JP6008134B2 - Lithium secondary battery positive electrode active material and lithium secondary battery using the positive electrode active material - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a positive electrode for a non-aqueous secondary battery using the same, and more specifically, a non-aqueous electrolyte having a spinel crystal structure and an expression potential of 4.7 V or more. The present invention relates to a positive electrode active material for a secondary battery and a method for producing the same.

  In recent years, with the widespread use of portable devices such as mobile phones and laptop computers, there is an increasing demand for small and lightweight secondary batteries having high energy density. As such, there is a non-aqueous electrolyte type lithium ion secondary battery, and its research and development has been actively conducted and its practical application has been achieved. This lithium ion secondary battery includes a positive electrode using a lithium-containing composite oxide as an active material, and a material capable of inserting and extracting lithium, such as lithium, a lithium alloy, a metal oxide, or carbon, as an active material. The main component is a negative electrode to be processed and a separator or solid electrolyte containing a non-aqueous electrolyte.

Among these components, those studied as positive electrode active materials include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ), and the like. There is. In particular, a battery using a lithium cobalt composite oxide for the positive electrode has been developed to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained and put into practical use. Has reached.

  However, the demand for higher energy density for secondary batteries is increasing year by year, and lithium ion secondary batteries using a lithium cobalt composite oxide currently in practical use as a positive electrode are expensive because cobalt is a scarce resource. Therefore, there is a need for an alternative material that is cheaper than cobalt and can realize a high energy density.

Therefore, as a positive electrode active material for a non-aqueous electrolyte secondary battery, a lithium manganese oxide material having a spinel crystal structure is drawing attention instead of LiCoO ₂ . The spinel-type lithium manganese oxide includes Li ₂ Mn ₄ O ₉ , Li ₄ Mn ₅ O ₁₂ , LiMn ₂ O _4, etc. Among them, LiMn ₂ O ₄ has a Li (lithium) potential. On the other hand, since charging and discharging are possible in the 4V region, research is actively conducted (Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and the like).

  By the way, in order to increase the energy density of a battery, one method is to use a positive electrode active material having a high potential, and a high voltage of 300 V or more is required as a power source for an electric vehicle. Therefore, development of a positive electrode active material that operates at a higher voltage than spinel type lithium manganese oxide has been studied.

For example, in a lithium manganese nickel composite oxide in which manganese of spinel type lithium manganese oxide is partially substituted with nickel, it has been confirmed that an operating voltage of 4.5 V or more can be obtained on the basis of a metal lithium potential (Patent Document). 5, Patent Document 6).
In particular, the spinel type lithium manganese nickel composite oxide represented by the chemical formula 1 is known to stably develop a high voltage of about 4.75V.

LiMn _1.5 Ni _0.5 O _4. Chemical formula 1

However, the high-voltage active positive electrode active material having such a spinel structure has a problem that the battery capacity decreases due to repeated charge and discharge, and much research and development effort is used. Nevertheless, it has not been put to practical use.

  One of the causes of the capacity reduction is a problem that the electrolytic solution is decomposed during charging / discharging due to high voltage. Since the decomposition of the electrolytic solution is an irreversible reaction, the electrolytic solution, which is a lithium ion carrier between the positive electrode and the negative electrode, gradually decreases and the capacity decreases each time charging and discharging are repeated. In addition, the decomposed electrolytic solution generates a gas mainly composed of hydrogen or the like, which causes problems such as battery swelling.

  Another problem is elution of Mn. This problem is also observed in spinel type lithium manganese oxide and is not a problem specific to high voltage. This is particularly noticeable in high-temperature tests using a carbon-based material for the negative electrode. The reason why this becomes a problem is thought to be that Mn eluted from the positive electrode is deposited on the negative electrode, hindering the battery reaction at the negative electrode and reducing the capacity.

It is considered that elution of Mn from the spinel type lithium manganese oxide occurs by a disproportionation reaction as shown in the following chemical reaction formula. Mn ³⁺ in the spinel compound is separated into Mn ⁴⁺ and Mn ²⁺ , and Mn ²⁺ is eluted into the electrolyte.

2Mn ³⁺ → Mn ⁴⁺ + Mn 2 ⁺ ... Chemical reaction formula

In the spinel type lithium manganese oxide having an operating voltage of about 4 V, the formal charge of Mn is 3.5, that is, Mn ⁴⁺ and Mn ³⁺ exist in a one-to-one ^relationship . This problem is essential in the spinel-type manganese oxide using LiMn ₂ O ₄ since the redox reaction of Mn ³⁺ / Mn ⁴⁺ is also used in the charge / discharge reaction.

  As countermeasures for this problem, for example, in Patent Document 7, Mn is replaced with a low-valent element such as Li, or a composition in which oxygen is excessive than usual is created by devising firing conditions during synthesis. Thus, a method of oxidizing trivalent Mn to tetravalent by the charge compensation is disclosed.

