JP7497115B2 - Lithium disilicate-containing lithium-containing silicon oxide and method for producing same - Google Patents

Description

The present invention relates to lithium disilicate-containing lithium-containing silicon oxide and a method for producing the same.

Lithium-containing silicon oxide is known as a material for forming the negative electrode of lithium-ion secondary batteries. This lithium-containing silicon oxide usually contains not only silicon oxide (SiO _x ) but also lithium silicate such as Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₄ Si ₃ O ₈ , Li ₂ Si ₂ O ₅ , etc. (see, for example, JP 2005-183264 A).

JP 2005-183264 A

In recent years, there has been a demand for improved output characteristics of batteries having electrodes made of the above-mentioned lithium-containing silicon oxide. The object of the present invention is to provide a lithium-containing silicon oxide that can improve the output characteristics of batteries.

The lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) ( excluding those having a composition represented by LiO ₂ ·xSiO ₂ , the same applies below) according to a first aspect of the present invention is a lithium-containing silicon oxide containing lithium disilicate ( excluding those having a composition represented by LiO ₂ ·xSiO ₂ , the same applies below), in which, in three peaks (peaks derived from lithium disilicate) appearing within a diffraction angle range of 23° to 25° in an X-ray diffraction measurement result, the ratio of the intensity of the central peak to the intensity of the peak having the smallest diffraction angle is greater than 1, and the ratio of the intensity of the central peak to the intensity of the peak having the largest diffraction angle is greater than 0.8.

By the way, the peak with the smallest diffraction angle is due to diffraction from the (130) plane, the central peak is due to diffraction from the (040) plane, and the peak with the largest diffraction angle is due to diffraction from the (111) plane. If the intensity of the peak with the largest diffraction angle is 1000, the theoretical intensity of the peak with the smallest diffraction angle is calculated to be 69.046, and the theoretical intensity of the central peak is calculated to be 42.632. Therefore, the ratio of the theoretical intensity of the central peak to the theoretical intensity of the peak with the smallest diffraction angle is 0.61744, and the ratio of the theoretical intensity of the central peak to the theoretical intensity of the peak with the largest diffraction angle is 0.42632 (Reference: https://materialsproject.org/materials/mp-4117/). That is, in the lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) according to the first aspect of the present invention, the ratio of the intensity of the central peak to the intensity of the peak having the smallest diffraction angle and the ratio of the intensity of the central peak to the intensity of the peak having the largest diffraction angle are sufficiently larger than the theoretical values.

As a result of the intensive research of the present inventors, it has become clear that the lithium-containing silicon oxide containing the lithium disilicate having the above-mentioned peak relationship has superior battery output characteristics when used as the main material of an electrode, compared with the lithium-containing silicon oxide containing the lithium disilicate not having the above-mentioned peak relationship. This is probably because the crystal of lithium disilicate (Li ₂ Si ₂ O ₅ ) has anisotropy (orientation), and lithium conductivity in a specific direction is high.

Of the three peaks mentioned above, it is preferable that the intensity of the central peak is the greatest. This is because lithium-containing silicon oxide containing lithium disilicate having such a peak relationship will have better output characteristics when used as the main material for an electrode.

The method for producing lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) according to a second aspect of the present invention includes a lithium-containing silicon oxide preparation step and a heat treatment step. In the lithium-containing silicon oxide preparation step, the lithium-containing silicon oxide is prepared so that the ratio of the number of lithium atoms to the number of oxygen atoms is in the range of more than 0 and less than 1/2 ( i.e. , 0<Li/O<1/2). In the lithium-containing silicon oxide preparation step, the lithium-containing silicon oxide is prepared by any one of the following methods (i) to (iii).
(i) A method in which silicon oxide powder and a lithium compound are mixed and heat-treated.
(ii) A method in which lithium is electrochemically reacted with lump silicon oxide or silicon oxide powder.
(iii) A method in which a thin film of lithium-containing silicon oxide is formed on a substrate and then the thin film is scraped off from the substrate.
In the lithium-containing silicon oxide preparation step , it is preferable to generate lithium-containing silicon oxide by co-depositing silicon monoxide gas and lithium gas. In the heat treatment step, the lithium-containing silicon oxide obtained in the lithium-containing silicon oxide preparation step is heat-treated at a temperature of 1030° C. or higher. The upper limit of the heat treatment temperature is 1400° C. In addition, this heat treatment is preferably performed in an inert gas atmosphere.

By utilizing this method for producing lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ), it is possible to obtain lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) according to the first aspect. Therefore, this production method can provide lithium-containing silicon oxide that improves the output characteristics of a battery.

