CN118919721A - All-solid-state battery anode coating agent, preparation method and application - Google Patents

Abstract

The invention relates to the technical field of all-solid-state batteries, in particular to an all-solid-state battery anode coating agent, a preparation method and application thereof, wherein the molecular formula of the all-solid-state battery anode coating agent is NaAlCl ₂ S. The NaAlCl ₂ S coating agent provided by the invention adopts an in-situ coating method, so that the interface problem between the layered oxide anode and the sodium sulfide electrolyte can be effectively solved, the energy density, the safety and the cycle life of the battery are improved, and the requirements of the market on the high-energy density and high-safety battery are met. Meanwhile, the coating agent can form a coating layer with planar uniform coating, has ion conductivity and promotes the formation of O-S bonds on the surface of the positive electrode, can improve the rate performance and capacity exertion of the battery, and meets the market demand on high-power density batteries. In addition, the coating is carried out at low temperature, so that the structural damage of the layered oxide positive electrode can be avoided, the performance of the battery is improved, and the market demand for high-performance batteries is met.

Description

A kind of all-solid-state battery positive electrode coating agent, preparation method and application

Technical Field

The present invention relates to the technical field of all-solid-state batteries, and in particular to an all-solid-state battery positive electrode coating agent, a preparation method and an application thereof.

Background Art

As the global demand for new energy sources grows, batteries are increasingly used as efficient and clean energy storage and conversion devices. All-solid-state batteries use solid electrolytes, which are non-flammable, thus reducing the risk of battery leakage, combustion or explosion. Sodium is abundant in the earth's crust and has a lower cost than lithium, which gives sodium-ion batteries an advantage in raw material costs. Therefore, sodium-ion all-solid-state batteries are regarded as an important development direction for the next generation of batteries due to their high energy density, high safety and long cycle life.

In sodium-ion all-solid-state batteries, the discharge platform of the layered oxide cathode is relatively high, which will lead to the decomposition and degradation of the sulfide electrolyte, thus affecting the performance of the battery. Therefore, one of the key technical challenges of sodium-ion all-solid-state batteries is how to solve the interface problem between the layered oxide cathode and the sulfide electrolyte.

At present, the method of coating the surface of the layered oxide positive electrode is usually adopted to reduce the interfacial reaction between the active material and the electrolyte. This method usually uses inert materials such as boron oxide or titanium oxide for coating. However, this method has some problems, such as: (a) The oxide used in the coating layer does not have ion conductivity, which will affect the ion transmission between the positive electrode active material and the electrolyte, thereby affecting the battery's rate performance and capacity; (b) The problem of uniformity of the coating layer. Even if nano-scale boron oxide and titanium oxide particles are used, agglomeration will inevitably occur during the coating process, forming a point coating instead of a uniform surface coating; (c) Existing coating methods are usually carried out at high temperatures, which may cause structural damage to the layered oxide positive electrode, thereby affecting battery performance.

In addition, the oxygen on the surface of the layered cathode will form O-S exchange products with the sulfide electrolyte, thereby reducing the electrolyte conductivity by three orders of magnitude. How to avoid the reaction between the layered cathode material and the sulfide electrolyte is also an urgent problem to be solved.

Summary of the invention

In view of this, the technical problem to be solved by the present invention is to provide a positive electrode coating agent for all-solid-state batteries, a preparation method and an application thereof

In one aspect, the present invention provides an all-solid-state battery positive electrode coating agent, the molecular formula of which is NaAlCl ₂ S.

On the other hand, the present invention provides a method for preparing the above-mentioned all-solid-state battery positive electrode coating agent, comprising the following steps:

Mix NaCl, AlCl ₃ , and Sb ₂ S ₃ and react at high temperature to obtain NaAlCl ₂ S;

The molar ratio of NaCl, AlCl ₃ and Sb ₂ S ₃ is 3:3:1.

The equation for the above reaction is as follows:

3NaCl+3AlCl ₃ +Sb ₂ S ₃ =3NaAlCl ₂ S+2SbCl ₃

The present invention has no particular limitation on the mixing method, and the mixing method may be any mixing method known to those skilled in the art, including but not limited to stirring mixing, ball milling mixing, and the like.

The temperature of the high temperature reaction is preferably 230-400°C. In some specific embodiments of the present invention, the temperature of the high temperature reaction includes but is not limited to 230, 260, 330, 350, 380, 400°C, or a range value with any of the above values as the upper or lower limit.

