Composite sodium ion positive electrode material, preparation method thereof, positive plate and sodium ion battery

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a composite sodium ion positive electrode material, a preparation method thereof, a positive electrode plate and a sodium ion battery. The general formula of the composite sodium ion positive electrode material is Na < x > MO < 2-alpha > Na Fe V < c > Md (PO4) e (P2O7) f (SO4) g Nh, the NaxMO2 comprises an O3-phase layered oxide positive electrode material and / or a P2-phase oxide positive electrode material; and NaaFebVcAd (PO4) e (P2O7) f (SO4) gGh is a polyanion material. According to the composite sodium ion positive electrode material, the phenomena of particle crushing and pole piece brittle failure caused by excessive extrusion of layered oxide particles in the pole piece rolling process can be effectively relieved, and meanwhile, the phenomenon of particle cracking caused by interlayer slippage after long circulation can be inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and in particular, to a composite sodium-ion cathode material, a preparation method thereof, a cathode sheet, and a sodium-ion battery. Background Art

[0002] Layered oxide cathode materials play an important role in battery technology, especially showing excellent performance in sodium-ion batteries. Among them, layered oxide cathode materials have the advantages of simple preparation methods, relatively high specific capacity, voltage, and safety, and can take into account both energy density and cycle life.

[0003] However, for the electrode sheet prepared with a single layered oxide cathode material, during the electrode sheet rolling process, the layered oxide particles are over-extruded, resulting in particle fragmentation, and the electrode sheet is prone to brittle fracture. At the same time, after long-term cycling, due to interlayer slip, particle cracking is likely to occur.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a composite sodium-ion cathode material, which can effectively alleviate the particle fragmentation and brittle fracture of the electrode sheet caused by over-extrusion of layered oxide particles during the electrode sheet rolling process, and at the same time is beneficial to suppressing particle cracking caused by interlayer slip after long-term cycling.

[0006] The second object of the present invention is to provide a preparation method of a composite sodium-ion cathode material. The composite sodium-ion cathode material prepared by this method has excellent cycle performance and high energy density.

[0007] The third object of the present invention is to provide a cathode sheet.

[0008] The fourth object of the present invention is to provide a sodium-ion battery.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] The present invention first provides a composite sodium-ion cathode material, which includes a layered oxide cathode material and a polyanion material. The polyanion material is coated on the surface of the layered oxide cathode material and filled between the particles of the layered oxide cathode material;

[0011] Among them, the layered oxide cathode material includes an O3-phase layered oxide cathode material and / or a P2-phase oxide cathode material. The general formula of the layered oxide cathode material is Na xMO2; wherein 0.6≤x≤1, and M includes at least two of the elements Cu, Ni, Fe, Mn, Zn, Mg, Zr, Ti, Li, Ca, Sr, Y, Ba, Co, Al and Cr;

[0012] The general formula of the polyanion material is Na a Fe b V c A d (PO4) e (P2O7) f (SO4) g G h ; wherein a is 1 or 2 or 3 or 4, 0≤b, c≤4, b+c<a, 0≤d≤1, 0≤e, f≤4, g≤4, 0≤h≤1, and b and c are not 0 at the same time, and e, f and g are not 0 at the same time; A is a doping modification element at the Fe position or V position, and A includes at least one of Ni, Mn, Co, Ti, Cr, Cu and Zn elements; G includes F - , O 2- 、CO3 2- 、SiO4 4- and B z O y n- At least one of .

[0013] Furthermore, when the layered oxide positive electrode material is an O3 phase layered oxide positive electrode material, the O3 phase layered oxide positive electrode material has a gram capacity of 130 to 150 mAh / g between 2.0 and 4.0 V, and the polyanion material must contain PO4 3- and SO4 2- At least one of .

[0014] Furthermore, when the layered oxide positive electrode material is a P2 phase layered oxide positive electrode material, the P2 phase layered oxide positive electrode material has a gram capacity of 80 to 120 mAh / g between 2.5 and 4.2 V, and the polyanion material must contain V 3+ and SO4 2- At least one of .

[0015] Furthermore, the polyanion material also includes a conductive carbon material.

[0016] Furthermore, the Na x The median particle size D50 of MO2 satisfies 3μm<D50<12μm.

[0017] Furthermore, the Na x The tap density TD of MO2 meets 1.5g / cm 3 <TD<2.5g / cm3 。

[0018] Furthermore, the median particle size D50 of the Na a Fe b V c A d (PO4) e (P2O7) f (SO4) g G h satisfies D50 < 1 μm.

[0019] Furthermore, the tapped density TD of the Na a Fe b V c A d (PO4) e (P2O7) f (SO4) g G h satisfies 0.3 g / cm 3 < TD < 1.5 g / cm 3 。

[0020] Furthermore, the percentage α of the mass of the polyanion material in the total mass of the composite sodium ion cathode material is 5% to 30%.

[0021] The present invention further provides a method for preparing the above composite sodium ion cathode material, comprising the following steps: Mix Na x MO2 and Na a Fe b V c M d (PO4) e (P2O7) f (SO4) g N h and bake, then perform coating and filling to obtain the composite sodium ion cathode material.

[0022] Furthermore, the baking temperature is 100 to 300 °C, and the heat preservation time is 1 to 10 h.

[0023] Furthermore, the baking atmosphere includes a nitrogen atmosphere or an air atmosphere.

