Additive for lithium-ion secondary battery positive electrode using electrolyte solution, lithium-ion secondary battery positive electrode material, and lithium-ion secondary battery

Abstract

Provided are: an effective additive for a lithium-ion secondary battery electrode, other than a ferroelectric material, which can improve input-output characteristics by lowering the electrode-electrolyte solution interfacial resistance R2 in a lithium-ion secondary battery positive electrode material that contains one or more of Mn, Fe and Ni; and a lithium ion secondary battery positive electrode material and a lithium ion secondary battery containing same.　An additive for a lithium ion secondary battery positive electrode is characterized by containing a composite oxide that is present together with a lithium ion secondary battery positive electrode material containing cations of one or more elements selected from among Mn, Fe, Ni and Co, and in that the composite oxide does not contain alkali metal ions or alkaline earth metal ions, has an acid point and a base point, and has a relative dielectric constant of 20 or more. Also provided are a lithium ion secondary battery positive electrode material and a lithium ion secondary battery containing the additive.

Description

Additive for positive electrode of lithium ion secondary battery using electrolyte, positive electrode material for lithium ion secondary battery, and lithium ion secondary battery

[0001] The present invention relates to an additive for a positive electrode of a lithium ion secondary battery that uses an electrolyte, a positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery.

[0002] Lithium-ion secondary batteries are widely used as batteries for electronic devices and communication devices. They are also used in automobiles and power storage facilities. One of the technologies to improve the performance of lithium-ion secondary batteries is the use of additives (composite oxides) in lithium-ion secondary batteries.

[0003] Patent Literature 1 discloses a positive electrode material for a lithium ion secondary battery, which comprises positive electrode active material particles and a ferroelectric material, the ferroelectric material being disposed on at least a portion of the surface of the positive electrode active material particles, and which is said to have excellent output characteristics in a low-temperature environment.

[0004] Patent Document 2 discloses a non-aqueous electrolyte secondary battery in which a ferroelectric material having a relative dielectric constant of 500 or more is sintered onto the surface of a positive electrode active material, which is said to enable sufficient output characteristics to be obtained even in a low temperature range.

[0005] Patent Document 3 discloses a positive electrode material for lithium ion secondary batteries, in which a cation A having an ionic radius smaller than that of lithium ions and a valence of 2 or more and a cation B having an ionic radius larger than that of lithium ions and a valence of 2 or more are present between layers of a positive electrode material having a layered crystal structure. Furthermore, typical elements of the cations A and B are disclosed for producing the positive electrode material for lithium ion secondary batteries. It is believed that this enables a positive electrode for lithium secondary batteries with high output characteristics.

[0006] JP 2018-181614 A JP 2011-210694 A JP 2023-52895 A

[0007] In order to improve the output / input characteristics (rate characteristics) of a lithium ion secondary battery, it is important to reduce the internal resistance.ｔ is roughly the internal resistance R of the electrode material (active material) １ , electrode-electrolyte interface resistance R ２ , electrolyte (diffusion) resistance R ３ It can be decomposed into R ｔ =R １ +R ２ +R ３

[0008] Patent Document 3 discloses a method for determining the internal resistance R of the particles of the positive electrode material. １ The internal resistance R of the positive electrode material particles is reduced to improve the input / output characteristics. １ It is also important to improve the input / output characteristics by reducing the internal resistance. However, the largest of the internal resistances is the electrode-electrolyte interface resistance R ２ By reducing this resistance, the input / output characteristics of the lithium ion secondary battery can be effectively improved.

[0009] Patent Documents 1 and 2 disclose the interfacial resistance R ２ The output characteristics at low temperatures are improved by reducing the interface resistance R ２ The inventors have found that because the ferroelectric material contains alkaline earth metal ions, when it is combined with a positive electrode material containing Mn, Ni, Fe, Co, etc., the components react with the alkaline earth metal ions. Similarly, they have found that alkali metal ions also react with the components.

[0010] Therefore, in order to improve the output / input characteristics of a lithium ion secondary battery, the interface resistance R ２ It is effective to reduce the interfacial resistance R between the electrode and the electrolyte other than the ferroelectric. ２ New materials that reduce this are desired.

[0011] The present invention has been made in view of the above-mentioned problems, and aims to provide a method for improving the interfacial resistance R between an electrode and an electrolyte of a positive electrode material for a lithium ion secondary battery containing one or more cations selected from the elements Mn, Fe, Ni, and Co. ２ The present invention addresses the problem of providing an effective additive material for lithium ion secondary battery electrodes, particularly positive electrodes, other than ferroelectrics, which can reduce the resistance and improve the input / output characteristics.

[0012] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that the input / output characteristics can be improved by coexisting a composite oxide containing both acid sites and base sites and having a relative dielectric constant of 20 or more with a positive electrode material for a lithium ion secondary battery. The present invention was made based on the above findings and further research, and the gist of the present invention is as follows.

