Sheath for calcining precursor materials

Abstract

The present invention relates to a sheath for firing a precursor, and more specifically, to a sheath provided with a space for loading the precursor inside, which suppresses the generation of by-products when firing the precursor using the sheath and can improve the durability of the main body.

Description

[Technical Field]

[0001] The present invention relates to a precursor calcination sheath, more specifically, a sheath having a space inside into which a precursor is placed, which suppresses the generation of by-products when calcining a precursor using the sheath and improves the durability of the sheath itself. [Background technology]

[0002] Various inorganic compounds are produced through heat treatment (calcination) of precursor materials.

[0003] Typically, calcination of inorganic compound precursors is performed by placing the precursor in a heat treatment container (hereinafter referred to as "sheath") that has heat resistance and chemical resistance and then heat-treating it at a predetermined temperature.

[0004] At this time, the precursor material, which is the heat-treated compound (inorganic compound or its raw material), is placed inside the scabbard and is fired by heating without direct contact with flames, smoke, etc.

[0005] Therefore, the sheath must ensure the stability of the precursor material at the firing temperature, i.e., the predetermined heat resistance and chemical resistance.

[0006] A typical example of an inorganic compound produced through heat treatment of a precursor material is the positive electrode active material used in lithium batteries.

[0007] Compounds used as positive electrode active materials for lithium batteries include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, or composite oxides thereof (e.g., NCM, NCA-based lithium composite oxides).

[0008] In the case of positive electrode active materials, these transition metal-containing precursors and lithium-containing raw materials (e.g., LiOH) are charged into a casing and then heat-treated at a temperature of 600 to 1,200°C to produce the active material.

[0009] Therefore, the sheath used in the production of the positive electrode active material is manufactured primarily from highly heat-resistant ceramic materials such as cordierite, mullite, and spinel to ensure sufficient heat resistance within the aforementioned heat treatment temperature range.

[0010] On the other hand, in recent years, attention has been drawn to the problem of byproducts being generated in the pod due to a side reaction (see reaction equation below) between the lithium-containing raw material and the main component of the pod at the heat treatment temperature of the precursor material.

[0011] Specifically, lithium contained in lithium-containing raw materials such as LiOH and Li2CO3, which are introduced into the pod for calcination of the precursor material, can penetrate the pod during the calcination process and react with the pod's main components, such as Al2O3 and SiO2.

[0012] Through this penetration and reaction of lithium, Li x -(Al / Si) y -O z By-products such as these are formed.

[0013] Due to the mechanism described above, the thickness of the by-product layer deposited on the scabbard increases as the firing process using the scabbard is repeated.

[0014] The more a by-product layer is formed on the inner wall of the sheath, the more damage it can cause to the inner wall of the sheath, thereby shortening the strength and lifespan of the sheath.

[0015] Furthermore, the by-product layer may peel off during firing due to the difference in thermal expansion coefficients between it and the sheath, potentially causing contamination of the positive electrode active material.

[0016] To improve this, techniques have been introduced to reduce the likelihood of byproduct generation by eliminating Si-containing raw materials from the main components of the pod, or to reduce side reactions between the pod and lithium-containing raw materials by coating the inner wall of the pod with spinel or similar material.

[0017] However, when reducing the Si-containing raw material among the main components of a setter, the content of the Al-containing raw material must be increased. In this case, there are problems that the possibility of generating Al-derived by-products instead of Si-derived by-products increases, and the overall strength of the setter decreases due to the elimination or reduction of the Si-containing raw material among the main components of the setter.

[0018] In addition, apart from the problems caused by peeling, due to the characteristics of setters that are repeatedly exposed to high temperatures, there is a problem that the volume fluctuates due to temperature changes, and the accumulated stress induces cracks in the setter, thereby degrading the lifespan performance.

Prior Art Literature

Patent Literature

[0019]

Patent Literature 1

Patent Literature 2

Patent Literature 3

Summary of the Invention

Problem to be Solved by the Invention

[0020] An object of the present specification is to provide a setter having sufficient heat resistance under the temperature conditions applied during firing of an inorganic compound precursor.

[0021] Another object of the present specification is, unlike conventional setters, to reduce side reactions between the lithium-containing raw material charged into the setter and the main components of the setter, and to prevent Li x -(Al / Si) y -O z from generating by-products such as the above. It is to provide a setter capable of preventing generation of such by-products.

[0022] Another object of this specification is to provide a sheath that has sufficient strength to effectively withstand the pressure or high-temperature firing conditions applied to the inner wall of the sheath during pressing after the precursor material has been charged into the sheath.

[0023] Furthermore, yet another objective of this specification is to provide a sheath in which the problem of stress due to volume fluctuations of the sheath itself inducing cracks is resolved.