The time of the high temperature reaction is preferably 1 to 3 hours; in some specific embodiments of the present invention, the time of the high temperature reaction includes but is not limited to 1 hour, 2 hours, 3 hours, or a range value with any of the above values as the upper or lower limit.

The high temperature reaction is preferably carried out in an inert atmosphere or a vacuum atmosphere, more preferably in a vacuum atmosphere.

The present invention has no special limitation on the inert atmosphere, including but not limited to argon or nitrogen.

In the above reaction, the boiling point of the product SbCl ₃ is 224°C, and the boiling point of NaAlCl ₂ S is about 300°C. Therefore, by heating the reaction system to above the boiling point of SbCl ₃ under vacuum, SbCl ₃ gas can be discharged to obtain NaAlCl ₂ S.

After the high temperature reaction, the obtained NaAlCl ₂ S is in a molten state. In order to make it contact with the positive electrode active material better, the present invention preferably cools the molten NaAlCl ₂ S to a solid state and then performs a pulverization process.

It is preferably pulverized into powder with a particle size of 1 to 10 microns.

The present invention has no particular limitation on the above-mentioned pulverization method, and it can be any pulverization method well known to those skilled in the art, including but not limited to grinding, ball milling, high-speed mixing, etc.

The present invention applies NaAlCl ₂ S to the positive electrode coating agent of the all-solid-state battery. The NaAlCl ₂ S can melt and coat the positive electrode active material at a relatively low temperature. Therefore, the NaAlCl ₂ S is mixed with the positive electrode active material and then heated to above its melting point to obtain the NaAlCl ₂ S-coated positive electrode material by simple melting heating.

Based on this, the present invention provides, on the other hand, an all-solid-state battery positive electrode material, comprising an all-solid-state battery positive electrode active material, and a coating layer coated on the surface of the all-solid-state battery positive electrode active material;

The coating layer includes NaAlCl ₂ S.

Preferably, the mass content of the NaAlCl ₂ S in the all-solid-state battery positive electrode material is 0.05% to 1%.

If the coating agent content is too low, the coating will be incomplete, resulting in a significant decrease in the battery cycle performance; if the coating agent content is too high, the coating layer will be too thick, affecting the battery's rate performance.

In the present invention, the all-solid-state battery positive electrode material has a core-shell structure, wherein the all-solid-state battery positive electrode material is a core and the coating layer is a shell.

The coating layer acts as a shell layer and is uniformly melted on the surface of the all-solid-state battery positive electrode material to form a uniform surface coating on the all-solid-state battery positive electrode material, thereby avoiding the problem of coating layer agglomeration and the problem of uneven coating such as point coating.

The shell layer prevents the positive electrode active material from contacting the electrolyte.

The present invention has no special limitation on the selection of the above-mentioned all-solid-state battery positive electrode material, which can be an all-solid-state battery positive electrode material well known to those skilled in the art, including but not limited to one or more of NaNi _0.5 Mn _0.1 Ti _0.4 O ₂ , NaFePO ₄ , Na ₂ MnFe(CN) ₆ , NaCoO ₂ , NaCrO ₂ , NaNiO ₂ , NaNi _0.5 Mn _0.5 O ₂ , NaFeO ₂ and the like.

On the other hand, the present invention provides a method for preparing the above-mentioned all-solid-state battery positive electrode material, comprising the following steps:

The all-solid-state battery positive electrode active material and NaAlCl ₂ S are mixed and melted at high temperature, so that the NaAlCl ₂ S is melted and coated on the surface of the all-solid-state battery positive electrode active material to obtain the all-solid-state battery positive electrode material.

The present invention has no particular limitation on the mixing method, and the mixing method may be any mixing method known to those skilled in the art, including but not limited to grinding, ball milling, high-speed mixing, and the like.

The high temperature melting temperature is preferably 300-400°C. In some specific embodiments of the present invention, the high temperature melting temperature is 300°C, 330°C, 350°C, 360°C, 380°C, 400°C, or a range value with any of the above values as the upper or lower limit.

This temperature range can ensure that the NaAlCl ₂ S is melted and uniformly coated on the surface of the positive electrode active material of the all-solid-state battery, and can also prevent the degradation of the positive electrode active material of the all-solid-state battery at high temperature.

