WO2015019483A1 - Positive electrode active material for nonaqueous secondary batteries, positive electrode for nonaqueous secondary batteries using same, and nonaqueous secondary battery - Google Patents

Abstract

The objective of the present invention is to provide a positive electrode active material which has high discharge capacity and high coulombic efficiency. A positive electrode active material for nonaqueous secondary batteries, which is composed of a lithium composite oxide that is represented by composition formula xLi₂MnO₃-(1-x)LiNiaMnbMcO₂ (wherein M represents at least one element selected from among Co, Ta, Zr, Cr, Ni, Fe, V, Al, Mg, Ti and W, and x, a, b and c respectively represent numbers that satisfy the following relations: 0.2 < x < 0.8; 0.5 <a < 1; 0 < b < 0.5; 0 ≤ c < 0.05; and a + b + c =1). In addition, the ratio of the intensity I(430), which is the intensity of the positive electrode active material at 430^cm-1 as determined by Raman spectroscopy, to the intensity I(600), which is the intensity of the positive electrode active material at 600^cm-1 as determined by Raman spectroscopy, satisfies I(430)/I(600) < 0.3.

Description

Positive electrode active material for non-aqueous secondary battery, positive electrode for non-aqueous secondary battery using the same, non-aqueous secondary battery

The present invention relates to a positive electrode active material for a non-aqueous secondary battery, a positive electrode for a non-aqueous secondary battery using the same, a non-aqueous secondary battery, and a manufacturing method thereof.

As a non-aqueous secondary battery, a lithium ion secondary battery using a non-aqueous electrolyte and using lithium ions for a charge / discharge reaction has been put into practical use. Lithium ion secondary batteries have a higher energy density than nickel metal hydride batteries and the like, and are used, for example, as power sources for portable electronic devices. In recent years, application to medium and large-sized applications such as hybrid vehicles, electric vehicles, stationary uninterruptible power supplies, and power leveling has been promoted. For example, in an electric vehicle, there is a demand for a longer travel distance, and a further increase in energy density is required. Further, in order to increase the energy density, not only the discharge capacity but also the improvement of the coulomb efficiency and the initial charge / discharge efficiency are required.

Currently, a layered oxide positive electrode active material of LiCoO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ is used as the positive electrode active material. The discharge capacity is 150 to 180 Ah / kg, and further higher capacity is required.

In recent years, an increase in capacity by enriching Li has been proposed, and layered solid solutions have attracted attention. For example, in Patent Document 1, the composition ratio of Li, Co, Ni, and Mn is Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2 )} An active material for a lithium secondary battery containing a solid solution of a lithium transition metal composite oxide satisfying _y has been proposed.

Patent Document 2 _discloses I (635) and I (605), which are represented by the chemical formula Li _1.2 Mn _0.54 Ni _0.13 Co _0.13 O ₂ and have respective intensities of 635 ^{cm −1} and 605 ^{cm −1} in Raman spectroscopic measurement. ), The discharge capacity and the charge / discharge efficiency are improved when 0.6 <I (635) / I (605) <1.5.

JP2011-066000A JP2011-096626A

However, in order to further improve battery performance, it is desired to improve the discharge capacity and Coulomb efficiency of the positive electrode active material made of the layered solid solution described in Patent Documents 1 and 2.

The present invention has been made in view of the above points, and the object thereof is a positive electrode active material for a non-aqueous secondary battery having a larger discharge capacity and a high Coulomb efficiency or initial charge / discharge efficiency, and It is to obtain a non-aqueous secondary battery.

In order to solve the above problems, the composition formula: xLi ₂ MnO ₃ — (1-x) LiNiaMnbMcO ₂ [M is at least one of Co, Ta, Zr, Cr, Ni, Fe, V, Al, Mg, Ti, and W. Wherein x, a, b and c are in the following relationship: 0.2 <x <0.8, 0.5 <a <1, 0 <b <0.5, 0 ≦ c <0. 05, a number satisfying a + b + c = 1], and I (430) and I (1) which are intensities of 430 ^{cm −1} and 600 ^{cm −1} in Raman spectroscopic measurement, respectively. 600), I (430) / I (600) <0.3.

According to the present invention, a positive electrode active material for a non-aqueous secondary battery having a large discharge capacity and high coulomb efficiency is provided. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

It is sectional drawing which shows the structure of a lithium ion secondary battery typically.