[0024] The objects of the present invention are not limited to those mentioned above, and other objects and advantages of the present invention not mentioned can be understood from the following description and will be more clearly understood from the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be achieved by the means and combinations thereof set forth in the claims. [Means for solving the problem]

[0025] According to one aspect of the present invention, a precursor calcination sheath is provided, which has a space inside into which a precursor is charged, wherein a protective layer having a spinel content of 50% by weight or more is formed on at least a part of the inner surface of the sheath into which the precursor is charged.

[0026] In one embodiment, the protective layer may further include at least one selected from corundum, mullite, petalite, spodumine, cordierite, quartz, and zircon.

[0027] As one example of various possibilities, the corundum content of the protective layer may be 25% by weight or less.

[0028] In other examples, the protective layer may be a spinel continuous phase matrix in which discontinuous phase aggregate is dispersed, the discontinuous phase aggregate containing at least one selected from corundum, mullite, petalite, spodumine, cordierite, quartz, and zircon.

[0029] In this case, the average particle diameter of the spinel base material may be 0.5 to 25 µm, and the average particle diameter of the aggregate may be 150 to 900 µm.

[0030] In one embodiment, the thickness of the protective layer may be 2.5 to 4.0 mm.

[0031] In one of the aforementioned examples, the saggar may be obtained by sintering a raw material containing petalite.

[0032] In this case, the saggar may be obtained by sintering a raw material in which discontinuous-phase aggregate containing at least one selected from the group consisting of spinel, corundum, mullite, cordierite, quartz and zircon is dispersed in a petalite continuous-phase base matrix.

[0033] In addition, the content of petalite in the raw material may be 20 to 40% by weight.

[0034] Furthermore, the saggar may contain 20 to 50% by weight of a solid solution containing β-spodumene and SiO₂.

Effects of the Invention

[0035] The saggar for firing precursors according to various embodiments of the present specification includes a ceramic material having sufficient heat resistance, and thus has an advantage that it can be used repeatedly in the step of firing a precursor of an inorganic compound.

[0036] In addition, the saggar for firing precursors according to various embodiments of the present specification includes a protective layer with low reactivity with lithium in at least a part of an internal space where the precursor is charged, and the ceramic material reacts with a lithium-containing raw material to form Li x- (Al / Si) y -O z side reactions that generate by-products such as the above can be minimized, and there is an advantage that the service life of the saggar can be extended compared to conventional saggars.

[0037] Furthermore, the aforementioned precursor calcination sheath has sufficient strength, generates little stress even during repeated temperature changes, and minimizes crack formation in the sheath, thus offering the advantage of excellent durability.

[0038] In addition to the effects described above, the specific effects of the present invention will be described below, along with explanations of specific matters for carrying out the invention. [Modes for carrying out the invention]

[0039] For the convenience of understanding the present invention, certain terms are defined herein. Unless otherwise defined herein, scientific and technical terms used herein have the meanings generally understood by those ordinary in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms.

[0040] Furthermore, unless otherwise specified in this application, each characteristic may be measured based on 25°C and 1 bar.

[0041] The precursor calcination scabbard described herein will be explained in more detail below.

[0042] Pod protective layer According to one aspect of the present invention, a precursor calcination sheath is provided, which has a space inside into which a precursor is charged, wherein a protective layer having a spinel content of 50% by weight or more is formed on at least a part of the inner surface of the sheath into which the precursor is charged.

[0043] A sheath is a type of refractory container used to manufacture a desired product by preventing direct contact with flames, smoke, etc., and by firing the precursor material.

[0044] Therefore, the shape of the sheath is not limited to a rectangular prism, cylindrical shape, elliptical shape, etc., as long as it has a space inside into which a precursor material can be inserted, and may be used in a variety of ways depending on the purpose.

[0045] Examples of such precursor materials include lithium-based oxides used to manufacture cathode active materials.

[0046] Generally, the precursor for producing a positive electrode active material may include at least one of cobalt, nickel, manganese, and iron, and lithium, and a lithium-based composite oxide may be formed by calcination and used as a positive electrode active material.

[0047] During this firing process, lithium can penetrate the pod and react, resulting in a problem where the pod's components deteriorate and peel off.

[0048] To minimize the manufacturing costs of the final fired product, the casings must be reused repeatedly. However, casings that have delaminated can degrade the performance of the product and are either impossible or extremely difficult to reuse.

[0049] According to one aspect of this specification, this problem can be mitigated by forming a lithium-reactive protective layer on at least a portion of the inner surface of the inner space of the casing into which the precursor material is charged.

