JP2012084358A - Lithium secondary battery anode material and manufacturing method thereof and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery anode material whose irreversible capacity (difference between charging and discharging capacities) is small and which has excellent charging-discharging cycle characteristics and a large discharging capacity.SOLUTION: A ramsdellite type lithium titanate LiTiO(0.75≤x≤2.66, 1.33≤y≤4, 3≤z≤7) subjected to post-annealing treatment under predetermined post-annealing conditions and having a three-dimensional tunnel structure is used as a lithium secondary battery anode material, and an anode active material pellet 2 containing at least the ramsdellite type lithium titanate is made the anode of a lithium secondary battery. The post-annealing condition is preferably such that post annealing be carried out in an inert gas atmosphere not containing oxygen, such as a nitrogen gas or an argon gas atmosphere, at any temperature in the range 100 to 400°C for any duration of time of at least 3 hours or more.

Description

  The present invention relates to a negative electrode material for a lithium secondary battery, a negative electrode material manufacturing method for a lithium secondary battery, and a lithium secondary battery, and in particular, lithium titanate having a large discharge capacity and excellent cycle characteristics is used as a negative electrode active material. The present invention relates to a negative electrode material for a lithium secondary battery, a method for producing a negative electrode material for a lithium secondary battery, and a lithium secondary battery.

  With the development of small ubiquitous devices and the development of environmentally friendly natural energy power generation systems, development of high-performance secondary batteries having a power storage function is highly expected.

The negative electrode material used in the current lithium secondary battery is generally a carbon material exhibiting an electrode potential of ⁰ to 0.1 V (vs. Li / Li ⁺ ) with respect to the metallic lithium standard.

In recent years, large lithium secondary batteries have a noble electrode potential that is nobler than the electrode potential of carbon materials to ensure a particularly high level of safety, and (1 × 1) tunnels are formed in the crystal structure. Attention has been focused on using spinel type lithium titanate (1.5 V vs. Li / Li ⁺ ) as a negative electrode material.

  However, the theoretical discharge capacity of spinel type lithium titanate is 175 mAh / g, which is the same level as lithium cobaltate which is the current positive electrode material, and has a noble electrode potential. Therefore, compared with a battery using a conventional carbon material. However, there is a problem that the battery voltage is lowered by 1 V or more and the energy density of the battery is lowered.

  On the other hand, the theoretical discharge capacity of Ramsdellite type lithium titanate having a larger (2 × 1) tunnel than that of the spinel type is 235 mAh / g, and a large discharge capacity is expected. This is advantageous for increasing the density (see Patent Document 1).

However, the ramsdellite type has a characteristic that the ionic conductivity is high because the oxygen content in the crystal is smaller than that of the spinel type. However, the ramsdelite type has a low oxygen content and high activity, so that the stability is high. It is relatively low and easily reacts with oxygen in the atmosphere. For this reason, by reacting with oxygen in the atmosphere, titanium on the particle surface is oxidized, titania (TiO ₂ ) is generated, and the surface resistance is increased, so that the conductivity of lithium ions is expected to decrease. The

  As a result of the above phenomena, when used as an actual lithium secondary battery, Ramsdelite type lithium titanate has an irreversible capacity (the difference between the charge capacity and the discharge capacity) more and more as the charge / discharge cycle operation is repeated. There was a problem of becoming (Non-Patent Document 1).

Japanese Patent Laid-Open No. 10-247496 “Lithium Battery and its Active Material”

R.K.B.Gover, et.al, “Investigation of Ramsdellite Titanates as Possible New Negative Electrode Materials for Li Batteries”, Journal of the Electrochemical Society, 146, (1999), pp. 4348-4353.

  Spinel type lithium titanate can realize a capacity close to the theoretical capacity because the diffusivity of lithium ions does not depend on the crystal orientation.

  On the other hand, the ramsdellite type lithium titanate has a high theoretical discharge capacity as described above, but has a problem that the irreversible capacity (difference between charge capacity and discharge capacity) is large.

  The present invention has been made in order to solve the above-described conventional problems, and reduces the irreversible capacity of ramsdelite type lithium titanate capable of increasing the discharge capacity, and has excellent cycle characteristics. It aims at providing the negative electrode material for secondary batteries, the negative electrode material manufacturing method for lithium secondary batteries, and a lithium secondary battery.

  The present invention comprises the following technical means in order to solve the above-mentioned problems.