Hereinafter, the present invention will be described in detail based on embodiments.
(Positive electrode active material)
In order to improve the performance of the non-aqueous secondary battery, it is necessary to further improve the energy density, the coulomb efficiency, and the cycle characteristics of the low-cost positive electrode active material.
The positive electrode active material for a non-aqueous secondary battery of the present invention that achieves high energy density can be expressed as a solid solution of Li ₂ MnO ₃ , LiNiO ₂ , and LiMnO ₂ . Note that a simple mixture of Li ₂ MnO ₃ powder, LiNiO ₂ powder, and LiMnO ₂ powder is clearly distinguished from a solid solution. Specifically, composition formula: xLi ₂ MnO ₃ — (1-x) LiNiaMnbMcO ₂ [M is Co, Ta, Zr, Cr, Ni, Fe, V, Al, Mg, Ti, W, etc. , X, a, b and c are as follows: 0.2 <x <0.8, 0.5 <a <1, 0 <b <0.5, 0 ≦ c <0.05, a + b + c = 1 It is a number satisfying]. X in the composition formula represents the ratio of Li ₂ MnO ₃ in xLi ₂ MnO ₃ — (1-x) LiNiaMnbMcO ₂ . When x is 0.2 or less, a high capacity cannot be obtained. On the other hand, when x is 0.8 or more, the proportion of electrochemically inactive Li ₂ MnO ₃ increases, so that the resistance of the positive electrode active material increases and the capacity decreases.

A in the composition formula indicates the content ratio (atomic weight ratio) of Ni in the positive electrode active material. When a is 0.5 or less, the content ratio of Ni mainly contributing to the charge / discharge reaction is decreased, and the capacity is decreased. In the composition formula, b represents the content ratio (atomic weight ratio) of Mn in the positive electrode active material. When b is 0.5 or more, the content ratio of Ni mainly contributing to the charge / discharge reaction is decreased, and the capacity is decreased. In addition, even if it contains element M other than Li, Mn, Ni, and O, the composition ratio of Li, Mn, Ni, and O may be in the above range. The composition ratio of M is preferably 5 mol% or less in the proportion of the entire transition metal.

The above composition contains Li, Ni, and Mn as main components and contains almost no Co. Since Co is expensive, the positive electrode active material in the present embodiment has an advantage of low cost in addition to high energy density. Moreover, decomposition of the electrolytic solution and suppression of gas generation are possible, and cycle characteristics are improved.

In the present invention, the intensities of the peak of 430 ^{cm −1} attributed to Li ₂ MnO ₃ and the peak of 600 ^{cm −1} attributed to layered LiMO ₂ in Raman spectroscopy are I (430) and I ( 600) (I (430) / I (600)) is less than 0.3. With this feature, an effect of improving the coulomb efficiency can be obtained. I (430) / I (600) is a value that changes by controlling the surface state of the positive electrode active material, and the Coulomb efficiency is improved by setting the above range.

Examples of the surface treatment method include sodium sulfate treatment, ammonium sulfate treatment, aluminum nitrate treatment, boric acid treatment, ammonium vanadate treatment, ammonium fluoride treatment, and mixed treatment thereof.

Furthermore, as a ratio of I (660) and I (600), which are intensities of 660 ^{cm −1} and 600 ^{cm −1} in Raman spectroscopic measurement, I (660) / I (600) is smaller than 0.35. preferable. I (660) / I (600) also changes depending on the surface state of the positive electrode active material, and the cycle characteristics are improved within the above range.

Therefore, the above configuration having these characteristics is preferable because it can provide a positive electrode active material for a non-aqueous secondary battery that has high energy density, high coulomb efficiency, high cycle characteristics, and low cost.

In order to further increase the energy density, x, a, and b in the above composition formula are 0.4 ≦ x ≦ 0.6, 0.525 ≦ a ≦ 0.75, 0.25 ≦ b ≦ 0.475, A number satisfying 0 ≦ c <0.05 and a + b + c = 1 is preferable. In particular, it is more preferable that the number satisfies 0.4 ≦ x ≦ 0.6, 0.525 ≦ a ≦ 0.7, 0.3 ≦ b ≦ 0.475, and a + b + c = 1, and 0.45 ≦ x. ≦ 0.55, 0.525 ≦ a ≦ 0.7, 0.3 ≦ b ≦ 0.475, and a number satisfying a + b + c = 1 are further preferable, and 0.45 ≦ x ≦ 0.55, 0. A number satisfying 6 ≦ a ≦ 0.65, 0.35 ≦ b ≦ 0.4, and a + b = 1 is particularly preferable.