[0024] The present invention also provides a positive electrode sheet comprising the above composite sodium ion cathode material.

[0025] Furthermore, the electrode compaction density of the positive electrode sheet is 3.1 to 3.5 g / cm 3 。

[0026] The present invention further provides a sodium ion battery comprising the above positive electrode sheet.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The composite sodium-ion cathode material provided by the present invention can effectively slow down the phenomena of particle breakage and electrode sheet brittle fracture caused by excessive extrusion of layered oxide particles during the electrode sheet rolling process, and at the same time is beneficial to inhibiting the particle cracking phenomenon caused by interlayer slip after long-term cycling.

[0029] (2) Due to the excellent ionic conductivity of the nano-sized polyanion material, the composite sodium-ion cathode material provided by the present invention is dispersed on the surface and in the surrounding voids of the layered oxide particles, which can effectively improve the overall ionic conductivity of the electrode sheet, reduce phenomena such as cell swelling and cycling degradation caused by interfacial side reactions, and is beneficial to achieving the long-term cycling performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 It is the SEM image of the O3-phase layered oxide cathode material prepared in Example 1 provided by the present invention;

[0032] Figure 2 It is the SEM image of the polyanion material prepared in Example 1 provided by the present invention;

[0033] Figure 3 It is the cyclic performance test comparison chart of the composite sodium-ion cathode material and the corresponding O3-phase layered oxide cathode material prepared in Example 3 provided by the present invention;

[0034] Figure 4 It is the SEM image of the composite sodium-ion cathode material particles after 100 cycles of the battery assembled with the composite sodium-ion cathode material in Example 3 provided by the present invention;

[0035] Figure 5 It is the SEM image of the pure layered oxide cathode material particles after 100 cycles of the battery assembled with the pure layered oxide cathode material prepared in step (1) of Example 3 provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For those reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0037] Unless otherwise specified, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0038] Unless otherwise specified, the "including" and "comprising" mentioned in the present invention mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or it can only include or comprise the listed components.

[0039] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two or any two or more of the listed items. Among them, "several" refers to any two or any two or more.

[0040] In a first aspect, the present invention provides a composite sodium ion cathode material that can effectively inhibit the fragmentation of layered oxide particles, which includes a layered oxide cathode material and a polyanion material. The polyanion material is coated on the surface of the layered oxide cathode material and filled between the layered oxide cathode material particles. The layered oxide cathode material includes an O3-phase layered oxide cathode material and / or a P2-phase oxide cathode material, and the general formula of the layered oxide cathode material is Na x MO2; wherein, 0.6 ≤ x ≤ 1 (for example, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or 0.98), and M includes at least two of the elements Cu, Ni, Fe, Mn, Zn, Mg, Zr, Ti, Li, Ca, Sr, Y, Ba, Co, Al and Cr, for example, three, four, five or more of them. The general formula of the polyanion material is Na a Fe b V c Ad (PO4) e (P2O7) f (SO4) g G h ; wherein, a is 1 or 2 or 3 or 4, 0 ≤ b, c ≤ 4, b + c < a, 0 ≤ d ≤ 1, 0 ≤ e, f ≤ 4, g ≤ 4, 0 ≤ h ≤ 1, and b and c are not both 0, and e, f, and g are not both 0; A is a doping and modifying element at the Fe site or V site, and A includes at least one of the elements Ni, Mn, Co, Ti, Cr, Cu, and Zn; G includes F - 、O 2- 、CO3 2- 、SiO4 4- and B z O y n- and at least one of the following.

[0041] That is, the general formula of the composite sodium ion cathode material is Na x MO2-αNa a Fe b V c M d (PO4) e (P2O7) f (SO4) g N h . Wherein, α is the percentage of the mass of the polyanion material in the total mass of the composite sodium ion cathode material.

[0042] Among them, the voltage window of the polyanion cathode material matches that of the layered oxygen cathode.

[0043] Among them, Fe is mainly an active element with a +2 valence state, and the valence state changes of Fe+3 / Fe+2 and / or V+4 / V+3 occur during charge and discharge to provide reversible capacity.

[0044] Among them, iron-based polyanions and phosphate-based polyanions often have relatively low voltage platforms and are suitable for low-voltage cathode materials in the O3 phase of layered oxygen; among them, vanadium-based polyanions and sulfate-based polyanions have relatively high voltage platforms and are suitable for high-voltage O3-phase and P2-phase cathode materials in layered oxygen.

[0045] Specific B z O y n- includes BO3 3- 、B2O4 4- 、BO4 5- 、B4O7 2- 、B5O 10 5-And other uncertain anion groups, which are not limited in the present invention.

[0046] It can be understood that Na x MO2 and Na a Fe b V c A d (PO4) e (P2O7) f (SO4) g G h The overall satisfies the valence balance.

[0047] The composite sodium ion cathode material provided by the present invention can effectively slow down the particle breakage and cathode brittle fracture caused by excessive extrusion of layered oxide particles during the roller pressing process of the cathode, and at the same time is beneficial to suppressing the particle cracking phenomenon caused by interlayer slip after long-term cycling.

[0048] The present invention improves the cycling performance by slowing down the particle cracking phenomenon, and at the same time improves the overall energy density of the battery cell by increasing the compaction density. Among them, cycling and energy density are two key indicators of battery cell products.