1 is a schematic diagram of a manufacturing apparatus for lithium-containing silicon oxide powder according to an embodiment of the present invention. 1 is an X-ray diffraction chart of a lithium-containing silicon oxide powder according to Example 1. 1 is an X-ray diffraction chart of a lithium-containing silicon oxide powder according to Example 2. 1 is an X-ray diffraction chart of a lithium-containing silicon oxide powder according to Comparative Example 1. 1 is an X-ray diffraction chart of a lithium-containing silicon oxide powder according to Comparative Example 2. 1 is an X-ray diffraction chart of a lithium-containing silicon oxide powder according to Comparative Example 3.

The lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) according to the embodiment of the present invention is a lithium-containing silicon oxide containing lithium disilicate, and in the three peaks (peaks derived from lithium disilicate) appearing within a diffraction angle range of 23° to 25° in the X-ray diffraction measurement result, the ratio of the intensity of the central peak to the intensity of the peak with the smallest diffraction angle exceeds 1, and the ratio of the intensity of the central peak to the intensity of the peak with the largest diffraction angle exceeds 0.8. Note that it is preferable that the intensity of the central peak is the largest among the above-mentioned three peaks.

Typically, the apex of the peak with the smallest diffraction angle is in the range of 23.6° to 24.0°, the apex of the peak with the largest diffraction angle is in the range of 24.6° to 25.0°, and the apex of the central peak is in the range of 24.1° to 24.5°.

The lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) according to the embodiment of the present invention is produced through a lithium-containing silicon oxide preparation step and a heat treatment step. These steps will be described in detail below.

(1) Lithium-containing silicon oxide preparation step In the lithium-containing silicon oxide preparation step, lithium-containing silicon oxide is prepared so that the ratio of the number of lithium atoms to the number of oxygen atoms is in the range of more than 0 and less than 1/2 (i.e., 0<Li/O<1/2).

The lithium-containing silicon oxide preparation process can be realized by using i) a method of mixing silicon oxide powder with a lithium compound and heat treating the mixture, ii) a method of electrochemically reacting lithium with lump silicon oxide or silicon oxide powder, or iii) a method of forming a thin film of lithium-containing silicon oxide on a substrate and then scraping the thin film off the substrate, but from the viewpoint of reducing manufacturing costs, it is preferable to carry out the process by the above iii) using a vapor deposition apparatus 100 as shown in FIG. 1. Therefore, first, the vapor deposition apparatus 100 will be described, and then the method of manufacturing lithium-containing silicon oxide using the vapor deposition apparatus 100 will be described.

As shown in FIG. 1, the deposition apparatus 100 is mainly composed of a crucible 110, a heater 120, a deposition drum 130, a scraper 141, a granular guide 143, a chamber 150, a raw material supply hopper 160, a raw material introduction pipe 170, a recovery container 180, a first valve VL1, and a second valve VL2.

As shown in FIG. 1, the crucible 110 is a heat-resistant container with an opening in the center of the top wall, and is installed in the chamber 150. A through hole (not shown) is formed in one location on the periphery of the top wall of the crucible 110, and a raw material introduction pipe 170 is inserted into this through hole. In other words, the raw material in the raw material supply hopper 160 is supplied to the crucible 110 through the raw material introduction pipe 170. A gas guide Gg is disposed on the upper side of the top wall of the crucible 110. This gas guide Gg is a member that guides the raw material gas generated in the crucible 110 to the deposition drum 130, and is installed on the upper surface of the top wall so as to surround the center of the top wall, as shown in FIG. 1.

The heater 120 is used to heat the crucible 110 to high temperatures and is positioned to surround the outer periphery of the crucible 110.

The deposition drum 130 is, for example, a cylindrical horizontal drum, and is disposed above the opening OP in the top wall of the crucible 110 as shown in FIG. 1, with its lower portion surrounded by a gas guide Gg. The deposition drum 130 is rotated in one direction by a driving mechanism (not shown). The deposition drum 130 is provided with a temperature regulator (not shown) for keeping the outer peripheral surface at a constant temperature. The temperature regulator cools the outer peripheral surface temperature of the deposition drum 130 to a temperature suitable for deposition of the deposition source gas by a cooling medium supplied from the outside. The outer peripheral surface temperature of the deposition drum 130 can also affect the crystallinity of the precipitate deposited on the precipitate remaining on the deposition drum. If the temperature is too low, the tissue structure of the precipitate may become too sparse, and conversely, if the temperature is too high, crystal growth due to disproportionation reaction may progress. The temperature is preferably 900°C or less, more preferably in the range of 150°C to 800°C, and particularly preferably in the range of 150°C to 700°C.

