Tin oxide particles

Abstract

To provide tin oxide particulates capable of improving battery cycle characteristics when applied to a separator for a lithium-ion battery.SOLUTION: A tin oxide particulate has: a volume cumulative particle diameter D90 which is 3 μm or less at cumulative volume of 90 vol.% by laser diffraction scattering type particle size distribution measurement method; and a ratio (S1 / D50) of a bet specific surface area S1 which is between 10 and 100 to a volume cumulative particle diameter D50 at a cumulative volume of 50 vol.%, by the laser diffraction scattering type particle size distribution measurement method; and is arranged on a lithium ion battery separator. It is also suitable that oxygen deficiency per mass of tin oxide particulates is between 1×1016 / g and 9×1016 / g. It is also suitable that the bet specific surface area S1 is between 20 m2 / g and 70 m2 / g. It is also suitable that the volume cumulative particle diameter D50 is between 0.3 μm and 2.0 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to tin oxide particles. [Background technology]

[0002] Lithium secondary batteries, such as lithium-ion batteries, are used as power sources for portable electronic devices such as laptops and mobile phones. In recent years, as these portable electronic devices have become more powerful and have longer lifespans, improvements in battery performance, such as higher capacity and the ability to maintain that capacity for a long period of time, are desired.

[0003] Patent Document 1 discloses a battery separator in which an acrylic adhesive containing dispersed tin oxide is applied to both sides of a polyethylene film, with the aim of obtaining a thin and compact separator.

[0004] Patent Document 2 discloses a separator for ensuring the safety of a battery, which comprises a porous substrate having pores and a porous active layer formed by coating at least one surface of the substrate with a mixture of inorganic particles and a binder polymer. The document also discloses that this separator can be used in lithium secondary batteries.

[0005] Patent Document 3 discloses a lithium secondary battery having a porous insulating layer that contains a low-absorbency inorganic filler with relatively low lithium absorption and a high-absorbency inorganic filler with relatively high lithium absorption, with the aim of preventing an internal short circuit in the battery.

[0006] Patent Document 4 discloses a battery that includes a positive electrode, a negative electrode, a separator, and an electrolyte containing particles having a predetermined flatness and refractive index, with the aim of ensuring capacity and safety.

[0007] Patent Document 5 discloses a battery that has a positive electrode, a negative electrode, a separator disposed between these electrodes, an electrolyte, and solid particles, with the solid particles being disposed in predetermined regions of the electrodes, with the aim of improving overcharge resistance. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-213979 [Patent Document 2] Special Publication No. 2009-518809 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-109866 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-090777 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-119213 Summary of the Invention [Problem to be solved by the invention]

[0009] Improvement of battery performance is related to various factors, including not only charge / discharge efficiency and capacity but also cycle characteristics such as rate, discharge capacity retention rate, etc. However, the separators containing particles or fillers described in Patent Documents 1 to 5, and the batteries equipped with such separators, have not been studied at all in terms of improving cycle characteristics.

[0010] Therefore, an object of the present invention is to provide tin oxide particles that, when applied to a separator for a lithium ion battery, can improve the cycle characteristics of the battery. [Means for solving the problem]

[0011] The present invention is characterized in that the volume cumulative particle size D90 at 90% by volume cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method is 3 μm or less, the ratio (S1 / D50) of the BET specific surface area S1 to the volume cumulative particle size D50 at 50% by volume of cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method is 10 or more and 100 or less, The present invention provides tin oxide particles that are disposed in a separator for a lithium ion battery. [Effects of the Invention]

[0012] According to the present invention, there is provided tin oxide particles that, when applied to a separator for a lithium ion battery, can improve the cycle characteristics of the battery. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a graph showing the charge / discharge curves of a battery when the tin oxide particles of Example 2 are used for the separator. [Figure 2] FIG. 2 is a graph showing charge / discharge curves of a battery when the alumina particles of Comparative Example 2 are used for the separator. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described below based on preferred embodiments. The tin oxide particles of the present invention contain tin oxide, and are SnO (2-X) The tin oxide particles mainly contain tin oxide represented by the chemical formula (where 0≦X≦1). In other words, the tin oxide particles include those that contain at least one of tin (II) oxide (SnO) and tin (IV) oxide (SnO2), or SnO2 with oxygen deficiency. It is preferable that 50 mol % or more of the tin oxide in the tin oxide particles is SnO2. In addition, the tin oxide particles may contain elemental tin. In either case, the tin oxide particles are suitable for use as a filler in a separator for a lithium ion battery.