[0013] [1] An additive for a positive electrode of a lithium ion secondary battery using an electrolyte solution, the additive comprising a complex oxide that coexists with a positive electrode material of a lithium ion secondary battery containing cations of one or more elements selected from Mn, Fe, Ni, and Co, the complex oxide not containing alkali metal ions or alkaline earth metal ions, having both acid sites and base sites, and having a relative dielectric constant of 20 or more.

[0014] [2] The composition formula of the composite oxide is M ｘ Zr １－ｘ O ２－ｙ The additive according to [1], wherein the element M contains a trivalent metal ion, and the molar ratios x and y satisfy 0<x<1 and 0<y<0.5, respectively.

[0015] [3] The additive according to [2], characterized in that M contains one or more trivalent metal ions selected from La, Pr, Sm, Nd, Gd, Yb, Ho, and Y.

[0016] [4] The additive according to [2] or [3], characterized in that M contains a metal ion of Ce.

[0017] [5] The specific surface area of ​​the composite oxide is 35 m ２ The additive according to any one of [1] to [4], characterized in that it has a molecular weight of 1000 or more.

[0018] [6] A positive electrode material for a lithium ion secondary battery, comprising the additive material according to any one of [1] to [5].

[0019] [7] A lithium ion secondary battery comprising the lithium ion secondary battery positive electrode material according to [6].

[0020] According to the present invention, it is possible to provide an additive for a positive electrode of a lithium ion secondary battery that can improve the input / output characteristics of a lithium ion secondary battery that uses an electrolyte solution.

[0021] Figure 1 shows the interfacial charge transfer resistance (LiCoO ２ = LCO standard). ０．５ Co ０．２ Mn ０．３ O ２ FIG. 1 is an equivalent circuit diagram for determining the rated current (=NCM standard).

[0022] <<Additive for Positive Electrode of Lithium Ion Secondary Battery>> The additive for the positive electrode of the lithium ion secondary battery using the electrolyte solution of the present invention will be described below.

[0023] The additive for a lithium-ion secondary battery positive electrode of the present invention (hereinafter also simply referred to as "additive") is used in assembling a lithium-ion secondary battery, producing a lithium-ion secondary battery positive electrode sheet, and manufacturing a lithium-ion secondary battery positive electrode material. The additive of the present invention is a composite oxide that coexists with a lithium-ion secondary battery positive electrode material containing one or more cations selected from the elements Mn, Fe, Ni, and Co, and the composite oxide does not contain alkali metal ions or alkaline earth metal ions, has both acid sites and base sites, and has a relative dielectric constant of 20 or more.

[0024] The positive electrode material for lithium ion secondary batteries is a lithium-containing transition metal composite oxide containing one or more cations among the elements Mn, Fe, Ni, and Co, such as LiMnO and LiNi. ｘ Co ｙ Mn ｚ O ２ (x+y+z=1), LiNi ｘ Co ｙ Al ｘ O ２ (x+y+z=1), LiNi ｘ Mn ｙ O ４ (x+y=1), LiCoO ２ , LiFePO ４ , Li(Fe ｘ Mn ｙ ) P.O. ４ (x+y=1), xLi２ MnO ３ -(1-x)LiMeO ２ (Me=Ni, Co, Mn), Li ２ MnO ｘ F ｙ (x+y=3) and other Li-containing compounds. ２ It can also be used for other positive electrode materials and is therefore effective, and can be widely used for a variety of positive electrode materials.

[0025] The additive of the present invention includes a composite oxide that does not contain alkali metal ions or alkaline earth metal ions. A composite oxide that contains alkali metal ions or alkaline earth metal ions would react when coexisting with a positive electrode material that is a lithium-containing transition metal composite oxide containing one or more cations selected from the elements Mn, Fe, Ni, and Co. Therefore, the additive of the present invention is a composite oxide that does not contain alkali metal ions or alkaline earth metal ions. The Mn, Fe, Ni, and Co cations contained in the positive electrode material are components that form acidic oxides, and therefore, in a composite oxide that contains alkali metal ions or alkaline earth metal ions, which are components that form basic oxides, the component that forms the acidic oxide and the component that forms the basic oxide undergo an acid-base reaction.

[0026] The composite oxide further has both acid sites and basic sites. It is believed that the acid sites and basic sites exert the effects of the present invention through the following mechanism.

