JP2016177867A - Solid solution lithium-containing transition metal oxide, and nonaqueous electrolyte secondary battery arranged by using solid solution lithium-containing transition metal oxide for positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid solution lithium-containing transition metal oxide which is used for a positive electrode of a lithium ion secondary battery, and which enables the achievement of a high initial discharge capacity, a high capacity-keeping rate, and a higher average voltage.SOLUTION: A solid solution lithium-containing transition metal oxide is expressed by the following composition formula: Li[NiCoMn[Li]]O(where Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese and O represents oxygen, and "a", "b", "c" and "d" satisfy the relation given by: 0.1≤d<0.4; a+b+c+d=1.5; 1.1<a+b+c≤1.4; and -2/3d+0.4<a<-2.5d+1.15). The solid solution lithium-containing transition metal oxide comprises: a layered structure part; and a part which is changed to a Spinel structure by charge or discharge in a predetermined electric potential range.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a solid solution lithium-containing transition metal oxide and a non-aqueous electrolyte secondary battery using the solid solution lithium-containing transition metal oxide as a positive electrode. More specifically, the non-aqueous electrolyte secondary battery of the present invention is used as a driving power source or an auxiliary power source for motors of vehicles such as electric vehicles, fuel cell vehicles, and hybrid electric vehicles. Further, the solid solution lithium-containing transition metal oxide of the present invention is usually used as a positive electrode active material of a lithium ion secondary battery.

  In recent years, in order to cope with air pollution and global warming, reduction of carbon dioxide emissions has been strongly desired. In the automobile industry, there is an expectation for the reduction of carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Electricity such as secondary batteries for motor drive is the key to the practical application of these. Device development is actively underway.

  As a secondary battery for driving a motor, a lithium ion secondary battery having a high theoretical energy is attracting attention, and is currently being developed rapidly. Lithium ion secondary batteries generally have a positive electrode formed by applying a positive electrode slurry containing a positive electrode active material to the surface of a current collector, and a negative electrode slurry containing a negative electrode active material applied to the surface of the negative electrode current collector. The negative electrode formed in this manner and the electrolyte positioned between them are housed in a battery case.

  In order to improve the capacity characteristics and output characteristics of the lithium ion secondary battery, selection of each active material is extremely important.

Conventionally, the formula (a) Li _y [M ¹ _(1-b) Mn _b ] O ₂ or (b) Li _x [M ¹ _(1-b) Mn _b ] O _{1.5 + c} (where 0 ≦ y < 1, 0 <b <1, and 0 <c <0.5, and M ¹ represents one or more metal elements, provided that in (a), M ¹ is a metal element other than chromium. A cathode composition for a lithium ion battery comprising 100 full charge / discharge cycles at 30 ° C. and a final capacity of 130 mAh / g using a discharge current of 30 mA / g when incorporated into a lithium ion battery. There has been proposed a cathode composition for a lithium ion battery that is in the form of a single phase having an O3 crystal structure that does not cause a phase transition to a spinel crystal structure when cycled (see Patent Document 1).

Japanese Patent Laid-Open No. 2004-538610

  However, in the study of the present inventors, even a lithium ion battery using the cathode composition for a lithium ion battery described in Patent Document 1 can achieve a high discharge capacity and a capacity retention rate. There was a problem that not. It has also been found that there is still room for improvement in the average voltage when the battery is constructed.

  The present invention has been made in view of such problems of the prior art. The object is to provide a solid solution lithium-containing transition metal oxide capable of realizing a high initial discharge capacity and capacity retention ratio and a higher average voltage, and a non-solution using the solid solution lithium-containing transition metal oxide as a positive electrode. The object is to provide a water electrolyte secondary battery.

The inventors of the present invention have made extensive studies in order to achieve the above object. As a result, it is a solid solution lithium-containing transition metal oxide represented by a specific composition formula, and a layered structure part and a part that changes to a spinel structure by charging or charging / discharging in a predetermined potential range (layered structure Li ₂ MnO ₃ ), the layered Li ₂ MnO _{3 in the} solid solution lithium-containing transition metal oxide is changed to a spinel-structured LiMn ₂ O ₄ , and the layered state in the solid solution lithium-containing transition metal oxide The average value k ′ of the spinel structure change ratio k of the solid solution lithium-containing transition metal oxide with respect to the spinel structure change ratio when all of the structure Li ₂ MnO ₃ is changed to the spinel structure LiMn ₂ O ₄ is controlled within a predetermined range. As a result, the inventors have found that the above object can be achieved and have completed the present invention.

  That is, the solid solution lithium-containing transition metal oxide according to one embodiment of the present invention has the following composition formula (1):

In the composition formula (1), Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, O represents oxygen, and a, b, c, and d have the following relationships:
0.1 ≦ d <0.4
a + b + c + d = 1.5
1.1 <a + b + c ≦ 1.4
-2 / 3d + 0.4 <a <-2.5d + 1.15
Satisfy,
It is represented by

  And the solid solution lithium containing transition metal oxide which concerns on one form of this invention has a layered structure site | part and the site | part which changes to a spinel structure by performing charge or charge / discharge in a predetermined electric potential range.

Furthermore, in the solid solution lithium-containing transition metal oxide according to an embodiment of the present invention, the solid solution lithium-containing transition metal with respect to the spinel structure change ratio when all of the layered structure Li ₂ MnO ₃ is changed to the spinel structure LiMn ₂ O ₄ When the rate of change of the spinel structure of the oxide is k, charging and discharging are performed in this order up to the respective maximum values of k (4.5 V, 4.6 V, 4.7 V, and 4.8 V (vs lithium metal)). When k ′ is 0.1 ≦ d ≦ 0.25, the following relationship is calculated:
4 / 3d + 1/15 ≦ k ′ ≦ 1
When 0.25 <d <0.4, the following relationship is satisfied:
0.4 ≦ k ′ ≦ 1.0
It is characterized by satisfying

  Moreover, the nonaqueous electrolyte secondary battery which concerns on the other form of this invention uses the solid solution lithium containing transition metal oxide which concerns on the said form for a positive electrode.

  According to the present invention, instead of the conventional cathode composition for a lithium ion battery, by using the solid solution lithium-containing transition metal oxide having the above-described configuration, it is possible to realize a high discharge capacity and a capacity retention ratio due to a high reversible capacity, and A solid solution cathode material capable of realizing a higher average voltage can be provided. Furthermore, it is possible to provide a high-performance nonaqueous electrolyte secondary battery using the solid solution lithium-containing transition metal oxide having the above-described configuration as a positive electrode. This is because by controlling the average value k ′ of the spinel structure change ratio k of the solid solution lithium-containing transition metal oxide to the predetermined value, the influence of the yarn teller strain of trivalent Ni is suppressed, and the stability of the crystal structure This is considered to be because the electron conductivity is improved by the divalent and trivalent Ni mixed valences while maintaining the above.

It is a graph explaining the definition of the spinel structure change ratio k. It is a graph explaining the actual capacity | capacitance of the plateau area | region used for the definition of the spinel structure change rate k. It is sectional drawing which shows the outline of an example of the lithium ion secondary battery which concerns on one Embodiment of this invention. Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.10) and different Ni compositions (value of a) It is the graph which plotted the average voltage on the vertical axis | shaft with respect to k (horizontal axis). For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) was obtained for each of the example groups having the same d value (d = 0.15) and different Ni compositions (value of a). It is a graph in which the average voltage is plotted with respect to the vertical axis. For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) is shown for each of the example groups having the same d value (d = 0.20) and different Ni compositions (value of a). It is a graph in which the average voltage is plotted with respect to the vertical axis. Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.25) and different Ni compositions (value of a) It is the graph which plotted the average voltage on the vertical axis | shaft with respect to k (horizontal axis). For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) was obtained for each of the example groups having the same d value (d = 0.30) and different Ni compositions (value of a). It is a graph in which the average voltage is plotted with respect to the vertical axis. Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.35) and different Ni compositions (value of a) It is the graph which plotted the average voltage on the vertical axis | shaft with respect to k (horizontal axis). Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.10) and different Ni compositions (value of a) It is the graph which plotted the discharge capacity with respect to k (horizontal axis) on the vertical axis. For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) was obtained for each of the example groups having the same d value (d = 0.15) and different Ni compositions (value of a). It is a graph in which the discharge capacity is plotted on the vertical axis with respect to (axis). For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) is shown for each of the example groups having the same d value (d = 0.20) and different Ni compositions (value of a). It is a graph in which the discharge capacity is plotted on the vertical axis with respect to (axis). Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.25) and different Ni compositions (value of a) It is the graph which plotted the discharge capacity with respect to k (horizontal axis) on the vertical axis. For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) was obtained for each of the example groups having the same d value (d = 0.30) and different Ni compositions (value of a). It is a graph in which the discharge capacity is plotted on the vertical axis with respect to (axis). Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.35) and different Ni compositions (value of a) It is the graph which plotted the discharge capacity with respect to k (horizontal axis) on the vertical axis. Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.10) and different Ni compositions (value of a) It is the graph which plotted the weight energy density on the vertical axis | shaft with respect to k (horizontal axis). For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) was obtained for each of the example groups having the same d value (d = 0.15) and different Ni compositions (value of a). It is a graph in which the weight energy density is plotted on the vertical axis with respect to (axis). For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) is shown for each of the example groups having the same d value (d = 0.20) and different Ni compositions (value of a). It is a graph in which the weight energy density is plotted on the vertical axis with respect to (axis). Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.25) and different Ni compositions (value of a) It is the graph which plotted the weight energy density on the vertical axis | shaft with respect to k (horizontal axis). For the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio k (horizontal) was obtained for each of the example groups having the same d value (d = 0.30) and different Ni compositions (value of a). It is a graph in which the weight energy density is plotted on the vertical axis with respect to (axis). Regarding the solid solution lithium-containing transition metal oxide used in the example column, the structural change ratio for each of the example and comparative example groups having the same d value (d = 0.35) and different Ni compositions (value of a) It is the graph which plotted the weight energy density on the vertical axis | shaft with respect to k (horizontal axis). It is a graph which shows the result of having plotted Ni composition (value of a) of the positive electrode active material (solid solution lithium containing transition metal oxide) in the battery of all the Examples and the comparative example with respect to each d value. It is a graph which shows the result of having plotted the average value k 'of the structure change rate k of the positive electrode active material (solid solution lithium containing transition metal oxide) in the battery of all the Examples and the comparative examples with respect to each d value.

