JP6834629B2 - Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

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

Conventionally, as a positive electrode active material for a non-aqueous electrolyte secondary battery represented by a lithium secondary battery, a "LiMeO _{type 2 " active material having an α-NaFeO type 2} crystal structure (Me is a transition metal element) has been studied. Non-aqueous electrolyte secondary batteries using LiCoO ₂ have been widely put into practical use. However, _{the discharge capacity of LiCoO 2} was about 120 to 130 mAh / g. It has been desired to use abundant Mn as an earth resource as the Me. However, when the molar ratio of Mn to Me to Mn / Me exceeds 0.5, _{the "LiMeO type 2} " active material containing Mn as Me undergoes a structural change to a spinel type when charged, resulting in crystals. Since the structure cannot be maintained, there is a problem that the charge / discharge cycle performance is significantly inferior.

_{Therefore, various "LiMeO type 2} " active materials having a molar ratio of Mn to Me of Mn / Me of 0.5 or less and excellent in charge / discharge cycle performance have been proposed and partially put into practical use. _{For example, a positive electrode active material containing LiNi 1/2} Mn _1/2 O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ which are lithium transition metal composite oxides has a discharge capacity of 150 to 180 mAh / g. Has.

On the other hand, with respect to the so-called "LiMeO _{type 2} " active material as described above, the molar ratio of Mn to Me, Mn / Me, exceeds 0.5, and the molar ratio of lithium (Li) to Me, Li / Me, is greater than 1. Since the so-called "lithium excess type" active material has _{a higher discharge capacity than the "LiMeO type 2} " active material, studies are being conducted toward its practical use.

Patent Document 1 states that "formula Li _{1 + x} M _1-x O _2-z F _z (M is a non-lithium metal element or a combination thereof, 0.01 ≦ x ≦ 0.3, 0 ≦ z). A lithium ion battery positive electrode material comprising a lithium metal oxide approximately represented by (≤0.2) and coated with about 0.1 to about 0.75 weight percent metal / semimetal oxide. (Claim 1), and for sample 1 of this positive electrode material, _{x in xLi 2} MnO ₃ · (1-x) LiMO ₂ is 0.5 and the Mn% transition metal is 65.63. Is listed in Table 3.

Then, as Example 5, "Example 5-Coating with bismuth oxide. In this example, it is represented by the formula of Sample 1 in Table 3 and is formed as described in Example 1 and is rich in high capacity lithium. The formation of a bismuth oxide coating on a metal oxide will be described. The coating of bismuth oxide on a high volume cathode material was carried out by drying bismuth nitrate on an active lithium metal oxide followed by a firing step. Specifically, bismuth nitrate was dissolved in a selected amount of water and the _{cathode material to be coated with Bi 2} O ₃ was dispersed in the bismuth nitrate solution. The mixture was then dried from 80 to 80 to dry. It was heated at 100 ° C. for about 2 hours. The resulting dry powder was recovered and fired in a conventional muffle furnace, in dry air, at 300-400 ° C. for 2 hours to form a bismuth oxide coating. " 0091] to [0092]), "Examine the material coated with bismuth oxide by X-ray diffraction. An X-ray diffraction diagram of four samples having different amounts of bismuth oxide coating of the same material together with the uncoated material is shown in FIG. Shown. Samples were prepared using about 0.1, 0.5.2.0 and 5.0 weight percent coating material. As can be seen from the diffraction diagram of FIG. 12, the coating is a crystal of the material. It did not significantly change the structure. ”(Paragraph [093]).

Patent Document 2 includes "Li element and at least one transition metal element selected from Ni, Co and Mn (however, the molar amount of Li element is 1.) with respect to the total molar amount of the transition metal element. It is more than twice.) The surface of the lithium-containing composite oxide is selected from Zr, Ti, Sn, Mg, Ba, Pb, Bi, Nb, Ta, Zn, Y, La, Sr, Ce, In and Al. A positive electrode active material for a lithium ion secondary battery, characterized in that it is composed of particles (II) to which fine particles of an oxide (I) of at least one metal element are attached. ”(Claim 1) is described.

As an example of this positive electrode active material, _{a lithium-containing composite oxide having a composition of "Li (Li 0.2} Ni _0.137 Co _0.125 Mn _0.538 ) O ₂ " was obtained (paragraphs [0049] to [0052] to [0052]. ]), lithium-containing composite oxide of the embodiment is "stirred against (15 g), was added by spraying ZrO ₂ dispersion (2.4 g), prepared, lithium-containing composite oxide of example The ZrO ₂ dispersion was brought into contact with each other while being mixed. Then, the obtained mixture was heated at 300 ° C. for 1 hour in an oxygen-containing atmosphere, and the surface of the lithium-containing composite oxide was coated with the oxide (I) of the Zr element. A positive electrode active material (A) of Example 1 composed of particles (II) to which fine particles adhere was obtained. ”(Paragraph [0053]).

Patent Document 3 states, "A positive electrode active material characterized in that at least one of oxide particles and carbon particles having an average particle size of 1 μm or less is attached to the surface of the parent active material." (Claim 1), ". The oxide particles adhering to the surface of the matrix active material are selected from SiO ₂ , SnO ₂ , Al ₂ O ₃ , TiO ₂ , MgO, Fe ₂ O ₃ , Bi ₂ O ₃ , Sb ₂ O ₃ and ZrO _2. The positive electrode active material according to claim 1, wherein the positive electrode active material is at least one kind of oxide particles. ”(Claim 4).

Then, regarding Examples 10 and 11 in which the base material active material (composite oxide) is LiCoO ₂ and the oxide is Bi ₂ O ₃ , "this composite oxide is dispersed in pure water to prepare an active material dispersion liquid. On the other hand, various oxide dispersions were prepared by dispersing each oxide particle and / or carbon particles having the average particle size shown in Table 1. Next, adhesion shown in Table 1 to the active material dispersion. Oxide dispersions and / or carbon dispersions are added in an amount so as to prepare each dispersion that is uniformly mixed, and then each dispersion is concentrated and dried to obtain oxide particles on the surface of the matrix active material particles. And / or produced the positive electrode active material according to each example to which carbon particles were attached ”(paragraphs [0069] to [0074], Table 1).

Japanese Patent Application Laid-Open No. 2013-503449 Japanese Unexamined Patent Publication No. 2012-138197 Japanese Unexamined Patent Publication No. 2003-109599

Although the lithium excess type active material has a high discharge capacity, the capacity decreases with the charge / discharge cycle, and there is a problem in the charge / discharge cycle performance. This problem is considered to be related to the elution of Mn from the positive electrode active material during charging and discharging. In the lithium excess type active material, Mn is more easily eluted than in the _{LiMeO type 2 active material.} The cause, in a lithium-excess type active material, than the molar ratio Mn / Me 0.5 of Mn relative to Me, higher than the LiMeO ₂ Katakatsu material, and, in LiMeO ₂ Katakatsu material, the charge and discharge Even if Mn is carried out, Mn basically maintains ^{Mn 4+ and elution of Mn 3+} is unlikely to occur, whereas the lithium excess type active material has a Li ₂ MnO ₃ structural portion, so that the _{Li 2 MnO 3 structural portion has a Li 2} MnO ₃ structural portion. ^{It is considered that Mn becomes Mn 3+} with charging and discharging, and Mn ³⁺ is likely to be eluted.

Patent Document 1 describes a cathode material obtained by dispersing a lithium metal oxide in an aqueous solution of bismuth nitrate, mixing it, drying it by heating, and firing it in air at 300 to 400 ° C. However, in FIG. 12 (shown in FIG. 4), which is an X-ray diffraction diagram, no diffraction peak attributed to bismuth oxide is found even in the sample to which _{5.0 wt% Bi 2} O _{3 is applied.} Therefore, it can be seen that the bismuth derived from bismuth nitrate does not exist as bismuth oxide on the surface of the positive electrode active material after undergoing the firing step at 300 to 400 ° C.