[0049] In some specific embodiments, when the layered oxide cathode material is an O3-phase layered oxide cathode material, the O3-phase layered oxide cathode material has a specific capacity of 130-150 mAh / g (such as 132 mAh / g, 135 mAh / g, 137 mAh / g, 140 mAh / g, 142 mAh / g, 145 mAh / g) between 2.0 and 4.0 V. At this time, the polyanion material must contain at least one of PO4 3- and SO4 2- in it.

[0050] In some specific embodiments, when the layered oxide cathode material is a P2-phase layered oxide cathode material, the P2-phase layered oxide cathode material has a specific capacity of 80-120 mAh / g (such as 85 mAh / g, 90 mAh / g, 95 mAh / g, 100 mAh / g, 105 mAh / g, 110 mAh / g, 115 mAh / g) between 2.5 and 4.2 V. At this time, the polyanion material must contain at least one of V 3+ and SO4 2- in it.

[0051] The above matching principle is based on a better match of the voltage range brought by the redox potential, that is, 2.0-4.0 V can well match the O3 phase and the polyanion cathode material containing PO4 3- and P2O7 4- and the polyanion cathode material containing V, 2.5-4.2 V can well match the P2 phase and3+ and SO4 2- and the polyanionic cathode material of the high potential type. Based on the matching of the charge-discharge voltage window, the electrochemical compatibility of the two materials will be better. The charge and discharge within the same or similar voltage range can play a synergistic role at the electrochemical level.

[0052] In some specific embodiments, the layered oxide cathode material is a dense, large-particle-size layered oxide cathode material. Specifically, the median particle size D50 of the layered oxide cathode material satisfies 3 μm < D50 < 12 μm, including but not limited to any point value among 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or the range value between any two of them. The tapped density TD of the layered oxide cathode material satisfies 1.5 g / cm 3 <TD<2.5 g / cm 3 , including but not limited to 1.6 g / cm 3 、1.8 g / cm 3 、2 g / cm 3 、2.2 g / cm 3 、2.3 g / cm 3 among any point value among them or the range value between any two of them.

[0053] In some specific embodiments, the polyanionic material is a nano-sized polyanionic material, that is, a loose, small-particle-size polyanionic material. Among them, the median particle size D50 of the polyanionic material satisfies D50 < 1 μm, including but not limited to any point value among 0.9 μm, 0.8 μm, 0.7 μm, 0.6 μm, 0.5 μm, 0.4 μm, 0.3 μm, 0.2 μm, 0.1 μm or the range value between any two of them; the tapped density TD of the polyanionic material satisfies 0.3 g / cm 3 <TD<1.5 g / cm 3 , including but not limited to 0.4 g / cm 3 、0.5 g / cm 3 、0.6 g / cm 3 、0.7 g / cm 3 、0.8 g / cm 3 、0.9 g / cm 3 、1.0 g / cm 3 、1.2 g / cm 3 、1.4 g / cm 3 、1.5 g / cm 3The point value of any one of them or the range value between any two of them. Among them, nanosizing can be achieved by crushing and grinding, and crushing and grinding are preferably carried out in an inert atmosphere, such as a nitrogen atmosphere. The polyanion material used in the present invention is a nanosized material, which has a low tap density.

[0054] Since the nanosized polyanion material has excellent ionic conductivity performance, it is dispersed on the surface and in the surrounding voids of the layered oxide particles, which can effectively improve the overall ionic conductivity performance of the electrode sheet, reduce phenomena such as cell swelling and cycling degradation caused by interfacial side reactions, and is beneficial to achieving the long cycling performance of the battery.

[0055] In some specific embodiments, the polyanion material further includes a conductive carbon material, such as conductive carbon black, but is not limited thereto.

[0056] When the polyanion material contains a conductive carbon material, the general formula of the polyanion material is Na a Fe b V c A d (PO4) e (P2O7) f (SO4) g G h @C.

[0057] In some specific embodiments, α is 5% to 30%, including but not limited to the point value of any one of 8%, 10%, 13%, 15%, 18%, 20%, 22%, 25%, 27% or the range value between any two of them. This is beneficial to further improving the cycling performance of the battery.

[0058] In a second aspect, the present invention provides a method for preparing the composite sodium ion cathode material, including the following steps: Mix Na x MO2 and Na a Fe b V c M d (PO4) e (P2O7) f (SO4) g N h and bake, perform coating and filling, and obtain the composite sodium ion cathode material after cooling. It can be understood that Na x MO2 is a dense, large-particle-size layered oxide cathode material. Na a Fe b V c A d (PO4) e (P2O7) f (SO4) g G hIt is a loose and small-particle-size polyanion material. After the two are mixed, a coating and filling effect is formed.

[0059] The preparation method of the composite sodium-ion cathode material provided by the present invention has a simple process, a short process flow, and is suitable for batch production. Moreover, the composite sodium-ion cathode material prepared by this method has excellent cycle performance and high energy density.

[0060] In some specific embodiments, the baking temperature is 100-300°C, including but not limited to any point value among 120°C, 150°C, 180°C, 200°C, 230°C, 250°C, 270°C or the range value between any two of them; the heat preservation time is 1-10h, including but not limited to any point value among 2h, 3h, 4h, 5h, 6h, 8h or the range value between any two of them. This temperature and time can make the small-particle-size polyanion material adsorb and adhere to the surface of the layered oxide cathode material.

[0061] In some specific embodiments, the baking atmosphere includes a nitrogen atmosphere or an air atmosphere.