  Hereinafter, the solid solution lithium-containing transition metal oxide of the present invention and the nonaqueous electrolyte secondary battery using the solid solution lithium-containing transition metal oxide as a positive electrode will be described in detail. In addition, the solid solution lithium-containing transition metal oxide of the present invention is preferably used, for example, as a positive electrode active material of a lithium ion secondary battery that is a non-aqueous electrolyte secondary battery. Then, the positive electrode for nonaqueous electrolyte secondary batteries and the nonaqueous electrolyte secondary battery according to one embodiment of the present invention will be described by taking the positive electrode for lithium ion secondary batteries and the lithium ion secondary battery as examples.

  First, a solid solution lithium-containing transition metal oxide according to an embodiment of the present invention will be described in detail.

  The solid solution lithium-containing transition metal oxide of the present embodiment is represented by the composition formula (1).

In the composition formula (1), Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, and O represents oxygen. A, b, c, and d have the following relationship:
0.1 ≦ d <0.4
a + b + c + d = 1.5
1.1 <a + b + c ≦ 1.4
-2 / 3d + 0.4 <a <-2.5d + 1.15
Satisfied.

Further, the solid solution lithium-containing transition metal oxide of a preferred embodiment has the following relationship in the composition formula (1):
0.1 ≦ d ≦ 0.35
a + b + c + d = 1.5
1.15 ≦ a + b + c ≦ 1.4
-D + 0.5 <a <-1.6d + 0.81
Satisfied. This can provide a battery that exhibits higher performance (average voltage and weight energy density).

Furthermore, the solid solution lithium-containing transition metal oxide of a more preferred embodiment has the following relationship in the composition formula (1):
0.15 ≦ d ≦ 0.35
a + b + c + d = 1.5
1.15 ≦ a + b + c ≦ 1.35
-D + 0.5 <a <-1.6d + 0.81
Satisfied. This can provide a battery that exhibits even higher performance (average voltage and weight energy density).

The solid solution lithium-containing transition metal oxide according to the present embodiment includes a layered structure portion and a portion that changes to a spinel structure by charging or charging / discharging in a predetermined potential range (Li ₂ MnO _{3 having a} layered structure). Have. Furthermore, Li ₂ MnO ₃ having a layered structure in the solid solution lithium-containing transition metal oxide is changed to LiMn ₂ O ₄ having a spinel structure.

  When such a solid solution lithium-containing transition metal oxide is used as a positive electrode active material of a lithium ion secondary battery, it can realize a high discharge capacity and capacity retention rate. It is suitably used for secondary batteries. As a result, it can be suitably used as a lithium-ion secondary battery for vehicle drive power or auxiliary power. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for home use and portable devices.

  In the formula (1), a, b, c and d are 0.1 ≦ d <0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c ≦ 1.4, and −2 / 3d + 0.4 <a When the relationship of <−2.5d + 1.15 is not satisfied, the structure in the solid solution is not stabilized.

Here, in this specification, the actual structural change ratio is represented by “k” when the spinel structure change ratio is 1 when all the sites that change to the spinel structure are changed to the spinel-structured LiMn ₂ O ₄ . This “spinel structure change ratio (k)” is obtained by performing charge or charge / discharge in a predetermined potential range, so that Li ₂ MnO ₃ having a layered structure in the solid solution lithium-containing transition metal oxide is converted to LiMn ₂ O having a spinel structure. _The ratio of change in spinel structure is defined as 1 when the Li ₂ MnO ₃ having a layered structure in the transition metal oxide containing solid solution lithium is all changed to LiMn ₂ O ₄ having a spinel structure. This is the relative value. Specifically, it is defined by the following formula. FIG. 1A is a graph illustrating the definition of the spinel structure change ratio k. FIG. 1B is a graph illustrating the actual capacity of the plateau region used to define the spinel structure change rate k. Specifically, in the case of performing electrochemical pretreatment and charge / discharge treatment, the total capacity of the plateau region used when calculating the structural change ratio k is the sum of the plateau capacities generated from around 4.5V (4.3V or more). It is a graph explaining that it is the calculated capacity (actual capacity; range B in the figure).

Regarding the definition of “spinel structure change ratio”, for a battery assembled using a positive electrode having the solid solution lithium-containing transition metal oxide as a positive electrode active material, 4.5 V (starting point of the plateau region) from the initial state A before the start of charging. ) To a charged state B that has been charged up to 4.8V, to an overcharged state C that has been charged to 4.8V (end point of the plateau region) through a plateau region, and to a discharged state D that has been further discharged to 2.0V. The case shown in FIG. 1A will be described as an example. The “actual capacity of the plateau region” in the above formula is the plateau region in FIG. 1A (specifically, the region from 4.5 V to 4.8 V (the actual capacity V _BC of the region BC from the charged state B to the overcharged state C) The actual capacity of the plateau region), which is the region resulting from the change in the crystal structure. The starting point of the plateau region is usually 4.5 V. However, depending on the specific composition (values of a to d) of the solid solution lithium-containing transition metal oxide, a lower potential, specifically 4.3 V to 4 V. The plateau region may start from a potential between .5V. That is, the potential at which a plateau capacity is generated due to a structural change differs depending on the composition of the solid solution lithium-containing transition metal oxide.

In practice, in the solid solution lithium-containing transition metal oxide of the composition formula (1), the practical amount V _{AB in} the region AB from the initial state A to the charged state B charged from 4.5 V (starting point of the plateau region). Corresponds to the composition ratio (y) and the theoretical capacity (V _L ) of LiM ¹ O ₂ , which is a layered structure site, from the charged state B charged to 4.5 V (starting point of the plateau region) to 4.8 V (plateau region) The actual capacity V _BC of the region BC in the overcharged state C charged up to the end point of E) corresponds to the composition ratio (x) and the theoretical capacity (V _S ) of Li ₂ MnO ₃ that is the spinel structure site, so that the initial state When the actual capacity (V _T ) measured from A to a predetermined plateau region is (V _T = V _AB + V _BC ), V _AB = y (V _L ) and V _BC = x (V _S ). It can also be calculated using the following formula (M is nickel (Ni), Baltic (Co) and manganese represents at least one selected from the group consisting of (Mn).). In addition, the state of being charged to 4.8 V (end point of the plateau region) is referred to as “overcharged state” because a battery of 4.8 V is actually used (usually used at an upper limit voltage of 4.5 V). This is because the battery is overcharged. Here, in the single evaluation of the active material (solid solution lithium-containing transition metal oxide) (especially calculation of the spinel structure change ratio k, etc.), in order to determine the performance limit of the single active material, the evaluation is performed with 4.8 V charge (k Value calculation, etc.).

Furthermore, the “composition ratio of Li ₂ MnO _{3 in} the solid solution” can be calculated from the composition formula of the solid solution lithium-containing transition metal oxide. In addition, the presence or absence of the layered structure site and the spinel structure site in the solid solution lithium-containing transition metal oxide can be determined by the presence of a peculiar peak in the layered structure and the spinel structure by X-ray diffraction analysis (XRD), and the ratio is It can be determined from the measurement and calculation of the capacity as described above.

  The solid solution lithium-containing transition metal oxide according to this embodiment is characterized in that the average value k ′ of the spinel structure change ratio k is controlled within a predetermined range as a function of the d value.