[0050] In other words, the sheath may have a double structure in which at least a part consists of a main body and a protective layer.

[0051] As an example of such a pod, a protective layer can be formed on the bottom surface of the internal space of the pod, allowing lithium to penetrate more easily due to the action of gravity, but this is not the only example.

[0052] Since the sheath must be repeatedly exposed to high-temperature firing processes, it may be manufactured from a ceramic material with a high melting point.

[0053] Ceramic materials are compounds formed by the bonding of metallic elements such as silicon (Si), aluminum (Al), titanium (Ti), zirconium (Zr), and magnesium (Mg) with nonmetallic or quasimetallic elements such as oxygen, carbon, and nitrogen through high-temperature heat treatment.

[0054] For example, the ceramic material constituting the precursor firing sheath of this invention is Al2O3, MgO, SiO2, K2O, ZrO, ZrO2, CaO, Fe x O y It may include various materials known as materials for constructing the sheath, such as those mentioned above.

[0055] In addition to the chemical composition represented by the aforementioned chemical formula, the properties of ceramic materials can vary depending on the form they form, that is, the type of mineral phase.

[0056] Examples of mineral phases of ceramic materials that can be used for sheaths in this specification include spinel, corundum, mullite, cordierite, spodumene, zircon, quartz, petalite, eucryptite, lithium disilicate, lithium metasilicate, forsterite, magnesium metasilicate, alumina, and silicate.

[0057] The general forms of these materials are described below, but are not limited to them. For example, the thermal expansion coefficients of each component are exemplary values ​​measured in the temperature range of 25°C to 800°C.

[0058] Spinel is a mineral with an isometric crystal system represented as MgO·Al2O3, for example, approximately 6.72 × 10⁻⁶ -6It may have a thermal expansion coefficient of / °C.

[0059] Corundum is a mineral with a hexagonal crystal structure represented as Al2O3, for example, approximately 7.26 × 10⁻⁶ -6 It may have a thermal expansion coefficient of / °C.

[0060] Mullite is a tetragonal crystal mineral represented as 3Al2O3·2SiO2, for example, approximately 5.84 × 10⁻⁶ -6 It may have a thermal expansion coefficient of / °C.

[0061] Cordierite is a tetragonal crystal mineral represented as 2MgO·2Al2O3~5SiO2, for example, approximately 1.76 × 10⁻⁶ -6 It may have a thermal expansion coefficient of / °C.

[0062] Spodumine is represented as Li2O·Al2O3·nSiO2 and is divided into monoclinic α-spodumine and tetragonal β-spodumine depending on the formation temperature, for example, approximately 0.44 × 10⁻⁶ -6 It may have a thermal expansion coefficient of / °C.

[0063] Zircon is a tetragonal crystal phase represented by ZrO2·SiO2, for example, approximately 2.03 × 10⁻¹⁴ -6 It may have a thermal expansion coefficient of / °C.

[0064] Quartz is a hexagonal crystal phase represented by SiO2, for example, approximately 7.64 × 10¹⁶ -6 It may have a thermal expansion coefficient of / °C.

[0065] These minerals can react with lithium and degrade into phases such as Li4SiO4, β-LiAlO2, γ-LiAlO2, and MgO.

[0066] Such a deterioration phase can reduce the bonding strength between components, potentially leading to sheath separation.

[0067] Specifically, when the precursor material is calcined using the aforementioned sheath, lithium from the lithium-containing raw material (such as LiOH) contained in the precursor material permeates into the sheath, and Li penetrates to the inside of the sheath. x -(Al / Si)) y -O z Impurities represented by a composition like this can be deposited.

[0068] By repeatedly using the aforementioned sheath, an impurity layer (or degradation layer) of a predetermined thickness may be formed on the inside of the sheath, particularly on the bottom surface.

[0069] If cracks occur in the impurity layer generated in this way, or if the impurity layer peels off from the scabbard, not only may the firing quality using the scabbard deteriorate rapidly, but the scabbard may also become unusable.

[0070] Therefore, in order to suppress the reaction in which lithium from the lithium-containing raw material (such as LiOH) contained in the precursor penetrates the sheath and forms impurities, it is preferable that the base material forming the protective layer of the internal space of the sheath into which the precursor is charged does not contain SiO2, or that the proportion of the phase containing SiO2 in the base material is half or less.

[0071] As a result, the reactivity of the base material of the protective layer to lithium may be less than the reactivity of the aggregate material of the protective layer to lithium.

[0072] Of the aforementioned components, spinel, mullite, cordierite, zircon, quartz, spodumine, and corundum become increasingly reactive with lithium in that order. This allows for adjustment of the composition of the protective layer, thereby suppressing sheath peeling.

