium battery positive electrode material prepared by the method described in the second aspect of the present application.

[0151] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, and the positive electrode film layer contains the sodium secondary battery positive electrode material.

[0152] In the present application, the positive electrode current collector may be, for example, a metal foil or a composite current collector. The metal foil may be, for example, aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. The metal layer may be made of, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material of the polymer base layer may be, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0153] In some embodiments, the sodium secondary battery positive electrode material is used as a positive electrode active material in a positive electrode film layer. In addition to the positive electrode material, the positive electrode film layer may optionally include a conductive agent and / or a binder. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers; the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorinated acrylate resin.

[0154] The present application does not particularly limit the preparation method of the positive electrode sheet, and the preparation method can refer to existing methods. For example, the positive electrode slurry is coated on the positive electrode current collector, dried, and cold pressed to form the positive electrode sheet. The positive electrode slurry can be formed by dispersing the sodium cathode material, optional conductive agent, optional binder, and other components in a solvent (e.g., N-methylpyrrolidone) and stirring them uniformly.

[0155] In addition, the positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive electrode film layer. For example, the positive electrode sheet may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the positive electrode current collector and the positive electrode film layer. For another example, the positive electrode sheet may also include a protective layer covering the surface of the positive electrode film layer.

[0156] The fourth aspect of the present application provides a sodium secondary battery, comprising the positive electrode sheet described in the third aspect of the present application.

[0157] In some embodiments, the sodium secondary battery comprises a sodium ion secondary battery.

[0158] In some embodiments, the sodium secondary battery further comprises a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0159] [Negative electrode]

[0160] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the negative electrode film layer may include a negative electrode active material.

[0161] In some embodiments, the negative electrode current collector may include a metal foil or a composite current collector. The metal foil is, for example, copper foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. The material of the metal layer includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, silver alloys, etc., and the polymer material of the polymer base layer includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0162] In some embodiments, the negative electrode active material may include negative electrode materials for secondary batteries known in the art. For example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxides, and tin alloys.

[0163] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may include, for example, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl cellulose (CMC), or carboxymethyl chitosan (CMCS).

[0164] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0165] In some embodiments, the negative electrode film layer may further optionally contain other additives, such as a thickener. Specific examples of thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC-Na).

[0166] The present application does not particularly limit the preparation method of the negative electrode sheet, and the negative electrode sheet can be prepared by referring to existing methods. For example, the negative electrode components, such as the negative electrode material, conductive agent, and binder, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is then coated on a negative electrode current collector, and the negative electrode sheet is obtained by drying and cold pressing.

[0167] [Electrolytes]

[0168] In the present application, the electrolyte can be selected with reference to existing secondary batteries.

[0169] In some embodiments, the electrolyte is an electrolyte solution.

[0170] In some embodiments, the electrolyte may include an organic solvent, a sodium salt, and an optional additive. The sodium salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, or Na(CH3)C6H4SO3. The organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), diethyl sulfone (ESE), or an ether solvent. The ether solvent may include cyclic ethers and / or chain ethers. Specific examples of cyclic ethers include, but are not limited to, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), etc. Specific examples of chain ethers include, but are not limited to, ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), etc.

[0171] In some embodiments, the additives in the electrolyte may include one or more of negative electrode film-forming additives and positive electrode film-forming additives; and may also include additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high temperature or low temperature performance of the battery, etc. As an example, the additives may include, but are not limited to, at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP) or tris(trimethylsilyl) borate (TMSB).

[0172] [Isolation film]

[0173] In the present application, the isolation membrane is arranged between the positive electrode plate and the negative electrode plate, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The present application has no particular restrictions on the type of isolation membrane, and various porous structure isolation membranes well known in the art can be selected. In some embodiments, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. In addition, the isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0174] In some embodiments, a ceramic coating and / or a metal oxide coating is further provided on the isolation membrane.

[0175] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0176] In some embodiments, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0177] In this application, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery can also be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0178] The battery of the present application may include a battery cell form, a battery module form, and a battery pack form. The battery cell, battery module, and battery pack of the present application will be described below with reference to the accompanying drawings as appropriate.

[0179] The present application has no particular limitation on the shape of the battery, which can be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 5 with a square structure as an example.

[0180] In some embodiments, referring to Figure 4, the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell can be one or more, and those skilled in the art can select according to specific actual needs.

[0181] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0182] Figure 5 shows an example battery module 4. Referring to Figure 5 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple cells may be secured together using fasteners.