When the temperature of high-temperature melting is too low, the coating agent fails to evenly coat the surface of the positive electrode active material particles, and an incomplete island coating will be formed, resulting in an increased risk of contact between the electrolyte and the positive electrode active material, which will significantly reduce the initial efficiency and cycle performance of the battery; when the temperature of high-temperature melting is too high, it will cause high-temperature oxygen release of the positive electrode active material, that is, the structure of the positive electrode active material collapses, causing the subsequent battery performance to be seriously reduced.

The high temperature melting time is preferably 30 to 180 minutes.

The high-temperature melting is preferably performed in an inert atmosphere.

The present invention has no special limitation on the inert atmosphere, including but not limited to argon or nitrogen.

The coating agent NaAlCl ₂ S selected in the present invention can be decomposed at a relatively low voltage, and in the charging process of the battery, an in-situ decomposition reaction occurs on the surface of the positive electrode active material to form a target coating.

When the voltage is increased to the decomposition voltage, the coating agent NaAlCl ₂ S undergoes the following in-situ decomposition reaction on the surface of the positive electrode active material of the all-solid-state battery:

3NaAlCl ₂ S=2NaCl+NaAlCl ₄ +Al ₂ S ₃

Thus, the coating agent can be decomposed during the first week of charging of the battery, and the coating product can be formed by in-situ decomposition.

Among them, the decomposition product NaAlCl ₄ has ionic conductivity and is an electronic insulator, and has the characteristics required for an ideal CEI (positive electrode surface coating layer); the decomposition product Al ₂ S ₃ is a sulfur-containing compound, which can form an OS bond with the oxygen on the surface of the layered oxide positive electrode, avoiding the formation of OS exchange products between the oxygen of the positive electrode particles and the sulfide electrolyte, which helps to stabilize the layered oxide positive electrode and reduce the occurrence of oxygen release. At the same time, the above-mentioned coating also has the characteristics of molecular-level mixing (the coating of the above-mentioned positive electrode active material: NaCl, NaAlCl ₄ , Al ₂ S ₃ is produced by the decomposition of the precursor NaAlCl ₂ S, so the several decomposition products are fully mixed together and can form a molecular-level mixture; compared with mixing the particles of several substances by traditional mechanical mixing methods, such as stirring, ball milling, etc., the above-mentioned substances prepared in the present invention have a higher degree of mixing).

In the above steps, in order to make the coating agent fully and evenly decompose into the coating layer, the charging system needs to be set during the charging process to avoid the positive electrode potential rising to the decomposition voltage of the sulfide electrolyte before the coating material is fully formed, causing the decomposition of the solid electrolyte.

Based on this, the present invention provides an all-solid-state battery, comprising the above-mentioned all-solid-state battery positive electrode material or the all-solid-state battery positive electrode material prepared by the above-mentioned preparation method.

Preferably, the all-solid-state battery is charged for the first week; the positive electrode coating agent of the all-solid-state battery is decomposed to form a coating layer on the surface of the positive electrode active material of the all-solid-state battery;

The coating layer includes NaCl, NaAlCl ₄ and Al ₂ S ₃ .

Preferably, the first week of charging preferably includes:

The all-solid-state battery is allowed to stand for 60 to 180 minutes at a charging rate of 0.01 to 0.05C and a positive electrode potential of 3 to 3.3V;

Then, the charging rate is 0.01-0.05C and the positive electrode potential is 3.3-3.5V, and the charging time is 30-180 minutes.

The all-solid-state battery positive electrode coating agent is completely decomposed to form a coating layer on the surface of the all-solid-state battery positive electrode active material.

If the charging rate is too high or the standing time is too short, the coating agent will not be able to decompose and crack completely and evenly, which will cause a decline in subsequent battery performance.

If the static voltage is too high, the coating agent cannot be fully converted into the target coating within the main decomposition voltage range.

If the static voltage is too low, the purpose of in-situ decomposition of the coating agent cannot be achieved.

If the standing time is too short, the coating agent will not be fully converted into the target coating within the main decomposition voltage range.

After the above first week of charging, the battery can undergo normal charge and discharge cycles.

The coated positive electrode material provided by the present invention is mixed with a sulfide all-solid electrolyte, a conductive agent, and a binder to obtain a positive electrode sheet.