[0073] In this specification, among the ceramic materials used for the sheath, spinel has the lowest lithium reactivity, and the protective layer contains 50% by weight or more of spinel, which can improve the problem of the sheath easily peeling off when the firing process is repeated.

[0074] For example, the protective layer may contain 50% or more by weight of spinel, preferably 50-85% by weight, which can improve the peel resistance of the sheath.

[0075] In one example, the protective layer may further contain, in addition to 50% by weight or more of spinel, at least one selected from corundum, mullite, petalite, spodumine, cordierite, quartz, and zircon.

[0076] In this way, the protective layer contains various components in addition to spinel, minimizing the difference in thermal expansion coefficient between it and the main body of the sheath.

[0077] For example, if the thermal expansion coefficient of the sheath body is 4.0 × 10 -6 If the temperature is / °C, the protective layer has a thermal expansion coefficient of 6.72 × 10⁻⁶. -6 It may be formed by mixing spinel with a temperature of / °C with a component having a relatively low coefficient of thermal expansion.

[0078] If there is a large difference in the coefficient of thermal expansion between the main body of the sheath and the protective layer formed on it, the lifespan of the sheath may be reduced, as stress formed in the protective layer or the main body during repeated firing processes can cause cracks to form.

[0079] Therefore, the difference in thermal expansion coefficients between the protective layer and the main body is 1.5 × 10⁻⁶. 6 Below / ℃, preferably 1.0 × 10 -6 / ℃ or lower, more preferably 0.5 × 10 -6 It may be below / ℃, but is not limited to this.

[0080] Furthermore, by adjusting the composition of the protective layer to increase its thermal conductivity, the efficiency of firing can be improved.

[0081] Since the scabbard is heat-treated in a kiln or similar device with the precursor material inside, if the thermal conductivity of the protective layer in direct contact with the precursor material is high, heat can be efficiently transferred to the precursor material.

[0082] On the other hand, in addition to the deterioration of the casing due to lithium penetration and reaction, the impacts applied by pressurization during the charging of precursor materials and volume changes during sintering can also reduce the lifespan of the casing.

[0083] Therefore, in another example, the mechanical strength of the sheath can be increased by adjusting the composition of the protective layer.

[0084] Furthermore, other components of the protective layer, excluding spinel, may be added to improve the bonding strength between the protective layer and the main body of the sheath.

[0085] As one example of various possibilities, the corundum content of the protective layer may be 25% by weight or less, and if corundum is included, the content may be 5 to 25% by weight, preferably 7.5 to 20% by weight.

[0086] If the protective layer contains corundum, its content may exceed 25% by weight, which may reduce the sheath's peel resistance.

[0087] In other examples, the protective layer may be a spinel continuous phase matrix in which discontinuous phase aggregate is dispersed, the discontinuous phase aggregate containing at least one selected from corundum, mullite, petalite, spodumine, cordierite, quartz, and zircon.

[0088] During the calcination of the precursor material, components with a small average particle size that make up the sheath are highly reactive with lithium, so spinel can be used as the base material for the protective layer, while other components can be used as aggregates with a relatively larger average particle size.

[0089] If the protective layer is in the form described above, fine powder base material may be filled between aggregates with a large average particle size.

[0090] As a result, during the sintering of the sheath, the base material and aggregate of the protective layer can bond to each other or to each other individually to form a dense structure.

[0091] Such a dense structure can suppress peeling phenomena due to lithium penetration and reaction, provide excellent impact resistance to the protective layer, and prevent the sheath from being damaged during the calcination of the precursor material.

[0092] Thus, by having aggregates and base materials with different average particle sizes in a mixed state in the protective layer of the precursor calcination sheath according to this specification, the porosity of the protective layer can be reduced and the specific gravity increased.

[0093] When the porosity of the protective layer is low, the possibility of lithium originating from the lithium-containing raw material in the precursor material penetrating the sheath may also be reduced by firing the precursor material using the sheath.

[0094] As an example of a protective layer composition that can form a dense structure, the average particle size of the spinel matrix material may be 0.5 to 25 μm, and the average particle size of the aggregate material may be 150 to 900 μm, but is not limited to this.

[0095] The method for producing particles having such particle size is not limited, and depending on the type of raw material and the desired properties, methods such as evaporation-condensation, chemical vapor deposition, gas-phase thermal decomposition, gas-phase reduction, coprecipitation, hydrolysis, spray drying, freeze-drying, thermal decomposition, reduction, solid-phase reaction, sublimation, and solution methods may be used.

[0096] In one example, a spinel matrix with a small average particle size can be obtained by pulverizing the raw material through various grinding methods.