On the other hand, in the spinel type lithium manganese nickel composite oxide having an operating voltage of about 5 V, the formal charge of Mn is ⁴⁺ . Mn ³⁺ does not exist, and instead Ni exists in a divalent state, so that the average formal charge of Mn and Ni is 3.5. Mn does not contribute to charging / discharging, and utilizes a redox reaction of Ni ²⁺ / Ni ³⁺ and Ni ³⁺ / Ni ⁴⁺ .

Ideally, in a spinel type lithium manganese nickel composite oxide having no Mn ³⁺ , the elution of Mn shown in the chemical reaction formula should not be an essential problem. However, in our study results, especially when a carbon negative electrode is used at high temperatures, the cycle characteristics of the spinel type lithium manganese nickel composite oxide are not practical, and the cause is mainly related to elution of Mn and Ni. thinking.

  The reason why Mn is eluted like the spinel type lithium manganese oxide is considered to be due to the property that the spinel type manganese oxide easily causes oxygen defects. When oxygen vacancies occur, tetravalent Mn is reduced to trivalent for charge compensation, causing elution.

  As described earlier, spinel lithium manganese oxide is effective to create an oxygen-excess composition as a countermeasure against elution. At that time, trivalent manganese becomes tetravalent in response to an increase in the negative charge of oxygen. Keep electrical neutrality. However, in spinel type lithium manganese nickel composite oxide, Ni is divalent and Mn is tetravalent, and extreme oxidation conditions are required for either or both metals to have an oxidation number higher than that. Not right. Therefore, it is difficult to produce an oxygen-excess composition excellent in cycle characteristics similar to that of a spinel type lithium manganese nickel composite oxide.

  In order to solve the above problems, it has been proposed to replace the spinel type lithium manganese oxide with a different element.

  For example, Patent Document 8 discloses that manganese of spinel type lithium manganese oxide is substituted with Ti, V, Cr, Fe, Co, Ni, Zn, Cu, W, Mg, and Al. However, the problem is elution of the positive electrode in a battery operating in the region of about 4 V, and the effect on the positive electrode active material of the present invention operating in the 5 V region is unclear.

Patent Document 9 discloses a dissimilar element substituted spinel type lithium manganese oxide containing at least cobalt on the premise of an operating voltage of 5V class. This material is a material utilizing the oxidation / reduction of Co ³⁺ / Co ⁴⁺ and is different from the material utilizing the oxidation / reduction of Ni ²⁺ / Ni ⁴⁺ of the present invention. The purpose of the additive element is also focused on changing the valence of Mn, but not on increasing the average oxidation number. In the examples, Li metal is used for the negative electrode, but it is considered that the cycle characteristics when the carbon negative electrode is used are insufficient.

JP-A-6-76824 Japanese Patent Laid-Open No. 7-73883 JP-A-7-230802 JP 7-245105 A JP-A-9-147867 Japanese Patent Application Laid-Open No. 11-73962 Japanese Patent No. 4830136 Japanese Patent No. 4734684 Japanese Patent No. 4192477

  In view of such problems, the present invention, when used as a positive electrode active material of a lithium secondary battery, provides spinel-type lithium manganese nickel composite oxide particles having excellent cycle characteristics even when a carbon negative electrode is used, and a non-aqueous electrolyte 2 using the same. The next battery is to provide.

  As a result of intensive studies by the present inventors, by replacing nickel, a part of manganese of spinel type lithium manganese nickel composite oxide with a trivalent or higher element, and further substituting a part of manganese with a divalent element. It has been found that a spinel type lithium manganese nickel composite oxide having an oxygen excess composition can be obtained.

  That is, in the chemical formula 1, if the firing at the time of synthesis is performed under normal oxidizing atmosphere conditions, it is difficult to obtain an oxidation number of Mn of 4 or more, Ni of 2 or more, and an average valence of 3.5 or more. Hard to become. By substituting Ni with an element having a higher valence, the average valence including the substitution element becomes 3.5 or more, and oxygen can have an excessive composition for charge compensation.

  However, it has been found that this alone compensates for charges by reducing Mn from tetravalent to trivalent without excessive oxygen. As a result of further detailed studies, it was found that Mn is not easily reduced to trivalent by substituting Mn with a small amount of a divalent element, and the present invention has been completed.

That is, the first invention of the present invention is represented by the following composition formula 1 and shows a diffraction pattern of a spinel type crystal structure of symmetry Fd-3m by XRD measurement, and the oxidation number of transition metal by potassium dichromate titration method in the oxidation number of Mn analysis in the analysis, the oxidation number of Mn is 3.97 or more, 4.00 Ri der below is calculated by the Scherrer equation from the full width at half maximum of the peak attributed to the XRD pattern (311) plane crystal child diameter 5000Å or less, the positive electrode active material for a non-aqueous electrolyte secondary battery, characterized der Rukoto than 1000 Å.