The present invention has no special limitation on the electrolyte layer of the all-solid-state battery, and may be any applicable electrolyte known to those skilled in the art, preferably a sulfide solid electrolyte, including but not limited to Na ₃ PS ₄ and the like.

The present invention has no special limitation on the negative electrode material of the above-mentioned all-solid-state battery, and it can be a suitable negative electrode material well known to those skilled in the art, preferably a carbon material, including but not limited to hard carbon.

Compared with the prior art, the present invention provides an all-solid-state battery positive electrode coating agent, the molecular formula of which is NaAlCl ₂ S.

The beneficial effects of this technical solution are as follows:

1. The coating layer formed by the coating agent provided by the present invention has the characteristic of uniform surface coating. Compared with the point coating in the prior art, it can more effectively isolate the direct contact between the positive electrode active material and the electrolyte, thereby reducing the interface reaction and improving the stability and life of the battery;

2. The coating layer formed by the coating agent provided by the present invention is composed of a substance with ion conductivity and an electronic insulator, and a sulfur-containing coating, which are uniformly mixed at the molecular level; it can not only isolate the direct contact between the positive electrode active material and the electrolyte, but also construct an ion channel in the coating layer structure, and at the same time, sulfurize the surface of the layered oxygen positive electrode, which is helpful to stabilize the active material;

3. The coating agent provided by the present invention forms a coating layer in situ during the charging process. Compared with the high-temperature coating method in the prior art, the coating process of the present invention is more gentle and will not cause damage to the structure of the layered oxide positive electrode material, thereby ensuring the performance of the battery;

4. The coating agent provided by the present invention has the characteristic of decomposing at a voltage above 2.5V. This characteristic enables the coating agent to decompose during the first week of battery charging to form a coating product. This is a new coating method, which is more innovative and practical than the existing technology.

5. The coating agent provided by the present invention contains S element, which helps to form O-S bonds on the surface of the positive electrode, thereby improving the stability of the active substance itself.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope image of the coating agent precursor powder prepared in Example 1;

FIG2 is an XRD pattern of the coating agent prepared in Example 1;

FIG3 is a scanning electron microscope image of the material after the precursor powder is mixed with the positive electrode active material;

FIG4 is a scanning electron microscope image of the positive electrode active material particles after the precursor powder is mixed with the positive electrode active material and heated;

FIG5 is a graph showing the decomposition potential of the coating agent;

FIG6 is a characterization of the element distribution of the positive electrode active material after forming the coating layer;

FIG7 is an XPS graph of the coated positive electrode material;

FIG8 is a graph showing the rate performance test of a battery prepared using the coating agent prepared in Example 1.

DETAILED DESCRIPTION

In order to further illustrate the present invention, the following describes in detail the all-solid-state battery positive electrode coating agent, preparation method and application provided by the present invention in combination with the embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

Example 1

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. At this time, the precursor was in a molten state.

In order to better contact with the positive electrode active material in the next step, the above-mentioned molten precursor is cooled to a solid, and then the above-mentioned coating agent precursor is crushed into a powder state with a particle size of 1 to 10 microns using a crusher. The scanning electron microscope spectrum of the powder is shown in Figure 1. It can be seen from Figure 1 that the coating agent precursor exists in the form of powder.

The XRD spectrum of the NaAlCl ₂ S coating agent precursor is shown in FIG2 .

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material NaNi _0.5 Mn _0.1 Ti _0.4 O ₂ (MN) by a grinder at a mixing speed of 60 rpm for 60 min.

The mixed material is shown in FIG3 . From the SEM image, it can be seen that the active material MN particles and the coating agent precursor particles are simply mixed together. The spherical particles are MN, and the dot-shaped particles are the coating agent precursor.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture is then heated at 350°C in an argon atmosphere to melt and flow the coating agent precursor, thereby coating the surface of the positive electrode active material. The changes in the positive electrode active material particles after heating are shown in Figure 4. It can be seen that after heating, the coating agent precursor is uniformly melted on the surface of the positive electrode active material, forming a uniform surface coating of the precursor on the positive electrode active material.

3. Formation of coating: The coating agent precursor has the characteristic of decomposing at a voltage above 3 V (vs Na). The decomposition potential test diagram is shown in FIG5 .

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 60 minutes. After standing, it was charged to 3.4V and left at this potential for 120 minutes. The coating agent precursor then decomposed to form a coating layer. The element distribution of the positive electrode active material after the coating layer was formed was characterized using EDS, as shown in Figure 6.