The scraper 141 is a member that scrapes off the laminated film formed on the deposition drum from the deposition drum 130, and is disposed near the deposition drum 130 as shown in FIG. 1. The flakes (active material particles) scraped off by the scraper 141 fall into the granule guide 143. The material of the scraper 141 also affects the impurity contamination of the active material particles. From the viewpoint of suppressing this effect, the material of the scraper 141 is preferably stainless steel or ceramics, and particularly preferably ceramics. In addition, it is preferable that the scraper 141 does not come into contact with the outer peripheral surface of the deposition drum 130. This is because it is possible to prevent the active material particles to be recovered from being contaminated by impurities that may occur due to direct contact between the deposition drum 130 and the scraper 141.

The granular guide 143 is, for example, a vibrating conveying member, and as shown in FIG. 1, is arranged so as to slope downward from the vicinity of the deposition drum toward the collection section 152 of the chamber 150, and receives the laminated film pieces scraped off by the scraper 141 arranged above it and sends them to the collection section 152 of the chamber 150.

As shown in FIG. 1, the chamber 150 is mainly composed of a chamber main body 151, a recovery section 152, and an exhaust pipe 153. As shown in FIG. 1, the chamber main body 151 is a box-shaped section having a deposition chamber RM therein, and contains the crucible 110, the heater 120, the deposition drum 130, the scraper 141, and the particle guide 143. As shown in FIG. 1, the recovery section 152 is a section that protrudes outward from the side wall of the chamber main body 151, and has a space that communicates with the deposition chamber RM of the chamber main body 151. As described above, the tip of the particle guide 143 is located in this recovery section 152.

The raw material supply hopper 160 is a raw material supply source, and as shown in FIG. 1, its outlet is connected to the raw material introduction pipe 170. That is, the raw material fed into the raw material supply hopper 160 is supplied to the crucible 110 via the raw material introduction pipe 170 at an appropriate timing. The raw material supplied to the crucible 110 becomes molten Sr, and then vaporizes to become raw material gas.

The raw material introduction pipe 170 is a round-hole nozzle for supplying the solid raw material put into the raw material supply hopper 160 to the crucible 110, and is arranged in the center of the top plate of the crucible 110 so that its mouth faces upward.

The collection container 180 is a container for collecting the laminated membrane pieces that have passed through the first valve VL1 and the second valve VL2.

The first valve VL1 and the second valve VL2 are opened and closed to adjust the amount of laminated membrane pieces collected in the collection container 180, and are provided in the collection pipe 190 that connects the collection section 152 of the chamber 150 to the collection container 180.

The following a) to e) show examples of the process for preparing lithium-containing silicon oxide using the deposition apparatus 100 described above.

a)
In this example, a mixed powder of silicon dioxide (SiO ₂ ) and lithium carbonate (Li ₂ CO ₃ ) is charged into the crucible 110. This raw material may be charged from a raw material supply hopper 160 via a raw material introduction pipe 170, or may be charged directly into the crucible 110.

After the raw materials are charged into the crucible 110, the crucible 110 is heated by the heater 120 to a temperature equal to or higher than the melting point of lithium carbonate while flowing an inert gas into the precipitation chamber RM. Note that the inert gas here is, for example, a rare gas (such as argon gas) or nitrogen gas.

_By heating _the mixed powder as described in the above paragraph, a powder of lithium-containing silicon oxide ( _SiLixOy ) is obtained. Then, the lithium-containing silicon oxide ( _SiLixOy ) powder is pulverized, and the pulverized lithium-containing silicon oxide powder is mixed with silicon (Si) powder and granulated. Then, the granulated material is charged into the crucible 110. The raw material may be charged from the raw material supply hopper 160 through the raw material introduction pipe 170, or directly into the crucible 110.

After the granulated material is put into the crucible 110, the crucible 110 is heated to a temperature of 700° C. or higher by the heater 120 while reducing the pressure inside the deposition chamber RM. At this time, the reaction of SiLi _x O _y + (y-1)Si → xLi↑ + ySiO↑ proceeds. Then, silicon monoxide gas and lithium gas generated from the crucible 110 are supplied to the deposition drum 130 through the gas guide Gg. At this time, the deposition drum 130 is rotated by the drive source. The temperature of the outer peripheral surface of the deposition drum 130 is set lower than the temperature inside the deposition chamber RM. More specifically, the temperature is set lower than the condensation temperature of the silicon monoxide gas and the lithium gas. With this setting, the silicon monoxide gas and lithium gas generated from the crucible 110 are deposited (precipitated) and accumulated on the outer peripheral surface of the rotating deposition drum 130, and the deposit is scraped off from the deposition drum 130 by the scraper 141. The scraped off pieces of the deposit fall along the outer circumferential surface of the deposition drum 130 into a particle guide 143 .

b)
In this example, a mixed powder of lithium carbonate powder, silicon dioxide powder, and silicon powder is charged as a raw material into the crucible 110. The raw material may be charged from a raw material supply hopper 160 through a raw material introduction pipe 170, or may be charged directly into the crucible 110.

