JP2008159543A - Positive electrode active material for non-aqueous type electrolyte secondary battery, and method for manufacturing the material, and non-aqueous type electrolyte secondary battery using the material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material by which a non-aqueous type electrolyte secondary battery can be implemented, which has two characteristics of exhibiting high thermal stability and safety compatible, and has a high charge and discharge capacity. <P>SOLUTION: A method for manufacturing the positive electrode active material includes the steps of mixing a lithium metal composite oxide powder with cold water, to obtain a slurry; adding a water solution containing nickel salt while stirring the slurry at a pH of 9.0, thereby adhering a nickel compound particle; and performing heat treatment at 300 to 700 degrees centigrade, thereby converting the nickel compound into lithium nickel-based composite oxide. The lithium metal composite oxide is expressed as general Formula Li<SB>z</SB>Ni<SB>1-x-y</SB>Co<SB>x</SB>M<SB>y</SB>O<SB>2</SB>(where, M is at least one element chosen from among Mn, V, Mg, Mo, Nb, Ti, and Al; 0.10≤x≤0.21; 0≤y≤0.08; 0.97≤z≤1.10). The number of Ni atoms lies between 0.5 and 1.5% of the total number of atoms of Ni, Co, and M which are contained in the lithium metal composite oxide powder. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery using the same.

  In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density is strongly desired. As such a secondary battery, there is a lithium ion secondary battery. A lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and inserting Li is used as an active material for the negative electrode and the positive electrode.

Research and development of such lithium ion secondary batteries is being actively conducted. Among these, a lithium metal secondary oxide using a lithium cobalt composite oxide (LiCoO ₂ ), which is a lithium metal composite oxide and is particularly easy to synthesize, as a positive electrode material can obtain a high voltage of 4V, Practical use is progressing as a battery having a high energy density. In the lithium ion secondary battery using this lithium cobalt composite oxide (LiCoO ₂ ), many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. ing.

However, since lithium cobalt complex oxide (LiCoO ₂ ) uses a rare and expensive cobalt compound as a raw material, it causes an increase in battery cost. For this reason, it is desired to use materials other than lithium cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material.

  Recently, not only small secondary batteries for portable electronic devices but also expectations for using lithium ion secondary batteries as large secondary batteries for power storage and electric vehicles are increasing. Yes. For this reason, reducing the cost of the positive electrode material and making it possible to manufacture a cheaper lithium ion secondary battery can be expected to have a large ripple effect in a wide range of fields.

Newly proposed materials for positive electrode active materials for lithium ion secondary batteries include lithium manganese composite oxide (LiMn ₂ O ₄ ) using Mn, which is cheaper than Co, and lithium nickel composite oxide using Ni. (LiNiO ₂ ).

Lithium-manganese composite oxide (LiMn ₂ O ₄ ) is an effective alternative to lithium cobalt composite oxide (LiCoO ₂ ) because it is inexpensive and has excellent thermal stability, especially safety with respect to ignition. However, since the theoretical capacity is only about half that of lithium cobalt composite oxide (LiCoO ₂ ), it has a drawback that it is difficult to meet the demand for higher capacity of lithium ion secondary batteries that are increasing year by year. . Moreover, at 45 degreeC or more, it has the fault that self-discharge is intense and a charge / discharge lifetime also falls.

On the other hand, lithium-nickel composite oxide (LiNiO ₂₎ has the almost the same theoretical capacity as the lithium cobalt complex oxide (LiCoO _2), it shows a slightly lower cell voltage than the lithium-cobalt composite oxide (LiCoO _2). For this reason, decomposition | disassembly by oxidation of electrolyte solution does not become a problem, and development is performed actively from expecting higher capacity | capacitance. However, when a lithium ion secondary battery is manufactured using lithium nickel composite oxide (LiNiO ₂ ) purely composed of Ni without replacing Ni with another element, a lithium cobalt composite is produced. Compared with the case where an oxide (LiCoO ₂ ) is used as the positive electrode active material, the cycle characteristics are inferior. In addition, when used or stored in a high temperature environment, the battery performance is relatively easily lost.

In order to solve such drawbacks, for example, in Patent Document 1, Li _w Ni _x Co _y B _{z is} used as a positive electrode active material capable of maintaining good battery performance during storage and use in a high temperature environment. Lithium nickel doped with cobalt and boron represented by O ₂ (0.05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.20, x + y + z = 1) Complex oxides have been proposed.

Further, in Patent Document 2, Li _x Ni _a Co _b M _c O ₂ (0.8 ≦ x ≦ 1.2, 0... Is intended to improve self-discharge characteristics and cycle characteristics of a lithium ion secondary battery. 01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al, V, Mn, Fe, Cu And at least one element selected from Zn) have been proposed.

However, the lithium nickel composite oxides obtained by these production methods have higher charge capacity and discharge capacity and improved cycle characteristics than the lithium cobalt composite oxide (LiCoO ₂ ). If left in a high temperature environment in a charged state, there is a problem that oxygen is released due to decomposition of the lithium nickel composite oxide from a temperature lower than that of the lithium cobalt composite oxide (LiCoO ₂ ). Furthermore, Ni in the lithium nickel composite oxide that has become unstable in a high temperature environment acts catalytically by contact with the electrolytic solution, promotes reaction with the released oxygen, and easily ignites. There was a safety problem.

