Positive electrode active material and method for manufacturing the same, positive electrode sheet, battery and power-using device

Abstract

A positive electrode active material and a method for manufacturing the same, a positive electrode sheet, a battery, and a power-using device, wherein the chemical formula of the positive electrode active material is Na x M (1-y) Ca y The material is O2, M contains a transition metal element, x = 0.8 to 1.1, 0.005 ≤ y ≤ 0.015, and 95 wt% or more of Ca elements are distributed within the surface layer of the single crystal particles of the positive electrode active material, with a surface layer thickness of 1 μm. The residual alkali content of the positive electrode active material is low, improving the stability of the positive electrode active material in air, and as a result, the cycle performance when applied to batteries is improved.

Description

Technical Field

[0001] This application relates to the field of new energy technologies, and particularly to a positive electrode active material, a method for manufacturing the same, a positive electrode sheet, a battery, and an electric power usage device.

Background Art

[0002] In recent years, as batteries are widely applied to various consumer products such as mobile phones and electric vehicles, the requirements for the cycle performance of batteries have been increasing. The positive electrode active material is one of the important materials of the battery, and the structural stability of the material affects the cycle performance of the battery.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In view of this, there is a need to provide a positive electrode active material, a method for manufacturing the same, a positive electrode sheet, a battery, and an electric power usage device that can improve the cycle performance of the battery.

Means for Solving the Problems

[0004] This application is realized by the following technical solutions.

[0005] One aspect of this application provides a positive electrode active material, and the chemical formula of the positive electrode active material is Na x M (1-y) Ca y O2, where M contains a transition metal element, x = 0.8 to 1.1, 0.005 ≤ y ≤ 0.015, 95 wt% or more of the Ca element is distributed within the surface layer of the single crystal particles of the positive electrode active material, and the thickness of the surface layer is 1 μm.

[0006] The above-mentioned positive electrode active material contains a specific chemical composition, and in particular, the Ca content y is controlled within the specified range. Furthermore, more than 95 wt% of Ca elements are distributed within a 1 μm thick surface layer of the single-crystal particles of the positive electrode active material. As a result, the Ca elements distributed on the surface of the single-crystal particles form relatively stable calcium carbonate with moisture and carbon dioxide in the air. At the same time, the single-crystal particles are protected from the reaction of moisture and carbon dioxide in the air with the Na elements in the single-crystal particles, thereby blocking the process by which Na constantly precipitates and forms residual alkali. This further reduces the residual alkali content of the positive electrode active material, improves the stability of the positive electrode active material in air, and suppresses the problem of deterioration of cycle performance due to complex phase transitions during the charge-discharge process of the positive electrode active material. Consequently, it improves the cycle performance when applied to batteries.

[0007] In some of these examples, M includes at least one of Fe, Ni, Mn, Co, V, Ti, Cr, Cu, and Zn.

[0008] In some of these embodiments, M includes at least one of Fe, Ni, Mn, Co, Ti, and Zn.

[0009] In some of the embodiments, the positive electrode active material is, (1) The condition that the Dv50 of the single crystal particles in the positive electrode active material is 6 to 11 μm, and (2) The positive electrode active material is an O3 phase layered oxide, and the condition includes at least one of these.

[0010] In some of the embodiments, the positive electrode active material is, (1) Using water as a solvent, the residual alkali CO3 of the positive electrode active material 2- The conditions are that the concentration is <6000 ppm, and (2) Using ethanol as a solvent, the residual alkali OH of the positive electrode active material - The condition includes at least one of the following: <900 ppm.

[0011] Other aspects of the present invention provide a method for manufacturing a positive electrode active material. Chemical formula Na x M (1-y) Ca y The steps include providing a sodium source, a calcium source and an M source according to O2, where M contains a transition metal element, and x = 0.8 to 1.1, 0.005 ≤ y ≤ 0.015, The process includes the steps of mixing the sodium source, the calcium source, and the M source, sintering them in an oxygen-containing atmosphere at 850°C to 1000°C for 8 to 16 hours, and then annealing them at 500°C to 650°C for 7 to 12 hours.

[0012] In some of the embodiments, the manufacturing method is (1) Under the condition that the heating rate to raise the temperature to the sintering temperature is 2 to 8°C / min, (2) The conditions further include the step of raising the temperature to 500°C to 700°C and pre-sintering for 2 to 6 hours before raising the temperature to the sintering temperature, (3) Conditions for lowering the temperature from the sintering temperature to the annealing temperature at a rate of 2 to 5°C / min, or lowering the temperature from the sintering temperature and then raising it to the annealing temperature, (4) The annealing treatment is carried out in an oxygen-containing atmosphere, and the conditions include at least one of these.