[0097] For example, raw materials can be ground using grinding methods such as ball mills, pebble mills, rod mills, roller mills, colloid mills, impact mills, and jet mills.

[0098] In one embodiment, if the thickness of the protective layer is too thin or too thick, the peel resistance may decrease.

[0099] Although the mechanism is not clearly understood, if the thickness of the protective layer is too thin, lithium may pass through the protective layer and penetrate into the main body of the sheath, reducing the bonding force with the protective layer and causing delamination.

[0100] Conversely, if the thickness of the protective layer is too thick, the protective layer may not be sintered sufficiently, resulting in insufficient formation of a dense structure, allowing lithium to penetrate more easily and potentially causing delamination.

[0101] Therefore, preferably, the thickness of the protective layer may be 2.5 to 4.0 mm.

[0102] Saya's body The body of the sheath according to one embodiment of this specification may be made of a ceramic material, as described above.

[0103] Examples of the mineral phases of ceramic materials mentioned above include spinel, corundum, mullite, cordierite, spodumine, zircon, quartz, petalite, eucryptite, lithium disilicate, lithium metasilicate, forsterite, magnesium metasilicate, alumina, and silicate.

[0104] These materials, even if they have similar chemical compositions, may have different rates of volume change due to temperature fluctuations.

[0105] In the calcination process of precursor materials using sheaths, in addition to delamination due to lithium penetration and reaction, cracks caused by repeated thermal shock can also act as one of the factors that determine the lifespan of the sheath.

[0106] For example, when the precursor material is fired and expands, pressure is applied to the casing, especially the walls, which can cause cracks to form.

[0107] Furthermore, cracks may occur due to the difference in thermal expansion coefficients between the protective layer and the main body.

[0108] As another example, volume changes of each component within the main composition of the sheath can act as a cause of cracking.

[0109] To minimize the occurrence of such cracks, a scabbard made from a sintered material containing petalite may be used.

[0110] Specifically, the main body of the sheath may be a spodumine phase sintered from a petalite-containing raw material, and may also contain β-spodumine.

[0111] The spodumine phase is susceptible to lithium penetration and reaction, and repeated calcination reactions of the precursor material when applied alone can cause sheath peeling. However, as mentioned above, a protective layer with excellent resistance to lithium reactivity can be formed to suppress the reduction in sheath life due to peeling.

[0112] The main body of the sheath may further contain components such as spinel, corundum, mullite, cordierite, spodumine, zircon, quartz, eucryptite, lithium disilicate, lithium metasilicate, forsterite, magnesium metasilicate, alumina, and silicate, in addition to petalite, and may be adjusted to have a coefficient of thermal expansion at a similar level to that of the protective layer mentioned above.

[0113] The difference in thermal expansion coefficients between the main body of the sheath and the protective layer is 1.5 × 10⁻⁶. -6 Below / ℃, preferably 1.0 × 10 -6 / ℃ or lower, more preferably 0.5 × 10 -6 The temperature may be adjusted to below / ℃, but is not limited to this.

[0114] On the other hand, the main body of the sheath may be composed of aggregate and base material, each having a specific coefficient of thermal expansion.

[0115] Although the aforementioned sheath is mainly used under high-temperature firing conditions, if the thermal expansion coefficient of the ceramic material used as aggregate and base material is large, the volume change rate before and after firing may be excessively large, which can cause cracks in the sheath.

[0116] Therefore, it is preferable that at least one of the aggregate and the base material constituting the main body of the sheath, or at least one of the ceramic material used as the aggregate and the base material, has a relatively small coefficient of thermal expansion.

[0117] The coefficient of thermal expansion of such base material or aggregate material may vary depending on the component composition of the sheath and the absolute magnitude of its coefficient of thermal expansion.

[0118] For example, in one example of the present invention, a sheath can be formed using aggregate whose thermal expansion coefficient is relatively smaller than that of the base material.

[0119] Since the aggregate exists as a discontinuous phase in the continuous phase matrix made up of the base material, if the coefficient of thermal expansion of the aggregate is large in a sheath of this type, the volume may change locally in some areas of the sheath, causing stress to form.

[0120] In general, ceramic materials containing SiO2 in their crystalline structure may have a lower coefficient of thermal expansion than ceramic materials that do not contain SiO2 in their crystalline structure.

[0121] However, as mentioned above, SiO2 can react with lithium-containing raw materials to form byproducts, so oxides containing SiO2 in the crystalline structure are more suitable as aggregate than as the base material.

[0122] In such a sheath, a ceramic material containing SiO2 in its crystalline structure, excluding petalite, may be used as the aggregate.

[0123] Furthermore, if the aggregate contains a high amount of ceramic material with SiO2 in its crystalline structure, the reactivity with lithium-containing raw materials may similarly increase.