It can be seen that the target characteristic elements Cl, Al, and S are evenly distributed on the surface of the positive electrode particles and present a uniform surface coating.

XPS was used to characterize the coated positive electrode in the binding energy range of 540-515 eV, and a characteristic peak was found at 530 eV, corresponding to the vibration peak of the O-S bond (Figure 7). This proves that after coating using the method of the present invention, S can react in situ to enter the surface of the positive electrode particles to form O-S bonds, thereby avoiding the formation of O-S exchange products between the oxygen of the positive electrode particles and the sulfide electrolyte, thereby stabilizing the layered oxide.

Example 2

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace, heated to 230°C under vacuum conditions, and kept warm for 3 hours to generate a NaAlCl ₂ S coating agent precursor. In order to better contact with the positive electrode active material in the next step, the above molten precursor was cooled and crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.05% of the above mixture.

The mixture is then heated at 300° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

After heating, the coating agent precursor is uniformly melted on the surface of the positive electrode active material, forming a uniform coating of the positive electrode active material by the precursor.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3V, it was left at this potential for 90 minutes. After standing still, it was charged to 3.4V and left at this potential for another 60 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Example 3

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace, heated to 400°C under vacuum conditions, and kept warm for 3 hours to generate a NaAlCl ₂ S coating agent precursor. In order to better contact with the positive electrode active material in the next step, the above molten precursor was cooled and crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coated positive electrode active material:

First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder, with a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.2% of the above mixture.

The mixture is then heated at 400° C. in an argon atmosphere to cause the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.01C. When the positive electrode potential rose to 3.3V, it was left at this potential for 120 minutes. After standing still, it was charged to 3.4V and left at this potential for another 90 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Example 4

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace, heated to 330°C under vacuum conditions, and kept warm for 3 hours to generate a NaAlCl ₂ S coating agent precursor. After the above molten precursor was cooled, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.4% of the above mixture.

The mixture was then heated at 330° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.02C. When the positive electrode potential rose to 3.1V, it was left at this potential for 180 minutes. After standing, it was charged to 3.5V and left at this potential for another 180 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Example 5

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 380°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. In order to better obtain contact with the positive electrode active material in the next step, the coating agent precursor was crushed into a powder state with a particle size of 1 to 10 microns using a crusher after cooling.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture was then heated at 360° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.04C. When the positive electrode potential rose to 3.2V, it was left at this potential for 150 minutes. After standing still, it was charged to 3.5V and left at this potential for another 70 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Example 6

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 260°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. In order to better contact with the positive electrode active material in the next step, the coating agent precursor was crushed into a powder state with a particle size of 1 to 10 microns using a crusher after cooling.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.8% of the above mixture.

The mixture was then heated at 380° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.3V, it was left at this potential for 110 minutes. After standing still, it was charged to 3.3V and left at this potential for 120 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Example 7

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. At this time, the precursor was in a molten state.

In order to better contact with the positive electrode active material in the next step, after the molten precursor is cooled to a solid state, a crusher is used to crush the precursor of the coating agent into a powder state with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material NaCoO ₂ by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture is then heated at 350°C in an argon atmosphere to melt and flow the coating agent precursor, thereby coating the surface of the positive electrode active material. The coating agent precursor is uniformly melted on the surface of the positive electrode active material, forming a uniform planar coating of the precursor on the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 60 minutes. After standing still, it was charged to 3.4V and left at this potential for 120 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Example 8

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. At this time, the precursor was in a molten state.

In order to better contact with the positive electrode active material in the next step, after the molten precursor is cooled to a solid state, a crusher is used to crush the precursor of the coating agent into a powder state with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material NaNiO ₂ by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture is then heated at 350°C in an argon atmosphere to melt and flow the coating agent precursor, thereby coating the surface of the positive electrode active material. The coating agent precursor is uniformly melted on the surface of the positive electrode active material, forming a uniform planar coating of the precursor on the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 60 minutes. After standing still, it was charged to 3.4V and left at this potential for 120 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Comparative Example 1

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.01% of the above mixture.

The mixture was then heated at 350° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 60 minutes. After standing still, it was charged to 3.4V and left at this potential for another 60 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Comparative Example 2

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 5% of the above mixture.