In order to solve such a problem, for example, in Patent Document 3, for the purpose of improving the thermal stability of the positive electrode material of a lithium ion secondary battery, Li _a M _b Ni _c Co _d O _e (M is It is at least one metal selected from the group consisting of Al, Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn, and Mo, and 0 <a <1.3, 0.02 ≦ b ≦ 0.5, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1)). Has been. In this case, for example, when Al is selected as the additive element M, it is confirmed that if the amount of substitution from Ni to Al is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved. . However, if Ni is replaced with an amount of Al effective to ensure sufficient stability, the amount of Ni contributing to the oxidation-reduction reaction decreases with the charge / discharge reaction. There is a problem that the discharge capacity is greatly reduced. This is because Al is stable at trivalent, and Ni is also stable at trivalent because the charge is matched, and a part that does not contribute to the oxidation-reduction reaction occurs, so that the initial discharge capacity is considered to decrease. .

  In recent years, the demand for higher capacity for small secondary batteries used in portable electronic devices and the like has been increasing, but sacrificing capacity to ensure safety is the high capacity of lithium nickel-based composite oxides. The merit will be lost and it will not be possible to meet the demand for higher capacity. In addition, a movement to use a lithium ion secondary battery for a large-sized secondary battery is also active, and among them, there is a great expectation as a power source for a hybrid vehicle and an electric vehicle. Thus, when used as a power source for automobiles, solving the problem of the lithium nickel composite oxide that is inferior in safety is a big problem.

  Therefore, in order to improve safety, a method has been proposed in which the positive electrode active material is covered with a different compound to prevent direct contact between the positive electrode active material and the electrolytic solution. For example, Non-Patent Document 1 proposes that the surface of a lithium nickel composite oxide is coated with magnesium oxide to improve thermal stability. However, in a secondary battery using such a lithium nickel composite oxide as a positive electrode active material, the charge / discharge capacity is low, and it is difficult to say that the problem of achieving both high capacity and safety is satisfied.

Patent Document 4 proposes coating the surface of a layered structure oxide for a positive electrode of a lithium secondary battery with a lithium transition metal oxide. In this technique, the surface treatment raw material solution is adjusted to pH 5 to 9 with an organic acid and ammonia, the solution concentration is adjusted to 0.1 to 2 molar concentration, and then a layer phase structure oxide is added, The coated layer phase structure oxide is heat-treated at 500 to 850 ° C. for 3 to 48 hours to obtain a positive electrode active material composed of a layer phase structure oxide whose surface is coated with a lithium transition metal oxide. Yes. However, as the lithium transition metal _{oxide, LiMn 2-X M1 X O} 4, LiCo 1-X Al X O 2, LiNi 1-X Al X O 2, LiNi 1-XY Co X Al Y O 2, LiNi 1- _{XYZ Co X M1 Y M2 Z O} 2 (M1 and M2, Al, Ni, Co, Fe , Mn, V, Cr, Cu, Ti, W, Ta, Mg or Mo, 0 ≦ X <0.5,0 ≦ Y <0.5, 0 ≦ Z <0.5), although these are oxides that can move lithium ions, A reduction in charge / discharge capacity as much as 8% occurs. Thus, even in this proposal, it cannot be said that the problem of achieving both high capacity and safety is satisfied.

  Further, Patent Document 5 proposes a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery in which a lithium compound is attached to the surface of lithium nickel oxide particles. However, this proposal is intended to suppress the decomposition of the electrolytic solution, and is not intended to achieve both high capacity and safety. In addition, although coating and doting have been proposed as modes to be attached to the surface, both modes have advantages and disadvantages, and both high capacity and safety are achieved from this viewpoint. Yes it is hard to say.

As described above, a lithium metal composite oxide that has both high charge / discharge capacity, thermal stability, and safety has not been found, and a nonaqueous electrolyte secondary battery that solves these problems is desired. Yes.
JP-A-8-45509 Japanese Patent Laid-Open No. 8-213015 Japanese Patent Laid-Open No. 5-242891 JP 2002-231227 A JP-A-2005-190996 HJKweon et al., Electrochem, and Solid-State lett., 3, 128 (2000)

  The present invention has been made in view of the above problems, and realizes a non-aqueous electrolyte secondary battery that has both thermal stability and safety and high charge / discharge capacity. An object of the present invention is to provide a positive electrode active material that can be used.

  The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is a first step of obtaining a slurry by mixing and stirring a lithium metal composite oxide powder with water, and stirring the obtained slurry. Meanwhile, by adding an aqueous solution containing a nickel salt, the second step of attaching the fine particles of the nickel compound to the surface of the primary particles of the lithium metal composite oxide, and the heat treatment at 300 to 700 ° C. It has the 3rd process which makes a nickel compound lithium nickel system complex oxide.

Further, the lithium metal composite oxide represented by the general formula _{Li z Ni 1-xy Co x} M y O 2 ( however, M is, Mn, V, Mg, Mo, Nb, at least one selected from Ti and Al Element, 0.10 ≦ x ≦ 0.21, 0 ≦ y ≦ 0.08, 0.97 ≦ z ≦ 1.10.