Patent Document 2 describes a positive electrode active material in which fine particles of an oxide of a metal element such as Zr are attached to the surface of a lithium-containing composite oxide, but specifically, for a lithium-containing composite oxide. It is only described that the ZrO ₂ dispersion was sprayed, added and mixed, and heated at 300 ° C. in an oxygen-containing atmosphere to obtain particles in which fine particles of the oxide of the Zr element adhered to the surface of the lithium-containing composite oxide. Not.

Patent Document 3 describes a positive electrode active material in which oxide particles such as _{Bi 2} O ₃ having an average particle size of 1 μm or less are attached to the surface of the parent active material. However, the _Bi 2 _{O 3} particles, are mixed with the dispersion of the dispersion and _Bi 2 _{O 3} of LiCoO _2, and concentrated to dryness, it has been described only depositing a _Bi 2 _{O 3} particles LiCoO ₂ surface Absent.

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance, a positive electrode for a non-aqueous electrolyte secondary battery containing the active material, and a non-aqueous electrolyte secondary battery provided with the positive electrode. An object of the present invention is to provide a method for producing the active material.

The first aspect of the present invention is an active material for a non-aqueous electrolyte secondary battery containing particles of a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ structure. Mn and Ni or Mn, Ni and Co are contained as transition metal elements (Me), the molar ratio of Mn to Me is 0.5 <Mn / Me, and the molar ratio of Li to Me is Li / Me. 1 <Li / Me, Be oxide , Ge oxide or Bi oxide is present on the surface of the particles, and in an X-ray diffraction diagram using CuKα rays, Be oxide , Ge oxide or Bi oxide A diffraction peak attributed to is observed (provided that a mixture of at least one metal oxide selected from the group consisting of La, Pr, Nd, Sm and Eu and an oxide of Ge, as well as La, Pr. , Nd, Sm and Eu, except for those in which a composite oxide of at least one metal and Ge selected from the group is present), a positive electrode active material for a non-aqueous electrolyte secondary battery.

The second and third aspects of the present invention are a positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material, and a non-aqueous electrolyte secondary battery provided with the positive electrode.

The fourth aspect of the present invention has an α-NaFeO ₂ structure, contains Mn and Ni or Mn, Ni and Co as transition metal elements (Me), and has a molar ratio of Mn to Me, Mn / Me of 0. A solid phase of lithium transition metal composite oxide particles having a molar ratio of Li to Me and Li / Me of 1 <Li / Me and Be oxide , Ge oxide, or Bi oxide. This is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery , in which Be oxide , Ge oxide or Bi oxide is adhered to the surface of the particles.

According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance, a method for producing the positive electrode active material, a positive electrode for a non-aqueous electrolyte secondary battery including the positive electrode active material, and the positive electrode. A non-aqueous electrolyte secondary battery having the above can be provided.

X-ray diffraction pattern of the positive electrode active material according to one embodiment of the present invention (Example 1-1) X-ray diffraction pattern of the positive electrode active material according to one embodiment of the present invention (Example 1-2). X-ray diffraction pattern of the positive electrode active material according to one embodiment of the present invention (Example 1-5). X-ray diffraction pattern of the positive electrode active material according to the prior art A perspective view showing an embodiment of a non-aqueous electrolyte secondary battery according to one aspect of the present invention. Schematic diagram showing a power storage device including a plurality of non-aqueous electrolyte secondary batteries according to one aspect of the present invention.

The configuration and action / effect of the present invention will be described with technical ideas. However, the mechanism of action includes estimation, and its correctness does not limit the present invention. It should be noted that the present invention can be practiced in various other forms without departing from its spirit or major features. Therefore, the embodiments or examples described below are merely examples in all respects and should not be construed in a limited manner. Furthermore, all modifications and modifications that fall within the equivalent scope of the claims are within the scope of the present invention.

[Positive electrode active material]
The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention (hereinafter referred to as “the present embodiment”) contains particles of a lithium transition metal composite oxide, and a Be compound is formed on the surface of the particles. , Ge compound or Bi compound is present in the positive electrode active material. Examples of each of the above compounds include oxides, hydroxides, nitrates, sulfates, carbonates, fluorides, chlorides, bromides, iodides, nitrides, hydrides, sulfides, etc. A certain Be oxide (BeO), Ge oxide (GeO ₂ ) or Bi oxide (Bi ₂ O ₃ ) is preferable. Further, the Be compound, Ge compound or Bi compound preferably exists in the form of particles.

The lithium transition metal composite oxide contains Mn and Ni, or Mn, Ni and Co as transition metal elements (Me) from the viewpoint of obtaining a high discharge capacity.
In order to obtain a non-aqueous electrolyte secondary battery having a high discharge capacity, the lithium transition metal composite oxide has a molar ratio of Mn to the transition metal element Me, which is Mn / Me larger than 0.5, and a molar ratio of Li to Me, Li. / Me is a lithium excess type active material of 1 <Li / Me.
The above lithium-rich active material is represented by the composition formula Li _{1 + α} Me _1-α O ₂ (0 <α) or Li _{1 + w} MeO _{2 + w} (0 <w), and is typically composed of the composition formula. _{li 1 + α (Ni x Co} y Mn z) 1-α O 2 expressed (0 <α, 0 <x , 0 ≦ y, 0.5 <z, x + y + z = 1) and.

The molar ratio of Li to Me, Li / Me, is preferably 1.1 to 1.45, more preferably 1.1 to 1.4, and particularly preferably 1.1 to 1.3. Within this range, the discharge capacity is particularly improved.
The molar ratio of Mn to Me, Mn / Me, is preferably 0.51 to 0.7, more preferably 0.51 to 0.60. Within this range, the tap density of the hydroxide precursor, which will be described later, can be improved, so that the discharge capacity per volume is improved.
Co contained in the lithium transition metal composite oxide has the effect of improving the initial efficiency and the high rate discharge performance, but increases the tap density of the precursor and thus increases the discharge capacity per volume of the positive electrode active material. In order to increase it, it is preferable that the amount is small. In addition, the cost is high because it is a rare resource. Therefore, the molar ratio of Co to the transition metal element Me, Co / Me, is preferably 0.20 or less, more preferably 0.10 or less, and may be 0.
The molar ratio of Ni to Me, Ni / Me, is preferably 0.2 to 0.5, more preferably 0.25 to 0.4. Within this range, the tap density of the hydroxide precursor can be improved, so that the discharge capacity per volume is improved.
By using the lithium transition metal composite oxide having the above composition, a non-aqueous electrolyte secondary battery having a large discharge capacity per volume can be obtained.

The number of moles of oxygen in the above composition formula is a value calculated stoichiometrically, but as long as the lithium transition metal composite oxide has an α-NaFeO _{type 2} crystal structure, it is not necessarily stoichiometric. It does not have to be the ratio.
Further, the lithium transition metal composite oxide is a transition typified by an alkali metal such as Na and K, an alkaline earth metal such as Mg and Ca, and a 3d transition metal such as Fe, as long as the effects of the present invention are not impaired. It does not preclude the inclusion of small amounts of other metals such as metals.

The lithium transition metal composite oxide according to this embodiment has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after combining (before charge and discharge) is assigned to the space group P3 1 _12, drawing X-ray diffraction using a CuKα tube, 2 [Theta] = 21 ° around the superlattice peak (Li [Li _1/3 Mn _{2/3] O 2} type peaks seen in monoclinic) is confirmed. However, if charging exceeds 4.5 V (Li / Li ⁺ ) even once, this superlattice peak disappears because the symmetry of the crystal changes with the desorption of Li in the crystal. , The lithium transition metal composite oxide will be assigned to the space group R3-m. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when order is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model. Is adopted. In addition, "R3-m" is originally described by adding a bar "-" on "3" of "R3m".