[0015] The tin oxide particles are either composed of tin and oxygen and contain no other elements except for inevitable impurities, or further contain elements other than tin and oxygen. The tin oxide particles are preferably composed of tin and oxygen in the former embodiment, but the inclusion of inevitable impurity elements other than tin and oxygen is permitted as long as the effects of the present invention are not impaired. In either embodiment, the content of elements other than tin and oxygen in the tin oxide particles is preferably 2 mass% or less. The content of these elements can be measured, for example, by gas composition analysis or ICP atomic emission spectroscopy.

[0016] The tin content in the tin oxide particles, as measured by ICP atomic emission spectroscopy, is preferably 76% by mass to 84% by mass, more preferably 76% by mass to 82% by mass, and even more preferably 76% by mass to 80% by mass. When the tin oxide particles are used in a separator, the insulating properties required for the separator can be easily maintained.

[0017] Furthermore, the oxygen content in the tin oxide particles, as measured by gas composition analysis, is preferably 13% by mass or more and 22% by mass or less, more preferably 15% by mass or more and 22% by mass or less, and even more preferably 17% by mass or more and 22% by mass or less. When the tin oxide particles are used in a separator, the insulating properties required for the separator can be easily maintained.

[0018] The total content of tin oxide in the tin oxide particles is preferably 98% by mass or more and 100% by mass or less, more preferably 99% by mass or more and 100% by mass or less, and even more preferably 99.5% by mass or more and 100% by mass or less. This range makes it easier to maintain sufficient insulating properties, which are important for the separator function, when the tin oxide particles are used in a separator. The tin oxide content can be measured by a method such as a quantitative determination method using a displacement dissolution method using a copper (II) chloride potassium solution.

[0019] The tin oxide particles preferably have a volume cumulative particle size D90 at 90% by volume as measured by a laser diffraction / scattering particle size distribution measurement method of 3.0 μm or less, more preferably 2.6 μm or less, and even more preferably 2.5 μm or less, with a practical value being 1.0 μm or more.

[0020] The D90 mentioned above is an index that indicates the size of relatively coarse particles present in tin oxide powder, which is an aggregate of tin oxide particles. Generally, lithium-ion batteries include a positive electrode, a negative electrode, and a separator disposed in a compressed state between these electrodes. When tin oxide particles are used as the separator, the separator is compressed together with the particles, causing mechanical damage to the separator. This can affect the insulating performance of the separator and lead to micro-short circuits between the positive and negative electrodes. These micro-short circuits can contribute to a deterioration in the lithium ion supply balance between the positive and negative electrodes during charge and discharge, ultimately leading to a decrease in battery performance. When the D90 is within the above range, even when the separator is compressed together with the particles, excessively coarse particles are not present, and therefore, even when the particles are disposed in the separator, the occurrence of mechanical damage to the separator is reduced, the insulating performance of the separator is less affected, and the occurrence of micro-short circuits is also reduced. As a result, the separator has the heat resistance, electrical insulation, and ionic conductivity required, while improving the cycle characteristics of the battery, particularly the characteristics related to rate and capacity maintenance during charge / discharge cycles. Tin oxide particles satisfying the above D90 can be produced, for example, by the production method described below.

[0021] The volume cumulative particle diameter D90 can be measured by the following method. Specifically, 0.1 g of the tin oxide particles to be measured is mixed with 100 mL of a 20 mg / L aqueous solution of sodium hexametaphosphate, and the mixture is dispersed for 10 minutes using an ultrasonic homogenizer (US-300T manufactured by Nippon Seiki Seisakusho). The particle size distribution is then measured using a laser diffraction / scattering particle size distribution analyzer (e.g., LA-920 manufactured by Horiba, Ltd.).

[0022] The tin oxide particles were measured by a laser diffraction / scattering particle size distribution measurement method, and the BET specific surface area S1 (m 2 / g) 2 / g / μm) is preferably within a predetermined range. Specifically, the S1 / D50 ratio in the tin oxide particles is preferably 10 or more and 100 or less, more preferably 20 or more and 90 or less, and even more preferably 45 or more and 90 or less.

[0023] The S1 / D50 ratio is a parameter that represents the BET specific surface area per unit particle diameter. A higher S1 / D50 ratio indicates a larger surface area per particle, for example, due to the particles being porous. By ensuring that the S1 / D50 ratio is within the above-mentioned range, the electrolyte constituting the lithium-ion battery is more easily retained in the pores or between the particles, thereby improving the retention of the electrolyte in or near the separator (so-called liquid replenishment). As a result, even under harsh conditions such as high temperatures or after multiple charge / discharge cycles, the electrolyte is prevented from escaping from the separator, allowing sufficient and reversible migration of lithium ions within the battery, thereby improving the durability of the charge / discharge cycle. Tin oxide particles satisfying such an S1 / D50 ratio can be produced, for example, by the production method described below.

