JP5412298B2 - Positive electrode material for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to a positive electrode material for a lithium ion secondary battery and a lithium ion secondary battery that have a high capacity, high output, and high safety.

  In order to adopt a lithium ion secondary battery as a plug-in hybrid vehicle battery, it is necessary to reduce costs, reduce volume, reduce weight, and increase output while maintaining high safety. The positive electrode material is required to have high capacity, high output, and high safety.

  Patent Document 1 describes that two or more types of lithium-containing compounds having different heat generation start temperatures are included, and at least a material having a heat generation start temperature of 300 ° C. or higher is included.

  Patent Document 2 discloses a lithium-containing transition metal compound prepared using a lithium compound, one or more transition metal compounds containing Mn, Ni, and Co, and an additive that suppresses grain growth and sintering during firing. A positive electrode active material for a lithium secondary battery is described in which A is mixed with Li and a lithium-containing transition metal composite oxide powder B having a layered structure and containing Ni and Co as transition metals. .

Patent Document 3 includes a lithium transition metal composite oxide A in which LiCoO ₂ contains at least both Zr and Mg, a layered structure, and contains at least both Mn and Ni as transition metals, and , A positive electrode material in which a lithium transition metal composite oxide B containing Mo is mixed is described.

JP 2007-048744 A JP 2009-032647 A JP 2006-164934 A

  Conventional positive electrode materials cannot provide such a high capacity as required for plug-in hybrid vehicle batteries.

  In addition, since the conventional positive electrode material cannot use the reduction of the amount of deoxygenated from the positive electrode material when the battery is heated and the heat dissipation effect of the battery, the positive electrode material having a high Ni content is used. It is not possible to solve the safety problem.

  As described above, the conventional technology cannot achieve the high capacity, high output, and high safety required for the battery for plug-in hybrid vehicles.

  The present invention provides a positive electrode material for a lithium ion secondary battery that can achieve the high capacity, high output, and high safety required for a battery for a plug-in hybrid vehicle.

  In order to adopt a lithium ion secondary battery for a plug-in hybrid vehicle battery, it is required to have a high capacity, a high output and a high safety.

  In a lithium ion secondary battery, these characteristics are closely related to the properties of the positive electrode material.

In the layered positive electrode material represented by the composition formula LiMO ₂ (M: transition metal), it is necessary to increase the Ni content in the transition metal layer in order to obtain a high capacity.

  However, the positive electrode material with high Ni content has low structural stability during charging, and when the temperature of the battery rises due to an internal short circuit or the like, the oxygen released from the positive electrode material and the electrolyte solution are relatively low when the battery temperature rises. There is a risk that the battery will ignite and explode because it reacts and a large exothermic reaction takes place.

Therefore, the positive electrode material for a lithium ion secondary battery of the present invention is
Composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂
(0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3, 0.05 ≦ c1 ≦ 0.3, a1 + b1 + c1 = 1.0) A first positive electrode active material,
Composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d2 O ₂
(0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 <0.25, 0.05 ≦ c2 <0.25, M = Al, Mg, 0 <d2 ≦ 0.06, a2 + b2 + c2 + d2 = 1.0),
Composition formula Li _x3 Ni _a3 Mn _b3 Co _c3 M _d3 O ₂
(0.2 ≦ x3 ≦ 1.2, 0.7 ≦ a3 ≦ 0.9, 0.05 ≦ b3 <0.25, 0.05 ≦ c3 <0.25, M = Mo, W, 0 <d3 ≦ 0.06, a3 + b3 + c3 + d3 = 1.0), a third positive electrode active material,
It is characterized by including.

  The average secondary particle size of the first and second positive electrode active materials is preferably larger than the average secondary particle size of the third positive electrode active material.

  Moreover, it is preferable that the average secondary particle diameter of a 3rd positive electrode active material is 1/2 or less of the average secondary particle diameter of a 1st positive electrode active material.