Specifically, when the average value k ′ of the spinel structure change ratio k is 0.1 ≦ d ≦ 0.25, the following relationship:
4 / 3d + 1/15 ≦ k ′ ≦ 1
When 0.25 <d <0.4, the following relationship is satisfied:
0.4 ≦ k ′ ≦ 1.0
It is characterized by satisfying

Here, the average value k ′ of the spinel structure change ratio k is 4.5V, 4.6V, 4.7V, and 4.8V (with respect to lithium metal) by the method described in the column of Examples described later. It is calculated as the average value of the respective k values when charging and discharging in this order up to the maximum voltage. If the calculation method is outlined for reference, a coin cell (lithium ion secondary battery) is first prepared using metallic lithium as a counter electrode, and the following charge / discharge steps are sequentially performed on the coin cell.
(1) After performing constant current (CC) charging at a 0.1 C rate until the maximum voltage is 4.2 V, after resting for about 24 hours, until the minimum voltage of the battery reaches 2.5 V, 0 .Constant current (CC) discharge is performed at a 1C rate.
(2) After charging by a constant current (CC) charging method in which charging is performed until the maximum voltage reaches 4.5 V at a 0.1 C rate, discharging is performed at a 0.1 C rate until the minimum voltage reaches 2.0 V. Two constant current charge / discharge cycles are performed.
(3) After charging by the constant current (CC) charging method in which charging is performed until the maximum voltage reaches 4.6 V at a 0.1 C rate, discharging is performed until the minimum voltage reaches 2.0 V at a 0.1 C rate. A constant current charge / discharge cycle is performed once.
(4) After charging by the constant current (CC) charging method in which charging is performed until the maximum voltage reaches 4.7 V at a 0.1 C rate, discharging is performed until the minimum voltage reaches 2.0 V at a 0.1 C rate. A constant current charge / discharge cycle is performed once.
(5) After charging at the 0.1C rate until the maximum voltage reaches 4.8V, perform the constant current / constant voltage (CCCV) charging method (15 hours for the entire charging) for about 1 to 1.5 hours. Then, a constant current discharge method is performed in which the battery is discharged at a rate of 0.1 C until the minimum voltage of the battery reaches 2.0V.

  And after completion | finish of each step of said (2)-(5), k value can be measured based on the method mentioned above, and k 'value can be calculated as the average value.

In the solid solution lithium-containing transition metal oxide of the present embodiment, the k ′ value calculated as described above has the following relationship as a function using the d value:
4 / 3d + 1/15 ≦ k ′ ≦ 1 (when 0.1 ≦ d ≦ 0.25)
0.4 ≦ k ′ ≦ 1.0 (when 0.25 <d <0.4)
It is characterized by satisfying With such a configuration, the solid solution lithium-containing transition metal oxide according to the present embodiment can provide a non-aqueous electrolyte secondary battery with improved average voltage and weight energy density.

Further, in the solid solution lithium-containing transition metal oxide of a preferred embodiment, the k ′ value has the following relationship:
2 / 3d + 0.7 / 30 ≦ k ′ ≦ 2d + 0.4 (when 0.1 ≦ d ≦ 0.25)
0.4 ≦ k ′ ≦ 0.9 (when 0.25 <d ≦ 0.35)
Satisfied. Thereby, a nonaqueous electrolyte secondary battery with further improved average voltage and weight energy density can be provided. At this time, in the composition formula (1), the following relationship:
0.1 ≦ d ≦ 0.35
a + b + c + d = 1.5
1.15 ≦ a + b + c ≦ 1.4
-D + 0.5 <a <-1.6d + 0.81
Is preferably satisfied.

And in the solid solution lithium-containing transition metal oxide of a more preferred embodiment, the k ′ value has the following relationship:
−d + 0.65 ≦ k ′ ≦ d + 0.55 (when 0.15 ≦ d ≦ 0.3)
0.4 ≦ k ′ ≦ 0.85 (when 0.3 <d ≦ 0.35)
Satisfied. Accordingly, a nonaqueous electrolyte secondary battery with further improved average voltage and weight energy density can be provided. At this time, in the composition formula (1), the following relationship:
0.15 ≦ d ≦ 0.35
a + b + c + d = 1.5
1.15 ≦ a + b + c ≦ 1.35
-D + 0.5 <a <-1.6d + 0.81
Is preferably satisfied.

  Next, the method for producing a solid solution lithium-containing transition metal oxide according to an embodiment of the present invention will be described in detail with some examples.

  First, as an example of a method for producing a solid solution lithium-containing transition metal oxide, raw materials containing lithium compounds such as sulfates and nitrates, nickel compounds, cobalt compounds and manganese compounds were mixed to obtain a mixture, and then obtained. A method for producing a solid solution lithium-containing transition metal oxide in which the mixture is fired at 800 ° C. or higher and 1000 ° C. or lower for 6 hours to 24 hours in an inert gas atmosphere can be given.

  As another example of the method for producing a solid solution lithium-containing transition metal oxide, raw materials containing lithium compounds such as sulfates and nitrates, nickel compounds, cobalt compounds and manganese compounds are mixed to obtain a mixture, and then obtained. The obtained mixture is fired at 800 ° C. or higher and 1000 ° C. or lower for 6 hours or longer and 24 hours or shorter to obtain a fired product, and then the obtained fired product is heat-treated at 600 ° C. or higher and 800 ° C. or lower in an inert gas atmosphere. The manufacturing method of a lithium containing transition metal oxide can be mentioned.

  However, a solid solution lithium-containing transition metal oxide having a desired spinel structure change ratio k has not been obtained at this stage. Therefore, a battery is prepared using the solid solution lithium-containing transition metal oxide obtained by heat treatment as a positive electrode, and a desired spinel structure change ratio k is obtained by performing charge / discharge treatment, preferably electrochemical pretreatment and charge / discharge treatment. A solid solution lithium-containing transition metal oxide having the following is obtained:

  That is, in a lithium ion secondary battery using a solid solution lithium-containing transition metal oxide obtained by the above-described firing or heat treatment as a positive electrode, the maximum potential of the battery (positive electrode) in a predetermined potential range is converted to a lithium metal counter electrode. A charge / discharge treatment is performed to charge or discharge at 4.8V. By this charge / discharge treatment, the desired spinel structure change ratio k of the solid solution lithium-containing transition metal oxide can be obtained. Preferably, an electrochemical pretreatment for performing charging or charging / discharging in which a maximum potential of a battery (positive electrode) in a predetermined potential range is 4.3 V or more and less than 4.8 V in terms of a lithium metal counter electrode, and the charge / discharge treatment Apply. By such electrochemical pretreatment and charge / discharge treatment, a more preferable range of spinel structure change ratio k can be obtained in the solid solution lithium-containing transition metal oxide. In the lithium ion secondary battery using the solid solution lithium-containing transition metal oxide according to the present embodiment for the positive electrode, the specific value of the spinel structure change ratio k of the solid solution lithium-containing transition metal oxide is not particularly limited. Preferably it is 0.1-0.9, More preferably, it is 0.3-0.9, More preferably, it is 0.5-0.9, Most preferably, it is 0.7-0.9 .

  More specifically, as shown in Table 1 of the example in conjunction with the method for calculating the k ′ value, as the electrochemical pretreatment, the maximum potential of the battery (positive electrode) is 4.3 V or more, which is the starting point of the plateau region, It is desirable to perform charging or charging / discharging up to a potential lower than 4.8 V (for example, 4.7 V), which is the end point of the plateau region. The reason why the starting point of the plateau region is set to 4.3 V or more is because the potential at which the plateau capacity is generated due to the structural change varies depending on the composition of the solid solution lithium-containing transition metal oxide. That is, depending on the composition of the solid solution lithium-containing transition metal oxide, for example, the value of a to d, a plateau capacity may be generated at less than 4.5 V (specifically, between 4.3 V and 4.5 V). 3V or higher. In the results of the examples, a plateau is generated from around 4.5 V, so the description of the examples is as such (see Table 1). In addition, in the electrochemical pretreatment, as shown in Table 1 of the example, in constant current charging / discharging (CC-CC mode), the starting point of the plateau region (4.3 V to 4.5 V) is sequentially 4.6 V from 4.6 V. It is desirable to perform charging / discharging so that a higher maximum potential is obtained in increments of 0.1V, such as 4.7V. This is because the spinel structure change ratio k can be set to a more preferable range (that is, a structure with a higher structure change ratio). Further, in the electrochemical pretreatment, as shown in Table 1 of the examples, charging and discharging may be repeated one or more times for each maximum potential. For example, as shown in Table 1 of Example 1, charging / discharging is performed a plurality of times (specifically, twice) for each maximum potential, as charging / discharging is repeated twice (2 cycles) at 4.5V. (About 5 times) may be repeated. In addition, as the current rate in the electrochemical pretreatment, both charging and discharging are performed in the range of 0.01 to 0.5 C rate, preferably 0.1 C rate, from the viewpoint of gradually changing and stabilizing the crystal structure. Preferred (see Table 1). As shown in Table 1 of the examples, from the viewpoint of stabilization of the crystal structure, before the electrochemical pretreatment, the maximum potential of the battery (positive electrode) is lower than 4.3 V (for example, 4.2 V). ), Charging or charging / discharging may be performed. Also in this case, charging and discharging may be performed at a constant current charging / discharging (CC-CC mode) in the range of 0.01 to 0.5 C, preferably 0.1 C, as in the electrochemical pretreatment. .

  Moreover, as a charging / discharging process, it charges or discharges with 4.8V used as the end point of a plateau area | region. Preferably, as described above, the charge / discharge treatment is performed after the electrochemical pretreatment. In the charge / discharge treatment, as shown in Table 2 of the embodiment, spinel is performed by performing charge / discharge in a range of 2.0 to 4.8 V in constant current constant voltage charge-constant current discharge (CCCV-CC mode). The structural change ratio k can be obtained. Moreover, as a current rate in the charge / discharge treatment, it is preferable that both charge and discharge be performed at a rate of 0.01 to 0.5C, preferably 0.1C from the viewpoint of changing and stabilizing the crystal structure ( (See Table 2).

  Next, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the dimension ratio of drawing quoted by the following embodiment is exaggerated on account of description, and may differ from an actual ratio.

  FIG. 2 is a cross-sectional view schematically illustrating an example of a lithium ion secondary battery according to an embodiment of the present invention. Such a lithium ion secondary battery is called a laminated lithium ion secondary battery.