[0024] The BET specific surface area S1 of the tin oxide particles is preferably 20 m 2 / g or more 70m 2 / g or less, more preferably 30m 2 / g or more 60m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less. With the BET specific surface area S1 in this range, the separator can adequately retain the electrolyte even when the battery is exposed to significant temperature changes or when the internal battery pressure increases due to electrode expansion during charging and discharging. As a result, the battery performance required for a secondary battery, such as rate characteristics and cycle characteristics, can be maintained for a long period of time.

[0025] The BET specific surface area S1 can be measured by a nitrogen adsorption method based on the BET method using, for example, a Monosorb MS-21 manufactured by Quantachrome Corp. The amount of powder to be measured is 0.3 g, and the preliminary degassing conditions can be atmospheric air at 105°C for 60 minutes.

[0026] The volume cumulative particle diameter D50 is preferably 0.30 μm or more and 2.0 μm or less, more preferably 0.60 μm or more and 1.3 μm or less, and even more preferably 0.50 μm or more and 1.2 μm or less. By having the particle diameter in such a range, the energy density of a battery including a separator in which tin oxide particles are disposed can be increased. In particular, when the tin oxide particles of the present invention are disposed on a separator by, for example, coating the surface of the separator, the thickness of the tin oxide particle layer can be formed thin, which is advantageous in that the required insulating properties can be maintained while further increasing the energy density of the battery.

[0027] The volume cumulative particle size D10 of the tin oxide particles at 10% cumulative volume as measured by a laser diffraction / scattering particle size distribution measurement method is preferably 0.30 μm or more and 0.80 μm or less, more preferably 0.30 μm or more and 0.70 μm or less, and even more preferably 0.50 μm or more and 0.70 μm or less. By having this range, when the tin oxide particles are disposed in a separator, appropriate voids are formed between the particles, improving the liquid replenishment property, and the rate characteristics of a battery including the separator can be maintained at a high level.

[0028] The volume cumulative particle diameter D100 of the tin oxide particles at 100% cumulative volume, as measured by a laser diffraction / scattering particle size distribution measurement method, is preferably 3 μm or more and 6 μm or less, more preferably 3 μm or more and 5 μm or less, and even more preferably 3 μm or more and 4 μm or less. By keeping the particle diameter within this range, when the tin oxide particles are disposed in a separator, micro-short circuits caused by coarse particles can be suppressed. The D50, D10 and D100 of the tin oxide particles can each be measured by the same measurement method as the measurement of D90 described above.

[0029] As a preferred embodiment, the tin oxide particles preferably contain oxygen deficiency in SnO2 which is tin oxide. For example, the tin oxide particles preferably contain a tin oxide represented by the chemical formula of SnO (2-X) (where 0 < X < 1). Specifically, the amount of oxygen deficiency contained in the tin oxide particles is preferably 1 × 10 16 atoms / g or more and 9 × 10 16 atoms / g or less, more preferably 2 × 10 16 atoms / g or more and 6 × 10 16 atoms / g or less, still more preferably 2 × 10 16 atoms / g or more and 4 × 10 16 atoms / g or less per unit mass of the particles. With such an amount of oxygen deficiency, when the tin oxide particles are disposed on the separator of a lithium ion battery, it is possible to prevent an unintended reaction with the electrolyte while sufficiently maintaining the insulating performance of the separator, so that the behavior of the charge-discharge voltage can be stably maintained and the cycle characteristics can be further improved.

[0030] The amount of oxygen deficiency can be measured by the following method by electron spin resonance (ESR) analysis. As a measuring device, for example, JES-X330 manufactured by JEOL can be used. Details of the measuring procedure will be described in detail in the examples described later.

[0031] A preferred manufacturing method of the tin oxide particles will be described below. In one embodiment of the manufacturing method, a water-soluble tin compound as a tin source is dissolved in a solvent to form a solution containing the tin compound (hereinafter, this is also referred to as a tin solution), and intermediate particles are obtained by neutralizing the tin solution. Then, the obtained intermediate particles are fired. Thereby, a tin oxide powder composed of an aggregate of the target tin oxide particles is obtained.