_{Li a Mn 2-x-y} -b Ni x-z T y + z A b O 4 composition formula 1

0.92 ≦ a ≦ 1.12
0.45 ≦ x ≦ 0.55
0 ≦ y <0.10
0.0010 ≦ z ≦ 0.20
0.0010 ≦ y + z ≦ 0.20
0.0010 <b ≦ 0.025
z> y

T = one or more elements selected from Co, Fe, Cr, Al, Ga, Ti and Si A = one or more elements selected from Mg and Zn

  A third invention of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein A is Mg.

A fourth aspect of the present invention, in the range of 400～700Cm ^-1 of FT-IR ^{measurement, 493~513cm -1, 549~559cm -1,} absorption peaks of infrared light in the range of 584～594Cm ^-1 One or more of them are not detected, which is a positive electrode active material for a non-aqueous electrolyte secondary battery.

A fifth invention of the present invention is manufactured by the manufacturing method according to the first invention, and the initial discharge capacity of the non-aqueous electrolyte secondary battery is a cutoff voltage of 2.5 to 4.8 V with respect to a lithium-based potential. A positive electrode active material for a non-aqueous electrolyte secondary battery, which is sometimes 200 mAh / g or more.

According to a sixth aspect of the present invention, a positive electrode is formed by the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of the first to fifth aspects, the initial discharge capacity is 125 mAh / g or more, and at 60 ° C. Charged to 0.6 mA / cm ² to a cut-off voltage of 4.9 V, and after a pause of 1 hour, the discharge was repeated 200 times to a cut-off voltage of 3.5 V. The discharge capacity at the 200th time was 70% of the discharge capacity at the second time. This is the nonaqueous electrolyte secondary battery.

  In the spinel type lithium manganese nickel composite oxide of the present invention, a positive electrode active material having an oxidation number of Mn of 3.97 or more and 4.00 or less is obtained, elution of manganese in the battery is suppressed, and an excellent cycle Show the characteristics.

FIG. 1 is a schematic cross-sectional view of a 2032 type coin battery used for battery evaluation. FIG. 2 is an FT-IR spectrum of the spinel type lithium manganese nickel composite oxide according to Example 1. 3 is an FT-IR spectrum of a spinel type lithium manganese nickel composite oxide according to Comparative Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail.
(1) Spinel-type lithium manganese nickel composite oxide The spinel-type lithium manganese nickel composite oxide of the present invention has the following composition formula.

_{Li a Mn 2-x-y} -b Ni x-z T y + z A b O 4 composition formula

0.92 ≦ a ≦ 1.12
0.45 ≦ x ≦ 0.55
0 ≦ y <0.10
0.0010 ≦ z ≦ 0.20
0.0010 ≦ y + z ≦ 0.20
0.0010 <b ≦ 0.025
z> y

T is one or more elements selected from Co, Fe, Cr, Al, Ga, Ti and Si. A is one or more elements selected from Mg and Zn.

The present invention relates to a positive electrode active material for a lithium secondary battery in which a part of a spinel type lithium manganese nickel composite oxide is replaced with Co, Fe, Cr, etc., and Mg or Zn in order to improve cycle characteristics.

In the formula, T is one or more trivalent or more elements selected from Co, Fe, Cr, Al, Ga, Ti, and Si. It is added mainly for the purpose of increasing the average oxidation number of Mn, Ni, and T, making it easy to produce an oxygen-excess composition, and improving cycle characteristics by substituting for Ni.
The spinel structure can be maintained even if the above elements are added to the spinel type lithium manganese nickel composite oxide. In particular, considering the ease of addition and element toxicity, it is preferable to use Co, Fe, or Ti.

In the formula, A is one or more divalent metal elements selected from Mg and Zn. Added to prevent Mn from being reduced to trivalent for charge compensation and preventing the formation of oxygen-excess composition by substituting for Mn to replace trivalent or higher T with Ni Is done.
The spinel type lithium manganese nickel composite oxide can maintain the spinel structure even when the above elements are added. In particular, Mg is a light element and is preferable because an effect of weight reduction can be obtained.

  Shifting the composition of Li from the stoichiometric ratio is a well-known method. A in the formula represents the composition of Li, 0.90 ≦ a ≦ 1.15, and more preferably 0.92 ≦ a ≦ 1.12. If a is less than 0.90, the amount of Li that contributes to charging and discharging in the battery decreases, and the battery capacity decreases, which is not preferable. If a is 1.15 or more, it is not preferable because a large amount of lithium that is inactive for redox reduction reduces the capacity.

  x is the substitution amount of Ni with respect to Mn. 0.40 ≦ x ≦ 0.60, more preferably 0.45 ≦ x ≦ 0.55. The range of the value is to obtain a stable capacity at an operating voltage of about 5 V, and when it is less than 0.40, Ni showing a redox potential of 5 V class is not preferable. If it exceeds 0.6, the number of divalent nickel increases and the average oxidation number decreases, which is not preferable.

  y and z represent the amount of substitution of T with respect to Mn and Ni, respectively, and 0.0010 ≦ y + z ≦ 0.20, more preferably 0.0050 ≦ y + z ≦ 0.10. If it is less than 0.0010, the addition of the expensive element of the present invention is not preferable because the average oxidation number of metals other than Li is increased and the object of producing an oxygen-excess spinel is not achieved, and the cycle characteristics deteriorate. . If it exceeds 0.20, the added expensive element T, itself, is not preferable because it does not undergo oxidation and reduction at the target voltage and the battery capacity decreases.

