JP6635906B2 - Lithium ion secondary battery and method for producing positive electrode active material for lithium ion secondary battery - Google Patents

Description

  The present invention relates to a method for producing a lithium ion secondary battery and a positive electrode active material for a lithium ion secondary battery.

Generally, a lithium-containing transition metal oxide is used as a positive electrode active material of a lithium ion secondary battery. Specifically, it is lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ) or the like, and the characteristics are improved (high capacity, cycle characteristics, storage characteristics, internal resistance reduction). , Rate characteristics) and security in order to improve the security. Lithium-ion rechargeable batteries for large-scale applications such as in-vehicle applications and road-leveling applications are required to have different characteristics from those of mobile phones and personal computers.

  Conventionally, various researches and developments have been made on the improvement of battery characteristics required for such a lithium ion secondary battery (Patent Documents 1 to 3).

Japanese Patent No. 3769871 Japanese Patent No. 4062856 JP-A-2005-3838

  Currently used lithium ion secondary batteries include a cylindrical type, a square type, a pouch type, and the like. The characteristics required for components are different between the cylindrical type and the square type / pouch type. Regarding the positive electrode active material, basically, the square type and the pouch type are required to have not only good battery capacity and cycle characteristics but also low impurities in order to prevent swelling.

Generally, in a prismatic / pouch-type lithium-ion secondary battery, as described above, it is important that impurities in the positive electrode active material are low, but this is due to the manufacturing process of the positive electrode active material. I have. That is, in the conventional manufacturing process, a lithium compound (lithium hydroxide, lithium carbonate, etc.) and a transition metal compound (carbonate, hydroxide, oxide, etc.) are mixed and fired. At this time, as for the ratio (Li / Me) between the amount of lithium and the amount of metal other than lithium (Me), for example, assuming a layered compound Li _{1 + α} MeO ₂ , a square-shaped / pouch-shaped lithium ion In the positive electrode active material for a secondary battery, α is 0.995 to 1.005, which is an amount much closer to the stoichiometric composition compared to the cylindrical type. This is because Li other than that reacted with Me remains in the positive electrode active material as alkaline impurities (Li ₂ CO ₃ , LiOH). Alkali impurities are decomposed inside to generate carbon dioxide, and the electrode plate is pressed against the cylindrical can to obtain better battery characteristics, or a safety valve provided at the top of the cylindrical battery when the internal pressure rises due to side reaction In the case of a square or pouch type, the carbon dioxide generated deforms the outer shape, making contact with the battery terminals worse, or contact between the electrode plate and the terminals. This is because the battery becomes worse and does not work as a battery. Here, when lithium hydroxide is selected as the lithium compound to be used for firing, it is a reality that a large amount of lithium carbonate or lithium hydroxide is detected after firing, and therefore, lithium carbonate is selected as the lithium compound before firing, It is common knowledge in the development of a positive electrode active material for a rectangular / pouch type lithium ion secondary battery to suppress the amount of lithium carbonate after firing.
In firing using lithium carbonate as a raw material, the melting point of lithium carbonate is generally 730 ° C. as measured by TG-DTA, so that the lithium carbonate is melted once at around 730 ° C., and then the main firing is performed. It is often brought to around 1000 ° C. However, the present inventor has studied and found that the actual reaction between the transition metal and lithium has started around 500 ° C., and if the above-mentioned melting step is performed, the fusion of the active material particles once formed may occur. It is generated and destroys the primary particles that have been created by excessive force when crushing after firing, and lithium carbonate originally inside the particles appears on the surface at this time, or it is in air. It was found that lithium carbonate was generated as an impurity due to contact between carbon dioxide and the new primary particle fracture surface of the positive electrode active material, and swelling was not suppressed. In order to prevent this, it is considered that the particles are crushed with a weak force and then classified with a sieve or the like, but even if the coarse particles are classified, aggregated particles that are not the original particles (for example, lithium nickel oxide-based positive electrode active material) In this case, the primary particles aggregate to form secondary particles, but secondary particles smaller than the average secondary particle diameter are tertiary aggregated, and particles having the same aggregate diameter as the average secondary particle diameter) are pressed during electrode fabrication. In this case, it was found that lithium carbonate appeared on the surface or lithium carbonate was generated as an impurity by a mechanism similar to the above, and this did not lead to suppression of blistering.
As a countermeasure, Li / Me may be charged slightly larger than the above range, and the resulting fired powder may be washed with water. However, in the positive electrode active material that has been washed with water, Li defects are generated on the surface. It was found that the cycle characteristics were poor, and when this was fired, a large amount of oxygen defects were generated on the surface, and the cycle characteristics were also poor.

  In view of such a problem, an object of the present invention is to provide a prismatic or pouch-type lithium ion secondary battery that has good charge / discharge efficiency and cycle characteristics and suppresses swelling.

  The present inventor has conducted various studies to solve the above problems, and as a result, using a positive electrode active material having a predetermined composition formula, a positive electrode having an ortho hydrogen-para hydrogen conversion rate of 0.2% or less, According to a lithium ion secondary battery including an electrolyte having a predetermined signal intensity ratio and a negative electrode having a predetermined configuration, a square-shaped battery having good charge / discharge efficiency and cycle characteristics and suppressed swelling is provided. It has been found that a pouch-type lithium ion secondary battery can be provided.