[0183] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0184] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0185] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0186] The fifth aspect of the present application provides an electrical device comprising the sodium secondary battery described in the fourth aspect of the present application. The sodium secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device.

[0187] Electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0188] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0189] Figure 8 shows an example of an electric device. This device can be a pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the battery, a battery pack or battery module can be used.

[0190] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0191] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0192] Polyacrylic acid was purchased from Aladdin Biochemical Technology Co., Ltd., catalog number P131659;

[0193] Polyurethane diol solution was purchased from Aladdin Biochemical Technology Co., Ltd., catalog number P477907;

[0194] The polyrotaxane is formed by using β-cyclodextrin and polyethylene glycol as reactants, wherein β-cyclodextrin and polyethylene glycol are purchased from Aladdin Biochemical Technology Co., Ltd. with product numbers C104384 and P103730, respectively.

[0195] Example 1

[0196] Cathode material matrix 1: single crystal sodium oxide Na 0.9 Ni 0.22 Mn 0.4 Fe 0.3 Zn 0.08 O2 is used as the positive electrode material to be coated.

[0197] 25g of nano-TiO2 (average particle size 30nm) was added to 3.2L of deionized water to obtain a mixed solution, which was added to a water-washed reactor, the rotation speed was adjusted to 1000rpm, and the mixture was evenly dispersed at 10°C (first temperature T1). Subsequently, 4kg of the positive electrode material to be coated was added, the rotation speed was lowered to 400rpm, and stirring was continued at 10°C (second temperature T2) for 1min. The mixture was then filtered, and the obtained solid was placed in a muffle furnace and sintered at 400°C for 5h in an oxygen atmosphere to obtain a single crystal sodium electrode oxide coated with nano-TiO2, i.e., a sodium electrode positive electrode material.

[0198] Examples 2 to 5

[0199] The sodium positive electrode material was prepared according to the method of Example 1, except that nano-TiO2 was replaced by nano-Al2O3 (average particle size of 40 nm), nano-ZrO2 (average particle size of 30 nm), nano-CaO (average particle size of 50 nm), and nano-MgO (average particle size of 30 nm).

[0200] Examples 6 to 10

[0201] The sodium cathode material was prepared according to the method of Example 1, except that the amount of nano-TiO2 was adjusted so that the mass proportion of nano-TiO2 relative to the cathode material matrix 1 was 3000ppm, 15000ppm, 20000ppm and 25000ppm respectively.

[0202] Examples 11 to 13

[0203] The sodium battery positive electrode material was prepared according to the method of Example 1, except that the temperature of the reactor before and after adding the positive electrode material was adjusted as shown in Table 1, that is, the first temperature T1 and the second temperature T2.

[0204] Examples 14-15

[0205] The sodium battery positive electrode material was prepared according to the method of Example 1, except that the stirring time after adding the positive electrode material was adjusted as shown in Table 1.

[0206] Examples 16-17

[0207] The sodium cathode material was prepared according to the method of Example 1, except that the amount of deionized water was adjusted so that the corresponding solid-liquid ratio 1 / a (relative to 1 kg of the cathode material matrix, the amount of solvent is a L) was 1 / 0.4 and 1 / 1 respectively.

[0208] Examples 18 to 21

[0209] Sodium battery positive electrode materials were prepared according to the method of Example 1, except that the sintering temperatures were adjusted to 280°C, 300°C, 420°C, and 450°C.

[0210] Examples 22-23

[0211] The sodium positive electrode material was prepared according to the method of Example 1, except that the positive electrode material matrix 1 was adjusted to be the positive electrode material matrix 2 and the positive electrode material matrix 3, wherein the positive electrode material matrix 2 was Na 0.92 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2, the positive electrode material matrix 3 is Na 0.92 Ni 0.23 Mn 0.4 Fe 0.3 Zn 0.04 Cu 0.03 O2, and adjust the sintering temperature and / or sintering time as shown in Table 1.

[0212] Comparative Examples 1 to 3

[0213] Positive electrode material matrix 1, positive electrode material matrix 2 and positive electrode material matrix 3 are respectively used as comparison samples.

[0214] Comparative Example 4

[0215] The sodium cathode material was prepared according to the method of Example 1, except that the coating was carried out by a dry method (without adding deionized water). The specific operation was as follows:

[0216] 25g of nano-TiO2 (average particle size of 30nm) and 4kg of the positive electrode material to be coated (positive electrode material matrix 1) were mixed evenly in a mixer. The resulting solid mixture was placed in a muffle furnace and sintered at 400°C for 5h under an oxygen atmosphere to obtain a single crystal sodium electrode oxide coated with nano-TiO2, i.e., a sodium electrode positive electrode material.