[0032] First, a tin solution is prepared (solution preparation step). The tin solution is preferably an aqueous tin solution using water as a solvent. Examples of tin compounds include salts of stannic acid with alkali metals such as sodium and potassium, and inorganic tin salts such as tin(II) chloride and tin(IV) chloride. These tin compounds may be anhydrous or hydrated. The tin compounds can be used alone or in combination. The use of a water-soluble inorganic tin salt such as an alkali metal salt of stannic acid as the tin compound is preferred, as it provides excellent handling during production, makes it easy to control D90 within a predetermined range, and makes it easy to obtain particles that satisfy a predetermined S1 / D50 ratio.

[0033] The tin compound is mixed so that the content of the tin element in the tin solution is preferably 0.14 mol / L to 0.28 mol / L, more preferably 0.17 mol / L to 0.24 mol / L. By adjusting the content to such an extent, D90 can be easily controlled within a predetermined range, and particles satisfying a predetermined S1 / D50 ratio can be easily obtained with high productivity.

[0034] The tin solution may be in a heated state or in an unheated state. It is preferable that the solvent is heated before the tin solution is prepared. That is, the tin solution is preferably prepared by mixing a tin compound with a heated solvent. When water is used as the solvent, the temperature of the solvent is preferably 30°C or higher and 70°C or lower, more preferably 40°C or higher and 65°C or lower. By heating to such a temperature, the tin compound can be sufficiently dissolved, and particles satisfying a predetermined D90 and S1 / D50 ratio can be easily obtained with high productivity.

[0035] Next, the tin solution obtained by the above method is neutralized to obtain a neutralized solution (neutralization step). The neutralizing agent used for neutralization can be an aqueous solution of various acids or bases. For example, when the tin solution is prepared using an alkali metal salt of stannic acid, the tin solution is alkaline. Therefore, an aqueous solution of a strong acid such as nitric acid or sulfuric acid is preferably used to neutralize the tin solution, and dilute sulfuric acid is more preferably used. The use of such a substance is advantageous in that the desired particles can be obtained efficiently in a fine particle state. The concentration of the acid or base in the aqueous acid or base solution can be adjusted as appropriate, but is preferably 1 mol / L or more and 5 mol / L or less from the viewpoint of achieving both ease of handling and favorable physical properties of the resulting particles.

[0036] In the neutralization step, the neutralizing agent may be added all at once or may be added dropwise or in multiple batches. In this production method, it is preferable to add the neutralizing agent gradually, and it is also preferable to add the neutralizing agent while stirring the heated tin solution. The liquid temperature when neutralizing the tin solution can be in the same range as the temperature of the above-mentioned solvent. In this case, the liquid temperature of the tin solution may be the same as or different from the temperature of the above-mentioned solvent.

[0037] When the neutralizer is added gradually, it is preferable that the neutralizer is added continuously at a predetermined rate within the above-mentioned addition time range, provided that the concentration of the neutralizer is adjusted to the above-mentioned range.For example, as in Example 1 described later, in the case of a charge amount of 2.2 liters, the neutralizer addition rate can be preferably 12 mL / min or more and 73 mL / min or less, more preferably 18 mL / min or more and 37 mL / min or less.By setting such an addition rate, particles that satisfy the predetermined D90 and S1 / D50 ratio can be easily obtained with high productivity.

[0038] The time from the start to the end of the addition of the neutralizing agent can be changed as appropriate depending on the desired physical properties of the particles, but is preferably 30 minutes or more and 180 minutes or less, more preferably 60 minutes or more and 120 minutes or less.

[0039] Furthermore, it is preferable to adjust the total amount of neutralizer added so that the pH of the neutralized solution at the solution temperature after addition of the neutralizer is preferably 2.0 to 4.0, more preferably 2.5 to 3.5. By adjusting the pH to such a range, particles with little particle size variation and satisfying the specified D90 and S1 / D50 ratio can be easily obtained with high productivity.

[0040] From the viewpoint of making the neutralization reaction occur more uniformly and facilitating the production of homogeneous particles, it is preferable to add the neutralizing agent to the tin solution and then age the solution for a predetermined period of time. Specifically, it is preferable to gradually add the entire amount of the neutralizing agent to the tin solution, adjust the pH of the neutralized solution to the above-mentioned range, and then stir the neutralized solution in a heated state for a predetermined period of time. The stirring time is preferably 30 minutes or more and 180 minutes or less. Furthermore, it is preferable that the temperature of the neutralized solution be maintained at the conditions used when neutralizing the tin solution.