[0124] Therefore, the formation of by-products can be suppressed by adjusting the content of the ceramic material containing SiO2 in the aggregate to an appropriate range, or by adjusting the content of the aggregate relative to the base material to an appropriate range.

[0125] On the other hand, in another example of the present invention, the sheath may be formed using a base material whose thermal expansion coefficient is relatively smaller than that of the aggregate.

[0126] In such a sheath, the occurrence of cracks in the sheath can be reduced by using a base material with a small rate of volume change at high temperatures to mitigate stress concentration in the continuous phase matrix.

[0127] In this type of sheath, there is a high possibility that a degradation layer will form due to lithium penetration and reaction, so it is necessary to form a protective layer as described above.

[0128] In other words, to manufacture a sheath using fetalite containing SiO2 in its crystalline structure as the base material, it is necessary to form a protective layer with low reactivity to lithium to improve peel resistance, as mentioned above.

[0129] In one embodiment of this specification, the sheath may be sintered from a raw material in which a discontinuous phase aggregate containing at least one selected from spinel, corundum, mullite, cordierite, quartz, and zircon is dispersed in a continuous phase matrix containing petalite.

[0130] Thus, by having the main body of the precursor calcination sheath according to this specification contain a mixture of aggregate and base material with different average particle size ranges, the porosity of the sheath body can be reduced and the specific gravity increased.

[0131] If the porosity of the main body of the sheath is low, the calcination of the precursor using the sheath can reduce the possibility that lithium derived from the lithium-containing raw material contained in the precursor that has passed through the protective layer will penetrate into the main body of the sheath.

[0132] As a result, even when using petalite raw materials that are highly reactive with lithium, the reduction in the lifespan of the sheath due to peeling can be minimized.

[0133] Furthermore, by increasing the specific gravity of the sheath body, it becomes possible to provide sufficient strength to withstand the pressure applied to the inner wall of the sheath during pressing after the precursor material has been loaded into the sheath.

[0134] In one example, the average particle size of the raw materials forming the continuous phase matrix may be 0.5 to 25 μm, and the average particle size of the raw materials forming the discontinuous phase aggregate may be 150 to 900 μm, but is not limited to these.

[0135] When petalite is included as a raw material for the continuous phase matrix, the occurrence of cracks in the sheath due to volume changes in the sheath body at high temperatures can be minimized.

[0136] Other components with relatively large volume change rates may be used in combination with components that can compensate for the volume change rate.

[0137] For example, components that expand in volume at the temperature during the firing process can be mixed with components that contract in volume to minimize the overall volume change.

[0138] On the other hand, the spodumine phase formed from petalite may have a lower coefficient of volume expansion than that formed from α-spodumine.

[0139] Specifically, the petalite may be converted into a solid solution containing β-spodumine and SiO2 during the sintering process of the sheath.

[0140] Such solid solutions have a low rate of volume change within the temperature range in which the precursor material is calcined, thus reducing the problem of cracks occurring in the sheath due to stress caused by volume change.

[0141] Specifically, the spodumine phase derived from petalite has a volume change rate of 0.020% or less in the range of 25 to 1,200°C, while the structure derived from α-spodumine may have a volume change rate exceeding 0.1% in the range of 25 to 1,200°C.

[0142] The petalite content in the above raw material may be 20 to 40% by weight, preferably 25 to 35% by weight, and more preferably 30 to 33% by weight.

[0143] When the petalite content in the raw materials meets the aforementioned range, the crack resistance performance of the sheath can be significantly improved.

[0144] Furthermore, the sheath may contain 20 to 50% by weight of a solid solution containing β-spodumine and SiO2.

[0145] While the solid solution can be formed by sintering petalite raw materials, other methods can also be used to form a solid solution containing β-spodumine and SiO2, thereby improving the crack resistance of the sheath.

[0146] In the solid solution, the molar ratio of Li2O·Al2O3 to SiO2 may be 1:7 to 9. If the molar ratio deviates from this range, the rate of volume change at high temperatures may increase, and the crack resistance of the sheath may decrease.

[0147] pod manufacturing method The sheaths described herein can be manufactured by mixing ceramic material raw materials, molding them into a predetermined shape, and then heat-treating them.

[0148] Among the raw materials, the base material may have an average particle size of 0.5 to 25 μm, and the aggregate may have an average particle size of 150 to 900 μm, but is not limited to these.

[0149] The method for producing particles having such particle size is not limited, and depending on the type of raw material and the desired properties, methods such as evaporation-condensation, chemical vapor deposition, gas-phase thermal decomposition, gas-phase reduction, coprecipitation, hydrolysis, spray drying, freeze-drying, thermal decomposition, reduction, solid-phase reaction, sublimation, and solution methods may be used.