  Further, the Ni content a1 of the first positive electrode active material is 0.7 ≦ a1 ≦ 0.9, and the Ni contents a2 and a3 of the second and third positive electrode active materials are 0.8 ≦ a2 ≦ 0. It is preferable that 0.9, 0.8 ≦ a3 ≦ 0.9.

  Moreover, it is preferable that the ratio which occupies for all the positive electrode active materials of the 1st, 2nd, 3rd positive electrode active material contained in the positive electrode material for lithium ion secondary batteries is less than 50% in a mass percentage, respectively.

  Furthermore, these positive electrode materials for lithium ion secondary batteries are lithium ion secondary batteries in which a positive electrode capable of occluding and releasing lithium and a negative electrode capable of occluding and releasing lithium are formed via a nonaqueous electrolyte and a separator. It can be used as a positive electrode material for a positive electrode.

  Thereby, this invention can provide the positive electrode material for lithium ion secondary batteries which can achieve the high capacity | capacitance, high output, and high safety which are requested | required of the battery for plug-in hybrid vehicles.

The figure which shows the DSC measurement result at the time of heating up both the positive electrode and electrolyte solution of a charge state. Sectional drawing which shows a lithium ion secondary battery.

  The features of this embodiment will be described below.

The positive electrode material for a lithium ion secondary battery of this embodiment is
Composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂
(0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3, 0.05 ≦ c1 ≦ 0.3, a1 + b1 + c1 = 1.0) A first positive electrode active material,
Composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d2 O ₂
(0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 <0.25, 0.05 ≦ c2 <0.25, M = Al, Mg, 0 <d2 ≦ 0.06, a2 + b2 + c2 + d2 = 1.0),
Composition formula Li _x3 Ni _a3 Mn _b3 Co _c3 M _d3 O ₂
(0.2 ≦ x3 ≦ 1.2, 0.7 ≦ a3 ≦ 0.9, 0.05 ≦ b3 <0.25, 0.05 ≦ c3 <0.25, M = Mo, W, 0 <d3 ≦ 0.06, a3 + b3 + c3 + d3 = 1.0), a third positive electrode active material,
It is characterized by including.

  A positive electrode active material having a high Ni content can provide a high capacity, but has a drawback of low thermal stability during charging.

  Therefore, a fourth metal element was added to the positive electrode active material having a high Ni content, and a material having a higher exothermic temperature region and a material having a lower temperature were mixed.

  Compared with a single high Ni-containing positive electrode active material, this mixed material has a wider heat generation temperature range and can make maximum use of the heat dissipation of the battery, which can lead to ignition and rupture when the battery is heated. Can be reduced.

  In addition, as the fourth metal element, a high Ni content positive electrode active material to which Mo and W were added was used as the material in which the heat generation temperature range according to the present embodiment was lowered.

  This material has the effect that the amount of oxygen released when the temperature is raised after desorption of lithium can be reduced to half or less, as well as the effect of changing the exothermic temperature region.

  Therefore, this material has an effect of expanding the heat generation temperature range of the positive electrode and the electrolytic solution that occurs when the temperature of the battery is raised, making maximum use of the heat dissipation of the battery, and reducing the total heat generation.

  Thus, by using this material, it is possible to provide a positive electrode material for a lithium ion secondary battery and a lithium ion secondary battery that are less likely to cause ignition when heated.

Furthermore, the average secondary particle size of the third positive electrode active material is smaller than the average secondary particle size of the first and second positive electrode active materials.

  Since the third positive electrode active material contains Mo and W, the resistance becomes high. Therefore, in order to adopt as a battery for a plug-in hybrid vehicle, it is necessary to reduce the particle size and the diffusion distance of lithium.

  Further, the abundance ratio of each positive electrode active material contained in the positive electrode material is assumed to be lower than 50% by mass percentage. If it is 50% or more, the influence of the exothermic reaction that occurs due to the positive electrode active material increases when the temperature is raised, so that there is a problem in safety.