  Furthermore, it is desirable to control the pH of the slurry obtained in the first step to exceed 9.0.

  Furthermore, it is desirable that the slurry obtained in the first step has a slurry concentration of 1000 to 2500 g / L.

  Further, the number of Ni atoms contained in the nickel salt used in the second step is based on the total number of Ni, Co and M atoms contained in the lithium metal composite oxide powder used in the first step. Thus, it is desirable that the content be 0.5 to 1.5 atomic%.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention have the general formula _{Li z Ni 1-xy Co x} M y O 2 ( however, M is selected Mn, V, Mg, Mo, Nb, Ti and Al At least one element, 0.10 ≦ x ≦ 0.21, 0 ≦ y ≦ 0.08, 0.97 ≦ z ≦ 1.10) primary particles, and A positive electrode active material for a non-aqueous electrolyte secondary battery comprising fine particles of a lithium nickel composite oxide adhering to the surface of the primary particles, and the number of Ni atoms contained in the fine particles is the number of Ni contained in the primary particles, It is 0.5 to 1.5 atomic% with respect to the total number of atoms of Co and M.

  Further, the diameter of the fine particles is preferably 100 nm or less.

  Furthermore, it is desirable that the initial discharge capacity of the non-aqueous electrolyte secondary battery obtained by using the positive electrode is 190 mAh / g or more.

  In the non-aqueous electrolyte secondary battery of the present invention, any of the positive electrode active materials for non-aqueous electrolyte secondary batteries described above is used for the positive electrode.

  A non-aqueous electrolyte secondary battery that achieves both of the two characteristics of high thermal stability and safety and high charge / discharge capacity by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention. A positive electrode active material that can be realized can be provided.

  By using the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention to obtain a non-aqueous electrolyte secondary battery, while satisfying the recent demand for higher capacity for small secondary batteries such as portable electronic devices, It is possible to ensure the safety required as a power source used for large-sized secondary batteries for hybrid vehicles and electric vehicles, which is extremely useful industrially.

  The present inventor has conducted a thorough examination on the compatibility between charge / discharge capacity and safety, which is important when a lithium metal composite oxide is used as a positive electrode active material in a non-aqueous electrolyte secondary battery. By attaching fine particles of lithium nickel-based oxide to the surface of the particles, and making Ni contained in the fine particles a predetermined amount, and controlling the morphology of the fine particles, high charge / discharge capacity and thermal stability and The inventors have found that both safety can be achieved and have completed the present invention.

  Hereinafter, the present invention will be described in detail.

(1) the positive electrode active material the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention have the general formula _{Li z Ni 1-xy Co x} M y O 2 ( however, M is Mn, V, Mg, Mo, Nb , At least one element selected from Ti and Al, 0.10 ≦ x ≦ 0.21, 0 ≦ y ≦ 0.08, 0.97 ≦ z ≦ 1.10) Primary particles and lithium nickel composite oxide fine particles adhering to the surfaces of the primary particles, and the number of Ni atoms contained in the fine particles is the number of Ni, Co and M atoms contained in the primary particles. It is 0.5-1.5 atomic% with respect to the sum total. Here, the fine particles are particles having a substantially spherical shape, a diameter of 5 nm to 100 nm, and a uniform diameter.

  The charge / discharge reaction of the secondary battery proceeds by reversibly entering and exiting lithium ions in the positive electrode active material. The positive electrode active material from which Li is extracted by charging is unstable at a high temperature, and when heated, the active material is decomposed to release oxygen, which causes combustion of the electrolyte solution and causes an exothermic reaction. Therefore, improving the thermal stability of the positive electrode material means suppressing the decomposition reaction of the positive electrode active material from which Li is extracted.

  As a known method for suppressing the decomposition reaction of the positive electrode active material, a part of Ni is generally substituted with an element having strong covalent bond with oxygen such as Al. Certainly, if the amount of substitution from Ni to Al is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved, but the amount of Ni contributing to the oxidation-reduction reaction accompanying the charge / discharge reaction is reduced. Therefore, since the charge / discharge capacity is reduced, the amount of substitution with Al must be limited to some extent. As a result, when sufficient thermal stability is ensured, sufficient reversible capacity cannot be obtained. Conversely, in order to obtain a certain level of capacity, thermal stability must be sacrificed.

Therefore, in the present invention, the general formula _{Li z Ni 1-xy Co x} M y O 2 ( however, M is at least one element Mn, V, Mg, Mo, Nb, selected from Ti and Al, 0 .. 10 ≦ x ≦ 0.21, 0 ≦ y ≦ 0.08, 0.97 ≦ z ≦ 1.10) to improve the thermal stability, High charge / discharge capacity and safety are sufficiently ensured by attaching fine particles of lithium nickel composite oxide to the surface of primary particles of the lithium metal composite oxide. That is, by reducing direct contact between the electrolyte and the primary particles of lithium metal composite oxide destabilized due to Li deprivation, ignition is suppressed or delayed, and at the same time, interface resistance is increased, The effect of reducing conduction and slowing temperature rise is obtained.