[0027] It is known that lithium ions in the electrolyte of a lithium ion secondary battery are solvated with organic solvent molecules. Specifically, during the charge transfer process at the interface between the positive electrode material and the electrolyte of a lithium ion secondary battery, the solvated lithium ions are desolvated when the lithium ions in the electrolyte migrate to the positive electrode, and solvated when the lithium ions leave the positive electrode into the electrolyte. This desolvation and solvation of lithium ions causes charge transfer resistance at the interface between the positive electrode material and the electrolyte, accounting for a large proportion of the internal resistance in lithium ion secondary batteries. In other words, this resistance hinders the high-power characteristics (rate performance) of lithium ion secondary batteries. In the present invention, by incorporating the additive of the present invention into the positive electrode material, the charge transfer resistance at the interface between the positive electrode material and the electrolyte can be reduced, thereby improving the high-power characteristics of lithium ion secondary batteries. That is, because the additive of the present invention is a composite oxide having both acid and base sites, the positively charged lithium ions of the solvated lithium ions tend to adsorb to the base sites (negatively polarized), and the negatively polarized portions of the solvated solvent molecules tend to adsorb to the acid sites (positively polarized). In other words, when both adsorb to the additive, the charge and polarized portions of the solvated lithium ions tend to be neutralized by the additive (the positive charge of the lithium ions receives electrons from the additive, and the negatively polarized portions of the solvated molecules receive electrons from the additive). As a result, the electrostatic attraction between the solvation and the lithium ions weakens, making desolvation easier. On the other hand, when the positive electrode material receives lithium ions (when discharging), electrons tend to be injected into the positive electrode material via the current collector, making it negative. This is advantageous for attracting lithium ions, but makes it difficult to desolvate the solvated molecules of the lithium ions. When the additive of the present invention, an electronic insulator, is present, the injected electrons do not reach the additive, so it does not become negative like the positive electrode material. When charging (when lithium ions are released from the positive electrode material into the electrolyte), the effect of the additive of the present invention can be interpreted as being the opposite of the above explanation.

[0028] The composite oxide contained in the additive of the present invention has a dielectric constant of 20 or greater. It is believed that when a lithium-ion secondary battery is charged and discharged, the electric field polarizes the surface of the composite oxide of the additive, adsorbing solvated lithium and promoting desolvation and solvation. That is, if the composite oxide is an insulator with a high dielectric constant, large polarization occurs due to the electric field gradient within the lithium-ion secondary battery. This effect, along with the acid and base sites, acts synergistically to facilitate desolvation and solvation of lithium ions, thereby achieving the effects of the present invention. If the dielectric constant of the composite oxide is less than 20, sufficient polarization does not occur due to the electric field gradient within the lithium-ion secondary battery, and the synergistic effect with the acid and base sites is not achieved. As a result, the input / output characteristics of the lithium-ion secondary battery are not sufficiently improved. Therefore, a higher dielectric constant of the composite oxide is preferable, and there is no upper limit. However, there are currently no paraelectric oxides with a dielectric constant of 500 or greater.

[0029] The relative dielectric constant in the present invention is the ratio of the dielectric constant of each complex oxide based on the dielectric constant of a vacuum. The dielectric constant is an index of the ease of polarization, and the higher the dielectric constant, the higher the relative dielectric constant. In other words, the higher the relative dielectric constant, the more easily the additive (containing the complex oxide) is polarized. For these reasons, the relative dielectric constant is more preferably 30 or more, and even more preferably 40 or more.

[0030] The acidic and basic sites referred to in the present invention are those that are detected by temperature-programmed desorption (TPD) of ammonia NH ３ The adsorption and desorption of carbon dioxide (CO ２ The basic sites are measured by adsorption and desorption of the standard substance of ammonia or carbon dioxide in advance to the measurement sample, and then the amount of the standard substance desorbed is measured while the temperature is raised to measure the acid sites and basic sites and their amounts. ２ The measurement sample is heat-treated at 370°C for 30 minutes in a / He atmosphere, and then the sample is exposed to a standard substance, ammonia or carbon dioxide, for 30 minutes at 50°C to adsorb the standard substance. The temperature is then increased from 50°C to 500°C at a rate of 20°C / min, and the amount of standard substance desorbed is measured.

[0031] In the present invention, having acid sites and basic sites means that the amount of acid sites measured at 50°C to 500°C is 0.25 mmol / g or more, and the amount of basic sites measured at 50°C to 500°C is 0.18 mmol / g or more. The amount of acid sites measured at 50°C to 500°C is more preferably 0.30 mmol / g or more, and even more preferably 0.40 mmol / g or more. The amount of basic sites measured at 50°C to 500°C is more preferably 0.25 mmol / g or more, and even more preferably 0.35 mmol / g or more.

[0032] Also, NH ４ -The maximum value (maximum peak) of the TPD curve is 3.0 × 10 －４ It is more preferable that the CO concentration is at least 100 mmol / g sec. ２ -The maximum value (maximum peak) of the TPD curve is 2.5 × 10 －４ It is more preferable that it is mmol / g·sec or more.

[0033] The measurement device used was BELCAT-A manufactured by Japan BEL, and the standard substance was NH ３ For the evaluation of base points, CO ２ The detector used was a TCD (Thermal Conductivity Detector).

[0034] Pretreatment with 20% O ２ After treatment at 370°C for 30 minutes in a 1 / He atmosphere, the sample was exposed to a standard substance at 50°C for 30 minutes to adsorb the standard substance. The temperature was then increased from 50°C to 500°C at a rate of 20°C / min, and the amount or temperature of the standard substance desorbed was evaluated.