  Since 0.0010 ≦ z for 0 ≦ y, substitution of T for Mn is not essential, but substitution of T for Ni is essential. Furthermore, y <z must be satisfied. This is because an increase in the average oxidation number oxidation number requires substitution of T for divalent Ni rather than tetravalent Mn.

  b is the substitution amount of A with respect to Mn. It serves to prevent Mn from becoming trivalent for charge compensation by replacing Ni with T. 0.0010 ≦ b ≦ 0.025, more preferably 0.0030 <b ≦ 0.010. If it is less than 0.0010, the effect of preventing Mn from becoming trivalent cannot be obtained. If it exceeds 0.025, excessive substitution of a divalent element such as A with tetravalent Mn will eventually lower the average oxidation number of metals other than Li and impair the cycle characteristics. It is.

  Note that the subscript 4 of O in the composition formula 1 does not have to be exactly 4. As the object of the present invention, a number other than 4 can be taken due to the influence of the synthesis conditions and additive elements.

  In order for a material having such a composition to exhibit high cycle characteristics with respect to the carbon negative electrode, it is preferable to further exhibit the following conditions.

  When the spinel type lithium manganese nickel composite oxide of the present invention is measured by XRD, it shows a diffraction pattern identified as a spinel type crystal structure of symmetry Fd-3m. The crystallite size calculated by the Scherrer equation from the half width of the peak attributed to the Miller index (311) near 2θ = 36 ° C. is preferably 5000 mm or less and 1000 mm or more. In the case of 5000 mm or more, since the size of the crystal is large, cracks may occur in the particles due to stress generated by the expansion and contraction of the crystal lattice during charge and discharge, and cycle stability during battery reaction may be lowered. Further, when the crystallite diameter is 1000 mm or less, the crystal structure of the particles is not sufficiently developed, so that Mn elution increases and the cycle characteristics may be lowered.

When the spinel-type lithium-manganese-nickel composite oxide FT-IR measurements, in the range of ^{400~700cm -1, 493~513cm -1, 549~559cm -1} , infrared light having a peak near 584～594Cm ^-1 Preferably, any one or more of the absorptions are not detected. In the spinel type lithium manganese nickel compound represented by Chemical Formula 1, the above three absorption peaks are detected (see FIG. 3 and Comparative Example 1). The reason why it is preferable not to observe any one or more of the absorptions of infrared light is unclear, but for example, these peaks may be attributed to the ordered arrangement of Mn and Ni in the crystal. When three peaks are present, it is considered that the crystal structure is an ordered arrangement of Mn and Ni, and the stability of the structure is lowered, so that Mn is likely to be eluted. The criteria for judging that there is no peak are as follows.

Absorbance maxima between 1) 493~513cm ^-1, the absorbance maximum between 480~490cm divided by the minimum value of absorbance between ^-1 1.30 2) 549~559cm ^-1, 560~570cm absorbance maxima between absorbance minimum divided by 1.30 or less in value 3) 584～594Cm ^-1 between ^-1, divided by the minimum value of absorbance between 606～616Cm ^-1 values Is 1.20 or less

The nitrogen 0.050 M ² / g or more in specific surface area measured by the BET method using, is preferably 2.0 m ² / g or less, more preferably 0.10 m ² / g or more, 1.0 m ² / g It is as follows. Both the decomposition of the electrolyte solution and the elution of Mn, which are considered to be the cause of the cycle characteristics, are reactions that occur at the oxide particle-electrolyte interface. When the specific surface area is 2.00 m ² / g or more, these side reactions tend to occur, which is not preferable for cycle characteristics. In the case of 0.05 m ² / g or less, the target charge / discharge reaction is also suppressed, and the battery capacity is reduced, which is not preferable.

In the transition metal oxidation number analysis by the potassium dichromate titration method, the Mn oxidation number analysis is 3.95 or more and 4.00 or less, more preferably 3.97 or more and 4.00 or less. In the case of 3.93 or less, oxygen defects are generated and cycle characteristics are deteriorated regardless of the addition of T element and A element. Since tetravalent or higher Mn is unlikely to be generated under normal oxidation conditions, it is difficult in principle to be 4.00 or higher.
(2) Method for Producing Spinel Type Lithium Manganese Nickel Composite Oxide Next, an example of a method for producing a compound having such a composition is shown below. The production method is not limited to the following production methods.
[First step]
A mixed aqueous solution of a manganese salt, a nickel salt, a salt of M element, and a salt of A element is prepared so that the atomic ratio of manganese and nickel in the aqueous solution is substantially the composition ratio of Composition Formula 1. At this time, it may be prepared as a third aqueous solution in which the concentration and amount are adjusted so as to achieve the target composition ratio without using only a specific element as a mixed solution.

