JP6394956B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

Conventionally, in a lithium secondary battery which is a non-aqueous electrolyte secondary battery, a “LiMeO ₂ type” active material (Me is a transition metal) having an α-NaFeO ₂ type crystal structure has been studied as a positive electrode active material, and LiCoO ₂ Has been widely used. The lithium secondary battery using LiCoO ₂ as the positive electrode active material had a discharge capacity of about 120 to 130 mAh / g.

Various “LiMeO ₂ type” active materials that are also excellent in charge / discharge cycle performance have been proposed and partially put into practical use. For example, LiNi _1/2 Mn _1/2 O ₂ and LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ have a discharge capacity of 150 to 180 mAh / g.

As the Me, it has been desired to use abundant Mn as a global resource. However, the “LiMeO ₂ type” active material in which the molar ratio of Mn to Me, Mn / Me exceeds 0.5, undergoes a structural change from α-NaFeO ₂ type to spinel type with charge, and the crystal structure cannot be maintained. There was a problem that the charge / discharge cycle was extremely inferior.
Therefore, in recent years, the molar ratio Mn / Me of manganese (Mn) to transition metal (Me) exceeds 0.5 for the “LiMeO ₂ type” active material as described above, and α-NaFeO ₂ even when charged. An active material capable of maintaining the structure was proposed.

Patent Document 1 discloses a non-aqueous solution using, as a positive electrode active material, a lithium transition metal composite oxide containing Ni, Co, and Mn as Me and having a molar ratio of Mn to Me, Mn / Me of 0.62 to 0.72. The electrolyte secondary battery is charged at 4.5 to 4.6 V (vs. Li / Li ⁺ ) in the initial charge / discharge performed during the manufacturing process, and the maximum potential of the positive electrode during charge during use is 4 It is described that a discharge capacity of 200 mAh / g or more can be obtained for a battery having a voltage of .4 V (vs. Li / Li ⁺ ) or less or 4.3 V (vs. Li / Li ⁺ ) or less. Also in Patent Document 2, for the same positive electrode active material, initial charging / discharging is performed at 4.6 V (vs. Li ^/ Li ⁺ ), and the subsequent charging / discharging cycle is 4.3 V (vs. Li / Li ⁺ ). It is described that the same discharge capacity is obtained by charging.

Thus, unlike the case of the conventional “LiMeO ₂ type” positive electrode active material, Me contains Ni, Co and Mn, and the molar ratio of Mn to Me Mn / Me exceeds 0.5. In the positive electrode active material capable of maintaining the α-NaFeO ₂ structure, a high discharge capacity can be obtained by performing charging (hereinafter referred to as “first charge”) until reaching a potential higher than the charge potential at the time of use. There is a feature.
In this material, the raw materials are mixed so that the composition ratio Li / Me of lithium (Li) to the ratio of transition metal (Me) is greater than 1, for example, Li / Me is 1.25 to 1.6. Since it is synthesized, it is also called a “lithium-excess type” active material, and the composition after synthesis can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0). Here, when the composition ratio Li / Me of lithium (Li) with respect to the ratio of the transition metal (Me) is β, β = (1 + α) / (1-α), and thus, for example, Li / Me is 1.5. In this case, α = 0.2.

Patent Document 3 discloses a solid solution lithium-containing transition metal oxide having a layered structure portion that changes into a spinel structure and a layered structure portion that does not change by charging or charging / discharging in a potential range of 4.3 V to 4.8 V. A positive electrode comprising a positive electrode active material containing A and a lithium-containing transition metal oxide B having a layered structure portion that does not change into a spinel structure by charging or charging / discharging in a potential range of 4.3 V to 4.8 V Lithium ion secondary batteries (paragraph 0010, claims, etc.) having the following characteristics are described: “As a charge / discharge pretreatment method with regulated potential, the highest potential in a predetermined potential range with respect to a lithium metal counter electrode (lithium metal or The upper limit potential of charge / discharge converted to lithium metal) is 4.3 V (vs. Li ^/ Li ⁺ ) or more and 4.8 V (vs. Li ^/ Li ⁺ ). It is desirable to perform 1 to 30 cycles of charging / discharging under the following conditions, more preferably 4.4 V (vs. Li ^/ Li ⁺ ) or more and 4.6 V (vs. Li ^/ Li ⁺ ) or less. It is desirable to perform charge and discharge for 1 to 30 cycles "(paragraph 0034).

Patent Document 4 discloses a lithium ion secondary battery having a positive electrode including a positive electrode active material represented by Chemical Formula 1, aLi ₂ MnO _3- (1-a) LiMO ₂ , and the initial charge is 4.5 V to 4. A lithium ion secondary battery (Claim 1) is described in which the positive electrode active material is activated at a voltage in the range of 7V.

WO2012 / 091015 WO2013 / 084923 JP 2013-1887023 A JP 2013-214491 A

In the above-described prior art, the initial charge is performed at a potential exceeding the operating potential at the time of use, for example, 4.35 V, and a high capacity is extracted from the positive electrode active material.
Then, when the battery is used at the actual operating potential after the first charge, an excess capacity as schematically shown in FIG. 4 is generated in the positive electrode, and in order to make up for this excess capacity, an excess that is involved only in the first charge / discharge Necessary amount of negative electrode material was required.
Therefore, a large volume is required to accommodate the negative electrode material, and this has been a factor that hinders the high capacity density of the battery.

  In view of such problems, the present invention provides a battery having a high volume capacity density in a nonaqueous electrolyte secondary battery having a positive electrode active material made of a lithium transition metal composite oxide in which the proportion of Mn in the transition metal is increased. For the purpose.

  In order to achieve the above object, the present inventor paid attention to a capacity region characterized in a cyclic voltammogram (CV) of a positive electrode active material composed of a lithium transition metal composite oxide in which the proportion of Mn in the transition metal is increased. .

The present invention has the following configuration.
A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode has a positive electrode active material containing a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure,
The lithium transition metal composite oxide has a molar ratio Li / Me of lithium (Li) to transition metal (Me) larger than 1 , and includes Mn and Ni and / or Co as the transition metal (Me), molar ratio Mn / Me of Mn to the transition metal (Me) is Ri Mn / Me ≧ 0.60 der,
The cyclic voltammogram (CV), the scanning potential range: 2.0-4.45V (vs.Li/Li ^+), scanning speed: When performed in 0.05 mV / sec, the oxidation side in the CV of the positive electrode, There are two peaks across the minimum point of the current density, and 3.6 V (vs. Li) with respect to the integral value in the region of potential higher than 3.6 V (vs. Li ^/ Li ⁺ ) in the CV on the oxidation side of the positive electrode. / Li ⁺ ), the ratio of the integration values in the lower potential region is in the range of 0.37 to 0.51;
A nonaqueous electrolyte secondary battery in which a ratio of a capacity of the positive electrode to a capacity of the negative electrode is in a range of 0.86 to 0.95.