[0035] The coexistence of the composite oxide contained in the additive of the present invention with the lithium-ion secondary battery positive electrode material means, as described above, a state in which the composite oxide is added during the assembly of a lithium-ion secondary battery, the preparation of a lithium-ion secondary battery positive electrode sheet, or the manufacture of a lithium-ion secondary battery positive electrode material. Generally, the lithium-ion secondary battery positive electrode material may be dispersed on the surface or in the layer of a positive electrode layer formed on a current collector. Therefore, preferably, the composite oxide as the additive coexists in the vicinity of the lithium-ion secondary battery positive electrode material on the surface or in the layer of the positive electrode layer. More preferably, the composite oxide as the additive coexists in contact with the lithium-ion secondary battery positive electrode material on the surface or in the layer of the positive electrode layer. While it is ideal for all of the added composite oxide to be in the above-described state, the effects of the present invention are sufficiently achieved even if only a portion of the composite oxide is in the above-described state.

[0036] The proximity of the positive electrode material for a lithium ion secondary battery is, for example, a distance at which lithium ions desolvated on the surface of the added composite oxide can reach the positive electrode material for a lithium ion secondary battery without resolvating in the solvent, and is, for example, 100 nm or less, more preferably 50 nm or less, and even more preferably 25 nm or less.

[0037] The composite oxide contained in the additive of the present invention preferably contains particles smaller than those of the positive electrode material of a lithium ion secondary battery. For example, ５０ So, D ５０ (composite oxide) <D ５０ It is more preferable that the relationship of (positive electrode material) is satisfied. ５０ (composite oxide) < [D ５０ (positive electrode material) / 10]. ５０is the particle size at which the cumulative volumetric frequency is 50%, and is also called the median size. The composite oxide contained in the additive of the present invention preferably contains 35% or more, more preferably 45% or more, of particles with a diameter of 1 μm or less on a volumetric basis. Since the effect of the composite oxide is greater with smaller particles, the content of such fine particles is preferable. In other words, it is more preferable for there to be many fine particles attached to or in close proximity to each particle of the positive electrode material. The above-mentioned state is more preferable because desolvation and solvation of lithium ions occur on the surface of the composite oxide that is the additive of the present invention, and lithium ions are efficiently supplied to each particle of the positive electrode material, as described above.

[0038] The composite oxide of the present invention is an oxide containing two or more types of cations (M １ , M ２ , M ３ , M ４ , ..., M ｎ ) O ｘ However, for the reasons mentioned above, M １ , M ２ , M ３ , M ４ , ..., M ｎ does not include alkali metal ions and alkaline earth metal ions. ｘ O ｙ Simple oxides such as these cannot have both acidic and basic sites, and therefore cannot achieve the effects of the present invention. Having both acidic and basic sites can be achieved by appropriately combining multiple cations. Combining multiple cations with different valences and electronegativity creates a large polarization state on the surface of the composite oxide, i.e., creates acidic and basic sites. However, since the polarization state varies depending on the coordination state of the cations and the crystalline structure of the composite oxide, there is no set rule for the combination. To achieve the effects of the present invention, the acidic and basic sites must be determined as described above. More preferably, oxygen vacancies are formed. The presence of oxygen vacancies facilitates the formation of acidic and basic sites.

[0039] The composite oxide is represented by the composition formula Mｘ Zr １－ｘ O ２－ｙ ...composition formula (1) and it is more preferable that M contains a trivalent metal ion. Zirconium (Zr) ions are stable against oxidation and reduction and are difficult to dissolve as a single cation ion, making them a preferable component of the additive material to be put into a battery. In addition, zirconium oxide (ZrO ２ By substituting a portion of x with a trivalent cation M, oxygen vacancies are formed, which makes it possible to effectively form acid sites and basic sites as described above, making this more preferable. While 0 < x < 1 and 0 < y < 0.5 are sufficient, from the viewpoint of the degree of association of the oxygen vacancies formed, 0 < x < 0.9, 0 < y < 0.45 are more preferable, and 0.1 < x < 0.6 and 0.05 < y < 0.3 are even more preferable. Furthermore, the composite oxide of composition formula (1) is preferably a cubic or pseudo-cubic crystal.

[0040] The M is preferably a trivalent cation of a rare earth element, scandium, or yttrium. More preferably, the M is a composite oxide containing one or more trivalent metal ions selected from La, Pr, Sm, Nd, Gd, Yb, Ho, and Y. Oxygen vacancies formed by these cations are easily arranged to form acid sites and base sites. In addition, composite oxides containing multiple types of cations as the M may be preferable.