  Next, the lithium ion secondary battery of the present embodiment is a lithium ion secondary battery in which a positive electrode capable of inserting and extracting lithium and a negative electrode capable of inserting and extracting lithium are formed via a nonaqueous electrolyte and a separator. The positive electrode has a positive electrode active material, and the positive electrode active material includes the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

Moreover, it is preferable that the average secondary particle diameter of a 3rd positive electrode active material is 1/2 or less of the average secondary particle diameter of a 1st positive electrode active material. This is because the effect of reducing the particle size appears more remarkably and the filling rate of the positive electrode material is also improved.

  Further, the Ni content a1 of the first positive electrode active material is 0.7 ≦ a1 ≦ 0.9, and the Ni contents a2 and a3 of the second and third positive electrode active materials are 0.8 ≦ a2 ≦ 0. It is preferable that 0.9, 0.8 ≦ a3 ≦ 0.9. By increasing the Ni content in the transition metal layer, a high capacity positive electrode material can be provided.

  Here, one of the examples for implementing this embodiment is shown below.

In the embodiment of the present invention, as the positive electrode material,
Composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂
(0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3, 0.05 ≦ c1 ≦ 0.3, a1 + b1 + c1 = 1.0) A first positive electrode active material,
Composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d2 O ₂
(0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 <0.25, 0.05 ≦ c2 <0.25, M = Al, Mg, 0 <d2 ≦ 0.06, a2 + b2 + c2 + d2 = 1.0),
Composition formula Li _x3 Ni _a3 Mn _b3 Co _c3 M _d3 O ₂
(0.2 ≦ x3 ≦ 1.2, 0.7 ≦ a3 ≦ 0.9, 0.05 ≦ b3 <0.25, 0.05 ≦ c3 <0.25, M = Mo, W, 0 <d3 ≦ 0.06, a3 + b3 + c3 + d3 = 1.0), a third positive electrode active material,
A mixed material is used.

  Here, the amount of Li in the first positive electrode active material is 0.2 ≦ x1 ≦ 1.2, and when x1 <0.2, the amount of Li present in the Li layer in the charged state is This is because the layered crystal structure cannot be maintained. In addition, when 1.2 <x1, the amount of transition metal in the composite oxide decreases, and the capacity decreases.

  The amount of Ni is 0.6 ≦ a1 ≦ 0.9. This is because the content of Ni mainly contributing to the charge / discharge reaction decreases and the capacity decreases when a1 <0.6. .

The amount of Mn is 0.05 ≦ b1 ≦ 0.3. However, when b1 <0.05, the structure in the charged state becomes unstable, and the oxygen release temperature from the positive electrode decreases. Further, when b1> 0.3, the content of Ni mainly contributing to the charge / discharge reaction is decreased, and the capacity is decreased.

The amount of Co is 0.05 ≦ c1 ≦ 0.3. However, when c1 <0.05, the structure in the charged state becomes unstable, and the volume change of the positive electrode active material during charge / discharge increases. Also,
When c1> 0.3, the content of Ni mainly contributing to the charge / discharge reaction is reduced, and the capacity is reduced.

  Here, the amount of Li in the second and third positive electrode active materials is 0.2 ≦ x2 ≦ 1.2, 0.2 ≦ x3 ≦ 1.2, which is x2 <0.2, x3. <0.2 is because the amount of Li present in the Li layer in the charged state is small, and the layered crystal structure cannot be maintained. Further, when 1.2 <x2 and 1.2 <x3, the amount of transition metal in the composite oxide is decreased, and the capacity is decreased.

  The amount of Ni is 0.7 ≦ a2 ≦ 0.9, 0.7 ≦ a3 ≦ 0.9, and this mainly contributes to the charge / discharge reaction when a2 <0.7 and a3 <0.7. This is because the Ni content is reduced and the capacity is reduced.