  According to the present invention, a nonaqueous electrolyte secondary battery having a high capacity density per volume can be provided.

Cyclic voltammogram (CV) of non-aqueous electrolyte secondary battery according to the present invention External view of non-aqueous electrolyte battery according to the present invention Conceptual diagram of a power storage device formed by assembling non-aqueous electrolyte batteries according to the present invention Schematic diagram showing the surplus capacity generated by the initial charge and discharge of the positive electrode

The lithium transition metal composite oxide of the present invention is such that the molar ratio of Mn to transition metal (Me) Mn / Me is 0.6 or more.
A lithium transition metal composite oxide having a molar ratio Mn / Me of 0.6 or more has a high capacity. Since Li / Me is larger than 1, the α-NaFeO ₂ structure can be maintained even when charged, and therefore the charge / discharge cycle performance is also excellent.

FIG. 1 includes a positive electrode having a positive electrode active material containing a lithium transition metal composite oxide having a molar ratio Mn / Me of 0.6 or more, as described in detail in the Examples section of the present invention. Assemble the non-aqueous electrolyte secondary battery and set the charging potential to 4.6 V (vs. Li ^/ Li ⁺ ), 4.5 V (vs. Li ^/ Li ⁺ ), or 4.45 V (vs. Li ^/ Li ⁺ ). After the first charge and discharge are performed, the positive electrode is used as a working electrode (WE) and is obtained by scanning the potential in the range of 2.0 V (vs. Li ^/ Li ⁺ ) to 4.45 V (vs. Li / Li ⁺ ). Is a cyclic voltammogram (CV).
As can be seen from FIG. 1, when the initial charge potential is set to 4.5 V (vs. Li ^/ Li ⁺ ) or more, two peaks clearly appear across 3.6 V (vs. Li ^/ Li ⁺ ). Since it appears, it can be divided into two potential regions each including these peaks across 3.6 V (vs. Li ^/ Li ⁺ ). Then, in contrast to setting the initial charging potential 4.45V (vs.Li/Li ^+), among these regions, a lower potential than 3.6V (vs.Li/Li ⁺⁾ (1) Is a region where the capacity is greatly increased by setting the initial charge potential high, and the region (2) having a potential higher than 3.6 V (vs. Li ^/ Li ⁺ ) is determined by the set value of the initial charge potential. It can be seen that this is a region where the capacitance does not change greatly.

The inventor found that the capacity development in the region (1) is due to redox of Mn and redox of O ₂ , and the capacity development in the region (2) is due to redox of Ni and Co. And by defining the state of the positive electrode using the ratio of the integral value in the region (1) and the integral value in the region (2), the capacity increase due to setting the initial charge potential high is increased. It was found that the negative electrode material required for only the first charge / discharge can be suppressed to an appropriate amount, and the capacity density per volume of the battery can be increased as a result.
Therefore, according to the present invention, in the CV on the oxidation side of the positive electrode using a lithium transition metal composite oxide having a molar ratio Mn / Me of 0.6 or more as an active material, The ratio of the integral value of the region (hereinafter referred to as “(1) / (2)”) is in the range of 0.37 to 0.51, preferably 0.37 to 0.48, and the ratio of the positive electrode capacity to the negative electrode (Hereinafter referred to as “positive electrode / negative electrode capacity ratio”) is set to 0.86 to 0.95.

When (1) / (2) is less than 0.37, since the effect of increasing the capacity density of the positive electrode by setting the initial charge potential high is not fully utilized, the negative electrode capacity required only for the initial charge / discharge is small. The positive electrode / negative electrode capacity ratio can be close to 1, but the capacity density per volume cannot be increased.
When (1) / (2) is in the range of 0.37 to 0.51, it is possible to make use of the effect of increasing the capacity density of the positive electrode by setting the initial charge potential high, and to cope with the surplus capacity of the positive electrode. The negative electrode capacity required only for the first charge / discharge is moderately reduced, and the positive electrode / negative electrode capacity ratio can be 0.86 to 0.95, which is close to 1, thereby improving the capacity density per volume of the battery.
When (1) / (2) exceeds 0.51, the positive electrode capacity density is increased by setting the initial charge potential high, but the negative electrode capacity required only for the initial charge / discharge increases, so the negative electrode capacity is reduced. The volume of the negative electrode material to be supplied is increased, and the capacity per volume of the battery is reduced.
In addition, the charge / discharge cycle performance tends to be inferior due to factors such as precipitation of Mn on the negative electrode due to the high initial charge potential.

  In particular, when (1) / (2) is within the range of 0.37 to 0.48, the charge / discharge cycle performance is improved, which is preferable. This is presumed to be because, when (1) / (2) is within the range of 0.37 to 0.48, side reactions can be suppressed as compared with a range exceeding 0.48. In the region (1), since a hysteresis is observed by CV measurement, it is assumed that a side reaction has occurred.

(Positive electrode active material)
The composition of the lithium transition metal composite oxide in the nonaqueous electrolyte secondary battery according to the present invention is such that the transition metal (Me) contains Co, Ni and Mn, and the molar ratio Mn / Me is from the point of obtaining a high discharge capacity. It is 0.6 or more. The molar ratio Mn / Me is preferably 0.6 to 0.75.

  In order to improve the initial efficiency and the high rate discharge performance of the non-aqueous electrolyte secondary battery, the lithium transition metal composite oxide has a molar ratio Co / Me of the transition metal element Me of 0.05 to 0.40. It is preferable to set it to 0.10 to 0.30.

Although the lithium transition metal composite oxide has a high Mn / Me, the molar ratio Li / Me of the lithium (Li) to the transition metal Me is more than 1 in order to maintain the α-NaFeO ₂ structure even when charged. Larger is preferred. This feature can be expressed as Li _{1 + α} Me _1-α O ₂ ((1 + α) / (1-α)> 1).
Among them, in order to obtain a nonaqueous electrolyte secondary battery with excellent initial efficiency and high rate discharge performance, the molar ratio Li / Me of the transition metal element Me should be larger than 1.2 and smaller than 1.6. That is, it is preferable that 1.2 <(1 + α) / (1-α) <1.6 in the composition formula Li _{1 + α} Me _1-α O ₂ . From the viewpoint that a non-aqueous electrolyte secondary battery having a particularly large discharge capacity and excellent high rate discharge performance can be obtained, it is preferable to select one having the Li / Me of 1.25 to 1.5.

In the present invention, the lithium transition metal composite oxide is typically Li _{1 + α} (Co _a Ni _b Mn _c ) _1-α O ₂ , where α> 0, a + b + c = 1, a> 0, b> 0. C ≧ 0.6, and is a composite oxide composed of Li, Co, Ni, and Mn. In order to improve the discharge capacity, it is preferable to contain 1000 ppm or more of Na. As for content of Na, 2000-10000 ppm is more preferable.