The mixed aqueous solution and the alkaline aqueous solution, if any, the third aqueous solution are simultaneously and continuously charged into the reaction vessel, and the temperature of the mixed solution in the reaction vessel is maintained in the range of 30 to 80 ° C., pH = 10. The coprecipitation is carried out while maintaining the range of 5 to 12.5.
Stirring is performed with a stirring blade of a stirrer so that the precipitate does not collect at the bottom of the tank and the particles of the precipitate grow stably.

  The amount of the mixed liquid charged into the reaction tank and the amount of precipitate generated are constant, and the amount of collected sediment discharged as an overflow from the reaction tank is constant. As a result, the slurry concentration in the reaction tank is constant. The collected precipitate is filtered and washed with water to obtain spherical or nearly spherical manganese nickel composite hydroxide particles. At this time, ammonia water may be added as a complexing agent together with a mixed aqueous solution of manganese salt and nickel salt and an alkaline aqueous solution, or air, nitrogen gas, etc. may be circulated in the reaction vessel to control the atmosphere in the reaction vessel. good.

  Here, the usable manganese salt is not particularly limited as long as it does not contain impurities that cause contamination when used as a positive electrode active material and is water-soluble. Specifically, manganese sulfate, manganese chloride Etc. Similarly, examples of usable nickel salts include nickel sulfate and nickel chloride.

  The same applies to the substitution elements of T and A. For example, Fe is iron sulfate, iron chloride, Co is cobalt sulfate and cobalt chloride, and Mg is magnesium sulfate and magnesium chloride.

  Furthermore, in Al, Si, etc., sodium aluminate, sodium silicate, etc. can be used as a water-soluble raw material. However, since these raw materials show alkalinity, they are not mixed with other aqueous raw materials exhibiting acidity, but are prepared as other third aqueous solutions, and dropped into the reaction tank while adjusting the flow rate so as to be the target composition. .

  The alkaline aqueous solution is not particularly limited as long as it does not contain impurities that may be mixed when used as the positive electrode active material, and an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or the like can be used.

  If the pH is less than 10.5, the solubility of manganese, nickel and the like is not sufficiently lowered, and the composition is eluted in the solution, and the composition of the resulting manganese nickel composite hydroxide may deviate from the target. When the pH exceeds 12.5, an alkaline aqueous solution is excessively used, and an extra volume of the reaction tank is required, which is not industrially preferable.

When the reaction temperature is less than 30 ° C., the solubility of manganese and nickel does not increase sufficiently, and the composition of the resulting manganese-nickel composite hydroxide may be deviated from the target. When it exceeds 80 ° C., energy is excessively required for heat retention, which is not industrially preferable.
[Second step]
Using a shaker mixer, a stirring mixer, a rocking mixer, etc. so that the composite hydroxide particles of metal such as manganese and nickel obtained in the first step and the lithium compound have the composition of composition formula 1, Firing is performed in an oxygen atmosphere or an air atmosphere at a temperature range of 800 ° C. to 1000 ° C. for 10 to 20 hours.

  Here, the usable lithium compound is not particularly limited as long as it does not contain impurities that may be mixed when used as the positive electrode active material, and specifically includes lithium carbonate, lithium hydroxide, lithium acetate, and the like. It is done.

  When the firing temperature is 800 ° C. or less, the firing temperature is too low, metal elements such as manganese, nickel, and lithium are not sufficiently diffused, the partial chemical composition is uneven, and the particles have a large specific surface area, which will be described later. The amount of manganese elution in the battery evaluation is increased, and the cycle characteristics are deteriorated. Firing at a temperature exceeding 1000 ° C. is not industrially preferable because it increases the capital investment cost of the firing furnace that can withstand it and consumes a large amount of energy.

  A firing time of less than 10 hours is not preferable because metal elements such as manganese, nickel, and lithium do not sufficiently diffuse and the partial chemical composition becomes nonuniform. Firing for more than 20 hours is not preferable because production efficiency decreases.

The fired particles are fired again at 600 to 800 ° C., which is lower than the firing temperature in the above step. This is to recover oxygen defects generated by the high-temperature firing in the above process. Oxygen defects are not recovered at a baking temperature of less than 600 ° C., and oxygen desorption proceeds again at a baking temperature of over 800 ° C.
(3) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and the like, and includes the same components as those of a general non-aqueous electrolyte secondary battery. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention can be variously modified based on the knowledge of those skilled in the art based on the embodiment described in the present specification. It can be implemented in an improved form. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.
(A) Positive electrode Using the positive electrode active material for a non-aqueous electrolyte secondary battery described above, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows.
First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and, if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste.
Each mixing ratio in the positive electrode mixture paste is also an important factor for determining the performance of the non-aqueous electrolyte secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass in the same manner as the positive electrode of a general non-aqueous electrolyte secondary battery, and the conductive material It is desirable to set the content of 1 to 20 parts by mass and the content of the binder to 1 to 20 parts by mass.