[0041] It is more preferable that the M contains a metal ion of Ce. The valence of the metal ion (cation) of Ce is preferably tetravalent. Tetravalent M cannot form oxygen vacancies, but has a higher electron density than Zr ions, which is more preferable as it increases the relative dielectric constant of the composite oxide. The Ce contained in the composite oxide is more preferably 0.05 or more and 0.9 or less, more preferably 0.1 or more and 0.8 or less, and even more preferably 0.1 or more and 0.6 or less, in terms of the Ce / (Ce+Zr) molar ratio.

[0042] The composite oxide contained in the additive of the present invention has a specific surface area of ​​35 m 2 / g or more. 2By making the specific surface area 55 m / g or more, the number of sites for solvation and desolvation of lithium ions increases, so that the effect of the present invention becomes more pronounced. Alternatively, a sufficient effect can be obtained with a small amount of additive. For the above reasons, the specific surface area is preferably even larger, and 55 m 2 / g or more is more preferable, and 60m 2 / g or more, 70m 2 / g or more, 80m 2 / g or more, 90m 2 / g or more, 100m 2 / g or more, 150m 2 / g or more is more preferable. Experimentally, it is possible to further increase the specific surface area of ​​the composite oxide, but industrially, it is not possible to increase the specific surface area to 200 m ２ The maximum is about / g.

[0043] The specific surface area can be measured by pre-treating the sample by placing about 0.3 g of the sample in a flask-type sample cell, degassing it using a FloVac degasser (manufactured by Anton Paar Japan) at 370°C for 40 minutes under a nitrogen gas flow, and then using a surface area measuring device (NOVAtouch NX-4LX-1, manufactured by Anton Paar Japan) by the BET method (single-point method) using nitrogen gas adsorption.

[0044] Next, a method for producing an additive for a positive electrode of a lithium ion secondary battery using the electrolyte solution of the present invention will be described.

[0045] The additive for the positive electrode of a lithium ion secondary battery using the electrolyte solution of the present invention may be prepared by any method that can produce a composite oxide that satisfies the requirements of the present invention. Examples include solid-state reaction, chemical vapor deposition, hydrothermal, wet synthesis, sol-gel, and spray pyrolysis. An example of wet synthesis is shown below.

[0046] First, the raw materials of the composite oxide contained in the additive are dissolved in water to prepare a raw material aqueous solution. Examples of the raw materials include water-soluble salts such as nitrates, chlorides, sulfates, and acetates. Specific examples of raw materials include zirconium oxychloride, and chlorides of cations other than zirconium, such as La, Pr, Sm, Nd, Gd, Yb, Ho, Ce, and Y. These raw materials are dissolved in water (preferably pure water or ion-exchanged water) at a predetermined molar ratio to obtain an aqueous solution containing all the raw materials. The dissolving and stirring methods are not particularly limited.

[0047] Next, a precipitant is added to the raw material aqueous solution to co-precipitate the composite oxide raw materials, obtaining a precipitate (slurry). The precipitant, for example, controls the pH to a pH range in which the metal ions precipitate. Typically, precipitation can be achieved by raising the pH (making the solution basic) by adding a basic compound such as aqueous ammonia or a hydroxide (NaOH, KOH, etc.). The resulting slurry is preferably heated to 70 to 90°C. The heating method is not particularly limited. Heating the slurry promotes olation and oxidation reactions within the precipitate. For example, the resulting slurry is heated to between 70 and 90°C and maintained at this temperature for 4 to 10 hours (aging). During the aging process, stirring operations commonly performed in the industry, such as stirring with a stirring blade or circulation using a pump, can be performed in combination, which is preferred.

[0048] Alternatively, the raw aqueous solution may be heated and the precipitant added. Heating the raw aqueous solution changes the behavior of nucleation, which can change the aggregate structure of the precipitate.

[0049] The aged slurry is subjected to solid-liquid separation and washing. There is no particular restriction on the means for the solid-liquid separation, and industrially used equipment such as a centrifugal separator or a filter can be used. The washing operation is an operation for reducing chloride ions from the hydroxide slurry containing zirconium and other cations, which is the raw material for the composite oxide. For example, the hydroxide is dispersed in pure water, and then the washing operation is carried out using a centrifugal separator and a filter. It is preferable to continue this washing operation until the chloride ion content in the hydroxide is 3% or less by mass.

[0050] The washed precipitate containing zirconium and other cations is then dried using an industrially used external heat or internal combustion drying device, for example, at a temperature of about 100 to 200°C using hot air or a heater. Alternatively, spray drying may be used.

[0051] Drying is followed by calcination. The temperature of the calcination furnace is appropriately determined so as to meet the requirements of the present invention in accordance with the precipitation and drying conditions, for example, 400 to 900°C. The calcination time is usually between 30 minutes and 10 hours and, like the calcination temperature, is appropriately determined so as to meet the requirements of the present invention. The drying and calcination operations can be performed independently or as a continuous series of operations. The precipitate can also be calcined directly without the drying step.

[0052] Composition formula M ｘ Zr １－ｘ O ２－ｙ In this case, the firing conditions are preferably such that a pseudocubic crystal is formed. For example, firing is performed at a temperature of 900°C or less, more preferably 600°C or less.