In one aspect, the present invention, which has been completed based on the above findings, has an α-NaFeO ₂ type structure, and has a composition formula of Li _{1 + α} TO ₂
(Where 0 ≦ α ≦ 0.002, and T is at least one selected from Ni, Co, Mn, Mg, and Al. When Mn is contained, the composition ratio: Mn / T is 0.1. (When Al is contained, the composition ratio: Al / T is 0.03 or less, and when Mg is contained, the composition ratio: Mg / T is 0.015 or less.)
With a positive electrode active material represented by
A positive electrode having an ortho-hydrogen / para-hydrogen conversion of 0.2% or less as measured by the following measurement procedures (1) to (3);
^An electrolyte having an intensity ratio of a signal of 160 to 170 ppm to a signal of 150 to 160 ppm when measuring ¹³ C NMR of 0.002 or less;
One or more of graphite, non-graphitizable carbon, and a compound having two or more aromatic rings and carbonyl groups in a molecule and having a structure in which the aromatic rings are stacked are used as a negative electrode active material. Negative electrode,
Is a lithium ion secondary battery provided with:
(1) A lithium ion secondary battery is disassembled, a positive electrode is taken out, the positive electrode active material layer is peeled off from the positive electrode, and dried at 120 ° C. for 10 hours to produce a dried electrode peeled product.
(2) The dried electrode peeled product was collected by ICP emission spectroscopy in such a manner that the T became 0.2 mol, and a ring-shaped orifice having an inner diameter of 0.7 cm and an outer diameter of 1 cm was fixed along the inner wall. After filling a 1 cm fluororesin straight pipe with a fluororesin mesh of 30 mesh having an outer diameter of 1 cm so as to come into contact with the ring-shaped orifice, the collected electrode-peeled and dried product is filled with the fluororesin in the straight pipe. Pack so that it contacts the surface of the mesh.
(3) The straight tube is cooled to 70K, and pure ortho hydrogen is fed as an inflow gas at a flow rate of 1.3 L / min for 10 seconds from an inlet of the straight tube on the side of the electrode-peeled dried product, and the fluororesin mesh of the straight tube is flown. By measuring the exhaust gas discharged from the outlet on the side with a thermal conductivity meter of Farcus, the volume of parahydrogen in the exhaust gas is defined as A, and the total volume of outflow gas is defined as B (A / B). An ortho-hydrogen-para-hydrogen conversion, which is a volume percentage indicated by × 100%, is determined.

In another aspect, the present invention has an α-NaFeO ₂ type structure and a composition formula of Li _{1 + α} TO ₂
(Where 0 ≦ α ≦ 0.002, and T is at least one selected from Ni, Co, Mn, Mg, and Al. When Mn is contained, the composition ratio: Mn / T is 0.1. (When Al is contained, the composition ratio: Al / T is 0.03 or less, and when Mg is contained, the composition ratio: Mg / T is 0.015 or less.)
A method for producing a positive electrode active material for a lithium ion secondary battery represented by
Producing a mixture of the hydroxide or oxide of T and lithium carbonate;
An atmosphere having a carbon dioxide gas partial pressure of 0.002 MPa or more and an oxygen partial pressure of 0.018 MPa or more when the temperature is raised to the maximum firing temperature of 760 to 1000 ° C. , And the maximum firing temperature is maintained after reaching the maximum firing temperature, and until the start of cooling, the oxygen partial pressure is 0.018 to 0.1 MPa without carbon dioxide gas. Controlling the atmosphere,
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising:

  ADVANTAGE OF THE INVENTION According to this invention, the charge / discharge efficiency and a cycle characteristic can be provided and the square-shaped / pouch-type lithium ion battery which suppressed generation | occurrence | production of swelling can be provided.

(A) is a compound which was circulated on the cathode side in Example 3. (B) is the compound recovered in Example 3. FIG. 13 is a schematic view of a firing device used in Example 12. FIG. 3 is a schematic diagram of a reaction system of Example 3. It is a schematic diagram of a measuring device of ortho hydrogen-para hydrogen conversion.

(Configuration of lithium-ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode, an electrolyte, and a negative electrode.
The positive electrode active material of the lithium ion secondary battery of the present invention has an α-NaFeO ₂ type structure, and has a composition formula of Li _{1 + α} TO ₂
(Where 0 ≦ α ≦ 0.002, and T is at least one selected from Ni, Co, Mn, Mg, and Al. When Mn is contained, the composition ratio: Mn / T is 0.1. (If Al is contained, the composition ratio: Al / T is 0.03 or less, and if Mg is contained, the composition ratio: Mg / T is 0.015 or less.) In the lithium ion secondary battery of the present invention, the ortho-hydrogen / para-hydrogen conversion rate of the positive electrode measured by the following measurement procedures (1) to (3) is 0.2% or less.
(1) A lithium ion secondary battery is disassembled, a positive electrode is taken out, the positive electrode active material layer is peeled off from the positive electrode, and dried at 120 ° C. for 10 hours to produce a dried electrode peeled product.
(2) The dried electrode peeled product was collected by ICP emission spectroscopy in such a manner that the T became 0.2 mol, and a ring-shaped orifice having an inner diameter of 0.7 cm and an outer diameter of 1 cm was fixed along the inner wall. After filling a 1 cm fluororesin straight pipe with a fluororesin mesh of 30 mesh having an outer diameter of 1 cm so as to come into contact with the ring-shaped orifice, the collected electrode-peeled and dried product is filled with the fluororesin in the straight pipe. Pack so that it contacts the surface of the mesh.
(3) The straight tube is cooled to 70K, and pure ortho hydrogen is fed as an inflow gas at a flow rate of 1.3 L / min for 10 seconds from an inlet of the straight tube on the side of the electrode-peeled dried product, and the fluororesin mesh of the straight tube is flown. By measuring the exhaust gas discharged from the outlet on the side with a thermal conductivity meter of Farcus, the volume of parahydrogen in the exhaust gas is defined as A, and the total volume of outflow gas is defined as B (A / B). An ortho-hydrogen-para-hydrogen conversion, which is a volume percentage indicated by × 100%, is determined.

  When the positive electrode active material of the lithium ion secondary battery of the present invention has the above-described composition, and a positive electrode is formed using the positive electrode active material, and this is used as a lithium ion secondary battery, the battery is disassembled. The ortho-hydrogen-para-hydrogen conversion of the positive electrode taken out in the above-described measurement procedures (1) to (3) is controlled to 0.2% or less. The value of the conversion rate has a correlation with the amount of surface oxygen defects and the amount of surface Li defects on the surface of the positive electrode active material particles from which impurities such as Li salts (lithium carbonate, lithium hydroxide, etc.) have been removed. The conversion ratio increases as the amount of surface Li defects increases. If this amount of surface defects is large, the insertion and detachment of lithium ions into and from the positive electrode active material particles during charging and discharging occur, particularly when the crystal lattice near the surface expands and contracts in an incomplete form. Each time the lattice goes through a cycle, the lithium ion conduction path is broken, resulting in a positive electrode active material having poor cycle characteristics. The vicinity of the surface is extremely important as a lithium ion conduction path, and has a greater effect than oxygen defects and Li defects inside the bulk. In this regard, if the ortho-hydrogen-para-hydrogen conversion rate defined in the present invention is an extremely small value of 0.2% or less, a rectangular / pouch type lithium ion secondary battery having good cycle characteristics is provided. be able to.

