Low-cost high-voltage-resistant composite positive electrode material and preparation method thereof

Abstract

The invention discloses a low-cost high-voltage-resistant composite positive electrode material and a preparation method thereof, and belongs to the technical field of sodium ion batteries. The chemical formula of the composite positive electrode material is Na < 0.67 > Ni Fe Tic Mn < d > O < 2 > (at) Na < 2 > Fe < 2 > (SO4) < 3 >, wherein a is greater than or equal to 0.1 and less than or equal to 0.2; 0.01 < = b < = 0.1; 0.01 < = c < = 0.1; d = 1-(a + b + c); in the composite material, the mass ratio of Na < 0.67 > Ni Fe T < c > Mn < d > O < 2 > to Na < 2 > Fe < 2 > (SO4) < 3 > is (1-5): 1. According to the invention, a sulfate polyanion material is introduced into a P-phase layered oxide material, the redox couple voltage of transition metal can be enhanced through an induction effect by using an anion group, and the polyhedral structure can provide good frame stability, so that the cycle life and the safety of the battery under high voltage are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a low-cost high-voltage-resistant composite cathode material and a preparation method thereof. Background Art

[0002] With the maturity of the research and industrial chain construction of lithium-ion batteries, the demand for lithium resources has also been increasing year by year. However, due to the low reserves of lithium resources in the earth's crust, it cannot meet the growing demand for lithium resources in contemporary society, resulting in high lithium prices. Therefore, it is necessary to accelerate the search for a new type of battery material as a substitute for lithium batteries. Sodium-ion batteries have received extensive attention due to their rich raw materials and low prices. And with the increasing maturity of sodium-ion battery technology, they show great application prospects in large-scale energy storage, small static energy storage power stations such as 5G base stations, and low-speed electric vehicles. However, sodium-ion batteries still have deficiencies in performance, including problems such as phase change, structural degradation, and voltage platform. Therefore, developing cathode materials with better performance plays a crucial role in the capacity and energy density of sodium-ion batteries.

[0003] Layered metal oxide cathode materials have received extensive attention due to their high theoretical capacity and easy synthesis. In particular, P-phase layered metal oxide cathode materials have been intensively studied for their high voltage platform and excellent cycling performance. However, they contain expensive metal elements such as nickel and manganese, resulting in high material prices at present stage, which restricts the development and large-scale application of the materials. On the other hand, alkaline substances are likely to remain in the preparation process of P-phase materials, which will affect the battery manufacturing process. Sulfate-based polyanion cathode material Na x Fe y (SO 4 ) z With its advantages in electronegativity, working voltage, and cost, it is also considered to be one of the key development directions of sodium battery materials in the future. However, the sulfate-based polyanion cathode material has poor conductivity and is very sensitive to moisture, and is prone to hydrolysis and dissociation. Its poor ionic conductivity and air stability restrict the application of the material.

[0004] Combining the above two mainstream cathode materials for sodium-ion batteries is a method that takes into account both performance and cost advantages. However, the P-phase layered oxide belongs to a single-phase layered oxide, while the sulfate-based polyanion material is composed of tetrahedral or octahedral anion units, and its crystal lattice structure is complex and variable. This structural difference may make it difficult to form a stable interface when the two are combined. On the other hand, the sulfate-based polyanion material usually has high chemical activity and is prone to react with the P-phase layered metal oxide, resulting in a decrease in the structural stability of the material. In addition, the P-phase layered oxide has a relatively low capacity (between 0.67 and 0.8), while the sulfate-based polyanion material has a relatively high capacity (up to 1.0). This difference in capacity may make it difficult to achieve the optimal matching of electrochemical performance when the two are combined, thus affecting the overall performance of the battery. Therefore, means such as reasonable material design, interface engineering, and process optimization are required to achieve the effective combination of the two and the improvement of performance. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a low-cost high-voltage-resistant composite cathode material;

[0006] Another objective of the present invention is to provide a preparation method for a low-cost high-voltage-resistant composite cathode material to solve the problems of poor interface stability and poor chemical stability during the composite process of the P-phase layered oxide material and the sulfate-based polyanion material in the background technology.