[0041] From the viewpoint of uniformly causing the neutralization reaction and obtaining particles with little variation in particle size, it is also preferable to continue stirring the neutralization solution at least from the start to the end of the neutralization step, more specifically, from the start of mixing the tin solution and the neutralizing agent to the end of the aging step, which is performed as needed. In this case, the stirring speed of the neutralization solution, expressed as a flow rate, is preferably 60 cm / sec or more and 140 cm / sec or less, more preferably 75 cm / sec or more and 120 cm / sec or less. The stirring speed of the neutralization solution may be constant or variable from the start to the end of the neutralization step. In addition, stirring may be performed at the above-mentioned stirring speed in the solution preparation step as well. The stirring speed employed in the neutralization step is faster than that conventionally employed. By employing such a stirring speed, it is easy to control the particle size of the resulting particles, the particle size variation can be reduced, and particles that satisfy the specified D90 and S1 / D50 ratio can be easily obtained with high productivity.

[0042] Through the above steps, a plurality of intermediate particles dispersed in water is obtained. These intermediate particles are typically tin hydroxide (Sn(OH)4). The intermediate particles are preferably washed by pure water repulp washing, decantation, or the like before being subjected to the firing step described below. From the viewpoint of reducing impurities, washing is carried out until the conductivity of the aqueous phase after washing the intermediate particles is preferably 1000 μS / cm or less. Water is preferably used as the washing liquid. In addition, after washing the intermediate particles, it is preferable to dry the solid content obtained by solid-liquid separation using a method such as dry heat drying or vacuum drying to obtain a dry powder that is an aggregate of intermediate particles. The dry powder of intermediate particles may be crushed using a known crushing device or sieved, and then subjected to subsequent steps.

[0043] Next, the dried powder of the intermediate particles is calcined (calcination step). The intermediate particles, which are tin hydroxide, are converted into tin oxide particles by calcining them under predetermined conditions. The atmosphere in the firing step can be an oxygen-containing atmosphere such as air, an inert atmosphere, or a reducing atmosphere. Among these, from the viewpoint of efficiently obtaining tin oxide particles that satisfy a predetermined amount of oxygen deficiency while improving convenience, firing in an oxygen-containing atmosphere is preferred, and firing in an air atmosphere is more preferred.

[0044] The firing temperature in the firing step is preferably 400°C or higher and 900°C or lower, more preferably 500°C or higher and 800°C or lower. Furthermore, the firing time is preferably 20 minutes or higher and 150 minutes or lower, more preferably 40 minutes or higher and 120 minutes or lower, provided that the firing temperature is within the above-mentioned firing temperature range. By keeping the firing time within this range, the reaction from tin hydroxide to tin oxide proceeds sufficiently, the BET specific surface area is easily controlled, and particles satisfying a predetermined S1 / D50 ratio are easily obtained with high productivity. In addition, when the calcination is performed in an air atmosphere, tin oxide particles having a predetermined amount of oxygen vacancies can be efficiently obtained. Generally, calcination is performed in a reducing atmosphere to generate oxygen vacancies. However, the reason why a predetermined amount of oxygen vacancies can be generated by calcination in an air atmosphere as in the present production method is presumably because it is easier to control the amount of oxygen atoms released from the intermediate particles during temperature rise and the amount of oxygen atoms added to the intermediate particles during temperature fall than in a reducing atmosphere.

[0045] From the viewpoint of efficiently obtaining fine tin oxide powder by removing coarsely grained particles unintentionally generated during firing, it is preferable to perform a coarsely grained removal process on the particles obtained after firing, such as by crushing or sieving.

[0046] Through the above steps, the target tin oxide particles can be obtained as a powder composed of aggregates of particles. The tin oxide particles thus obtained preferably contain, mainly, a tin oxide represented by the chemical formula SnO (2-X) (where 0 < X < 1). The tin oxide particles are small in particle size and spherical without undergoing a coating treatment for enhancing the dispersibility among the particles. The reason is considered to be that the degree of aggregation of the particles generated during production by this production method is low, so that production can be carried out while maintaining a small particle size. As long as the effects of the present invention are achieved, it does not exclude the inevitable trace inclusion of other elements other than tin and oxygen in the tin oxide particles, or the inevitable slight oxidation of the surface of the tin oxide particles.

[0047] The tin oxide particles can be used by disposing them on a separator constituting a lithium ion battery in the form of the powder itself composed of aggregates of particles without any special treatment. A lithium ion battery typically comprises a non-aqueous battery including a positive electrode made of a lithium-containing oxide, a negative electrode made of a carbon material, a separator disposed between these electrodes, and an electrolytic solution containing an organic solvent and a lithium salt. One surface of the separator is adjacent to the positive electrode, and the other surface is disposed adjacent to the negative electrode.