[0013] In some of the embodiments, the step of mixing the sodium source, the calcium source and the M source is, The steps include mixing the sodium source, the calcium source, and the M source with a solvent to form a slurry, The steps include drying the slurry to obtain a mixed powder, The process includes the step of performing the subsequent sintering with the mixed powder.

[0014] In some of the embodiments, the manufacturing method is: (1) Under the condition that the solid mass content in the slurry is 20% to 50%, (2) Conditions for controlling the Dv50 of the solid in the slurry to 0.5 to 1 μm, (3) The drying method employs spray drying, and the spray drying is carried out under conditions in which the intake air temperature is 200°C to 270°C and the exhaust air temperature is controlled to 95°C to 145°C, (4) Conditions for controlling the Dv50 of the mixed powder to 20-30 μm, including at least one of these conditions.

[0015] Another aspect of the present application provides a positive electrode sheet comprising a positive electrode active material described in any one of the above paragraphs, or a positive electrode active material manufactured by a manufacturing method described in any one of the above paragraphs.

[0016] Another aspect of the present invention provides a battery including the above-described positive electrode sheet.

[0017] Another aspect of the present invention provides a power-using device including the above-mentioned battery. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional HADDF and Ca elemental distribution diagram of the cathode active material produced in Example 1. [Figure 2] This is a distribution diagram of Ca elements at different distances from the surface of single crystal particles of the cathode active material manufactured in Example 1. [Figure 3] This is a diagram showing the distribution of Ca elements at different distances from the surface of the single crystal particles of the cathode active material manufactured in Example 2. [Figure 4] This is a diagram showing the distribution of Ca elements at different distances from the surface of the single crystal particles of the cathode active material manufactured in Example 3. [Figure 5] This is a distribution diagram of Ca elements at different distances from the surface of single crystal particles of the cathode active material manufactured in Example 4. [Figure 6] This is an SEM image of the cathode active material manufactured in Comparative Example 1. [Figure 7] This diagram shows a schematic representation of the approximately flaky EDS (Energy Dispersive Spectrometer) analysis sampling of the surface of the cathode active material manufactured in Comparative Example 1, and the EDS elemental composition analysis results corresponding to each spectral label. [Figure 8] SEM and Ca element distribution diagrams of the EDS test of the positive electrode active material produced in Comparative Example 3. [Figure 9] Ca element distribution diagrams at different distances from the surface of the single crystal particles of the positive electrode active material produced in Comparative Example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] To facilitate the understanding of the present application, the present application will be more comprehensively described below while referring to the related drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be implemented in various different forms and is not limited to the embodiments described in this specification. It should be understood that the purpose of providing these embodiments is to thoroughly and comprehensively understand the disclosure content of the present application.

[0020] All technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art of the present application, unless otherwise specifically defined. In this specification, the terms used in the specification of the present application are only for explaining specific embodiments and do not limit the present application. The term "and / or" used in this specification includes any and all combinations of one or more of the listed items.

[0021] One embodiment of the present application provides a positive electrode active material, and the chemical formula of the positive electrode active material is Na x M (1-y) Ca y O2, M contains transition metal elements, x = 0.8 to 1.1, 0.005 ≤ y ≤ 0.015.

[0022] 95 wt% or more of the Ca element is distributed within the surface layer of the single crystal particles of the positive electrode active material, and the thickness of the surface layer is 1 μm. [[ID=(31)]]

[0023] In this specification, the surface layer of a single crystal particle includes the outer surface and the region close to the outer surface of the single crystal particle, and specifically, the thickness of the surface layer is 1 μm. In other words, 95 wt% or more of the element Ca is distributed within the 1 μm thick surface layer of the single crystal particle of the positive electrode active material. The thickness of the surface layer can be determined by measurement using a transmission electron microscope or a scanning electron microscope.

[0024] The Ca element distribution of the above-mentioned cathode active material is obtained by performing high-resolution transmission electron microscopy (HADDF) measurements on the cross-section of the single crystal grains of the cathode active material, and by performing Ca elemental analysis on the spectra obtained from the HADDF measurements. Specifically, from the Ca element distribution maps obtained at different distances from the surface of the single crystal grains of the cathode active material, it can be seen that more than 95 wt% of the Ca element is distributed within the 1 μm thick surface layer of the single crystal grains of the cathode active material.