In the positive electrode active material according to the present embodiment, a Be compound, a Ge compound, or a Bi compound is present on the surface of the particles of the lithium transition metal composite oxide. The presence of the Be compound, the Ge compound, or the Bi compound makes it possible to provide a positive electrode active material having excellent charge / discharge cycle performance. The reason is not always clear, but the presence of a specific metal compound such as Be compound, Ge compound or Bi compound on the surface of the particles fills Mn, which is a constituent element of the lithium excess type lithium transition metal composite oxide. ^{It is presumed that the phenomenon that Mn 3+} becomes Mn 3+ with discharge and elutes into the non-aqueous electrolyte is suppressed, and the charge / discharge cycle performance is improved.

In the positive electrode active material according to the present embodiment, the Be compound, Ge compound or Bi compound present on the surface of the lithium transition metal composite oxide is preferably present in an amount that coats at least a part of the surface of the particles. The addition is preferably 0.01 to 5% by mass, more preferably 0.1 to 1% by mass, in terms of Be, Ge or Bi elements with respect to the lithium transition metal composite oxide.
When it is 0.01% by mass or more ^{, elution of Mn 3+} due to charging and discharging can be suppressed, and when it is 5% by mass or less, the discharge capacity is lowered due to the resistance derived from the compound that coats the positive electrode active material. Can be suppressed.

In the positive electrode active material according to the present embodiment, the presence of Be compound, Ge compound or Bi compound on the particle surface is determined by performing X-ray diffraction measurement, and performing X-ray diffraction measurement, Be compound such as BeO, Ge compound such as _{GeO 2 or Bi 2} O ₃ It can be confirmed by observing the diffraction peak attributed to the Bi compound such as.
The diffraction peak can be confirmed both before and after the charge / discharge cycle.
Before the charge / discharge cycle, the positive electrode active material before being incorporated into the battery may be subjected to X-ray diffraction measurement.
After the charge / discharge cycle, when collecting a sample from the electrode taken out by disassembling the battery, the battery is discharged by the following procedure before disassembling the battery. First, with a current of 0.1 C, constant current charging is performed up to a battery voltage at which the potential of the positive electrode becomes 4.3 V (vs. Li ^/ Li +), and at the same battery voltage, the current value decreases to 0.01 C. It is charged at a constant voltage until it reaches the end of charging. After a 30-minute rest, ^{constant current discharge is performed with a current of 0.1 C until the potential of the positive electrode reaches a battery voltage of 2.0 V (vs. Li /} Li +), and the state is at the end of discharge. If the battery uses a metallic lithium electrode as the negative electrode, the battery may be disassembled and the electrode may be taken out after the battery is in the end-discharged state or the end-of-charge state. In order to accurately control the positive electrode potential, after disassembling the battery and taking out the electrode, the battery with the metal lithium electrode as the counter electrode is assembled, and then the battery is adjusted to the end-discharge state according to the above procedure. The work from battery disassembly to measurement is performed in an argon atmosphere with a dew point of -60 ° C or lower. The removed positive electrode plate is thoroughly washed with dimethyl carbonate to thoroughly wash the electrolyte adhering to the electrodes, dried at room temperature for a whole day and night, and then the mixture on the aluminum foil current collector is collected. Lightly loosen the collected mixture in an agate mortar and place it in a sample holder for X-ray diffraction measurement for measurement.

In the specification of the present application, the X-ray diffraction measurement and the measurement of the half width using the same are performed under the following conditions. The radiation source is CuKα, the applied voltage is 30 kV, and the applied current is 15 mA. The sampling width is 0.01 deg, the scanning time is 14 minutes (scan speed is 5.0 deg / min), the divergent slit width is 0.625 deg, the light receiving slit width is open, and the scattering slit is 8.0 mm. The analysis software uses "PDXL" attached to the X-ray diffractometer.

[Manufacturing method of positive electrode active material]
Next, a method for producing a positive electrode active material containing particles of a lithium transition metal composite oxide according to the present embodiment will be described.
The lithium transition metal composite oxide according to the present embodiment is basically prepared with a raw material containing a metal element (Li, Ni, Co, Mn, etc.) so as to have an amount ratio based on the composition of the target oxide. It can be obtained by firing this. However, regarding the amount of the Li raw material, it is preferable to add an excess of about 1 to 5% in anticipation that a part of the Li raw material will disappear during firing.
In producing an oxide having the desired composition, the so-called "solid phase method" in which salts of Li, Ni, Co, and Mn are mixed and fired, or Ni, Co, and Mn are present in one particle in advance. A "coprecipitation method" is known in which a coprecipitation precursor is prepared, and a Li compound is mixed and calcined therein. In the synthesis process by the "solid phase method", it is difficult to obtain a sample in which each element is uniformly distributed in one particle, because Mn is particularly difficult to dissolve uniformly in Ni and Co. In the literature, many attempts have been made to dissolve Mn in a part of Ni or Co by the solid phase method (LiNi _1-x Mn _x O ₂ etc.), but the "coprecipitation method" is selected. It is easier to obtain a uniform phase at the atomic level. Therefore, in the examples described later, the "coprecipitation method" was adopted.

In producing a coprecipitation precursor, Mn among Co, Ni, and Mn is easily oxidized, and it is not easy to produce a coprecipitation precursor in which Co, Ni, and Mn are uniformly distributed in a divalent state. , Co, Ni, Mn at the atomic level tends to be inadequate. In particular, in the composition range of the present invention, the Mn ratio is higher than the Co and Ni ratios, so it is important to remove the dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas containing no oxygen. The gas containing no oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ) and the like can be used. Further, a reducing agent such as hydrazine may be contained in the aqueous solution.

The pH in the step of coprecipitating a compound containing Co, Ni and Mn in a solution to produce a precursor is not limited, but when the coprecipitated precursor is produced as a coprecipitated hydroxide precursor. Can be 8-14. In order to increase the tap density, it is preferable to control the pH. By setting the pH to 11.5 or less, the tap density can be set to 1.00 g / cm ³ or more, and the discharge capacity per volume can be improved. Further, by setting the pH to 11.0 or less, the particle growth rate can be promoted, so that the stirring duration after the completion of dropping the raw material aqueous solution can be shortened.

The coprecipitation precursor is preferably a compound in which Mn and Ni or Mn, Ni and Co are uniformly mixed. In the present embodiment, the coprecipitation precursor is preferably a hydroxide in order to make the inside of the positive electrode active material dense. Further, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent or the like. In this case, since a higher density active material can be obtained by mixing and firing with the Li source, the energy density per volume of the electrode can be improved.

The raw material of the co-precipitation precursor is manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate or the like as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate as the Ni compound. As examples of the Co compound, cobalt sulfate, cobalt nitrate, cobalt acetate and the like can be mentioned.

In the present embodiment, it is preferable to adopt a reaction crystallization method in which an aqueous solution of a raw material for the coprecipitation precursor is dropped and supplied to a reaction vessel maintained alkaline to obtain a coprecipitation hydroxide precursor. Here, sodium hydroxide, lithium hydroxide, or potassium hydroxide can be used as the neutralizing agent.

The dropping rate of the raw material aqueous solution greatly affects the uniformity of the element distribution within one particle of the produced coprecipitation precursor. In particular, it is necessary to note that Mn does not easily form a uniform element distribution with Co and Ni. The preferable dropping rate is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is preferably 30 mL / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 mL / min or less, and most preferably 5 mL / min or less.