[0217] Comparative Example 5

[0218] A sodium cathode material was prepared according to the method of Example 1, except that the sintering temperature was increased to 800°C.

[0219] Example 24

[0220] 40 g of polyacrylic acid was added to 3.2 L of deionized water to obtain a mixed solution, which was added to a water-washed reactor. The speed was adjusted to 700 rpm to fully disperse and dissolve the polyacrylic acid in the water. The temperature was controlled to 10°C (first temperature T1). Subsequently, 4 kg of positive electrode material (positive electrode material matrix 1) was added to the above mixed solution, the speed was lowered to 400 r / min, the temperature was raised to 30°C (second temperature T2), stirred for 1 min, and then filtered. The resulting solid was placed in a muffle furnace and sintered at 200°C for 4 h in an oxygen atmosphere to obtain a polyacrylic acid-coated single crystal sodium electrode oxide, i.e., a sodium electrode positive electrode material.

[0221] Examples 25-26

[0222] The sodium positive electrode material was prepared according to the method of Example 24, except that polyacrylic acid was replaced by polyrotaxane and polyurethane respectively.

[0223] Examples 27 to 30

[0224] The sodium battery positive electrode material was prepared according to the method of Example 24, except that the stirring temperature after adding the positive electrode material was adjusted as shown in Table 1, that is, the second temperature T2.

[0225] Examples 31-32

[0226] The sodium positive electrode material was prepared according to the method of Example 24, except that the amount of deionized water was adjusted so that the corresponding solid-liquid ratios 1 / a were 1 / 0.4 and 1 / 1, respectively.

[0227] Examples 33 to 36

[0228] The sodium positive electrode material was prepared according to the method of Example 24, except that the sintering temperature and / or sintering time were adjusted as shown in Table 1.

[0229] Comparative Example 6

[0230] The sodium cathode material was prepared according to the method of Example 24, except that the polyacrylic acid was coated by a dry method (without adding deionized water). The specific operation was as follows:

[0231] 40 g of polyacrylic acid and 4 kg of the positive electrode material to be coated (positive electrode material matrix 1) were mixed evenly in a mixer, and the obtained solid mixture was placed in a muffle furnace and sintered at 200 ° C for 4 h under an oxygen atmosphere to obtain a single crystal sodium electrode oxide coated with polyacrylic acid, i.e., a sodium electrode positive electrode material.

[0232] Comparative Example 7

[0233] The sodium positive electrode material was prepared according to the method of Example 24, except that the sintering temperature was increased to 500°C.

[0234] The main parameters in the above embodiments and comparative examples are shown in Table 1.

[0235] Table 1

[0236] Note: The inorganic oxide in the “coating material” column refers to nano inorganic oxide, and the “stirring time” refers to the stirring time after adding the positive electrode material to be coated.

[0237] Test section

[0238] 1. Characterization of cathode materials

[0239] (1) Median particle size (Dv 50 )test

[0240] The particle size test was performed using a Malvern laser particle size analyzer (Mastersizer-3000) with the reference standard being GB / T19077-2016.

[0241] Pretreatment: Add an appropriate amount of the sample to be tested and water into a beaker, and add a dispersant (sodium hexametaphosphate) and disperse by ultrasonication to ensure that the sample is completely dispersed in the dispersant.

[0242] (2) Specific surface area BET test

[0243] The specific surface area tester F-Sorb 1400CES was used for the test, referring to the GB / T 19587-2017 standard.

[0244] Pretreatment: Take a certain amount of powder and degas it in a nitrogen atmosphere at 80℃ for 12h.

[0245] (3) Morphological characterization:

[0246] The surface morphology of the materials was characterized using a field emission scanning electron microscope (Sigma300) from ZEISS, Germany.

[0247] (4) Effective internal friction angle test

[0248] The effective internal friction angle was calculated using a strain-controlled triaxial tester (Shanghai Huayan Instrument Co., Ltd.). The powder sample was placed in the sample chamber with the pressure piston aligned with the chamber top. Ambient pressure was applied while the shear strain rate was controlled to 0.5% / min. The shear start was controlled, and the changes in axial strain and dynamometer readings were recorded.

[0249] According to the Mohr-Coulomb failure criterion, the obtained data is substituted into the following formula for calculation. The total stress circle of failure is drawn with (σ1+σ3) / 2 as the horizontal coordinate and (σ1-σ3) / 2 as the vertical coordinate, and the envelope of the circles is drawn. The inclination angle of the envelope is the effective internal friction angle.