  As shown in FIG. 2, the lithium ion secondary battery 1 of the present embodiment has a configuration in which a battery element 10 to which a positive electrode lead 21 and a negative electrode lead 22 are attached is enclosed in an exterior body 30 formed of a laminate film. have. In the present embodiment, the positive electrode lead 21 and the negative electrode lead 22 are led out in the opposite direction from the inside of the exterior body 30 to the outside. Although not shown, the positive electrode lead and the negative electrode lead may be led out in the same direction from the inside of the exterior body toward the outside. Moreover, such a positive electrode lead and a negative electrode lead can be attached to a positive electrode current collector and a negative electrode current collector described later by, for example, ultrasonic welding or resistance welding.

  The positive electrode lead 21 and the negative electrode lead 22 are made of, for example, a metal material such as aluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), alloys thereof, and stainless steel (SUS). However, the material is not limited thereto, and a conventionally known material used as a lead for a lithium ion secondary battery can be used.

  The positive electrode lead and the negative electrode lead may be made of the same material or different materials. Further, as in the present embodiment, a separately prepared lead may be connected to a positive electrode current collector and a negative electrode current collector described later, and each positive electrode current collector and each negative electrode current collector described later are extended. The lead may be formed by this. Although not shown, the positive lead and the negative lead taken out from the exterior body do not affect products (for example, automobile parts, especially electronic devices) by contacting with peripheral devices or wiring and causing electric leakage. Thus, it is preferable to coat with a heat-resistant insulating heat-shrinkable tube or the like.

  Further, although not shown, a current collector plate may be used for the purpose of taking out the current outside the battery. The current collector plate is electrically connected to a current collector or a lead, and is taken out of a laminate film that is an exterior material of the battery. The material which comprises a current collector plate is not specifically limited, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), alloys thereof, and stainless steel (SUS) are preferable, and light weight and corrosion resistance. From the viewpoint of high conductivity, aluminum (Al), copper (Cu), and the like are more preferable. Note that the same material may be used for the positive electrode current collector plate and the negative electrode current collector plate, or different materials may be used.

  For example, the exterior body 30 is preferably formed of a film-shaped exterior material from the viewpoints of miniaturization and weight reduction, but is not limited thereto, and the exterior body for a lithium ion secondary battery is not limited thereto. The conventionally well-known thing used for the body can be used. That is, a metal can case can also be applied.

  From the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for batteries for large equipment of electric vehicles and hybrid electric vehicles, for example, a polymer-metal composite laminate film having excellent thermal conductivity is used. Can be mentioned. More specifically, an outer package formed of a three-layer laminated film outer package in which polypropylene as a thermocompression bonding layer, aluminum as a metal layer, and nylon as an outer protective layer are laminated in this order is suitably used. Can be used.

  Note that the exterior body may be constituted by another structure, for example, a laminate film not having a metal material, a polymer film such as polypropylene, or a metal film, instead of the above-described laminate film.

  Here, the general structure of an exterior body can be represented by the laminated structure of an external protective layer / metal layer / thermocompression bonding layer (however, the external protective layer and the thermocompression bonding layer may be composed of a plurality of layers. .) As the metal layer, it is sufficient to function as a moisture-permeable barrier film, and not only aluminum foil, but also stainless steel foil, nickel foil, plated iron foil, etc. can be used, but it is thin and lightweight. Thus, an aluminum foil excellent in workability can be suitably used.

  The structures that can be used as the outer package are listed in the form of (external protective layer / metal layer / thermocompression bonding layer): nylon / aluminum / non-stretched polypropylene, polyethylene terephthalate / aluminum / unstretched polypropylene, polyethylene terephthalate / aluminum / polyethylene Terephthalate / unstretched polypropylene, polyethylene terephthalate / nylon / aluminum / unstretched polypropylene, polyethylene terephthalate / nylon / aluminum / nylon / unstretched polypropylene, polyethylene terephthalate / nylon / aluminum / nylon / polyethylene, nylon / polyethylene / aluminum / linear Low density polyethylene, polyethylene terephthalate / polyethylene / aluminum / polyethylene terephthalate / Density polyethylene, and a polyethylene terephthalate / nylon / aluminum / low density polyethylene / cast polypropylene.

  As shown in FIG. 2, the battery element 10 includes a positive electrode 11 having a positive electrode active material layer 11B formed on both main surfaces of the positive electrode current collector 11A, an electrolyte layer 13, and a negative electrode current collector 12A. A plurality of negative electrodes 12 each having a negative electrode active material layer 12 </ b> B formed on the main surface are stacked. At this time, one main surface of the positive electrode active material layer 11B formed on one main surface of the positive electrode current collector 11A of one positive electrode 11 and the negative electrode current collector 12A of the negative electrode 12 adjacent to the one positive electrode 11 The negative electrode active material layer 12 </ b> B formed above faces the electrolyte layer 13. In this way, a plurality of layers are laminated in the order of the positive electrode, the electrolyte layer, and the negative electrode.

  As a result, the adjacent positive electrode active material layer 11B, electrolyte layer 13 and negative electrode active material layer 12B constitute one unit cell layer. Therefore, the lithium ion secondary battery 1 of the present embodiment has a configuration in which a plurality of single battery layers 14 are stacked and electrically connected in parallel. In addition, the positive electrode and the negative electrode may have each active material layer formed on one main surface of each current collector. In the present embodiment, for example, the negative electrode current collector 12a located in the outermost layer of the battery element 10 has the negative electrode active material layer 12B formed on only one side.

  In addition, an insulating layer (not shown) may be provided on the outer periphery of the unit cell layer to insulate between the adjacent positive electrode current collector and negative electrode current collector. Such an insulating layer is preferably formed of a material that retains the electrolyte contained in the electrolyte layer and the like and prevents electrolyte leakage from the outer periphery of the single cell layer. Specifically, general-purpose plastics such as polypropylene (PP), polyethylene (PE), polyurethane (PUR), polyamide resin (PA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polystyrene (PS), etc. Or thermoplastic olefin rubber can be used. Silicone rubber can also be used.

  The positive electrode current collector 11A and the negative electrode current collector 12A are made of a conductive material. The size of the current collector can be determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm. The shape of the current collector is not particularly limited. In the battery element 10 shown in FIG. 2, in addition to the current collector foil, a mesh shape (expanded grid or the like) can be used.

  In addition, when forming the thin film alloy which is an example of a negative electrode active material directly on the negative electrode collector 12A by sputtering method etc., it is desirable to use a current collection foil.

  There is no particular limitation on the material constituting the current collector. For example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material can be employed.

  Specifically, examples of the metal include aluminum (Al), nickel (Ni), iron (Fe), stainless steel (SUS), titanium (Ti), copper (Cu), and the like. In addition to these, it is preferable to use a clad material of nickel (Ni) and aluminum (Al), a clad material of copper (Cu) and aluminum (Al), or a plating material combining these metals. Moreover, the foil by which the metal surface was coat | covered with aluminum (Al) may be sufficient. Among these, aluminum (Al), stainless steel (SUS), copper (Cu), and nickel (Ni) are preferable from the viewpoint of electronic conductivity, battery operating potential, and the like.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS), and the like. Such a non-conductive polymer material has excellent potential resistance or solvent resistance.

  A conductive filler can be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, a metal, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion interruption | blocking property.

  As metals, nickel (Ni), titanium (Ti), aluminum (Al), copper (Cu), platinum (Pt), iron (Fe), chromium (Cr), tin (Sn), zinc (Zn), indium Preferred examples include those containing at least one metal selected from the group consisting of (In), antimony (Sb), and potassium (K), or an alloy or metal oxide containing these metals. In addition, preferred examples of the conductive carbon include those containing at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. Can be mentioned. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

  However, the material is not limited to these, and a conventionally known material used as a current collector for a lithium ion secondary battery can be used.

  The positive electrode active material layer 11B includes at least one solid solution lithium-containing transition metal oxide according to the above-described embodiment of the present invention as a positive electrode active material, and a binder or a conductive auxiliary agent as necessary. May be included.

  Although it does not specifically limit as a binder (binder), For example, the following materials are mentioned.

  Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile (PAN), polyimide (PI), polyamide (PA), cellulose, carboxymethylcellulose (CMC), ethylene-acetic acid Vinyl copolymer, polyvinyl chloride (PVC), styrene / butadiene rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer, and Its hydrogenated product, thermoplastic polymer such as styrene / isoprene / styrene block copolymer and its hydrogenated product, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoro Tylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / Fluoropolymers such as chlorotrifluoroethylene copolymer (ECTFE) and polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluoropolymer), vinylidene fluoride-hexafluoropropylene-tetra Fluoroethylene fluoro rubber (VDF-HFP-TFE fluoro rubber), vinylidene fluoride-pentafluoropropylene fluoro rubber (VDF-PFP fluoro rubber), vinylidene fluoride- Interfluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride -Vinylidene fluoride-based fluororubber such as chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), epoxy resin and the like. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the positive electrode (and negative electrode) active material layer.

  However, the material is not limited to these, and a known material conventionally used as a binder for a lithium ion secondary battery can be used. These binders may be used alone or in combination of two or more.

  The amount of the binder (binder) contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the positive electrode active material, but is preferably 0 with respect to the positive electrode active material layer. It is 5-15 mass%, More preferably, it is 1-10 mass%.