[0025] The above-mentioned positive electrode active material contains a specific chemical composition, and in particular, the Ca content y is controlled within the specified range. Furthermore, more than 95 wt% of Ca elements are distributed within a 1 μm thick surface layer of the single-crystal particles of the positive electrode active material. As a result, the Ca elements distributed on the surface of the single-crystal particles form relatively stable calcium carbonate with moisture and carbon dioxide in the air. At the same time, the single-crystal particles are protected from the reaction of moisture and carbon dioxide in the air with the Na elements in the single-crystal particles, thereby blocking the process by which Na constantly precipitates and forms residual alkali. This further reduces the residual alkali content of the positive electrode active material, improves the stability of the positive electrode active material in air, and suppresses the problem of deterioration of cycle performance due to complex phase transitions during the charge-discharge process of the positive electrode active material. Consequently, it improves the cycle performance when applied to batteries.

[0026] If the Ca doping rate is too high, i.e., if y is too high, the Ca element forms flaky fine particles on the surface of the single crystal grains. Conversely, a large amount of Ca element precipitates, preventing it from blocking the Na reaction, thus failing to provide a stabilizing effect and affecting the capacity.

[0027] The above-mentioned cathode active material is a sodium ion active material. Compared to lithium ion active materials, sodium ion active materials are abundant in resources, inexpensive, and boast superior performance and safety performance at high and low temperatures.

[0028] In some of these embodiments, x may be in the range of 0.8, 0.85, 0.9, 0.95, 1, 1.1, or any two endpoints. Furthermore, x = 0.8 to 1, and furthermore, x = 0.95 to 1.

[0029] In some of these embodiments, y may be in the range of 0.005, 0.01, 0.015, or any two endpoints. Furthermore, y = 0.01 to 0.015.

[0030] In some of these embodiments, M comprises at least one of Fe, Ni, Mn, Co, V, Ti, Cr, Cu, and Zn. As can be understood, M may be one or more of the above elements.

[0031] Furthermore, M includes at least one of Fe, Ni, Mn, Co, Ti, and Zn.

[0032] For example, M may be Fe, Ni, Mn, Co, Ti, or Zn, or it may be two, three, four, or five of Fe, Ni, Mn, Co, and Zn.

[0033] For example, M may be all three elements: Ni, Fe, and Mn, or it may be all three elements: Ni, Fe, and Mn, plus either Ti or Zn.

[0034] Furthermore, the chemical formula for the positive electrode active material is Na x (NiFeMn) a Zn b Ti c Ca y It is O2. a + b + c = 1 - y, and furthermore, b = 0 to 0.2 and c = 0 to 0.2. Furthermore, b = 0.1 to 0.2 and c = 0.1 to 0.2.

[0035] For example, the cathode active material is Na 0.95 Ni 0.33 Fe 0.33 Mn 0.33 Ca 0.01 O2, NaNi 0.2 Fe 0.25 Mn 0.4 Zn 0.14 Ca 0.01 O2, NaNi 0.19 Fe 0.25 Mn 0.38 Ti 0.17 Ca 0.01 O2, NaNi 0.325 Fe 0.33 Mn 0.33 Ca 0.015 O2, NaNi 0.205 Fe 0.25 Mn 0.4 Zn 0.13 Ca 0.015 O2, Na 0.95 Ni 0.33 Fe 0.33 Mn 0.335 Ca 0.005 O2, Na 0.95 Ni 0.33 Fe 0.33 Mn 0.325 Ca 0.015 O2 and NaNi 0.185 Fe 0.25 Mn 0.38 Ti 0.17 Ca 0.015 It may be at least one of the O2 components.

[0036] In some of the embodiments, the cathode active material includes single crystal particles. Furthermore, the cathode active material is a single crystal particle. The Dv50 of the single crystal particles is 6 to 11 μm. The Dv50 particle diameter is the volume-average diameter and represents the particle diameter corresponding to the point when the cumulative volume distribution ratio of the particles reaches 50%.

[0037] In some of these embodiments, the positive electrode active material is an O3-phase layered oxide. Furthermore, the positive electrode active material is a single crystal particle. Moreover, the morphology of the positive electrode active material is a rectangular single crystal particle with rounded corners.

[0038] In some of the examples, water was used as the solvent, and the residual alkali CO3 of the cathode active material was used. 2- <6000 ppm, and furthermore, residual alkali CO3 2- It is <4000 ppm. ppm is calculated using mass.

[0039] In some of the examples, ethanol was used as the solvent, and the residual alkali OH of the positive electrode active material was used. - It is <900 ppm, and furthermore, the residual alkali OH - It is <500 ppm. ppm is calculated using mass.

[0040] Other embodiments of the present application provide a method for producing any of the above-described cathode active materials. Chemical formula Na x M (1-y) Ca y S10 provides a sodium source, a calcium source and an M source according to O2, where M contains a transition metal element, and x = 0.8 to 1.1, 0.005 ≤ y ≤ 0.015. S20 is prepared by mixing a sodium source, a calcium source, and an M source, sintering them in an oxygen-containing atmosphere at 850°C to 1000°C for 8 to 16 hours, and then annealing them at 500°C to 650°C for 7 to 12 hours.