  In addition, although details are unknown, it is necessary to completely cover the surface of primary particles of lithium metal composite oxide when fine particles of lithium nickel composite oxide are attached to the surface of primary particles of lithium metal composite oxide. There is no. By only partially depositing lithium nickel composite oxide fine particles, the stability of the lithium metal composite oxide is improved and the safety effect of suppressing ignition or slowing the temperature rise is greatly improved. It is possible. In this respect, it is greatly different from the case where a conventional lithium compound is attached or coated.

  In general, if the surface of the positive electrode active material is completely covered with a different compound, the movement (intercalation) of lithium ions is greatly limited, resulting in the high capacity of the lithium nickel composite oxide. The advantage of being erased. However, in the present invention, the fine particles adhering to the primary particles of the lithium metal composite oxide are lithium nickel oxides having a high lithium ion conductivity, and the primary particles of the lithium metal composite oxide are coated with such fine particles. Even so, the movement of lithium ions is hardly restricted.

  In addition, the lithium nickel oxide fine particles covering the primary particles of the lithium metal composite oxide have sufficient Li in the crystals in any charge / discharge state. In addition, it is always present as a thermally stable oxide and does not become a thermally unstable state that causes ignition.

  In addition, since the lithium nickel composite oxide is attached in the form of fine particles, the specific surface area is increased, so that the contact area with the electrolytic solution is increased. The movement of lithium ions is hardly hindered between the primary particles of the object and the electrolyte.

  Furthermore, since the effect of improvement can be obtained without completely covering the surfaces of the primary particles of the lithium metal composite oxide, lithium ions can freely move in the non-adhered portion as in the conventional case.

  For the reasons mentioned above, in the present invention, a high charge / discharge capacity can be maintained with sufficient safety.

  Here, when the surface of the primary particles is coated in layers instead of as fine particles, the specific surface area decreases regardless of the coating thickness, so even if the coated material has a high lithium ion conductivity. Even if it has, the contact area with the electrolytic solution becomes small, which tends to cause a decrease in charge / discharge capacity.

  In addition, when adhered to the surface of the primary particles in the form of a lump, the specific surface area is reduced at that portion, and the contact area with the electrolytic solution is reduced correspondingly, thereby easily reducing the charge / discharge capacity. In addition to the lithium nickel-based composite oxide, the lithium metal composite oxide is in an unstable state at the portion in direct contact with the electrolytic solution as in the prior art, and the safety improvement effect is reduced.

  On the other hand, in the present invention, since the fine particles of the lithium nickel composite oxide are attached to the primary particles of the lithium metal composite oxide, the lithium metal composite oxide destabilized in the charged state. , The above-described effects are produced, and high safety can be imparted. In addition, lithium ion conduction can be effectively maintained with a high specific surface area, and since the lithium metal composite oxide and the electrolyte are partially blocked, the reduction in charge / discharge capacity can be minimized.

  The number of Ni atoms contained in the fine particles of the lithium nickel composite oxide is 0.5 to 1.5 atoms with respect to the total number of Ni, Co, and M atoms contained in the primary particles of the lithium metal composite oxide. By setting it as%, it is possible to achieve both high charge / discharge capacity and safety. If it is less than 0.5 atomic%, the amount of fine particles sufficient to produce an effect cannot be adhered to the surface of the primary particles, and safety is lowered. On the other hand, if it exceeds 1.5 atomic%, the amount of adhering fine particles increases too much, and the lithium ion conductivity is impaired, resulting in a decrease in charge / discharge capacity.

  The fine particles of the lithium nickel composite oxide preferably have a diameter of 100 nm or less. As a result, the contact area between the fine particles and the electrolytic solution is increased even in the portion where the lithium nickel composite oxide is adhered, and lithium ions can be sufficiently transferred.

  Further, when the diameter of the fine particles of the lithium nickel composite oxide is larger than 100 nm, the contact area between the fine particles and the electrolyte is reduced, and the thickness of the portion to which the fine particles of the lithium nickel composite oxide are attached increases. This is not preferable because it may adversely affect the movement of lithium ions. The thickness of the part to which the fine particles are attached is preferably 100 nm or less. In addition, when the diameter of the fine particles of the lithium nickel-based composite oxide is less than 5 nm, the aggregation of the fine particles is likely to proceed, adversely affecting the lithium ion conductivity, and the above-described effects are reduced.

  The surface properties of such a lithium metal composite oxide can be determined by observing with a field emission scanning electron microscope (FE-SEM, manufactured by HITACHI, S-4700), and the non-aqueous electrolyte secondary battery of the present invention. As for the positive electrode active material for use, it has been confirmed that fine particles of a lithium nickel composite oxide having a diameter of 5 nm or more and 100 nm or less are attached to the surface of primary particles of the lithium metal composite oxide.

  The effects of attaching fine particles of lithium nickel composite oxide to the surface of primary particles of lithium metal composite oxide include, for example, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel cobalt manganese composite oxide The present invention can be applied not only to the positive electrode active material of the present invention but also to a commonly used positive electrode active material for a lithium secondary battery.