The first technical means is Li _x Ti _y O _z (0.75 ≦ x ≦ 2.66, 1.33 ≦) which is a ramsdellite type lithium titanate having a three-dimensional tunnel structure as a lithium titanate-based negative electrode material. In a negative electrode material for a lithium secondary battery using y ≦ 4, 3 ≦ z ≦ 7), the ramsdelite-type lithium titanate is subjected to a post-annealing treatment under a predetermined post-annealing condition to produce a negative electrode material It is characterized by being.

  According to a second technical means, in the negative electrode material for a lithium secondary battery described in the first technical means, the atmosphere condition of the post-annealing condition is a non-oxygen-containing non-oxygen to the ramsdelite type lithium titanate. The negative electrode material is produced by performing a post-annealing process in an active gas atmosphere.

  In the negative electrode material for a lithium secondary battery according to the second technical means, a third technical means uses either nitrogen gas or argon gas as the inert gas atmosphere as the atmospheric condition of the post-annealing condition. It is characterized by using.

  According to a fourth technical means, in the negative electrode material for a lithium secondary battery according to any one of the first to fourth technical means, the ramsdellite type titanic acid is used as a temperature condition and a treatment time condition of the post-annealing condition. It is produced as the negative electrode material by performing post-annealing treatment for any time of at least 3 hours at any temperature within a temperature range of 100 to 400 ° C. with respect to lithium. To do.

The fifth technical means is Li _x Ti _y O _z (0.75 ≦ x ≦ 2.66, 1.33 ≦ y ≦ 4, 3 ≦ z ≦) which is a ramsdelite type lithium titanate having a three-dimensional tunnel structure. 7) is a method for producing a negative electrode material for a lithium secondary battery, wherein the ramsdelite type lithium titanate is subjected to a post-annealing process under predetermined post-annealing conditions. It includes a step of producing as a negative electrode material.

  Sixth technical means, in the method for producing a negative electrode material for a lithium secondary battery according to the fifth technical means, contains oxygen relative to the ramsdellite type lithium titanate as the atmospheric condition of the post-annealing condition. The post-annealing process is performed in an inert gas atmosphere.

  Seventh technical means is the method for producing a negative electrode material for a lithium secondary battery according to the sixth technical means, wherein the inert gas atmosphere as the atmospheric condition of the post-annealing condition is any one of nitrogen gas and argon gas. It is characterized by using or.

  According to an eighth technical means, in the method for producing a negative electrode material for a lithium secondary battery according to any one of the fifth to seventh technical means, the temperature condition and the processing time condition of the post-annealing condition are the Ramsdelite type. The lithium titanate is subjected to a post annealing treatment at any temperature within a temperature range of 100 to 400 ° C. for any time of at least 3 hours.

  A ninth technical means includes a negative electrode containing a lithium titanate-based material as a negative electrode material for a lithium secondary battery, and a positive electrode containing a positive electrode material capable of inserting and removing lithium ions. In the lithium secondary battery configured by disposing a conductive electrolyte between the negative electrode and the positive electrode, the negative electrode material for the lithium secondary battery contained in the negative electrode includes the first to fourth elements. It consists of the lithium secondary battery negative electrode material as described in any one of the technical means.

  A tenth technical means is the lithium secondary battery according to the ninth technical means, wherein the negative electrode material for a lithium secondary battery is mixed with powder of the negative electrode material for a lithium secondary battery, carbon, and a binder. It is formed into either a rolled sheet or a pellet and used as the negative electrode.

The problem in the prior art that the irreversible capacity of ramsdelite-type lithium titanate is large is that the surface of the particles is caused by the reaction with oxygen in the atmosphere in the manufacturing process of ramsdelite-type lithium titanate used for the anode material for lithium secondary batteries. This is due to the generation of an inert phase called titania (TiO ₂ ).

  Therefore, in the present invention, in order to remove the inert phase generated on the particle surface, a step of performing a post-annealing process is newly introduced in the manufacturing process of the negative electrode material for a lithium secondary battery. By introducing the post-annealing process, a clean particle surface is obtained as ramsdelite type lithium titanate, so that the diffusibility of lithium ions is improved, the irreversible capacity is small, and the excellent charge / discharge cycle characteristics are obtained. A lithium titanate-based negative electrode material having a large discharge capacity can be obtained.

  Thus, according to the present invention, the irreversible capacity (difference between the charge capacity and the discharge capacity) is smaller than that of the conventional ramsdelite type lithium titanate negative electrode material, and has excellent charge / discharge cycle characteristics, and Thus, it is possible to realize a negative electrode material for a lithium secondary battery having a larger discharge capacity than a spinel type lithium titanate negative electrode material which is a known material.