  In order to contain Na, in the step of preparing a hydroxide precursor or a carbonate precursor, a sodium compound such as sodium hydroxide or sodium carbonate is used as a neutralizing agent, and Na is left in the washing step. And the method of adding sodium compounds, such as sodium carbonate, in a subsequent baking process is employable.

  In addition, the lithium transition metal composite oxide is a transition metal typified by an alkali metal other than Na, an alkaline earth metal such as Mg and Ca, and a 3d transition metal such as Fe and Zn, as long as the effects of the present invention are not impaired. A small amount of other metals can be contained.

The lithium transition metal composite oxide is produced from a carbonate precursor or a hydroxide precursor.
In the lithium fiber metal composite oxide particles produced from the carbonate precursor, D50, which is a particle diameter at which the cumulative volume in the particle size distribution of the secondary particles is 50%, is preferably 5 μm or more, and is 5 to 18 μm. More preferably. Moreover, it is preferable that D50 is 8 micrometers or less, and, as for the lithium transition metal complex oxide particle produced from a hydroxide precursor, it is more preferable that it is 8-1 micrometer.

In the present invention, in order to obtain a positive electrode active material for a nonaqueous electrolyte secondary battery having excellent initial efficiency and charge / discharge cycle performance, a lithium transition metal composite oxide produced from a carbonate precursor is subjected to a nitrogen gas adsorption method. The peak differential pore volume is 0.75 mm ³ / (g · nm) or more in the pore diameter range of 30 to 40 nm where the differential pore volume obtained by the BJH method is the maximum value from the adsorption isotherm used. Is preferable (see Patent Document 2).

  In addition, the tap density of the positive electrode active material according to the present invention is preferably 1.25 g / cc or more in order to obtain a nonaqueous electrolyte secondary battery excellent in charge / discharge cycle performance and high rate discharge performance, and is 1.7 g / cc. More than cc is more preferable.

(Method for producing positive electrode active material)
Next, a method for producing a lithium transition metal composite oxide will be described.
The lithium transition metal complex oxide is basically prepared by preparing a raw material containing a metal element (Li, Mn, Co, Ni) constituting the lithium transition metal complex oxide in accordance with the intended composition, and firing it. Can be obtained. However, with respect to the amount of the Li raw material, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li raw material during firing.
In producing an oxide having a desired composition, a so-called “solid phase method” in which salts of Li, Co, Ni, and Mn are mixed and fired, or Co, Ni, and Mn were previously present in one particle. A “coprecipitation method” is known in which a coprecipitation precursor is prepared, and a Li salt is mixed and fired therein. In the synthesis process by the “solid phase method”, especially Mn is difficult to uniformly dissolve in Co and Ni, so it is difficult to obtain a sample in which each element is uniformly distributed in one particle. In literatures and the like, many attempts have been made to dissolve Mn in a part of Ni or Co (LiNi _1-x Mn _x O ₂ etc.) by solid phase method, but the “coprecipitation method” is selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, lithium transition metal composite oxides used in Examples described later were prepared by employing the “coprecipitation method”.

When preparing a coprecipitation precursor, Mn is easily oxidized among Co, Ni and Mn, and it is not easy to prepare a coprecipitation precursor in which Co, Ni and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level of Co, Ni and Mn tends to be insufficient. In particular, in the composition range of the present invention, since the Mn ratio is higher than the Co and Ni ratios, it is particularly important to remove dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used. Among these, when producing a coprecipitated carbonate precursor, it is preferable to employ carbon dioxide as a gas not containing oxygen because an environment in which carbonate is more easily generated is provided.

  Although the pH in the step of producing a precursor by co-precipitation of a compound containing Co, Ni and Mn in a solution is not limited, an attempt is made to produce the co-precipitation precursor as a co-precipitation hydroxide precursor. When it does, it can be set to 10-14, and when it is going to produce the said coprecipitation precursor as a coprecipitation carbonate precursor, it can be set to 7.5-11. In order to increase the tap density, it is preferable to control the pH. About a coprecipitation carbonate precursor, tap density can be made into 1.25 g / cc or more by making pH into 9.4 or less, and a high rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by adjusting the pH to 8.0 or less, the stirring continuation time after the raw material aqueous solution dropping is completed can be shortened.

  The coprecipitation precursor is preferably a compound in which Mn, Ni, and Co are uniformly mixed. In addition, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent. At that time, a higher density active material can be obtained by mixing and firing with a Li source, so that the energy density per electrode area can be improved.

  The raw material of the coprecipitation precursor is manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc. 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 given as examples.

  In the present invention, a reaction crystallization method is employed in which a raw material aqueous solution of the coprecipitation precursor is continuously supplied dropwise to a reaction tank that maintains alkalinity to obtain a coprecipitation precursor. Here, lithium compounds, sodium compounds, potassium compounds and the like can be used as the neutralizing agent, but when the coprecipitation precursor is prepared as a coprecipitation hydroxide precursor, sodium hydroxide, hydroxide It is preferable to use a mixture of sodium and lithium hydroxide, or sodium hydroxide and potassium hydroxide, and when preparing the coprecipitation precursor as a coprecipitation carbonate precursor, sodium carbonate, sodium carbonate It is preferable to use lithium carbonate or a mixture of sodium carbonate and potassium carbonate. Na / Li, which is a molar ratio of sodium carbonate (sodium hydroxide) and lithium carbonate (lithium hydroxide), or sodium carbonate (sodium hydroxide) and potassium carbonate (potassium hydroxide) in order to leave Na 1000 ppm or more It is preferable that Na / K which is the molar ratio is 1/1 [M] or more. By setting Na / Li or Na / K to 1/1 [M] or more, it is possible to reduce the possibility that Na will be excessively removed in the subsequent washing step and become less than 1000 ppm.

  The dropping speed of the raw material aqueous solution greatly affects the uniformity of element distribution in one particle of the coprecipitation precursor to be generated. In particular, Mn is difficult to form a uniform element distribution with Co and Ni, so care must be taken. The preferred dropping rate is influenced by the reaction vessel size, 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.

  In addition, when a complexing agent is present in the reaction tank and a certain convection condition is applied, the particle rotation and revolution in the stirring tank are promoted by continuing the stirring after the dropwise addition of the raw material aqueous solution. In this process, the particles grow concentrically in stages while colliding with each other. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. 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 dropping of the raw material aqueous solution.

  The preferable stirring duration after completion of dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 h or more is required to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Moreover, in order to reduce the possibility that the output performance in the low SOC region of the battery is not sufficient due to the particle size becoming too large, it is preferably 30 h or less, more preferably 25 h or less, and most preferably 20 h or less.

