JP2001297765A - Lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary cell with high capacity and good charging and discharging cycle characteristics. SOLUTION: The lithium secondary cell comprises a liquid including electrolyte, and a cathode including a cathode activator made of a compound expressed by the formula, LixNi1-yMyO2, (where; M represents at least one element chosen from B, Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Cu, Al, In, Nb, Mo, W, Y and Rh, 0.05<=x<=1.1, 0<=y<=0.5). The diffraction strength of crystal faces (006), (102), (101) are measured by X-ray analysis by powder method. The cathode activator is characterized by its peak strength ratio (I006+I102)/I101 of less than 0.427, and by its organic electrolyte. At the lithium secondary cell, as the reaction between the cathode activator and the organic electrolyte causing the increase of internal resistance at the cathode side is restrained, characteristics of the cell is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having a positive electrode active material and an electrolyte.

[0002]

2. Description of the Related Art In recent years, a lithium secondary battery has been becoming mainstream because of its high weight energy density as a power source for electric equipment such as a portable telephone and a portable video camera. This lithium secondary battery generally has a positive electrode active material containing lithium, and has a positive electrode capable of releasing lithium as lithium ions during charging and occluding lithium ions during discharging, and a negative electrode active material. The battery comprises a negative electrode capable of absorbing lithium ions during charging and releasing lithium ions during discharging, and an electrolytic solution in which an electrolyte containing lithium in an organic solvent is dissolved.

Here, as the positive electrode active material used for the lithium secondary battery, Li _x CoO ₂ , Li _x NiO ₂ , Li
_x Mn ₂ O ₄ , Li _x FeO ₂ , V ₂ O ₅ , Cr ₂ O ₅ , Mn
Transition metal oxides such as O ₂ , TiS ₂ and MoS ₂ and chalcogen oxides have been proposed.

As a positive electrode active material for these lithium secondary batteries, Li _x CoO ₂ , Li _x NiO ₂ , and Li _x Mn _{2 are particularly used.}
It is known that O ₄ is promising as a positive electrode active material for a ₄ V class non-aqueous electrolyte lithium secondary battery. These Li
Among the compounds, Li _x NiO ₂ , which can be supplied stably at low cost and has a large theoretical capacity, is expected as a positive electrode active material. This means that Co is rare and expensive,
This is because stable supply is difficult and the cost of the manufactured battery becomes excessive. Li _x NiO ₂ may be a compound represented by Li _x Ni _{1- y My} O _{2 to} which the additional element M is added.

[0005] As an electrolyte for a lithium secondary battery using these positive electrode active materials, an electrolyte in which an electrolyte is dissolved in a non-aqueous solvent is used.

The non-aqueous solvent includes a main solvent having a high dielectric constant such as ethylene carbonate (EC) and propylene carbonate (PC), and dimethyl carbonate (DM).
A mixed solvent obtained by mixing C) and a low-viscosity secondary solvent such as diethyl carbonate (DEC) is known.

[0007] LiPF ₆ , LiB
Organic electrolytes such as inorganic electrolytes such as F ₄ and LiClO ₄ , imide salts such as lithium bistrifluoromethanesulfonylimide, and methide salts such as lithium tristrifluoromethanesulfonylmethide are known. Here, among these electrolytes, inorganic electrolytes have a problem that when the battery is heated to a high temperature due to charging and discharging, or react with moisture contained in the electrolyte to generate harmful substances such as hydrogen fluoride. Was. On the other hand, it is known that an organic electrolyte has higher thermal stability and better charge / discharge cycle characteristics than an inorganic electrolyte.

However, Li _x NiO _{2 is} used as the positive electrode active material.
In a lithium secondary battery using an imide salt as an organic electrolyte as a system compound, there is a problem that the battery characteristics deteriorate when charge and discharge are repeated. That is, in this lithium secondary battery, by repeating charge and discharge, a reaction between the positive electrode active material and the imide salt occurs on the positive electrode side, and the internal resistance on the positive electrode side increases due to this reaction.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a lithium secondary battery having high capacity and excellent charge / discharge cycle characteristics.