  The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

  In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used.

  The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin, polyacrylic. An acid or the like can be used.

If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.
(B) Negative electrode A negative electrode mixture in which a negative electrode active material capable of occluding and desorbing lithium ions is mixed with a binder and an appropriate solvent is added to the negative electrode. Is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.

As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, or a powdery carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the case of the positive electrode, and as a solvent for dispersing these active materials and the binder, N-methyl-2-pyrrolidone or the like can be used. Organic solvents can be used.
(C) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.
(D) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used.

Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.
(E) Battery shape and configuration The shape of the non-aqueous electrolyte secondary battery of the present invention composed of the positive electrode, negative electrode, separator and non-aqueous electrolyte described above can be various, such as a cylindrical type and a laminated type. Can be.

In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like and sealed in a battery case to complete a non-aqueous electrolyte secondary battery. .
(F) Characteristics The nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention has high capacity and high cycle characteristics even when the temperature is increased and the carbon negative electrode is used.
In particular, the non-aqueous electrolyte secondary battery using the positive electrode active material according to the present invention obtained in a more preferable form is a secondary battery having a high capacity and a high cycle characteristic when used for the positive electrode of a 2032 type coin battery, for example. It is done.

The secondary battery having a positive electrode using the positive electrode active material obtained according to the present invention will be described with respect to its production method and performance (initial discharge capacity, cycle characteristics) evaluation method.
(Battery manufacture and evaluation)
For the evaluation of the positive electrode active material, a 2032 type coin battery 1 (hereinafter referred to as a coin type battery) shown in FIG. 1 was used.

  The coin-type battery 1 includes a case 2 and an electrode 3 accommodated in the case 2.

The case 2 has a positive electrode can 2a that is hollow and open at one end, and a negative electrode can 2b that is disposed in the opening of the positive electrode can 2a. When the negative electrode can 2b is disposed in the opening of the positive electrode can 2a, A space for accommodating the electrode 3 is formed between the negative electrode can 2b and the positive electrode can 2a.
The electrode 3 includes a positive electrode 3a, a separator 3c, and a negative electrode 3b, which are stacked in this order. The positive electrode 3a contacts the inner surface of the positive electrode can 2a, and the negative electrode 3b contacts the inner surface of the negative electrode can 2b. As shown in FIG.

  The case 2 includes a gasket 2c, and relative movement is fixed by the gasket 2c so as to maintain a non-contact state between the positive electrode can 2a and the negative electrode can 2b. Further, the gasket 2c also has a function of sealing a gap between the positive electrode can 2a and the negative electrode can 2b to block the inside and outside of the case 2 in an airtight and liquid tight manner.

  The coin-type battery 1 was manufactured as follows.

  First, 52.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) are mixed and thinned to a weight of about 10 mg with a diameter of 10 mm. 3a was produced. The produced positive electrode 3a was dried at 120 ° C. for 12 hours in a vacuum dryer.

Using the positive electrode 3a, the negative electrode 3b, the separator 3c, and the electrolytic solution, the coin-type battery 1 described above was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C.
For the negative electrode 3b, a lithium metal foil was used for initial capacity evaluation, and graphite powder with an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and polyvinylidene fluoride were used for high temperature cycle characteristics evaluation. A negative electrode sheet coated with copper foil was used.

As the separator 3c, a polyethylene porous film having a film thickness of 25 μm was used. As the electrolytic solution, a 3: 7 mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF6 as a supporting electrolyte was used.
The initial discharge capacity and positive electrode resistance showing the performance of the manufactured coin battery 1 were evaluated as follows.

  The initial discharge capacity is left for about 24 hours after the coin-type battery 1 is manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm 2 and the cutoff voltage is 5. The capacity when the battery was charged to 0 V and discharged to a cutoff voltage of 3.5 V after a pause of 1 hour was defined as the initial discharge capacity.

  The cycle characteristic is 0.6 mA / cm 2 at 60 ° C., the battery is charged to a cut-off voltage of 4.9 V, and after a pause of 1 hour, the discharge is repeated 200 times to a cut-off voltage of 3.5 V, with respect to the second discharge capacity. The ratio of discharge capacity was evaluated as the capacity maintenance rate.

  When used as a practical battery material, it is preferable that the initial discharge capacity is 120 mAh / g or more and the capacity maintenance rate is 70% or more.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
[Example 1]
A mixed stock solution in which crystals of hydrates of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate are dissolved in pure water in a reaction vessel containing pure water preheated to 40 ° C. (Mn: Ni: in terms of metal element molar ratio) Co: Mg = 1.495: 0.400: 0.100: 0.005), reaction by dropping aqueous sodium hydroxide solution so as to maintain the pH at 11.5 while dropping ammonia water at a prescribed flow rate. First, a nickel manganese cobalt composite hydroxide slurry as a precursor is obtained by crystallization. Next, the obtained composite hydroxide is filtered and dried to obtain a powder. Lithium hydroxide monohydrate was calculated and weighed in an amount of 50 atomic% with respect to the total number of nickel, manganese and cobalt atoms in the powdered composite hydroxide, and a tumbler shaker mixer (D2 made by T2F). ).

