JP2016149270A - Method of manufacturing positive material for lithium ion battery and electrode material manufactured by the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a positive electrode for a lithium ion battery that has an enhanced capacity characteristic at a high charging/discharging rate, and an electrode material manufactured by the method.SOLUTION: A method of manufacturing a positive electrode for a lithium ion battery comprises a dispersion liquid preparing step of dispersing, in liquid, an active material raw material including powdered active material constituting a positive electrode for the lithium ion battery, a powdered first element raw material containing a first element which constitutes ferroelectric material containing the first element and a second element, and a powered second element raw material containing a second element to prepare dispersion liquid, a gelation step of making the dispersion liquid gelate, and a heating step of heating the gel to carry the ferroelectric material on the active material raw material.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a method for producing a positive electrode material for a lithium ion battery and an electrode material produced by this method.

  Conventionally, in a lithium ion battery, a composite positive electrode in which a ferroelectric is supported on the surface of active material particles and sintered is used as the positive electrode.

As such a composite positive electrode, on the particle surface of the LiCoO ₂ type positive electrode powder, a ferroelectric barium titanate BaTiO ₃ is added in a range of 0.1 mol% to 5 mol%, and the particle diameter is 100 nm to 5 μm or less. A composite positive electrode supported in a range and sintered in a temperature range of 400 ° C. to 750 ° C. has been proposed (see, for example, Patent Document 1). The purpose of this composite positive electrode is to improve the output characteristics at low temperature. Specifically, 1 mol% of BaTiO ₃ is mechanically added at 700 ° C to Li _1.1 Ni _0.5 Co _0.2 Mn _0.3 O ₂ particles as the active material. It is reported that the composite positive electrode supported by mixing is improved by 139.5% in the output characteristics at a low temperature of −30 ° C. with respect to the untreated product.

The above composite positive electrode uses a non-aqueous electrolyte as an electrolyte of a lithium ion battery, but is a composite positive electrode of an all solid lithium ion battery in which the electrolyte is a sulfide solid, and the amount is 1 wt% with respect to the active material. There has also been proposed a composite positive electrode in which a ferroelectric barium titanate BaTiO ₃ having an average particle diameter of 50 nm is combined in a liquid phase (see, for example, Patent Document 2). This composite positive electrode is intended to improve the discharge capacity, and it has been reported that the resistance at the interface between the solid electrolyte and the active material can be reduced by about 20% and the discharge capacity can be improved by about 5%.

JP 2011-210694 A JP 2014-116129 A

  For lithium-ion batteries, improvement of output characteristics at low temperatures and improvement of discharge capacity are important performance improvement items, but improvement of capacity characteristics at high-speed charge / discharge rates is also an important item, but conventional composite positive electrodes Thus, improvement in capacity characteristics at a high-speed charge / discharge rate could not be expected.

  In the positive electrode of a lithium ion battery, an insertion / release reaction of Li ions occurs at the interface between the active material constituting the positive electrode and the electrolytic solution, but a composite in which a ferroelectric material is supported on the particle surface of the active material. The positive electrode aims to promote the insertion and desorption reaction of Li ions by utilizing the polarization of the ferroelectric, and the ferroelectric is supported on the active material in the fine particle state as much as possible, especially at high charge / discharge rates. There is a possibility that improvement in capacity characteristics can be expected.

  However, in the conventional method in which the ferroelectric material is mechanically coated with the active material and subjected to the heat treatment, the ferroelectric grows as a result of the growth of the ferroelectric particles, and the ferroelectric material is supported on the active material in the fine particle state as much as possible. It was difficult.

  In view of such a current situation, the present inventors conducted a study to improve the capacity characteristics at a high-speed charge / discharge rate by using a composite positive electrode in which a ferroelectric is supported on an active material in a fine particle state as much as possible. The present invention has been achieved.

  The method for producing a positive electrode material for a lithium ion battery according to the present invention comprises an active material raw material in powder form of an active material constituting a positive electrode of a lithium ion battery, and a ferroelectric containing a first element and a second element. A dispersion preparation step for preparing a dispersion by dispersing a powdered first element material containing a first element and a powdered second element material containing a second element in a solution And a gelling step in which the dispersion is used as a gel, and a heating step in which the gel is heated and the ferroelectric material is supported on the active material material.