The mixture was then heated at 350° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 60 minutes. After standing still, it was charged to 3.4V and left at this potential for another 60 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Comparative Example 3

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture was then heated at 280°C in an argon atmosphere to cause the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material. However, due to the low temperature, the coating agent failed to evenly coat the surface of the positive electrode active material particles, but formed an incomplete island coating.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 60 minutes. After standing still, it was charged to 3.4V and left at this potential for another 60 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Comparative Example 4

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture is then heated at 700°C in an argon atmosphere to cause the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material. The coating temperature is too high, and the positive electrode active material undergoes structural collapse due to high-temperature oxygen release.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 60 minutes. After standing still, it was charged to 3.4V and left at this potential for another 60 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Comparative Example 5

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture was then heated at 350° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate is 1C. When the positive electrode potential rises to 3.2V, it is left at this potential for 5 minutes. After standing, it is charged to 3.4V and left at this potential for 60 minutes. Then the coating agent precursor is decomposed to form a coating layer.

Comparative Example 6

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture was then heated at 350° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05 C. When the positive electrode potential rose to 4 V, it was left at this potential for 60 min.

Comparative Example 7

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture was then heated at 350° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05 C. When the positive electrode potential rose to 2.8 V, it was left at this potential for 60 min.

Comparative Example 8

1. Synthesis of coating precursor: NaCl, AlCl ₃ , Sb ₂ S ₃ were mixed in a ball mill at 400 rpm for 3 hours according to the chemical molar ratio of 3:3:1 to obtain a mixture of the above substances. The mixture was then placed in a vacuum tube furnace and heated to 350°C under vacuum conditions. After keeping the temperature for 3 hours, the NaAlCl ₂ S coating agent precursor was generated. After cooling, the coating agent precursor was crushed into a powder state using a crusher with a particle size of 1 to 10 microns.

2. Precursor coating of positive electrode active material: First, the precursor powder prepared in step 1 is mixed with the positive electrode active material MN by a grinder at a mixing speed of 60 rpm and a mixing time of 60 min.

In the mixed material, the active material MN particles and the coating agent precursor particles are simply mixed together.

The mass of the coating agent precursor accounts for 0.6% of the above mixture.

The mixture was then heated at 350° C. in an argon atmosphere to allow the coating agent precursor to melt and flow, thereby coating the surface of the positive electrode active material.

3. Formation of coating:

During the first week of charging, the charging rate was 0.05C. When the positive electrode potential rose to 3.2V, it was left at this potential for 5 minutes. After standing, it was charged to 3.4V and left at this potential for another 5 minutes. Then the coating agent precursor was decomposed to form a coating layer.

Comparative Example 9

MN without any treatment was used as an active substance.

Performance Testing

Full battery test

Cycle performance and rate performance test:

(1) Preparation of positive electrode sheet:

The sulfide solid electrolyte Na ₃ PS ₄ , the conductive agent Super P, the coated positive electrode material prepared above, and the binder PTFE were mixed in a mass ratio of 22:2:75:1 to prepare a positive electrode sheet.

(2) Assembly of sodium-ion all-solid-state batteries:

The solid electrolyte Na ₃ PS ₄ of sulfide was used, and the block made by pressing at 200 MPa was used as the electrolyte layer, and hard carbon was used as the negative electrode active material. The composition of the negative electrode sheet was hard carbon, Na ₃ PS ₄ and conductive carbon mixed in a mass ratio of 70:29:1.

The battery is assembled into a full battery structure of positive electrode plate/electrolyte layer/hard carbon, and the rate performance and cycle performance tests are carried out in the voltage range of 2 to 4V.

The rate performance test of the material prepared in Example 1 is shown in FIG8 below.

The first efficiency, rate performance and cycle performance of each embodiment and comparative example are shown in Table 1 below.

Table 1 First efficiency, rate performance and cycle performance of materials prepared in Examples 1-6 and Comparative Examples 1-9

It can be seen from Table 1 that:

The coating agent content in Comparative Example 1 is too low, resulting in incomplete coating and a significant decrease in cycle performance.

The coating agent content of Comparative Example 2 is too high, resulting in an overly thick coating layer, which affects the rate performance of the battery.

In comparative example 3, the coating treatment temperature was too low, so that the precursor of the coating agent could not be evenly coated on the positive electrode active material particles, forming an incomplete island coating, thereby increasing the contact risk between the electrolyte and the positive electrode active material, resulting in a significant decrease in the first efficiency and cycle performance.