  A conductive support agent is mix | blended in order to improve the electroconductivity of a positive electrode active material layer. As a conductive support agent, carbon materials, such as carbon black, such as acetylene black, a graphite, and a vapor growth carbon fiber, can be mentioned, for example. When the positive electrode active material layer contains a conductive additive, an electronic network inside the positive electrode active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  However, the material is not limited to these, and a conventionally known material that is used as a conductive additive for a lithium ion secondary battery can be used. These conductive assistants may be used alone or in combination of two or more.

  In addition, the conductive binder having the functions of the conductive assistant and the binder may be used in place of the conductive assistant and the binder, or one or both of the conductive assistant and the binder. You may use together. As the conductive binder, for example, commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used.

Furthermore, the density of the positive electrode active material layer is preferably 2.5 g / cm ³ or more and 3.0 g / cm ³ or less. When the density of the positive electrode active material layer is 2.5 g / cm ³ or more, the weight per unit volume (filling amount) can be improved, and the discharge capacity can be improved. Moreover, if the density of the positive electrode active material layer is 3.0 g / cm ³ or less, the porosity of the non-aqueous electrolyte and the lithium ion diffusibility are excellent without significantly reducing the void amount of the positive electrode active material layer. It is advantageous.

  The negative electrode active material layer 12B includes, as a negative electrode active material, lithium, a lithium alloy, or a negative electrode material capable of occluding and releasing lithium, and includes a binder and a conductive aid as necessary. May be. In addition, what was demonstrated above can be used for a binder and a conductive support agent.

Examples of the negative electrode material capable of inserting and extracting lithium include graphite (natural graphite, artificial graphite, etc.), which is highly crystalline carbon, low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen) Carbon materials such as black, acetylene black, channel black, lamp black, oil furnace black, thermal black), fullerenes, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon fibrils (containing 10% by mass or less of silicon nanoparticles) Silicon (Si), germanium (Ge), tin (Sn), lead (Pb), aluminum (Al), indium (In), zinc (Zn), hydrogen (H), calcium (Ca), strontium( r), barium (Ba), ruthenium (Ru), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), cadmium (Cd), mercury ( Hg), gallium (Ga), thallium (Tl), carbon (C), nitrogen (N), antimony (Sb), bismuth (Bi), oxygen (O), sulfur (S), selenium (Se), tellurium ( Te), elemental elements that form an alloy with lithium such as chlorine (Cl), and oxides containing these elements (silicon monoxide (SiO), SiO _x (0 <x <2), tin dioxide (SnO ₂ )) , SnO _x (0 <x <2), SnSiO _{3 and the} like) and carbides (silicon carbide (SiC) and the like); metal materials such as lithium metal; lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂₎ lithium such as It can be mentioned transition metal composite oxide. However, it is not limited to these, The conventionally well-known material used as a negative electrode active material for lithium ion secondary batteries can be used. These negative electrode active materials may be used alone or in combination of two or more.

Further, in the present embodiment, the carbon material is made of a graphite material that is coated with an amorphous carbon layer and is not scale-like, and the BET specific surface area of the carbon material is 0.8 m ² / g or more and 1.5 m. ² / g or less and the tap density is preferably 0.9 g / cm ³ or more and 1.2 g / cm ³ or less. A carbon material made of a graphite material that is coated with an amorphous carbon layer and is not scale-like is preferable because of its high lithium ion diffusibility into the graphite layered structure. Moreover, it is preferable that the BET specific surface area of such a carbon material is 0.8 m ² / g or more and 1.5 m ² / g or less because the capacity retention rate can be further improved. Furthermore, when the tap density of such a carbon material is 0.9 g / cm ³ or more and 1.2 g / cm ³ or less, the weight (filling amount) per unit volume can be improved, and the discharge capacity is improved. be able to.

Furthermore, in the present embodiment, it is preferable that the negative electrode active material layer containing at least the carbon material and the binder has a BET specific surface area of 2.0 m ² / g or more and 3.0 m ² / g or less. When the BET specific surface area of the negative electrode active material layer is 2.0 m ² / g or more and 3.0 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved, and the capacity retention rate is further improved, Gas generation due to decomposition of the non-aqueous electrolyte can be suppressed.

In the present embodiment, the negative electrode active material layer containing at least a carbon material and a binder preferably has a BET specific surface area after pressure molding of 2.01 m ² / g or more and 3.5 m ² / g or less. It is. By setting the BET specific surface area of the negative electrode active material layer after pressure molding to 2.01 m ² / g or more and 3.5 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved and the capacity can be maintained. The rate can be improved and gas generation due to decomposition of the non-aqueous electrolyte can be suppressed.

Furthermore, in this embodiment, the increase in the BET specific surface area before and after pressure press molding of the negative electrode active material layer containing at least the carbon material and the binder is 0.01 m ² / g or more and 0.5 m ² / g or less. Preferably it is. Since the BET specific surface area after pressure molding of the negative electrode active material layer can be 2.01 m ² / g or more and 3.5 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved. The capacity retention rate can be improved and gas generation due to decomposition of the non-aqueous electrolyte can be suppressed.

  Further, the thickness of each active material layer (active material layer on one side of the current collector) is not particularly limited, and conventionally known knowledge about the battery can be referred to as appropriate. For example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm in consideration of the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity.

  Furthermore, when the optimum particle diameter is different for expressing the unique effect of each active material, the optimum particle diameters may be used in combination for expressing each unique effect. There is no need to make the particle size of the material uniform.

  For example, when an oxide in the form of particles is used as the positive electrode active material, the average particle size of the oxide may be approximately the same as the average particle size of the positive electrode active material included in the existing positive electrode active material layer, and is not particularly limited. . From the viewpoint of increasing the output, it is preferably in the range of 1 to 20 μm. In the present specification, the “particle diameter” refers to the outline of active material particles (observation surface) observed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among any two points. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted. The particle diameters and average particle diameters of other components can be defined in the same manner.

  However, it is not limited to such a range at all, and it goes without saying that it may be outside this range as long as the effects of the present embodiment can be expressed effectively.

  As the electrolyte layer 13, for example, an electrolyte solution, a polymer gel electrolyte, a solid polymer electrolyte formed in a separator described later, and a layer structure formed using a solid polymer electrolyte, or a polymer gel electrolyte or a solid polymer electrolyte are used. Examples thereof include those having a laminated structure formed thereon.

For example, the electrolyte solution is preferably one that is usually used in a lithium ion secondary battery, and specifically has a form in which a supporting salt (lithium salt) is dissolved in an organic solvent. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), six Inorganic acid anion salts such as lithium fluorotantalate (LiTaF ₆ ), lithium tetrachloroaluminate (LiAlCl ₄ ), lithium decachlorodecaborate (Li ₂ B ₁₀ Cl ₁₀ ), lithium trifluoromethanesulfonate (LiCF ₃₎ Organic acids such as SO ₃ ), lithium bis (trifluoromethanesulfonyl) imide (Li (CF ₃ SO ₂ ) ₂ N), lithium bis (pentafluoroethanesulfonyl) imide (Li (C ₂ F ₅ SO ₂ ) ₂ N) Examples include at least one lithium salt selected from anionic salts. Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC); chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC). Ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane; lactones such as γ-butyrolactone; nitriles such as acetonitrile; methyl propionate; Esters such as: amides such as dimethylformamide; those using an organic solvent such as an aprotic solvent in which at least one selected from methyl acetate and methyl formate or a mixture of two or more thereof can be used. Examples of the separator include a microporous film made of polyolefin such as polyethylene (PE) and polypropylene (PP), a porous flat plate, and a nonwoven fabric.

  Examples of the polymer gel electrolyte include those containing a polymer constituting the polymer gel electrolyte and an electrolytic solution in a conventionally known ratio. For example, from the viewpoint of ionic conductivity and the like, it is desirable to set it to about several mass% to 98 mass%.

  The polymer gel electrolyte is a solid polymer electrolyte having ion conductivity containing the above-described electrolytic solution usually used in a lithium ion secondary battery. However, the present invention is not limited to this, and includes a structure in which a similar electrolyte solution is held in a polymer skeleton having no lithium ion conductivity.

  Examples of the polymer having no lithium ion conductivity used for the polymer gel electrolyte include polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). Can be used. However, it is not necessarily limited to these. In addition, since polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and the like are in a class that has almost no ionic conductivity, it can be a polymer having the ionic conductivity. Here, the polymer used for the polymer gel electrolyte is exemplified as a polymer having no lithium ion conductivity.

  Examples of the solid polymer electrolyte include a structure in which the lithium salt is dissolved in polyethylene oxide (PEO), polypropylene oxide (PPO), and the like, and does not contain an organic solvent. Therefore, when the electrolyte layer is composed of a solid polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  The thickness of the electrolyte layer is preferably thinner from the viewpoint of reducing internal resistance. The thickness of the electrolyte layer is usually 1 to 100 μm, preferably 5 to 50 μm.

  A polymer gel electrolyte or a solid polymer electrolyte matrix polymer can exhibit excellent mechanical strength by forming a cross-linked structure. In order to form a crosslinked structure, a suitable polymerization initiator is used to polymerize a polymer for forming a polymer electrolyte (for example, polyethylene oxide (PEO) or polypropylene oxide (PPO)) by thermal polymerization, ultraviolet polymerization, A polymerization treatment such as radiation polymerization or electron beam polymerization may be performed.