[0007] The objectives of the present invention can be achieved through the following technical solutions:

[0008] In the first aspect, the present invention provides a low-cost high-voltage-resistant composite cathode material, and the chemical formula of the composite cathode material is: Na 0.67 Ni a Fe b Ti c Mn d O 2 @Na 2 Fe 2 (SO 4 ) 3 , where 0.1 ≤ a ≤ 0.2; 0.01 ≤ b ≤ 0.1; 0.01 ≤ c ≤ 0.1; d = 1 - (a + b + c);

[0009] In the composite material, Na 0.67 Ni a Fe b Ti c Mn d O 2 and Na 2 Fe 2 (SO 4 ) 3The mass ratio is 1-5:1.

[0010] In a second aspect, the present invention provides a method for preparing a low-cost high-voltage-resistant composite cathode material, comprising the following steps:

[0011] Step 1. Mix nickel oxide, iron oxide, titanium dioxide, manganese tetroxide and sodium carbonate evenly and then sinter them. After pulverizing and sieving, a P-phase cathode material is obtained, with the chemical formula: Na 0.67 Ni a Fe b Ti c Mn d O 2 , where 0.1 ≤ a ≤ 0.2, 0.01 ≤ b ≤ 0.1, 0.01 ≤ c ≤ 0.1, and d = 1-(a + b + c);

[0012] Step 2. Mix the P-phase cathode material, sodium sulfate, ferrous sulfate heptahydrate and water to form a slurry, stir and mix until uniform, and then pulverize after spray drying to obtain the composite cathode material.

[0013] As a further scheme of the present invention, in Step 1, the sintering temperature is 800-1000 °C.

[0014] As a further scheme of the present invention, in Step 1, the sintering time is 10-15 h.

[0015] As a further scheme of the present invention, in Step 1, the sintering atmosphere is air, and the air flow rate is 4-6 m 3 / h.

[0016] As a further scheme of the present invention, in Step 2, the solid content of the slurry is 30%-50%.

[0017] As a further step of the present invention, in Step 2, the solid content of the slurry is 40%.

[0018] As a further scheme of the present invention, in Step 2, the outlet temperature of spray drying is 400-500 °C.

[0019] As a further scheme of the present invention, in Step 2, the stirring speed is 200-400 rpm.

[0020] As a further scheme of the present invention, in Step 2, the stirring time is 10-40 min.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. The present invention provides a low-cost high-voltage resistant composite cathode material. By introducing a sulfate-based polyanion material into the P-phase layered oxide material, the anionic group can enhance the redox potential of transition metals through the inductive effect, and its polyhedral structure can provide good framework stability, thereby improving the cycle life and safety of the battery under high voltage.

[0023] 2. In the preparation method, the present invention first prepares the P-phase layered oxide by high-temperature solid-phase reaction. After mixing it with sodium sulfate and ferrous sulfate to form a slurry with a certain proportion, spray drying is carried out to convert the mixed slurry into powder in a very short time, improving the composite rate of the sulfate-based polyanion material to the P-phase layered oxide. In addition, sodium iron sulfate formed by spray drying is connected by strong covalent bonds to form a three-dimensional network structure with excellent stability. Sulfurous acid can further react with the surface residual alkali of the P-phase layered oxide to form an electrolyte layer similar to a sodium ion channel, inlaying and connecting sodium iron sulfate and the P-phase layered oxide, not only reducing the surface residual alkali of the material, but also inhibiting the reaction of the P-phase layered oxide with air, reducing the gas generated by the layered oxide during charge and discharge, thereby effectively improving the interfacial stability between the two, and further improving the cycle stability of the composite material.

[0024] 3. By preparing the P-phase layered oxide cathode material by the solid-phase method and mixing it with sodium sulfate and ferrous sulfate to prepare the composite material by the spray drying method, the disadvantages of single P-phase material and sodium iron sulfate cathode material can be effectively solved. This method can not only improve the energy density and cycle performance of the battery, but also reduce the sensitivity to moisture, broaden the application scenarios of the battery, and the preparation cost is low. In the future, with the further optimization of the preparation process and the reduction of cost, this composite material is expected to be widely used in the field of sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] Figure 1 is the SEM image of the Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite cathode material prepared in Example 2 of the present invention;

[0027] Figure 2 is the Na 0.67 Ni 0.2 Fe 0.05T i 0.05 Mn 0.7 O 2 SEM image of the positive electrode material;

[0028] Figure 3 is the Na prepared in Example 4 of the present invention 0.67 N i 0.2 Fe 0.08 T i 0.07 Mn 0.65 O 2 @Na 2 Fe 2 (SO 4 ) 3 Charge-discharge curve of the composite positive electrode material. Detailed implementation manners