[0048] The separator for a lithium ion battery is composed of a porous resin film containing a polyolefin resin such as polyethylene or polypropylene, and has fluid permeability in the thickness direction. The separator may have a single-layer structure or a multilayer structure. Tin oxide particles are placed in the separator in a state where the particles are dispersed in a polyolefin resin during the separator manufacturing process, or are attached to at least one surface of a porous resin film and placed on the surface of the film. This improves the heat resistance of the separator and the high-temperature stability of the battery. When particles are placed in the separator, the content of tin oxide particles in the separator is usually about 30% by mass to 75% by mass.

[0049] When tin oxide particles are disposed on the surface of a porous resin film, the tin oxide particles are preferably disposed at least on the surface of the separator facing the positive electrode, and more preferably disposed adjacent to the surface as a particle layer containing tin oxide particles and a binder resin. This can further improve the heat resistance of the separator and the high-temperature stability of the battery. Preferred examples of the binder resin constituting the particle layer include heat-resistant resins, such as polyimide resins and aromatic polyamide resins. When a particle layer is formed, the content of tin oxide particles in the particle layer is typically about 80% by mass to 95% by mass.

[0050] When the tin oxide particles having the above-described configuration are disposed in a separator for a lithium-ion battery, they can reduce mechanical damage to the separator, have excellent electrolyte replenishment properties that constitute the lithium-ion battery, and can sufficiently maintain lithium ion conductivity within the battery. As a result, they can be used as a filler to enhance the heat resistance and durability of the separator and improve the charge-discharge cycle characteristics.

[0051] In addition to electrolytes such as lithium-containing compounds, sulfur-containing additives such as vinylene carbonate (VC) and 1,3-propane sultone (PS) are sometimes added to the electrolytes that make up lithium-ion batteries to suppress decomposition caused by charging and discharging. PS, in particular, is often used when a compound with a high Ni ratio is used as the positive electrode in order to obtain high-capacity lithium-ion batteries. These additives contribute to suppressing electrolyte decomposition by forming a film derived from PS or VC and PS at the electrode interface in lithium-ion batteries. However, the present inventors have newly discovered that when alumina or magnesia, which have been conventionally used as inorganic fillers for separators in lithium-ion batteries equipped with electrolytes containing the above-mentioned additives, are used, the battery capacity may decrease and the charge / discharge cycle characteristics may be significantly affected. The reason for this adverse effect is thought to be the generation of sulfides due to an unintended chemical reaction between the inorganic filler and PS. In this regard, by using the tin oxide particles of the present invention as a constituent material of the separator, even when PS is added to the electrolyte, high battery capacity and high capacity retention can be achieved without interacting with compounds in the electrolyte, and charge / discharge cycle characteristics can also be sufficiently improved. These findings were newly discovered by the present inventors and are also evident from the results of the examples described below. [Example]

[0052] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. In the tables, the "-" column indicates that no measurement was performed.

[0053] Example 1 (1. Solution preparation process) 1.35 kg of sodium stannate trihydrate (purity 92 mass%) was dissolved as a tin source in 22.1 L of pure water heated to 50°C to obtain an aqueous tin solution with a sodium stannate concentration of 61 g / L (elemental tin concentration: 0.21 mol / L).

[0054] (2. Neutralization process) Next, the tin aqueous solution was heated to 60°C, and in this state, 2.2 liters of a 20% by mass dilute sulfuric acid aqueous solution was sequentially and continuously added over 84 minutes (acid concentration: 2.3 mol / L, addition rate: 26 mL / min) until the pH at 60°C reached 3.0 for neutralization to obtain a neutralized solution. Then, this neutralized solution was aged for 0.5 hours while maintaining the liquid temperature at 60°C to precipitate tin hydroxide particles as intermediate particles. Also, continuously in each of the solution preparation process and the neutralization process, the aqueous solution and the neutralized solution were continuously stirred at a constant speed of 110 cm / second.

[0055] (3. Firing process) Subsequently, the neutralized solution after aging was subjected to solid-liquid separation, and the obtained solid content was washed with water until the conductivity of the water reached 580 μS / cm. The washed solid was subjected to solid-liquid separation and dried to obtain a dried product. This dried product was crushed with a mixer to form a dry powder, and then this dry powder was fired in a box-type electric furnace. The firing conditions were 500°C for 2 hours under an air atmosphere. Thereafter, the fired particles were sieved to remove coarse particles. Through this process, the target tin oxide particles were obtained. These tin oxide particles contained 98% by mass or more of a tin oxide represented by the chemical formula SnO (2-X) (where 0 < X < 1).