(2) Method for Producing Positive Electrode Active Material The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a first method of obtaining a slurry by mixing lithium metal composite oxide powder with water and stirring. A second step of attaching nickel compound fine particles to the surface of the primary particles of the lithium metal composite oxide by adding an aqueous solution containing a nickel salt while stirring the obtained slurry, and 300 to 700 A third step is performed in which the nickel compound is made into fine particles of a lithium nickel-based composite oxide by performing a heat treatment at a temperature of ° C.

(First step)
First, a lithium metal composite oxide powder is mixed with water and stirred to obtain a slurry. Lithium metal composite oxide, from the viewpoint of high capacity and thermal stability, the general formula _{Li z Ni 1-xy Co x} M y O 2 ( however, M is, Mn, V, Mg, Mo , Nb, Ti and Al At least one element selected from 0.10 ≦ x ≦ 0.21, 0 ≦ y ≦ 0.08, and 0.97 ≦ z ≦ 1.10). preferable.

  In order to obtain a high charge / discharge capacity, it is preferable to use, as the water for obtaining the slurry, general pure water that does not contain impurities harmful to the positive electrode active material.

  The slurry concentration is preferably 1000 to 2500 g / L. When the slurry concentration is less than 1000 g / L, the volume of the slurry increases, and when considering the amount of drainage and the amount that can be produced at one time, the efficiency is low and the cost tends to be disadvantageous. On the other hand, if the concentration exceeds 2500 g / L, the viscosity of the slurry becomes too high, and it becomes difficult to stir uniformly.

(Second step)
Next, an aqueous solution containing a nickel salt is added while stirring the obtained slurry. The nickel salt is not particularly limited, but it is preferable to use a nickel salt that is readily soluble in water, such as nickel sulfate, nickel nitrate, nickel chloride, nickel acetate, nickel citrate, and nickel oxalate. It is preferable from the uniformity of crystallization that the nickel salt is completely dissolved in water and added while stirring the slurry. The nickel concentration in the aqueous solution containing the nickel salt and the rate at which the aqueous solution containing the nickel salt is added are not particularly limited, but the crystal on the surface of the primary particles of the lithium metal composite oxide in consideration of the amount of slurry and the slurry concentration. It can be arbitrarily determined to analyze.

  Ni present as ions in the aqueous solution containing the nickel salt to be added is crystallized as a nickel compound mainly composed of hydroxide, and then collides with primary particles of the lithium metal composite oxide in the slurry. It adheres to the surface or by crystallization on the surface of primary particles. At that time, since almost all of the Ni contained in the aqueous solution crystallizes and adheres to the surface of the primary particles of the lithium metal composite oxide, the aqueous solution contains an amount corresponding to the desired amount of Ni contained in the fine particles. Is preferred. That is, the Ni contained in the aqueous solution is preferably 0.5 to 1.5 atomic% with respect to the total number of Ni, Co and M atoms contained in the primary particles of the lithium metal composite oxide.

  Moreover, when adding the aqueous solution containing nickel salt to a slurry, it is preferable to control so that the pH of a slurry exceeds 9.0. When the pH of the slurry is 9.0 or less, a nickel compound is hardly generated due to the neutralization reaction, and a large amount of Li is desorbed from the primary particles of the lithium metal composite oxide during the process. Incurs a noticeable decline. Furthermore, the influence of pH is very large on the shape of the lithium nickel composite oxide covering the surface. When the pH is 9.0 or less, the nickel compound tends to be coarse particles, and tends to be a layered coating after firing, resulting in a decrease in contact area with the electrolytic solution, resulting in a decrease in charge / discharge capacity.

  On the other hand, in the present invention, by dissolving lithium hydroxide in the slurry, the pH is always adjusted to exceed 9.0 to cause nucleation of a large amount of nickel compound. By controlling the growth, deposits of uniform fine particles of the nickel compound are obtained.

  In the first step, when lithium metal composite oxide powder and water are mixed to form a slurry, a small amount of lithium ions in the lithium metal composite oxide powder elute into the slurry, Although there is an effect of increasing the pH, the pH of the slurry is increased by adjusting the pH so as to exceed 9.0.

  The upper limit of the pH of the slurry by such control is not particularly limited, but it is sufficient if it can be maintained at a level exceeding 9.0 and not exceeding 13.5.

  It is preferable to dissolve an appropriate amount of lithium hydroxide in advance in the water to be mixed. In the first step of obtaining a slurry of lithium metal composite oxide powder, a predetermined amount of lithium hydroxide is dissolved in the water to be used in advance to stabilize pH fluctuations, and then crystallize the nickel compound. And the uniformity of the crystallization product is improved. In addition, it is possible to prevent excessive Li desorption from the powder of the lithium metal composite oxide that is the positive electrode active material. Li in the slurry crystallizes on the surface of the primary particles of the lithium metal composite oxide together with Ni in the nickel salt, and forms a lithium nickel-based oxide in the subsequent heat treatment. Therefore, the amount of lithium hydroxide added in advance is sufficient for the amount of lithium nickel-based oxide in the subsequent heat treatment. Moreover, when lithium hydroxide is added excessively, excess Li increases and battery characteristics deteriorate. In addition, wasted Li is increased, which is not preferable from the viewpoint of cost.