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Example 1

[0031] A low-cost high-voltage-resistant composite positive electrode material, the chemical formula of which is: Na 0.67 N i 0.2 Fe 0.05 T i 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 , the preparation method of the composite positive electrode material includes the following steps:

[0032] Step 1. Mix 290 g of nickel oxide (N iO, 3.883 mo l), 80 g of iron oxide (Fe 2 O 3 , 0.5 mo l), 83 g of titanium dioxide (T i O 2 , 1.045 mo l), 1035 g of manganese tetraoxide (Mn 3 O 4 , 4.54 mo l) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) at a high speed of 800 rpm for 1 h. After mixing evenly, load it into a crucible and put it into an atmosphere furnace for sintering. The sintering temperature is 900 °C, the sintering time is 15 h, the sintering atmosphere is air, and the air flow rate is 5 m3 / h, and after sintering, it is naturally cooled to room temperature (25 - 30 °C), and then pulverized and sieved to obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 positive electrode material;

[0033] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 positive electrode material, 257 g of sodium sulfate (Na 2 SO 4 , 1.809 mol), 1241 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 4.464 mol), add 3750 g of deionized water, and prepare a slurry with a solid content of 40%. Stir at a speed of 300 rpm for 20 min until evenly mixed, then perform spray drying. The outlet temperature is 450 °C, collect the dried powder, pulverize it to obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite positive electrode material.

[0034] Example 2

[0035] A low-cost high-voltage-resistant composite positive electrode material, with the chemical formula: Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 , and the preparation method of the composite positive electrode material includes the following steps:

[0036] Step 1. Put 290 g of nickel oxide (NiO, 3.883 mol), 80 g of iron oxide (Fe 2 O 3 , 0.5 mol), 83 g of titanium dioxide (TiO 2, 1.045 mol), 1035 g of manganese tetraoxide (Mn 3 O 4 , 4.54 mol) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) were mixed at a high speed of 800 rpm for 1 h. After mixing evenly, they were loaded into a sagger and put into an atmosphere furnace for sintering. The sintering temperature was 900 °C, the sintering time was 15 h, the sintering atmosphere was air, and the air flow rate was 5 m 3 / h. After sintering, it was naturally cooled to room temperature and then pulverized and sieved to obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material;

[0037] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material, 127 g of sodium sulfate (Na 2 SO 4 , 0.894 mol), 623 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 2.241 mol), add 2620 g of deionized water, and prepare a slurry with a solid content of 40%. Stir it at a speed of 300 rpm for 20 min until it is evenly mixed, then carry out spray drying. The outlet temperature is 450 °C, collect the dried powder, and pulverize it to obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite cathode material.

[0038] Example 3

[0039] A low-cost high-voltage-resistant composite cathode material, with the chemical formula: Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO4 ) 3 , the preparation method of the composite cathode material includes the following steps:

[0040] Step 1. Mix 290 g of nickel oxide (NiO, 3.883 mol), 80 g of iron oxide (Fe 2 O 3 , 0.5 mol), 83 g of titanium dioxide (TiO 2 , 1.045 mol), 1035 g of manganese tetroxide (Mn 3 O 4 , 4.54 mol) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) at a high speed of 800 rpm for 1 h. After mixing evenly, load them into a crucible and put them into an atmosphere furnace for sintering. The sintering temperature is 900 °C, the sintering time is 15 h, the sintering atmosphere is air, and the air flow rate is 5 m 3 / h. After sintering, cool it naturally to room temperature, and obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material;

[0041] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material, 64 g of sodium sulfate (Na 2 SO 4 , 0.45 mol), 263 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 0.946 mol), add 1993 g of deionized water, and prepare a slurry with a solid content of 40%. Stir it at a speed of 300 rpm for 20 min until it is evenly mixed, and then perform spray drying. The outlet temperature is 450 °C. Collect the dried powder, and obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite cathode material.