  Moreover, the preferable stirring continuation time for making 50% particle diameter (D50) of lithium transition metal complex oxide produced from a coprecipitation hydroxide precursor into 1-8 micrometers, the lithium transition metal produced from a coprecipitation carbonate precursor A preferable stirring duration time for setting the 50% particle diameter (D50) of the composite oxide to 5 to 18 μm varies depending on the pH to be controlled. For example, for the coprecipitated hydroxide precursor, when the pH is controlled to 10 to 12, the stirring duration is preferably 1 to 10 h, and when the pH is controlled to 12 to 14, the stirring duration is 3 ~ 20h is preferred. For the coprecipitated carbonate precursor, when the pH is controlled to 7.5 to 8.2, the stirring duration is preferably 1 to 20 h, and when the pH is controlled to 8.3 to 9.4. The stirring duration is preferably 3 to 24 hours.

  When coprecipitation precursor particles are prepared using sodium compounds such as sodium hydroxide and sodium carbonate as neutralizing agents, sodium ions adhering to the particles are washed away in the subsequent washing step. In the present invention, it is preferable to wash and remove under conditions such that Na remains at 1000 ppm or more. For example, when the produced coprecipitation precursor is taken out by suction filtration, a condition such that the number of washings with 200 ml of ion-exchanged water is 5 times can be employed.

  In the present invention, the lithium transition metal composite oxide can be preferably prepared by mixing the hydroxide precursor or carbonate precursor and the Li compound and then heat-treating them. As a Li compound, it can manufacture suitably by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc. However, with respect to the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

  In order to set the Na content in the lithium transition metal composite oxide to 1000 ppm or more, even if the Na contained in the hydroxide precursor or carbonate precursor is 1000 ppm or less, Na is contained together with the Li compound in the firing step. The amount of Na contained in the active material can be 1000 ppm or more by mixing the compound with the hydroxide precursor or carbonate precursor. As the Na compound, sodium carbonate is preferable.

The firing temperature affects the reversible capacity of the active material.
When the firing temperature is too high, the obtained active material collapses with an oxygen releasing reaction, and in addition to the hexagonal crystal of the main phase, the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type is obtained. The defined phase tends to be observed as a phase separation rather than as a solid solution phase. If too many such phase separations are contained, it is not preferable because it leads to a reduction in the reversible capacity of the active material. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably less than the temperature at which the oxygen release reaction of the active material affects. The oxygen release temperature of the active material is approximately 1000 ° C. or higher in the composition range according to the present invention. However, there is a slight difference in the oxygen release temperature depending on the composition of the active material. It is preferable to keep it. In particular, it is 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. As a method for confirming the oxygen release temperature of the active material, a mixture of a coprecipitation 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 Li component volatilized, and the instrument may be damaged. Therefore, a composition in which crystallization is advanced to some extent by adopting a firing temperature of about 500 ° C. in advance. Goods should be subjected to thermogravimetric analysis.

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 present invention, when coprecipitated hydroxide is used as a precursor, the firing temperature is preferably at least 700 ° C. or higher. When coprecipitated carbonate is used as a precursor, the firing temperature is preferably at least 800 ° C. or higher. In particular, when the precursor is a coprecipitated carbonate, the optimum firing temperature tends to be lower as the amount of Co contained in the precursor is larger. Thus, by sufficiently crystallizing the crystallites constituting the primary particles, the resistance of the crystal grain boundaries can be reduced and smooth lithium ion transport can be promoted.
The present inventors analyzed the half width of the diffraction peak of the active material of the present invention in detail, and in the case where the precursor is a coprecipitated hydroxide, in the sample synthesized at a temperature of less than 650 ° C. Strain remains in the lattice and can be remarkably removed by synthesizing at a temperature of 650 ° C. or higher, and when the precursor is a coprecipitated carbonate, the firing temperature is 750. In the sample synthesized at a temperature of less than 0 ° C., strain remained in the lattice, and it was confirmed that the strain could be remarkably removed by synthesis at a temperature of 750 ° C. or higher. The crystallite size was increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material of the present invention, a favorable discharge capacity can be obtained by aiming at a particle having almost no lattice distortion in the system and having a sufficiently grown crystallite size. Specifically, it is preferable to employ a synthesis temperature (firing temperature) and a Li / Me ratio composition in which the strain amount affecting the lattice constant is 2% or less and the crystallite size is grown to 50 nm or more. all right. Although changes due to expansion and contraction are observed by charging and discharging by molding these as electrodes, it is preferable as an effect that the crystallite size is maintained at 30 nm or more in the charging and discharging process.

As described above, the firing temperature is related to the oxygen release temperature of the active material, but the crystallization phenomenon is caused by the primary particles growing greatly at 900 ° C. or higher without reaching the firing temperature at which oxygen is released from the active material. Is seen. This can be confirmed by observing the fired active material with a scanning electron microscope (SEM). The active material synthesized through a synthesis temperature exceeding 900 ° C. has primary particles grown to 0.5 μm or more, which is disadvantageous for Li ⁺ movement in the active material during the charge / discharge reaction, and has a high rate discharge performance. descend. The size of the primary particles is preferably less than 0.5 μm, and more preferably 0.3 μm or less.

  In view of the above, in the lithium transition metal composite oxide, when the Li / Me molar ratio (1 + α) / (1-α) is 1.2 <(1 + α) / (1-α) <1.6 The firing temperature is preferably 750 to 900 ° C, more preferably 800 to 900 ° C.

Through the above steps, for example, the following lithium transition metal composite oxide is produced.
Li _1.18 Co _0.10 Ni _0.17 Mn _0.55 O ₂
(Li / Me = 1.44, Mn / Me = 0.67)
Li _1.13 Co _0.21 Ni _0.17 Mn _0.49 O ₂
(Li / Me = 1.30, Mn / Me = 0.56)
Li _1.18 Co _0.17 Ni _0.17 Mn _0.49 O ₂
(Li / Me = 1.44, Mn / Me = 0.60)
Li _1.20 Co _0.10 Ni _0.15 Mn _0.55 O ₂
(Li / Me = 1.50, Mn / Me = 0.69)

(Negative electrode material)
The negative electrode material is not limited, and any negative electrode material may be selected as long as it can release or occlude lithium ions. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and 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 oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

(Positive plate / Negative plate)
The positive electrode active material and the negative electrode material are main components of the positive electrode and the negative electrode of the present invention. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, a filler, and the like. However, it may be contained as another component.

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

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by mass to 50% by mass, and particularly preferably 0.5% by mass to 30% by mass with respect to the total mass of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing 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, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by mass, and particularly preferably 2 to 30% by mass with respect to the total mass of the positive electrode or the negative electrode.

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

The positive electrode and the negative electrode are obtained by kneading the main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials to form a positive electrode mixture and a negative electrode mixture, and organic materials such as N-methylpyrrolidone and toluene After mixing with a solvent or water, the resulting mixture is applied on a current collector or pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. The About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.
As the current collector, a current collector foil such as an aluminum foil or a copper foil can be used. As the current collector foil of the positive electrode, an aluminum foil is preferable. The thickness of the current collector foil is preferably 10 to 30 μm. The thickness of the composite material layer is preferably 40 to 150 μm (excluding the current collector foil thickness) after pressing.