  The ratio of the amount of Li in lithium carbonate to the total amount of elements (Mg, Al, Ni, Co, Mn) constituting T (that is, 1 + α in the above composition formula) is 1.000. ~ 1.002 is preferred. If this ratio is less than 1.000, unreacted T compounds will remain after firing, and if the battery is assembled in such a state, the remaining components will have some adverse effect on the charge / discharge reaction. There is a risk. When the ratio is greater than 1.002, the battery outer shape may change when the battery is assembled and charged and discharged as described above, and the battery having the changed outer shape may come into contact with the terminal or contact between the electrode plate and the terminal. May worsen.

In the electrolytic solution constituting the lithium ion secondary battery of the present invention, when ¹³ C NMR is measured, the intensity ratio of the signal of 160 to 170 ppm to the signal of 150 to 160 ppm is 0.002 or less. As a main component of such an electrolytic solution, for example, a cyclic carbonate such as ethylene carbonate and a chain carbonate such as propylene carbonate are mixed at a volume ratio of 2: 8 to 6: 4, and 0% is contained therein. It is preferable to dissolve LiPF ₆ at a concentration of 0.8 to 1.6 mol / L. These volume ratios, compound types, and concentrations are merely examples, and can be appropriately changed within a range normally considered by those skilled in the art. ^{When 13} C NMR is measured, if an organic compound of a cyclic or chain carbonate is present, a signal appears at 150 to 160 ppm, but when it becomes a carbonate ion, the signal shifts to 160 to 170 ppm. The carbonate ions are partially dissolved from the surface of the positive electrode active material on the positive electrode and are present in the electrolytic solution, which promotes swelling of the battery. Therefore, if carbonate ions originally present on the surface of the positive electrode active material and dissolved in the electrolytic solution at the time of battery production are 0.002 or less in molar ratio with respect to carbonate in the electrolytic solution, swelling of the electrolytic solution is suppressed. can do. Note that carbonate ions can also be generated when a partial decomposition product of an organic compound of cyclic or chain carbonate by lithium hydroxide is oxidized on the positive electrode. When this oxidation occurs, oxygen on the surface of the positive electrode active material particles may be used, and the amount of surface oxygen deficiency increases, so that the ortho-hydrogen-para-hydrogen conversion rate may increase.

  The negative electrode constituting the lithium ion secondary battery of the present invention includes graphite, non-graphitizable carbon, and a compound having a structure in which two or more aromatic rings and carbonyl groups are present in a molecule and the aromatic rings are stacked. One or more of them are used as the negative electrode active material.

  Incidentally, the positive electrode constituting the lithium ion secondary battery of the present invention can be prepared by applying a positive electrode active material prepared by the method described below, for example, by a person skilled in the art by, for example, aluminum foil. A positive electrode core material comprising a positive electrode mixture composed of 3 kg of the positive electrode active material, 1 kg of N-methyl-2-pyrrolidone containing 2% by mass of polyvinylidene fluoride, and 90 g of acetylene black, made of an aluminum foil having a thickness of 15 μm The positive electrode of the present invention can be easily manufactured by forming a positive electrode having a total thickness of 130 μm by coating on both sides, drying and rolling to form a positive electrode active material layer. The method for producing a positive electrode from the positive electrode active material can be modified within a range that can be normally considered by those skilled in the art.

(Method for producing positive electrode active material for lithium ion secondary battery)
Next, a method for producing the positive electrode active material for a lithium ion secondary battery of the present invention will be described in detail.
The method for producing the positive electrode active material for a lithium ion secondary battery of the present invention will be described. First, a mixture (mixed powder) of a hydroxide or oxide of T in the composition formula of the positive electrode active material for a lithium ion secondary battery and lithium carbonate is prepared. In this case, when coprecipitating T as a carbonate, it is preferable to calcine it before mixing it with a lithium compound to form an oxide of T in advance. Also, the T hydroxide can be converted to a T oxide by calcining before mixing with the lithium compound. The calcination is performed, for example, in a rotary furnace at a temperature of 300 to 500 ° C. for about 1.5 to 5 hours, but it is possible to convert T carbonate or T hydroxide to T oxide. Since it is an object, it can be appropriately changed within a range in which a person skilled in the art can determine that the object has been achieved.

  Next, the mixture is fired. Here, as the firing conditions, the firing atmosphere is controlled to an atmosphere having a carbon dioxide gas partial pressure of 0.002 MPa or more and an oxygen partial pressure of 0.018 MPa or more when the temperature is raised to the maximum firing temperature. After reaching the temperature, the firing maximum temperature is maintained, and the atmosphere is controlled so as not to contain carbon dioxide gas and to have an oxygen partial pressure of 0.018 MPa until cooling is started. The type of the firing furnace is not particularly limited, as long as the atmosphere and the gas partial pressure can be appropriately adjusted.However, when a roller hearth kiln, a pusher kiln, a tube furnace, a muffle furnace, or the like, which is usually used for producing a positive electrode active material, The method for producing a positive electrode active material of the present invention can be easily implemented. At this time, as shown in FIG. 2, a closed batch furnace and a mass flow controller (mascon) were used in the heating process in which the partial pressure of carbon dioxide was particularly required to be adjusted and the portion of carbon dioxide to be driven out at high temperature. It is particularly preferable to use a complex furnace having a structure in which the partial pressure of each gas is precisely controlled and a continuous furnace is used in the high-temperature holding process and the cooling process after the carbon dioxide drive. Here, "sealing" does not always mean completely closed, and the part corresponding to the gas introduction port and the exhaust port that exhausts when the pressure rises are automatically opened and closed by issuing instructions from the control panel as necessary It is designed to be. In Example 12 described below, carbon dioxide was expelled at 1000 ° C., but the timing of carbon dioxide expelling can be appropriately changed according to the reaction system. The continuous furnace in the combined furnace may be a roller hearth kiln or a pusher kiln. When the total pressure is set to 0.1 MPa or more when using an open furnace, the entire furnace is placed in a closed room and the total pressure is adjusted, or a shutter is installed in the furnace and a part of the furnace is partially installed. By sealing, the gas composition can be easily adjusted while keeping the total pressure at 0.1 MPa.