(Third step)
Furthermore, after performing filtration and drying, the nickel compound containing Li present on the surface of the primary particles of the lithium metal composite oxide is obtained by performing a heat treatment at a temperature of 300 to 700 ° C. Thus, a positive electrode active material for a non-aqueous electrolyte secondary battery comprising primary particles of a lithium metal composite oxide and fine particles of a lithium nickel composite oxide adhering to the surface of the primary particles is obtained.

  The slurry may be filtered by any of the commonly used methods, such as suction filtration, filter press, and centrifugal separation. The drying method is not particularly limited, but in order to prevent deterioration of electrical characteristics when used as a positive electrode active material for a non-aqueous electrolyte secondary battery, it is preferable to dry in an inert atmosphere or vacuum. preferable. For example, it is preferable to vacuum dry at 90 to 210 ° C., preferably 150 ° C. or higher for 14 hours or longer.

  The heat treatment temperature is preferably 300 to 700 ° C. If it is less than 300 degreeC, conversion to a lithium nickel type complex oxide is not enough, and since it exceeds 700 degreeC, since the primary particle of lithium metal complex oxide will raise | generate sintering or aggregation, it is not preferable. The atmosphere during the heat treatment is preferably an oxidizing atmosphere such as an air atmosphere or an oxygen atmosphere in order to convert the lithium nickel-based composite oxide. The heat treatment time is not particularly limited, but it may be a time during which the conversion to the lithium nickel composite oxide is sufficiently performed in consideration of the amount of the lithium metal composite oxide and the heat treatment temperature.

  Furthermore, before the heat treatment is performed, it is preferable to crush with a sieve having an opening of 100 to 200 μm, preferably 100 μm. By crushing, aggregation of the lithium metal composite oxide during heat treatment can be prevented.

(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 obtained as 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 above-described examples, 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 holding 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 secondary battery using the positive electrode active material of the present invention has an initial discharge capacity of 190 mAh / g or more. Also, in differential scanning calorimetry (DSC, manufactured by BRUKER, DSC3100SA), compared with a positive electrode active material that is not covered with fine particles of lithium nickel-based oxide, the heat generation start temperature is significantly increased and the heat generation amount is reduced. It has been confirmed and it can be said that it is excellent in safety.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a partially broken perspective view showing a coin battery used for battery evaluation.

(Example 1)
200 g of lithium metal composite oxide powder represented by Li _1.05 Ni _0.85 Co _0.15 Al _0.03 O ₂ was added to 80 mL of pure water and stirred to form a slurry at a slurry concentration of 2500 g / L. The pH of the slurry was adjusted with lithium hydroxide to 12.0. Furthermore, stirring the obtained slurry, it is an aqueous solution of nickel sulfate (made by Wako Pure Chemical Industries, Ltd., nickel (II) sulfate hexahydrate), and the Ni, Co and Al in the lithium metal composite oxide An aqueous solution containing 0.5 atomic% of Ni was added dropwise over 1 hour with respect to the total number of atoms. After completion of dropping, the slurry was suction filtered, and the obtained powder was vacuum-dried at 150 ° C. for 14 hours, and further crushed through a sieve having an opening of 100 μm.

  20 g of the obtained powder was weighed and placed in a 10 cm × 5 cm × 5 cm alumina firing container, and a temperature increase rate of 5 ° C./min in a 100% oxygen stream at a flow rate of 1.5 L / min using a tubular electric furnace. In minutes, the temperature was raised to 500 ° C., heat-treated for 10 hours, and then cooled to room temperature. Finally, it was passed through a sieve having an opening of 50 μm and pulverized again to obtain a positive electrode active material which was a powder composed of primary particles of a lithium metal composite oxide in which fine particles of the lithium nickel composite oxide adhered to the surface. .

  The initial capacity evaluation of the obtained positive electrode active material was performed as follows.

70% by mass of the positive electrode active material powder was mixed with 20% by mass of acetylene black (manufactured by Denki Kogyo Co., Ltd.) and 10% by mass of PTFE (manufactured by Daikin Kogyo Co., Ltd.), 150 mg was taken out, and the diameter was 11 mm at a pressure of 100 MPa. A pellet was prepared as a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (made by Toyama Pharmaceutical Co., Ltd.) using 1M LiClO ₄ as a supporting salt was used as the electrolyte. Using these, a 2032 type coin battery as shown in a partially broken perspective view in FIG. 1 was fabricated in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

The produced battery is left to stand for about 24 hours, and after the open circuit voltage (OCV) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm ² and charged to a cutoff voltage of 4.3 V. The initial charge capacity was defined as the capacity when the battery was discharged to a cut-off voltage of 3.0 V after 1 hour of rest.