[0250] σ1 is the major principal stress, σ3 is the minor principal stress, C is the cohesion of the sample, and Φ is the effective internal friction angle of the sample.

[0251] (5) Residual sodium test

[0252] The alcohol method is used to test the residual sodium content of the material. The specific operation is as follows:

[0253] 30g of sample was placed in 100mL of ethanol, stirred for 30min, and then allowed to stand for 5min. Filtered, 10mL of supernatant was taken, and sodium carbonate and sodium hydroxide dissolved in the positive electrode material were titrated with 0.05mol / L hydrochloric acid standard solution. The pH electrode was used as the indicator electrode, and the end point was determined by the sudden jump caused by the potential change. The residual sodium on the surface of the positive electrode material, i.e., the residual Na + content.

[0254] (6) Sample thickness ratio test

[0255] In the field of view of a scanning electron microscope, 20 flaky particles were selected, and the longest side of the particles and the short side perpendicular to the longest side of the particles were measured. The ratio of the longest side to the short side was the flake thickness ratio. The flake thickness ratio of each particle was calculated separately, and the average flake thickness ratio of the material was obtained.

[0256] (7) Sample powder compaction density:

[0257] Determine the compaction density of the cathode material at 3 T according to GB / T 24533-2019. Remove the top pin and upper gasket, weigh 20 g of the sample into the sleeve to the nearest 0.0001 g, and record the weight as m.

[0258] Powder compaction density = 10m / (S×H),

[0259] m is the sample weight in grams (g);

[0260] H is the thickness of the sample after compaction, in millimeters (mm);

[0261] S is the cross-sectional area of ​​the top column, in square centimeters (cm 2 ).

[0262] 2. Performance Testing

[0263] The following is a performance test of the sodium cathode materials of the examples and comparative examples applied to batteries.

[0264] 1. Preparation of button batteries:

[0265] The positive electrode material, PVDF, and conductive carbon are added to NMP in a weight ratio of 90:5:5, stirred in a drying room to form a slurry, coated on aluminum foil, dried, and cold-pressed to form a positive electrode sheet. A sodium sheet is used as the negative electrode. The electrolyte consists of an organic solvent and NaPF6, with a NaPF6 concentration of 1 mol / L. The organic solvent consists of EC, DEC, and DMC in a volume ratio of 1:1:1. The battery is assembled into a button cell in a button box.

[0266] Test method for initial gram capacity after power-off:

[0267] At 1.5V~4.0V, charge to 4.0V at 0.1C, then charge at constant voltage at 4.0V to a current ≤ 0.05mA, let stand for 2 minutes, the charge capacity at this time is recorded as C0, then discharge to 1.5V at 0.1C, the discharge capacity at this time is the initial gram capacity, recorded as D0.

[0268] 2. Preparation of full battery

[0269] The positive electrode material (active material), conductive agent acetylene black, and binder PVDF were mixed thoroughly in NMP at a weight ratio of 95:3:2, and then coated on one side of aluminum foil (thickness 60μm), dried, and cold pressed to obtain a positive electrode sheet. The active material loading was 16mg / cm 2 .

[0270] The negative electrode material (active material) hard carbon, conductive agent acetylene black, binder SBR, and thickener sodium carboxymethyl cellulose were mixed thoroughly in deionized water at a weight ratio of 95:2:2:1. The mixture was then coated on both sides of a copper foil (8 μm thick), dried, and cold pressed to obtain a negative electrode sheet. The active material loading was 11 mg / cm 2 .

[0271] PE porous polymer film is used as the isolation membrane.

[0272] Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is uniformly dissolved in the above organic solvent to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0273] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to provide isolation. The cells are then wound to form a bare cell. The bare cell is then placed in an outer packaging, injected with electrolyte, and sealed to form a full battery.

[0274] Battery cycle performance test:

[0275] Under a constant temperature environment of 25°C, charge the battery to 4.0V at 1C at 1.5V~4.0V, then charge it at a constant voltage at 4.0V until the current is ≤0.05mA, let it stand for 5 minutes, and then discharge it to 1.5V at 1C. The capacity is recorded as Dn (n=0, 1, 2, ...). Repeat the above process until the number of cycles reaches 100, record the capacity fading value, and obtain the capacity retention rate (%) = (D 100 / D1)×100%.

[0276] The test results are shown in Table 2.