  The shape (configuration) of the lithium ion secondary battery of the present embodiment is not particularly limited, and in addition to a laminate type (and a laminate type) as shown in FIG. 2, a square, a paper type, a laminate type, and a cylinder Various shapes such as a mold and a coin mold can be adopted. Moreover, although there exist a collector, an insulating board, etc. (refer the coin cell of an Example), these components are not specifically limited, What is necessary is just to select according to said shape.

  Next, the manufacturing method of the lithium ion secondary battery of the present embodiment described above will be described with some examples.

  An example of a method for manufacturing a lithium ion secondary battery will be described. First, a positive electrode is produced. For example, when a granular positive electrode active material is used, the above-described solid solution lithium-containing transition metal oxide (for example, one obtained by firing as an example of the above-described production method) and, if necessary, a conductive additive and a binder. (Binder) and a viscosity adjusting solvent are mixed to prepare a positive electrode slurry.

  Subsequently, this positive electrode slurry is applied to a positive electrode current collector, dried, and compression molded to form a positive electrode active material layer, whereby a positive electrode is obtained.

  Moreover, a negative electrode is produced. For example, when a granular negative electrode active material is used, a negative electrode active material and, if necessary, a conductive additive, a binder (binder), and a viscosity adjusting solvent are mixed to prepare a negative electrode slurry. Then, this negative electrode slurry is applied to a negative electrode current collector, dried, and compression molded to form a negative electrode active material layer, whereby a negative electrode is obtained.

  Next, the positive electrode lead is attached to the positive electrode obtained above, and the negative electrode lead is attached to the negative electrode obtained above, and then the positive electrode, the separator, and the negative electrode are laminated. Further, the laminated product is sandwiched between polymer-metal composite laminate sheets, and the outer peripheral edge except one side is heat-sealed to form a bag-like exterior body.

  After that, a non-aqueous electrolyte containing a lithium salt such as lithium hexafluorophosphate and an organic solvent such as ethylene carbonate is prepared and injected into the interior through the opening of the exterior body, and the opening of the exterior body is thermally melted. Wear and enclose. Thereby, a laminate-type lithium ion secondary battery is obtained. Next, the obtained lithium ion secondary battery is subjected to the above-described charge / discharge treatment, preferably electrochemical pretreatment and charge / discharge treatment, so that the spinel structure of the solid solution lithium-containing transition metal oxide used for the positive electrode active material The change ratio k can be set to a desired range (0.25 ≦ k <1.0). Thereby, the lithium ion secondary battery of this embodiment is completed.

  Another example of a method for producing a lithium ion secondary battery will be described. First, a positive electrode is produced. For example, when a granular positive electrode active material is used, the above-described solid solution lithium-containing transition metal oxide (for example, one obtained by heat treatment as an example of the above-described production method) and, if necessary, a conductive additive, a binder A positive electrode slurry is prepared by mixing an agent (binder) and a viscosity adjusting solvent.

  Subsequently, this positive electrode slurry is applied to a positive electrode current collector, dried, and compression molded to form a positive electrode active material layer, whereby a positive electrode is obtained.

  Moreover, a negative electrode is produced. For example, when a granular negative electrode active material is used, a negative electrode active material and, if necessary, a conductive additive, a binder (binder), and a viscosity adjusting solvent are mixed to prepare a negative electrode slurry. Then, this negative electrode slurry is applied to a negative electrode current collector, dried, and compression molded to form a negative electrode active material layer, whereby a negative electrode is obtained.

  Next, the positive electrode lead is attached to the positive electrode and the negative electrode lead is attached to the negative electrode, and then the positive electrode, the separator, and the negative electrode are laminated. Further, the laminated product is sandwiched between polymer-metal composite laminate sheets, and the outer peripheral edge except one side is heat-sealed to form a bag-like exterior body.

  After that, a non-aqueous electrolyte containing a lithium salt such as lithium hexafluorophosphate and an organic solvent such as ethylene carbonate is prepared and injected into the interior through the opening of the exterior body, and the opening of the exterior body is thermally melted. Wear and enclose. Furthermore, the predetermined charging or charging / discharging described above is performed, whereby a laminate-type lithium ion secondary battery is obtained. Next, the obtained lithium ion secondary battery is subjected to the above-described charge / discharge treatment, preferably electrochemical pretreatment and charge / discharge treatment, so that the spinel structure of the solid solution lithium-containing transition metal oxide used for the positive electrode active material The change ratio k can be set to a desired range (0.25 ≦ k <1.0). Thereby, the lithium ion secondary battery of this embodiment is completed.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited only to these.

[Examples 1 to 4]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.61 Co _0.10 Mn _0.69 [Li] _0.10 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.61, b = 0.10, c = 0.69, d = 0.10, a + b + c + d = 1.50, a + b + c = 1. .40). This positive electrode active material was synthesized as follows.

<Synthesis of positive electrode active material>
The positive electrode active material (solid solution lithium-containing transition metal oxide) of this example was synthesized using a composite carbonate method. First, Li, Ni, Co, and Mn sulfates were used as starting materials, and each metal was mixed in a predetermined amount so as to satisfy the above composition formula, and then a 2M (mol / L) composite sulfate aqueous solution was prepared. . A 2M (mol / L) aqueous sodium carbonate solution was used as the precipitant, and a 0.2M (mol / L) aqueous ammonia solution was used for pH adjustment. The sodium carbonate aqueous solution was dropped into the composite sulfate aqueous solution stirred with a magnetic stirrer to precipitate the precursor. The obtained precipitate was dried to obtain a precursor. Thereafter, the obtained precursor and lithium carbonate are pulverized and mixed at a predetermined molar ratio, preliminarily fired at 500 ° C., and then fired in air at 800 ° C. to 1000 ° C. for 12 to 24 hours, thereby obtaining the target sample (positive electrode Active material).

<Composition of slurry for positive electrode>
Positive electrode active material: 90 parts by weight of positive electrode active material powder Conductive aid: 1 part by weight of flake graphite
Acetylene black 4 parts by weight Binder: Polyvinylidene fluoride (PVDF) 5 parts by weight Viscosity adjusting solvent: N-methylpyrrolidone (NMP) 74 parts by weight <Production of slurry for positive electrode>
A positive electrode slurry having the above composition was prepared as follows. First, a binder solution was prepared by dissolving 5.0 parts by weight of PVDF as a binder (binder) in 50.0 parts by weight of NMP as a viscosity adjusting solvent. Next, 1.0 parts by weight of flake graphite and 4.0 parts by weight of acetylene black (a total of 5.0 parts by weight) as conductive assistants, and positive electrode active material powder 90 obtained by the above synthesis as positive electrode active material powder. Part by weight is added to 60.0 parts by weight of the above binder solution and kneaded with a planetary mixer (manufactured by Primics, Hibismix 2P-03), and then 24.0 parts by weight of NMP as a viscosity adjusting solvent is added to the kneaded product. In addition, a positive electrode slurry (solid content concentration 60 wt%) was obtained.

<Application and drying of positive electrode slurry>
The positive electrode slurry is applied to one side of a 20 μm-thick (sheet-like) aluminum current collector foil as a current collector using a bar coater (so that the weight of the positive electrode active material layer after drying is approximately 3.5 mg / cm ^2). ) Applied. Subsequently, the current collector foil coated with the positive electrode slurry was dried on a hot plate (120 ° C. to 130 ° C., drying time 10 minutes) to form a positive electrode active material layer. The amount of NMP remaining in the positive electrode active material layer by drying was set to 0.02% by weight or less. Thereby, a sheet-like positive electrode was obtained.

<Positive electrode press>
Next, the sheet-like positive electrode is compression-molded by a roller press and cut, and the weight of the positive electrode active material layer on one side is about 3.5 mg / cm ² , the thickness is about 50 μm, and the density is 2.70 g / cm ^2. Adjusted to cm ³ .

<Drying the positive electrode>
Next, using this positive electrode, a drying treatment was performed in a vacuum drying furnace. After the positive electrode was installed inside the drying furnace, the air in the drying furnace was removed under reduced pressure (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.). Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 120 ° C. at 10 ° C./min, the pressure was reduced again at 120 ° C., and the nitrogen in the furnace was kept exhausted for 12 hours, The temperature was lowered. Thus, the positive electrode was completed.

<Production of lithium ion secondary battery>
The production of the lithium ion secondary battery was performed as follows.

  After the positive electrode produced above was punched out to a diameter (φ) of 15 mm, it was used again after drying at 100 ° C. for 2 hours in a vacuum dryer before battery production. Further, a polypropylene porous film punched to 15 mm in diameter (φ) used as a separator, a coin cell member, and the like were previously dried at room temperature for 24 hours or more in a glove box in an argon gas atmosphere.

A coin cell 2032 type was produced as a lithium ion secondary battery. As the negative electrode (active material), metallic lithium punched to a diameter (φ) of 15 mm was used. The non-aqueous electrolyte is an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC: DEC = 1: 2 (volume ratio), and LiPF ₆ as a supporting salt has a concentration of 1M ( mol / L) was used in an amount of 150 μL. No special additives were used in the electrolyte.