[0062] In the third aspect, the present invention provides a positive electrode sheet including the composite sodium-ion cathode material.

[0063] The positive electrode sheet provided by the present invention is not easy to break during the rolling process, and is not easy to have the phenomenon of brittle fracture of the electrode sheet. The positive electrode sheet has excellent cycle performance and high energy density.

[0064] In some specific embodiments, the electrode compaction density of the positive electrode sheet is 3.1-3.5 g / cm 3 , such as 3.2 g / cm 3 , 3.3 g / cm 3 or 3.4 g / cm 3 . The high compaction density can effectively improve the problem of low energy density of single-layered oxides or polyanions.

[0065] In the fourth aspect, the present invention provides a sodium-ion battery including the positive electrode sheet.

[0066] The sodium-ion battery provided by the present invention has the advantages of good cycle performance, good safety performance, high energy density, etc., and can be widely applied to various fields, such as the transportation field, the electronic product field, the aerospace field, the medical field, and the energy storage field, etc. The present invention does not limit this.

[0067] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those conditions not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchases.

[0068] Example 1

[0069] The general formula provided in this example is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The preparation method of the composite sodium-ion cathode material of O2-5%Na4Fe3(PO4)2P2O7@C includes the following steps:

[0070] (1) Preparation of O3-phase layered oxide cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2: According to the proportion of the target chemical formula, the nickel-iron-manganese hydroxide precursor Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 is fully mixed with the corresponding amount of sodium carbonate, and then sintered in an air atmosphere at 980 °C for 15 h, cooled and pulverized to obtain the target O3-phase layered oxide cathode material. As Figure 1 shown is the SEM image of the O3-phase layered oxide cathode material prepared in Example 1.

[0071] (2) Preparation of polyanion material Na4Fe3(PO4)2P2O7@C: Na2CO3, Na2HPO4, FePO4 and glucose (as the carbon source of the conductive carbon material) are fully dissolved in pure water according to a molar ratio of 1:1:3:0.5, and then obtained as a powdery intermediate product through sand grinding and spray drying. The intermediate product is calcined in a nitrogen atmosphere at 600 °C for 12 h, and then the calcined product is pulverized and ground under the protection of a nitrogen atmosphere to obtain the target polyanion material. As Figure 2 shown is the SEM image of the polyanion material prepared in Example 1.

[0072] (3) After the above O3-phase layered oxide cathode material and polyanion material are fully mixed according to a mass ratio of 0.95:0.05, they are baked in a nitrogen atmosphere at 150 °C for 5 h, and the target composite sodium-ion cathode material is obtained after cooling. Among them, the polyanion material is coated on the surface of the O3-phase layered oxide cathode material, and the polyanion material is filled between the O3-phase layered oxide cathode material particles and the O3-phase layered oxide cathode material particles.

[0073] Example 2

[0074] The general formula provided in this embodiment is NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 The preparation method of the composite sodium-ion cathode material of O2-8% Na2Fe(PO4)2F includes the following steps:

[0075] (1) Preparation of the O3-phase layered oxide cathode material NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2: According to the proportion of the target chemical formula, the carbonate precursor Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 CO3 is fully mixed with the corresponding amount of sodium carbonate, then sintered in an air atmosphere at 980 °C for 15 h, cooled and pulverized to obtain the target O3-phase layered oxide cathode material.

[0076] (2) Preparation of the polyanion material Na2Fe(PO4)2F: NaF, NaH2PO4 and FePO4 are fully dissolved in pure water according to a molar ratio of 1:1:1, then obtained as a powdery intermediate product through sand grinding and spray drying. The intermediate product is calcined in a nitrogen atmosphere at 500 °C for 5 h, and then the calcined product is pulverized and ground under the protection of a nitrogen atmosphere to obtain the target polyanion material.

[0077] (3) After the above O3-phase layered oxide cathode material and polyanion material are fully mixed according to a mass ratio of 0.92:0.08, they are baked in a nitrogen atmosphere at 200 °C for 2 h, and the target composite sodium-ion cathode material is obtained after cooling.

[0078] Example 3

[0079] The general formula provided in this embodiment is NaCu 0.1 Ni 0.4 Mn 0.3 Ti 0.2 The preparation method of the composite sodium-ion cathode material of O2-10% Na4Fe3(PO4)2P2O7@C includes the following steps:

[0080] (1) O3-phase layered oxide cathode material NaCu 0.1 Ni 0.4 Mn 0.3 Ti 0.2Preparation of O2: According to the proportion of the target chemical formula, copper oxide, nickel hydroxide, manganese tetroxide, titanium dioxide and sodium carbonate are fully mixed, and then sintered in an air atmosphere at 950 °C for 15 h, cooled and pulverized to obtain the target O3-phase layered oxide cathode material.

[0081] (2) Preparation of the polyanion material Na4Fe3(PO4)2P2O7@C: Fe3(PO4)2P2O7 precursor and the corresponding amount of sodium carbonate are fully mixed according to a molar ratio of 2:1, and then calcined in a nitrogen atmosphere at 700 °C for 10 h. After that, the calcined product is pulverized and ground under the protection of a nitrogen atmosphere, and 3% by mass of conductive carbon black (conductive carbon material) based on the mass of Na4Fe3(PO4)2P2O7 is added during the pulverization and grinding process to obtain the target polyanion material.