[0041] In the above manufacturing method, after mixing a sodium source, a calcium source, and an M source, the mixture is first heated to a high temperature in an oxygen-containing atmosphere and sintered. During high-temperature sintering, the Ca element is mixed into the material lattice, and then the mixture is cooled to a low temperature and annealed. During the annealing process, the Ca element migrates from the lattice to the surface of the single crystal particles, thereby forming a relatively uniform segregation and concentration on the surface of the single crystal particles.

[0042] In some of the embodiments, the sodium source includes, but is not limited to, at least one of the following: sodium carbonate, sodium hydroxide, sodium oxalate, sodium citrate, sodium acetate, etc.

[0043] In some of the examples, the calcium source includes, but is not limited to, at least one of calcium hydroxide, calcium carbonate, calcium oxalate, calcium citrate, or calcium acetate. Preferably, calcium hydroxide, which has good reaction activity, is used as the calcium source.

[0044] In some of the embodiments, the M source includes, but is not limited to, at least one of the following: oxides, hydroxides, carbonates, oxalates, citrates, and acetates of transition metals.

[0045] In some of the embodiments, the heating rate for raising the sintering temperature to 850°C to 1000°C is 2 to 8°C / min.

[0046] In some of the embodiments, step S20 further includes a step in which the product, a mixture of a sodium source, a calcium source, and an M source, is heated to 500°C to 700°C and pre-sintered for 2 to 6 hours before raising the temperature to the sintering temperature of 850°C to 1000°C. Furthermore, the heating rate for raising the temperature to the pre-sintering temperature of 500°C to 700°C is 2 to 8°C / min, and the heating rate for raising the temperature from 500°C to 700°C to the sintering temperature of 850°C to 1000°C is also 2 to 8°C / min. Furthermore, the product can be cooled from the annealing temperature of 500 to 650°C to room temperature together with the furnace.

[0047] In some of these examples, the temperature is lowered from a sintering temperature of 850°C to 1000°C to an annealing temperature of 500°C to 650°C at a rate of 2 to 5°C / min.

[0048] Alternatively, the material may first be heated to 850°C to 1000°C, then allowed to cool naturally to room temperature, and then placed in a furnace for annealing, where it is heated again to 500°C to 650°C. The subsequent cooling process is left uncontrolled, and the material is allowed to cool naturally to room temperature.

[0049] In some of these embodiments, the sintering and annealing processes are carried out in an oxygen-containing atmosphere. The oxygen-containing atmosphere includes, but is not limited to, air and an oxygen atmosphere.

[0050] In some of the embodiments, the step of mixing the sodium source, calcium source and M source in S20 includes steps S21 to S22.

[0051] In step S21, the sodium source, calcium source, and M source are mixed with the solvent to form a slurry. Furthermore, the solid mass content in the slurry can be controlled to 20% to 50%, and may be selectively set to 25% to 45% or 30% to 40%.

[0052] Furthermore, the Dv50 of the solid particles in the slurry can be controlled to 0.5-1 μm, or selectively controlled to 0.6-0.9 μm.

[0053] Furthermore, the solvent may be water.

[0054] In S22, the slurry is dried to obtain a mixed powder. The subsequent sintering step in S20 is then carried out using this mixed powder.

[0055] Furthermore, spray drying is employed as the drying method, and the intake air temperature is controlled to 200°C to 270°C, and the exhaust air temperature to 95°C to 145°C. Preferably, the intake air temperature for spray drying is 230°C to 250°C, and the exhaust air temperature is 110°C to 120°C.

[0056] Furthermore, the Dv50 of the mixed powder is controlled to 20-30 μm. To understand this, the Dv50 of the mixed powder can be controlled by adjusting the centrifugal frequency and feed rate of the spray drying process.

[0057] To understand this, during the spray drying process, primary particles (i.e., single-crystal particles) aggregate to form secondary particles. By controlling the Dv50 of the solid in the slurry to 0.5-1 μm, the mixed powder forms relatively densely distributed secondary particles, which can then be further increased in subsequent pre-sintering, sintering, and annealing processes.

[0058] To make it clear, in addition to the steps described above, the mixing may involve combining the sodium source, calcium source, and M source by methods such as solid ball milling.

[0059] To make it easier to understand, secondary particles in the mixed powder are gradually converted into single-crystal particles through subsequent sintering and annealing processes.

[0060] Furthermore, the Dv50 of the single crystal particles in the above-mentioned cathode active material is 6 to 11 μm. Another embodiment of the present application further provides a cathode sheet containing the above-mentioned cathode active material.

[0061] Typically, a positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is positive electrode It is provided on at least one surface of the current collector. The positive electrode active material layer contains the positive electrode active material.