[0150] Base materials with a small average particle size may be pulverized through various grinding methods before use. For example, grinding methods such as ball mills, pebble mills, rod mills, roller mills, colloid mills, impact mills, and jet mills can be utilized.

[0151] Here, the method of mixing the raw materials is not limited to any method that can uniformly mix the raw materials, such as a dry mixing method in which the powders are mixed directly, or a wet mixing method in which the powders are slurryed before mixing.

[0152] Furthermore, the raw materials may be mixed in a form that further includes organic binders such as binders to facilitate molding.

[0153] In such cases, the type of organic binder is not limited, as long as it can be removed by a high-temperature heat treatment process.

[0154] In this case, the amount of organic binder used is not limited, as long as it is sufficient to provide the necessary level of bonding strength without adversely affecting the physical properties of the pod after removal in the heat treatment process.

[0155] Alternatively, the mixed raw materials may be molded into a predetermined shape to produce the aforementioned form of pod.

[0156] For example, it may be formed into a columnar shape with an internal space by applying pressure through a press.

[0157] In one example, the protective layer inside the sheath may be provided by molding the raw materials for the sheath body and the raw materials for the protective layer together.

[0158] For example, the method is not limited to laminating the raw materials for the sheath body and the raw materials for the protective layer and then pressing them, or laminating the raw materials for the protective layer after pressing the sheath body, or applying the raw materials for the protective layer after pressing the sheath body, or laminating and pressing the raw materials for the protective layer after pressing the sheath body.

[0159] The pods may also be manufactured by sintering the molded pod raw materials through heat treatment.

[0160] At this time, the heat treatment temperature of the raw materials may be adjusted according to the composition of the raw materials of the pod, for example, it may be 1,150 to 1,800°C.

[0161] The sintering temperature can vary depending on the chemical composition and phase of the raw materials, and phase changes can occur depending on the sintering temperature.

[0162] Therefore, the heat treatment temperature can vary depending on the desired final pod composition and phase.

[0163] The heat treatment may be performed once or multiple times.

[0164] If the aforementioned heat treatment is performed multiple times, the phase of the sheath may be adjusted by varying the temperature and time for each stage.

[0165] The sheaths produced through such heat treatment may be used directly, or they may be used after further forming a coating layer or the like.

[0166] The present invention will be described in more detail below through examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0167] Experimental Example 1. Evaluation of crack resistance properties based on the composition of the sheath body. To evaluate the crack resistance characteristics based on the main body composition, the raw materials were hydraulically press-molded and then sintered at 1,250°C to produce sheaths with the compositions shown in Table 1 below.

[0168] In this example, Comparative Example 2 used α-spodumine as the base material, while Examples 1 and 2 used petalite as the base material.

[0169] The α-spodumine (Li2O·Al2O3·4SiO2; monoclinic) and petalite (Li2O·Al2O3·8SiO2) added as raw materials all underwent a phase change to β-spodumine (Li2O·Al2O3·4SiO2; tetragonal) during the sintering process.

[0170] [Table 1]

[0171] After charging each scabbard with the same type of lithium composite oxide, the chambers were fired in an O2 atmosphere, increasing the temperature by 2°C per minute to 780°C for 12 hours.

[0172] This firing process is repeated until just before the cycle in which the scabbard becomes unusable due to cracking. The number of cycles was determined as the crack resistance life, and is shown in Table 2 below.

[0173] [Table 2]

[0174] Referring to Table 2, the crack resistance of Examples 1 and 2, in which petalite was added during the manufacturing of the sheath body, was superior to that of the comparative example.

[0175] In particular, it can be confirmed that Comparative Example 2 has a crack resistance life at the same level as Comparative Example 1, unlike Examples 1 and 2, which exhibited excellent crack resistance even in the presence of the spodumine phase.

[0176] Although the mechanism of action is not clearly understood, it is expected that petalite with a high SiO2 content forms a solid solution with β-spodumine and SiO2, minimizing volume changes at high temperatures and resulting in excellent crack resistance.

[0177] Experimental Example 2. Evaluation of Lithium Reactivity of Raw Materials LiOH may melt at 450°C and be lithiumized as shown in the following reaction equation.

[0178] Therefore, after mixing the components of the pod with LiOH, the lithium reactivity of each raw material can be confirmed by calcining at 450°C.

[0179] [Reaction Equation] 2LiOH → Li2O + H2O

[0180] Spinel, mullite, cordierite, zircon, quartz, petalite, and corundum were each sintered at 1,250°C, and then mixed with LiOH in a 1:4 weight ratio.