[0010]

Means for Solving the Problems In order to solve the above problems, the present inventors have repeated charging and discharging in a lithium secondary battery having a positive electrode active material of Li _x NiO ₂ -based compound and an organic electrolyte. As a result of repeated studies on a method of suppressing the rise in internal resistance that sometimes occurs on the positive electrode side, while improving the crystallinity of the positive electrode active material, a lithium secondary battery having an organic electrolyte allows the positive electrode active material and the electrolyte to be It has been found that the above reaction can be suppressed and the above problem can be solved.

That is, the lithium secondary battery of the present invention is:
Formula _{Li x Ni 1-y M y} O 2 (M is B, Mg, Ca, Sr, B
a, Ti, V, Cr, Mn, Fe, Co, Cu, Al,
At least one element selected from the group consisting of In, Nb, Mo, W, Y and Rh, 0.05 ≦ x ≦ 1.1,
0 ≦ y ≦ 0.5) in a lithium secondary battery including a positive electrode including a positive electrode active material composed of a compound represented by the formula (1) and an electrolyte including an electrolyte, the positive electrode active material is determined by X-ray powder analysis measurement results. (006) plane, (102) plane and (10) plane
1) The peak intensity ratio of the plane (I ₀₀₆ + I ₁₀₂ ) / I ₁₀₁ is
0.427 or less, and the electrolyte is an organic electrolyte.

In the lithium secondary battery of the present invention, the reaction between the positive electrode active material and the organic electrolyte, which causes an increase in the internal resistance on the positive electrode side, is suppressed. Is improving.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A lithium secondary battery of the present invention is a lithium secondary battery having a positive electrode containing a positive electrode active material and an electrolyte containing an electrolyte.

The positive electrode active material has the formula Li _x Ni _{1 -y My} O ₂ (M
Is B, Mg, Ca, Sr, Ba, Ti, V, Cr, M
n, Fe, Co, Cu, Al, In, Nb, Mo, W,
At least one element selected from the group consisting of Y and Rh, and a compound represented by 0.05 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5). These compounds have a large theoretical capacity as a positive electrode active material, and can provide a lithium secondary battery having high battery characteristics.

The positive electrode active material is included in the results of X-ray powder analysis measurement.
(006) plane, (102) plane and (101) plane
Peak intensity ratio (I₀₀₆+ I₁₀₂) / I₁₀₁Is 0.427
It is as follows. In other words, more than lithium nickel compounds
By increasing the crystallinity of the positive electrode active material,
The reactivity with the electrolyte decreases and the internal resistance increases on the positive electrode side
Can be suppressed. As a result, the lithium secondary battery
A decrease in cycle characteristics can be suppressed. This positive electrode active
The crystallinity of the substance was determined by the (00
6) Peak intensity of plane, (102) plane and (101) plane
Ratio (I₀₀₆+ I_{1 02}) / I₁₀₁Can be indicated by this
The smaller the peak intensity ratio, the higher the crystallinity.

[0016] That is, the lithium nickel compounds mainly Ni represented by the formula _{Li x Ni 1-y M y} O 2 are known to be a layered rock salt structure. In this layered rock salt structure, the sum of the diffraction intensity I ₀₀₆ caused by the (006) plane and the diffraction intensity I ₁₀₂ caused by the (102) plane by the crystal structure analysis using X-ray diffraction is caused by the (101) plane. divided by the diffraction intensity I ₁₀₁ of _{(I 006 + I 102) /} I 101
It is said that the smaller the is, the smaller the crystal defects and the higher the crystallinity.

Further, the (006) plane, (1) in the results of X-ray powder analysis measurement of the lithium nickel compound as the positive electrode active material.
02) and (101) plane peak intensity ratio (I ₀₀₆ +
By setting I ₁₀₂ ) / I ₁₀₁ to 0.427 or less, crystallinity of the lithium nickel compound is improved, and an increase in internal resistance due to a reaction with the organic electrolyte can be suppressed. When the peak intensity ratio of the lithium nickel compound in the X-ray powder analysis exceeds 0.427, a reaction between the positive electrode active material and the organic electrolyte occurs on the positive electrode side, and the internal resistance on the positive electrode side increases. However, the performance of the lithium secondary battery deteriorates.