Further, when a complexing agent is present in the reaction vessel and certain convection conditions are applied, the rotation of the particles and the revolution in the stirring vessel are promoted by further stirring after the completion of dropping the raw material aqueous solution. In this process, the particles gradually grow into convective spheres while colliding with each other. That is, the coprecipitation precursor undergoes a two-step reaction of a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction vessel and a precipitation formation reaction that occurs while the metal complex is retained in the reaction vessel. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for continuing stirring after the completion of dropping of the raw material aqueous solution.

The preferable stirring duration after the completion of dropping the aqueous solution of the raw material is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is 0.5 hours or more in order to grow the particles as uniform spherical particles. Is preferable, and 1 hour or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery becomes insufficient due to the particle size becoming too large, 15 hours or less is preferable, 10 hours or less is more preferable, and 5 hours or less is most preferable.

Further, the preferable stirring duration for making the particle size of the secondary particles of the hydroxide precursor and the lithium transition metal composite oxide suitable depends on the pH to be controlled. For example, when the pH is controlled to 8 to 14, the stirring duration is preferably 0.5 to 5 hours, and when the pH is controlled to 8 to 11.5, the stirring duration is 0.5 to 3 Time is preferred.

When the particles of the hydroxide precursor are prepared by using a sodium compound such as sodium hydroxide as a neutralizing agent, sodium ions adhering to the particles are washed and removed in the subsequent washing step. For example, when the produced hydroxide precursor is suction-filtered and taken out, a condition can be adopted such that the number of washings with 100 mL of ion-exchanged water is 5 times or more.

The particles of the lithium transition metal composite oxide according to the present embodiment can be suitably produced by mixing the hydroxide precursor and the Li compound and then heat-treating the particles. As the Li compound, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate and the like can be suitably produced. However, regarding the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in anticipation that a part of the Li compound will disappear during firing.

The calcination temperature affects the reversible capacity of the active material containing the particles of the lithium transition metal composite oxide.
If the firing temperature is too high, the obtained active material will disintegrate with an oxygen release reaction, and in addition to the hexagonal crystals of the main phase, the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type will be formed. The defined phase tends to be observed as a phase split rather than as a solid solution phase. If too much of such a phase separation is contained, it leads to a decrease in the reversible capacity of the active material, which is not preferable. In such a material, impurity peaks are observed near 35 ° and around 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably lower than the temperature affected by the oxygen release reaction of the active material. The oxygen release temperature of the active material is approximately 1000 ° C. or higher in the composition range of the lithium transition metal composite oxide according to the present embodiment, but since there is a slight difference in the oxygen release temperature depending on the composition, the oxygen release temperature of the active material is preliminarily used. It is preferable to check the oxygen release temperature. In particular, it has been confirmed that the oxygen release temperature of the precursor shifts to the lower temperature side as the amount of Co contained in the sample increases, so caution is required. As a method for confirming the oxygen release temperature of the active material, a mixture of a co-precipitation precursor and a lithium compound may be subjected to thermogravimetric analysis (DTA-TG measurement) in order to simulate the firing reaction process. In this method, the platinum used in the sample chamber of the measuring instrument may be corroded by the volatilized Li component and damage the instrument. Therefore, a firing temperature of about 500 ° C. is adopted in advance to promote crystallization to some extent. It is preferable to subject the object to thermogravimetric analysis.
Further, if the firing temperature is too high, even if phase separation is not confirmed in the active material, the crystallization of the lithium transition metal composite oxide in the active material proceeds too much, the crystallites become large, and the diffusion of Li ions is sufficient. Since this is not done, the discharge capacity per volume decreases.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the lithium transition metal composite oxide according to the present embodiment, the firing temperature is preferably at least 700 ° C. or higher. Sufficient crystallization can reduce the resistance of grain boundaries and promote smooth lithium ion transport.

As described above, since the preferable firing temperature differs depending on the oxygen release temperature of the active material, it is difficult to generally set a preferable range of the firing temperature, but the molar ratio Li / Me is 1.1 to 1.4. In some cases, the firing temperature is preferably 700 to 900 ° C. in order to make the discharge capacity per volume sufficient.

The active material according to the present embodiment is a means for allowing the Be compound, Ge compound or Bi compound to exist on the surface of the particles of the lithium transition metal composite oxide obtained by the above production method, and the particles and the Be compound, Ge compound or It is preferable to mix the Bi compound in a solid phase.

Specifically, solid phase mixing can be performed using a ball mill device.
Particles of lithium transition metal composite oxide and powders of Be compound such as BeO _{, Ge compound such as GeO 2} or Bi compound such as Bi ₂ O ₃ are put into a pot together with a ceramic ball such as ZrO _{2 and rotated.} It is preferable to carry out dry mixing. Wet mixing may be performed by adding toluene or the like, but it is preferable to select dry mixing because a large shearing force can be applied to reduce the possibility of particle cracking. Further, since the risk of particle cracking can be reduced by not increasing the rotation speed and the rotation time at the time of mixing too much, the rotation speed is preferably 50 to 300 rpm, and the rotation time is preferably 5 to 120 minutes.
It is presumed that the Be compound, Ge compound, or Bi compound is attached to the surface of the particles of the lithium transition metal composite oxide in the form of particles by performing the solid phase mixing as described above.
In the present embodiment, the particles of the lithium transition metal composite oxide are mixed in a solid phase with a Be compound, a Ge compound or a Bi compound, and then the positive electrode active material is used as it is without firing.

[Negative electrode active material]
The negative electrode active material is not limited, and any material may be selected as long as it is in a form capable of precipitating or occluding lithium ions. For _{example, Li [Li 1/3 Ti 5/3]} O 4 titanium-based material of lithium titanate having a spinel type crystal structure typified by, Si and Sb, the alloy-based material such as Sn-based, lithium metal, lithium Alloys (lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxides (lithium-titanium), oxidation In addition to silicon, alloys capable of storing and releasing lithium, carbon materials (for example, graphite, hard carbon, low-temperature calcined carbon, amorphous carbon, etc.) and the like can be mentioned.

The powder of the negative electrode active material preferably has an average particle size of 100 μm or less. A crusher or a classifier is used to obtain the powder in a predetermined shape. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. The classification method is not particularly limited, and a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

[Other electrode components]
The positive electrode active material and the negative electrode active material, which are the main constituents of the positive electrode and the negative electrode, have been described in detail above. A filler or the like may be contained as another constituent component.

The conductive agent is not limited as long as it is an electronically conductive material that does not adversely affect the battery performance, but is usually natural graphite (scaly graphite, scaly graphite, earthy graphite, etc.), artificial graphite, carbon black, acetylene black, etc. Conductive materials such as Ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, conductive ceramic material, etc. can be included as one kind or a mixture thereof. ..

Among these, acetylene black is preferable as the conductive agent from the viewpoint of electron conductivity and coatability. The amount of the conductive agent added is preferably 0.1% by weight to 50% by weight, particularly preferably 0.5% by weight to 30% by weight, based on the total weight of the positive electrode or the negative electrode. In particular, it is preferable to use acetylene black pulverized into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, it is possible to mix powder mixers such as V-type mixers, S-type mixers, scouring machines, ball mills, and planetary ball mills in a dry or wet manner.

Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene and polypropylene, ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM and styrene butadiene. A polymer having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

As the filler, a material that does not adversely affect the battery performance can be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The amount of the filler added is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

For the positive electrode and the negative electrode, the main components (positive electrode active material for the positive electrode, negative electrode material for the negative electrode) and other materials are kneaded to form a mixture, which is mixed with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained mixed solution is coated on a current collector described in detail below, or crimped and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours to be suitably produced. .. Regarding the coating method, for example, it is preferable to apply the coating to an arbitrary thickness and an arbitrary shape by using a means such as a roller coating such as an applicator roll, a screen coating, a doctor blade method, a spin coating, or a bar coater. It is not limited.