[0277] Table 2

[0278] In combination with Table 1 and Table 2, by comparing Examples 1-36 with Comparative Examples 1-7, it can be seen that Examples 1-36 use a wet coating process to form a smooth coating layer on the surface of the single crystal sodium oxide, which can effectively reduce the effective internal friction angle of the positive electrode material; the prepared sodium positive electrode material has a higher powder compaction density, and can increase the gram capacity of the battery and enable the battery to have a higher capacity retention rate.

[0279] By comparing Examples 1-20, 24-36 with Comparative Example 1, Example 22 with Comparative Example 2, and Example 23 with Comparative Example 3, it can be seen that under the same conditions of single-crystalline sodium oxides, the uncoated single-crystalline sodium oxides (Comparative Examples 1-3) not only have a higher effective internal friction angle, but also have a higher specific surface area and residual sodium content, and the corresponding powder compaction density is also lower. The prepared batteries cannot have both high gram capacity and cycle stability.

[0280] Comparing Example 1 with Comparative Examples 4-5 and Comparative Examples 6-7, it can be seen that Comparative Examples 4 and 6 respectively use nano-inorganic materials and polymers in combination with a dry coating process to form a coating layer, and Comparative Examples 5 and 7 respectively use nano-inorganic materials and polymers using a wet coating process but perform high-temperature sintering to form a coating layer. Comparative Examples 4-7 are unable to effectively reduce the effective internal friction angle of single-crystalline sodium oxides, the powder compaction density of the prepared sodium cathode material is too low, and the cycle stability of the battery is not high.

[0281] Figure 1 is an SEM image of the sodium cathode material prepared in Example 1, and Figure 2 is an SEM image of the single crystal sodium cathode material of Comparative Example 1. It can be seen from Figures 1 and 2 that the sodium cathode material after coating in Example 1 is in a flaky single crystal state with a smooth surface, while the single crystal sodium cathode material of Comparative Example 1 that is not coated is in a flaky single crystal state, has more surface impurities, and has a rough surface.

[0282] In summary, the coating material selected in this application can reduce the effective internal friction angle and further increase the slip between material particles, significantly reducing the surface residual alkali of single-crystalline sodium oxide, and the surface of the positive electrode material particles is smooth after coating.

[0283] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A sodium cathode material, wherein: The sodium-ion positive electrode material comprises a positive electrode material matrix and a coating layer located on at least a portion of the surface of the positive electrode material matrix, wherein the effective internal friction angle of the sodium-ion positive electrode material is less than 30°.

2. The sodium cathode material according to claim 1, wherein The coating layer includes at least one of nano-scale particles or polymers; wherein the nano-scale particles include nano-inorganic matter and / or nano-organic matter; and the polymer includes one or more of the following groups: carboxyl group, sulfonic acid group, phenolic hydroxyl group, cycloalkyl group, and heterocycloalkyl group.

3. The sodium cathode material according to claim 2, wherein The nano-inorganic material satisfies one or more of the following conditions: (a) comprising nano-oxides; (b) includes at least one of Al2O3, ZrO2, CaO, MgO or TiO2.

4. The sodium cathode material according to claim 2 or 3, wherein The polymer includes at least one of polyacrylic acid, polyrotaxane or polyurethane.

5. The sodium cathode material according to any one of claims 1 to 4, wherein The residual Na + The content is less than 1300ppm.

6. The sodium cathode material according to any one of claims 1 to 5, wherein: The sodium battery positive electrode material includes flaky single crystal particles.

7. The sodium cathode material according to any one of claims 1 to 6, wherein: The thickness ratio γ of the sodium cathode material is 1 to 10, and / or The median particle size d of the sodium cathode material is 2 μm to 15 μm.

8. The sodium cathode material according to any one of claims 1 to 7, wherein: The chemical formula of the positive electrode material matrix is ​​Na a [Ni b Mn c M d ]O2, wherein 0.65≤a≤1.1, 0.1≤b≤0.5, 0.1≤c≤0.5, 0.1≤d≤0.5, b+c+d=1, and M is selected from one or more of Fe, Cu, Zn, Ti, Zr, Mg, La, Y, Ca, Sb or Sn.

9. The sodium cathode material according to any one of claims 1 to 8, wherein: The sodium cathode material meets one or more of the following conditions: (a) The median particle size d is 3 μm to 10 μm; (b) sheet thickness ratio γ is 2 to 6.5; (c) The effective internal friction angle is 10° to 25°.