(Nonaqueous electrolyte)
The nonaqueous electrolyte used for the nonaqueous electrolyte secondary battery according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Examples of the nonaqueous solvent used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone 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 and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

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, and NaBr. , KClO ₄ , KSCN, and other inorganic ion 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 , (nC 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-phthalate, Examples thereof include organic ionic salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture 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 reduced, The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous 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 reliably obtain a non-aqueous electrolyte battery having high battery characteristics. 0.5 mol / L.

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

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

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

(Configuration of non-aqueous electrolyte secondary battery)
The configuration of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, and a flat battery.
FIG. 2 shows an example of a prismatic battery. An electrode group 2 composed of a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a rectangular battery container 3. A positive electrode terminal 4 is connected via a positive electrode lead 4 ′, and a negative electrode terminal 5 is connected via a negative electrode lead 5 ′. It is led out of the battery container.

(Configuration of power storage device)
The non-aqueous electrolyte secondary battery according to the present invention includes a plurality of non-aqueous electrolyte secondary batteries, particularly when used as a power source for an automobile such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV). It can be mounted as a power storage device (battery module) configured as a group.
FIG. 3 shows an example of a power storage device 30 in which the power storage units 20 in which the nonaqueous electrolyte secondary batteries 1 are assembled are further assembled.

Example 1
<Synthesis of positive electrode active material>
Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00 g) and manganese sulfate pentahydrate (65.27 g) were weighed, and all of these were dissolved in 200 ml of ion-exchanged water, and Co: Ni: Mn A 2.0 M sulfate aqueous solution with a molar ratio of 10:17:55 was prepared. On the other hand, 750 ml of ion exchange water was poured into a ₂ L reaction tank, and CO ₂ gas was bubbled for 30 minutes to dissolve CO _{2 in the} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred at a rate of 3 ml / min while stirring the inside of the reaction vessel at a rotational speed of 700 rpm using a paddle blade equipped with a stirring motor. It was dripped. Here, during the period from the start to the end of the dropwise addition, an aqueous solution containing 2.0 M sodium carbonate and 0.4 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 7.9 (± 0. 05). After completion of the dropping, stirring in the reaction vessel was further continued for 5 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.

  Next, using a suction filtration device, the coprecipitated carbonate particles produced in the reaction vessel are separated, and sodium ions adhering to the particles are washed away using ion-exchanged water, and an electric furnace is used. Then, it was dried at 100 ° C. for 20 hours in an air atmosphere under normal pressure. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

Lithium carbonate was added to 2.278 g of the coprecipitated carbonate precursor so that the molar ratio of Li: (Co, Ni, Mn) was 1.44: 1, and mixed well using a smoked automatic mortar, A mixed powder was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), and heated in an air atmosphere at normal pressure to a temperature of 900 ° C. over 10 hours. And calcined for 10 hours at the temperature after the temperature elevation. The box-type electric furnace has internal dimensions of 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 turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. In this way, lithium transition metal composite oxide A containing 2100 ppm Na and having a D50 of 13 μm: Li _1.18 Co _0.10 Ni _0.17 Mn _0.55 O ₂ (Li / Me = 1.44, Mn / Me = 0.67) was produced.

<Preparation of positive electrode plate>
N-methylpyrrolidone is used as a dispersion medium, and the above lithium transition metal composite oxide A, acetylene black (AB) and polyvinylidene fluoride (PVdF) are contained in a mass ratio of 92.5: 5: 2.5 as a positive electrode active material. A coating paste was prepared. The coating paste was applied to one surface of a 15 μm thick aluminum foil current collector. The application area was 12 cm ² , and the mass of the active material applied per unit area was 15 mg / cm ² . Next, pressing was performed using a roll press so that the porosity of the electrode was 35%, and vacuum drying was performed at 100 ° C. In this way, a positive electrode plate was produced.
The positive electrode mixture obtained had a positive electrode mixture density of 2.434 g / cc and a positive electrode mixture mass of 0.200 g.

<Preparation of positive electrode single electrode test battery>
For the purpose of accurately confirming the unipolar behavior of the positive electrode, a test battery was prepared by bringing metallic lithium into close contact with the nickel current collector at the counter electrode, that is, the negative electrode.
In the test battery, a sufficient amount of metallic lithium was placed on the negative electrode so that the capacity of the nonaqueous electrolyte secondary battery was not limited by the negative electrode.
As the non-aqueous electrolyte, a solution in which LiPF ₆ was dissolved in a mixed solvent having a volume ratio of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) of 3: 7 to a concentration of 1 mol / L was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the exterior body, and the electrodes are exposed so that the open ends of the positive terminal and the negative terminal are exposed to the outside. The metal resin composite film was hermetically sealed with the fusion allowance where the inner surfaces of the metal resin composite films faced each other except for the portion serving as the injection hole, and the injection hole was sealed after the electrolyte solution was injected.

<First charge / discharge>
The initial charge / discharge of the test battery was charged at a constant current of 0.1 CmA up to 4.50 V (vs. Li / Li ⁺ ) at 25 ° C., and then at a constant voltage of 0.02 CmA. It was performed by discharging to 2.0 V with a constant current. 1 CmA was 40 mA (3.33 mA / cm ² ).

<Positive electrode capacity>
Subsequently, when the positive electrode capacity was confirmed under the following charge / discharge conditions, it was 41.9 mAh.
Temperature: 25 ° C
Charge: Constant current (CC) of 0.1 CmA up to 4.45 V (vs. Li / Li ⁺ ), then 0.02 CmA at constant voltage (CV) Discharge: With constant current CC of 0.1 CmA 2.・ To 0V 1CmA = 40mA (200mA / g)

<Charge / discharge cycle test>
When the initial capacity confirmation test and the charge / discharge cycle test were performed on the test battery in which the positive electrode capacity was confirmed under the following conditions, the capacity retention rate after the cycle was 98%.
First, an initial discharge capacity confirmation test is performed, and the discharge capacity at this time is defined as “initial discharge capacity”.
Temperature: 25 ° C
Charge: 4.45 V (vs. Li / Li ⁺ ) at a constant current of 0.1 CmA, and then 0.02 CmA at a constant voltage. Discharge: Up to 2.0 V at a constant current of 1.0 CmA 1 CmA is 40 mA ( 200mA / g)
Further, a charge / discharge cycle test was conducted, and the discharge capacity at the 10th cycle was defined as “discharge capacity after cycle”.
Charge: 1.0CmA constant current to 4.45V (vs. Li / Li ⁺ ) respectively, then constant voltage to 0.05CmA Discharge: 1.0CmA constant current to 2.0V The capacity maintenance rate is calculated by the discharge capacity ratio after the cycle with respect to the initial discharge capacity.