[0082] (3) The above-mentioned O3-phase layered oxide cathode material and polyanion material are fully mixed according to a mass ratio of 0.90:0.10, and then baked in a nitrogen atmosphere at 120 °C for 10 h, and cooled to obtain the target composite sodium-ion cathode material.

[0083] Example 4

[0084] The composite sodium-ion cathode material with the general formula Na 0.93 Zn 0.05 Ni 0.25 Fe 0.33 Mn 0.37 O2 - 15% Na3Fe2(SO4) 3.5 @C provided in this example has a preparation method including the following steps:

[0085] (1) Preparation of the O3-phase layered oxide cathode material Na 0.93 Zn 0.05 Ni 0.25 Fe 0.33 Mn 0.37 O2: According to the proportion of the target chemical formula, zinc oxide, nickel hydroxide, manganese tetroxide, titanium dioxide and sodium carbonate are fully mixed, and then sintered in an air atmosphere at 950 °C for 15 h, cooled and pulverized to obtain the target O3-phase layered oxide cathode material.

[0086] (2) Preparation of the polyanion material Na3Fe2(SO4) 3.5 @C: Na2SO4 and FeSO4 are fully mixed according to a molar ratio of 3:4, and then calcined in a nitrogen atmosphere at 380 °C for 15 h. After that, the calcined product is pulverized and ground under the protection of a nitrogen atmosphere, and 3% by mass of conductive carbon black based on the mass of Na3Fe2(SO4) 3.5 is added to obtain the target polyanion material.

[0087] (3) The above-mentioned O3 phase layered oxide positive electrode material and the polyanion material are fully mixed in a mass ratio of 0.85:0.15, baked at 250° C. in a nitrogen atmosphere for 10 h, and cooled to obtain the target composite sodium ion positive electrode material.

[0088] Example 5

[0089] The general formula provided in this embodiment is Na 2 / 3 Cu 1 / 3 Mn 2 / 3 O2-20%Na3Fe2(SO4) 3.5 The preparation method of the composite sodium ion positive electrode material of @C comprises the following steps:

[0090] (1) P2-phase layered oxide cathode material Na 2 / 3 Cu 1 / 3 Mn 2 / 3 Preparation of O2: Copper oxide, manganese tetraoxide and sodium carbonate were fully mixed according to the target chemical formula ratio, then sintered in an air atmosphere at 850°C for 15 hours, and crushed after cooling to obtain the target P2 phase layered oxide positive electrode material.

[0091] (2) Polyanion material Na3Fe2(SO4) 3.5 Preparation of @C: Na2SO4 and FeSO4 were fully mixed in a molar ratio of 3:4, and then calcined at 380°C in a nitrogen atmosphere for 15 hours. The calcined product was then crushed and ground under the protection of a nitrogen atmosphere, and Na3Fe2(SO4) was added during the crushing and grinding process. 3.5 The conductive carbon black is 3% by mass to obtain the target polyanion material.

[0092] (3) The P2 phase layered oxide positive electrode material and the polyanion material are fully mixed in a mass ratio of 0.80:0.20, baked at 250° C. in a nitrogen atmosphere for 10 h, and cooled to obtain the target composite sodium ion positive electrode material.

[0093] Example 6

[0094] The general formula provided in this embodiment is Na 0.7 Mg 0.15 Ni 0.2 Mn 0.5 Ti 0.15 The preparation method of the composite sodium ion positive electrode material of O2-25%Na3V2(PO4)3@C comprises the following steps:

[0095] (1) P2-phase layered oxide cathode material Na 0.7 Mg 0.15 Ni0.2 Mn 0.5 Ti 0.15 Preparation of O₂: Magnesium oxide, nickel hydroxide, manganese tetroxide, titanium dioxide and sodium carbonate were fully mixed according to the proportion of the target chemical formula, and then sintered in an air atmosphere at 900 °C for 15 h, cooled and pulverized to obtain the target P2-phase layered oxide cathode material.

[0096] (2) Preparation of polyanion material Na₃V₂(PO₄)₃@C: NaH₂PO₃ and V₂O₅ were fully mixed in a molar ratio of 3:1, and then calcined in a nitrogen atmosphere at 500 °C for 5 h. After that, the calcined product was pulverized and ground under the protection of a nitrogen atmosphere, and 3% conductive carbon black by mass of Na₃V₂(PO₄)₃ was added during the pulverization and grinding process to obtain the target polyanion material.

[0097] (3) The above-mentioned P2-phase layered oxide cathode material and polyanion material were fully mixed in a mass ratio of 0.75:0.25, and then baked in a nitrogen atmosphere at 150 °C for 2 h, and cooled to obtain the target composite sodium-ion cathode material.

[0098] Example 7

[0099] The composite sodium-ion cathode material of the general formula Na 0.7 Cu 0.10 Ni 0.25 Mn 0.5 Ti 0.15 O₂ - 30% Na₃V₂(PO₄)₂FO₂@C is prepared by the following steps:

[0100] (1) Preparation of P2-phase layered oxide cathode material Na 0.7 Cu 0.10 Ni 0.25 Mn 0.5 Ti 0.15 O₂: Copper oxide, nickel hydroxide, manganese tetroxide, titanium dioxide and sodium carbonate were fully mixed according to the proportion of the target chemical formula, and then sintered in an air atmosphere at 900 °C for 15 h, cooled and pulverized to obtain the target P2-phase layered oxide cathode material.