[0062] In some of these embodiments, the positive electrode current collector includes, but is not limited to, a metal current collector, such as a metal foil like aluminum foil.

[0063] In some of these embodiments, the cathode active material layer optionally further includes a binder. The binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and fluorine-containing acrylate resins.

[0064] In some of these embodiments, the cathode active material layer optionally further includes a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Koché black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] Other embodiments of the present invention further provide a battery comprising the positive electrode sheet, negative electrode sheet, and electrolyte described above.

[0066] In some of these embodiments, the negative electrode sheet includes a negative electrode current collector. Furthermore, the negative electrode sheet further includes a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer may also include a negative electrode active material.

[0067] Furthermore, the negative electrode active material may include, but is not limited to, at least one of graphite, soft carbon, hard carbon, silicon-based materials, etc.

[0068] In some of these embodiments, the negative electrode film layer optionally further includes a binder. The binder may include at least one of the following: styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0069] In some of these embodiments, the negative electrode film layer optionally further contains a conductive agent. The conductive agent may include at least one of the following: superconducting carbon, acetylene black, carbon black, Kocheng black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some of the embodiments, the electrolyte is in the form of an electrolyte solution, which contains an electrolyte sodium salt and a solvent.

[0071] Furthermore, the electrolyte sodium salt includes, but is not limited to, at least one of the following: sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoride arsenate, sodium bisfluorosulfonylimide, sodium bistrifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluoro(oxalato)borate, sodium bis(oxalato)borate, sodium bis(trifluoromethanesulfonyl)imide, sodium difluorodisoxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0072] Furthermore, the solvent may include, but is not limited to, at least one of the following: ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropylene carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0073] To make it clear, the electrolyte may contain several additives, including, but is not limited to, film-forming additives.

[0074] In some embodiments thereof, the battery further includes a separator, which is provided between the positive electrode sheet and the negative electrode sheet and is used to prevent electrical conductivity between the positive electrode sheet and the negative electrode sheet.

[0075] In some of these embodiments, the separator includes, but is not limited to, at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0076] In some of these embodiments, the battery includes, but is not limited to, at least one of laminated batteries and wound batteries.

[0077] Another embodiment of the present application provides a power-using device including the above-mentioned battery.

[0078] In some of these embodiments, the power-using devices include, but are not limited to, mobile devices, electric vehicles, electric trains, and ships.

[0079] Mobile devices include, but are not limited to, mobile phones and laptop computers. Electric vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric trucks.

[0080] To make the purpose, technical solution, and advantages of this application more concise and clear, this application will be described using the following specific embodiments, but this application is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of this application and are used to illustrate this application, and should not be understood as limiting the scope of this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should all be included within the scope of protection of this application.

[0081] To better explain the present application, the contents of the present application will be further described by combining the following examples. The following are specific examples.

[0082] Example 1

[0083] 1. Target chemical formula Na 0.95 Ni 0.33 Fe 0.33 Mn 0.33 Ca 0.01According to O2, 2.237 kg of NiO, 2.392 kg of Fe2O3, 2.285 kg of Mn2O3, 67.25 g of Ca(OH)2, and 4.563 kg of Na2CO3 were weighed out and added to 25 L of deionized water to form a slurry with a solid mass content of 25%. 2. The slurry described above was sanded until the Dv50 was 0.9 μm. 3. The sanded slurry is spray-dried, the intake air temperature is controlled to 250°C, the exhaust air temperature to 115°C, and the centrifugal frequency is adjusted to 325Hz. dry The Dv50 of the subsequent mixed powder was controlled to 22 μm. 4. The mixed powder was heated to 550°C at a heating rate of 2°C / min and pre-sintered for 5 hours. Then, it was heated to 935°C at a heating rate of 2°C / min and sintered for 11 hours. Next, it was cooled to 600°C at a rate of 5°C / min and annealed for 10 hours. Finally, it was crushed to obtain a single-crystal particle product with a Dv50 particle size of 9 μm.

[0084] Examples 2-5 This is almost identical to Example 1, the only difference being that the composition of the target chemical formula in Step 1 is different (the addition ratio of the corresponding raw materials is different), that is, the composition of the cathode active material is different, as shown in Table 1 below.

[0085] Example 6 This example is almost identical to Example 1, the only difference being that the pre-sintering step is omitted and the temperature is directly raised to 935°C at a heating rate of 2°C / min for 11 hours of sintering. The subsequent processes remain unchanged, as shown in Table 1 below.

[0086] Examples 7-8 This example is almost identical to Example 1, with the only difference being the temperature and time of the sintering process, which are specifically shown in Table 1 below.

[0087] Examples 9-10 This is almost identical to Example 1, with the only difference being the temperature and time of the pre-sintering treatment, which are specifically shown in Table 1 below.