After the raw materials are put into the crucible 110, the pressure in the precipitation chamber RM is reduced, and the crucible 110 is heated by the heater 120 to a temperature in the range of 400°C or higher and lower than the melting point of lithium carbonate. If the pressure in the precipitation chamber RM is too high, the reaction that generates SiO gas from the raw materials becomes difficult to occur. For this reason, the pressure in the precipitation chamber RM is preferably 1000 Pa or lower, more preferably 750 Pa or lower, and particularly preferably 20 Pa or lower. The temperature in the precipitation chamber RM affects the reaction rate of SiO. If the temperature is too low, the reaction rate will be slow, and if the temperature is too high, there are concerns that side reactions will occur due to the melting of the raw materials and that energy efficiency will decrease. From this viewpoint, the temperature in the precipitation chamber RM is preferably in the range of 425°C to 675°C, more preferably in the range of 450°C to 650°C, even more preferably in the range of 475°C to 625°C, even more preferably in the range of 500°C to 600°C, and particularly preferably in the range of 525°C to 575°C. It is also possible to assume that the pressure in the precipitation chamber RM is not reduced, and in that case, it is preferable to pass an inert gas through the precipitation chamber RM. Here, the inert gas is, for example, a rare gas (such as argon gas) or nitrogen gas. Also, at this stage, the raw material powder maintains its powder shape as it is.

By heating the raw material as described in the above paragraph, _the progress of the reaction for producing silicon carbide ( _Li2CO3 +Si→ _Li2SiO3 + _SiC ) is suppressed while the decarbonation reaction of lithium carbonate ( _Li2CO3 → _Li2O + _CO2 ↑) proceeds. At this time, the progress of the decarbonation reaction of lithium carbonate can be confirmed by monitoring the weight of the raw material or detecting carbon dioxide. In addition, when the method according _to this example is repeated after the above confirmation, the progress of the decarbonation reaction of lithium carbonate can also be controlled by time management.

The progress of the decarbonation reaction of lithium carbonate is controlled as described above, and from the point when the decarbonation reaction of lithium carbonate is considered to be completed, the pressure in the deposition chamber RM is reduced and the crucible 110 is heated to a temperature of 700°C or higher by the heater 120. Then, silicon monoxide gas and lithium gas generated from the crucible 110 are supplied to the deposition drum 130 through the gas guide Gg. At this time, the deposition drum 130 is rotated by the drive source. The temperature of the outer peripheral surface of the deposition drum 130 is set lower than the temperature in the deposition chamber RM. More specifically, the temperature is set lower than the condensation temperature of the silicon monoxide gas and lithium gas. With this setting, the silicon monoxide gas and lithium gas generated from the crucible 110 are deposited and deposited on the outer peripheral surface of the rotating deposition drum 130, and the deposit is scraped off from the deposition drum 130 by the scraper 141. The scraped off debris falls along the outer periphery of the deposition drum 130 into the particle guide 143.

c)
In this example, when the lithium carbonate powder, silicon dioxide powder, and silicon powder are charged into the crucible 110 as raw materials, the lithium carbonate powder, silicon dioxide powder, and silicon powder are stacked in layers so that the layer of silicon dioxide powder is located between the layer of lithium carbonate powder and the layer of silicon powder. That is, in this example, the lithium carbonate powder and the silicon powder do not come into contact with each other, but the lithium carbonate powder and the silicon dioxide powder come into contact with each other. Note that such raw material charging is performed directly into the crucible 110. In addition, it is preferable that the layer of silicon powder is the bottom layer. In addition, in this case, the layer of lithium carbonate powder and the layer of silicon dioxide powder may be stacked one by one, or the layer of lithium carbonate powder and the layer of silicon dioxide powder may be stacked alternately in a plurality of layers.

After the raw materials are put into the crucible 110, the crucible 110 is heated by the heater 120 to a temperature equal to or higher than the melting point of lithium carbonate while reducing the pressure in the precipitation chamber RM. If the pressure in the precipitation chamber RM is too high, the reaction of generating SiO gas from the raw materials becomes difficult to occur. For this reason, the pressure in the precipitation chamber RM is preferably 1000 Pa or less, more preferably 750 Pa or less, and particularly preferably 20 Pa or less. In addition, the temperature in the precipitation chamber RM affects the reaction rate of SiO, and if the temperature is too low, the reaction rate slows down, and if the temperature is too high, there are concerns about the progression of side reactions due to the melting of the raw materials and reduced energy efficiency. From this perspective, the temperature in the precipitation chamber RM is preferably above 800°C, more preferably above 900°C, even more preferably above 1000°C, even more preferably above 1100°C, even more preferably above 1200°C, and particularly preferably above 1300°C. The upper limit of this temperature is 1400°C. In this case, the raw materials may be stirred using a stirrer or the like after a certain period of time has passed.