  Next, the atmosphere is set to the atmosphere, held at 1000 ° C. for 12 hours, and fired in an atmosphere firing furnace (manufactured by Hiroki, model number HAF-2020S). Re-firing was performed using a model number HAF-2020S) to obtain a lithium manganese nickel cobalt composite oxide.

  The composition ratio of each component of the lithium manganese nickel cobalt composite oxide was chemically analyzed by ICP (Varian, 725ES). Table 1 shows the composition formula of the sample calculated from the chemical analysis results.

  When the lithium manganese nickel composite oxide was measured by XRD (manufactured by PANALYTICAL, X'Pert PROMRD), a peak of LiMn2O4 having a spinel crystal structure of the space group Fd-3m was detected. The crystallite diameter measured from the half width of the peak attributed to the (311) plane was 2297 mm.

A mixture of lithium manganese nickel composite oxide and KBr was pelletized, and the pellet was measured by FT-IR to obtain an FT-IR spectrum as shown in FIG. From the FT-IR ^{spectrum, 493~513cm -1, 549~559cm -1,} peak in the vicinity of 584~594cm ^-1 was observed.

When the BET specific surface area of the lithium manganese nickel cobalt composite oxide (manufactured by Mountech Co., Ltd., Macsorb) was measured, the BET value was 0.55 m ² / g.
The oxidation number analysis of Mn was performed using the potassium dichromate titration method. A 0.1 g sample was dissolved in a 0.025 mol / L FeCl ₂ aqueous solution, and 2 times diluted phosphoric acid 5.0 ml sulfuric acid and 2 times diluted sulfuric acid 10 ml were added dropwise. And titration with 0.017 mol / L potassium dichromate solution. The same test was performed on an undissolved aqueous solution of the sample, and the difference between the two was considered to be caused by Fe ³⁺ produced by the oxidation-reduction reaction. Under the assumption that it exists, the average valence of Mn was calculated. The oxidation number of Mn was 3.98.

Further, when the battery evaluation measurement was performed, as shown in Table 2, the initial charge capacity was 128 mAh / g, the initial discharge capacity was 125 mAh / g, and the capacity maintenance rate after 200 cycles by the cycle evaluation using the carbon negative electrode was 79%. there were.
[Example 2]
A mixed stock solution in which crystals of hydrates of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate are dissolved in pure water in terms of metal element molar ratio Mn: Ni: Co: Mg = 1.495: 0.450: 0.050 : A sample was synthesized in the same manner as in Example 1 except that it was prepared as 0.005.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.
Example 3
A mixed stock solution in which crystals of hydrates of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate are dissolved in pure water is expressed in terms of metal element molar ratio: Mn: Ni: Co: Mg = 1.495: 0.470: 0.030 : A sample was synthesized in the same manner as in Example 1 except that it was prepared as 0.005.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.
Example 4
A sample was synthesized in the same manner as in Example 2 except that the cobalt sulfate was changed to iron (II) sulfate.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. In the calculation of the Mn oxidation number, the calculation was performed under the assumption that all Fe is trivalent. The battery evaluation results are summarized in Table 2.
Example 5
A sample was synthesized in the same manner as in Example 2 except that cobalt sulfate was changed to chromium (III) chloride hexahydrate.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. In the calculation of the Mn oxidation number, the calculation was performed under the assumption that all of the Cr is trivalent. The battery evaluation results are summarized in Table 2.
Example 6
A sample was synthesized in the same manner as in Example 2 except that cobalt sulfate was changed to aluminum sulfate.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. In the calculation of the Mn oxidation number, calculation was performed under the assumption that all Al is trivalent. The battery evaluation results are summarized in Table 2.
Example 7
A sample was synthesized in the same manner as in Example 2 except that the cobalt sulfate was changed to a titanium sulfate solution.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. In the calculation of the Mn oxidation number, the calculation was performed under the assumption that all Ti is tetravalent. The battery evaluation results are summarized in Table 2.
Example 8
A sample was synthesized in the same manner as in Example 2 except that magnesium sulfate was changed to zinc sulfate.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. In the calculation of the Mn oxidation number, the calculation was performed under the assumption that all Zn is tetravalent. The battery evaluation results are summarized in Table 2.
Example 9
A mixed stock solution in which crystals of hydrates of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate are dissolved in pure water in terms of metal element molar ratio Mn: Ni: Co: Mg = 1.497: 0.450: 0.050 : A sample was synthesized in the same manner as in Example 8 except that it was prepared as 0.003.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.
Example 10
A mixed stock solution in which crystals of hydrates of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate are dissolved in pure water in terms of metal element molar ratio Mn: Ni: Co: Mg = 1.493: 0.450: 0.050 : A sample was synthesized in the same manner as in Example 8 except that it was adjusted to 0.007.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.
[Comparative Example 1]
A mixed stock solution in which crystals of hydrates of nickel sulfate and manganese sulfate were dissolved in pure water was prepared in the same manner as in Example 1 except that the molar ratio of metal elements was Mn: Ni = 1.500: 0.500. Samples were synthesized.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. FIG. 3 shows the FT-IR spectrum. ^{500cm -1,} 556cm ^-1, the infrared absorption peak was observed at 588cm ^-1. The battery evaluation results are summarized in Table 2.
[Comparative Example 2]
A mixed stock solution in which crystals of nickel sulfate, manganese sulfate, and cobalt sulfate hydrates were dissolved in pure water was prepared at a metal element molar ratio of Mn: Ni: Co: Mg = 1.500: 0.450: 0.050. A sample was synthesized in the same manner as in Example 1 except for the above.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.
[Comparative Example 3]
A mixed stock solution in which crystals of hydrates of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate were dissolved in pure water was Mn: Ni: Co: Mg = 1.495: 0.200: 0.300 in terms of metal element molar ratio. : A sample was synthesized in the same manner as in Example 1 except that it was prepared as 0.005.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.
[Comparative Example 4]
A mixed stock solution in which crystals of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate hydrates were dissolved in pure water was expressed in terms of metal element molar ratio: Mn: Ni: Co: Mg = 1.445: 0.500: 0.050 : A sample was synthesized in the same manner as in Example 1 except that it was prepared as 0.005.

Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.
[Comparative Example 5]
A mixed stock solution in which crystals of nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate hydrates were dissolved in pure water in terms of metal element molar ratio was Mn: Ni: Co: Mg = 1.470: 0.450: 0.050. : A sample was synthesized in the same manner as in Example 1 except that the sample was prepared as 0.030.

  Table 1 summarizes the composition, XRD, FT-IR, BET specific surface area, and Mn oxidation number of the sample measured. The battery evaluation results are summarized in Table 2.

[Evaluation of the present invention]
As shown in Examples 1 to 10, the spinel type lithium manganese nickel composite oxide having the composition of the composition formula 1 has an oxidation number of Mn of 3.97 or more, and generation of trivalent manganese that causes capacity deterioration Was suppressed. Moreover, it became clear from the FT-IR analysis that the crystal structure has a stable structure in which Mn and Ni are irregularly arranged.

  A secondary battery manufactured using this positive electrode active material has an initial discharge capacity of 125 mAh / g or more, and a capacity retention rate after 200 cycles is 70% or more even in cycle evaluation at 60 ° C. using a carbon negative electrode. This makes it possible to produce a secondary battery with excellent cycle characteristics.

1 Positive electrode (Evaluation electrode)
2 Carbon negative electrode 3 Separator 4 Gasket 5 Wave washer

Claims (6)

The diffraction pattern of the spinel crystal structure of symmetry Fd-3m shown by the following composition formula 1 is shown by XRD measurement, Mn oxidation number analysis in transition metal oxidation number analysis by potassium dichromate titration method, an oxidation number of 3.97 or more, 4.00 Ri der hereinafter in the XRD pattern (311) crystallite diameter calculated by the Scherrer equation from the full width at half maximum of the peak attributed to face is 5000Å or less, der least 1000Å A positive electrode active material for a non-aqueous electrolyte secondary battery.

_{Li a Mn 2-x-y} -b Ni x-z T y + z A b O 4 composition formula 1

0.92 ≦ a ≦ 1.12
0.45 ≦ x ≦ 0.55
0 ≦ y <0.10
0.0010 ≦ z ≦ 0.20
0.0010 ≦ y + z ≦ 0.20
0.0010 <b ≦ 0.025
z> y

T = one or more elements selected from Co, Fe, Cr, Al, Ga, Ti and Si A = one or more elements selected from Mg and Zn
  T is Co, Fe, Ti, The positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 1 characterized by the above-mentioned.   A is Mg, The positive electrode active material for nonaqueous electrolyte secondary batteries in any one of Claims 1-2 characterized by the above-mentioned. Within the scope of 400～700Cm ^-1 of FT-IR ^{measurement, 493~513cm -1, 549~559cm -1,} that one or more of the absorption peak of the infrared light in the range of 584～594Cm ^-1 is not detected The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3 . Nitrogen 0.050 M ² / g or more in specific surface area measured by the BET method using a non-aqueous electrolyte battery according to any one of claims 1 to 4, characterized in that it is 2.0 m ² / g or less Positive electrode active material. A positive electrode is formed by the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5 , an initial discharge capacity is 125 mAh / g or more, and a cutoff of 0.6 mA / cm ² at 60 ° C. The battery is charged to a voltage of 4.9 V, and after a pause of 1 hour, the discharge is repeated 200 times to a cutoff voltage of 3.5 V, and the discharge capacity at the 200th time is 70% or more with respect to the discharge capacity at the second time. Water-based electrolyte secondary battery.