[0042] Example 4

[0043] A low-cost high-voltage-resistant composite cathode material with the chemical formula: Na 0.67 Ni 0.2 Fe 0.08 Ti 0.07 Mn 0.65 O 2 @Na 2 Fe 2 (SO 4 ) 3 , and a preparation method of the composite cathode material, comprising the following steps:

[0044] Step 1. Mix 290 g of nickel oxide (NiO, 3.883 mol), 125 g of iron oxide (Fe 2 O 3 , 0.783 mol), 121 g of titanium dioxide (TiO 2 , 1.515 mol), 973 g of manganese tetraoxide (Mn 3 O 4 , 4.25 mol) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) at a high speed of 800 rpm for 1 h. After mixing evenly, load them into a crucible, put them into an atmosphere furnace for sintering. The sintering temperature is 900 °C, the sintering time is 15 h, the sintering atmosphere is air, and the air flow rate is 5 m 3 / h. After sintering, cool naturally to room temperature, and obtain Na 0.67 Ni 0.2 Fe 0.08 Ti 0.07 Mn 0.65 O 2 cathode material after pulverizing and sieving;

[0045] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.08 Ti 0.07 Mn 0.65 O 2 cathode material, 64 g of sodium sulfate (Na 2 SO 4 , 0.45 mol), 263 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 0.946 mol), add 1993 g of deionized water, prepare a slurry with a solid content of 40%, stir at a speed of 300 rpm for 20 min until evenly mixed, carry out spray drying, the outlet temperature is 450 °C, collect the dried powder, and obtain Na 0.67 Ni0.2 Fe 0.08 Ti 0.07 Mn 0.65 O 2 @Na 2 Fe 2 (SO 4 ) 3 Composite cathode material.

[0046] Example 5

[0047] A low-cost high-voltage-resistant composite cathode material, with the chemical formula: Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 , The preparation method of the composite cathode material includes the following steps:

[0048] Step 1. Mix 290 g of nickel oxide (NiO, 3.883 mol), 80 g of iron oxide (Fe 2 O 3 , 0.5 mol), 83 g of titanium dioxide (TiO 2 , 1.045 mol), 1035 g of manganese tetraoxide (Mn 3 O 4 , 4.54 mol) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) at a high speed of 800 rpm for 1 h. After mixing evenly, load it into a crucible and put it into an atmosphere furnace for sintering. The sintering temperature is 900 °C, the sintering time is 15 h, the sintering atmosphere is air, and the air flow rate is 5 m 3 / h. After sintering, cool it naturally to room temperature, and obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material;

[0049] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material, 127 g of sodium sulfate (Na 2 SO 4, 0.894 mol), 623 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 2.241 mol), add 4084 g of deionized water, and prepare a slurry with a solid content of 30%. Stir at a speed of 300 rpm for 20 min until evenly mixed, then perform spray drying. The outlet temperature is 450 °C. Collect the dried powder, and after pulverization, obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite cathode material.

[0050] Example 6

[0051] A low-cost high-voltage-resistant composite cathode material with the chemical formula: Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 , The preparation method of the composite cathode material includes the following steps:

[0052] Step 1. Mix 290 g of nickel oxide (NiO, 3.883 mol), 80 g of iron oxide (Fe 2 O 3 , 0.5 mol), 83 g of titanium dioxide (TiO 2 , 1.045 mol), 1035 g of manganese tetraoxide (Mn 3 O 4 , 4.54 mol) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) at a high speed of 800 rpm for 1 h. After mixing evenly, load it into a crucible, put it into an atmosphere furnace for sintering. The sintering temperature is 900 °C, the sintering time is 15 h, the sintering atmosphere is air, and the air flow rate is 5 m 3 / h. After sintering, cool it naturally to room temperature, and obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material;

[0053] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 positive electrode material, 127 g of sodium sulfate (Na 2 SO 4 , 0.894 mol), 623 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 2.241 mol), add 1750 g of deionized water, configure into a slurry with a solid content of 50%, stir at a speed of 300 rpm for 20 min until evenly mixed, perform spray drying, the outlet temperature is 450 °C, collect the dried powder, and obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite positive electrode material.

[0054] Comparative Example 1

[0055] A positive electrode material, the chemical formula is: Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 , The preparation method of the positive electrode material includes the following steps:

[0056] Step 1. Put 290 g of nickel oxide (NiO, 3.883 mol), 80 g of iron oxide (Fe 2 O 3 , 0.5 mol), 83 g of titanium dioxide (TiO 2 , 1.045 mol), 1035 g of manganese tetraoxide (Mn 3 O 4 , 4.54 mol) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) into high-speed mixing at a speed of 800 rpm for 1 h. After mixing evenly, load into a crucible, put it into an atmosphere furnace for sintering, the sintering temperature is 900 °C, the sintering time is 15 h, the sintering atmosphere is air, and the air flow rate is 5 m 3 / h, After sintering, it is naturally cooled to room temperature, and after pulverization and sieving, Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 positive electrode material.