By heating the raw material under reduced pressure as described in the above paragraph, the reaction represented by Li ₂ CO ₃ +SiO ₂ →SiLi _x O _y +CO ₂ ↑ takes precedence over the reaction of producing silicon carbide (Li ₂ CO ₃ +Si→Li ₂ SiO ₃ +SiC). Then, the reaction of SiLi _x O _y +(y-1)Si→xLi↑+ySiO↑ proceeds. Silicon monoxide gas and lithium gas generated from the crucible 110 are supplied to the deposition drum 130 through the gas guide Gg. At this time, the deposition drum 130 is rotated by the drive source. The temperature of the outer circumferential surface of the deposition drum 130 is set lower than the temperature in the deposition chamber RM. More specifically, the temperature is set lower than the condensation temperature of silicon monoxide gas and lithium gas. With this setting, silicon monoxide gas and lithium gas generated from the crucible 110 are deposited (precipitated) and accumulated on the outer circumferential surface of the rotating deposition drum 130, and the deposit is scraped off from the deposition drum 130 by the scraper 141. The scraped off pieces of the deposit fall along the outer circumferential surface of the deposition drum 130 into a particle guide 143.

d)
In this example, when lithium carbonate powder, silicon dioxide powder, and silicon powder are charged into the crucible 110 as raw materials, the lithium carbonate powder and the silicon dioxide powder are mixed, and the mixed powder and the silicon powder are stacked in layers so that the mixed powder layer and the silicon powder layer are adjacent to each other. Such raw material charging is performed directly into the crucible 110. In addition, it is preferable that the silicon powder layer is disposed below the mixed powder layer, and it is preferable that the silicon powder layer is the bottom layer. In addition, in this case, the mixed powder layer and the silicon powder layer may be stacked one by one, or the mixed powder layer and the silicon powder layer may be stacked alternately in a plurality of layers.

After the raw materials are put into the crucible 110, the crucible 110 is heated by the heater 120 to a temperature equal to or higher than the melting point of lithium carbonate while reducing the pressure in the precipitation chamber RM. If the pressure in the precipitation chamber RM is too high, the reaction of generating SiO gas from the raw materials becomes difficult to occur. For this reason, the pressure in the precipitation chamber RM is preferably 1000 Pa or less, more preferably 750 Pa or less, and particularly preferably 20 Pa or less. In addition, the temperature in the precipitation chamber RM affects the reaction rate of SiO, and if the temperature is too low, the reaction rate slows down, and if the temperature is too high, there are concerns about the progression of side reactions due to the melting of the raw materials and reduced energy efficiency. From this perspective, the temperature in the precipitation chamber RM is preferably above 800°C, more preferably above 900°C, even more preferably above 1000°C, even more preferably above 1100°C, even more preferably above 1200°C, and particularly preferably above 1300°C. The upper limit of this temperature is 1400°C. In this case, the raw materials may be stirred using a stirrer or the like after a certain period of time has passed.

By heating the raw material under reduced pressure as described in the above paragraph, the reaction represented by Li ₂ CO ₃ +SiO ₂ →SiLi _x O _y +CO ₂ ↑ takes precedence over the reaction of producing silicon carbide (Li ₂ CO ₃ +Si→Li ₂ SiO ₃ +SiC). Then, the reaction of SiLi _x O _y +(y-1)Si→xLi↑+ySiO↑ proceeds. Silicon monoxide gas and lithium gas generated from the crucible 110 are supplied to the deposition drum 130 through the gas guide Gg. At this time, the deposition drum 130 is rotated by the drive source. The temperature of the outer circumferential surface of the deposition drum 130 is set lower than the temperature in the deposition chamber RM. More specifically, the temperature is set lower than the condensation temperature of silicon monoxide gas and lithium gas. With this setting, silicon monoxide gas and lithium gas generated from the crucible 110 are deposited (precipitated) and accumulated on the outer circumferential surface of the rotating deposition drum 130, and the deposit is scraped off from the deposition drum 130 by the scraper 141. The scraped off pieces of the deposit fall along the outer circumferential surface of the deposition drum 130 into a particle guide 143.

e)
In this example, first, a mixed powder of lithium carbonate powder and silicon dioxide powder is charged as a raw material into the crucible 110. The raw material may be charged from the raw material supply hopper 160 through the raw material introduction pipe 170, or may be charged directly into the crucible 110.

After the raw materials are charged into the crucible 110, the crucible 110 is heated by the heater 120 to a temperature equal to or higher than the melting point of lithium carbonate. In this case, the pressure inside the precipitation chamber RM may be reduced, or an inert gas may be passed through the precipitation chamber RM. Here, the inert gas may be, for example, a rare gas (such as argon gas) or nitrogen gas.