[0053] The calcination process dehydrates the hydroxide containing zirconium and other cations, which are the raw materials for the composite oxide, to form these composite oxides. The composite oxide thus obtained may be pulverized to adjust the particle size, as necessary. The pulverization may be carried out using an industrially used mill such as a stamp mill, roller mill, jet mill, or ball mill, as long as the desired particle size is achieved.

[0054] In one embodiment of the present invention, a lithium-ion secondary battery positive electrode material is provided, which contains the additive for the lithium-ion secondary battery positive electrode. The composite oxide obtained above is used as the additive and mixed with a lithium-ion secondary battery positive electrode material containing one or more cations selected from the elements Mn, Fe, Ni, and Co to obtain a positive electrode active material. When the additive coexists with the positive electrode material, mixing may be performed using an industrial mixer such as a V-type mixer, a screw mixer, or an air mixer. Furthermore, heat treatment at 200°C to 400°C may be performed after mixing.

[0055] In one embodiment of the present invention, a lithium ion secondary battery is provided that includes the above-described lithium ion secondary battery positive electrode material. When the lithium ion secondary battery positive electrode material containing the above-described additive is used as the positive electrode active material, a material capable of absorbing and releasing lithium, such as a carbon material or a lithium absorbing alloy, is used as the negative electrode active material, and a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous electrolyte solution or a resin can be used as the electrolyte. For example, lithium hexafluorophosphate (LiPF ６ ) is used, and a mixed solution of ethylene carbonate and diethyl carbonate is used as the non-aqueous electrolyte. ４ , LiAsF ６ , LiBF ４ , LiSO ３ CF ３ , LiN(SO ３ CF ３ ) ２ As the non-aqueous electrolyte, diethyl carbonate, propylene carbonate, vinylene carbonate, or a mixture thereof can be used.

[0056] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0057] Example 1 Composition Formula Y ０．３ Zr ０．７ O １．８５Zirconium oxychloride and yttrium chloride adjusted to the above pH were mixed to prepare an aqueous solution. Ammonia water was added dropwise to the aqueous solution while stirring to raise the pH and cause co-precipitation, obtaining a precipitate. The solution slurry containing the precipitate was aged at 80°C for 6 hours. The slurry was subjected to a filtration-washing procedure five times using a filtration device to obtain a precipitate cake. The obtained cake was placed in a sagger and dried at 120°C for 10 hours. The dried sample was fired at 600°C for 10 hours. The fired sample obtained was pulverized using a jet mill to be used as an additive for the positive electrode of a lithium-ion secondary battery.

[0058] Examples 2 to 11 In Examples 2 to 11, the aqueous solutions were prepared to have the compositions shown in Table 1, and the additives for the positive electrodes of lithium ion secondary batteries were prepared under the same conditions as in Example 1.

[0059] Comparative Example 1 In Comparative Example 1, no additive was added, and only the positive electrode material was used as the positive electrode active material.

[0060] (Comparative Example 2) ZrO was used as a comparative oxide. ２ was prepared. ２ In the study, an aqueous solution of zirconium oxychloride was prepared by dissolving it in water, and ammonia water was added dropwise to the aqueous solution while stirring to raise the pH and cause co-precipitation, thereby obtaining a precipitate. The solution slurry containing the precipitate was aged at 80°C for 6 hours. The slurry was subjected to a filtration-washing procedure five times using a filtration device to obtain a precipitate cake. The obtained cake was placed in a sagger and dried at 120°C for 10 hours. The dried sample was calcined at 600°C for 10 hours. The calcined sample was then pulverized using a jet mill.

[0061] (Comparative Example 3) BaTiO ３ The reagent KZM-50 manufactured by Sakai Chemical Industry Co., Ltd. was used.

[0062] Comparative Examples 4 and 5 Comparative Examples 4 and 5 were prepared under the same conditions as in Example 1, except that zirconium oxychloride and chlorides containing each element were used as starting materials so as to have the compositions shown in Table 1.

[0063] The obtained sample was evaluated by X-ray diffraction. A sample of the composite oxide (=additive) for use as a positive electrode active material in a lithium-ion secondary battery was placed in a sample holder, and X-ray diffraction measurement was performed using a Rigaku MiniFlex 600 desktop X-ray diffractometer (CuKα radiation source) under the conditions of a 2θ measurement angle range of 20 to 80°, a step of 0.02°, and a scan speed of 5° / min.

[0064] <Reactivity with Positive Electrode Material> To evaluate whether the composite oxide coexists with the positive electrode material of a lithium ion secondary battery, the base positive electrode material and the additive composite oxide were mixed, and it was confirmed by X-ray diffraction whether only the diffraction peaks of the positive electrode material and the composite oxide were observed. ２ or LiNi ０．５ Co ０．２ Mn ０．３ O ２ The powder was mixed with additives such as composite oxides in a mortar at a mass ratio of 5:1, and then fired at 400°C for 10 hours. X-ray diffraction measurements were performed on the fired product (Rigaku MiniFlex 600 desktop X-ray diffractometer, CuKα radiation source). The X-ray diffraction measurements were performed under the following conditions: 2θ measurement angle range of 20 to 80°, step of 0.02°, and scan speed of 5° / min.