With such a configuration, it is possible to produce a positive electrode active material having high charge / discharge efficiency and cycle characteristics and a low alkali, and when using this to form a prismatic or pouch-type lithium ion secondary battery, suppressing swelling Thus, a battery having high charge / discharge efficiency and high cycle characteristics can be constructed. When TG-DTA of lithium carbonate is measured in the air in the first place, an endothermic peak accompanying melting appears around 730 ° C., but this is not pure lithium carbonate melting, but some carbon dioxide is desorbed from lithium carbonate. It is the melting point as a result of the separation and the eutectic compound of lithium carbonate and lithium oxide. Therefore, it was considered that it was difficult to expect the action as a flux at the temperature in the actual firing reaction. That is, the original melting point of lithium carbonate needs to be measured in carbon dioxide, which is 997 ° C., and if carbon dioxide is present in the firing furnace, any temperature above 730 ° C. and below 997 ° C. It is considered that "lithium carbonate" or "lithium carbonate and lithium oxide" melts. Therefore, it is necessary to regulate the oxygen concentration and the carbon dioxide concentration in the firing furnace and to perform the firing, whereby the carbon dioxide elimination reaction from lithium carbonate, the anion elimination reaction from the transition metal raw material, and the timing of lithium compound flux generation Is properly controlled, when the ortho-hydrogen-para-hydrogen conversion of the positive electrode is 0.2% or less during the production of the battery and the ¹³ C NMR of the electrolyte is measured, the signal of 160 to 170 ppm with respect to the signal of 150 to 160 ppm is measured. A positive electrode having an intensity ratio of 0.002 or less, which can be used for a prismatic or pouch-type lithium ion secondary battery having an unprecedented level of high charge / discharge efficiency / cycle characteristics and little swelling Active material can be manufactured. Conventionally, in such a case, a large amount of air was flowed during the firing to drive out carbon dioxide to produce a positive electrode active material. The firing material can be filled only thinly, which is an obstacle to filling the firing material in large quantities in the sagger, and the amount of lithium volatilized from the positive electrode active material particles also increases, so the essential charge and discharge Efficiency had been reduced. For this reason, conventionally, it has been difficult to realize good charge / discharge efficiency, cycle characteristics, and suppression of blistering at a high level as in the present invention.

  Next, the fired powder (fired powder) is crushed using a roll mill, a pulverizer or the like, if necessary, to obtain a positive electrode active material having a predetermined average particle diameter. The average particle diameter can be appropriately changed according to the intended use of the lithium ion secondary battery by a method usually performed by those skilled in the art.

Hereinafter, examples for better understanding of the present invention and its advantages will be provided, but the present invention is not limited to these examples.
In the examples described below, the CO ₂ partial pressure at 400 to 1000 ° C. was set to 0.002 MPa or more, lithium carbonate was not melted, and at around 997 ° C., an atmosphere containing no carbon dioxide was introduced at once to cause a reaction. Manufactured. Since some reaction systems react at low temperatures, examples in which air is introduced at an arbitrary temperature of 760 to 997 ° C. are also shown.

-Example 1
<Synthesis of precursor>
The synthesis of the precursor was performed as follows. In the following, "control" is described, but the control may be automatic, such as with a pump, or may be performed visually or manually.
First, cobalt sulfate and magnesium sulfate were dissolved in water to prepare an aqueous solution A in which cobalt sulfate and magnesium sulfate were dissolved. At this time, the aqueous solution was adjusted so that the Co concentration was 0.982 mol / L and the Mg concentration was 0.015 mol / L. Separately, sodium aluminate was dissolved in water to prepare an aqueous solution B in which sodium aluminate was dissolved. At this time, the aqueous solution was prepared such that the Al concentration was 0.003 mol / L. Further, an aqueous sodium carbonate solution C was prepared such that the Na concentration became 1 mol / L. An empty reaction vessel was prepared, the contents were replaced with nitrogen gas, and A and B were simultaneously charged at first while simultaneously rotating the stirrer so as not to splash water to prepare an initial mixed solution. The charging speed at this time was 0.5 L / min for both A and B. Thereafter, the pH was monitored while A and B were continuously added, and C was added so as to increase by 0.1 every 5 minutes. When the pH reached 8.0, the control of the increase in the pH was stopped, and the on / off control of the C solution sending was performed so that the pH became 8.2 ± 0.2. In this way, particles were grown from the initial mixed solution to obtain (Mg, Al) -added transition metal carbonate. When the particle size of the (Mg, Al) -added transition metal carbonate reached 10 μm, the addition of A, B, and C was stopped. During the preparation of the (Mg, Al) -added transition metal carbonate, the oxygen concentration inside the reaction vessel was maintained at 0.1 ppm or less, and the reaction solution containing A, B or a mixture of A, B, and C was 50 ± 2. C., and the rotation speed of the stirrer was adjusted such that the stirring blade was fast enough not to splash water until it was almost immersed in water. After the stirring blade was almost immersed in water, it was rotated at a constant speed. This was transferred to a relay tank and filtered and washed with water. The (Mg, Al) -added transition metal carbonate cake after water washing was spread on a vat so as to have a thickness of 2 cm or less, and dried at 120 ° C. for 10 hours. Thus, (Mg, Al) -added transition metal carbonate powder was synthesized. The (Mg, Al) -added transition metal carbonate powder is placed in a rotary furnace, and thermally decomposed at 400 ° C. for 3 hours while introducing air into the rotary furnace to convert the carbonate powder into (Mg, Al). A powder of the added transition metal oxide was used as a precursor.