By _heating the raw material as described above, the reaction represented by _Li2CO3 + _SiO2 → SiLi _{x Oy} + _CO2 ↑ can be carried out. At this time, the progress of the reaction can be confirmed by monitoring the weight of the raw material or detecting carbon dioxide. In addition, when the method according to this example is repeated after the above confirmation, the progress of the reaction can also be controlled by time management.

The progress of the reaction is controlled as described above, and when the reaction is considered to be completed, silicon powder is fed from the raw material supply hopper 160 to the crucible 110 through the raw material introduction pipe 170. If the precipitation chamber RM has already been depressurized before the silicon powder is fed, the above-mentioned degree of depressurization and temperature may be maintained as they are or may be appropriately changed. If the precipitation chamber RM has not been depressurized before the silicon powder is fed, the precipitation chamber RM is depressurized. If the pressure in the precipitation chamber RM is too high, the reaction of generating SiO gas from the raw material is difficult to occur. For this reason, the pressure in the precipitation chamber RM is preferably 1000 Pa or less, more preferably 750 Pa or less, and particularly preferably 20 Pa or less. The temperature in the precipitation chamber RM affects the reaction rate of SiO, and if the temperature is too low, the reaction rate will be slow, and if the temperature is too high, there are concerns about side reactions caused by melting the raw material and reduced energy efficiency. From this viewpoint, the temperature in the precipitation chamber RM is preferably above 800°C, more preferably above 900°C, even more preferably above 1000°C, even more preferably above 1100°C, even more preferably above 1200°C, and particularly preferably above 1300°C. The upper limit of this temperature is 1400°C. In addition, at this time, the raw materials may be stirred and mixed by a stirrer or the like.

Then, the reaction of SiLi _x O _y + (y-1)Si → xLi↑ + ySiO↑ proceeds. Then, silicon monoxide gas and lithium gas generated from the crucible 110 are supplied to the deposition drum 130 through the gas guide Gg. At this time, the deposition drum 130 is rotationally driven by the drive source. The temperature of the outer peripheral surface of the deposition drum 130 is set lower than the temperature in the deposition chamber RM. More specifically, the temperature is set lower than the condensation temperature of the silicon monoxide gas and the lithium gas. With this setting, the silicon monoxide gas and lithium gas generated from the crucible 110 are deposited (precipitated) and accumulated on the outer peripheral surface of the rotating deposition drum 130, and the deposit is scraped off from the deposition drum 130 by the scraper 141. The scraped off pieces of the deposit fall along the outer peripheral surface of the deposition drum 130 into the particle guide 143.

(2) Heat Treatment Step In the heat treatment step, the lithium-containing silicon oxide obtained in the lithium-containing silicon oxide preparation step is heat-treated at a temperature of 1030°C or higher. During this heat treatment, lithium disilicate (Li ₂ Si ₂ O ₅ ) crystals are formed in the lithium-containing silicon oxide. The upper limit of the heat treatment temperature is 1400°C. The heat treatment time and the heat treatment time vary depending on the type of the firing furnace, the powder filling method, and the processing amount per batch. For example, when about 10 g of lithium-containing silicon oxide powder is fired in a static electric furnace, a sufficient effect can be obtained by treating it at 1200°C for about 10 minutes, but when 10 kg of powder is fired in a static electric furnace, a treatment of about 1 hour will be required. Examples of the calcination furnace include a stationary electric furnace capable of controlling the atmosphere, a rotary kiln, a roller hearth kiln, and a fluidized bed type heat treatment furnace, but from the industrial viewpoint of uniformly treating a large amount of powder, a rotary kiln or a fluidized bed type heating furnace capable of heating while stirring is preferable. Basically, the higher the temperature and the longer the time, the stronger the central peak becomes relative to the two peaks adjacent to it (the peak with the smallest diffraction angle and the peak with the largest diffraction angle among the above three peaks).

<Characteristics of the lithium disilicate-containing lithium-containing silicon oxide powder according to the embodiment of the present invention>
In the lithium disilicate-containing lithium-containing silicon oxide powder according to the embodiment of the present invention, in the three peaks (peaks derived from lithium disilicate) appearing within the diffraction angle range of 23° to 25° in the X-ray diffraction measurement result, the ratio of the intensity of the central peak to the intensity of the peak with the smallest diffraction angle is more than 1, and the ratio of the intensity of the central peak to the intensity of the peak with the largest diffraction angle is more than 0.8. When used as the main material of an electrode, such lithium disilicate-containing lithium-containing silicon oxide is superior in battery output characteristics to lithium disilicate-containing lithium-containing silicon oxide that does not have the above-mentioned peak relationship.

The following examples and comparative examples are presented to explain the present invention in more detail, but the present invention is not limited to these examples.