  The procedure for manufacturing the coin cell 2032 type lithium ion secondary battery is as follows. Inside the glove box in an argon gas atmosphere, the positive and negative electrodes are opposed to each other through two 20 μm-thick polypropylene porous films between the positive electrode and the negative electrode (metallic lithium), in this order: negative electrode, separator, and positive electrode A laminated body was produced. On the bottom of a coin cell (exterior can; CR2032, material: stainless steel (SUS316)), a laminated body in which a negative electrode, a separator, and a positive electrode were stacked in this order was disposed. Next, in order to maintain the insulation between the positive and negative electrodes, install the gasket, inject the electrolyte using a syringe, stack the spring and spacer, then overlap the upper part of the coin cell (exterior can lid) and caulk A coin cell 2032 type lithium ion secondary battery was obtained.

<1. Electrochemical pretreatment (process)>
Electrochemistry that performs charging or charging / discharging using the lithium ion secondary battery obtained above in which the maximum potential of the battery in a predetermined potential range is 4.3 V or more and less than 4.8 V in terms of a lithium metal counter electrode. Pretreatment was performed as follows.

  Charging was performed by a constant current (CC) charging method in which charging was performed at a 0.1 C rate until the maximum voltage reached 4.2 V. Then, it rested for about 24 hours. The discharge was performed by a constant current (CC) discharge method in which the battery was discharged at a rate of 0.1 C until the minimum voltage of the battery reached 2.5V.

  Next, charging is performed by a constant current (CC) charging method in which charging is performed until the maximum voltage reaches 4.5 V at a 0.1 C rate, and then discharging is performed at a 0.1 C rate until the minimum voltage reaches 2.0 V. A current charge / discharge cycle was performed twice to obtain a battery of Example 1. In addition, the value of the discharge capacity and average voltage at the time of the second discharge at this time, and the value of weight energy density (product of the discharge capacity and the average voltage) are shown in Table 3 below.

  The battery of Example 1 was further charged by a constant current (CC) charging method in which the maximum voltage reached 4.6 V at a 0.1 C rate, and then the minimum voltage was 2 at a 0.1 C rate. The battery of Example 2 was obtained by performing a constant-current charge / discharge cycle that discharges to 0.0 V once. In addition, the value of the discharge capacity and average voltage at the time of discharge at this time, and the value of weight energy density (product of discharge capacity and average voltage) are shown in Table 3 below.

  The battery of Example 2 was charged by the constant current (CC) charging method in which the battery was further charged at a 0.1 C rate until the maximum voltage reached 4.7 V, and then the minimum voltage was 2 at the 0.1 C rate. A battery of Example 3 was obtained by performing a constant current charge / discharge cycle for discharging until 0.0 V was reached. In addition, the value of the discharge capacity and average voltage at the time of discharge at this time, and the value of weight energy density (product of discharge capacity and average voltage) are shown in Table 3 below.

  In either case, the operation was performed at room temperature. The conditions (specifications) of the electrochemical pretreatment are shown in Table 1 below.

<2. Charging / discharging treatment (process) and initial characteristics evaluation>
For the battery of Example 3 subjected to the electrochemical pretreatment, charge / discharge treatment for charging or charging / discharging where the highest potential of the battery in a predetermined potential range is 4.8 V in terms of a lithium metal counter electrode. The battery of Example 4 was obtained as follows.

  Charging is performed at a constant current constant voltage (CCCV) charging method (15 hours for the entire charging) that is held for about 1 hour to 1.5 hours after charging at a 0.1 C rate until the maximum voltage reaches 4.8 V. The discharge was performed by a constant current discharge method in which the battery was discharged at a 0.1 C rate until the minimum voltage of the battery reached 2.0V. In either case, the operation was performed at room temperature. The conditions (specifications) for the charge / discharge treatment are shown in Table 2 below. In addition, Table 3 below shows the values of the discharge capacity and the average voltage at the time of discharge and the value of the weight energy density (the product of the discharge capacity and the average voltage).

  Thus, the value of the spinel structure change ratio k was calculated | required from the calculation formula defined in this specification about each of the battery of Examples 1-4 obtained when performing electrochemical pre-processing and charging / discharging processing. (See FIG. 1B). And the average value k 'of each k value of Examples 1-4 was calculated. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below.

[Examples 5 to 8]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.40 Co _0.40 Mn _0.60 [Li] _0.10 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.40, b = 0.40, c = 0.60, d = 0.10, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 5 to 8 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by (.40) was synthesized and used in the same manner as described above. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 5-8, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 9 to 12]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.50 Co _0.16 Mn _0.69 [Li] _0.15 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.50, b = 0.16, c = 0.69, d = 0.15, a + b + c + d = 1.50, a + b + c = 1. The batteries of Examples 9 to 12 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by (.35) was synthesized and used in the same manner as described above. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 9-12, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 13 to 16]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.43 Co _0.30 Mn _0.62 [Li] _0.15 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.43, b = 0.30, c = 0.62, d = 0.15, a + b + c + d = 1.50, a + b + c = 1. The batteries of Examples 13 to 16 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by (.35) was synthesized and used in the same manner as described above. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 13-16, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 17 to 20]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.35 Co _0.35 Mn _0.65 [Li] _0.15 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.35, b = 0.35, c = 0.65, d = 0.15, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 17 to 20 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by (.35) was synthesized and used in the same manner as described above. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 17-20, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 21 to 24]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.45 Co _0.11 Mn _0.74 [Li] _0.20 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.45, b = 0.11, c = 0.74, d = 0.20, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 21 to 24 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 21-24, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 25 to 28]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.41 Co _0.12 Mn _0.77 [Li] _0.20 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.41, b = 0.12, c = 0.77, d = 0.20, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 25 to 28 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of this Example 25-28, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 29 to 32]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.38 Co _0.15 Mn _0.78 [Li] _0.20 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.38, b = 0.15, c = 0.78, d = 0.20, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 29 to 32 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 29-32, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 33 to 36]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.33 Co _0.16 Mn _0.76 [Li] _0.25 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.33, b = 0.16, c = 0.76, d = 0.25, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 33 to 36 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 33-36, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 37 to 40]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.29 Co _0.18 Mn _0.79 [Li] _0.25 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.28, b = 0.18, c = 0.79, d = 0.25, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 37 to 40 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 37-40, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 41 to 44]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.25 Co _0.25 Mn _0.75 [Li] _0.25 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.25, b = 0.25, c = 0.75, d = 0.25, a + b + c + d = 1.50, a + b + c = 1. The batteries of Examples 41 to 44 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 41-44, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 45 to 48]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.22 Co _0.18 Mn _0.79 [Li] _0.30 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.23, b = 0.18, c = 0.79, d = 0.30, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 45 to 48 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 45-48, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 49 to 52]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.20 Co _0.20 Mn _0.80 [Li] _0.30 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.20, b = 0.20, c = 0.80, d = 0.30, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 49 to 52 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 49-52, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 53 to 56]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.25 Co _0.16 Mn _0.79 [Li] _0.30 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.25, b = 0.16, c = 0.79, d = 0.30, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 53 to 56 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 53-56, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 57 to 60]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.19 Co _0.12 Mn _0.84 [Li] _0.35 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.19, b = 0.12, c = 0.84, d = 0.35, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 57 to 60 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 57-60, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 61 to 64]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.22 Co _0.10 Mn _0.83 [Li] _0.35 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.22, b = 0.10, c = 0.83, d = 0.35, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 61 to 64 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by .15 is synthesized and used in the same manner as described above. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Examples 61-64, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Examples 65 to 68]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.18 Co _0.13 Mn _0.84 [Li] _0.35 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.18, b = 0.13, c = 0.84, d = 0.35, a + b + c + d = 1.50, a + b + c = 1. The battery of Examples 65 to 68 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of this Examples 65-68, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Comparative Examples 1-4]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.10 Co _0.10 Mn _0.90 [Li] _0.40 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.10, b = 0.10, c = 0.90, d = 0.40, a + b + c + d = 1.50, a + b + c = 1. The battery of Comparative Examples 1 to 4 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of this Comparative Examples 1-4, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Comparative Examples 5 to 8]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.11 Co _0.09 Mn _0.90 [Li] _0.40 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.11, b = 0.09, c = 0.90, d = 0.40, a + b + c + d = 1.50, a + b + c = 1. The battery of Comparative Examples 5 to 8 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of this Comparative Examples 5-8, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Comparative Examples 9-12]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.30 Co _0.51 Mn _0.60 [Li] _0.10 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.30, b = 0.51, c = 0.60, d = 0.10, a + b + c + d = 1.50, a + b + c = 1. The batteries of Comparative Examples 9 to 12 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these comparative examples 9-12, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Comparative Examples 13 to 16]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.53 Co _0.08 Mn _0.65 [Li] _0.25 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.53, b = 0.08, c = 0.65, d = 0.25, a + b + c + d = 1.50, a + b + c = 1. The batteries of Comparative Examples 13 to 16 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these comparative examples 13-16, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Comparative Examples 17 to 20]
<Composition of positive electrode active material (transition metal oxide containing solid solution lithium)>
As a positive electrode active material,
Composition formula: Li _1.5 [Ni _0.30 Co _0.05 Mn _0.80 [Li] _0.35 ] O ₃
(Here, when the above composition formula is applied to the composition formula (1), a = 0.30, b = 0.05, c = 0.80, d = 0.35, a + b + c + d = 1.50, a + b + c = 1. The batteries of Comparative Examples 17 to 20 corresponding to the batteries of Examples 1 to 4 except that the solid solution lithium-containing transition metal oxide represented by. Obtained. And k value was calculated | required similarly to the above about each of the battery of these Comparative Examples 17-20, and the average value k 'was computed. The values of the spinel structure change ratio k calculated in this way and the average value k ′ are shown in Table 3 below. The values of the discharge capacity and average voltage of each battery and the value of weight energy density (product of discharge capacity and average voltage) are also shown in Table 3 below.