  The amount of Mn is 0.05 ≦ b2 <0.25, 0.05 ≦ b3 <0.25, but this is unstable in the charged state when b2 <0.05 and b3 <0.05. As a result, the oxygen release temperature from the positive electrode decreases. In addition, when b2 ≧ 0.25 and b3 ≧ 0.25, the content of Ni mainly contributing to the charge / discharge reaction is decreased, and the capacity is decreased.

  The amount of Co is 0.05 ≦ c2 <0.25, 0.05 ≦ c3 <0.25, which is unstable in the charged state when c2 <0.05 and c3 <0.05. Thus, the volume change of the positive electrode active material during charge / discharge increases. Further, when c2 ≧ 0.25 and c3 ≧ 0.25, the content of Ni mainly contributing to the charge / discharge reaction is decreased, and the capacity is decreased.

  The amount of M is 0 <d2 ≦ 0.06, 0 <d3 ≦ 0.06, and when d2> 0.06 and d3> 0.06, the content of Ni mainly contributes to the charge / discharge reaction. This is because the amount decreases and the capacity decreases.

(Preparation of positive electrode active material)
Nickel oxide, manganese dioxide, cobalt oxide, (aluminum oxide, magnesium oxide, molybdenum oxide, tungsten oxide) were used as raw materials, weighed so as to have a predetermined atomic ratio, and then pure water was added to form a slurry.

  The slurry was pulverized with a zirconia bead mill until the average particle size became 0.2 μm.

  A polyvinyl alcohol (PVA) solution was added to this slurry in an amount of 1 wt.% In terms of the solid content ratio, further mixed for 1 hour, and granulated and dried by a spray dryer.

  Lithium hydroxide and lithium carbonate were added to the granulated particles so that the Li: (NiMnCoM) ratio was 1.05: 1.

  Next, this powder was fired at 850 ° C. for 10 hours to have a layered crystal, and then pulverized to obtain a positive electrode active material 1-1.

  Further, coarse particles having a particle size of 30 μm or more were removed by classification, and then used for electrode production.

  Further, the method for producing the positive electrode active material in this example is not limited to the above method, and other methods such as a coprecipitation method may be used.

  The composition ratios of the transition metals of the synthesized first positive electrode active material, second positive electrode active material, and third positive electrode active material are shown in Table 1, Table 2, and Table 3, respectively.

  In addition, the composition shown in Table 1, Table 2, and Table 3 shows things other than Li. Li shows approximately 1.05.

  The positive electrode active material 1-1 and the carbon-based conductive agent were weighed so as to have a mass ratio of 85: 10.7, and the active material and the conductive agent were combined using mechanofusion.

  Here, each active material and the conductive agent may be combined using a device such as a hybridizer.

  The same operation was performed on the positive electrode active materials 2-1 and 3-1.

  Next, the three types of composite materials were mixed at a mass ratio of 30:40:30.

  By this method, the conductive agent can be highly dispersed on the surface of each active material, and the surface of the particles can be coated with the conductive agent.

  Since the electron conductivity is improved by the coating of the conductive agent, a high capacity is maintained even when a large current is passed when used as a positive electrode material.

  In addition, since a conductive agent exists between the active materials when mixing different active materials, a conductive network is formed between the active materials, which may reduce the proportion of isolated active materials that do not contribute to the charge / discharge reaction. And high capacity can be maintained.

  On the other hand, when the three active materials and the conductive agent are mixed without combining the active material and the conductive agent, the surface of each active material is not coated with the conductive agent, so that the electron conductivity Decreases. Furthermore, the mixed state of each active material and the conductive agent is deteriorated, it becomes difficult to form a conductive network between the active materials, the ratio of the isolated active material is increased, and the capacity is decreased.

  Thereafter, a mixed material of three kinds of active materials and a conductive agent and a binder dissolved in NMP were mixed so that the mixed material and the binder were in a mass ratio of 95.7: 4.3.

The uniformly mixed slurry was applied onto an aluminum current collector foil having a thickness of 20 μm, dried at 120 ° C., and compression-molded with a press so that the electrode density was 2.7 g / cm ³ .

