Corrosion-resistant crucible and method of making

Abstract

The application relates to the material field, in particular to a corrosion-resistant saggar, a preparation method and application. The raw material of the saggar comprises spinel, petalite, metal silicon, sodium zirconium phosphate, polyvinyl alcohol and water. The saggar provided by the application can replace the graphite saggar used by negative electrode materials, has low porosity, long service life, and greatly improved product performance-price ratio, and can effectively reduce the cost of production enterprises.

Description

Technical Field

[0001] This invention relates to the field of materials, and specifically to a corrosion-resistant crucible and its preparation method. Background Technology

[0002] Lithium-ion batteries generally consist of three parts: a positive electrode material, a negative electrode material, and an electrolyte solution. The positive electrode material mainly consists of lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4). The negative electrode primarily uses graphite.

[0003] In the production of lithium-ion battery anode materials, the conventional sagger is the graphite sagger. Due to environmental protection requirements and supply and demand, the price of graphite materials has increased significantly. The purchase price of a single 330*330*210 graphite sagger is between 1800 and 2400 yuan, which is very expensive. The processing fees and graphite purchase fees of the graphite sagger manufacturers alone reach this cost. The extracted center graphite is the profit. If it is not used, there is no profit. Many manufacturers have mountains of center blocks. The usage fee for anode material manufacturers is 170 to 200 yuan per unit per month. How to reduce production and usage costs has become one of the assessment indicators for production units.

[0004] In addition, the sintering temperature of the negative electrode material is between 1000 and 1100℃. The main component of the negative electrode material is graphitized needle-shaped petroleum coke. Other components are introduced to modify its surface. The binder is mainly resin and special asphalt. During the production process, tar and other sticky substances are easily generated, which adhere to the surface of the graphite crucible or stick together through the holes of the graphite crucible. They are not easy to clean and need to be cleaned every time. Sometimes the graphite crucible is broken during the cleaning process.

[0005] Therefore, manufacturers purchase graphite saggers made from high-purity, high-density, and low-porosity graphite. However, due to the characteristics of graphite, its melting point is very high, its shrinkage during sintering is small, and its porosity is high. Multiple dip-coating methods are used to improve density and reduce porosity, generally requiring three dips and four firings, resulting in high prices. Even then, the surface porosity remains at 10-15%, and for ultra-high density, the porosity is 8%. To solve this problem and reduce operating costs, those skilled in the art have combined surface glazing techniques used in coal coking to prevent coking at furnace doors and tar adhesion, applying a surface glaze to the cathode material sagger. This effectively solves the problem. However, during use, it was found that the glaze, due to its low temperature, exhibits glaze run-through after long-term use. Additionally, the glaze on the upper part and part of the exterior tends to adhere to the bottom roller conveyor. To address this newly emerging problem...

[0006] The crucible is prepared using ceramic technology. Ceramic materials have higher strength and a porosity as low as 0 compared to graphite. This can solve the problems of adhesion and peeling caused by the decomposition of organic materials in the negative electrode material and the infiltration of tar and other organic materials into the crucible. However, for long-term use at 1000-1100℃, better thermal shock resistance is required.

[0007] Therefore, this application uses spinel, metallic silicon, lithium feldspar and sodium zirconium phosphate fine powder as raw materials to prepare ceramic saggers, which solves the problems of pore penetration and anti-scraping, while having a good service life. Summary of the Invention

[0008] In order to improve the problems existing in the application of positive electrode material saggers in negative electrode materials, and at the same time reduce the cost of using negative electrode saggers, this application provides a corrosion-resistant sagger.

[0009] In one aspect, this application provides a corrosion-resistant sagger, the raw materials of which include: spinel, petalite, metallic silicon, sodium zirconium phosphate, polyvinyl alcohol and water.

[0010] Specifically, the raw materials for the sagger include the following components by weight: 40 parts spinel, 20-30 parts petalite, 20-30 parts metallic silicon, 8-12 parts sodium zirconium phosphate, 2-3 parts polyvinyl alcohol, and 80-120 parts water.

[0011] Preferably, the raw materials for the sagger include the following components in parts by weight: 40 parts spinel, 25 parts petalite, 25 parts metallic silicon, 10 parts sodium zirconium phosphate, 2.5 parts polyvinyl alcohol, and 100 parts water.