[0065] <Evaluation of acid and base sites> The acid and base sites were measured using a BELCAT-A made by Japan BEL, and the amount of desorption of the standard substance or the temperature was evaluated. The standard substance was NH ３ For the evaluation of base points, CO ２ The detector used was a TCD (Thermal Conductivity Detector). ２ After treatment at 370°C for 30 minutes in a / He atmosphere, the sample was exposed to a standard substance at 50°C for 30 minutes to adsorb the standard substance. The temperature was then increased from 50°C to 500°C at a rate of 20°C / min, and the amount or temperature of the standard substance desorbed was evaluated.

[0066] <Particle Size Distribution Measurement> The particle size distribution was measured by dispersing a sample in a sodium hexametaphosphate solution using an ultrasonic homogenizer (US-300AT, manufactured by Nippon Seiki Seisakusho) and evaluating the dispersion using a particle size distribution measuring instrument MT3300EXII (manufactured by Microtrac Bell).

[0067] <Measurement of Specific Surface Area> The specific surface area was measured by pretreatment, in which approximately 0.3 g of a sample was placed in a flask-type sample cell, and degassed using a FloVac degasser (manufactured by Anton Paar Japan) at 370°C for 40 minutes under a nitrogen gas flow. Thereafter, the specific surface area was measured by the BET method (single-point method) using nitrogen gas adsorption using a surface area measuring device (NOVAtouch NX-4LX-1, manufactured by Anton Paar Japan).

[0068] <Dielectric Constant Measurement> The dielectric constant of the obtained composite oxide was measured at 25°C. The instrument used was an Agilent 4294A (manufactured by Agilent Technologies). Evaluation was performed in the frequency range of 40 Hz to 110 MHz. The Cole-Cole function was used for fitting, and the powder dielectric constant was calculated using the Bruggman model. The relative dielectric constant was calculated as the ratio of the dielectric constant of each composite oxide based on the dielectric constant of a vacuum.

[0069] <Battery Fabrication> The additives such as the composite oxides synthesized in each example and comparative example were mixed with the positive electrode material to prepare a positive electrode active material. ２ and LiNi ０．５ Co ０．２ Mn ０．３ O ２ In Comparative Example 1, a battery was fabricated using only the positive electrode material as the positive electrode active material without adding any composite oxide. In Examples 1 to 11 and Comparative Examples 2 to 5, 1 mol % of an additive such as a composite oxide was weighed out relative to the positive electrode material, and they were mixed in a mortar. The mixed powder was kept at 400°C for 10 hours, and the resulting fired powder was used as the positive electrode active material to fabricate a positive electrode.

[0070] Acetylene black was used as the conductive additive, and PVdF was used as the binder. The positive electrode active material, conductive additive, and binder were weighed out in a weight ratio of 7:2:1, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode slurry. The resulting slurry was applied to an aluminum current collector, dried, punched into a disk, and pressed to prepare a positive electrode.

[0071] The positive electrode, negative electrode, and electrolyte of the examples and comparative examples were, in that order, metallic lithium cut into a disk shape, a solvent made of a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 3:7, and a solute LiPF ６ The resulting solution was used (laminated) at 1 mol / L to assemble a coin-type battery CR2032 type (diameter 20 mm, height 3.2 mm), and the battery was evaluated and measured.

[0072] <Charge / discharge test> LiCoO ２ A charge-discharge test of a coin-type lithium-ion secondary battery fabricated using this as the positive electrode material was conducted using a TOSCAT-3100 (manufactured by Toyo Systems). The coin-type lithium-ion secondary battery was placed in a thermostatic chamber at 25°C, with a reference capacity of 1C set to 160 mA / g, an upper limit voltage of 4.5 V, and a lower limit voltage of 3.3 V. The charge rate was 1C, and the discharge rate ranged from 0.1C to 100C, with 41 repeated charge-discharge tests. Two cycles were conducted at 0.1C, one each at 0.2C and 0.5C, and five cycles at 1C or higher. A four-hour wait was allowed before the start of the test. A one-hour rest period was allowed after each charge and discharge.

[0073] <Deterioration test> LiNi ０．５ Co ０．２ Mn ０．３ O ２ A deterioration test was conducted on a coin-type lithium-ion secondary battery fabricated using the above as the positive electrode material. The test was conducted using an Electrofield ABE1024-5V device. The coin-type lithium-ion secondary battery was placed in a thermostatic chamber at 45°C, and was charged at a constant current rate of 0.2C with a reference capacity of 1C of 140mA / g. After the voltage reached 4.2V, constant voltage charging was continued for 336 hours.