In Comparative Example 4, the coating treatment temperature was too high, resulting in high-temperature oxygen release from the positive electrode active material, i.e., structural collapse of the positive electrode active material, which was the main reason for the serious reduction in subsequent performance.

In Comparative Example 5, the charging rate is too high and the standing time is too short during the in-situ decomposition of the coating agent precursor, so that the coating agent precursor fails to be completely and evenly decomposed and cracked, thereby causing a decrease in subsequent battery performance.

In Comparative Example 6, the static voltage during the in-situ decomposition of the coating agent precursor was too high, so that the coating agent precursor could not be fully converted into the target coating within the main decomposition voltage range.

In the process of in-situ decomposition of the coating agent precursor in Comparative Example 7, the static voltage is too low, and the purpose of in-situ decomposition of the coating agent precursor cannot be achieved.

In Comparative Example 8, the standing time during the in-situ decomposition of the coating agent precursor is too short, so that the coating agent precursor cannot be fully converted into the target coating within the main decomposition voltage range.

Comparative Example 9 is a positive electrode active material without any treatment.

The above embodiments are only used to help understand the method and core idea of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims (12)

1. An all-solid-state battery positive electrode coating agent, characterized in that: the molecular formula is NaAlCl ₂ S.

2. The method for preparing the all-solid-state battery positive electrode coating agent according to claim 1, characterized in that: the method comprises the following steps:

Mixing NaCl and AlCl ₃、Sb₂S₃, and performing high-temperature reaction to obtain NaAlCl ₂ S;

The molar ratio of NaCl to AlCl ₃、Sb₂S₃ is 3:3:1.

3. The preparation method according to claim 2, wherein the high temperature reaction is carried out at a temperature of 230-400 ℃ for a time of 1-3 hours;

The high temperature reaction is performed in an inert atmosphere or a vacuum atmosphere.

4. An all-solid-state battery positive electrode material, characterized in that: comprises an all-solid-state battery positive electrode active material and a coating layer coated on the surface of the all-solid-state battery positive electrode active material;

The coating layer comprises NaAlCl ₂ S.

5. The positive electrode material for all-solid battery according to claim 4, wherein the mass content of NaAlCl ₂ S in the positive electrode material for all-solid battery is 0.05% to 1%.

6. The all-solid-state battery cathode material according to claim 4, wherein the all-solid-state battery cathode material has a core-shell structure, wherein the all-solid-state battery cathode material is a core and the coating layer is a shell.

7. The method for producing an all-solid-state battery positive electrode material according to any one of claims 4 to 6, characterized in that: the method comprises the following steps:

And mixing the all-solid-state battery positive electrode active material with NaAlCl ₂ S, melting at high temperature, and coating the NaAlCl ₂ S on the surface of the all-solid-state battery positive electrode active material to obtain the all-solid-state battery positive electrode material.

8. The method according to claim 7, wherein the high-temperature melting temperature is 300 to 400 ℃ for 30 to 180 minutes;

the high temperature melting is performed in an inert atmosphere.

9. The method of manufacturing according to claim 7, wherein the all-solid-state battery positive electrode active material is selected from one or more of NaNi_0.5Mn_0.1Ti_0.4O₂、NaCoO₂、NaFePO₄、Na₂MnFe(CN)₆、NaCrO₂、NaNiO₂、NaNi_0.5Mn_0.5O₂、NaFeO₂.

10. An all-solid-state battery characterized by: an all-solid battery positive electrode material comprising the all-solid battery positive electrode material according to any one of claims 4 to 6 or the all-solid battery positive electrode material produced by the production method according to any one of claims 7 to 9.

11. The all-solid battery according to claim 10, wherein the all-solid battery is charged at the first cycle to decompose the all-solid battery positive electrode coating agent and form a coating layer on the surface of the all-solid battery positive electrode active material;

The coating layer comprises NaCl, naAlCl ₄ and Al ₂S₃.

12. The all-solid-state battery according to claim 11, wherein the first-week charging includes:

Allowing the all-solid-state battery to stand for 60-180 min under the condition that the charging multiplying power is 0.01-0.05 ℃ and the positive electrode potential is 3-3.3V;

Then standing for 30-180 min under the condition that the charging multiplying power is 0.01-0.05 ℃ and the positive electrode potential is 3.3-3.5V.