  Thereafter, it was punched into a disk shape having a diameter of 15 mm to produce a positive electrode.

Prototype battery using prepared positive electrode, metallic lithium as negative electrode, non-aqueous electrolyte (1.0 mol / liter LiPF ₆ dissolved in 1: 2 mixed solvent by volume ratio of EC and DMC) Was made.

  Further, in the test battery relating to this example, the conductive agent, binder, negative electrode, electrolytic solution, and electrolyte used are not limited to those described in this example, and for example, the following may be used.

  Examples of the conductive agent include graphite, acetylene black, and carbon black.

  Examples of the binder include polytetrafluoroethylene and a rubber binder.

  Examples of the electrolytic solution include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyl lactone, tetrahydrofuran, and dimethoxyethane.

Examples of the electrolyte include LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

  Tables 4 and 5 below show the mixing ratios of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material.

  Next, the following tests were performed using the prototype battery described above.

(Charge / discharge test)
The charge rate was set to 0.1 C, and the battery was charged at a constant current / constant voltage up to 4.3 V, and then discharged at a constant current up to 2.5 V at 0.1 C.

Example 1,2,4～6,8～10,12～ 17, Comparative Examples 1, 4, 6, in 10 to 11, the initial discharge capacity of Comparative Example 1 described below the value of the initial discharge capacity obtained The values divided by the values are shown in the following Table 6, Table 7, and Table 8 (capacity ratio).

In Examples 3 and 7 , and Comparative Examples 2, 3 , 5 and 7, the values obtained by dividing the obtained initial discharge capacity value by the initial discharge capacity value of Comparative Example 2 described later are shown in Tables 6 and 6 below. 7 and Table 8 show.

(Differential scanning calorimetry)
After charging to 4.3 V at a constant current / constant voltage, the electrode is removed from the test battery, washed with DMC, punched into a disk with a diameter of 3.5 mm, placed in a sample pan, 1 μl (liter) of electrolyte is added, and sealed. did.

  The heat generation behavior when this sample was heated at 5 ° C./min was examined.

In Examples 1, 2, 4 to 6, 8 to 10 , 12 to 17 , and Comparative Examples 1, 4, 6, 10 to 11, the obtained maximum value of heat generation (maximum heat generation value) and value of heat generation amount are described later. The values divided by the initial discharge capacity value of Comparative Example 1 are shown in Table 6, Table 7 and Table 8 (maximum heat generation value ratio and heat generation amount ratio) below.

In Examples 3 and 7 , and Comparative Examples 2, 3 , 5, and 7, the obtained maximum value of heat generation (maximum heat generation value) and the value of the heat generation amount are divided by the initial discharge capacity value of Comparative Example 2 described later. The obtained values are shown in Table 6, Table 7 and Table 8 below.

(DC resistance measurement)
The electrode resistance at room temperature was measured using a test battery.

  Constant current discharge was performed when the open circuit voltage of the test battery was in the range of 3.7 V to 4.4 V, and the voltage at the time of discharge was recorded at intervals of 0.1 seconds.

  Next, the voltage drop at 10 seconds from the open circuit voltage was measured to determine the electrode resistance.

In Examples 1, 2, 4 to 6, 8 to 10 , 12 to 17 and Comparative Examples 1, 4, 6, 10 to 11 , the obtained electrode resistance value is the initial discharge capacity value of Comparative Example 1 described later. The values divided by are shown in Table 6, Table 7 and Table 8 (resistance ratio) below.

In Examples 3 and 7 , and Comparative Examples 2, 3 , 5, and 7, values obtained by dividing the obtained electrode resistance value by the initial discharge capacity value of Comparative Example 2 described later are shown in Tables 6 and 7 below. Table 8 shows.