Here, the crystallinity of the positive electrode active material made of a lithium nickel compound is determined by the mixing ratio of the raw materials, the sintering temperature, the atmosphere (oxygen concentration, dew point, CO ₂₎ during the production of the positive electrode active material.
It can be produced by adjusting conditions such as content.

The electrolyte is an organic electrolyte. Organic electrolytes have better thermal stability and better charge / discharge cycle characteristics than inorganic electrolytes, and thus improve the battery characteristics of lithium secondary batteries.

Here, examples of the organic electrolyte include imide salt electrolytes such as lithium nonafluorobutane-trifluoromethanesulfonylimide, lithium bistrifluoromethanesulfonylimide, and lithium bispentafluoroethanesulfonylimide, and lithium perfluorosulfonylmethyl. And methide salt electrolytes such as lithium tristrifluoromethanesulfonyl methide and lithium trispentafluoroethanesulfonyl methide.

The organic electrolyte is preferably an imide salt electrolyte. That is, the imide salt electrolyte can provide an electrolytic solution having high electric conductivity and ion transport number, a wide electrochemical potential window, excellent thermal stability, and good compatibility with other battery members. .

The imide salt electrolyte is preferably the imide salt electrolyte shown in Chemical formula 1. That is, the electrolyte is lithium perfluorosulfonylimide, ie, L
_{iN (SO 2 C m F 2m} + 1) (SO 2 C n F 2n + 1) (m = 1,
By setting 2, 3, 4, n = 1, 2, 3, 4), the reaction between the positive electrode active material and the electrolyte due to the charge / discharge cycle is suppressed, and the increase in the internal resistance of the battery is suppressed. Where m,
When n is a value of 5 or more, the molecular weight of the imide salt increases, leading to a decrease in conductivity and a decrease in battery performance.

The lithium secondary battery of the present invention can be in a form used for a normal lithium secondary battery except for the positive electrode active material and the electrolyte. In addition, the structure of the lithium secondary battery of the present invention is not particularly limited, and a stacked type having a stacked electrode body in which a positive electrode and a negative electrode are formed in a sheet shape and alternately stacked via a separator. The electrode battery may be a wound electrode battery having a wound electrode body in which a sheet-shaped positive electrode and a negative electrode are wound with a separator interposed therebetween, or may have another form.

As the negative electrode active material, current collector, and separator that can be used in the lithium secondary battery of the present invention, for example, the following materials can be used.

Examples of the negative electrode active material include carbon materials capable of occluding and releasing lithium, such as flaky graphite, spherical graphite, and amorphous carbon, and lithium metal.

The current collector of the positive electrode may be, for example, aluminum or stainless steel, and the current collector of the negative electrode may be, for example, copper, punched metal, foam metal, or a plate-shaped foil of copper or nickel. Can be used.

As the separator, for example, a thickness of 10 to 10 is used.
A microporous polypropylene film or a microporous polyethylene film having a pore size of 50 (μm) and a porosity of 30 to 70% can be used.

As a solvent for dissolving the electrolyte,
For example, 1,2-dimethoxyethane, 1,2-diethoxyethane, propylene carbonate, ethylene carbonate, γ-butyrolactone, tetrahydrafuran, 1,
A single solvent such as 3-dioxolan, diethylene carbonate, dimethyl carbonate, ethyl methyl carbonate or a mixture of two or more solvents can be used.

Further, in addition to the positive electrode active material, a conductive material and a binder can be used for the positive electrode. Examples of the binder include an organic binder and an inorganic binder.

The lithium secondary battery of the present invention can be manufactured by using a usual method for manufacturing a lithium secondary battery. As a method for producing this lithium secondary battery, for example, a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material are stacked in a battery container with a separator interposed therebetween, and stored in a battery container. A method in which an electrolytic solution is injected and hermetically sealed is provided.