[Non-aqueous electrolyte]
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to the present embodiment is not limited, and those generally proposed for use in lithium batteries and the like can be used. Examples of the non-aqueous solvent used for the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butylolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; Chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane, methyl diglime; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sulton or derivatives thereof, etc. alone or two or more thereof Examples thereof include, but are not limited to, mixtures.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF _{4 , LiAsF 6} , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN and other inorganic ionic salts containing one of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅₎ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C) ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthate, lithium stearyl sulfonate, lithium octyl sulfonate, Examples thereof include organic ionic salts such as lithium dodecylbenzenesulfonate, and these ionic compounds can be used alone or in combination of two or more.

Further, _{by using a mixture of LiPF 6} or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further lowered, so that the temperature is low. It is more preferable because the characteristics can be further enhanced and self-discharge can be suppressed.
Further, a room temperature molten salt or an ionic liquid may be used as the non-aqueous electrolyte.

The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to surely obtain a non-aqueous electrolyte battery having high battery characteristics. It is .5 mol / l.

[Separator]
As the separator, it is preferable to use a porous membrane, a non-woven fabric, or the like exhibiting excellent high-rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, foot Vinylidene-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene Examples thereof include a copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like.

The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, from the viewpoint of charge / discharge characteristics, the porosity is preferably 20% by volume or more.

Further, as the separator, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, polyvinylidene fluoride and the like and an electrolyte may be used. It is preferable to use the non-aqueous electrolyte in the gel state as described above because it has an effect of preventing liquid leakage.

Further, it is preferable to use the separator in combination with the above-mentioned porous membrane, non-woven fabric or the like and the polymer gel because the liquid retention property of the electrolyte is improved. That is, the pro-solvent polymer is formed by forming a film coated with a pro-solvent polymer having a thickness of several μm or less on the surface of the polyethylene micropore membrane and the micropore wall surface, and retaining the electrolyte in the micropores of the film. Gells.

Examples of the prosolve polymer include, in addition to polyvinylidene fluoride, a polymer in which an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a monomer having an isocyanato group or the like is crosslinked. The monomer can be subjected to a cross-linking reaction by heating or using ultraviolet rays (UV) in combination with a radical initiator, or by using active rays such as an electron beam (EB).

[Structure of non-aqueous electrolyte secondary battery]
The configuration of the non-aqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and is a cylindrical battery having a positive electrode, a negative electrode, and a roll-shaped separator, a square battery (rectangular battery), and a flat battery. Etc. are given as an example.
FIG. 5 shows an external perspective view of a rectangular lithium secondary battery 1, which is an embodiment of the non-aqueous electrolyte secondary battery according to the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 1, the electrode group 2 is housed in the battery container 3. The electrode group 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'.

[Configuration of power storage device]
The present invention can also be realized as a power storage device in which a plurality of the above-mentioned non-aqueous electrolyte secondary batteries are assembled. An embodiment of the power storage device is shown in FIG. In FIG. 6, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

<Preparation of positive electrode active material>
(Example 1-1)
≪Preparation of precursor≫
In preparing the positive electrode active material, a hydroxide precursor was prepared using a reaction crystallization method. First, 315.4 g of nickel sulfate hexahydrate, 168.6 g of cobalt sulfate heptahydrate, and 530.4 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water. A 1.0 M sulfate aqueous solution having a Co: Mn molar ratio of 30:15:55 was prepared. Next, 2 L of ion-exchanged water was poured into a 5 L reaction vessel, and N ₂ gas was bubbled for 30 minutes in order to reduce the oxygen concentration contained in the ion-exchanged water. The temperature of the reaction vessel is set to 50 ° C. (± 2 ° C.), and the inside of the reaction vessel is stirred at a rotation speed of 1500 rpm using a paddle blade equipped with a stirring motor so that convection occurs sufficiently in the reaction layer. did. The sulfate stock solution was added dropwise to the reaction vessel at a rate of 1.3 mL / min for 50 hours. Here, from the start to the end of the dropping, the pH in the reaction vessel is adjusted by appropriately dropping a mixed alkaline solution consisting of 4.0 M sodium hydroxide, 1.25 M ammonia, and 0.1 M hydrazine. It was controlled so as to always maintain 9.8 (± 0.1), and a part of the reaction solution was discharged by overflow so that the total amount of the reaction solution did not always exceed 2 L. After completion of the dropping, stirring in the reaction vessel was continued for another 1 hour. After stopping the stirring, the mixture was allowed to stand at room temperature for 12 hours or more. Next, the hydroxide precursor particles generated in the reaction vessel are separated using a suction filtration device, and the sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, the particles were dried at 80 ° C. for 20 hours under normal pressure in an air atmosphere. Then, in order to make the particle size uniform, it was crushed in an agate automatic mortar for several minutes. In this way, a hydroxide precursor was prepared.

≪Preparation of particles of lithium transition metal composite oxide (firing process) ≫
To 2.262 g of the hydroxide precursor, 1.294 g of lithium hydroxide monohydrate was added and mixed well using an automatic agate mortar, and the molar ratio of Li :( Ni, Co, Mn) was 120 :. A mixed powder of 100 was prepared. It was molded at a pressure of 6 MPa using a pellet molding machine to obtain pellets having a diameter of 25 mm. The amount of the mixed powder used for pellet molding was determined by converting so that the assumed mass of the final product was 2.5 g. One of the pellets was placed on an alumina boat having a total length of about 100 mm, installed in a box-type electric furnace (model number: AMF20), and heated in an air atmosphere under normal pressure from room temperature to 800 ° C. over 10 hours. It was fired at 800 ° C. for 4 hours. The internal dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was switched off and the alumina boat was allowed to cool naturally while still in the furnace. As a result, the temperature of the furnace drops to about 200 ° C. after 5 hours, but the subsequent temperature lowering rate is rather slow. After a day and night, after confirming that the temperature of the furnace was 100 ° C. or lower, the pellets were taken out and crushed in an agate automatic mortar for several minutes in order to make the particle size uniform. In this way, particles of lithium transition metal composite oxide Li _1.09 Ni _0.27 Co _0.14 Mn _0.50 O ₂ were prepared.

≪Surface coat≫
0.034 g of beryllium oxide as an additive compound was added to 4.500 g of the lithium transition metal composite oxide, and the mixture was charged into an 80 ml pot made of _{ZrO 2} together with 87.3 g of balls made of _{ZrO 2 having a diameter of 5 mm.} The pot was installed in a ball mill device (pulversette 6 manufactured by FRITSCH), and ball mill treatment was performed in an air atmosphere under normal pressure, at room temperature, and at a rotation speed of 100 rpm for 15 minutes. Then, the powder was taken out from the pot and crushed in an agate automatic mortar for several minutes in order to make the particle size uniform. In this way, the particles of the lithium transition metal composite oxide in which BeO is present on the particle surface according to Example 1-1 were produced. The amount of Be element added to the lithium transition metal composite oxide corresponds to 0.3% by mass.
The presence of BeO on the particle surface is determined by performing powder X-ray diffraction measurement under the above conditions using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II), together with a diffraction peak peculiar to the _{α-NaFeO 2 structure.} It was confirmed by observing the diffraction peak attributed to BeO (see FIG. 1).

(Example 1-2)
The same as in Example 1-1 except that 0.019 g of germanium dioxide (the amount of Ge element added to the lithium transition metal composite oxide corresponds to 0.3% by mass) was used instead of beryllium oxide. , Particles of the lithium transition metal composite oxide according to Example 1-2 were prepared. By the same powder X-ray diffraction measurement as described above, _{it was confirmed that GeO 2} was present on the surface of the particles (see FIG. 2).