[0012] In the sagger:

[0013] The spinel is selected from sintered spinel or fused spinel, preferably fused spinel;

[0014] The lithium feldspar contains Li2O ≥ 4.0% (content not less than 4.0%), and has a fineness of <10% residue on a 320-mesh sieve.

[0015] The silicon content in the metallic silicon is ≥98%, and the particle size is 325 mesh.

[0016] The sodium zirconium phosphate content is ≥95%, and the particle size is 325 mesh.

[0017] (Note: The above particle size limits are for ease of preparation and do not impose any essential limitations on the product.)

[0018] Of the above components:

[0019] Spinel is a mineral composed of magnesium aluminum oxide. Because it contains elements such as magnesium, iron, zinc, and manganese, spinel has good resistance to erosion, abrasion, and thermal shock.

[0020] The chemical composition of petalite is Li[AlSi4O] 10 It belongs to the monoclinic crystal system, and the crystals are plate-like. Introducing petalite into the sagger further reduces the sagger expansion coefficient and improves the product's thermal shock resistance. It is widely used in the field of ceramic thermal shock resistance and can also lower the sintering temperature of the product.

[0021] Sodium zirconium phosphate exhibits near-zero expansion from room temperature to 1100℃. For sintered zirconium phosphate materials, the coefficient of thermal expansion decreases with increasing sintering temperature and duration, especially after sintering at 1400℃, where the percentage of negative expansion increases. Purity is greater than 95%.

[0022] Metallic silicon is used to achieve low-temperature sintering of spinel materials. Silicon nitride is produced by nitriding the surface of the crucible, encapsulating the metallic silicon within the crucible. The crucible has high thermal conductivity and strong resistance to thermal stress damage. Metallic silicon is a semi-metal with a melting point of 1420℃, and is hard and brittle. It is insoluble in acids at room temperature but readily soluble in alkalis. The properties of metallic silicon are similar to those of germanium, lead, and tin, exhibiting semiconductor properties. Its softening temperature is 900℃. The oxidation temperature of metallic silicon is affected by various factors, such as oxygen partial pressure, atmosphere, and the quality and morphology of the silicon material. Crystalline silicon and polycrystalline silicon have different oxidation temperatures; crystalline silicon has a higher oxidation temperature, generally above 1000℃, while polycrystalline silicon has a lower oxidation temperature, generally around 800℃. Furthermore, the quality and morphology of the silicon material also affect the oxidation temperature; for example, silicon with a higher impurity content has a higher oxidation temperature than silicon with a lower impurity content. Silicon and nitrogen begin to react at approximately 970–1000℃, and the reaction rate increases with increasing temperature. However, if the temperature rises rapidly above the melting point of silicon, the billet will collapse due to the melting of silicon.

[0023] Excessive silicon metal can cause deformation during use; spinel acts as a framework for the high-temperature phase to prevent deformation, but too much spinel will increase porosity; sodium zirconium phosphate mainly provides good thermal shock resistance; petalite should be used in moderation, otherwise the operating temperature will drop; polyvinyl alcohol acts as a binder, working together to construct the crucible.

[0024] Secondly, this application provides a method for preparing a corrosion-resistant sagger, comprising the following steps:

[0025] 1) Ball milling powder: spinel, metallic silicon, lithium feldspar, sodium zirconium phosphate, polyvinyl alcohol and water are ground and granulated in a ball mill to obtain sagger granulated material for later use.

[0026] 2) Pour the prepared sagger granulation material into the sagger mold, press it into shape, take it out, let it stand for 12-24 hours, and then dry it;

[0027] 3) Place the dried saggers into the kiln. Initially, sinter without nitrogen for 3-5 hours. Then, introduce nitrogen and sinter for 0.5-1 hour. Finally, slowly cool down.

[0028] In the above methods:

[0029] In step 1), the grinding time is 24-36 hours;

[0030] Granulation, spray granulation is preferred;

[0031] In step 2):

[0032] Drying conditions: time 24–72 hours, temperature 50–60℃.

[0033] In step 3):

[0034] Nitrogen-free sintering, with a sintering temperature of 1340–1370℃;

[0035] After nitrogen is introduced, the following conditions are maintained: nitriding gas pressure 0.02-0.04 MPa, O2 content in the furnace atmosphere less than 0.01%, and final nitriding temperature 1340-1370℃.