(Positive electrode active material manufacturing method)
The method for producing the positive electrode active material according to the present invention is not particularly limited, and various methods such as a coprecipitation method and a solid phase method can be employed.

For pulverization and mixing of raw materials, for example, a dry ball mill, a dry bead mill, a dry planetary ball mill, a dry attritor, a dry jet mill, a wet ball mill, a wet bead mill, a wet planetary ball mill, a wet attritor, and a wet jet mill are used. be able to.

Examples of the compound containing Li include lithium acetate, lithium nitrate, lithium carbonate, and lithium hydroxide. Examples of the Ni-containing compound include nickel acetate, nickel nitrate, nickel carbonate, nickel sulfate, and nickel hydroxide. Examples of the compound containing Mn include manganese acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide, and the like.
The composition of the positive electrode active material can be determined by elemental analysis such as inductively coupled plasma (ICP).

The method for controlling the surface state of the positive electrode active material is as follows. A predetermined amount of the starting nitrate, acetate, sulfate, and ammonium salt is dissolved in water or an organic solvent. This solution was mixed with the positive electrode active material, and the solvent was evaporated. The solvent is preferably evaporated by heating and stirring or spray drying. Finally, the obtained powder is heat-treated at 200 ° C. or higher and 600 ° C. or lower, preferably 300 ° C. or higher and 500 ° C. or lower. The heating time is 1 hour or more and 20 hours or less, preferably 3 hours or more and 8 hours or less. The compound dissolved in water or an organic solvent may be an inorganic compound or a compound containing a metal element selected from the group of Na, Li, B, Al, Si, P, and V.

(Positive electrode)
A positive electrode for a non-aqueous secondary battery according to the present invention includes the above positive electrode active material. By using the positive electrode active material for the positive electrode, energy density can be improved, coulombic efficiency can be improved, cycle characteristics can be improved, and cost can be reduced.

(Non-aqueous secondary battery)
A nonaqueous secondary battery according to the present invention includes the positive electrode described above. By using it for the positive electrode, a non-aqueous secondary battery with low resistance (high output) can be obtained. The non-aqueous secondary battery according to the present invention can be preferably used for, for example, an electric vehicle.
The non-aqueous secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator, an electrolytic solution, an electrolyte, and the like.

The negative electrode active material is not particularly limited as long as it is a material that can occlude and release lithium ions. A material generally used in non-aqueous secondary batteries can be used as the negative electrode active material. For example, graphite, silica, lithium alloy, silicon alloy, tin alloy, aluminum alloy and the like can be exemplified.

As the separator, those generally used in non-aqueous secondary batteries can be used. Examples thereof include polyolefin microporous films and nonwoven fabrics such as polypropylene, polyethylene, and a copolymer of propylene and ethylene.

As the electrolytic solution and the electrolyte, those generally used in non-aqueous secondary batteries can be used. For example, diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, methyl acetate, ethyl methyl carbonate, methyl propyl carbonate, dimethoxyethane and the like can be exemplified as the electrolytic solution. Further, as the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN Examples thereof include (CF ₃ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ .

An embodiment of the structure of a non-aqueous secondary battery according to the present invention will be described with reference to FIG. The lithium ion secondary battery 1 includes an electrode group having a positive electrode 2 with a positive electrode active material applied to both sides of a current collector, a negative electrode 3 with a negative electrode active material applied to both sides of the current collector, and a separator 4. The positive electrode 2 and the negative electrode 3 are wound through a separator 4 to form a wound electrode group. This wound body is inserted into the battery can 5.

The negative electrode 3 is electrically connected to the battery can 5 via the negative electrode lead piece 7. A sealing lid 8 is attached to the battery can 5 via a packing 9. The positive electrode 2 is electrically connected to the sealing lid 8 through the positive electrode lead piece 6. The wound body is insulated by the insulating plate 10.
The electrode group may not be the wound body shown in FIG. 1, but may be a laminated body in which the positive electrode 2 and the negative electrode 3 are laminated via the separator 4.