  Example 2 was the same as Example 1 except that the produced positive electrode active materials 1-2, 2-1, 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 3 was the same as Example 1 except that the produced positive electrode active materials 1-3, 2-1 and 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 4 is the same as Example 1 except that the produced positive electrode active materials 1-1, 2-2, 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 5 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-3, and 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 6 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-5, and 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 7 was the same as Example 1 except that the produced positive electrode active materials 1-2, 2-6, and 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 8 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-2 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 9 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-3 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 10 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-5 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 11 is the same as Example 1 except that the produced positive electrode active materials 1-2, 2-1 and 3-6 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 12 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-1 were mixed at a mass ratio of 20:40:40 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 13 is the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-1 were mixed at a mass ratio of 40:20:40 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 14 is the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-1 were mixed at a mass ratio of 40:40:20 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Example 15 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-8 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[Comparative Example 1]
In Comparative Example 1, a prototype battery was produced in the same manner as in Example 1 except that only the produced positive electrode active material 1-2 was used as the positive electrode active material, and a charge / discharge test, differential scanning calorimetry, and direct current resistance measurement were performed. Went.

[Comparative Example 2]
In Comparative Example 2, a prototype battery was produced in the same manner as in Example 1 except that only the produced positive electrode active material 1-3 was used as the positive electrode active material, and a charge / discharge test, differential scanning calorimetry, and DC resistance measurement were performed. Went.

[Comparative Example 3]
Comparative Example 3 was the same as Example 1 except that the produced positive electrode active materials 1-4, 2-1, 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[Comparative Example 4]
Comparative Example 4 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-4, and 3-1 were mixed and used as a positive electrode active material at a mass ratio of 30:40:30. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[Comparative Example 5]
Comparative Example 5 was the same as Example 1 except that the produced positive electrode active materials 1-2, 2-7, 3-1 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[Comparative Example 6]
Comparative Example 6 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-4 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[Comparative Example 7]
Comparative Example 7 was the same as Example 1 except that the produced positive electrode active materials 1-2, 2-1 and 3-7 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

Example 16
Example 16 is the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-1 were mixed at a mass ratio of 50:20:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[ Example 17 ]
Example 17 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-1 were mixed at a mass ratio of 20:50:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[Comparative Example 10]
Comparative Example 10 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, 3-1 were mixed at a mass ratio of 20:30:50 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

[Comparative Example 11]
Comparative Example 11 was the same as Example 1 except that the produced positive electrode active materials 1-1, 2-1, and 3-9 were mixed at a mass ratio of 30:40:30 and used as the positive electrode active material. Prototype batteries were prepared in the same manner, and charge / discharge tests, differential scanning calorimetry, and DC resistance measurements were performed.

  Examination of the results shown in Table 6 revealed that the discharge capacities in Examples 1, 2, 4 to 6, 8 to 10 were larger than Comparative Example 1.

  Moreover, it became clear that the discharge capacities in Examples 3 and 7 were larger than Comparative Example 2.

  The reason why the discharge capacity shows a large value is considered that the positive electrode material selected in each example has a large amount of Ni present in the transition metal layer.

  In addition, it has been clarified that the maximum heat generation value and the heat generation amount in Examples 1, 2, 4 to 6, 8 to 10 are smaller than those of Comparative Example 1.

  In addition, in Examples 3 and 7, it was revealed that the value was smaller than Comparative Example 2.

  The maximum exothermic value decreased because the mixing ratio of the active materials having the respective compositions was all lower than 50%.

  Moreover, the amount of generated heat is reduced because Mo and W having an effect of reducing the amount of oxygen released from the positive electrode active material when the temperature is raised are added.

  Moreover, although the resistance increased, the rate of increase was 10% or less.

  On the other hand, in Comparative Examples 4 and 6, compared with Comparative Example 1, it was not possible to achieve both capacity increase, maximum heat generation value, and heat generation amount reduction.

  In Comparative Examples 3, 5, and 7, compared with Comparative Example 2, it was impossible to achieve both an increase in capacity, a maximum heat generation value, and a reduction in heat generation.

  In Comparative Example 4, the capacity was reduced because 8% Al was present in the second positive electrode active material.