<Cyclic voltammogram (CV)>
CV measurement was performed by performing potential scanning under the following conditions using the following measuring apparatus. In the CV measurement, the test battery after the cycle test was used without being disassembled. That is, the working electrode (WE) cable of the measuring device was connected to the positive terminal of the battery, and the negative terminal of the counter electrode (CE) cable and the reference electrode (RE) cable battery.
Device name: Solartron, Multistat 1470E type
Scanning potential range: 2.0-4.45 V (vs. Li / Li ⁺ )
Scanning speed: 0.05mV / sec
Cycle: 3 cycles Test temperature: 25 ° C
Electrode plate area (working electrode): 12 cm ²
Electrode plate area (counter electrode): 12.6 cm ²

With respect to the scanning curve on the oxidation side in the third cycle obtained by the CV measurement, an integral value in the region (1) is obtained for a potential range from 2.0 V to 3.6 V (vs. Li ^/ Li ⁺ ), For the potential range from 3.6 V to 4.45 V (vs. Li / Li ⁺ ), the integral value in the region (2) is obtained. The scanning curve on the reduction side is not considered in the calculation of the integral value.
Since the integral value in the region (1) was 12.7 mJ / g and the integral value in the region (2) was 26.3 mJ / g, (1) / (2) in the oxidation side CV was 0.48. Met.

<Preparation of negative electrode plate>
A planetary mixer was used to produce a negative electrode paste containing water as a dispersion medium and containing a graphitic carbon material, styrene butadiene rubber and carboxymethyl cellulose in a mass ratio of 97: 2: 1. This negative electrode paste was applied to one side of a Cu foil, dried and pressed to produce a negative electrode plate. The coating amount of the negative electrode paste was adjusted so that the mass of the negative electrode mixture became a predetermined mass ratio shown in Table 1 in relation to the positive electrode. In Example 1, the mixture density of the obtained negative electrode plate was 1.517 g / cc, and the mass of the negative electrode mixture was 0.133 g.

<Negative electrode capacity>
The same procedure as for the positive electrode single electrode test battery described above was used, except that the negative electrode plate was used instead of the positive electrode plate of the test battery, and the test battery was prepared by bringing metallic lithium into close contact with the nickel current collector as the counter electrode. When a test battery was prepared and the negative electrode capacity was confirmed under the following charge / discharge conditions, it was 45.4 mAh.
Temperature: 25 ° C
Charging: 0.02 V (vs. Li / Li ⁺ ) at a constant current of 0.1 CmA, and then 0.02 CmA at a constant voltage. Discharging: up to 2.0 V at a constant current of 0.1 CmA 1 CmA = 40 mA (200 mA / g)

<Battery capacity>
When a non-aqueous electrolyte secondary battery actually provided with a positive electrode and a negative electrode is produced, the newly produced positive electrode plate is combined with the newly produced negative electrode plate (positive electrode / negative electrode mass ratio: 1.50, positive electrode / negative electrode). Capacity ratio: 0.92), otherwise, a battery was prepared in the same procedure as the positive electrode single electrode test battery, and the initial charge / discharge was performed at 25 ° C. with a constant current of 0.1 CmA up to a voltage of 4.40 V. Thereafter, the battery is charged at a constant voltage until 0.02 CmA, and discharged to a voltage of 2.0 V with a constant current of 0.1 CmA. Subsequently, the battery capacity at 1 CmA measured under the following conditions is 38.2 mAh. Note that the voltage of 4.40 V assumes a potential of 4.50 V (vs. Li / Li ⁺ ).
Charge: constant current and constant voltage charge with current of 1 CmA and voltage of 4.35 V, charge termination when current value decays to 1/6 discharge: constant current discharge with current of 1 CmA and end voltage of 2.0 V

<Capacity density per volume>
The capacity density per volume of the non-aqueous electrolyte secondary battery obtained by the following formula is 225 mAh / cc.
Capacity density per volume = battery capacity / (positive electrode volume + negative electrode volume)
Volume of positive electrode = mass of positive electrode mixture / density of positive electrode mixture Volume of negative electrode = mass of negative electrode mixture / density of negative electrode mixture

(Example 2)
Using the lithium transition metal composite oxide A as a positive electrode active material, a positive electrode plate having a composite material mass of 0.188 g and a capacity of 42.6 mAh, and a negative electrode plate having a composite material mass of 0.141 g and a capacity of 48.0 mAh A battery was prepared in the same manner as in Example 1 except that the positive electrode / negative electrode mass ratio was 1.33 and the positive electrode / negative electrode capacity ratio was 0.89, and the charge voltage of the first charge / discharge was 4.45V (4. The same test as in Example 1 is performed except that the potential is 55 V (assuming a potential of vs. Li ^/ Li ⁺ ). The capacity density per volume of this nonaqueous electrolyte secondary battery is 226 mAh / cc.
In the following examples, the capacity of the positive electrode plate and the capacity of the negative electrode plate were determined by conducting a positive electrode single electrode test and a negative electrode single electrode test using the positive electrode and negative electrode newly produced in the same manner as in Example 1. The charge potential at the first charge / discharge in the positive electrode single electrode test was the same as the charge potential at the first charge / discharge adopted in each example.
As a result of the positive electrode single electrode test used in Example 2, the capacity retention after the cycle was 94%, and (1) / (2) in CV was 0.51.

(Example 3)
A positive electrode plate having a composite material mass of 0.203 g and a capacity of 42.5 mAh / g, a negative electrode plate having a composite material mass of 0.132 g and a capacity of 44.8 mAh / g, and a positive electrode / negative electrode capacity ratio of 0.95 A battery similar to that of Example 1 was manufactured except that the combinations were made so that the charge voltage of the first charge / discharge was 4.40 V (assuming a potential of 4.50 V (vs. Li / Li ⁺ )). Except for, the same test as in Example 1 is performed. The capacity density per volume of this nonaqueous electrolyte secondary battery is 227 mAh / cc.
As a result of the positive electrode single electrode test, (1) / (2) in CV was 0.48.

(Comparative Example 1)
A positive electrode plate having a composite material mass of 0.250 g and a capacity of 34.2 mAh, and a negative electrode plate having a composite material mass of 0.103 g and a capacity of 34.9 mAh / g, the positive electrode / negative electrode capacity ratio is 0.98. A battery similar to that of Example 1 was prepared except that the combinations were made as described above, except that the charge voltage of the first charge / discharge was 4.35 V (assuming a potential of 4.45 V (vs. Li ^/ Li ⁺ )). Then, the same test as in Example 1 is performed. The capacity density per volume of this nonaqueous electrolyte secondary battery is 177 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 107%, and (1) / (2) in CV was 0.24.