[0181] The mixture was heated to 450°C at a rate of 2.5°C per minute for 5 hours, and then the lithium reactivity of the raw materials was evaluated by XRD phase analysis, as shown in Table 3 below.

[0182] [Table 3]

[0183] The lithium reactivity was evaluated according to the rate at which it degrades with LiOH and undergoes phase changes to Li4SiO4, β-LiAlO2, γ-LiAlO2, MgO, etc. The results confirmed that spinel exhibits the lowest reactivity.

[0184] Corundum exhibiting the highest lithium reactivity was prepared with varying average particle sizes, and then mixed with LiOH in a 1:4 weight ratio.

[0185] The mixture was heated to 450°C at a rate of 2.5°C per minute for 1 hour, and then the lithium reactivity of corundum based on average particle size was evaluated by XRD phase analysis, as shown in Table 4 below.

[0186] [Table 4]

[0187] Referring to Table 4, it can be confirmed that lithium reactivity decreases as the average particle size of the raw material increases. Furthermore, when particles belonging to the range of 150-900 μm, which are larger than the corundum in Table 4, were used and calcined under the same conditions, no lithium reaction was observed.

[0188] According to the results described above, the lifespan of the sheath can be increased by using raw materials with relatively low lithium reactivity as the base material for the fine powder and raw materials with high lithium reactivity as aggregate with a large average particle size.

[0189] Experimental Example 3. Evaluation of peel resistance properties using a sheath protective layer. In Example 2, the raw materials were stacked in two layers so that a protective layer having the composition shown in Table 5 below was formed on the bottom surface of the internal space of the sheath into which the positive electrode precursor was charged. After forming the sheath with a hydraulic press, it was sintered at 1,250°C to produce the sheath.

[0190] [Table 5]

[0191] After charging each scabbard with the same type of lithium composite oxide, the chambers were fired in an O2 atmosphere, increasing the temperature by 2°C per minute to 780°C for 12 hours.

[0192] This firing process is repeated, and the cycle immediately preceding the one in which the scabbard becomes unusable due to peeling of the bottom surface is determined as the peeling resistance life, as shown in Table 6 below.

[0193] [Table 6]

[0194] Referring to the results of Experimental Example 2 and Table 6, in Comparative Example 1, which lacked a separate protective layer, 14.36% of the total floor surface area peeled off after the 5th firing process due to lithium penetration and reaction, making the sheath unusable. On the other hand, all examples in which a protective layer with a spinel content of 50% by weight or more was formed were confirmed to have a peel resistance life of 8 or more firings.

[0195] This demonstrates that a double-layer structure can be formed on the bottom surface of the sheath that comes into contact with the charged lithium composite oxide, providing a protective layer with low lithium reactivity and thus enabling the production of a sheath with excellent peel resistance.

[0196] In the sheath of Example 3, the thickness of the protective layer was varied, and the peel resistance life was measured, as shown in Table 7 below.

[0197] [Table 7]

[0198] Referring to Table 7, it can be seen that if the protective layer is too thin or too thick, the peel resistance life will decrease.

[0199] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A sheath having a space inside into which a precursor material is inserted, In the aforementioned sheath, a protective layer having a spinel content of 50% by weight or more is formed on at least a portion of the inner surface into which the precursor material is inserted. The protective layer further comprises at least one selected from corundum, mullite, petalite, spodumine, cordierite, quartz, and zircon. The protective layer is a continuous spinel matrix in which discontinuous aggregate containing at least one selected from corundum, mullite, petalite, spodumine, cordierite, quartz, and zircon is dispersed. A scabbard for calcining precursor materials, wherein the average particle size of the spinel matrix is ​​0.5 to 25 μm, and the average particle size of the aggregate is 150 to 900 μm.

2. The precursor calcination sheath according to claim 1, wherein the corundum content of the protective layer is 25% by weight or less.

3. The precursor calcination sheath according to claim 1, wherein the thickness of the protective layer is 2.5 to 4.0 mm.

4. The aforementioned sheath is a precursor calcination sheath according to any one of claims 1 to 3, wherein the sheath is made by sintering a raw material containing petalite.

5. The precursor firing sheath according to claim 4, wherein the sheath is sintered from a raw material in which discontinuous aggregate containing at least one selected from spinel, corundum, mullite, cordierite, quartz, and zircon is dispersed in a continuous phase matrix containing petalite.

6. The precursor calcination sheath according to claim 4, wherein the petalite content in the raw material is 20 to 40% by weight.

7. The aforementioned pod contains β-spodumine and SiO ２ A precursor calcination sheath according to claim 4, comprising 20 to 50% by weight of a solid solution containing the above.

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