[0101] (2) Preparation of polyanion material Na₃V₂(PO₄)₂FO₂@C: NaH₂PO₃, V₂O₅ and NaF were fully mixed in a molar ratio of 2:1:1, and then calcined in a nitrogen atmosphere at 500 °C for 5 h. After that, the calcined product was pulverized and ground under the protection of a nitrogen atmosphere, and 3% conductive carbon black by mass of Na₃V₂(PO₄)₂FO₂ was added during the pulverization and grinding process to obtain the target polyanion material.

[0102] (3) After thoroughly mixing the above P2-phase layered oxide cathode material and polyanion material in a mass ratio of 0.70:0.30, bake them in a nitrogen atmosphere at 150 °C for 2 h, and obtain the target composite sodium-ion cathode material after cooling.

[0103] Example 8

[0104] The composite sodium-ion cathode material provided in this example with the general formula Na 0.9 Cu 0.05 Ca 0.02 Ba 0.01 Sr 0.01 Li 0.01 Al 0.01 Ni 0.35 Mn 0.44 Ti 0.08 Zr 0.02 O2 - 30% Na4Fe3(PO4)2(P2O4) 0.9 (SiO4) 0.1 @C includes the following steps:

[0105] (1) Preparation of O3-phase layered oxide cathode material Na 0.9 Cu 0.05 Ca 0.02 Ba 0.01 Sr 0.01 Li 0.01 Al 0.01 Ni 0.35 Mn 0.44 Ti 0.08 Zr 0.02 O2: According to the target chemical formula ratio, fully mix copper oxide, nickel hydroxide, manganese tetroxide, titanium dioxide with calcium oxide, strontium carbonate, barium carbonate, lithium carbonate, aluminum hydroxide, zirconium oxide, and sodium carbonate, then sinter in an air atmosphere at 900 °C for 15 h, and obtain the target O3-phase layered oxide cathode material after cooling and pulverizing.

[0106] (2) Preparation of polyanion material Na4Fe3(PO4)2(P2O4) 0.9 (SiO4) 0.1 @C: Dissolve Na2CO3, Na2SiO4, Na2HPO4, FePO4, and glucose in pure water in a molar ratio of 0.9:0.1:1:3:0.5, then obtain a powdery intermediate product through sand grinding and spray drying. Calcinate the intermediate product in a nitrogen atmosphere at 600 °C for 12 h, and then pulverize and grind the calcined product under nitrogen atmosphere protection to obtain the target polyanion material.

[0107] (3) After the above O3-phase layered oxide cathode material and polyanion material are fully mixed in a mass ratio of 0.90:0.10, they are baked in a nitrogen atmosphere at 150 °C for 2 h, and the target composite sodium-ion cathode material is obtained after cooling.

[0108] The α in the general formula of the composite sodium-ion cathode material prepared in each example, the median particle size D50, the tapped density TD, and the specific capacity results of the layered oxide cathode material and polyanion material prepared in each example are shown in Table 1 below.

[0109] Among them: The particle size D50 test method is as follows: Use a HITACHI (S 4800) scanning electron microscope for testing, with an acceleration voltage of 10 kV, general morphology shooting, perform particle size statistics in the plane of the obtained SEM image, and at least count the sizes of 100 particles, and calculate the average value to obtain the D50 value (unit: μm).

[0110] The measurement method of the tapped density TD is as follows: Weigh 25 g of the layered oxide cathode material and add it to a standard measuring cylinder (volume 50 ml, inner diameter 22 mm), and use a vibrating machine table to vibrate the measuring cylinder. The set parameters of the vibrating machine table are: stroke 3 mm, vibration frequency 100 times / min, time 30 min. Read the volume of the cathode material in the measuring cylinder after vibration, and divide the powder mass by the volume to obtain the tapped density (unit: g / cm 3 )

[0111] The specific capacity test method is as follows:

[0112] Respectively use the layered oxide cathode material and polyanion material prepared in each example as the cathode active material, and make a coin cell in the following way: Mix the cathode active material, SP (Super P, a highly conductive carbon black from TIMCAL), and polyvinylidene fluoride (PVDF, purchased from SOLVAY PVDF5130) colloidal solution (mass fraction 10%, solvent is N-methylpyrrolidone (NMP)) in a mass ratio of 80:10:10 based on dry weight, and add NMP to make a viscous colloidal solution. Coat this colloidal solution on an aluminum foil (thickness 16 μm), and then bake it in a vacuum drying oven at 120 °C for 12 h to obtain the cathode electrode sheet. Then use a sodium metal sheet (Aladdin) as the counter electrode (thickness 300 μm). Use a glass fiber (Waterman) as the separator (thickness 675 μm), and use a NaPF6 solution with a sodium ion concentration of 1 mol / L (the solvent is a mixture of EC and DMC, and the volume ratio of EC to DMC is 1:1) (Alfa) as the electrolyte, and assemble a 2032 coin cell in a glove box under Ar atmosphere protection.

[0113] Then, under the condition of room temperature at 25 °C, the specific capacity of the O3-phase layered oxide cathode materials and the corresponding polyanion materials prepared in Examples 1 to 4 and Example 8 was tested in the voltage range of 2.0 to 4.0 V. Charging was carried out with a small current of 0.1C, and discharging was also carried out with a small current of 0.1C. The specific discharge capacity at 0.1C (unit: mAh / g) was measured. For the P2-phase layered oxide cathode materials and the corresponding polyanion materials prepared in Examples 5 to 7, the specific capacity was tested in the voltage range of 2.5 to 4.2 V. Charging was carried out with a small current of 0.1C, and discharging was also carried out with a small current of 0.1C. The specific discharge capacity at 0.1C (unit: mAh / g) was measured.