  In Comparative Example 6, the capacity decreased because 8% of Mo was present in the third positive electrode active material.

  In Comparative Example 3, the capacity was reduced because the Ni content in the first positive electrode active material was as low as 50%.

  In Comparative Example 5, the capacity was reduced because the Ni content in the second positive electrode active material was as low as 60%.

  In Comparative Example 7, the capacity was lowered because the Ni content in the third positive electrode active material was as low as 60%.

Examination of the results shown in Table 7 revealed that the discharge capacities in Examples 12 to 14 , 16 and 17 were larger than Comparative Example 1.

  The reason why the discharge capacity shows a large value is considered that the positive electrode material selected in each example has a large amount of Ni present in the transition metal layer.

  Moreover, it became clear that the maximum heat generation value and the heat generation amount in Examples 12 to 14 are smaller than those of Comparative Example 1.

  The maximum exothermic value decreased because the mixing ratio of the active materials having the respective compositions was all lower than 50%.

  The reason why the calorific value is reduced is that Mo and W having an effect of reducing the amount of oxygen released from the positive electrode active material when the temperature is raised are added.

  Moreover, although the resistance increased, the rate of increase was 10% or less.

On the other hand, in Comparative Example 10 , compared with Comparative Example 1, it was not possible to achieve both an increase in capacity and a reduction in heat generation.

In Examples 16 and 17 , since the mixing ratio of the first and second positive electrode active materials was 50%, the maximum heat generation value increased.

  In Comparative Example 10, since the mixing ratio of the third positive electrode active material was 50%, the discharge capacity was reduced.

  Examination of the results shown in Table 8 revealed that the discharge capacity in Example 15 was larger than that in Comparative Example 1.

  This is presumably because the positive electrode active material selected in Example 15 has a large amount of Ni present in the transition metal layer.

  Further, it was revealed that the maximum heat generation value and the heat generation amount in Example 15 were smaller than those in Comparative Example 1.

  The maximum exothermic value decreased because the mixing ratio of the active materials having the respective compositions was all lower than 50%.

  The reason why the calorific value is reduced is that Mo and W having an effect of reducing the amount of oxygen released from the positive electrode active material when the temperature is raised are added.

  Moreover, although the resistance increased, the rate of increase was 10% or less.

  On the other hand, in Comparative Example 11, compared with Comparative Example 1, it was not possible to achieve both an increase in capacity, a reduction in heat generation, and a suppression of increase in resistance.

  In Comparative Example 11, the resistance increased due to the large secondary particle diameter of the third positive electrode active material having high resistance. Therefore, the resistance increase rate of the mixed positive electrode material was as large as 13.1%.

  FIG. 1 shows a case where both the charged positive electrode and the electrolyte solution are heated in a positive electrode active material made of a single transition metal oxide and a positive electrode active material made of three or more kinds of transition metal oxides. The DSC measurement result of is shown.

  In FIG. 1, when the result 1 of the differential scanning calorimetry of the positive electrode material of Example 1 is compared with the result 2 of the differential scanning calorimetry of the positive electrode material of Comparative Example 1, it occurs when the battery is heated. It can be seen that the heating temperature range of the positive electrode and the electrolyte can be expanded.

  FIG. 2 is a cross-sectional view showing a lithium ion secondary battery.

  The lithium ion secondary battery shown in FIG. 2 has a positive electrode plate 3 coated with a positive electrode material on both sides of a current collector and a negative electrode plate 4 coated with a negative electrode material on both sides of the current collector through a separator 5. These are formed by winding.

  Such a wound body is inserted into the battery can 6. Then, the negative electrode plate 4 is electrically connected to the battery can 6 via the negative electrode lead piece 7.

  Further, the sealing lid 8 is formed on the battery can 6 via the packing 9. Then, the positive electrode plate 3 is electrically connected to the sealing lid portion 8 through the positive electrode lead piece 10.

  The wound body is insulated by the insulating plate 11.