(Examples 1-3 to 1-5)
Instead of berylium oxide, dibismuth trioxide 0.005 g, 0.015 g, and 0.050 g (the amount of Bi element added to the lithium transition metal composite oxide is 0.1, 0.3, and 1.0 mass, respectively. In the same manner as in Example 1-1, except that (corresponding to%) was used, the lithium transition metal composite oxides according to Examples 1-3, 1-4, and 1-5. Particles were made. By the same powder X-ray diffraction measurement as described above, _{it was confirmed that Bi 2} O ₃ was present on the surface of the particles of Example 1-5 (see FIG. 3).

(Comparative Example 1-1)
The lithium transition metal composite oxide produced in Example 1-1 was used as it was as particles (without coating) of the lithium transition metal composite oxide according to Comparative Example 1-1.

(Comparative Example 1-2)
The same operation as in Example 1-1 was carried out except that beryllium oxide was not added, and particles (without coating) of the lithium transition metal composite oxide according to Comparative Example 1-2 were prepared.

(Comparative Example 1-3)
The lithium transition metal composite oxide coated with K according to Comparative Example 1-3 in the same manner as in Example 1-1 except that 0.027 g of potassium carbonate was used instead of beryllium oxide. Particles were made.

<Manufacturing positive electrodes for non-aqueous electrolyte secondary batteries>
Using the particles of the lithium transition metal composite oxide according to the above Examples and Comparative Examples as the positive electrode active material for the non-aqueous electrolyte secondary battery, a positive electrode for the non-aqueous electrolyte secondary battery was prepared by the following procedure. Using N-methylpyrrolidone as a dispersion medium, a coating paste in which the positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 5: 5 was prepared. The coating paste was applied to one surface of an aluminum foil current collector having a thickness of 20 μm to prepare a positive electrode. The mass and coating thickness of the active material applied per fixed area were unified so that the test conditions would be the same for the non-aqueous electrolyte secondary batteries according to all the examples and comparative examples.

<Manufacturing of non-aqueous electrolyte secondary battery>
For the purpose of accurately observing the single behavior of the positive electrode with respect to the positive electrode, metallic lithium was used in close contact with the nickel foil current collector for the counter electrode, that is, the negative electrode. Here, a sufficient amount of metallic lithium was arranged on the negative electrode so that the capacity of the non-aqueous electrolyte secondary battery was not limited by the negative electrode.

As a non-aqueous electrolyte (electrolyte solution), LiPF is added to a mixed solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) has a volume ratio of 6: 7: 7 so that the concentration is 1 mol / l. _{A solution in which 6} was dissolved was used. As a separator, a polypropylene microporous membrane surface-modified with polyacrylate was used. For the exterior body, a metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) is used, and electrodes are used so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside. Was sealed, and the fusion allowance in which the inner surfaces of the metal resin composite film faced each other was hermetically sealed except for the portion to be the liquid injection hole. After the electrolytic solution was injected, the liquid injection hole was sealed.

The non-aqueous electrolyte secondary battery (hereinafter, referred to as Example 1-1 battery, Comparative Example 1-1 battery, etc.) produced by the above procedure was subjected to an initial charge / discharge step at 25 ° C. Charging was a constant current constant voltage charge with a current of 0.1 C and a voltage of 4.6 V, and the charge termination condition was the time when the current value was attenuated to 0.02 C. The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.0 V. This charge / discharge was performed for 2 cycles. Here, a pause process of 30 minutes was provided after charging and after discharging, and the initial discharge capacity was confirmed.

[Charge / discharge cycle test]
Next, a 30-cycle charge / discharge test was performed. Charging was a constant current constant voltage charge with a current of 0.5 C and a voltage of 4.45 V, and the charge termination condition was the time when the current value was attenuated to 0.02 C. The discharge was a constant current discharge with a current of 0.5 C and a final voltage of 2.0 V. Here, a rest process of 10 minutes was provided after charging and after discharging. The percentage of the discharge capacity in the 30th cycle to the discharge capacity in the 1st cycle in the charge / discharge cycle test was calculated and used as the "capacity retention rate".
The above results are shown in Table 1.

According to Table 1, the batteries of Examples 1-1 to 1-5 having a positive electrode active material prepared by solid-phase mixing the particles of the lithium transition metal composite oxide with the Be compound, the Ge compound or the Bi compound in a ball mill device are available. Comparative Example 1-1 having an active material without adding a compound as a coating raw material and not performing ball milling, and Comparative Example 1- having an active material having been subjected to ball milling without adding a compound as a coating material. It can be seen that the capacity retention rate after 30 cycles is higher than that of the two batteries.
This effect was not observed in Comparative Example 1-3 batteries having an active material to which potassium carbonate was added as a coating raw material and subjected to ball mill treatment.

[X-ray diffraction measurement]
With respect to the batteries of Examples 1-1, 1-2 and 1-5, the positive electrode active material after the charge / discharge cycle test was taken out in the discharged state, and the above was used using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). Powder X-ray diffraction measurement was performed under the conditions.
The results are shown in FIGS. In the active material according to the above-mentioned example, a diffraction peak peculiar to the _{α-NaFeO 2 structure and a diffraction peak attributed to BeO, Geo 2} or Bi ₂ O ₃ were observed, respectively.

(Example 2-1)
Weighing 473.1 g of nickel sulfate hexahydrate and 530.4 g of manganese sulfate pentahydrate, and dissolving all of them in 4 L of ion-exchanged water, the molar ratio of Ni: Mn becomes 45:55. A 0M aqueous sulfate solution was prepared. The same as in Example 1-1 except that the pH in the reaction vessel was controlled to be always maintained at 10.2 (± 0.1) from the start to the end of dropping the aqueous sulfate solution into the reaction vessel. , A hydroxide precursor was prepared.
1.371 g of lithium hydroxide monohydrate was added to 2.211 g of the hydroxide precursor to prepare a mixed powder having a molar ratio of Li :( Ni, Mn) of 130: 100. Except for the above points, a lithium transition metal composite oxide Li _1.13 Ni _0.39 Mn _0.48 O ₂ was prepared in the same manner as in Example 1-1.
_{Lithium in which GeO 2} is present on the surface according to Example 2-1 in the same manner as in Example 1-1 except that 0.019 g of germanium dioxide is added to 4.500 g of the lithium transition metal composite oxide. Particles of transition metal composite oxide were prepared.

(Example 2-2)
A lithium transition metal in _{which Bi 2} O ₃ is present on the surface according to Example 2-2 in the same manner as in Example 2-1 except that 0.015 g of bismuth trioxide was used instead of germanium dioxide. Particles of composite oxide were prepared.

(Example 2-3)
Weighing 315.4 g of nickel sulfate hexahydrate, 112.4 g of cobalt sulfate, and 578.6 g of manganese sulfate pentahydrate, the molar ratio of Ni: Co: Mn is 1.0 M at 30:10:60. An aqueous sulfate solution was prepared. From the start to the end of dropping the aqueous sulfate solution into the reaction vessel, a mixed alkaline solution consisting of 4.0 M sodium hydroxide, 0.6 M ammonia, and 0.3 M hydrazine is appropriately dropped to react. The pH in the tank was controlled to always be maintained at 9.55 (± 0.1). A hydroxide precursor was prepared in the same manner as in Example 1-1 except for the above points.
A mixed powder having a Li: (Ni, Co, Mn) molar ratio of 130: 100 was prepared by adding 1.373 g of lithium hydroxide monohydrate to 2.211 g of the hydroxide precursor. , Lithium transition metal composite oxide Li _1.13 Ni _0.26 Co _0.09 Mn _0.52 O ₂ was prepared in the same manner as in Example 1-1.
The same ball mill treatment as in Example 1-1 was performed on the surface according to Example 2-3, except that 0.019 g of germanium dioxide was used for 4.500 g of the lithium transition metal composite oxide. Particles of a lithium transition metal composite oxide in which GeO _{2 is present were prepared.}

(Example 2-4)
A lithium transition metal in _{which Bi 2} O ₃ is present on the surface according to Example 2-4 in the same manner as in Example 2-3 except that 0.015 g of bismuth trioxide was used instead of germanium dioxide. Particles of composite oxide were prepared.