[0114] Table 1 Parameter indexes of each example

[0115]

[0116] Comparative Example 1

[0117] The composite sodium-ion cathode material with the general formula NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 - 3%Na4Fe3(PO4)2P2O7@C was prepared in substantially the same manner as in Example 1, except that: in step (3), the mass ratio of the O3-phase layered oxide cathode material to the polyanion material was replaced with 0.97:0.03, that is, α = 3% in this comparative example.

[0118] Comparative Example 2

[0119] The composite sodium-ion cathode material Na 0.7 Cu 0.10 Ni 0.25 Mn 0.5 Ti 0.15 O2 - 32%Na3V2(PO4)2FO2@C was prepared in substantially the same manner as in Example 7, except that: in step (3), the mass ratio of the O3-phase layered oxide cathode material to the polyanion material was replaced with 0.68:0.32, that is, α = 32% in this comparative example.

[0120] Comparative Example 3

[0121] The composite sodium-ion cathode material Na 2 / 3 Cu 1 / 3 Mn 2 / 3 O2 - 20%Na3Fe2(SO4) 3.5 @C was prepared in substantially the same manner as in Example 5, except that: in step (2), by controlling the grinding particle size, the median particle size D50 of the target polyanion material was adjusted to 1.2 μm.

[0122] Experimental Example

[0123] 100 - cycle retention rate test: The composite sodium - ion cathode materials prepared in each example and each comparative example were used as the cathode active materials respectively, and the battery cells were made according to the following method: The anode used commercially available industrial hard carbon (performance: capacity of 300 mAh / g, first - cycle efficiency of 91%); the electrolyte used commercially available high - voltage - resistant sodium - ion battery electrolyte; the NP ratio of the battery cell design was 1.08 (the N / P calculation formula is: N / P = gram capacity of anode active material × anode surface density × anode active material content ratio ÷ (gram capacity of cathode active material × cathode surface density × cathode active material content ratio)); the cathode sheet was added with the cathode active material, conductive carbon, and PVDF in a mass ratio of 95:2.5:2.5, and standardized 26700 cylindrical battery cells were prepared under the condition that all conditions except the cathode sheet were the same. And according to the above method, the battery cells were made using the pure layered oxide cathode material prepared in step (1) of each example as the cathode active material as the control example. Then, the 1C cycle retention rate performance of each battery cell in the corresponding voltage range at room temperature of 25°C for 100 cycles and the improvement value of the cycle retention rate were tested. The results are shown in Table 2. Among them, the improvement value of the cycle retention rate = 100 - cycle retention rate of the battery cell assembled with the composite sodium - ion cathode material - 100 - cycle retention rate of the battery cell assembled with the pure layered oxide cathode material.

[0124] Anode compaction density test: The composite sodium - ion cathode materials prepared in each example and each comparative example, the pure layered oxide cathode material prepared in step (1) of each example, and the pure polyanion material in step (2) were subjected to the anode compaction density test according to the following method: The compaction density test was based on the actual ultimate compaction density of the anode during the whole - battery - cell preparation process. The specific method was to take a small piece of the anode coated during the whole - battery preparation process, and gradually reduce the roll - pressing gap using an anode roll - press until the anode after roll - pressing reached the critical point. The compaction density obtained by converting the thickness and coating amount was used as the anode compaction density of the material. The judgment basis for the critical point was: After the rolled anode was folded in half and pressed along the fold mark, and then folded in half three times repeatedly. When the folded anode was observed under light and it was found that the anode was not transparent through the fold mark, that is, the anode did not crack. When the anode would crack slightly after being over - pressed, and at this time the anode still met the normal winding use requirements of the subsequent battery - cell processing steps, the compaction density measured at this time was determined as the anode compaction density of the material (unit: g / cm 3 )), and the results are shown in Table 2 below. Among them, the improvement value of the anode compaction density = anode compaction density of the composite sodium - ion cathode material - anode compaction density of the pure layered oxide cathode material.

[0125] After 100 cycles of cycling, it was detected whether the composite sodium-ion cathode materials prepared in each example and each comparative example and the pure layered oxide cathode materials prepared in step (1) of each example had particle cracking. The results are shown in Table 2 below.

[0126] Table 2 Test results of electrode compaction density and cycling performance

[0127]

[0128] As can be seen from Table 2, particle cracking occurred in all the pure layered oxide cathode materials after 100 cycles of cycling, while none of the composite sodium-ion cathode materials prepared in each example cracked after 100 cycles of cycling. Among them, the cycling performance test diagrams of the composite sodium-ion cathode material (referred to as composite material) prepared in Example 3 and the corresponding O3-phase layered oxide cathode material (referred to as pure oxide) are as shown in Figure 3 shown. After 100 cycles of cycling of the battery cell assembled with the composite sodium-ion cathode material of Example 3, the SEM image of the composite sodium-ion cathode material particles is as shown in Figure 4 shown. It can be seen that the composite sodium-ion cathode material particles did not crack after cycling. After 100 cycles of cycling of the battery cell assembled with the pure layered oxide cathode material prepared in step (1) of Example 3, the SEM image of the pure layered oxide cathode material particles is as shown in Figure 5 shown. It can be seen that obvious cracking occurred in the pure layered oxide cathode material particles after cycling. It can be seen that the composite sodium-ion cathode material provided by the present invention can effectively alleviate the phenomena of particle breakage and electrode brittle fracture caused by excessive extrusion of layered oxide particles during the electrode rolling process.