  Evaluation of the safety of the positive electrode was performed as follows using a 2032 type coin battery manufactured by the same method as described above. First, CCCV charge up to a cut-off voltage of 4.5 V (constant current-constant voltage charge. First, a charging method using a charging process of two phases in which charging is operated at a constant current and then charging is terminated at a constant voltage. ) And then disassembled with care so as not to short-circuit, and the positive electrode was taken out. 3.0 mg of the obtained positive electrode was weighed, 1.3 mg of the electrolyte was added, sealed in an aluminum measurement container, and the temperature rising rate was 10 ° C. using a differential scanning calorimeter (DSC, manufactured by BRUCKER, DSC3100SA). The rate of heat generation from room temperature to 400 ° C. was measured per minute, and the heat generation start temperature and the heat generation peak intensity were measured. The heat generation starting temperature was 255 ° C. The exothermic peak intensity was 3 cal / sec · g, and the exothermic peak relative intensity, which is a ratio with Comparative Example 1 described later as 100, was calculated.

  Table 1 shows the initial discharge capacity, heat generation start temperature, and heat generation peak relative intensity obtained by battery evaluation.

(Example 2)
In the same manner as in Example 1, except that the aqueous solution of nickel sulfate contains 0.8 atomic% of Ni with respect to the total number of Ni, Co and Al atoms in the lithium metal composite oxide. Obtained material.

  In FIG. 2, the photograph of the surface fine area | region of the positive electrode active material obtained using FE-SEM (The product made by Carl Zeiss, ULTRA55) is shown.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

(Example 3)
In the same manner as in Example 1, except that the aqueous solution of nickel sulfate contains 1.0 atomic% of Ni with respect to the total number of Ni, Co and Al atoms in the lithium metal composite oxide, Obtained material.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

Example 4
In the same manner as in Example 1, except that the aqueous solution of nickel sulfate contains 1.5 atomic% of Ni with respect to the total number of Ni, Co and Al atoms in the lithium metal composite oxide. Obtained material.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

(Example 5)
The aqueous solution of nickel sulfate contains 0.8 atomic% of Ni with respect to the total number of Ni, Co and Al atoms in the lithium metal composite oxide, and the pH of the slurry is adjusted. A positive electrode active material was obtained in the same manner as in Example 1 except that 5.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

(Comparative Example 1)
200 g of lithium metal composite oxide powder represented by Li _1.05 Ni _0.85 Co _0.15 Al _0.03 O ₂ was added to 133 mL of pure water and stirred to form a slurry at a slurry concentration of 1500 g / L. Further, the obtained slurry was stirred for 30 minutes, and the powder was washed with water. Then, the slurry was subjected to suction filtration, and the obtained powder was vacuum dried at 150 ° C. for 14 hours, and further passed through a sieve having an opening of 50 μm. By crushing, a positive electrode active material made of a lithium metal composite oxide powder was obtained.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

(Comparative Example 2)
In the same manner as in Example 1, except that the aqueous solution of nickel sulfate contains 0.3 atomic% of Ni with respect to the total number of Ni, Co and Al atoms in the lithium metal composite oxide, Obtained material.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

(Comparative Example 3)
In the same manner as in Example 1, except that the aqueous solution of nickel sulfate contains 2.0 atomic% of Ni with respect to the total number of Ni, Co and Al atoms in the lithium metal composite oxide, Obtained material.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

(Reference Example 1)
The aqueous solution of nickel sulfate contains 0.8 atomic% of Ni with respect to the total number of Ni, Co and Al atoms in the lithium metal composite oxide, and the pH of the slurry is adjusted. A positive electrode active material was obtained in the same manner as in Example 1 except that 5.

  Thereafter, the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Evaluation]
As can be seen from FIG. 2, fine particles of lithium nickel composite oxide having a diameter of 10 to 20 nm are attached to the surface of primary particles of a lithium metal composite oxide having a diameter of about 0.3 to 0.5 μm.

  From Table 1, it can be seen that in Examples 1 to 5 of the present invention, a very high capacity can be obtained even when the lithium metal composite oxide washed with water as in Comparative Example 1 is used for the positive electrode. That is, the lithium nickel composite oxide fine particles adhered to the surface have a sufficiently high lithium ion conductivity and are considered to have little influence on the capacity of the positive electrode active material.

  Moreover, in Examples 1-5, compared with the comparative example 1, it turns out that heat_generation | fever start temperature is 30-40 degreeC higher, and heat_generation | fever peak relative intensity | strength is also reducing significantly. This is because the lithium nickel composite oxide fine particles adhering to the surface of the primary particles of the lithium metal composite oxide increased the interfacial resistance and the heat conduction was suppressed to some extent, and Li was lost. The direct contact between the primary particles of the destabilized lithium metal composite oxide and the electrolyte is suppressed, and the reaction with oxygen desorbed from the positive electrode active material becomes relatively slow. An effect peculiar to the fine particles of the composite oxide is considered as the reason.

  On the other hand, in Comparative Example 2, although the initial discharge capacity is high, it can be seen that the heat generation start temperature by DSC is low and the heat generation peak relative intensity is hardly reduced. This is because the amount of fine particles of lithium-nickel composite oxide is too small, so the effect of fine particles of lithium-nickel composite oxide is small, and the lithium-nickel composite oxide that covers the surface of the primary particles of lithium metal composite oxide It is considered that there are few fine particles of the product and there are many contacts between the lithium metal composite oxide and the electrolyte.