Hereinafter, the present invention will be described in more detail using examples and comparative examples, but the technical scope of the present invention is not limited thereto.

Lithium carbonate, manganese carbonate, and nickel carbonate were added to a zirconia pot, acetone was further added, and the mixture was pulverized and mixed without dissolution using a planetary ball mill apparatus. The obtained slurry was dried to obtain a raw material powder. This raw material powder was calcined in the atmosphere at 500 ° C. for 12 hours to obtain a lithium transition metal oxide. The obtained lithium transition metal oxide was added to a zirconia pot, further added with acetone, and pulverized and mixed without dissolution using a planetary ball mill apparatus. The obtained slurry was dried and then fired in the atmosphere at 1000 ° C. for 12 hours to produce the target positive electrode active material. The composition of the positive electrode active material was 0.5Li ₂ MnO ₃ -0.5LiNi _0.625 Mn _0.375 O ₂ .

(Examples 1 to 4)
Four types of samples prepared by adding 5, 7.5, 10, and 15% by mass of sodium sulfate to the above positive electrode active material 0.5Li ₂ MnO ₃ -0.5LiNi _0.625 Mn _0.375 O ₂ and mixing them at 300 ° C. After calcination for a period of time, it was washed with water to produce four active materials of Examples 1 to 4.

(Comparative Example 1)
The positive electrode active material 0.5Li ₂ MnO ₃ -0.5LiNi _0.625 Mn _0.375 O ₂ was used as the active material of Comparative Example 1 without performing ammonium sulfate treatment.

(Raman spectroscopy measurement)
For the five types of active materials shown in Examples 1 to 4 and Comparative Example 1, peak intensity ratios of 430 ^cm-1 , 600 ^cm-1 , and 660 ^cm-1 were determined by Raman spectroscopy.

(Production of prototype battery)
In each of the examples and comparative examples, positive electrodes were prepared using the five types of positive electrode active materials prepared as described above, and five types of prototype batteries were manufactured. The positive electrode active material, the conductive additive, and the binder were weighed so as to have a weight ratio of 85: 10: 5 and mixed uniformly to prepare a positive electrode slurry. The positive electrode slurry was applied on an aluminum current collector foil having a thickness of 15 μm, dried at 120 ° C., and compression-molded so as to have an electrode density of 2.0 g / cm ³ with a press to obtain an electrode plate. Thereafter, the electrode plate was punched into a disk shape having a diameter of 15 mm to produce a positive electrode.

The negative electrode was produced using metallic lithium. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 2 was used.

(Battery characteristics evaluation)
In each example and comparative example, a charge / discharge test was performed on the five types of prototype batteries produced as described above. The prototype battery was subjected to a charge / discharge test with a current equivalent to 0.05C and an upper limit voltage of 4.6V, and a discharge equivalent to a current equivalent to 0.05C and a lower limit voltage of 2.5V. The discharge capacity obtained in this test is the 1st discharge capacity, the Coulomb efficiency which is the ratio of the discharge capacity to the charge capacity (initial discharge capacity / initial charge capacity), and the charge / discharge cycle test equivalent to 1C. The capacity maintenance rate was evaluated.

Table 1 summarizes the Raman spectroscopic measurement results (I ₄₃₀ / I ₆₀₀ , I ₆₆₀ / I ₆₀₀ ), 1 ^st discharge capacity, Coulomb efficiency (%), and capacity retention rate at the 60th cycle for five positive electrode active materials. Indicates

As shown in Table 1, by setting I (430) / I (600) <0.3, the discharge capacity exceeded 250 Ah / kg, the coulomb efficiency exceeded 80%, and good performance was obtained. . This is a peak attributed to I (600) attributed to layered LiMO ₂ and I (430) attributed to Li ₂ MnO ₃ . Here, the increase in the initial discharge capacity or the decrease in the initial charge capacity contributes to the increase in coulomb efficiency. Li ₂ MnO ₃ has a high resistance, and it is easy to release oxygen from the surface during the first charge, and the irreversible capacity It is considered that the 1 ^st discharge capacity and Coulomb efficiency have been improved by removing Li ₂ MnO ₃ from the surface, that is, by lowering I (430) / I (600) because it is a substance that tends to increase. .

Further, as shown in Table 1, the capacity maintenance rate can be increased by setting I (660) / I (600) <0.35. This, I (660) is because the peak attributable to the Li ₄ Mn ₅ O _12, it is considered that the cycle characteristic is deteriorated by that there is a certain level of Li ₄ Mn ₅ O ₁₂ on the surface.
It should be noted that I (600) is a layered structure and I (660) is a peak due to the spinel structure, and it is presumed that there is no direct correlation between the composition and the value of I (660) / I (600). Even when the composition range is changed, it is considered that there is a certain effect within the above numerical range.

As described above, composition formula: xLi ₂ MnO ₃ — (1-x) LiNiaMnbMcO ₂ [M is Co, Ta, Zr, Cr, Ni, Fe, V, Al, Mg, Ti, W, etc. x, a, b and c are the following relationships: 0.2 <x <0.8, 0.5 <a <1, 0 <b <0.5, 0 ≦ c <0.05, a + b + c = 1. In the layered solid solution represented by the following formula, the irreversible capacity was reduced by reducing the ratio of Li ₂ MnO _{3 in} the surface layer portion, and the effects of improving the initial discharge capacity and Coulomb efficiency were obtained. Furthermore, it is preferable to reduce the ratio of Li ₄ Mn ₅ O ₁₂ because an effect of improving cycle characteristics is obtained.

As described above, composition formula: xLi ₂ MnO ₃ — (1-x) LiNiaMnbMcO ₂ [M is Co, Ta, Zr, Cr, Ni, Fe, V, Al, Mg, Ti, W, etc., x, a, b and c are the following relationships: 0.2 <x <0.8, 0.5 <a <1, 0 <b <0.5, 0 ≦ c <0.05, a + b + c = 1. The ratio of I (430) and I (600), which are the respective intensities of 430 ^{cm −1} and 600 ^{cm −1} in the Raman spectroscopic measurement, By setting I (430) / I (600) <0.3, a positive electrode active material with improved discharge capacity and coulomb efficiency is provided.

Furthermore, by setting I (660) / I (600) <0.35 as the ratio of I (660) and I (600), which are intensities of 660 ^cm-1 and 600 ^cm-1 in Raman spectroscopy, Provided is a positive electrode active material that also achieves improved cycle characteristics.

The positive electrode active material of the present invention can be used as a positive electrode by being slurried with various binders and conductive materials that are disclosed, and using this positive electrode, a negative electrode such as graphite or Si, and a non-aqueous electrolyte. When used as a battery, a lithium ion battery capable of increasing energy density and improving cycle characteristics can be provided.

1 ·· Lithium ion secondary battery 2 ·· Positive electrode 3 ·· Negative electrode 4 ·· Separator 5 ·· Battery can 6 ·· Positive lead piece 7 ·· Negative lead piece 8 ··· Sealing lid 9 .... Packing, 10 .... Insulating plate

Claims (5)

1. Composition formula: xLi ₂ MnO ₃ — (1-x) LiNiaMnbMcO ₂ [M is at least one of Co, Ta, Zr, Cr, Ni, Fe, V, Al, Mg, Ti, and W, where x , A, b and c satisfy the following relationships: 0.2 <x <0.8, 0.5 <a <1, 0 <b <0.5, 0 ≦ c <0.05, a + b + c = 1 The ratio of I (430) and I (600), which are the respective intensities of 430 ^{cm −1} and 600 ^{cm −1} in Raman spectroscopic measurement. A positive electrode active material for a non-aqueous secondary battery, wherein I (430) / I (600) <0.3.
2. The positive electrode active material for a non-aqueous secondary battery according to claim 1,
   The ratio of I (660) and I (600), which are intensities of 660 ^cm-1 and 600 ^cm-1 in Raman spectroscopic measurement, is I (660) / I (600) <0.35. Positive electrode active material for non-aqueous secondary batteries.
3. A positive electrode active material for a non-aqueous secondary battery according to claim 1 or 2,
   A positive electrode active material for a non-aqueous secondary battery, wherein 0.45 ≦ x ≦ 0.55, 0.6 ≦ a ≦ 0.65, 0.35 ≦ b ≦ 0.4, and a + b = 1 are satisfied.
4. A positive electrode for a non-aqueous secondary battery comprising the positive electrode active material for a non-aqueous secondary battery according to any one of claims 1 to 3.
5. A non-aqueous secondary battery comprising the positive electrode active material for a non-aqueous secondary battery according to any one of claims 1 to 3.

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