[0036] Thirdly, the present invention also provides a sagger for sintering the above-mentioned lithium battery anode material.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. The sagger provided in this application:

[0039] 1) The dense crucible prevents the penetration of organic media and material adhesion, resulting in a long product life;

[0040] 2) The sintering temperature of the negative electrode material is 1050 degrees Celsius. The metallic silicon in the sagger is in a plastic state and has good ductility properties like metal, which can effectively prevent the generation and propagation of cracks.

[0041] 3) Nitrogen protection is used in the production process of negative electrode materials. While the microcracks generated in the sagger stop propagating at the metal silicon material, the nitrogen in the kiln can enter from the microcracks and react with the metal silicon to generate silicon nitride, which can heal the cracks and has the characteristics of self-healing, thus improving the service life of the sagger.

[0042] 4) The sagger has high cold strength and a low breakage rate during use due to mechanized and automated operation.

[0043] 2. Experimental studies have shown that the sagger provided by this invention can replace the graphite sagger used in the preparation of negative electrode materials, with a service life exceeding 180 cycles. The product's cost-effectiveness is significantly improved, effectively reducing production costs for manufacturers. Attached Figure Description

[0044] Figure 1 The black particles in the middle are metallic silicon particles, which can undergo plastic deformation during the expansion process, thereby preventing crack propagation.

[0045] Figure 2 The middle 1234 are metallic silicon particles, which act as bridges to prevent crack propagation;

[0046] Figure 3 The central spherical shape is made of metallic silicon particles, which can undergo plastic deformation during the expansion process, causing the crack to deflect and thus extending the service life.

[0047] Figure 4 : This involves nitriding metallic silicon to generate silicon nitride, which promotes crack healing. Detailed Implementation

[0048] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0049] Examples and Comparative Examples: A Corrosion-Resistant Sagger

[0050] 1. Raw material formula: See Table 1

[0051] Table 1: Formulation of corrosion-resistant crucibles (unit: mg or g)

[0052]

[0053]

[0054] 2. Preparation method:

[0055] 1) Ball milling powder: Add spinel powder, metallic silicon powder, lithium feldspar, sodium zirconium phosphate, polyvinyl alcohol and water into a ball mill and grind for 24 hours. Spray granulation is then performed to obtain granulated powder for later use.

[0056] (The advantages of spray drying are: good fluidity during molding, which can fill every corner, and the particles have more polyvinyl alcohol binder on the surface, which binds them together during the pressing process, resulting in high strength of the green body.)

[0057] 2) After weighing the bundled material, pour it into the sagger mold, press it into shape, remove it from the mold, place it on the kiln car, and let it stand on the kiln car for 12 to 24 hours (for natural air drying and stress release). Then send it to the drying room to dry at a temperature of 50 to 60°C for 24 to 72 hours.

[0058] 3) Place the dried saggers into the nitriding kiln, close the kiln door, and evacuate the kiln. Initially, sintering is carried out without nitrogen at a temperature of 1340–1370℃ for 3–5 hours. Then, nitrogen gas is introduced at a pressure of 0.02–0.04 MPa, with an O2 content of less than 0.01% in the kiln atmosphere. The final nitriding temperature is 1340–1370℃, and the temperature is held for 0.5–1 hour. Then, the kiln is slowly cooled down until it is below 400℃, at which point the kiln door is opened and the saggers are removed from the kiln.

[0059] 3. Principle Explanation: Figure 1-4 This describes the relevant role of metallic silicon in the crucible.

[0060] Figure 1 This is a schematic diagram of the toughening effect of metal silicon particles through plastic deformation. The black particles in the middle are metal silicon particles, which can undergo plastic deformation during the expansion process, absorb stress, and thus prevent crack propagation.

[0061] Figure 2 This is a schematic diagram of metal silicon particle bridging toughening, where 1234 in the middle are metal silicon particles that play a bridging role to prevent crack propagation.

[0062] Figure 3 This diagram illustrates how silicon particles hinder crack propagation. The spherical shape in the center represents a silicon particle. During crack propagation, it can undergo plastic deformation or impede the crack from moving forward, causing the crack to deflect. Crack propagation requires greater stress, thus extending the service life.

[0063] Figure 4 The diagram illustrates crack healing. The negative electrode material is sintered in a nitrogen protective atmosphere at a sintering temperature of 1050℃. The crucible cracks, exposing the internal silicon metal to the crack surface. Nitrogen gas enters the crack, causing the silicon metal on the crack surface to nitride, generating silicon nitride to promote crack healing.