(Comparative Example 2)
A positive electrode plate having a composite material mass of 0.183 g and a capacity of 38.2 mAh and a negative electrode plate having a composite material mass of 0.144 g and a capacity of 49.1 mAh were combined, and the positive electrode / negative electrode mass ratio was 1.27. A battery similar to that of Example 1 was prepared except that the negative electrode capacity ratio was set to 0.78, and the initial charge / discharge charge voltage was 4.40 V (assuming a potential of 4.50 V (vs. Li / Li ⁺ )). Except for the above, the same test as in Example 1 is performed. The capacity density per volume of this nonaqueous electrolyte secondary battery is 203 mAh / cc.
As a result of the positive electrode single electrode test, (1) / (2) in CV was 0.48.

(Comparative Example 3)
A battery similar to that of Example 1 except that the positive electrode plate and the negative electrode plate having the same mixture weight as Comparative Example 2 were combined so that the positive electrode capacity was 41.4 mAh and the positive electrode / negative electrode capacity ratio was 0.84. The same test as in Example 1 is performed except that the charge voltage of the first charge / discharge is 4.45 V (assuming a potential of 4.55 V (vs. Li ^/ Li ⁺ )). The capacity density per volume of this nonaqueous electrolyte secondary battery is 220 mAh / cc.
As a result of the positive electrode single electrode test, (1) / (2) in CV was 0.51.

(Comparative Example 4)
A battery similar to that of Example 1 except that the positive electrode plate and the negative electrode plate having the same mixture weight as Comparative Example 2 were combined so that the positive electrode capacity was 49.1 mAh and the positive electrode / negative electrode capacity ratio was 0.86. The same test as in Example 1 is performed except that the charge voltage of the first charge / discharge is 4.50 V (assuming a potential of 4.60 V (vs. Li ^/ Li ⁺ )). The capacity density per volume of this nonaqueous electrolyte secondary battery is 223 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 94%, and (1) / (2) in CV was 0.52 .

(Example 4)
A coprecipitated carbonate precursor was prepared from cobalt sulfate heptahydrate, nickel sulfate hexahydrate and manganese sulfate pentahydrate from a sulfate aqueous solution having a Co: Ni: Mn molar ratio of 17:17:49. To this, lithium carbonate was added so that the molar ratio of Li: (Co, Ni, Mn) was 1.44: 1, and lithium transition metal composite oxide B: Li ₁ was added in the same manner as in Example _{1. 18} Co _0.17 Ni _0.17 Mn _0.49 O ₂ (Mn / Me = 0.60) was produced.
A positive electrode plate having a composite material mass of 0.202 g and a capacity of 40.5 mAh was prepared, and this positive electrode plate was combined with a negative electrode plate having a composite material mass of 0.132 g and a capacity of 45.1 mAh to obtain a positive electrode / negative electrode mass ratio. The battery was prepared in the same manner as in Example 1 except that the positive electrode / negative electrode capacity ratio was 0.90, and the charge voltage of the initial charge / discharge was 4.40 V (4.50 V (vs. Li / Li The same test as in Example 1 is performed except that the potential of ⁺ ) is assumed). The capacity density per volume of this nonaqueous electrolyte secondary battery is 213 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 100%, and (1) / (2) in CV was 0.37.

(Example 5)
Using the lithium transition metal composite oxide B as a positive electrode active material, a positive electrode plate having a composite material mass of 0.191 g and a capacity of 40.9 mAh, and a negative electrode plate having a composite material mass of 0.139 g and a capacity of 47.4 mAh A battery was prepared in the same manner as in Example 1 except that the positive electrode / negative electrode mass ratio was 1.37 and the positive electrode / negative electrode capacity ratio was 0.86, and the charge voltage of the first charge / discharge was 4.45V (4. The same test as in Example 1 is performed except that the potential is 55 V (assuming a potential of vs. Li ^/ Li ⁺ ). The capacity density per volume of this nonaqueous electrolyte secondary battery is 212 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 98%, and (1) / (2) in CV was 0.41.

(Comparative Example 5)
Using the lithium transition metal composite oxide B as a positive electrode active material, a positive electrode plate having a composite material mass of 0.236 g and a capacity of 38.0 mAh, and a negative electrode plate having a composite material mass of 0.111 g and a capacity of 37.9 mAh Except that the positive electrode / negative electrode mass ratio was 2.12 and the positive electrode / negative electrode capacity ratio was 1.00. The same test as in Example 1 is performed except that 4.45 V (vs. Li / Li ⁺ ) is assumed. The capacity density per volume of this nonaqueous electrolyte secondary battery is 192 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 105%, and (1) / (2) in CV was 0.23.

(Comparative Example 6)
Using the lithium transition metal composite oxide B as a positive electrode active material, a positive electrode plate having a composite material mass of 0.185 g and a capacity of 40.8 mAh, and a negative electrode plate having a composite material mass of 0.143 g and a capacity of 48.6 mAh Except that the positive electrode / negative electrode mass ratio was 1.30 and the positive electrode / negative electrode capacity ratio was 0.84, and a charge voltage for initial charge / discharge was 4.50 V ( The same test as in Example 1 is performed except that 4.60 V (assuming a potential of vs. Li / Li ⁺ ) is used.
The capacity density per volume of this nonaqueous electrolyte secondary battery is 211 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 98%, and (1) / (2) in CV was 0.42.

(Comparative Example 7)
A coprecipitated carbonate precursor was prepared from cobalt sulfate heptahydrate, nickel sulfate hexahydrate and manganese sulfate pentahydrate from a sulfate aqueous solution having a Co: Ni: Mn molar ratio of 21:17:49. To this, lithium carbonate was added so that the molar ratio of Li: (Co, Ni, Mn) was 1.30: 1, and lithium transition metal composite oxide C: Li _{1 was obtained in} the same manner as in Example _{1. 13} Co _0.21 Ni _0.17 Mn _0.49 O ₂ (Mn / Me = 0.56) was produced.
A positive electrode plate having a composite material mass of 0.243 g and a capacity of 35.5 mAh was prepared, and this positive electrode plate was combined with the negative electrode plate having a composite material mass of 0.107 g and a capacity of 36.4 mAh to obtain a positive electrode / negative electrode A battery having a mass ratio of 2.27 and a positive / negative electrode capacity ratio of 0.98 was prepared, and the charge voltage of the initial charge / discharge was 4.35 V (assuming a potential of 4.45 V (vs. Li ^/ Li ⁺ )). Except for the above, the same test as in Example 1 is performed. The capacity density per volume of this nonaqueous electrolyte secondary battery is 174 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention ratio after cycling was 100%, and (1) / (2) in CV was 0.17.