[0056] [Example 2] In the solution preparation process, 81 kg of sodium stannate trihydrate as a tin source was dissolved in 1246 liters of pure water heated to 30°C to obtain a tin aqueous solution with a sodium stannate concentration of 65 g / L (tin element concentration: 0.22 mol / L). Next, the tin aqueous solution was heated to 60°C, and in this state, 132 liters of a 20% by mass dilute sulfuric acid aqueous solution was sequentially added over 82 minutes (acid concentration: 2.3 mol / L, addition rate: 1.61 L / min) until the pH at 60°C reached 3.1 for neutralization to obtain a neutralized solution. Then, this neutralized solution was aged for 1 hour while maintaining the liquid temperature at 60°C to precipitate tin hydroxide particles as intermediate particles. Furthermore, the target tin oxide particles were obtained under the same conditions as in Example 1, except that the stirring speed of the aqueous solution and the neutralization solution was changed to a constant speed of 100 cm / sec.

[0057] Example 3 The target tin oxide particles were obtained under the same conditions as in Example 2, except that the stirring speed of the aqueous solution and neutralization solution was changed to a constant speed of 80 cm / sec.

[0058] Example 4 The target tin oxide particles were obtained under the same conditions as in Example 2, except that in the firing step, the firing conditions were changed to 700° C. in an air atmosphere for 2 hours.

[0059] Example 5 The target tin oxide particles were obtained under the same conditions as in Example 2, except that in the firing step, the firing conditions were changed to a 3 vol% H2 / 97 vol% N2 mixed atmosphere in a rotary kiln at 500°C for 45 minutes.

[0060] Comparative Example 1 As the tin oxide particles, model number SNO03PB manufactured by Kojundo Chemical Laboratory Co., Ltd. was used.

[0061] Comparative Example 2 Alumina (Al2O3) particles, model number 013-11525, manufactured by Wako Pure Chemical Industries, Ltd., were used instead of tin oxide particles.

[0062] Comparative Example 3 Instead of tin oxide particles, magnesia (MgO) particles manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., model number: 131-10851, were used.

[0063] [Evaluation of particle properties] The BET specific surface areas S1, D10, D50, D90, and D100 of the inorganic particles of the Examples and Comparative Examples were measured by the methods described above.

[0064] [Measurement of oxygen deficiency] The amount of oxygen vacancy in the inorganic particles of the Examples and Comparative Examples was measured by the following method. A measurement sample was placed in a quartz tube with an outer diameter of 5 mm, and measurements were carried out under the following measurement conditions to obtain an ESR spectrum. For tin oxide particles, the absorption intensity of the obtained ESR spectrum was converted to a value per 1 g of sample. The number of unpaired electrons was calibrated using a 0.1 to 2 mM TEMPOL-toluene solution as a standard. Sample mass: 120 mg Quartz tube: JEOL Ltd. LST-5HS 300MM Microwave output: 0.5mW ·Magnetic field sweep width: 338±25mT Modulated magnetic field: 0.6mT Sensitivity: 100 ·Time constant: 0.1 seconds Measurement time: 120 seconds ·Measurement temperature: 293K

[0065] [Evaluation of Battery Characteristics] The battery characteristics were evaluated when the inorganic particles of the examples and comparative examples were disposed on the separator. Specifically, N-methylpyrrolidone was used as a solvent. 90 parts by mass of inorganic particles and 10 parts by mass of binder resin (polyvinylidene fluoride, hereinafter also referred to as PVdF) were mixed into the solvent to prepare an inorganic particle slurry. This slurry was dispersed using a paint shaker, and then coated onto one side of a polyolefin porous resin film using a bar coater to form a coating film, thereby producing a separator with a 3-4 μm-thick layer of inorganic particles formed on one side.

[0066] Next, lithium nickel manganese cobalt composite oxide (LiNi 0.6 Mn 0.2 Co 0.2 89 parts by mass of 02), 5% by mass of acetylene black as a conductive additive, and 6 parts by mass of PVdF as a binder were mixed, and N-methyl-2-pyrrolidone was further added to form a paste. This paste was applied to one side of aluminum foil to prepare a positive electrode sheet.

[0067] Separately, 96 parts by mass of graphite as a negative electrode active material and 2 parts by mass each of carboxymethyl cellulose and styrene-butadiene rubber as binders were mixed, and water was added to form a paste, which was then applied to one side of copper foil to prepare a negative electrode sheet. The electrolyte used was a PS-free electrolyte prepared by adding 0.5 mass% vinylene carbonate (VC) as an additive to 1 mol / L LiPF6 (ethylene carbonate (EC): dimethyl carbonate (DMC) = 3:7 volume mixture).

[0068] Six coin-type batteries were fabricated by placing a separator between the positive and negative electrode sheets and filling them with either a PS-free electrolyte or a PS-added electrolyte. In each battery, the separator was positioned so that the inorganic particle layer faced the positive electrode sheet.