[0057] Comparative Example 2

[0058] A positive electrode material, the chemical formula is: Na 2 Fe 2 (SO 4 ) 3 , The preparation method of the positive electrode material includes the following steps:

[0059] Weigh 127 g of sodium sulfate (Na 2 SO 4 , 0.894 mol), 623 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 2.241 mol), add 1125 g of deionized water, configure it into a slurry with a solid content of 40%, stir for 20 min at a speed of 300 rpm until it is evenly mixed, carry out spray drying, the outlet temperature is 450 °C, collect the dried powder, and after pulverization, obtain Na 2 Fe 2 (SO 4 ) 3 positive electrode material.

[0060] Comparative Example 3

[0061] A composite positive electrode material, the chemical formula is: Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 , The preparation method of the composite positive electrode material includes the following steps:

[0062] Step 1. Put 290 g of nickel oxide (NiO, 3.883 mol), 80 g of iron oxide (Fe 2 O 3 , 0.5 mol), 83 g of titanium dioxide (TiO 2 , 1.045 mol), 1035 g of manganese tetraoxide (Mn 3 O 4 , 4.54 mol) and 681 g of sodium carbonate (Na 2CO 3 , 6.42 mol) was mixed at a high speed of 800 rpm for 1 h. After mixing evenly, it was loaded into a sagger and sintered in an atmosphere furnace. The sintering temperature was 900 °C, the sintering time was 15 h, the sintering atmosphere was air, and the air flow rate was 5 m 3 / h. After sintering, it was naturally cooled to room temperature and obtained Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material;

[0063] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material, 127 g of sodium sulfate (Na 2 SO 4 , 0.894 mol), 623 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 2.241 mol), add 7000 g of deionized water, and prepare a slurry with a solid content of 20%. Stir at a speed of 300 rpm for 20 min until evenly mixed, and perform spray drying. The outlet temperature is 450 °C. Collect the dried powder and obtain Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite cathode material.

[0064] Comparative Example 4

[0065] A low-cost high-voltage-resistant composite cathode material, with the chemical formula: Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 , The preparation method of the composite cathode material includes the following steps:

[0066] Step 1. Mix 290 g of nickel oxide (NiO, 3.883 mol), 80 g of iron oxide (Fe 2 O 3 , 0.5 mol), 83 g of titanium dioxide (TiO 2 , 1.045 mol), 1035 g of manganese tetraoxide (Mn 3 O 4 , 4.54 mol) and 681 g of sodium carbonate (Na 2 CO 3 , 6.42 mol) at a high speed of 800 rpm for 1 h. After mixing evenly, load them into a sagger and put it into an atmosphere furnace for sintering. The sintering temperature is 900 °C, the sintering time is 15 h, the sintering atmosphere is air, and the air flow rate is 5 m 3 / h. After sintering, cool it naturally to room temperature, and obtain the Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material after pulverizing and sieving;

[0067] Step 2. Weigh 1000 g of Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 cathode material, 127 g of sodium sulfate (Na 2 SO 4 , 0.894 mol), 623 g of ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O, 2.241 mol), add 1167 g of deionized water, and prepare a slurry with a solid content of 60%. Stir it at a speed of 300 rpm for 20 min until it is evenly mixed, and then carry out spray drying. The outlet temperature is 450 °C. Collect the dried powder, and obtain the Na 0.67 Ni 0.2 Fe 0.05 Ti 0.05 Mn 0.7 O 2 @Na 2 Fe 2 (SO 4 ) 3 composite cathode material.

[0068] The summary of relevant parameters in Examples 1 - 6 and Comparative Examples 1 - 4 is shown in Table 1.

[0069] Table 1

[0070]

[0071] Performance tests were carried out on the positive electrode materials prepared in Examples 1 - 6 and Comparative Examples 1 - 4:

[0072] (1) Scanning electron microscopy (SEM) tests were carried out on the positive electrode materials. The SEM images of the positive electrode materials prepared in Example 2 are as shown in Figure 1 and the SEM images of the positive electrode materials prepared in Comparative Example 1 are as shown in Figure 2 . By comparing Figure 1 and Figure 2 , it can be seen that sodium iron sulfate forms an effective composite with the P-phase oxide in a loaded form.

[0073] (2) Physical property tests:

[0074] Particle size: Tested using a laser particle size analyzer with reference to the GB / T 19077 standard;

[0075] Tap density: Determined according to the method for determining the tap density of metal powders in accordance with the provisions of GB / T 5162;

[0076] pH: Determined in accordance with the provisions of GB / T9724;

[0077] The results of the physical property tests are shown in Table 2.