  By using the material shown in this embodiment as the positive electrode material of the lithium ion secondary battery, the lithium ion secondary battery that can achieve the high capacity, high output, and high safety required for the plug-in hybrid vehicle battery. A positive electrode material for a secondary battery can be provided.

  The present invention is particularly promising as a positive electrode material for lithium ion secondary batteries, and can be used for lithium ion secondary batteries for plug-in hybrid vehicles.

1 Results of Differential Scanning Calorimetry of Positive Electrode Material of Example 1 2 Results of Differential Scanning Calorimetry of Positive Electrode Material of Comparative Example 1 3 Positive Electrode Plate 4 Negative Electrode Plate 5 Separator 6 Battery Can 7 Negative Electrode Lead Piece 8 Sealing Lid 9 Packing 10 Positive electrode lead piece 11 Insulating plate

Claims (8)

Composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂
(0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3, 0.05 ≦ c1 ≦ 0.3, a1 + b1 + c1 = 1.0) A first positive electrode active material,
Composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d2 O ₂
(0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 <0.25, 0.05 ≦ c2 <0.25, M = Al, Mg, 0 <d2 ≦ 0.06, a2 + b2 + c2 + d2 = 1.0),
Composition formula Li _x3 Ni _a3 Mn _b3 Co _c3 Md ₃ O ₂
(0.2 ≦ x3 ≦ 1.2, 0.7 ≦ a3 ≦ 0.9, 0.05 ≦ b3 <0.25, 0.05 ≦ c3 <0.25, M = Mo, W, 0 <d3 ≦ 0.06, a3 + b3 + c3 + d3 = 1.0), a third positive electrode active material,
A carbon-based conductive agent;
Including
The first positive electrode active material, the second positive electrode active material, and the third positive electrode active material are each compounded with the carbon-based conductive agent,
The mass ratio of the third positive electrode active material is 40 or less, where 100 is the total mass of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material,
The average secondary particle size of the third positive electrode active material is 7.08 μm or less,
The average secondary particle size of the first positive electrode active material and the second positive electrode active material is larger than the average secondary particle size of the third positive electrode active material,
A positive electrode material for a lithium ion secondary battery. In claim 1,
The average secondary particle size of the third positive electrode active material is 5.98 μm to 6.86 μm.
A positive electrode material for a lithium ion secondary battery. In claim 1,
The average secondary particle size of the first positive electrode active material is 15.3 μm to 16.7 μm,
The average secondary particle size of the second positive electrode active material is 13.2 μm to 13.8 μm.
A positive electrode material for a lithium ion secondary battery. In claim 1,
The mass ratio of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material is R1: R2: R3 (where 20 ≦ R1 ≦ 40, 20 ≦ R2 ≦ 40, 20 ≦ R3 ≦ 40, and R1 + R2 + R3 = 100).
A positive electrode material for a lithium ion secondary battery. In claim 1,
The average secondary particle size of the third positive electrode active material is half or less than the average secondary particle size of the first positive electrode active material.
A positive electrode material for a lithium ion secondary battery. In claim 1,
The Ni content a1 of the first positive electrode active material is 0.7 ≦ a1 ≦ 0.9,
The Ni content a2 of the second positive electrode active material is 0.8 ≦ a2 ≦ 0.9,
The Ni content a3 of the third positive electrode active material is 0.8 ≦ a3 ≦ 0.9.
A positive electrode material for a lithium ion secondary battery. In claim 1,
The ratio of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material contained in the lithium ion secondary battery positive electrode material to all the positive electrode active materials is mass. Less than 50% in percentage,
A positive electrode material for a lithium ion secondary battery. In a lithium ion secondary battery formed by arranging a positive electrode capable of occluding and releasing lithium and a negative electrode capable of occluding and releasing lithium via a nonaqueous electrolyte and a separator,
The said positive electrode has the positive electrode material for lithium ion secondary batteries of Claim 1, The lithium ion secondary battery characterized by the above-mentioned.

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