  In Comparative Example 3, the heat generation start temperature by DSC is higher than those in Examples 1 to 5 and the heat generation peak relative intensity is also reduced, but the initial discharge capacity is greatly reduced. The reason for this is that the amount of fine particles of the lithium nickel composite oxide is too large, and the fine particles of the lithium nickel composite oxide are adhered to the surface of the primary particles of the lithium metal composite oxide, This is probably because the conductivity of lithium ions has deteriorated.

  Therefore, the number of Ni atoms contained in the fine particles of the lithium nickel composite oxide is 0.5 to 1. with respect to the total number of Ni, Co and M atoms contained in the primary particles of the lithium metal composite oxide. It turns out that it is suitable to set it as 5 atomic%.

  In Reference Example 1, the initial discharge capacity is greatly reduced. This is considered to be because the pH of the slurry was too low, and Li was excessively eluted from the positive electrode active material. Moreover, although the exothermic start temperature and exothermic peak relative intensity in DSC are worse than those in Example 2, the cause of this is that the pH of the slurry is too low and the lithium-nickel composite oxide causes agglomeration. This is probably because the lithium nickel composite oxide was hardly adhered as fine particles to the surface of the primary particles of the metal composite oxide.

  In Example 5, the initial discharge capacity is higher than in Reference Example 1, the heat generation start temperature in DSC is on the high temperature side, and the heat generation peak relative intensity is also low. This is because the fine particles of the lithium nickel composite oxide can be attached to the surface of the primary particles of the lithium metal composite oxide. Therefore, it is suggested that the pH of the slurry has a great influence on the reaction and properties.

  From the above results, by controlling the pH of the slurry to exceed 9.0 and adhering a sufficient amount of fine particles of the lithium nickel composite oxide to the surface of the primary particles of the lithium metal composite oxide, When used as an active material, it was shown that sufficient safety can be ensured while maintaining a high charge / discharge capacity.

  The non-aqueous electrolyte secondary battery of the present invention, which is excellent in safety and has a high charge / discharge capacity, is a small portable electronic device (a notebook personal computer, a mobile phone terminal, etc.) that always requires a high capacity. ) Is suitable for the power source.

  Further, in a power source for an electric vehicle, it is indispensable to ensure safety by increasing the size of the battery and an expensive protection circuit for ensuring higher safety. On the other hand, the non-aqueous electrolyte secondary battery of the present invention has excellent safety, so that not only is it easy to ensure safety, but also an expensive protection circuit is simplified to reduce the cost. Therefore, it is also suitable as a power source for electric vehicles. The present invention can be used not only as a power source for an electric vehicle driven purely by electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

It is a partially broken perspective view which shows the coin battery used for battery evaluation. 3 is a photograph of a surface fine region of a positive electrode active material for a non-aqueous electrolyte secondary battery obtained in an example of the present invention.

Explanation of symbols

1 Lithium metal negative electrode 2 Separator (electrolyte impregnation)
3 Positive electrode (Evaluation electrode)
4 Gasket 5 Negative electrode can 6 Positive electrode can 7 Current collector

Claims (9)

  The first step of obtaining a slurry by mixing the powder of lithium metal composite oxide with water and stirring, and adding the aqueous solution containing nickel salt while stirring the resulting slurry, thereby adding lithium metal composite oxide A second step of attaching nickel compound fine particles to the surface of the primary particles, and a third step of converting the nickel compound into a lithium nickel based composite oxide by heat treatment at 300 to 700 ° C. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The lithium metal composite oxide represented by the general formula _{Li z Ni 1-xy Co x} M y O 2 ( however, M is at least one element Mn, V, Mg, Mo, Nb, selected from Ti and Al, 0.10 ≦ x ≦ 0.21, 0 ≦ y ≦ 0.08, 0.97 ≦ z ≦ 1.10), for a non-aqueous electrolyte secondary battery according to claim 1 A method for producing a positive electrode active material.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the pH of the slurry obtained in the first step is controlled to exceed 9.0.   3. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the slurry obtained in the first step has a slurry concentration of 1000 to 2500 g / L.   The number of Ni atoms contained in the nickel salt used in the second step is based on the total number of Ni, Co and M atoms contained in the lithium metal composite oxide powder used in the first step. It is 0.5-1.5 atomic%, The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 1 or 2 characterized by the above-mentioned. Formula _{Li z Ni 1-xy Co x} M y O 2 ( however, M is at least one element Mn, V, Mg, Mo, Nb, selected from Ti and Al, 0.10 ≦ x ≦ 0. 21, 0 ≦ y ≦ 0.08, 0.97 ≦ z ≦ 1.10), and lithium nickel composite oxide attached to the surface of the primary particles. A positive electrode active material for a non-aqueous electrolyte secondary battery comprising fine particles, and the number of Ni atoms contained in the fine particles is 0.5 with respect to the total number of Ni, Co and M atoms contained in the primary particles. A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that it is ˜1.5 atomic%.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the fine particles have a diameter of 100 nm or less.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6 or 7, wherein an initial discharge capacity of the non-aqueous electrolyte secondary battery obtained by using the positive electrode is 190 mAh / g or more.   A non-aqueous electrolyte secondary battery, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6 is used for a positive electrode.