[0064] Test Example 1: Quality Assessment of Corrosion-Resistant Saggers

[0065] 1. Samples, see Examples 1-3 and Comparative Examples 1, 2, and 4.

[0066] 2. Data evaluation indicators and related standards:

[0067] 2.1 Test indicators and standards for density, flexural strength, porosity, etc. are shown in Table 2.

[0068] Table 2: Detection Indicators and Detection Methods

[0069] detection indicators unit Detection methods Standard value density <![CDATA[g / cm 3 ]]> GB / T30873—2014 2.7～3.0 Flexural strength MPa GB / T2997-2015 ≥60 Porosity ％ GB / T2997-2015 ≤2.0

[0070] 2.2 Service life:

[0071] Samples are prepared according to the configuration, and qualified samples are sent to the factory for trial use in the furnace. The cathode material manufacturer will test the appearance, size, and physicochemical indicators according to the company's internal quality requirements to confirm that the product will not have an adverse effect on its production. Then, it is arranged to be used in the production line in the workshop. Generally, one sintering cycle is about 24 hours. After one sintering is completed, the sagger is tested for cracking or peeling. If there are no problems, it continues to be used until the product cracks or peels and is scrapped. The service life of each sagger is calculated. Based on the number of samples of each sagger, the average number of uses is obtained as the service life of the sagger for each formula.

[0072] 3. Experimental results: See Table 3

[0073] Table 3: Results of each evaluation indicator

[0074]

[0075] Table 3 shows that the porosity of Comparative Example 2 was not within the standard value; in terms of porosity and service life, Examples 1-3 were superior to Comparative Examples 1, 2, and 4.

[0076] Comparative Example 3 was not formed. Polyvinyl alcohol was mainly used as a binder. Due to the lack of polyvinyl alcohol, there was no bonding force between the powder particles. Although it could be formed during the pressing process, the bonding force was very poor, making it impossible to demold. It would break upon demolding. Therefore, no relevant investigation data was available.

[0077] The results show that the sagger provided by the present invention can not only replace graphite in the preparation of negative electrode materials for lithium batteries, but also has low porosity and long service life.

[0078] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A corrosion-resistant sagger, characterized in that, The raw materials for the sagger include the following components by weight: 40 parts spinel, 20-30 parts petalite, 20-30 parts metallic silicon, 8-12 parts sodium zirconium phosphate, 2-3 parts polyvinyl alcohol, and 80-120 parts water.

2. The sagger according to claim 1, characterized in that, The raw materials for the sagger include the following components by weight: 40 parts spinel, 25 parts petalite, 25 parts metallic silicon, 10 parts sodium zirconium phosphate, 2.5 parts polyvinyl alcohol, and 100 parts water.

3. The sagger according to claim 1 or 2, characterized in that, The spinel is selected from sintered spinel or fused spinel.

4. The sagger according to claim 1 or 2, characterized in that, The spinel is an electrofused spinel.

5. The sagger according to claim 1 or 2, characterized in that, The Li2O content in the lithite is not less than 4.0%.

6. The method for preparing the sagger according to any one of claims 1-5, characterized in that, Includes the following steps: 1) Ball milling powder: spinel, metallic silicon, lithium feldspar, sodium zirconium phosphate, polyvinyl alcohol and water are ground and granulated using a ball mill to obtain crucible granulated material for later use. 2) Pour the prepared sagger granulation material into the sagger mold, press it into shape, take it out, let it stand for 12-24 hours, and then dry it; 3) Place the dried saggers into the kiln. Initially, sinter without nitrogen for 3-5 hours. Then, introduce nitrogen gas and maintain the temperature for 0.5-1 hour. Finally, slowly cool down.

7. The preparation method according to claim 6, characterized in that, In step 2), the drying conditions are: time is 24-72 hours, and temperature is 50-60℃.

8. The preparation method according to claim 6, characterized in that, In step 3): Nitrogen-free sintering, with a sintering temperature of 1340~1370℃; After nitrogen is introduced, the following conditions are maintained: nitriding gas pressure 0.02~0.04MPa, O2 content in the furnace atmosphere less than 0.01%, and final nitriding temperature 1340~1370℃.

9. The sagger according to any one of claims 1-5 is used for sintering lithium battery anode materials.

Images