<Synthesis of positive electrode active material>
The produced precursor and Li ₂ CO ₃ (manufactured by SQM) were charged so that the molar ratio of Li / (transition metal + Al + alkaline earth metal) was 1.002, and mixed with a Henschel mixer to obtain a mixed powder. Produced. This mixed powder was filled in a sagger, and (1) the temperature was raised to 1000 ° C at a rate of 2 ° C / min, (2) the temperature was kept at 1000 ° C for 10 hours, and (3) the temperature was cooled to 300 ° C at a rate of 2 ° C / min. (4) After that, firing was performed in a firing pattern of allowing to cool at room temperature. At that time, the flow rates of CO ₂ : N ₂ : O ₂ were set to 0.8: 0: 0.2 in (1) and 0: 0.8: 0.2 in (2) and (3). The cooled product was crushed using a roll mill and a pulverizer to obtain a positive electrode active material. The total pressure during firing was maintained at 0.1 MPa.

<Evaluation of positive electrode active material>
-Composition-
The powder of the obtained positive electrode active material was measured for the content of Li, Ni, Mn, Co and other metal elements by ICP and ion chromatography, and the molar ratio of Li to metals other than Li, except for Li, The molar ratio of each metal to metal was evaluated.

-Residual alkali-
After adding the obtained powder of the positive electrode active material to water and stirring for 10 minutes, it is assumed that the lithium compound present in the water is the residual alkali in the positive electrode active material, and the pH is titrated with an acid. To determine the mass of the residual alkali (Li ₂ CO ₃ and LiOH), and the ratio of the mass to the positive electrode active material (% by mass).

<Preparation of prismatic lithium ion secondary battery>
-Preparation of positive electrode-
3 kg of the obtained positive electrode active material, 1 kg of PVDF # 1320 (N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) solution containing 12% by weight of PVDF) manufactured by Kureha Chemical Co., Ltd., and 90 g of acetylene black And an appropriate amount of NMP were stirred with a double-arm kneader to prepare a positive electrode mixture paste. This paste was applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried, and rolled to form a positive electrode active material layer, thereby obtaining a positive electrode having a total thickness of 130 μm. The positive electrode was cut into a strip having a width of 43 mm.

-Preparation of negative electrode A-
3 kg of artificial graphite, 75 g of BM-400B (aqueous dispersion containing modified styrene-butadiene rubber of 40% by mass) manufactured by Zeon Corporation, 30 g of CMC, and an appropriate amount of water were stirred with a double-arm kneader. , To prepare a negative electrode mixture paste. This paste was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode active material layer, thereby obtaining a negative electrode having a total thickness of 140 μm. The negative electrode was cut into a band having a width of 45 mm. This negative electrode is referred to as negative electrode A.

-Preparation of prismatic lithium ion secondary battery-
The prepared positive electrode and the prepared negative electrode A were wound between them with a separator (A089 (trade name) manufactured by Celgard Co., Ltd.) made of a polyethylene microporous film having a thickness of 20 μm. A substantially elliptical electrode group was formed. The electrode group was housed in a square battery can made of aluminum. The battery can has a bottom and a side wall. The upper part of the battery can is open, and its shape is substantially rectangular. The thickness of the main flat portion of the side wall was 80 μm. Thereafter, an insulator for preventing a short circuit between the battery can and the positive electrode lead or the negative electrode lead was disposed on the upper part of the electrode group. Next, a rectangular sealing plate having a negative electrode terminal surrounded by an insulating gasket at the center was arranged at the opening of the battery can. The negative electrode lead was connected to the negative electrode terminal. The positive electrode lead was connected to the lower surface of the sealing plate. The end of the opening and the sealing plate were welded with a laser to close the opening of the battery can. Thereafter, 2.5 g of the non-aqueous electrolyte was injected into the battery can from the injection hole of the sealing plate. Finally, the injection hole was closed by welding with a stopper. In this state, it was left on the insulator for 24 hours. Thus, a plurality of prismatic lithium ion secondary batteries having a height of 50 mm, a width of 34 mm, an inner space thickness of about 5.2 mm, and a design capacity of 850 mAh were completed. As the non-aqueous electrolyte, a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) in a volume ratio of 30:70 was mixed with LiPF _{6 at} a ratio of 1 M (mol / liter). The solution dissolved in was used in a state in which argon gas was ventilated to sufficiently remove carbon dioxide dissolved in the solution. The completed prismatic lithium-ion secondary battery is disassembled and a non-aqueous electrolyte is sucked out. The ¹³ C NMR spectrum of the sucked-out non-aqueous electrolyte is measured by a conventional method. The signal (attributable to the carbonate group) that appeared in the region of 160 to 170 ppm with respect to the signal (attributable to the carbonyl group of the electrolytic solution) that appeared in the above was determined. When the open circuit voltage of this prismatic lithium ion secondary battery was measured, it was 3.0 V.

-Measurement of ortho-hydrogen-para-hydrogen conversion-
Disassemble the produced rectangular lithium ion secondary battery, take out the positive electrode sheet, peel off the coating film of the positive electrode active material layer from the positive electrode sheet with a PTFE spatula, dry at 120 ° C. for 10 hours to obtain an electrode peeled dry product, The apparatus in FIG. 4 was packed with the dried electrode peeled product, and 1.3 L / min of pure ortho-hydrogen was allowed to flow for 10 seconds. The ratio of ortho-hydrogen to para-hydrogen was measured by a Farkas thermal conductivity meter for the gas discharged from the outlet. From this, the ortho-hydrogen-para-hydrogen conversion (%) was calculated as a percentage of (amount of para-hydrogen in outlet gas) / (total amount of outlet gas).