1. Production of lithium-containing silicon oxide powder A mixed powder of silicon dioxide (SiO ₂ ) and lithium carbonate (Li ₂ CO ₃ ) (silicon dioxide powder:lithium carbonate powder=120:74 (mass ratio)) was placed in the crucible 110 of the deposition apparatus 100 shown in Fig. 1, and the crucible 110 was heated to 1000°C by the heater 120 while flowing argon gas into the deposition chamber RM. This heating was continued until carbon dioxide was no longer detected in the exhaust gas.

After confirming that carbon dioxide was no longer detected in the exhaust gas from the system, the crucible 110 was naturally cooled, and the lithium-containing silicon oxide ( _SiLixOy ) powder was taken out from the crucible. The lithium-containing silicon oxide ( _{SiLixOy )} powder was then mixed with silicon (Si) powder and granulated. The granulated material was then charged into _the crucible 110.

Then, the output of the heater 120 was increased to raise the temperature of the crucible 110 to 1300°C, generating silicon monoxide gas and lithium gas. The silicon monoxide gas and lithium gas were then deposited (precipitated) on the outer peripheral surface of the deposition drum 130, and the deposit was scraped off from the deposition drum 130 by the scraper 141.

The scraped-off deposit was then pulverized, and the pulverized material was then heat-treated at 1100°C for 30 minutes. The pulverized material was then further pulverized using a ball mill until the median diameter (D50) was 5 μm, and the pulverized material was classified using a sieve with 45 μm openings. The particle size of the pulverized material was then adjusted to obtain the desired lithium-containing silicon oxide powder.

2. Physical properties of lithium-containing silicon oxide powder (1) X-ray diffraction characteristics The above-mentioned heat-treated powder was analyzed with an X-ray diffractometer (manufactured by Malvern Panalytical Co., Ltd., wavelength 1.5418 nm (CuKα), no monochromator, scan step 0.01313°), and the X-ray diffraction chart shown in FIG. 1 was obtained. As shown in FIG. 1, three peaks were observed in the diffraction angle range of 23° to 25° in the above-mentioned X-ray diffraction chart. Among these peaks, the apex of the peak with the smallest diffraction angle was located at 23.8°, the apex of the peak with the largest diffraction angle was located at 24.8°, and the apex of the central peak was located at 24.3°. Next, the intensities of the above-mentioned peaks were determined as follows, and the intensity of the peak with the smallest diffraction angle was 2889.28 cps, the intensity of the peak with the largest diffraction angle was 3413.73 cps, and the intensity of the central peak was 2971.43 cps (see Table 1).

First, the straight line connecting the 23° point and the 26° point is subtracted as the base intensity. Then, in the X-ray diffraction chart in this state, the maximum peak intensity in the range of 23.6° to 24.0° is found and used as the intensity of the peak with the smallest diffraction angle, the maximum peak intensity in the range of 24.1° to 24.5° is found and used as the intensity of the central peak, and the maximum peak intensity in the range of 24.6° to 25.0° is found and used as the intensity of the peak with the largest diffraction angle.

From the above results, it is clear that the ratio of the intensity of the central peak to the intensity of the peak with the smallest diffraction angle is 1.02843 (= 2971.43/2889.28), which is greater than 1, and the ratio of the intensity of the central peak to the intensity of the peak with the largest diffraction angle is 0.87069 (= 2971.43/3413.73), which is greater than 0.8, and the desired lithium-containing silicon oxide powder was obtained (see Table 1).

(2) Measurement of electrode characteristics of lithium-containing silicon oxide powder a) Preparation of negative electrode The lithium-containing silicon oxide powder obtained as described above, Ketjen black, and a polyimide precursor, which is a non-aqueous solvent-based binder, were mixed in a mass ratio of 85:5:10, and N-methylpyrrolidone was added to the mixture, and the mixture was kneaded to prepare a slurry. The slurry was then applied onto a copper foil having a thickness of 40 μm, and the coating was pre-dried at 80° C. for 15 minutes, after which the copper foil with the dried coating was punched out to a diameter of 11 mm, and then heated at 350° C. under reduced pressure to prepare a negative electrode. Note that by heating the copper foil with the dried coating at 350° C., the polyimide precursor in the dried coating was imidized.

b) Preparation of coin cell (lithium ion secondary battery) and measurement of battery properties A coin cell was prepared using lithium foil as the counter electrode, a solution of hexafluorophosphoric acid ( _LiPF6 ) dissolved in a 1:1 volumetric mixture of ethylene carbonate and diethyl carbonate to give a concentration of 1 mol/L, and a 20 μm thick polyethylene porous film as the separator.