10. The sodium cathode material according to any one of claims 1 to 9, wherein: The BET specific surface area of ​​the sodium cathode material is ≤0.6 g / m 2 .

11. The sodium cathode material according to any one of claims 1 to 10, wherein: The powder compaction density of the sodium cathode material under 3T pressure is greater than 3.12 g / cm 3 .

12. A method for preparing a sodium cathode material, wherein: include: In the presence of a solvent, a positive electrode material substrate and a coating layer raw material are mixed and sintered to form a coating layer on at least a portion of the surface of the positive electrode material substrate.

13. The preparation method according to claim 12, wherein: The coating layer includes at least one of nano-scale particles or polymers; the nano-scale particles include nano-inorganic matter and / or nano-organic matter; the polymer includes one or more of the following groups: carboxyl group, sulfonic acid group, phenolic hydroxyl group, cycloalkyl group, and heterocycloalkyl group.

14. The preparation method according to claim 13, wherein The nano-inorganic material satisfies one or more of the following conditions: (a) comprising nano-oxides; (b) includes at least one of Al2O3, ZrO2, CaO, MgO or TiO2.

15. The preparation method according to claim 13 or 14, wherein The polymer includes at least one of polyacrylic acid, polyrotaxane or polyurethane.

16. The preparation method according to any one of claims 12 to 15, wherein: The sintering temperature is 150°C to 450°C, and / or The sintering time is 3 hours to 12 hours.

17. The preparation method according to claim 13 or 14, wherein The coating layer raw material includes the nano inorganic substance, and the sintering temperature is 300°C to 420°C, and / or The sintering time is 3 hours to 7 hours.

18. The preparation method according to claim 13 or 15, wherein The coating layer raw material includes the polymer, and the sintering temperature is 180°C to 220°C, and / or The sintering time is 3h to 6h.

19. The preparation method according to any one of claims 12 to 18, wherein: One or more of the following conditions are met: (a) the solvent comprises at least one of water or alcohol; (b) The amount of the solvent used is 0.4 L to 1 L relative to 1 kg of the positive electrode material matrix.

20. The preparation method according to any one of claims 12 to 19, wherein: The mixing methods include: Performing a first dispersion of the coating layer raw material in the solvent, and then adding the positive electrode material matrix to perform a second dispersion; The first dispersion is performed at a first temperature T1 under stirring conditions, and the stirring speed of the first dispersion is P1; The second dispersion is carried out under stirring conditions at a second temperature T2, and the stirring speed of the second dispersion is P2; wherein, T1≤T2, P1>P2.

21. The preparation method according to claim 20, wherein One or more of the following conditions are met: (a) The coating layer raw material includes nano-inorganic substances, T1 is 5°C to 15°C, P1 is 800rpm to 1000rpm, T2 is 5°C to 15°C, and P2 is 300rpm to 500rpm; (b) the coating layer raw material includes a polymer, T1 is 5°C to 15°C, P1 is 600rpm to 800rpm, T2 is 20°C to 35°C, and P2 is 300rpm to 500rpm; (c) The second dispersion time is 1 min to 10 min.

22. The preparation method according to any one of claims 12 to 21, wherein: One of the following conditions is met: (a) Based on the mass of the positive electrode material matrix, the mass proportion of the coating layer raw material is 2000ppm to 30000ppm; (b) Based on the mass of the positive electrode material matrix, the mass of the coating layer raw material accounts for 5000ppm to 20000ppm.

23. The preparation method according to any one of claims 12 to 22, wherein: The chemical formula of the positive electrode material matrix is ​​Na a [Ni b Mn c M d ]O2, wherein 0.65≤a≤1.1, 0.1≤b≤0.5, 0.1≤c≤0.5, 0.1≤d≤0.5, b+c+d=1, and M is selected from one or more of Fe, Cu, Zn, Ti, Zr, Mg, La, Y, Ca, Sb or Sn.

24. The preparation method according to any one of claims 12 to 23, wherein: The positive electrode material matrix includes flaky single crystal particles, and the flaky single crystal particles meet one or more of the following conditions: (a) Sheet thickness ratio γ0 is 1 to 10; (b) The median particle size d0 is 2 μm to 15 μm.

25. A positive electrode sheet, wherein: The invention relates to a sodium battery positive electrode material according to any one of claims 1 to 11 or a sodium battery positive electrode material prepared by the preparation method according to any one of claims 12 to 24.

26. A sodium secondary battery, wherein: Including the positive electrode sheet as described in claim 25.

27. An electrical device, wherein: Including the sodium secondary battery according to claim 26.

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