[0129] In the present invention, the SEM test was carried out using HITACHI (S 4800). Among them, the pure layered oxide cathode material and the pure polyanion material were directly tested alone, and the powder material was carefully scraped off from the cycled positive electrode sheet in an inert atmosphere glove box for powder testing.

[0130] At the same time, compared with the pure layered oxide cathode material and the pure polyanion material, the electrode compaction density of the composite sodium-ion cathode material is higher. Among them, compared with the pure layered oxide cathode material, the increase value of the electrode compaction density of the composite sodium-ion cathode material in each example is ≥0.05.

[0131] Compared with the pure layered oxide cathode material, the battery cell prepared with the composite sodium-ion cathode material has a higher cycling retention rate. Among them, compared with the pure layered oxide cathode material, the increase value of the cycling retention rate of the composite sodium-ion cathode material in each example is ≥0.4%, even up to 2.1%; while the increase value of the cycling retention rate of Comparative Examples 1 to 3 is below 0.3%.

[0132] It can be seen that the composite sodium-ion cathode material provided by the present invention can effectively improve the cycling performance of sodium-ion batteries. Moreover, the positive electrode sheet prepared from the composite sodium-ion cathode material provided by the present invention has a higher tap density, which can improve the energy density of sodium-ion batteries.

[0133] Although the present invention has been illustrated and described with reference to specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; those of ordinary skill in the art should understand that without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A composite sodium ion positive electrode material, characterized in that: It comprises a layered oxide positive electrode material and a polyanion material, wherein the polyanion material is coated on the surface of the layered oxide positive electrode material and filled between particles of the layered oxide positive electrode material; Wherein, the layered oxide positive electrode material comprises an O3 phase layered oxide positive electrode material and / or a P2 phase oxide positive electrode material, and the general formula of the layered oxide positive electrode material is Na x MO2; wherein 0.6≤x≤1, and M includes at least two of the elements Cu, Ni, Fe, Mn, Zn, Mg, Zr, Ti, Li, Ca, Sr, Y, Ba, Co, Al and Cr; The general formula of the polyanion material is Na a Fe b V c A d (PO4) e (P2O7) f (SO4) g G h ; wherein a is 1 or 2 or 3 or 4, 0≤b, c≤4, b+c<a, 0≤d≤1, 0≤e, f≤4, g≤4, 0≤h≤1, and b and c are not 0 at the same time, and e, f and g are not 0 at the same time; A is a doping modification element at the Fe position or V position, and A includes at least one of Ni, Mn, Co, Ti, Cr, Cu and Zn elements; G includes F - , O 2- 、CO3 2- 、SiO4 4- and B z O y n- At least one of .

2. The composite sodium ion positive electrode material according to claim 1, characterized in that: When the layered oxide positive electrode material is an O3 phase layered oxide positive electrode material, the O3 phase layered oxide positive electrode material has a gram capacity of 130 to 150 mAh / g between 2.0 and 4.0 V, and the polyanion material must contain PO4 3- and SO4 2- At least one of .

3. The composite sodium ion positive electrode material according to claim 1, characterized in that: When the layered oxide positive electrode material is a P2 phase layered oxide positive electrode material, the P2 phase layered oxide positive electrode material has a gram capacity of 80 to 120 mAh / g between 2.5 and 4.2 V, and the polyanion material must contain V 3+ and SO4 2- At least one of .

4. The composite sodium ion positive electrode material according to claim 1, characterized in that: At least one of the following conditions is met: (1) The median particle size D50 of the layered oxide positive electrode material satisfies 3 μm<D50<12 μm; (2) The tap density TD of the layered oxide positive electrode material satisfies 1.5 g / cm 3 <TD<2.5g / cm 3 .

5. The composite sodium ion positive electrode material according to claim 1, characterized in that: At least one of the following conditions is met: (1) The median particle size D50 of the polyanion material satisfies D50<1 μm; (2) The tap density TD of the polyanion material satisfies 0.3 g / cm 3 <TD<1.5g / cm 3 ; (3) The polyanion material also includes a conductive carbon material; (4) The percentage α of the mass of the polyanion material to the total mass of the composite sodium ion positive electrode material is 5% to 30%.

6. The method for preparing the composite sodium ion positive electrode material according to any one of claims 1 to 5, characterized in that: The steps include: x MO2 and Na a Fe b V c M d (PO4) e (P2O7) f (SO4) g N h After mixing, baking is performed, and coating and filling are performed to obtain the composite sodium ion positive electrode material.

7. The method for preparing the composite sodium ion positive electrode material according to claim 6, characterized in that: The baking temperature is 100-300° C., and the heat preservation time is 1-10 hours.

8. The method for preparing the composite sodium ion positive electrode material according to claim 6, characterized in that: The baking atmosphere includes a nitrogen atmosphere or an air atmosphere.

9. A positive electrode sheet, characterized in that: Comprising the composite sodium ion positive electrode material according to any one of claims 1 to 5; Preferably, the cathode plate has a compaction density of 3.1 to 3.5 g / cm 3 .

10. A sodium ion battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 9.

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