[Results and discussion]
FIG. 3A is a graph in which the average voltage is plotted on the vertical axis with respect to the structural change ratio k (horizontal axis) for each of the example and comparative example groups having the same d value and different Ni compositions (value of a). -Shown in Figure 3F. In addition, the plots of the graphs described in FIGS. 3A to 3F and FIGS. 4A to 4F and FIGS. 5A to 5F to be described later are younger (smaller numbers) as the structural change ratio k is smaller. It corresponds.

  From the results shown in FIGS. 3A to 3F, it can be seen that if the d value is the same, the average voltage at the same structural change ratio increases as the Ni composition (value of a) increases.

  FIG. 4A is a graph in which the discharge capacity is plotted on the vertical axis with respect to the structural change ratio k (horizontal axis) for each of the example and comparative example groups having the same d value and different Ni compositions (value of a). -Shown in FIG. 4F.

  From the results shown in FIGS. 4A to 4F, unlike the results for the average voltage described above with reference to FIGS. 3A to 3F, the discharge capacity necessarily increases as the Ni composition (value a) increases. It can be seen that an excessive Ni composition decreases the discharge capacity. This is considered to be because the stability of the crystal structure is lowered due to the increase of trivalent Ni having yarn teller strain. As a result, when the energy density of each material was compared in the same d value, it became like FIG. 5A-FIG. 5F, and all the examples showed a value higher than a comparative example.

  By the way, since the Ni composition (value of a) also depends on the d value, the preferable composition cannot be uniquely defined by numerical values. Thus, FIG. 6 shows the Ni composition (value of a) of the positive electrode active material (solid solution lithium-containing transition metal oxide) in the batteries of all the examples and comparative examples described above plotted against each d value. . As shown in FIG. 6, it has been found that the Ni composition (value of a) that can improve the average voltage and thus the energy density is limited to a specific range defined by d. From this result, it is essential that the value of d is 0.1 ≦ d <0.4, preferably 0.1 ≦ d ≦ 0.35, and more preferably 0.15 ≦ d ≦ 0.35. Is done. The value of a as a function of d essentially satisfies −2 / 3d + 0.4 <a <−2.5d + 1.15, preferably −d + 0.5 <a <−1.6d + 0.81 (0. 1 ≦ d ≦ 0.35), more preferably −d + 0.5 <a <−1.6d + 0.81 (0.15 ≦ d ≦ 0.35).

  Finally, the relationship between the d value and the average value k ′ of the structure change ratio k is defined. The average value k ′ of the structural change ratio k mainly depends on the Ni composition (value of a) and the d value. Since the preferable range of the Ni composition (value of a) is defined above, the preferable range of the value of k ′ is defined here in relation to the d value. Specifically, the average value k ′ of the structural change ratio k of the positive electrode active material (solid solution lithium-containing transition metal oxide) in the batteries of all the examples and comparative examples described above is plotted against each d value. FIG. Since both the capacity decrease due to the increase in the Ni composition (value of a) and the capacity decrease due to the increase in the d value are reflected in the decrease in the structural change ratio k (and its average value k ′), k ′ of the comparative example. All values (□ shown in FIG. 7) were low. From the results shown in FIG. 7, the average value k ′ of the structural change ratio k satisfies 2 / 3d + 0.7 / 30 ≦ k ′ ≦ 2d + 0.4 when 0.1 ≦ d ≦ 0.25, and 0.25 < It can be seen that when d ≦ 0.35, it is essential to satisfy 0.4 ≦ k ′ ≦ 0.9. Further, in a preferable form showing higher performance, when 0.1 ≦ d ≦ 0.25, 2 / 3d + 0.7 / 30 ≦ k ′ ≦ 2d + 0.4 is satisfied, and when 0.25 <d ≦ 0.35 0.4 ≦ k ′ ≦ 0.9 is satisfied. Furthermore, in a more preferable embodiment, when 0.15 ≦ d ≦ 0.3, −d + 0.65 ≦ k ′ ≦ d + 0.55 is satisfied, and when 0.3 <d ≦ 0.35, 0.4 ≦ k ′ ≦. It satisfies 0.85.

  As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.

  That is, in the above-described embodiments and examples, as the lithium ion secondary battery, a laminate type battery or a coin type battery is exemplified, but the present invention is not limited to this, but a button type battery, a can such as a square shape or a cylindrical shape can be used. The present invention can also be applied to conventionally known forms and structures such as type batteries.

  In addition, for example, the present invention can be applied not only to the above-described stacked type (flat type) battery but also to a conventionally known form / structure such as a wound type (cylindrical) battery.

  Furthermore, for example, the present invention is not only the above-described normal type (internal parallel connection type) battery but also a bipolar type (internal series connection) when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery. It can also be applied to conventionally known forms and structures such as type) batteries. A battery element in a bipolar battery generally has a bipolar electrode in which a negative electrode active material layer is formed on one surface of a current collector and a positive electrode active material layer is formed on the other surface, and an electrolyte layer. A plurality of layers.

1 Lithium ion secondary battery,
10 battery elements,
11 positive electrode,
11A positive electrode current collector,
11B positive electrode active material layer,
12 negative electrode,
12A negative electrode current collector,
12B negative electrode active material layer,
13 electrolyte layer,
14 cell layer,
21 positive lead,
22 negative lead,
30 Exterior body.

Claims (4)

The following composition formula (1):
In the composition formula (1), Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, O represents oxygen, and a, b, c, and d have the following relationships:
0.1 ≦ d <0.4
a + b + c + d = 1.5
1.1 <a + b + c ≦ 1.4
-2 / 3d + 0.4 <a <-2.5d + 1.15
Satisfy,
It is a solid solution lithium-containing transition metal oxide having a layered structure part and a part that changes to a spinel structure by charging or charging / discharging in a predetermined potential range,
In this case, the spinel structure change of the solid solution lithium-containing transition metal oxide with respect to the spinel structure change ratio when all of the layered Li ₂ MnO ₃ in the solid solution lithium-containing transition metal oxide is changed to the spinel LiMn ₂ O ₄ As the average value when charging / discharging in this order up to the maximum values of k (4.5V, 4.6V, 4.7V and 4.8V (vs lithium metal)) when the ratio is k Calculated k) is 0.1 ≦ d ≦ 0.25, the following relationship:
4 / 3d + 1/15 ≦ k ′ ≦ 1
When 0.25 <d <0.4, the following relationship is satisfied:
0.4 ≦ k ′ ≦ 1.0
A solid solution lithium-containing transition metal oxide characterized by satisfying The following composition formula (1):
In the composition formula (1), Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, O represents oxygen, and a, b, c, and d have the following relationships:
0.1 ≦ d ≦ 0.35
a + b + c + d = 1.5
1.15 ≦ a + b + c ≦ 1.4
-D + 0.5 <a <-1.6d + 0.81
Satisfy,
It is a solid solution lithium-containing transition metal oxide having a layered structure part and a part that changes to a spinel structure by charging or charging / discharging in a predetermined potential range,
In this case, the spinel structure change of the solid solution lithium-containing transition metal oxide with respect to the spinel structure change ratio when all of the layered Li ₂ MnO ₃ in the solid solution lithium-containing transition metal oxide is changed to the spinel LiMn ₂ O ₄ As the average value when charging / discharging in this order up to the maximum values of k (4.5V, 4.6V, 4.7V and 4.8V (vs lithium metal)) when the ratio is k Calculated k) is 0.1 ≦ d ≦ 0.25, the following relationship:
2 / 3d + 0.7 / 30 ≦ k ′ ≦ 2d + 0.4
When 0.25 <d ≦ 0.35, the following relationship is satisfied:
0.4 ≦ k ′ ≦ 0.9
A solid solution lithium-containing transition metal oxide characterized by satisfying The following composition formula (1):
In the composition formula (1), Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, O represents oxygen, and a, b, c, and d have the following relationships:
0.15 ≦ d ≦ 0.35
a + b + c + d = 1.5
1.15 ≦ a + b + c ≦ 1.35
-D + 0.5 <a <-1.6d + 0.81
Satisfy,
It is a solid solution lithium-containing transition metal oxide having a layered structure part and a part that changes to a spinel structure by charging or charging / discharging in a predetermined potential range,
In this case, the spinel structure change of the solid solution lithium-containing transition metal oxide with respect to the spinel structure change ratio when all of the layered Li ₂ MnO ₃ in the solid solution lithium-containing transition metal oxide is changed to the spinel LiMn ₂ O ₄ As the average value when charging / discharging in this order up to the maximum values of k (4.5V, 4.6V, 4.7V and 4.8V (vs lithium metal)) when the ratio is k Calculated k) is 0.15 ≦ d ≦ 0.3, the following relationship:
−d + 0.65 ≦ k ′ ≦ d + 0.55
When 0.3 <d ≦ 0.35, the following relationship is satisfied:
0.4 ≦ k ′ ≦ 0.85
A solid solution lithium-containing transition metal oxide characterized by satisfying   The nonaqueous electrolyte secondary battery using the solid solution lithium containing transition metal oxide of any one of Claims 1-3 as a positive electrode active material.