-Charge and discharge of prismatic lithium ion secondary battery-
The prepared rectangular lithium ion secondary battery was charged at 25 ° C. to a charge cut-off potential of 4.2 V at a charge current of 850 mA, and then discharged at 25 ° C. to a discharge cut-off potential of 3.0 V at a discharge current of 850 mA. This charge / discharge is repeated in the same manner at 25 ° C. for 20 cycles, and the percentage (%) of the initial discharge capacity (mAh / g) to the initial charge capacity (mAh / g) is defined as the charge / discharge efficiency, and the initial discharge capacity (mAh) / G), the percentage (%) of the discharge capacity (mAh / g) for 20 cycles was defined as the capacity retention rate after 20 cycles. In addition, in order to investigate the swelling of the battery after the high-temperature cycle, the battery was charged at 90 ° C. with a charging current of 850 mA to a charging end potential of 4.2 V, and then discharged at 90 ° C. with a discharging current of 850 mA to a discharging end potential of 3.0 V. did. This charging / discharging is repeated in the same manner at 90 ° C. for 100 cycles, and the thickness change from the initial inner space thickness of 5.2 mm is measured by an X-ray CT scan. mm). X-ray CT scan measurement was performed by a conventional method.
The results are shown in Tables 1 and 2.

-Example 2
A negative electrode B was prepared as described below, and the same operation as in Example 1 was performed except that the negative electrode B was used instead of the negative electrode A. The results are shown in Tables 1 and 2.
(Preparation of negative electrode B)
3 kg of Carbotron P manufactured by Kureha Battery Materials Japan Co., Ltd., 75 g of BM-400B (aqueous dispersion containing 40% by mass of modified styrene butadiene rubber) manufactured by Zeon Corporation, 30 g of CMC, and an appropriate amount of water, The mixture was stirred with a double-arm kneading machine to prepare a negative electrode mixture paste. This paste was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode active material layer, thereby obtaining a negative electrode having a total thickness of 140 μm. The negative electrode was cut into a band having a width of 45 mm. This negative electrode is referred to as negative electrode B.

-Example 3
A negative electrode C was prepared as described below, and the same operation as in Example 1 was performed except that the negative electrode C was used instead of the negative electrode A. The results are shown in Tables 1 and 2.
(Preparation of negative electrode C)
As shown in FIG. 3, hydrogen flows on the anode side, the compound of FIG. 1A flows on the cathode side at 500 ° C., the anode is composed of M oxide, and the cathode is composed of M graphite intercalation compound. Decomposition was performed. The principle of operation is the same as that of the existing steam electrolysis, but the ions traveling in the solid electrolyte are M cations. Although not shown in the figure, the oxide of M at the anode was Ni-Zn-Cu ferrite, and the graphite intercalation compound of M was (Ni ²⁺ , Fe ³⁺ ) -graphite intercalation compound. The generated vapor of the compound of FIG. 1B (M is Ni ²⁺ , Fe ²⁺ , Ni: Fe in a molar ratio of 1: 3) was separated by a magnet, collected by cooling with a cooled magnet, and collected. 1 kg of the collected compound of FIG. 1 (b), 105 g of KF polymer manufactured by Kureha Battery Materials Japan Co., Ltd., and 1050 g of NMP were stirred with a double-arm kneader to prepare a negative electrode mixture paste. This paste was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode active material layer, thereby obtaining a negative electrode having a total thickness of 140 μm. The negative electrode was cut into a band having a width of 45 mm. This negative electrode is referred to as negative electrode C.

-Example 4
In the method for producing the positive electrode active material, the same procedure as in Example 1 was performed except that Li / (transition metal + Al + alkaline earth metal) was 1.000. The results are shown in Tables 1 and 2.

-Example 5
A precursor was synthesized as follows, and carried out in the same manner as in Example 1 except that the maximum temperature during firing was 760 ° C. The results are shown in Tables 1 and 2.
<Synthesis of precursor>
The synthesis of the precursor was performed as follows. Although "control" is described in the middle, it may be automatic or visual or manual by a pump or the like.
First, nickel sulfate and cobalt sulfate were dissolved in water to prepare an aqueous solution A in which nickel sulfate and cobalt sulfate were dissolved. At this time, the aqueous solution was adjusted so that the Ni concentration was 0.82 mol / L and the Co concentration was 0.15 mol / L. Separately, aluminum sulfate and ammonia were dissolved in water to prepare an aqueous solution B in which aluminum sulfate and ammonia were dissolved. At this time, the aqueous solution was prepared such that the Al concentration was 0.03 mol / L and the ammonium ion concentration was 2.003 mol / L. Further, an aqueous sodium hydroxide solution C for pH adjustment was prepared such that the Na concentration became 1 mol / L. An empty reaction vessel was prepared, the contents were replaced with nitrogen gas, and A and B were simultaneously charged first while rotating the stirrer so fast as not to splash water, thereby producing a seed crystal. The charging speed at this time was 0.5 L / min for both A and B. Thereafter, the pH was monitored while A and B were continuously added, and C was added so as to increase by 0.1 every 5 minutes. When the pH reached 10.8, the control of the increase in the pH was stopped, and the ON / OFF control of the C solution sending was performed so that the pH became 11.0 ± 0.2. In this way, the grains were grown from the seed crystal to obtain an Al-added transition metal hydroxide. When the particle diameter of the Al-added transition metal hydroxide reached 10 μm, the addition of A, B, and C was stopped. During the preparation of the Al-added transition metal hydroxide, the oxygen concentration inside the reaction tank was maintained at 0.1 ppm or less, and the reaction solution containing A, B or a mixture of A, B, and C was maintained at 50 ± 2 ° C. The rotation speed of the stirrer was adjusted such that the rotation speed was high enough not to splash the water until the stirring blade was almost immersed in water. After the stirring blade was almost immersed in water, it was rotated at a constant speed. This was transferred to a relay tank and filtered and washed with water. The Al-added transition metal hydroxide cake after water washing was dried at 120 ° C. Thus, a powder of an Al-added transition metal hydroxide as a precursor was synthesized.