Furthermore, the method for producing a positive electrode material for a lithium ion battery of the present invention is also characterized by the following points.
(1) The first element material and the second element material should be 5 mol% or less with respect to the active material material when the first element material and the second element material become a ferroelectric in the heating process.
(2) The active material material is lithium cobaltate, the first element material is barium acetate, the first element material is titanium butoxide, and the active material constituting the positive electrode of the lithium ion battery is supported with barium titanate. .
(3) In the gelation step, the dispersion is gelled by drying with stirring at 70 ° C. for 6 hours, and in the heating step, it is heated at 600 ° C. for 20 hours.

  In addition, the electrode material of the present invention is a gel obtained by drying a dispersion obtained by dispersing powdered lithium cobaltate, powdered barium acetate, and powdered titanium butoxide in a solution while stirring. And an electrode material in which barium titanate is supported on lithium cobaltate by heating the gel, and the particle size of barium titanate is 100 nm or less.

  According to the present invention, it is possible to synthesize and adhere a ferroelectric substance in the form of nanoparticles to the active material surface by a soft chemical liquid phase method, and to enable homogenization and uniform film thickness of the ferroelectric substance. In addition, the insertion and release of Li ions into the active material can occur more smoothly, and the capacity characteristics at a high-speed charge / discharge rate can be improved.

It is the STEM image and STEM-EDS image of the powder after a heating process. It is the XRD pattern of the powder after a heating process. It is a STEM image of the sample heat-processed at 600 degreeC by the heating process. It is a graph of the capacity | capacitance characteristic in a high-speed charging / discharging rate. It is the XRD pattern of the powder after a heating process (600 degreeC). It is the STEM image and STEM-EDS image after a heating process (600 degreeC). It is a graph of the capacity | capacitance characteristic in a high-speed charging / discharging rate.

  In the present invention, the ferroelectric particles are synthesized and attached to the active material surface as nano-particles by the soft chemical liquid phase method, rather than attaching the ferroelectric particles to the active material surface by a mechanical method. It is.

  That is, the method for producing a positive electrode material for a lithium ion battery according to the present invention includes a ferroelectric material containing an active material raw material in powder form of an active material constituting a positive electrode of a lithium ion battery, and a first element and a second element. Preparation of a dispersion by dispersing a first element material in powder form containing the first element and a second element material in powder form containing the second element in a solution A step, a gelation step using the dispersion as a gel, and a heating step of heating the gel and supporting the ferroelectric on the active material raw material.

  Hereinafter, specific examples will be described with reference to examples.

<Manufacture of positive electrode material>
The active material used was lithium cobaltate (LiCoO ₂ ) that has been put to practical use in lithium ion batteries. Lithium cobaltate was powdered and had an average particle size of 3 μm. The ferroelectric material supported on lithium cobaltate was barium titanate (BaTiO ₃ ), the first element material was barium acetate as a Ba source, and the second element material was titanium butoxide as a Ti source.

  Lithium cobaltate is a lithium cobaltate solution dispersed in ethanol, barium acetate is an acetic acid solution dissolved in acetic acid, titanium butoxide is a methoxyethanol solution dissolved in 2-methoxyethanol, lithium cobaltate solution A predetermined amount of an acetic acid solution and a methoxyethanol solution were added to the solution and ultrasonically dispersed to obtain a dispersion. This is the dispersion preparation process. Here, the lithium cobaltate solution is a solution in which 5 g of lithium cobaltate is dispersed in 40 mL of ethanol, the acetic acid solution is a solution of 1.31 g of barium acetate in 20 ml of acetic acid, and the methoxyethanol solution is A solution in which 1.76 g of titanium butoxide was dissolved in 20 ml of 2-methoxyethanol was adjusted so that barium titanate was 10 mol% with respect to lithium cobaltate.

  The dispersion was stirred and dried at 70 ° C. for 6 hours to obtain a gel. This is the gelation process.

The obtained gel was heat-treated at 400 ° C, 500 ° C, 600 ° C, 700 ° C and 800 ° C for 20 hours, respectively. This is the heating process. The STEM image and STEM-EDS image of each powder after a heating process are shown in FIG. In Fig. 1, "LC-BT-400" is 400 ° C, "LC-BT-500" is 500 ° C, "LC-BT-600" is 600 ° C, "LC-BT-700" In the case of 700 ° C, “LC-BT-800” shows the case of 800 ° C. The same applies to FIGS. 2 and 4 described later. “Bare LC” is a state of only untreated LC, ie, LiCoO ₂ not carrying BaTiO ₃ .