The lithium secondary battery of the present invention is a battery having a positive electrode active material composed of a lithium nickel compound and an organic electrolyte, wherein the reaction between the positive electrode active material and the organic electrolyte salt is suppressed, and Increase in internal resistance is suppressed. For this reason, the battery characteristics of the lithium secondary battery have been improved.

[0032]

The present invention will be described below with reference to examples.

As an example of the present invention, a cylindrical lithium secondary battery was manufactured.

(Cylindrical Lithium Secondary Battery) A cylindrical lithium secondary battery 100 of the embodiment is shown in FIG.

The cylindrical lithium secondary battery 100 has a positive electrode 1 having a positive electrode active material containing lithium, capable of releasing lithium as lithium ions during charging and absorbing lithium ions during discharging, and a carbon material. A negative electrode 2 having a negative electrode active material that can occlude lithium ions during charging and release lithium ions during discharging, and a non-aqueous electrolyte 3 formed by dissolving an electrolyte containing lithium in an organic solvent. A lithium secondary battery provided with:

The positive electrode 1 includes a positive electrode current collector, a positive electrode mixture layer having a positive electrode active material and a binder formed on the surface of the positive electrode current collector, and a positive electrode current collector bonded to the positive electrode current collector. And an electric lead.

The positive electrode 1 and the negative electrode 2 are
And is held in the case 7 in a state wound. Also, the current collecting leads 13 and 23 of the positive electrode 1 and the negative electrode 2
Are the positive terminal part 5 and the negative terminal part 6 of the case, respectively.
Is connected to

As a separator, a microporous polyethylene film having a thickness of 25 μm was used.

As an electrolyte, lithium nonafluorobutane-trifluoromethanesulfonylimide [LiN (S
O ₂ C ₄ F ₉ ) (SO ₂ CF ₃ )] and ethylene carbonate (EC) and diethylene carbonate (DEC).
A solution obtained by dissolving 1 mol / liter in a solvent mixed at a volume ratio of 0:70 was used as an electrolyte.

The lithium secondary battery of the example was manufactured according to the following procedure.

(Manufacture of Positive Electrode) First, 85 w of a positive electrode active material was used.
t%, acetylene black as conductive agent (Model: HS-
An N-methyl-2-pyrrolidone (NMP) solution in which 10% by weight of (100) was dissolved and polyvinylidene fluoride (PVDF) equivalent to 5% by weight as a binder was prepared. This paste is applied to both surfaces of an aluminum foil with a comma coater at a basis weight of 8.78 (mg / cm ² ) per side.

Next, the electrode was passed through a roll press to apply a load, and a positive electrode plate having an electrode density of 2.41 (g / cm ² ) was prepared. Thereafter, the positive electrode plate has a width of 5.4 (c).
m), cut into a length of 86 (mm), and the electrode mixture for a length of 2.5 (cm) was scraped off as a lead tab weld for current extraction. The effective reaction area of this positive electrode plate is 5.
4 (cm) x 83.5 (cm) x 2 = 901.8 (cm
² ).

(Production of Negative Electrode) 92.5 wt% of flaky graphite as a negative electrode active material and PVDF7.
A paste in which graphite was dispersed in a solution in which PVDF was dissolved in NMP using 5 wt% was prepared, and the basis weight per side was 5.1 (mg / mg) on both surfaces of the copper foil surface using a comma coater similarly to the positive electrode. cm ² ). Thereafter, the copper foil coated with the paste was passed through a roll press, and a linear pressure of 0.25 (ton / c) was applied.
m) and an electrode density of 1.25 (g / cm ² )
To produce a negative electrode plate rising to.

Next, this negative electrode plate was cut into a width of 5.6 (cm) and a length of 90.5 (cm), and was used as a lead tab weld for current extraction for a length of 0.5 (cm). The agent was scraped. The effective reaction area of this negative electrode plate was 5.6 (c
m) × 90 (cm) × 2 = 1,008 (cm ² ).