[0088] Examples 11-12 This example is almost identical to Example 1, with the differences being the intake and exhaust temperatures controlled during spray drying, and the Dv50 after slurry sanding, which are specifically shown in Table 1 below.

[0089] Comparative Example 1 This is almost identical to Example 1, with the only difference being the amount of Ca(OH)2 added, which is as follows: 1. Target chemical formula Na 0.95 Ni 0.3 Fe 0.33 Mn 0.33 Ca 0.04 According to the O2 content, the corresponding masses of NiO, Fe2O3, Mn2O3, Ca(OH)2, and Na2CO3 were weighed and added to deionized water to form a slurry. 2. The above slurry is D v The material was sanded until the thickness of the 50mm layer was reduced to 0.9μm. 3. The sanded slurry is spray-dried, the intake air temperature is controlled to 250°C, the exhaust air temperature to 115°C, and the centrifugal frequency is adjusted to 325Hz. dry D of the subsequent mixed powder v The value was controlled to 50 to 22 μm. 4. The mixed powder was heated to 550°C at a heating rate of 2°C / min for 5 hours for pre-sintering, then heated to 935°C at a heating rate of 2°C / min for 11 hours for sintering, and then cooled to 600°C at a rate of 5°C / min for 10 hours for annealing to obtain the product.

[0090] Comparative Example 2 1. Target chemical formula Na 0.95 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 According to the O2 standard, NiO, Fe2O3, Mn2O3, and Na2CO3 were weighed and added to deionized water to form a slurry. 2. The above slurry is D v The material was sanded until the thickness of the 50mm layer was reduced to 0.9μm. 3. The sanded slurry is spray-dried, the intake air temperature is controlled to 250°C, the exhaust air temperature is controlled to 115°C, and the centrifugal frequency is adjusted to 325Hz. The mixed powder after spraying is D v The value was controlled to 50 to 22 μm. 4. The mixed powder was heated to 550°C at a heating rate of 2°C / min for 5 hours for pre-sintering, then heated to 935°C at a heating rate of 2°C / min for 11 hours for sintering, and then cooled to 600°C at a rate of 5°C / min for 10 hours for annealing to obtain the product.

[0091] Comparative Example 3 This is almost identical to Example 1, the only difference being that in Step 4, the temperature is raised to 935°C and sintered for 11 hours, after which it is cooled to room temperature along with the furnace.

[0092] Comparative Example 4 This is almost identical to Example 1, the only difference being the amount of Ca(OH)2 added. Specifically, it is as follows: 1. Target chemical formula Na 0.95 Ni 0.315 Fe 0.33 Mn 0.33 Ca 0.025 According to the O2 content, the corresponding masses of NiO, Fe2O3, Mn2O3, Ca(OH)2, and Na2CO3 were weighed and added to deionized water to form a slurry. Subsequent steps were carried out similarly.

[0093] [Table 1]

[0094] In Table 1, D1 to D4 represent Comparative Example 1 to Comparative Example 4, respectively.

[0095] The following is a performance test. 1. A high-resolution transmission electron microscope (HADDF) test was performed on a cross-section of the cathode active material manufactured in Example 1, yielding the left image in Figure 1. Ca element distribution marking was then applied to the left image to obtain the right image in Figure 1. As can be seen from Figure 1, the cathode active material manufactured in Example 1 is in the form of single crystal particles.

[0096] Next, based on the right-hand figure in Figure 1, the statistical results in Figure 2 were obtained, that is, the distribution diagrams of Ca elements at different distances from the surface of the single-crystal particles of the positive electrode active material manufactured in Example 1. As can be seen from this, more than 95 wt% of Ca elements are distributed within the 1 μm thick surface layer of the single-crystal particles of the positive electrode active material.

[0097] The morphology and Ca element distribution diagrams of the other embodiments are similar to those of Example 1. As shown in Figures 3 to 5, the Ca element distribution diagrams at different distances from the surface of the single crystal particles of the cathode active material produced in Examples 2 to 4 are shown, and as can be seen, more than 95 wt% of the Ca element is distributed within the 1 μm thick surface layer of the single crystal particles of the cathode active material.

[0098] 2. Scanning electron microscopy was performed on the cathode active material produced in Comparative Example 1. As shown in Figure 6, in Comparative Example 1, the doping rate of Ca element was too high, i.e., y was too high, resulting in the formation of flaky fine particles of Ca element on the surface of the single crystal grains, i.e., a large amount of Ca element precipitated. As shown in the upper part of Figure 7, flaky fine particles were selected at four points and EDS analysis was performed on each of them, and quantitative analysis results for each element were obtained as shown in the lower part of Figure 7.