(Comparative Example 8)
Using the lithium transition metal composite oxide C as a positive electrode active material, a positive electrode plate with a composite material mass of 0.211 g and a capacity of 38.6 mAh, a negative electrode plate with a composite material mass of 0.127 g and a capacity of 43.2 mAh, Except that the positive electrode / negative electrode mass ratio was 1.66 and the positive electrode / negative electrode capacity ratio was 0.89, and the same charge as that of Example 1 was prepared. The same test as in Example 1 is performed except that the potential is 4.50 V (assuming a potential of vs. Li / Li ⁺ ).
The capacity density per volume of this nonaqueous electrolyte secondary battery is 190 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 99%, and (1) / (2) in CV was 0.28.

(Comparative Example 9)
Using the lithium transition metal composite oxide C as a positive electrode active material, a positive electrode plate having a composite material mass of 0.203 g and a capacity of 39.3 mAh, a negative electrode plate having a composite material mass of 0.131 g and a capacity of 44.8 mAh, Except that the positive electrode / negative electrode mass ratio was 1.55 and the positive electrode / negative electrode capacity ratio was 0.88. A battery similar to that of Example 1 was prepared, and the charge voltage for the initial charge / discharge was 4.425V ( A test similar to that of Example 1 is performed except that the potential is 4.525 V (assuming a potential of vs. Li / Li ⁺ ). The capacity density per volume of this nonaqueous electrolyte secondary battery is 193 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 98%, and (1) / (2) in CV was 0.31.

(Comparative Example 10)
Using the lithium transition metal composite oxide C as a positive electrode active material, a positive electrode plate having a composite material mass of 0.199 g and a capacity of 39.0 mAh, and a negative electrode having a composite material mass of 0.134 g and a capacity of 45.7 mAh A battery was prepared in the same manner as in Example 1 except that the positive electrode / negative electrode mass ratio was 1.48 and the positive electrode / negative electrode capacity ratio was 0.85, and the charge voltage for the first charge / discharge was 4.45V. A test similar to that of Example 1 is performed except that the potential is 4.55 V (assuming a potential of 4.55 V (vs. Li ^/ Li ⁺ )). The capacity density per volume of this nonaqueous electrolyte secondary battery is 192 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 97%, and (1) / (2) in CV was 0.33.

(Comparative Example 11)
Using the lithium transition metal composite oxide C as a positive electrode active material, a positive electrode plate having a composite material mass of 0.193 g and a capacity of 39.0 mAh, and a negative electrode having a composite material mass of 0.138 g and a capacity of 47.0 mAh A battery was prepared in the same manner as in Example 1 except that the positive electrode / negative electrode mass ratio was 1.40 and the positive electrode / negative electrode capacity ratio was 0.83, and the charge voltage for the first charge / discharge was 4.50 V. A test similar to that of Example 1 is performed except that the potential is 4.60 V (assuming a potential of vs. Li / Li ⁺ ). The capacity density per volume of this nonaqueous electrolyte secondary battery is 190 mAh / cc.
As a result of the positive electrode single electrode test, the capacity retention rate after cycling was 96%, and (1) / (2) in CV was 0.36.

  Table 1 summarizes the above results. For the batteries of Examples 1 to 5 and Comparative Examples 1 to 11, the capacity density per volume and the positive electrode capacity retention rate after 10 cycles are shown in Table 1 below.

  In Examples 1 to 5, a lithium transition metal composite oxide having Mn / Me of 0.60 or more is used as a positive electrode active material, and initial charge potentials are appropriately increased to 4.50 V and 4.55 V, respectively (1) / (2) is in the range of 0.37 to 0.51, and the capacity density of the positive electrode is greatly increased. At the same time, by setting the positive electrode / negative electrode capacity ratio in the range of 0.86 to 0.95, the negative electrode capacity required only for the first charge / discharge is appropriate, so that the capacity density per volume of the battery can be increased. did it.

  In Comparative Examples 1 and 5, the lithium transition metal composite oxide having Mn / Me of 0.6 or more is used as the positive electrode active material, but the initial charge potential is 4.45 V, and (1) / (2) is The effect of increasing the positive electrode capacity density is small. Therefore, the negative electrode capacity required only for the first charge / discharge is small and the positive electrode / negative electrode capacity ratio can be close to 1, but the capacity density per volume of the battery is small.

  In Comparative Examples 2 and 3, the lithium transition metal composite oxide having Mn / Me of 0.6 or more was used as the positive electrode active material, and the initial charge potential was moderately high at 4.50 V and 4.55 V. (1) / ( Since 2) is large, the effect of increasing the positive electrode capacity density is large. However, since the negative electrode material is included in an amount exceeding the negative electrode capacity necessary only for the first charge / discharge (the positive electrode / negative electrode capacity ratio is small), the negative electrode volume is large. Therefore, the capacity density per volume of the battery was small.

  In Comparative Examples 4 and 6, the lithium transition metal composite oxide having Mn / Me of 0.6 or more was used as the positive electrode active material, the initial charge potential was 4.60 V, and (1) / (2) was large. The effect of increasing the positive electrode capacity density by setting the initial charge potential high is great. However, it is necessary to increase the negative electrode capacity required only for the first charge / discharge in response to this increase. Therefore, the volume of the negative electrode material that supplies this capacity is increased, and the capacity density per volume of the battery is small.

  Since the batteries of Comparative Examples 7 to 11 use the lithium transition metal composite oxide C having a Mn / Me of less than 0.60 as the positive electrode active material, even if the initial charge potential is set high, (1) / ( 2) is small, and the increase in positive electrode capacity density is relatively small. Therefore, even if the positive electrode / negative electrode capacity ratio is close to 1, the capacity density per volume of the battery is low.

  In addition, among the examples, the initial charge potential was low, and the capacity retention rate after cycling was high when (1) / (2) was in the range of 0.37 to 0.48.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery with a high volume capacity density in which the excess capacity of the positive electrode generated by the initial charge is optimized and the positive electrode capacity and the negative electrode capacity are balanced. Of course, it can be used for hybrid vehicles and electric vehicles.

Claims (2)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode has a positive electrode active material containing a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure,
The lithium transition metal composite oxide has a molar ratio Li / Me of lithium (Li) to transition metal (Me) larger than 1 , and includes Mn and Ni and / or Co as the transition metal (Me), molar ratio Mn / Me of Mn to the transition metal (Me) is Mn / Me ≧ 0.60,
The cyclic voltammogram (CV), the scanning potential range: 2.0-4.45V (vs.Li/Li ^+), scanning speed: When performed in 0.05 mV / sec, the oxidation side in the CV of the positive electrode, Has two peaks,
The ratio of the integral value of the region having a potential lower than 3.6 V (vs. Li ^/ Li ⁺ ) to the integral value of the region having a potential higher than 3.6 V (vs. Li ^/ Li ⁺ ) in the CV on the oxidation side of the positive electrode is In the range of 0.37 to 0.51,
The nonaqueous electrolyte secondary battery, wherein a ratio of a capacity of the positive electrode to a capacity of the negative electrode is in a range of 0.86 to 0.95.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio of the integral value in CV on the oxidation side of the positive electrode is 0.37 to 0.48.