[0078] Table 2

[0079] <![CDATA[Particle size D 50 > <![CDATA[Tap density (g / cm 3 )]]> pH Example 1 4.85 1.71 11.26 Example 2 5.31 1.68 11.37 Example 3 4.57 1.51 11.55 Example 4 4.92 1.50 11.61 Example 5 5.13 1.53 11.55 Example 6 4.88 1.52 11.62 Comparative Example 1 5.48 1.85 12.78 Comparative Example 2 2.61 1.05 5.84 Comparative Example 3 4.53 1.42 11.48 Comparative Example 4 4.68 1.48 11.44

[0080] (3) Electrical property tests: A slurry was coated to make a pole piece according to the mass ratio of 90 (positive electrode material prepared in the example or comparative example): 5 (polyvinylidene fluoride PDVF): 5 (conductive carbon black SP). Sodium metal was used as the counter electrode, glass fiber was used as the separator, and a 1 mol / L solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1) of NaPF 6 was used as the electrolyte. A CR2032 coin cell was assembled, and finally the cell was placed in a BlueTEC test system for electrical property tests at a rate of 0.2C between 2.0V and 4.25V.

[0081] The test results of the discharge specific capacity at 0.2C and the capacity retention rate after 100 cycles are shown in Table 3.

[0082] Table 3

[0083] Discharge capacity at 0.2C (mAh / g) Capacity retention rate (%) Example 1 105.7 95.4 Example 2 112.4 98.6 Example 3 107.2 94.9 Example 4 109.1 95.6 Example 5 108.5 95.6 Example 6 110.1 95.1 Comparative Example 1 118.3 92.9 Comparative Example 2 84.2 97.2 Comparative Example 3 102.3 93.4 Comparative Example 4 99.1 93.1

[0084] Among them, the charge-discharge curve of the composite positive electrode material prepared in Example 4 is as shown in Figure 3 .

[0085] As can be seen from the above test results, the composite cathode material is prepared by using the composite P-phase layered oxide material and sodium iron sulfate in the present invention, which can combine the advantages of the two materials. The prepared composite cathode material has good electrochemical performance. During its preparation process, by controlling the solid content of the slurry, the tap density and particle size of the material can be further controlled. After spray drying, a stable three-dimensional network structure interface is formed, the interfacial bonding force between the two is increased, the interfacial stability is improved, and stable cycling is achieved.

[0086] It should be noted that in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0087] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-cost high-voltage resistant composite positive electrode material, characterized in that: The chemical formula of the composite positive electrode material is: Na 0.67 Ni a Fe b Ti c Mn d O2@Na2Fe2(SO4)3, where 0.1≤a≤0.2; 0.01≤b≤0.1; 0.01≤c≤0.1; d=1-(a+b+c); In the composite material, Na 0.67 Ni a Fe b T i c Mn d The mass ratio of O2 to Na2Fe2(SO4)3 is 1-5:

1.

2. A method for preparing a low-cost high-voltage composite positive electrode material as claimed in claim 1, characterized in that: The following steps are involved: Step 1. Nickel oxide, iron oxide, titanium dioxide, manganese tetraoxide and sodium carbonate are uniformly mixed, sintered, crushed and sieved to obtain a P-phase positive electrode material; Step 2. Mix the P-phase positive electrode material, sodium sulfate, ferrous sulfate heptahydrate and water to form a slurry, stir and mix until uniform, and then pulverize by spray drying to obtain a composite positive electrode material.

3. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 2, characterized in that: In the step 1, the sintering temperature is 800-1000°C.

4. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 2, characterized in that: In the step 1, the sintering time is 10-15 hours.

5. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 2, characterized in that: In step 1, the sintering atmosphere is air, and the air flow rate is 4-6m 3 / h.

6. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 2, characterized in that: In step 2, the solid content of the slurry is 30%-50%.

7. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 6, characterized in that: The solid content of the slurry was 40%.

8. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 2, characterized in that: In step 2, the spray drying outlet temperature is 400-500°C.

9. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 2, characterized in that: In step 2, the stirring speed is 200-400 rpm.

10. The method for preparing a low-cost high-voltage resistant composite positive electrode material according to claim 2, characterized in that: In step 2, the stirring time is 10-40 minutes.

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