-Example 6
A precursor was synthesized as follows, and the same procedure as in Example 1 was performed except that the maximum temperature during firing was set to 780 ° C. The results are shown in Tables 1 and 2.
<Synthesis of precursor>
The synthesis of the precursor was performed as follows. Although "control" is described in the middle, it may be automatic or visual or manual by a pump or the like.
First, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water to prepare an aqueous solution A in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved. At this time, the aqueous solution was adjusted so that the Ni concentration was 0.80 mol / L, the Co concentration was 0.10 mol / L, and the Mn concentration was 0.10 mol / L. Separately, ammonia was dissolved in water to prepare an aqueous solution B in which ammonia was dissolved. At this time, the aqueous solution was prepared such that the ammonium ion concentration was 2.003 mol / L. Further, an aqueous sodium hydroxide solution C for pH adjustment was prepared such that the Na concentration became 1 mol / L. An empty reaction vessel was prepared, the contents were replaced with nitrogen gas, and A and B were simultaneously charged first while rotating the stirrer so fast as not to splash water, thereby producing a seed crystal. The charging speed at this time was 0.5 L / min for both A and B. Thereafter, the pH was monitored while A and B were continuously added, and C was added so as to increase by 0.1 every 5 minutes. When the pH reached 10.8, the control of the rise of the pH was stopped, and the on / off control of the C solution sending was performed so that the pH became 11 ± 0.2. In this way, particles were grown from the seed crystal to obtain a transition metal hydroxide. When the particle size of the transition metal hydroxide reached 10 μm, the addition of A, B, and C was stopped. During the preparation of the transition metal hydroxide, the oxygen concentration inside the reaction tank is maintained at 0.1 ppm or less, and the reaction solution in which A, B or A, B, C is mixed is maintained at 50 ± 2 ° C. The rotation speed of the stirrer was adjusted so that the rotation speed was high enough not to splash water until the stirring blades were almost immersed in water. After the stirring blade was almost immersed in water, it was rotated at a constant speed. This was transferred to a relay tank and filtered and washed with water. The transition metal hydroxide cake after washing with water was dried at 120 ° C. Thus, a transition metal hydroxide powder as a precursor was synthesized.

-Example 7
The synthesis was performed in the same manner as in Example 1 except that the ratio of CO ₂ : N ₂ : O ₂ was changed to 0.6: 0.2: 0.2 in the step (1) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

-Example 8
The synthesis was performed in the same manner as in Example 1 except that the ratio of CO ₂ : N ₂ : O ₂ was changed to 0.02: 0.8: 0.18 in the step (1) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

-Example 9
The synthesis was performed in the same manner as in Example 1 except that CO ₂ : N ₂ : O ₂ was changed to 0: 0.5: 0.5 in steps (2) and (3) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

-Example 10
The procedure was performed in the same manner as in Example 1 except that pure oxygen was passed in steps (2) and (3) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

Example 11
The synthesis was carried out in the same manner as in Example 1 except that CO ₂ : N ₂ : O ₂ was changed to 0: 0.82: 0.18 in the steps (2) and (3) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

-Example 12
In this embodiment, an apparatus as shown in FIG. 2 was used during firing. At the time of firing in the synthesis of the positive electrode active material in Example 1, first, a sagger containing the mixed powder was placed in the batch firing section, and the CO ₂ partial pressure in the firing atmosphere was 0.06 MPa or more and the O ₂ partial pressure was 0. The temperature was raised to 1000 ° C. at a rate of 2 ° C./min while controlling with a control panel and a mass flow controller (mass control in FIG. 2) so as to maintain the temperature at a rate of 0.02 MPa or more. Stop the introduction of ₂ , adjust the atmosphere so that the O ₂ partial pressure becomes 0.1 MPa or more, and open the shutter to the continuous firing section when CO ₂ is no longer detected by the CO ₂ sensor. Then, it was kept at 1000 ° C. for 9.5 hours in a continuous baking section while flowing pure O ₂ through it, cooled to 300 ° C. at 2 ° C./min and taken out. At this time, the heater output was adjusted so that the temperature rise at 2 ° C./min for the batch firing section was a firing pattern of time control as it was, and for the continuous firing section, the temperature was lowered at 2 ° C./min after holding at 1000 ° C. The heater output above and below the kiln and the roller speed were adjusted so that the firing pattern of the time control was changed to the firing pattern of the space (position of the sagger) control. The resulting fired product was crushed using a roll mill and a pulverizer, and the same operation as in Example 1 was carried out except that this was used as a positive electrode active material. The control range of the total pressure during the batch furnace firing was set to 0.12 ± 0.02 MPa, and the control target was set to 0.1 MPa so as to approach 0.1 MPa as much as possible. In some cases, the total pressure instantaneously rises to a maximum of 0.2 MPa. The results are shown in Tables 1 and 2.

-Example 13
The powder of the Al-added transition metal hydroxide, which is the precursor of Example 5, was placed in a rotary furnace, and (a mixed gas having a volume ratio of N ₂ : O ₂ of 97: 3) was introduced into the rotary furnace. Except that it was thermally decomposed at 320 ° C. for 2.5 hours to turn the hydroxide powder into an Al-added transition metal oxide powder, which was mixed with Li ₂ CO ₃ as a precursor during the synthesis of the positive electrode active material. Performed in the same manner as in Example 5. The results are shown in Tables 1 and 2.

-Example 14
The powder of the transition metal hydroxide, which is the precursor of Example 6, was placed in a rotary furnace, and 320 ° C was introduced into the rotary furnace while introducing (a mixed gas having a volume ratio of N ₂ : O ₂ of 95: 5). Example 6 except that the above-mentioned hydroxide powder was converted into a transition metal oxide powder by pyrolysis for 2.5 hours, and this was mixed with Li ₂ CO ₃ as a precursor during the synthesis of the positive electrode active material. Performed similarly. The results are shown in Tables 1 and 2.

-Comparative example 1
Example 6 was the same as Example 6, except that the Ni concentration in the aqueous solution A was adjusted to 0.70 mol / L, the Co concentration to 0.10 mol / L, and the Mn concentration to 0.20 mol / L. went. The results are shown in Tables 1 and 2.