(Assembly of Battery) The positive electrode plate and the negative electrode plate obtained above were wound with a separator interposed therebetween to form a wound electrode body. The obtained wound electrode body was inserted into the case and held in the case. At this time, the current collecting lead having one end welded to the lead tab welding portion of the positive electrode plate and the negative electrode plate was joined to the positive terminal or the negative terminal of the case.

Thereafter, an electrolytic solution in which an electrolyte is dissolved in an organic solvent is injected into a case holding the spirally wound electrode body,
The case was hermetically sealed.

By the above procedure, a cylindrical lithium secondary battery having a diameter of 18 mm and an axial length of 65 mm was manufactured.

The XRD ratio and the rate of increase in internal resistance of the positive electrode active material used in the examples were measured by the following measuring methods.

(Measurement of XRD intensity ratio) X-ray source: CuKα ₁ , manufactured by Rigaku Co., Ltd.
Tube voltage: 50 (kV), tube current: 100 (mA), divergence slit: 1/2 (deg), scattering slit: 1/2
(Deg), light receiving slit: 0.15 (mm), scanning mode: continuous, scanning range: 15 ° to 75 °, the diffraction intensity was measured.

After the data was subjected to background removal at a curvature of 5.0 using a RISM qualitative analysis program, the intensity ratio of (Kα ₁ / Kα ₂ ) was set to 0.5 and Kα
_The effect of ₂ was removed.

From the data obtained here, the diffraction intensity of X-rays corresponding to each index plane was read, and the (006) plane, (10) plane (10) serving as an index of crystallinity in the LiNiO ₂ -based positive electrode active material were measured.
2) The peak intensity ratio between the plane and the (101) plane: (I ₀₀₆₎
+ I ₁₀₂ ) / I ₁₀₁ was determined.

(Initial Discharge Capacity) First, CC-CV charging is performed up to 4.1 (V) at a charging current of 250 (mA),
CC discharge was performed with a discharge current of 333 (mA) to 3.0 (V).

Next, when the charging current is 1000 (mA), the charging current is 4.1.
CC-CV charge and discharge current up to (V) 1000 (mA)
After performing CC discharge four times to 3.0 (V), CC-CV charge is performed to 4.1 (V) at a charging current of 1000 (mA).
CC discharge was performed to 3.0 (V) with a discharge current of 333 (mA).

The discharge capacity at this time was defined as the initial capacity of the battery, and a comparison was made using a value standardized by the weight of the positive electrode active material filled in the battery. The measurement was performed in a 25 ° C. atmosphere.

(High temperature cycle characteristic test) A lithium secondary battery was placed in a thermostat at an ambient temperature of 60 ° C, and a charge current of 1
The cycle of charging the battery with CC at 984 (mA) to 4.1 (V) and charging the battery with CC at a discharge current of 1984 (mA) up to 3.0 (V) was repeated 500 times.

(Measurement of rate of increase in internal resistance) Measurement of the internal resistance of the battery was performed by first measuring the charging current at 20 ° C. and the charging current being 1.1 (mA / c).
m ² ) and charged to CC-CV up to 3.75 (V), and using an AC impedance measuring device (manufactured by Toyo Corp .: frequency response analyzer solartron1260, potentio / galvanostat solartron1287), frequency 100 kHz to 0.02 Hz. , And a Cole-Cole plot showing an imaginary part on the vertical axis and a real part on the horizontal axis was created. Subsequently, in this Cole-Cole plot, the arc portion is fitted with a circle,
The larger value of the two points intersecting the real part of the circle was taken as the resistance value and taken as the internal resistance of the battery.

The internal resistance increase rate is determined by measuring the internal resistance before and after the cycle test. (Internal resistance increase rate) = (resistance value after cycle test) /
(Resistance value before cycle test).

Example 1 In Example 1, the positive electrode active material was
Peak intensity ratio by XRD: (I ₀₀₆ + I ₁₀₂ ) / I ₁₀₁
Is 0.427, LiNi _0.81 Co _0.16 Al _0.03 O ₂
This is a lithium secondary battery using the same.