(Example 2-5)
Weighing 262.8 g of nickel sulfate hexahydrate, 224.9 g of cobalt sulfate, and 530.4 g of manganese sulfate pentahydrate, the molar ratio of Ni: Co: Mn is 25:20:55 at 1.0 M. An aqueous sulfate solution was prepared. The reaction is carried out by appropriately dropping a mixed alkaline solution consisting of 4.0 M sodium hydroxide, 1.5 M ammonia, and 0.2 M hydrazine from the start to the end of dropping the sulfate aqueous solution into the reaction vessel. A hydroxide precursor was prepared in the same manner as in Example 1-1 except that the pH in the tank was controlled to always be maintained at 9.8 (± 0.1).
1.294 g of lithium hydroxide monohydrate was added to 2.262 g of the hydroxide precursor to prepare a mixed powder having a molar ratio of Li: (Ni, Co, Mn) of 120: 100. Except for the above points, a lithium transition metal composite oxide Li _1.09 Ni _0.23 Co _0.18 Mn _0.50 O ₂ was prepared in the same manner as in Example 1-1.
The same ball mill treatment as in Example 1-1 was performed with respect to 4.500 g of the lithium transition metal composite oxide except that 0.019 g of germanium dioxide was used, and GeO was applied to the surface according to Example 2-5. Particles of a lithium transition metal composite oxide in which _{2 is present were prepared.}

(Example 2-6)
A lithium transition metal in _{which Bi 2} O ₃ is present on the surface according to Example 2-6 in the same manner as in Example 2-5 except that 0.015 g of bismuth trioxide was used instead of germanium dioxide. Particles of composite oxide were prepared.

(Comparative Example 2-1)
The lithium transition metal composite oxide Li _1.13 Ni _0.39 Mn _0.48 O _{2 produced} in Example 2-1 was used as it was with the particles (without coating) of the lithium transition metal composite oxide according to Comparative Example 2-1. did.

A non-aqueous electrolyte secondary battery was produced in the same manner as in the battery of Example 1-1 except that the particles according to Examples 2-1 to 2-6 and Comparative Example 2-1 were used as the positive electrode active materials. , Example 1-1 A charge / discharge cycle test similar to that of the battery was performed, and the capacity retention rate after 30 cycles was measured. The results are shown in Table 2 below.

According to Table 2, the batteries of Examples 2-1 to 2-6 having a lithium excess type active material in which a Ge compound or a Bi compound is present on the particle surface are lithium transition metal with the batteries of Examples 1-1 to 1-5. Although the composition of the composite oxide is different, it can be seen that the capacity retention rate is high and the charge / discharge cycle performance is improved.

(Comparative Example 3-1)
0.060 g of copper sulfate pentahydrate was dissolved in 100 mL of ion-exchanged water. 4.500 g of the lithium transition metal composite oxide prepared in Example 1-1 was added to a 300 mL beaker, the temperature of the solution was set to 25 ° C., and the mixture was stirred using a magnetic stirrer at a rotation speed of 400 rpm. 100 mL of the aqueous solution of copper sulfate pentahydrate was added dropwise to the reaction vessel at a rate of 1.3 mL / min. After completion of the dropping, a 0.2 M aqueous sodium hydroxide solution was added dropwise until the pH of the solution reached 11.0. Next, the powder in the reaction vessel was separated using a suction filtration device, and dried in an air atmosphere under normal pressure at 80 ° C. for 20 hours using an electric furnace. Then, in order to make the particle size uniform, it was crushed in an agate automatic mortar for several minutes. In this way, particles of the lithium transition metal composite oxide having a surface coated with Cu according to Comparative Example 3-1 were produced.

(Comparative Example 3-2-3-4)
An aqueous solution was prepared by dissolving 0.076 g of iron sulfate heptahydrate, 0.044 g of cerium sulfate tetrahydrate, and 0.059 g of zirconium sulfate tetrahydrate in 100 mL of ion-exchanged water. Comparative Example 3-2, Comparative Example 3-3, and Comparative Example in the same manner as in Comparative Example 3-1 except that the above aqueous solution was used instead of the aqueous solution of copper sulfate pentahydrate. Particles of a lithium transition metal composite oxide whose surface was coated with Fe, Ce, or Zr according to 3-4 were prepared.

(Comparative Example 3-5)
The amount of the lithium transition metal composite oxide particles produced in Example 1-1 is 0.1% by mass according to the method described in paragraph [0092] of Japanese Patent Application Laid-Open No. 2013-503449. Liquid phase treatment was performed using bismuth nitrate pentahydrate. Specifically, 4.500 g of the lithium transition metal composite oxide particles prepared in Example 1-1 was dispersed in an aqueous solution of bismuth nitrate in which 0.0045 g of bismuth nitrate was dissolved in 45 ml of ion-exchanged water. Next, this dispersion was heated at 100 ° C. for about 2 hours while stirring at a rotation speed of 400 rpm using a magnetic stirrer, and dried. The obtained dry powder was placed in a box-type electric furnace (model number: AMF20) and fired in a dry air atmosphere under normal pressure at 400 ° C. for 2 hours to obtain a lithium transition metal composite oxide according to Comparative Example 3-5. Particles (without coating) were prepared.

(Comparative Example 3-6)
The same treatment as in Comparative Example 3-1 was carried out except that ion-exchanged water was used instead of the aqueous solution of copper sulfate pentahydrate to obtain the lithium transition metal composite oxide according to Comparative Example 3-6. Particles (without coating) were prepared.

In the same manner as in the battery of Example 1-1 except that the particles of the lithium transition metal composite oxide according to Comparative Examples 3-1 to 3-6 were used as the positive electrode active material, Comparative Examples 3-1 to 3-6 The non-aqueous electrolyte secondary battery was prepared, and the same charge / discharge cycle test as that of the battery of Example 1-1 was performed to measure the capacity retention rate after 30 cycles. The results are shown in Table 3 below together with the batteries of Example 1-3 and Comparative Example 1-1.

According to Table 3, Comparative Examples 3-1 to 3-4 batteries in which the particles of the lithium transition metal composite oxide were subjected to liquid phase treatment by adding Cu, Fe, Ce or Zr sulfate hydrate. , And the liquid phase by applying the coating method of bismuth oxide in Example 5 of Patent Document 1 (Japanese Patent Laid-Open No. 2013-503449) mentioned above to a lithium transition metal composite oxide having a Li / Me of 1.2. The treated Comparative Example 3-5 battery not only has a lower capacity retention rate than the battery of Example 1-3 in which _{Bi 2} O _{3 is added and ball milled, but also contains particles that are not treated at all.} It can be seen that the capacity retention rate is even lower than that of the Comparative Example 1-1 battery used and the Comparative Example 3-6 battery in which only the liquid phase treatment was performed without adding the compound.

(Comparative Example 4-1)
To 2.227 g of the hydroxide precursor prepared in Example 1-1, 1.312 g of lithium hydroxide monohydrate and 0.021 g of beryllium oxide were added and mixed well using an automatic aquarium dairy pot. The molar ratio of Li: (Ni, Co, Mn, Be) is 120: 100, and the molar ratio of (Ni, Co, Mn): Be is 100: 3 (the amount of Be element added to the lithium transition metal composite oxide is 0. The firing step was carried out in the same manner as in Example 1-1 except that the mixed powder (corresponding to 3% by mass) was prepared, and the particles of the lithium transition metal composite oxide containing Be according to Comparative Example 4-1 were obtained. Made.