[0074] <Impedance Measurement> After the charge / discharge test and the deterioration test, the coin-type lithium ion secondary battery was subjected to impedance measurement in a thermostatic chamber at 20°C using VSP-300 (manufactured by biologic).

[0075] LiCoO ２ The coin-type lithium ion secondary battery using LiCoO as the positive electrode material was measured at a potential of 4.5 V, an AC amplitude of 10 mV, and a frequency range of 5 mHz to 7 MHz. The obtained data was fitted to the equivalent circuit shown in Figure 1, and the ２ The interfacial charge transfer resistance R of the coin cell using only ＬＣＯ and the charge transfer resistance R of each battery ｃｔ－ＬＣＯ was calculated. ２ The interfacial charge transfer resistance R of a coin-type lithium ion secondary battery using only ＬＣＯ is used as a reference, and R ｃｔ－ＬＣＯ Ratio R ｃｔ－ＬＣＯ / R ＬＣＯ asked for.

[0076] LiNi ０．５ Co ０．２ Mn ０．３ O ２ The coin-type lithium ion secondary battery using the positive electrode material was measured at a potential of 4.2 V, an AC amplitude of 10 mV, and a frequency range of 10 mHz to 200 kHz. The obtained data was fitted to the equivalent circuit shown in Figure 2 to obtain the interfacial charge transfer resistance R ｃｔ－ＮＣＭ was calculated. ０．５ Co ０．２ Mn ０．３ O ２ The interfacial charge transfer resistance R of a coin-type lithium ion secondary battery using only ＮＣＭ is used as the standard, and the R ｃｔ－ＮＣＭ Ratio R ｃｔ－ＮＣＭ / R ＮＣＭ asked for.

[0077]

[0078] As shown in Table 1, Examples 1 to 11 have a relative dielectric constant of 20 or more and contain both acid sites and basic sites, and the effects of the present invention were confirmed. The specific amounts of acid sites and basic sites in Examples 1 to 11 are 0.25 mmol / g or more when measured at 50°C to 500°C, and 0.18 mmol / g or more when measured at 50°C to 500°C. These composite oxides were prepared by mixing LiNi ０．５ Co ０．２ Mn ０．３ O ２ The mixture was mixed at a mass ratio of 5:1 and fired at 400°C for 10 hours to give LiCoO ２ or LiNi ０．５ Co ０．２ Mn ０．３ O ２ Only diffraction peaks attributable to the composite oxides of the examples were observed. This confirmed that these composite oxides do not react with the positive electrode material containing Ni, Co, Mn, or Fe. On the other hand, in Comparative Examples 4 and 5, the base material LiCoO ２ or LiNi ０．５ Co ０．２ Mn ０．３ O ２ Peaks other than the diffraction peaks attributable to the additives and LiCoO ２ or LiNi ０．５ Co ０．２ Mn ０．３ O ２ It was confirmed that the compound reacts with the formula M ｘ Zr １－ｘ O ２－ｙ Even when M is an element in Table 1 and x is 0.1, 0.5, 0.7, 0.9, etc., composite oxides that satisfy the requirements of the present invention can be produced, and the effects of the present invention have been confirmed.

[0079] For each battery, the ratio of interfacial charge transfer resistances R ｃｔ / R was calculated, and ２ or LiNi ０．５ Co ０．２ Mn ０．３ O ２ It was confirmed that when the positive electrode material was used, the battery using the additive material of the example showed a smaller value than the comparative example. ｃｔThe smaller the value of / R, the smaller the charge transfer resistance and the more improved the rate characteristics. From this, it was confirmed that the composite oxides described in the examples have the effect of improving the rate characteristics of coin-type lithium ion secondary batteries.

Claims

1. An additive for a positive electrode of a lithium ion secondary battery that uses an electrolyte, the additive comprising a complex oxide that coexists with a positive electrode material of a lithium ion secondary battery that contains cations of one or more elements selected from Mn, Fe, Ni, and Co, the complex oxide being free of alkali metal ions and alkaline earth metal ions, having both acid sites and base sites, and having a relative dielectric constant of 20 or greater.

2. The composition formula of the composite oxide is: M ｘ Zr １－ｘ O ２－ｙ 2. The additive according to claim 1, wherein the element M contains a trivalent metal ion, and the molar ratios x and y satisfy 0<x<1 and 0<y<0.5, respectively.

3. The additive according to claim 2, wherein M contains one or more trivalent metal ions selected from the group consisting of La, Pr, Sm, Nd, Gd, Yb, Ho, and Y.

4. The additive according to claim 2 or 3, wherein said M contains a metal ion of Ce.

5. The specific surface area of ​​the composite oxide is 35 m ２ 2. The additive according to claim 1, wherein the additive has a molecular weight of 1 / g or more.

6. A positive electrode material for a lithium ion secondary battery, comprising the additive material according to claim 1.

7. A lithium ion secondary battery comprising the positive electrode material of claim 6.

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