The XRD pattern of the obtained powder is shown in FIG. As shown in FIG. 2, when the heat treatment temperature is 500 ° C. or lower, BaTiO ₃ (BT) is not sufficiently formed, BaCO ₃ (BC) is the main component, and when it is 600 ° C. or higher, BaTiO ₃ (BT) is the main component. It can be seen that

  In particular, as can be seen from the STEM-EDS image in FIG. 1, it was confirmed that a two-phase composite structure of LC phase and BT phase (or BC phase) nanoparticles was obtained at all heat treatment temperatures.

Furthermore, BaTiO ₃ particle growth was observed as the heat treatment temperature increased. Among the samples with BaTiO ₃ particles formed, the sample with the smallest particle size was a sample heat-treated at 600 ° C. The STEM image is shown in FIG. As can be seen from FIG. 3, the surface of the active material is coated with nanoparticles having a uniform particle diameter. When the particle size of the BaTiO ₃ particles was confirmed, the average particle size was 65 nm.

<Performance evaluation method of positive electrode material>
In order to evaluate whether the composite powder produced by the above method has performance as a positive electrode material, performance evaluation was performed by the following method.

  First, a composite sheet, a conductive additive (acetylene black), and a binder polymer (PVDF) were mixed at a mass ratio of 7: 2: 1 to prepare a positive electrode sheet.

The counter electrode was Li metal, and the electrolyte was 1 mol / L lithium fluorophosphate LiPF _{6 in} which ethylene carbonate and diethyl carbonate were dissolved in a solvent having a volume ratio of 3: 7. Then, a charge / discharge test was performed in a potential range of 3.3 V to 4.5 V using a 2023 type coin cell. The charge / discharge rate was controlled by stepping up the rate in 5 cycles for each rate in the range of current density from 0.1C to 5C or 10C [1C = 160 mA / g (LC theoretical capacity conversion)].

The result of the capacity | capacitance characteristic in a high-speed charging / discharging rate is shown in FIG. For the samples heat-treated at 400 ° C. and 500 ° C., the initial capacity and the discharge capacity at the fast charge / discharge rate were extremely low compared to lithium cobaltate alone (untreated product). This is probably because BaCO ₃ (BC) is an impurity phase that is not a ferroelectric substance. On the other hand, when the heat treatment temperature is 600 ° C. or higher, almost single-phase BaTiO ₃ particles are formed, so the effect of BaTiO ₃ particles can be expected.

“Capacity at 0.1C-1 cycle” in the above table is “initial capacity”, and “capacity retention ratio relative to initial capacity at 10C-5th cycle (35th cycle in total)” is calculated.
In addition, “Improvement ratio relative to untreated products” is a comparison between the capacity of untreated products and the capacity of 600 ° C heated products in “5C-5th cycle (total 30th cycle) capacity” and This is a comparison between the capacity and the capacity of the 800 ° C heated product.

As shown in Table 1, the initial capacities of the 600 ° C and 800 ° C heated products were both slightly lower than the untreated products, but this was due to the effect of the mass fraction of BaTiO ₃ that did not contribute to the capacity. is there.

  The capacity at the high-speed charge / discharge rate shows excellent capacity (122 mAh / g) with a product heated at 600 ° C after 30 cycles of 5C-5th cycle, and heating at 800 ° C with an average particle size of 158 nm It can be seen that there is a significant improvement compared to the product. In particular, the value of “122 mAh / g” significantly reverses the discharge capacity (78 mAh / g) of the untreated product, and the improvement rate is 158%. From this, it is understood that the characteristics of the high-speed charge / discharge rate are further improved by making the particle size of the ferroelectric particles smaller than 100 nm.

As described above, in Example 1, it was confirmed that the particle size of BaTiO ₃ particles can be minimized by setting the optimum heat treatment temperature to 600 ° C. However, it is necessary to examine the optimum amount of BaTiO ₃ particles with respect to LiCoO ₂ . The following Example 2 was carried out.

In <Manufacture of positive electrode material> described above, when the temperature of the heating step is 600 ° C. and becomes BaTiO ₃ , 1 mol%, 2.5 mol%, 5 mol%, 10 mol%, 15 mol% of BaTiO _{3 with} respect to LiCoO ₂ Each powder was prepared by adjusting the dispersion liquid so as to cause the above. Here, the acetic acid solution and the methoxyethanol solution to be added to the lithium cobaltate solution do not simply adjust the addition amount to the lithium cobaltate solution, but appropriately adjust the barium concentration of the acetic acid solution and the titanium concentration of the methoxyethanol solution, Addition of acetic acid and 2-methoxyethanol more than necessary to the lithium cobaltate solution was suppressed. Specifically, the acetic acid solution is a solution in which 0.13 g to 1.96 g of barium acetate is dissolved in 2 ml to 20 ml of acetic acid, and the methoxyethanol solution is 0.18 g to 2.63 g in 2 ml to 20 ml of 2-methoxyethanol. A solution in which titanium butoxide was dissolved was used.