[0069] Each battery thus obtained was charged and discharged under the following conditions using a charge-discharge tester (manufactured by Toyo Systems Co., Ltd., "TOSCAT"). The charge-discharge cycle consisted of charging at a constant current of 0.1 C up to 4.3 V at 25°C, followed by constant voltage charging until the current decayed to 0.02 C, and then discharging at a current of 0.1 C until the voltage reached 3.0 V relative to the lithium potential. This cycle was repeated three times to determine the initial activation. After initial activation, the charge-discharge cycle consisted of a constant current charge at 55°C to 4.3 V at a current value of 0.1 C, followed by a constant voltage charge until the current value decayed to 0.05 C. Next, one cycle of discharge at a current value of 0.1 C until the voltage reached 3.0 V relative to the lithium potential was performed. Subsequently, a cycle of constant current charge at a current value of 1 C to 4.3 V, followed by constant voltage charge until the current value decayed to 0.05 C, and then discharge at a current value of 1 C until the voltage reached 3.0 V relative to the lithium potential was repeated.

[0070] The rate characteristic (1C / 0.1C [%]) was calculated by taking the discharge capacity at 0.1C in the first cycle at 55°C as 100% and then calculating the ratio of the discharge capacity at 1C in the 31st cycle. The higher the value, the better the rate characteristic. Similarly, the ratio of the discharge capacity at 1 C in the 31st cycle to the discharge capacity at 1 C in the 2nd cycle, which was taken as 100%, was calculated and used as the capacity retention rate (1 C / 1 C [%]). The higher the value, the better the capacity retention rate.

[0071] Separately, six batteries were fabricated using an electrolyte containing 5% by mass of propane sultone (PS) and otherwise similar to the above. The rate characteristics and capacity retention were measured and calculated using the methods described above, and the voltage behavior was also measured. The operating rate (percentage) of each battery was evaluated based on the number of batteries fabricated according to the following criteria. The results are shown in Table 1. 1 and 2 show charge / discharge curves of the batteries using the inorganic particles of Example 2 and Comparative Example 2, respectively.

[0072] <Evaluation of operation rate> A: The percentage of working batteries is over 70% and it has stable and excellent voltage behavior. B: The percentage of working batteries is 30% or more and less than 70%, and the battery has voltage behavior that allows it to function as a battery. C: The percentage of working batteries is less than 30% and the battery does not function.

[0073] As shown in Table 1, when the tin oxide particles of each Example were used in a separator for a lithium ion battery, no short circuit was observed during the initial charge / discharge, and the rate characteristics and capacity retention rate were good, resulting in excellent charge / discharge cycle characteristics, even under high temperature conditions, compared to the case where the inorganic particles of the Comparative Examples were used. In particular, the tin oxide particles of Examples 1 to 4 exhibit excellent operating efficiency and voltage behavior as batteries without any interaction even when the electrolyte contains propane sultone, as is evident from a comparison of the charge-discharge curves of Example 2 shown in Figure 1 and Comparative Example 2 shown in Figure 2.

[0074] Specifically, in the battery using the tin oxide particles of Example 2, no unstable voltage behavior was observed during either the charge or discharge process, as shown in Figure 1. In contrast, in the battery using the alumina particles of Comparative Example 2, as shown in Figure 2, the end-of-charge voltage was reached in the early stage of charging, indicating an increase in the internal resistance of the battery. This suggests that by-products were generated by the chemical reaction between the propane sultone additive and alumina, and these by-products were deposited over the entire separator, increasing the resistance between the electrodes and preventing the battery from exhibiting its performance.

[0075] [Table 1]

Claims

1. The volume cumulative particle size D90 at 90% by volume of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method is 3 μm or less, the ratio (S1 / D50) of the BET specific surface area S1 to the volume cumulative particle size D50 at a cumulative volume of 50% by volume, as determined by a laser diffraction / scattering particle size distribution measurement method, is 10 or more and 100 or less; Tin oxide particles for use in a lithium ion battery separator, the tin oxide in the particles has oxygen vacancies; Tin oxide particles, wherein the amount of oxygen deficiency per mass of the particles is 1×10 16 or more / g and 9×10 16 or less / g.

2. The BET specific surface area S1 is 20 m ２ / g or more 70m ２ 10. The tin oxide particles of claim 1, wherein the tin oxide particles have a SiO2 content of 1000 ppm or less.

3. 3. The tin oxide particles according to claim 1, wherein the volume cumulative particle diameter D50 is 0.3 μm or more and 2.0 μm or less.

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