Example 2 In Example 2, a positive electrode active material was used.
Peak intensity ratio by XRD: (I ₀₀₆ + I ₁₀₂ ) / I ₁₀₁
Is 0.4157, LiNi _0.81 Co _0.16 Al _0.03 O
A battery similar to that of Example 1 except that No. ₂ was used.

Comparative Example 1 In Comparative Example 1, a positive electrode active material was used.
Peak intensity ratio by XRD: (I ₀₀₆ + I ₁₀₂ ) / I ₁₀₁
Is a battery similar to that of Example 1 except that LiNi _0.8 Co _0.15 Al _0.05 O ₂ having a value of 0.440 was used.

(Comparative Example 2) In Comparative Example 2, LiP was used as the electrolyte.
Li wherein F ₆ is used and the positive electrode active material has a peak intensity ratio by XRD: (I ₀₀₆ + I ₁₀₂ ) / I ₁₀₁ of 0.427.
A battery similar to that of Example 1 except that Ni _0.81 Co _0.16 Al _0.03 O ₂ was used.

(Evaluation) Examples 1-2 and Comparative Examples 1-2
As for the evaluation of the batteries, each battery was subjected to the above-described high-temperature cycle characteristic test, and the increase rate of the internal resistance of the battery before and after the high-temperature cycle characteristic test was measured. The measurement results are shown in Table 1.

[0063]

[Table 1]

As shown in Table 1, in the batteries of Examples 1 and 2 and Comparative Example 1 using an imide salt as the electrolyte and a lithium nickel compound as the positive electrode active material, the smaller the XRD ratio of the lithium nickel compound, the higher the internal resistance increase rate. It can be seen that is also smaller.

In Examples 1 and 2, the rate of increase in internal resistance is lower than that in Comparative Example 2, which is a battery using a conventional LiPF ₆ electrolyte. In Comparative Example 1 in which the crystallinity of the positive electrode active material was low, the increase rate of the internal resistance was as high as 2.71, and the performance of the battery was reduced.

According to the examples, by increasing the crystallinity of the positive electrode active material, that is, by reducing the XRD peak intensity ratio, in a battery using an imide salt electrolyte as the electrolyte, an increase in internal resistance on the positive electrode side was suppressed. Can be Therefore, a lithium secondary battery having high charge / discharge characteristics is obtained.

[0067]

According to the lithium secondary battery of the present invention using a lithium nickel compound as a positive electrode active material and an organic electrolyte salt as an electrolyte, the reaction between the positive electrode active material and the organic electrolyte is suppressed, and The increase in internal resistance is suppressed. As a result, the lithium secondary battery of the present invention has improved battery performance.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a cylindrical lithium secondary battery produced in an example.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 lithium secondary battery 1 positive electrode 2 negative electrode 3 electrolyte 4 separator 5 positive electrode terminal 6 negative electrode terminal 7 case

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hirohiko Saito 1-1-1, Showa-cho, Kariya-shi, Aichi F-term in Denso Corporation (reference) 5H029 AJ03 AJ05 AK03 AL07 AM03 AM04 AM05 AM07 EJ11 HJ02 HJ13 5H050 AA07 AA08 BA17 CA08 CB08 HA02 HA13

Claims (3)

[Claims] The formula Li _x Ni _{1- y My} O ₂ (M is B, Mg,
Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, C
o, Cu, Al, In, Nb, Mo, W, Y and Rh
At least one element selected from the group consisting of: 0.0
5 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5) in a lithium secondary battery including a positive electrode including a positive electrode active material comprising a compound represented by the formula: Is (00) in the X-ray powder analysis measurement result.
6) The lithium, wherein the peak intensity ratio (I ₀₀₆ + I ₁₀₂ ) / I _{101 of} the (102) plane and the (101) plane is 0.427 or less, and the electrolyte is an organic electrolyte. Rechargeable battery. 2. The lithium secondary battery according to claim 1, wherein the organic electrolyte is an imide salt electrolyte. 3. The lithium secondary battery according to claim 2, wherein the imide salt electrolyte is an imide salt electrolyte represented by Chemical Formula 1. Embedded image