Then, a charge/discharge test was performed on this coin cell using a secondary battery charge/discharge tester manufactured by Electrofield Corporation. The test conditions for the charge/discharge test were as shown in Table 2. From this charge/discharge test, the initial charge capacity, initial discharge capacity, ratio of initial discharge capacity to initial charge capacity (initial coulombic efficiency), and ratio of third discharge capacity to initial discharge capacity (output characteristics) were determined. The measurement results were as shown in Table 1. Note that "output characteristics" here refers to the ratio of "discharge capacity when charged/discharged at 0.5C in the third cycle" to "discharge capacity when charged/discharged at 0.1C in the first cycle."

A lithium-containing silicon oxide powder was obtained in the same manner as in Example 1, except that the heat treatment temperature in Example 1 was changed from 1100°C to 1200°C, and the X-ray diffraction characteristics and electrode output characteristics of the lithium-containing silicon oxide powder were measured in the same manner as in Example 1. The results are shown in Table 1. It was clear from these results that the desired lithium-containing silicon oxide powder was obtained.

(Comparative Example 1)
A lithium-containing silicon oxide powder was obtained in the same manner as in Example 1, except that a mixed powder of silicon dioxide (SiO ₂ ) and silicon (Si) (silicon dioxide powder:silicon powder = 60:28 (mass ratio)) was used as the raw material, and the X-ray diffraction characteristics and electrode characteristics of the lithium-containing silicon oxide powder were measured in the same manner as in Example 1. The results are shown in Table 1. It became clear from these results that the desired lithium-containing silicon oxide powder was not obtained.

(Comparative Example 2)
A lithium-containing silicon oxide powder was obtained in the same manner as in Example 1, except that the heat treatment temperature in Example 1 was changed from 1100° C. to 700° C., and the X-ray diffraction characteristics of the lithium-containing silicon oxide powder and the output characteristics of the electrodes were measured in the same manner as in Example 1. The results are shown in Table 1. It became clear from these results that the desired lithium-containing silicon oxide powder was not obtained.

(Comparative Example 3)
A lithium-containing silicon oxide powder was obtained in the same manner as in Example 1, except that the heat treatment temperature in Example 1 was changed from 1100° C. to 1000° C., and the X-ray diffraction characteristics and electrode output characteristics of the lithium-containing silicon oxide powder were measured in the same manner as in Example 1. The results are shown in Table 1. It became clear from these results that the desired lithium-containing silicon oxide powder was not obtained.

In Table 1, "Pmin" indicates the peak with the smallest diffraction angle, "Pmid" indicates the central peak, and "Pmax" indicates the peak with the largest diffraction angle.

(summary)
The results shown in Table 1 make it clear that the coin cells of Examples 1 and 2 exhibited superior output characteristics to the coin cells of Comparative Examples 1-3.

Reference Signs List 100 Vapor deposition apparatus 110 Crucible 120 Heater 130 Vapor deposition drum 141 Scraper 143 Particle guide 150 Chamber 151 Chamber body 152 Recovery section 153 Exhaust pipe 160 Raw material supply hopper 170 Raw material introduction pipe 180 Recovery container 190 Recovery pipe Gg Gas guide OP Opening RM Deposition chamber Sr Molten metal VL1 First valve VL2 Second valve

Claims (3)

A lithium-containing silicon oxide containing lithium disilicate (Li 2 Si 2 O 5 ) (excluding those having a composition represented by LiO 2 .xSiO 2 ) in which, among three peaks appearing within a diffraction angle range of 23° or more and 25° _or less in an X-ray diffraction measurement result, the ratio of the intensity of the central peak to the intensity of the peak having the smallest diffraction angle exceeds 1, and the ratio of the intensity of the central peak to _the intensity of the peak _{having the largest} diffraction angle exceeds 0.8 . The lithium-containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) according to claim 1 ( excluding those having a composition represented by LiO ₂ .xSiO ₂ ) in which the intensity of the central peak among the three peaks is the greatest. A lithium-containing silicon oxide preparation step of preparing lithium-containing silicon oxide ( excluding those having a composition represented by LiO2.xSiO2) _so that the ratio of the number of lithium atoms to the number of oxygen atoms is in the range of more than ₀ and less than 1/2 ;
A heat treatment step of heat treating the lithium-containing silicon oxide at a temperature in the range of 1030° C. to 1400° C. ,
In the lithium-containing silicon oxide preparation step, the lithium-containing silicon oxide (excluding those whose composition is expressed by LiO2.xSiO2) is prepared by any one of the following methods: (i) a method of mixing silicon oxide powder with a lithium compound and heat-treating the mixture; (ii) a method of electrochemically reacting lithium with lump silicon oxide or silicon oxide powder; and (iii) a method of forming a thin film of lithium-containing silicon oxide on a substrate and then _scraping the thin film off the substrate _.
A method for producing lithium - containing silicon oxide containing lithium disilicate (Li ₂ Si ₂ O ₅ ) ( excluding those having a composition represented by LiO _{2.xSiO 2} ).

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