[0099] In the lower diagram of Figure 7, the units for each element are in wt%, and as can be seen from this, the Ca content of the flaky microparticles on the surface is too high. This is because there is too much Ca doping, causing a large amount of Ca to precipitate during the annealing process, which then aggregates with other metallic elements to form flaky microparticles. The Ca content of the flaky particles and the composition of other elements differ significantly from the designed mixing ratio, and the flaky particles are an unpredictable substance produced when excess Ca element re-reacts with the surface during the precipitation process.

[0100] 3. The SEM image obtained by performing an EDS test on the cathode active material manufactured in Comparative Example 3 is shown in the left figure of Figure 8. Then, Ca element distribution marking was applied to the left figure to obtain a Ca element distribution map, which is shown in the right figure of Figure 8. Furthermore, from the right figure of Figure 8, Ca element distribution curves at different distances from the surface of the single crystal particles of the cathode active material manufactured in Comparative Example 3, shown in Figure 9, can be obtained. As can be seen from this, the Ca element at different distances from the surface of the single crystal particles of the cathode active material manufactured in Comparative Example 3 is basically uniformly distributed.

[0101] 4. Residual alkalinity test After storing the cathode active material sample in a room at room temperature and pressure for 7 days, the residual alkali of the sample was detected using an 888 / 905 automatic potentiometer according to GB / T 9725-2007, and CO3 2- When detecting OH, the solvent is deionized water. - When detecting the substance, ethanol was used as the solvent.

[0102] 5. Cycle performance Initial Capacity: The battery was charged and discharged for two cycles at 0.1C, then for two cycles at 0.33C. After that, the battery was charged and discharged at a rate of 1C at 25°C, and the capacity per gram of the battery was tested. The initial capacity was defined as the discharge capacity of the first cycle at 1C. Capacity retention rate after 50 cycles = Discharge capacity at 50th cycle / Discharge capacity at 1st cycle * 100% Capacity retention rate after 100 cycles = Discharge capacity at 100th cycle / Discharge capacity at 1st cycle * 100% The battery was charged and discharged twice at 0.1C, then twice at 0.33C, and then the battery was cycled at a rate of 1C at 25°C. The initial volume of the battery before the start of the cycle was set as V0, and the volume after 50 cycles was set as V 50 The volume at the 100th cycle is V 100 That's what I decided. Volume expansion coefficient in 50 cycles: (V 50 - V0) / V0×100%. Volume expansion coefficient in 100 cycles: (V 100 - V0) / V0×100%.

[0103] Table 2 shows the residual alkali test results for the positive electrode active material of each example and comparative example, as well as the corresponding battery performance test results.

[0104] [Table 2]

[0105] In Comparative Example 1, the doping rate of Ca element was too high, i.e., y was too high. As a result, the Ca element formed flaky fine powder on the surface of the single crystal particles, and conversely, a large amount of Ca element precipitated, preventing it from blocking the reaction with Na, thus failing to exhibit a stabilizing effect, and simultaneously affecting the capacity.

[0106] In Comparative Example 2, the element Ca was not doped, and the residual alkali content was higher than in Comparative Example 1. On the other hand, although its initial capacity was greater than that of Comparative Example 1, the capacity decay and volume expansion rate were greater than in Comparative Example 1 as charge and discharge cycles were repeated, confirming that the deterioration of its cycle performance was serious.

[0107] In Comparative Example 3, the material was cooled directly to room temperature along with the furnace after sintering without annealing. The resulting calcium elements were uniformly distributed on the surface, and its initial capacity was greater than that of Example 1. However, as the charge-discharge cycles repeated, the capacity decay and volume expansion rate were greater than in Example 1, confirming that the deterioration of its cycle performance was severe.

[0108] In Comparative Example 4, the calcium content was still at a high level compared to Example 1. As can be seen from the results, similar to Comparative Example 1, the high doping rate of Ca element caused the Ca element to form flaky fine particles on the surface of the single crystal grains, affecting the capacity output, and the improvement in cycle performance was lower than in Example 1.

[0109] Comparing Comparative Example 1 and Comparative Example 4, it was confirmed that the residual alkali content of the cathode active material produced in Comparative Example 4 was lower, and although the volume expansion rate in Comparative Example 1 was small during the first 50 cycles, the degradation in subsequent cycles became more severe, and the expansion rate at 100 cycles was significantly higher than that of Comparative Example 4. This may be due to the shedding of flaky microparticles from the surface of Comparative Example 1.

[0110] Compared to Comparative Examples 1-4, the cathode active materials produced in each example show a significantly reduced residual alkali content, and their capacity decay and volume expansion rates are clearly lower than those in Comparative Examples 1-4 as charge-discharge cycles are repeated, indicating a remarkable improvement in their cycle performance.