FIG. 5 shows an XRD pattern of the obtained powder. As the amount of BaTiO ₃ contained in the powder decreases, the peak intensity of BaTiO ₃ (BT) decreases, which is considered to be due to the decrease in the relative amount with respect to LiCoO ₂ . Even so, it can be considered that BaTiO ₃ is formed.

FIG. 6 shows STEM-EDS images of the sample in the case of BaTiO ₃ (BT) 1 mol% and the sample in the case of BaTiO ₃ (BT) 5 mol%. It can be confirmed from FIG. 6 that the BT phase-LC phase has a two-phase composite structure. Although not shown, it was confirmed that all other samples had a two-phase composite structure of BT phase and LC phase.

Fig. 7 shows the capacity characteristics at a fast charge / discharge rate for a sample with BaTiO ₃ (BT) 1 mol%, a sample with BaTiO ₃ (BT) 5 mol%, and a sample with LiCoO ₂ alone (untreated product). The results are shown. Based on this capacity characteristic, a comparison of various characteristics is shown in the table below.

“Capacity at 0.1C-1 cycle” in the above table is “initial capacity”, and “capacity retention ratio relative to initial capacity at 10C-5th cycle (35th cycle in total)” is calculated.
“Improvement ratio relative to untreated products” is the comparison between the capacity of untreated products and the capacity of BT1 mol% products in “capacity of 10C-5th cycle (35th cycle in total)” And the capacity of BT5mol% product.

As shown in Table 2, the initial capacity decreased with an increase in the added amount of BaTiO ₃ , which is an effect of the mass fraction of the ferroelectric BaTiO ₃ that does not contribute to the capacity.

Further, as shown in Table 2, significantly impact on the capacity characteristics in a high-speed charge and discharge rate of the BaTiO ₃ additive amount, BaTiO ₃ added amount is more effective than 5 mol% is more of 1 mol%, in particular BaTiO ₃ When the addition amount is 1 mol%, after 35 cycles (5th cycle at 10C), the untreated product to be compared, that is, LiCoO ₂ alone has a capacity of 62 mAh / g, whereas 146 mAh / g and 238% improvement. Furthermore, regarding the capacity retention rate at the high-speed charge / discharge rate, when the addition amount of BaTiO ₃ is 1 mol%, the initial capacity value is 78% at the 35th cycle, whereas only the untreated product, that is, LiCoO ₂ Was 33%, confirming a significant improvement.

Claims (5)

An active material raw material in powder form of an active material constituting a positive electrode of a lithium ion battery, and a first powder form containing a first element for constituting a ferroelectric containing a first element and a second element A dispersion preparing step of preparing a dispersion by dispersing a single element raw material and a powdered second element raw material containing a second element in a solution;
A gelation step using the dispersion as a gel;
A method for producing a positive electrode material of a lithium ion battery, comprising: a heating step of heating the gel and supporting the ferroelectric on the active material material.   2. The positive electrode of the lithium ion battery according to claim 1, wherein the first element material and the second element material are 5 mol% or less with respect to the active material material when the ferroelectric material is formed in the heating step. Material manufacturing method.   The active material raw material is lithium cobalt oxide, the first element raw material is barium acetate, the first element raw material is titanium butoxide, and the active material constituting the positive electrode of the lithium ion battery supports barium titanate. Item 3. A method for producing a positive electrode material for a lithium ion battery according to Item 2.   4. The lithium ion battery according to claim 3, wherein in the gelation step, the dispersion is gelled by drying with stirring at 70 ° C. for 6 hours, and in the heating step, the dispersion is heated at 600 ° C. for 20 hours. Manufacturing method of positive electrode material. A dispersion in which powdered lithium cobaltate, powdered barium acetate, and powdered titanium butoxide are dispersed in a solution is dried with stirring to form a gel, and the gel is heated. An electrode material in which barium titanate is supported on lithium cobaltate,
An electrode material having a particle size of the barium titanate of 100 nm or less.