(Comparative Example 4-2)
To 2.186 g of the hydroxide precursor prepared in Example 1-1, 1.288 g of lithium hydroxide monohydrate and 0.032 g of germanium dioxide were added, and the mixture was well mixed using an automatic dairy pot made of amber. The molar ratio of Li: (Ni, Co, Mn, Ge) is 120: 100, and the molar ratio of (Ni, Co, Mn): Ge is 100: 0.6 (the amount of Ge element added to the lithium transition metal composite oxide). The firing step was carried out in the same manner as in Example 1-1 except that the mixed powder was prepared in the same manner as in Example 1-1, and the Lithium transition metal composite oxide containing Ge according to Comparative Example 4-2 was prepared. Particles were made.

(Comparative Example 4-3)
To 2.103 g of the hydroxide precursor prepared in Example 1-1, 1.239 g of lithium hydroxide monohydrate and 0.035 g of dibismuth trioxide were added and mixed well using an automatic dairy pot made of amber. The molar ratio of Li: (Ni, Co, Mn, Bi) is 120: 100, and the molar ratio of (Ni, Co, Mn): Bi is 100: 1.2 (the Bi element to the lithium transition metal composite oxide). The firing step was carried out in the same manner as in Example 1-1 except that the mixed powder (the amount of addition was equivalent to 0.7% by mass) was prepared, and the lithium transition metal composite oxidation containing Bi according to Comparative Example 4-3 was carried out. A particle of an object was produced.

A non-aqueous electrolyte secondary battery was produced in the same manner as in the battery of Example 1-1 except that the particles of the lithium transition metal composite oxide according to Comparative Examples 4-1 to 4-3 were used as the positive electrode active material. Example 1-1 A charge / discharge cycle test similar to that of the battery was performed, and the capacity retention rate after 30 cycles was measured. The results are shown in Table 4 below together with the batteries of Examples 1-1 to 1-3 and the batteries of Comparative Example 1-1.

In Comparative Examples 4-1 to 4-3 batteries, the active material is prepared using the same additive compounds as in Examples 1-1 to 1-3, but the additive compounds are mixed with the precursor and the lithium compound. Since it is fired in, the added compound is incorporated into the crystal structure of the active material.
The comparative example 4-1 to 4-3 battery has a lower capacity retention rate than the battery of Examples 1-1 to 1-3 in which a Be compound, a Ge compound or a Bi compound is present on the surface of the particles, and the added compound. The capacity retention rate was even lower than that of the untreated Comparative Example 1-1 battery.

(Comparative Example 5-1)
Particles of the lithium transition metal composite oxide according to Comparative Example 5-1 in the same manner as in Examples 1-3 except that 4.500 g of LiCoO _{2 (manufactured by Sumitomo Metal Mining Co., Ltd.) was used as the lithium transition metal composite oxide.} Was produced.

(Comparative Example 5-2)
_{A dispersion in which LiCoO 2} (manufactured by Sumitomo Metal Mining Co., Ltd.) is dispersed as a lithium transition metal composite oxide in ion-exchanged water is prepared in accordance with the description of Example 10 of Patent Document 3 (Japanese Unexamined Patent Publication No. 2003-109599). _{On the other hand, a dispersion liquid in which Bi 2} O ₃ corresponding to 0.1% by mass based on the lithium transition metal composite oxide was dispersed in ion-exchanged water was prepared, and then the entire amount of each dispersion liquid was mixed. It was concentrated and dried at 100 ° C. with stirring at a rotation speed of 400 rpm using a magnetic stirrer. In this way, particles of the lithium transition metal composite oxide according to Comparative Example 5-2 were prepared.

(Comparative Example 5-3)
_{The LiCoO 2} used in Comparative Example 5-1 was used as it was as particles (without coating) of the lithium transition metal composite oxide according to Comparative Example 5-3.

Comparative Examples 5-1 to 5-3 are described in the same manner as in the battery of Example 1-1 except that the particles of the lithium transition metal composite oxide according to Comparative Examples 5-1 to 5-3 were used as the positive electrode active material. Such a non-aqueous electrolyte secondary battery was manufactured. In the non-aqueous electrolyte secondary batteries according to Comparative Examples 5-1 to 5-3, LiCoO ₂ is inactivated if the charging potential is set too high, so the charging voltage in the initial charge / discharge step is set to 4.45 V. .. Except for this point, a charge / discharge cycle test similar to that of the battery of Example 1-1 was performed, and the capacity retention rate after 30 cycles was measured. The results are shown in Table 5 below together with the batteries of Example 1-3.

Comparing the battery of Example 1-3 and the battery of Comparative Example 5-1, even if Bi ₂ O ₃ was added and the same ball milling treatment was performed to prepare an active material, particles of the lithium transition metal composite oxide were formed. It _{can be seen that the Comparative Example 5-1 battery, which is LiCoO 2} , has a lower capacity retention rate than the Example 1-3 battery using the lithium excess active material. Further, comparing the battery of Comparative Example 5-1 and the battery of Comparative Example 5-3, when the particles of the lithium transition metal composite oxide are LiCoO ₂ , the presence or absence of the ball mill treatment does not contribute to the improvement of the capacity retention rate. I understand.
Comparative Example 5-2 cells, with respect to the LiCoO ₂ particles, the particles of _Bi 2 _{O 3} are solid-phase mixing in the wet, it can be seen that the capacity retention ratio decreased significantly.
From the above results, it can be seen that the improvement of the capacity retention rate by the presence of the Bi compound on the surface of the active material is an effect peculiar to the lithium excess type active material.

Electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid vehicles (PHEVs), and the like are required to have excellent charge / discharge cycle performance. By using the positive electrode active material containing the lithium transition metal composite oxide according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having improved charge / discharge cycle performance. Therefore, this non-aqueous electrolyte secondary battery can be used. In particular, it is useful as a non-aqueous electrolyte secondary battery for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV).

1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (4)

An active material for non-aqueous electrolyte secondary batteries containing particles of lithium transition metal composite oxide.
The lithium transition metal composite oxide has an α-NaFeO ₂ structure and has an α-NaFeO 2 structure.
Mn and Ni or Mn, Ni and Co are contained as transition metal elements (Me), and the molar ratio of Mn to Me is Mn / Me of 0.5 <Mn / Me.
The molar ratio of Li to Me, Li / Me, is 1 <Li / Me.
Be oxide , Ge oxide or Bi oxide is present on the surface of the particles, and a diffraction peak attributed to Be oxide , Ge oxide or Bi oxide is observed in an X-ray diffraction diagram using CuKα rays. (However, it consists of a mixture of an oxide of at least one metal selected from the group consisting of La, Pr, Nd, Sm and Eu and an oxide of Ge, and La, Pr, Nd, Sm and Eu. Except for those in which a composite oxide of at least one metal selected from the group and Ge is present.), Positive active material for non-aqueous electrolyte secondary batteries. A positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material according to claim 1. A non-aqueous electrolyte secondary battery provided with the positive electrode according to claim 2. It has an α-NaFeO ₂ structure, contains Mn and Ni or Mn, Ni and Co as transition metal elements (Me), and the molar ratio of Mn to Me is 0.5 <Mn / Me, and Me. Particles of a lithium transition metal composite oxide in which the molar ratio of Li to Li / Me is 1 <Li / Me,
A positive electrode activity for a non-aqueous electrolyte secondary battery in which Be oxide , Ge oxide or Bi oxide is mixed in a solid phase and Be oxide , Ge oxide or Bi oxide is adhered to the surface of the particles. Method of manufacturing the substance.