[0111] The technical features of the above embodiments can be combined in any way, and for the sake of brevity, not all possible combinations of the technical features of the above embodiments have been described one by one. However, any combination of these technical features should be interpreted as falling within the scope described herein, provided that it does not lead to any contradiction.

[0112] The above embodiments are merely examples of some embodiments of the present application, and although their descriptions are specific and detailed, they should not be interpreted as limiting the scope of the patent being filed. Those skilled in the art will be able to make some modifications and improvements without departing from the concept of the present application, and all such modifications and improvements will fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be based on the attached claims, and the specification and drawings may be used to interpret the contents of the claims.

[0113] <Cross-reference of related applications> This application claims priority to the Chinese patent application filed with the China National Patent Office on October 9, 2023, with application number 202311296382.2 and title "Cathode Active Material and Method for Manufacturing the Same, Cathode Sheet, Battery and Power Utilization Device," the entire contents of which are incorporated herein by reference.

Claims

1. A positive electrode active material, wherein the chemical formula of the positive electrode active material is Na ｘ M （１－ｙ） Ca ｙ O ２ Therefore, M contains transition metal elements, x = 0.8 to 1.1, and 0.005 ≤ y ≤ 0.

015. A positive electrode active material in which 95 wt% or more of Ca elements are distributed within the surface layer of the single crystal particles of the positive electrode active material, and the thickness of the surface layer is 1 μm.

2. The positive electrode active material according to claim 1, wherein M comprises at least one of Fe, Ni, Mn, Co, V, Ti, Cr, Cu, and Zn.

3. The positive electrode active material according to claim 2, wherein M comprises at least one of Fe, Ni, Mn, Co, Ti, and Zn.

4. The aforementioned positive electrode active material is (1) The condition that the Dv50 of the single crystal particles in the positive electrode active material is 6 to 11 μm, and (2) The positive electrode active material according to any one of claims 1 to 3, comprising at least one of the conditions that the positive electrode active material is an O3 phase layered oxide.

5. The aforementioned positive electrode active material is (1) Using water as a solvent, the residual alkali CO of the positive electrode active material ３ ２－ <Conditions of 6000 ppm, (2) Using ethanol as a solvent, the residual alkali OH of the positive electrode active material － A positive electrode active material according to any one of claims 1 to 3, comprising at least one of the conditions of being <900 ppm.

6. A method for producing a positive electrode active material, Chemical formula Na ｘ M （１－ｙ） Ca ｙ O ２ According to this, supplying a sodium source, a calcium source, and an M source, where M contains a transition metal element, and the steps where x = 0.8 to 1.1 and 0.005 ≤ y ≤ 0.015, A method for producing a positive electrode active material, comprising the steps of mixing the sodium source, the calcium source, and the M source, sintering them in an oxygen-containing atmosphere at 850°C to 1000°C for 8 to 16 hours, and further annealing them at 500°C to 650°C for 7 to 12 hours.

7. The aforementioned manufacturing method is (1) The heating rate at which the temperature is raised to the sintering temperature is 2 to 8°C / min, (2) The conditions further include the step of raising the temperature to 500°C to 700°C and pre-sintering for 2 to 6 hours before raising the temperature to the sintering temperature, (3) Conditions for lowering the temperature from the sintering temperature to the annealing temperature at a rate of 2 to 5°C / min, or lowering the temperature from the sintering temperature and then raising it to the annealing temperature, The manufacturing method according to claim 6, comprising at least one of the following conditions: (4) The annealing treatment is carried out in an oxygen-containing atmosphere.

8. The step of mixing the sodium source, the calcium source and the M source is, The steps include mixing the sodium source, the calcium source, and the M source with a solvent to form a slurry, The steps include drying the slurry to obtain a mixed powder, The manufacturing method according to any one of claims 6 to 7, further comprising the step of performing the subsequent sintering with the mixed powder.

9. The aforementioned manufacturing method is (1) Under the condition that the solid mass content in the slurry is 20% to 50%, (2) Conditions for controlling the Dv50 of the solid in the slurry to 0.5 to 1 μm, (3) The drying method employs spray drying, and the spray drying is carried out under conditions in which the intake air temperature is 200°C to 270°C and the exhaust air temperature is controlled to 95°C to 145°C, The manufacturing method according to claim 8, comprising at least one of the following: (4) a condition for controlling the Dv50 of the mixed powder to 20 to 30 μm.

10. A positive electrode sheet comprising a positive electrode active material according to any one of claims 1 to 5, or a positive electrode active material manufactured by a manufacturing method according to any one of claims 6 to 9.

11. A battery comprising the positive electrode sheet described in claim 10.

12. A power-using device including a battery according to claim 11.

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