-Comparative example 2
In Example 5, the Ni concentration in the aqueous solution A was adjusted to be 0.78 mol / L, the Co concentration was adjusted to be 0.15 mol / L, the Al concentration in the aqueous solution B was 0.07 mol / L, and the ammonium ion concentration was The procedure was performed in the same manner as in Example 5, except that it was prepared to be 2.003 mol / L. The results are shown in Tables 1 and 2.

-Comparative example 3
Example 1 was repeated in the same manner as in Example 1 except that the Co concentration in the aqueous solution A was adjusted to 0.979 mol / L and the Mg concentration to 0.018 mol / L. The results are shown in Tables 1 and 2.

-Comparative example 4
The synthesis was carried out in the same manner as in Example 1 except that CO ₂ : N ₂ : O ₂ was changed to 0: 0.8: 0.2 in the step (1) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

-Comparative example 5
The synthesis was carried out in the same manner as in Example 1 except that the ratio of CO ₂ : N ₂ : O ₂ was changed to 0.6: 0.4: 0 in the step (1) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

Comparative Example 6
The synthesis was carried out in the same manner as in Example 1 except that CO ₂ : N ₂ : O ₂ was changed to 0.02: 0: 0.98 in the steps (2) and (3) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

Comparative Example 7
The synthesis was performed in the same manner as in Example 1 except that CO ₂ : N ₂ : O ₂ was changed to 0: 0.9: 0.1 in the steps (2) and (3) during the synthesis of the positive electrode active material. The results are shown in Tables 1 and 2.

Comparative Example 8
The transition metal hydroxide powder, which is the precursor of Comparative Example 1, was placed in a rotary furnace, and 340 ° C. while introducing (a mixed gas having a volume ratio of N ₂ : O ₂ of 92: 8) into the rotary furnace. Comparative Example 1 except that the above-mentioned hydroxide powder was converted to a transition metal oxide powder by pyrolysis for 2.7 hours, and this was mixed with Li ₂ CO ₃ as a precursor during the synthesis of the positive electrode active material. Performed similarly. The results are shown in Tables 1 and 2.

Each of the lithium ion secondary batteries of Examples 1 to 14 was a prismatic lithium ion secondary battery having good charge / discharge efficiency and cycle characteristics and suppressed occurrence of swelling.
The lithium ion secondary batteries of Comparative Examples 1 to 8 had poor charge / discharge efficiency and cycle characteristics, or had blisters.
Although the prismatic lithium ion secondary battery was manufactured in the example, the mechanism of swelling due to the generation of gas and causing terminal contact failure and the like is the same for both the prismatic type and the pouch type. It can be said that not only the pouch type but also the pouch type lithium ion secondary battery has the same effect.

Claims (2)

It has an α-NaFeO ₂ type structure and the composition formula is Li _{1 + α} TO ₂
(Where 0 ≦ α ≦ 0.002, and T is at least one selected from Ni, Co, Mn, Mg, and Al. When Mn is contained, the composition ratio: Mn / T is 0.1. (When Al is contained, the composition ratio: Al / T is 0.03 or less, and when Mg is contained, the composition ratio: Mg / T is 0.015 or less.)
With a positive electrode active material represented by
A positive electrode having an ortho-hydrogen / para-hydrogen conversion of 0.2% or less as measured by the following measurement procedures (1) to (3);
^An electrolyte having an intensity ratio of a signal of 160 to 170 ppm to a signal of 150 to 160 ppm when measuring ¹³ C NMR of 0.002 or less;
One or more of graphite, non-graphitizable carbon, and a compound having two or more aromatic rings and carbonyl groups in a molecule and having a structure in which the aromatic rings are stacked are used as a negative electrode active material. Negative electrode,
A lithium ion secondary battery provided with.
(1) A lithium ion secondary battery is disassembled, a positive electrode is taken out, the positive electrode active material layer is peeled off from the positive electrode, and dried at 120 ° C. for 10 hours to produce a dried electrode peeled product.
(2) The dried electrode peeled product was collected by ICP emission spectroscopy in such a manner that the T became 0.2 mol, and a ring-shaped orifice having an inner diameter of 0.7 cm and an outer diameter of 1 cm was fixed along the inner wall. After filling a 1 cm fluororesin straight pipe with a fluororesin mesh of 30 mesh having an outer diameter of 1 cm so as to come into contact with the ring-shaped orifice, the collected electrode-peeled and dried product is filled with the fluororesin in the straight pipe. Pack so that it contacts the surface of the mesh.
(3) The straight tube is cooled to 70K, and pure ortho hydrogen is fed as an inflow gas at a flow rate of 1.3 L / min for 10 seconds from an inlet of the straight tube on the side of the electrode-peeled dried product, and the fluororesin mesh of the straight tube is flown. By measuring the exhaust gas discharged from the outlet on the side with a thermal conductivity meter of Farcus, the volume of parahydrogen in the exhaust gas is defined as A, and the total volume of outflow gas is defined as B (A / B). An ortho-hydrogen-para-hydrogen conversion, which is a volume percentage indicated by × 100%, is determined. It has an α-NaFeO ₂ type structure and the composition formula is Li _{1 + α} TO ₂
(Where 0 ≦ α ≦ 0.002, and T is at least one selected from Ni, Co, Mn, Mg, and Al. When Mn is contained, the composition ratio: Mn / T is 0.1. (When Al is contained, the composition ratio: Al / T is 0.03 or less, and when Mg is contained, the composition ratio: Mg / T is 0.015 or less.)
A method for producing a positive electrode active material for a lithium ion secondary battery represented by
Producing a mixture of the hydroxide or oxide of T and lithium carbonate;
An atmosphere having a carbon dioxide gas partial pressure of 0.002 MPa or more and an oxygen partial pressure of 0.018 MPa or more when the temperature is raised to the maximum firing temperature of 760 to 1000 ° C. , And the maximum firing temperature is maintained after reaching the maximum firing temperature, and until the start of cooling, the oxygen partial pressure is 0.018 to 0.1 MPa without carbon dioxide gas. Controlling the atmosphere,
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: