JP2000200607A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery using a lithium-transition metal compound oxide as a positive-electrode active material, and having small internal resistance and good charging/discharging cycle characteristics. SOLUTION: Two or more kinds of elements (including at least Ti) selected from among Li, Fe, Mn, Ni, Mg, Zn, B, Al, Co, Cr, Si, Ti, Sn, P, V, Sb, Nb, Ta, Mo, and W are substituted for part of a transition element, Co or Ni, contained in lithium cobaltate (LiCoO2) or lithium nickelic oxide (LiNiO2) used as a positive-electrode active material. M is a substitution element, M≠Co or Ni, and Z stands for a substitution quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a secondary battery used as a power source for operating a portable electronic device and a power source for driving a motor such as an electric vehicle or a hybrid electric vehicle. The present invention relates to a lithium secondary battery having a low internal resistance and good charge / discharge cycle characteristics, used as a substance.

[0002]

2. Description of the Related Art In recent years, portable electronic devices such as mobile phones, VTRs, and notebook computers have been rapidly reduced in size and weight. A secondary battery using an organic electrolytic solution obtained by dissolving a carbonaceous material as an anode active material and a Li-ion electrolyte in an organic solvent as an electrolytic solution has been used.

[0003] Such a battery is generally called a lithium secondary battery or a lithium ion battery, and has a large energy density and a cell voltage of about 4V.
Due to its high degree of characteristics, not only the portable electronic device but also a motor of an electric vehicle or a hybrid electric vehicle which is actively spread as a low-emission vehicle due to recent environmental problems. It is also attracting attention as a drive power supply.

In such a lithium secondary battery, its battery capacity and charge / discharge cycle characteristics (hereinafter, referred to as “cycle characteristics”) largely depend on the material characteristics of the positive electrode active material used. Specific examples of the lithium transition element composite oxide used as the positive electrode active material include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O).
₄ ) etc.

[0005] Here, LiCoO ₂ and LiNiO ₂ are
It has features such as a large Li capacity, a simple structure, excellent reversibility, and a two-dimensional layered structure excellent in ion diffusion. However, on the other hand, LiCoO ₂
As for Co, the production area of Co is limited, and the production amount is not so large and it is expensive. Therefore, there is a problem in terms of cost when used for a general-purpose lithium secondary battery.
There is a problem that the output density is small as compared with iMn ₂ O ₄ . Further, with respect to LiNiO _2, it is difficult to synthesize a compound having a stoichiometric composition because the trivalent state of Ni is relatively unstable, and when the amount of desorbed Li increases, Ni becomes 2%. In addition to the transition to the valence state, oxygen is released to form NiO, which not only does not function as a battery, but also causes a risk of battery rupture due to oxygen release.

On the other hand, LiMn ₂ O ₄ is characterized in that the raw material is inexpensive, the output density is high, and the potential is high. However, when LiMn ₂ O ₄ is used as the positive electrode active material, there is a problem that the discharge capacity gradually decreases with repetition of the charge / discharge cycle, and good cycle characteristics cannot be obtained. This is considered to be largely due to the decrease in the positive electrode capacity due to the irreversible change in the crystal structure due to the insertion and removal of Li ⁺ .

As described above, since each of the lithium transition element composite oxides such as LiCoO ₂ has both advantages and disadvantages as a positive electrode active material, it is not necessary to uniformly use any material. It is considered that it is desirable to appropriately select and use a positive electrode active material that can exhibit characteristics suitable for the intended use.

[0008]

[0007] Regardless of the type of the positive electrode active material, it is preferable that the internal resistance of the battery is small in terms of battery characteristics. In reducing this internal resistance, the resistance of the positive electrode active material (electron Reducing the conduction resistance), in other words, improving the electron conductivity,
This is a common problem for all positive electrode active materials. In particular, in the case of a large-capacity lithium secondary battery used as a power source for driving a motor of an electric vehicle or the like, reducing the internal resistance of the battery can obtain a large current output necessary for acceleration, climbing a slope, etc. It is very important to increase discharge efficiency.

Therefore, conventionally, attempts have been made to improve the electronic conductivity by adding conductive fine particles such as acetylene black to the positive electrode active material to reduce the internal resistance of the battery.
This is because the above-mentioned lithium transition element composite oxide is a mixed conductor having both lithium ion conductivity and electron conductivity, but the electron conductivity is not necessarily large.

[0010] However, the addition of acetylene black
There is a problem in that the battery capacity is reduced due to the decrease in the amount of the positive electrode active material. In addition, acetylene black is a kind of carbon and is a semiconductor, and thus it is considered that there is a limit in improving electron conductivity. In addition, acetylene black is bulky and has problems such as difficulty in handling the electrode plate during production. Therefore, the amount of addition is set to an appropriate amount by comparing and considering the positive effect of reducing the internal resistance, the negative effect of lowering the battery capacity, ease of manufacture, and the like.

By the way, when acetylene black is added as described above, since acetylene black is present only on the surface of the positive electrode active material particles, it contributes to improvement in electron conductivity between the positive electrode active material particles. Although,
It does not contribute to improving the electron conductivity inside the positive electrode active material particles. As described above, conventionally, in improving the electron conductivity of the positive electrode active material, only the electron conductivity between the positive electrode active material particles has been focused on, and the diffusion of Li ⁺ and the electron conduction in the positive electrode active material particles during a battery reaction have been focused. The relationship with gender was not an issue.

In other words, the desorption of Li ⁺ from the positive electrode active material particles and the insertion of Li ⁺ into the positive electrode active material particles are caused by the diffusion of Li ^{+ in the} positive electrode active material particles, and the When the electron conductivity in the positive electrode active material particles is small, diffusion of Li ⁺ is difficult to occur, and the desorption / insertion rate of Li ⁺ , that is, In addition, it has not been considered that the reaction speed of the battery is slowed and the internal resistance is increased.

The inventors pay attention to this point, and reduce the resistance of the positive electrode active material itself by improving the electron conductivity of the positive electrode active material itself so that Li ⁺ diffuses well in the positive electrode active material. At the same time, when the battery was assembled without increasing the amount of acetylene black added, intensive studies were conducted to reduce the internal resistance of the battery, and arrived at the present invention.

[0014]

That is, according to the present invention, a part of the transition element Co or Ni in lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ) is converted into Li, Fe, Mn, Ni, Mg, Z
n, B, Al, Co, Cr, Si, Ti, Sn, P,
V, Sb, Nb, Ta, Mo, 2 or more elements selected from among W (provided that at least Ti) becomes replaced by LiM _Z Co _1-Z O ₂ or LiM _Z Ni _1-Z There is provided a lithium secondary battery using O ₂ (where M is a substitution element and M ≠ Co or Ni, and Z represents a substitution amount) as a positive electrode active material.

In the present invention, as the substitution element M,
Among the above-mentioned elements, Li, Fe, Mn, M
g, Zn, Si, Ti, Sn, P, V, Sb, Nb, T
It is preferable to select two or more elements selected from a, Mo, and W. Substituted a part of LiM _Z Co _1-Z O ₂ during transition elements Co containing two or more substitution elements M thus obtained, further B, Al, at least one element selected from among Cr to it, _{also, LiM Z Ni 1-Z O} 2 in the transition element Ni containing two or more substitution elements M
Is preferably further substituted with at least one or more elements selected from Al, Co, and Cr. In lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ), the ratio Z / X between the substitution amount Z of the substitution element M and the original amount X of the transition element Co or Ni is 0.005. It is preferable to satisfy the condition of ≦ Z / X ≦ 0.3.

In the present invention, the average valence of the substitution element M for partially substituting cobalt or nickel in lithium cobaltate or lithium nickelate is preferably 3. However, the case where all the substitution elements M have a trivalent ionic valence is excluded. Replacement amount Z here
Is preferably in the range of 0.005 ≦ Z ≦ 0.3, and more preferably satisfying the condition of 0.05 ≦ Z ≦ 0.3.

[0017] LiM _Z Co _1-Z O ₂ or LiM _Z Ni _1-Z O ₂ for use in a lithium secondary battery of the present invention described above,
A mixture of the salts and / or oxides of the respective elements adjusted to a predetermined ratio is mixed in an oxidizing atmosphere at a temperature of 600 ° C. to 1000 ° C. for 5 minutes.
It is synthesized by firing over a period of time to 50 hours. At this time, a method in which the firing is performed in two or more times and the firing temperature in the next step is higher than the firing temperature in the previous step to perform the synthesis is also suitably adopted. When firing is performed a plurality of times, the firing conditions for the final firing are as follows:
000 ° C., 5 hours to 50 hours.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium secondary battery of the present invention
In addition, lithium cobaltate (LiCoO_Two) Or
Lithium nickelate (LiNiO_Two) In the transition element Co
Alternatively, replace part of Ni with two or more elements.
LiM_ZCo_1-ZO _TwoOr LiM_ZNi_1-ZO_TwoThe positive electrode active material
Use as quality. Here, M represents a substitution element.
The element M is of a type different from the transition elements Co or Ni
And Z represents the substitution amount. Strictly speaking, the substitution element M
Since there are two or more kinds, the chemical formula of the positive electrode active material is n kinds
Li ((M₁)_x1(M_Two)
_x2・ ・ (M_n)_xn)_Z(Co or Ni)_1-ZO_Two(M₁,
M_Two, ..., M_nIs the total of the different elements x1 to xn
The sum is represented as 1). It should be noted that, in the present invention, such
Elemental substitution by multiple elements is hereinafter referred to as “composite substitution”
It shall be.

As the substitution element M, at least Ti is essential, and in addition, Li, Fe, Mn, Ni, M
g, Zn, B, Al, Co, Cr, Si, Sn, P,
One or more elements are selected from V, Sb, Nb, Ta, Mo, and W. These elements are Acta Crys
t. (1976). SHANO described in A32,751
Hume Rosalie's rule is applied to the ionic radius according to N et al., And the ionic radius of the transition element Me substituted in the space group R (-3) m ("-" indicates reversion) or Fd3m (spinel structure) On the other hand, the coordination number for oxygen is the same as that of the transition element Me, the average ionic radius of the substitution element M is within ± 15% of the ionic radius of the transition element Me, and the radioactive element, gas, and toxicity are large. It was determined by selecting combinations of elements that satisfy the condition that they are not equivalent. Here, the transition element Me is based on Co and Ni used in the present invention.

The average ionic radius of the substitution element M refers to an average value of ionic radii of two or more types of elements, and is determined in consideration of the ratio of each element. In the present invention, it is preferable that all ionic radii of the substitution element M be within a range of ± 15% of the ionic radius of the transition element Me. However, if such a condition is not satisfied, for example, one substitution element M large _first ion radius out of the 15% + of the ionic radius of the transition element Me, 2 of the substitution element M ₂ ion radius, even if the smaller out of the -15% of the ionic radius of the transition element Me If the average ionic radius of the substitution elements M ₁ and M ₂ falls within the range of ± 15% of the ionic radius of the transition element Me, complex substitution is possible.

However, when Li is used, it can be used as a replacement element M even if the above-mentioned condition regarding the ionic radius is not satisfied. This is because the ion radius is due to Polling or the like in addition to the above-mentioned SHANNON, but there is a large difference in these specified values, and there is a problem in the index itself only for the ion radius of Li, One of the reasons is that it is an original constituent element, and it is experimentally possible to dissolve Li.

[0022] The substitution element M is theoretically
Li is +1, Fe, Mn, Ni, Mg, and Zn are +2.
Val, B, Al, Co, and Cr are +3, Si, Ti, Sn
Is +4 valence, P, V, Sb, Nb and Ta are +5 valence, Mo,
W becomes a + 6-valent ion, and LiM _Z Co ₁ -Z O ₂ or L
an element which forms a solid solution with _{iM Z Ni 1-Z O 2} . Where C
When o and Sn have a valence of +2, Fe, Sb and Ti
For +3, Mn for +3, +4
In the case of valence, Cr may be +4 or +6.

Therefore, as shown in the actual positive electrode active material, when the valence of some ions is changed due to various crystal chemistry defects or the like, the substitution element M
May not match the theoretical valence of 3 of the transition element Co or Ni before complex substitution.

For example, in addition to the state of +4 valence, Ti
Can exist relatively stably even in the +3 valence state.
If you are a solid solution in _Z Co _1-Z O ₂ or LiM _Z Ni _1-Z O _2, the average valence of Ti is between + 3 + 4. Further, in Fe, +2 valence and +3 valence are equally stable, and it is known that a +4 valence state is stably present in a specific compound. Therefore, Fe LiM _Z Co ₁ -Z O ₂ or LiM _Z Ni _1-Z O average valence of ₂ in becomes be between + 2 + 4. Incidentally, _{similarly, LiM Z Co 1-Z O} 2
Or for even LiM _Z Ni _1-Z O amount of oxygen in the _2, deficient in the range for maintaining the crystalline structure, or it may be excessively present.

In the present invention, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ )
Since the average valency of the substitution element M that partially substitutes for Co or Ni in Example 1 is 3, the substitution element M includes at least an element that becomes an ion other than +3 valence. That is, the case where all of the substitution elements M have a trivalent ionic valence is excluded from the composite substitution of the present invention.

When a battery is assembled using the positive electrode active material subjected to such composite replacement, an effect of remarkably reducing internal resistance appears. This means that the electron conductivity in the skeleton of lithium cobaltate or lithium nickelate (the portion excluding Li contributing to ionic conduction) is improved,
It is considered that this is because the insertion / desorption speed of Li ions in the battery reaction is increased.
The improvement in electron conductivity in this skeleton is considered from the fact that the lattice constant is reduced by the complex substitution, and the transition elements Co or Ni and / or the substitution element M are considered.
Is a transition metal element, the substitution element M and the transition element C
It is presumed that the d orbital between o and Ni is likely to overlap, and that the movement of electrons largely depends on the fact that the d orbital is used to facilitate smooth progress.

Further, even when a battery is assembled using the material subjected to composite replacement and charge / discharge is repeated, deterioration is not recognized as compared with the case where a material not subjected to composite replacement is used. It is believed that the stability of the skeleton has not been adversely affected.

By the way, a part of the transition element Co or Ni is replaced with another element (hereinafter, such replacement with one element is referred to as “single element replacement”). According to the composite substitution, the problem that the positive electrode capacity is reduced more than the substitution amount in the single element substitution is also avoided. Next, for the sake of convenience, LiMn in which the transition element Me is Mn is used for convenience.
_As will be described with reference to ₂ O ₄ , LiCoO ₂ and LiN
It goes without saying that the same applies to iO ₂ .

When Mn ³⁺ in LiMn ₂ O ₄ is replaced with an element having a valence of 2 or less, for example, a monovalent ion such as Li ⁺ , the charge of Mn ³⁺ with Mn ³⁺ is reduced. Since the difference of +2 valence charge is insufficient, two Mn ³⁺ are changed to Mn ⁴⁺ in order to maintain the electrical neutrality of the substance. Thus, as a result, one Li ⁺ becomes Mn.
^{By forming} a solid solution in place of ³⁺ , Mn ³⁺ is reduced by about three.

Here, in LiMn ₂ O ₄ , Mn ³⁺ changes to Mn ⁴⁺ to compensate for the shortage of charge caused by the desorption of Li ⁺ during charging, and the electric charge of the substance is reduced. It is considered that the neutral reaction is maintained and the opposite reaction occurs in the case of discharge. That is, the amount of Mn ³⁺ in LiMn ₂ O ₄ determines the positive electrode capacity, and the amount of Li ⁺ corresponding to this Mn ³⁺ contributes to the charge / discharge reaction. Therefore, in order for Li ⁺ to be desorbed from the crystal lattice or inserted into the crystal lattice, a cation other than Li ⁺ , that is, a substitution element M and / or a transition element Me causes a valence change. Is required.

However, in the above example, Mn³⁺To
Li substituted⁺Does not cause a valence change, so Mn³⁺Is
It remains reduced by three. Therefore, three Li ⁺Is full
It does not contribute to the discharge reaction. In other words, as a result,
In addition, there is a problem that the capacity of the positive electrode is reduced. Such a problem
Is the same for single element substitution with +2 valent ions.
You.

On the other hand, in the composite substitution of the present invention, the substitution element M is Li, Fe, Mn, Ni, Mg, Zn, S
i, Ti, Sn, P, V, Sb, Nb, Ta, Mo, W
(Hereinafter, these substitution elements M are referred to as “substituted element groups in a reduced range”), and at least two or more elements are selected from among them. Thus, the problem that the capacity of the positive electrode decreases more than the above-described element replacement amount is avoided.

That is, +1 or +2 ion,
When +4 to +6 valence ions are combined, +1 valence or +
The lack of positive charge caused by solid solution of divalent ions is compensated not by Mn ³⁺ changing to Mn ⁴⁺ to compensate for charges but by solid solution of +4 to +6 ions. By doing so, Mn can be replaced without reducing the number of Mn ³⁺ more than the replacement amount and reducing the positive electrode capacity.

For example, when two Mn ³⁺ are replaced with one Li ⁺ and one V ⁵⁺ , the decrease in the positive electrode capacity is limited to the decrease of two Mn ³⁺ , Of Mn ³⁺ to one Li
It is possible to reduce the reduction amount of Mn ³⁺ more than the reduction amount of three Mn ³⁺ when the single element is replaced by ⁺ . Further, when two Mn ³⁺ are replaced by one Mg ²⁺ and one Ti ⁴⁺ , the decrease in the positive electrode capacity is limited to the decrease of two Mn ^{3+ and} two Mn ^{3+ This} is less than the decrease of four Mn ³⁺ when ³⁺ is replaced by two Mg ²⁺ . Thus, Mn
The amount of reduction of ³⁺ is the same as the amount of substitution of the element, and therefore, it is possible to prevent a decrease in the positive electrode capacity exceeding the amount of substitution.

In the compound substitution, it is preferable to include at least Ti as the substitution element M, since the effect of improving the electron conductivity is remarkably obtained. Further, Ti can be effectively used for preventing a decrease in the capacity of the positive electrode, and is thus preferable.

LiM _Z Co ₁ -Z O ₂ or LiM _Z containing two or more kinds of substituting elements M obtained when performing compound substituting using elements in the substituting element group in the reduced range described above.
In Ni ₁ -Z O ₂ , part of the remaining transition element Co or Ni is further converted to B, Al, Co, Cr (where Co is LiM
It applies only to _Z Ni _1-Z O _2. ) May be replaced with at least one element selected from the group consisting of: In this case, complex replacement with at least three types of elements is performed.

The elements such as B and Al are theoretically LiM _Z Co ₁ -Z O ₂ or LiM _Z N
Present in i _1-Z O ₂ . However, as described above, in the actual positive electrode active material, the ionic valence does not necessarily have to match the theoretical valence. +3 ion is Co ³⁺
Alternatively, since the substitution with Co ³⁺ is performed on a one-to-one basis, the decrease in the cathode capacity is the same as the substitution amount, and the cathode capacity does not decrease beyond the substitution amount. On the other hand, the electron conductivity of the cathode active material itself is improved. To contribute.

Next, the substitution amount Z in the compound substitution will be described. In the present invention, the ratio Z / X between the substitution amount Z by the substitution element M and the original amount X of the transition element Co or Ni.
Preferably satisfies the condition of 0.005 ≦ Z / X ≦ 0.3. When Z / X is less than 0.005, the resistance of the positive electrode active material does not decrease significantly, and improvement in cycle characteristics hardly appears. That is, the effect of the compound substitution does not appear. On the other hand, when Z / X is more than 0.3, formation of a different phase in the synthesis of the positive electrode active material was observed by powder X-ray diffraction (XRD), and a single-phase substance was not obtained. In a battery, since such a heterophase only increases the weight of the positive electrode active material and does not contribute to the battery reaction, it is needless to say that it is preferable to avoid the generation of the heterophase and the contamination of the battery during the synthesis. .

In the present invention, the substitution amount Z is
0.005 ≦ Z ≦ 0.3, more preferably 0.0
It is preferable to be in the range of 5 ≦ Z ≦ 0.3, and in the preferable range of the substitution amount Z, the effect of improving the electron conductivity of the positive electrode active material is remarkably exhibited, which is preferable.

After the compound replacement, B, Al, C
When element substitution with one or more elements selected from o and Cr is also performed, the substitution amount Z of the substitution element M selected from the substitution element group in the reduced range and the substitution of B, Al, etc. The total replacement amount (Z + w) with the amount (assumed to be w) is 0.01 ≦
It is necessary to satisfy the relationship of Z + w ≦ 0.5.

Now, the lithium secondary battery of the present invention is used.
LiM_ZCo_1-ZO _TwoOr LiM_ZNi_1-ZO_TwoIs the place
Each element adjusted to constant ratio (substitution elements M and Li, transition source
A mixture of a salt and / or oxide of hydrogen (Co or Ni)
Atmosphere, 600 ° C. to 1000 ° C. for 5 hours to 5 hours
It is synthesized by firing over 0 hours, thus
The product can be obtained. Here, the oxidizing atmosphere is
Generally, the atmosphere in the furnace has an oxygen partial pressure that causes an oxidation reaction.
Refers to the atmosphere. In this case, the oxygen partial pressure should be 10% or more.
Are preferable, and specifically, air atmosphere, oxygen atmosphere, etc.
Is applicable.

When the firing temperature is as low as less than 600 ° C., a peak indicating the residual raw material in the XRD chart of the fired product, for example, lithium carbonate (Li ₂ C
When O ₃ ) is used, a peak of Li ₂ CO ₃ is observed, and a single-phase product cannot be obtained. On the other hand, if the firing temperature is 100
When the temperature is higher than 0 ° C., a high-temperature phase is generated in addition to the target crystalline compound, and a single-phase product cannot be obtained.

The firing may be performed twice or more. In this case, it is preferable that the baking temperature in the next step is higher than the baking temperature in the previous step, and the baking conditions for the final baking are an oxidizing atmosphere, 600 ° C. to 1000 ° C., and 5 hours to 50 hours. . Thus, for example, in the case of the second baking, the product obtained when the synthesis is performed with the second baking temperature set to be equal to or higher than the first baking temperature is obtained by using the conditions of the second baking temperature and the baking time. The peak shape on the XRD chart protrudes sharper than the product obtained by performing the baking multiple times, and the crystallinity is improved.

The salt of each element is not particularly limited, but it goes without saying that it is preferable to use a high-purity and inexpensive raw material. Therefore, it is preferable to use carbonates, hydroxides, and organic acid salts that do not generate harmful decomposition gases at the time of raising the temperature or firing. However, this does not mean that nitrates, hydrochlorides, sulfates, and the like cannot be used. Generally, in the synthesis of LiCoO ₂ or LiNiO ₂ , it is known that the synthesis temperature is lowered by using a salt instead of an oxide as a raw material. As for the Li raw material, the oxide Li ₂ O is generally rarely used because it is chemically unstable.

As described above, by performing the composite substitution of the present invention, the electron conductivity of the positive electrode active material is improved, and the positive electrode active material has preferable electric characteristics, and the internal resistance of the battery is reduced. Further, the problem that the positive electrode capacity is reduced beyond the element replacement amount, which has conventionally been a problem with single element replacement, is solved, and the reduction in the positive electrode capacity is suppressed to be equal to the element replacement amount.

A battery in which the internal resistance is reduced, the positive electrode capacity is ensured, and the cycle characteristics are improved, particularly EV
When used as a power source for motor drive of HEVs and HEVs, there are obtained excellent effects that predetermined running performance such as acceleration performance and uphill running performance is maintained, and a long running distance per charge is maintained.

Other materials used for manufacturing the battery are not particularly limited, and various conventionally known materials can be used. For example, an amorphous carbonaceous material such as soft carbon or hard carbon, artificial graphite such as highly graphitized carbon material, or a carbonaceous material such as natural graphite is used as the negative electrode active material.

As the organic electrolyte, ethylene carbonate (EC), diethyl carbonate (DE)
C), carbonates such as dimethyl carbonate (DMC), propylene carbonate (PC) and γ
- butyrolactone, dissolved in tetrahydrofuran, alone or a mixed solvent of an organic solvent such as acetonitrile, lithium complex fluorine compound such as LiPF ₆ and LiBF ₄ as an electrolyte, or one or two or more kinds of LiClO ₄ lithium halides such as Can be used.

[0049]

EXAMPLE Next, a description will be given of a composite substitution by two kinds of elements including Ti as a substitution element M which obtains the most remarkable effect in the present invention as a main example based on the experimental results.

(Positive electrode active materials LiM _Z Co ₁ -Z O ₂ and LiM _Z
Synthesis of Ni _{1 -Z} O ₂ ) As a starting material, commercially available Li ₂ C
Using O ₃ , Co ₃ O ₄ , NiO, MgO, and TiO ₂ , they were weighed and mixed so as to have various compositions in the examples shown in Tables 1 and 2 (cathode active materials for measuring internal resistivity). And
For LiM _Z Co _1-Z O ₂ , 900 ° C. in air atmosphere
For 20 hours to synthesize, while LiM _Z Ni _1-Z
O ₂ was synthesized by firing at 750 ° C. for 20 hours in an oxygen atmosphere. As shown in Tables 1 and 2, LiCoO ₂ and Li
Samples according to the comparative example using NiO _{2 and} single element substitution were also synthesized under the same conditions. It was confirmed by XRD that the produced various positive electrode active materials of the example and the comparative example were in a single phase.

[0051]

[Table 1]

[0052]

[Table 2]

(Manufacture of Battery) First, various prepared positive electrodes
Using the active material, the positive electrode active material and acetylene
Rack powder and polyvinylidene fluoride as binder
The mixture was mixed at a ratio of 50: 2: 3 to prepare a positive electrode material.
0.02 g of the positive electrode material was added to 300 kg / cm ^TwoAt the pressure of
It was press-molded into a disk having a diameter of 20 mm to obtain a positive electrode.
Next, according to the purpose of the test, as shown below, two types of coin cells
Was prepared. That is, the internal resistivity measurement shown in Tables 1 and 2
The coin cell for the battery consists of the positive electrode fabricated as described above,
Carbonate and diethyl carbonate in equal volume ratio
LiPF as electrolyte in the combined organic solvent₆1 mo
an electrolytic solution prepared by dissolving to a concentration of 1 / L;
A negative electrode made of carbon, and a separator separating the positive electrode and the negative electrode
It was produced using

(Method of Measuring Internal Resistance of Battery and Result)
Using the various positive electrode active materials described in Tables 1 and 2, the coin cell manufactured as described above was charged to 4.1 V at a constant current-constant voltage at a rate of 1 C according to the capacity of the positive electrode active material, and similarly charged at 1 C. A charge / discharge test for discharging to 2.5 V at a constant current of a rate is performed only for one cycle, and a difference (potential difference) between a potential in a rest state after charging and a potential immediately after starting discharge is divided by a discharge current. , The internal resistance of the battery was determined. Then, a value obtained by dividing the internal resistance of the battery using the positive electrode active material subjected to the single element substitution and the composite substitution by the internal resistance of the battery using the original compounds (LiCoO ₂ , LiNiO ₂ ) not subjected to the element substitution, respectively. Was defined as the internal resistivity. Therefore, the smaller the value of the internal resistivity, the greater the effect of reducing the internal resistance. Tables 1 and 2 show the results.
Are listed together.

From Table 1, it was confirmed that, in comparison with Comparative Examples 2 to 4 in which LiCoO _{2 was} subjected to single element substitution, in Examples 1 to 8 in which compound substitution was performed, a reduction in internal resistivity was remarkably exhibited. Was done. Then, as shown in Examples 2 to 4 and Examples 6 to 8, the substitution amount Z is 0.1 ≦ Z
Within the range of ≦ 0.3, a remarkable effect of reducing the internal resistance appears.

The values of the internal resistivity due to single element substitution and composite substitution when LiNiO ₂ was used as the base material were similar to those when LiCoO ₂ was used, and Comparative Example 6 where single element substitution was performed As compared with Example 7, in Examples 9 to 12 in which the compound substitution was performed, the internal resistivity was significantly reduced. In particular, as shown in Examples 10 to 12, the substitution amount Z was 0.05 ≦ Z ≦ 0. In the range of 0.3, the effect of reducing the internal resistance is remarkably exhibited.

Based on these results, Li, Fe, C
r, Mn, Ni, Mg, Zn, B, Al, Co, Cr,
Si, Ti, Sn, P, V, Sb, Nb, Ta, Mo,
The composite substitution with at least two or more elements selected from W was performed, and the process from the preparation of the positive electrode active material to the measurement of the internal resistance was performed by the same method as described above. The same tendency as in the case of was confirmed.

[0058]

As described above, according to the lithium secondary battery of the present invention, as the positive electrode active material, a lithium cobalt oxide or a lithium nickel oxide obtained by performing composite substitution of a transition element and having a low electron conductivity is obtained. Since a resistant material is used, the internal resistance of the battery is significantly reduced. Further, according to the present invention, a decrease in the positive electrode capacity exceeding the element replacement amount is suppressed. As a result, the lithium secondary battery of the present invention has a very high output and a high capacity, has excellent charge-discharge cycle characteristics, is excellent, and has an extremely excellent effect that energy loss during charge-discharge is reduced. .

Claims (10)

[Claims] 1. A method for converting part of a transition element Co or Ni in lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ) into Li, Fe, Mn, N
i, Mg, Zn, B, Al, Co, Cr, Si, Ti,
LiM _Z Co ₁ -Z O ₂ or LiM _Z substituted by two or more elements selected from Sn, P, V, Sb, Nb, Ta, Mo, and W (including at least Ti) Ni
A lithium secondary battery using _1-Z O ₂ (where M is a substitution element and M ≠ Co or Ni, and Z represents a substitution amount) as a positive electrode active material. 2. The method according to claim 1, wherein the substitution element M is Li, Fe, Mn,
Mg, Zn, Si, Ti, Sn, P, V, Sb, Nb,
The lithium secondary battery according to claim 1, wherein the lithium secondary battery is at least two elements selected from Ta, Mo, and W. 3. Li containing two or more kinds of said substitution elements M
Part of the transition element Co in M _Z Co _1-Z O ₂ further includes
3. The composition according to claim 2, wherein the element is substituted with at least one element selected from the group consisting of B, Al, and Cr.
The lithium secondary battery as described in the above. 4. Li containing two or more kinds of said replacement elements M
Part of the transition element Ni in M _Z Ni _1-Z O ₂
The lithium secondary battery according to claim 2, wherein the lithium secondary battery is substituted with at least one element selected from the group consisting of B, Al, Co, and Cr. 5. The substitution amount Z and the transition element Co or N
The ratio Z / X to the amount X of i is 0.005 ≦ Z / X ≦ 0.3
The lithium secondary battery according to any one of claims 1 to 4, wherein the following relationship is satisfied. 6. The lithium manganese oxide or lithium nickelate according to claim 1, wherein the substitution element M for partially substituting cobalt or nickel has an average valence of 3. 4. The lithium secondary battery according to 1. 7. The replacement amount Z is 0.005 ≦ Z ≦ 0.
The lithium secondary battery according to any one of claims 1 to 6, wherein the lithium secondary battery is within the range of (3). 8. The replacement amount Z is 0.05 ≦ Z ≦ 0.3.
The lithium secondary battery according to claim 7, wherein: 9. The LiM _Z Co ₁ -Z O ₂ or LiM _Z
A mixture of salts and / or oxides of each element in which Ni ₁ -Z O ₂ is adjusted to a predetermined ratio is placed in an oxidizing atmosphere at 600 ° C. to 1000 ° C.
The lithium secondary battery according to any one of claims 1 to 8, which is obtained by firing in a range of 5 ° C for 5 hours to 50 hours. 10. The LiM _Z Co ₁ -Z O ₂ or Li
M _Z Ni _{1 -Z} O ₂ is synthesized by firing two or more times,
10. The lithium secondary battery according to claim 9, wherein the firing temperature in the next step is higher than the firing temperature in the previous step.