  In addition, a negative electrode containing a lithium secondary battery negative electrode material as described above and a positive electrode containing a positive electrode material capable of inserting and removing lithium, and an electrolyte having lithium ion conductivity between the positive electrode and the negative electrode By disposing, a lithium secondary battery having a small irreversible capacity, excellent charge / discharge cycle characteristics, and a large discharge capacity can be produced.

It is a characteristic view which shows the XRD pattern of the ramsdellite type lithium titanate which performed the post-annealing process for 5 hours at various temperatures in the negative electrode material manufacturing method for lithium secondary batteries which concerns on this invention. It is a characteristic view which shows the XRD pattern of the ramsdellite type lithium titanate which performed the post-annealing process for the various process time in the temperature of 90 degreeC and 450 degreeC in the negative electrode material manufacturing method for lithium secondary batteries which concerns on this invention. The XRD pattern of the ramsdellite type lithium titanate which performed the post-annealing process in various atmospheres in the same temperature and time (250 degreeC, 5 hours) in the manufacturing method of the negative electrode material for lithium secondary batteries which concerns on this invention is shown. FIG. It is battery sectional drawing which shows an example of the cross-sectional structure of the test cell of the lithium secondary battery using the negative electrode material for lithium secondary batteries which concerns on this invention. It is battery sectional drawing which shows an example of the cross-sectional structure of the coin cell of the lithium secondary battery using the negative electrode material for lithium secondary batteries which concerns on this invention. In a method for producing a negative electrode material for a lithium secondary battery according to the present invention, a lithium secondary battery using, as a working electrode material, ramsdellite type lithium titanate that has been post-annealed at 250 ° C. and 450 ° C. for 5 hours. It is a characteristic view which shows an example of the charging / discharging curve of 10th cycle. It is a characteristic view which shows an example of the charging / discharging cycle characteristic of the test cell of the lithium secondary battery using the negative electrode material for lithium secondary batteries which concerns on this invention.

  Hereinafter, examples of preferred embodiments of a negative electrode material for a lithium secondary battery, a method for producing a negative electrode material for a lithium secondary battery, and a lithium secondary battery according to the present invention will be described in detail with reference to the drawings.

(Features of the present invention)
Prior to the description of the embodiments of the present invention, an outline of the features of the present invention will be described first. The present invention relates to a negative electrode material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery using the negative electrode material, and a three-dimensional tunnel subjected to post-annealing treatment as a negative electrode material for a lithium secondary battery By using the Ramsdellite Type lithium titanate structure, it is possible to realize a lithium secondary battery with low irreversible capacity, excellent charge / discharge cycle characteristics, and high discharge capacity. It is said.

That is, Li _x Ti _y O _z (0.75), which is a ramsdellite-type lithium titanate having a three-dimensional tunnel structure, synthesized by heat-treating non-tunneled lithium titanate in a temperature range of 900 ° C. to 1250 ° C. ≦ x ≦ 2.66, 1.33 ≦ y ≦ 4, 3 ≦ z ≦ 7) under the conditions determined in advance as the post-annealing conditions, for example, a non-concentration composed of either a nitrogen bath or argon (Ar) gas. A post-annealing treatment is performed in an active gas at any temperature within a temperature range of 100 ° C. to 400 ° C. for any treatment time of at least 3 hours to produce a negative electrode material for a lithium secondary battery. A negative electrode containing the negative electrode material for the lithium secondary battery, and a positive electrode material capable of easily inserting and removing lithium ions A positive electrode containing, is characterized in that to realize a lithium secondary battery composed of an electrolyte having lithium ion conductivity.

(Method for producing negative electrode material for lithium secondary battery according to the present invention)
Next, an example of a method for producing a negative electrode material for a lithium secondary battery according to the present invention will be described. The negative electrode material for a lithium secondary battery according to the present invention is synthesized by the following procedure.

  First, lithium titanate having no tunnel structure is synthesized by reacting a titanium oxide and a lithium compound by various methods.

  For example, lithium titanate not having a tunnel structure is prepared by using a solid phase reaction method, a sol-gel method, a precipitation method, or the like to prepare a mixed precursor of a titanium oxide and a lithium compound, and a temperature range of 600 to 800 ° C. It can be produced by performing a heat treatment in the inside.

Next, the produced non-tunneled lithium titanate is subjected to heat treatment at a high temperature within a temperature range of 900 to 1250 ° C., so that the ramsdellite-type lithium titanate Li _x Ti _y O _z having a three-dimensional tunnel crystal structure is obtained. (0.75 ≦ x ≦ 2.66, 1.33 ≦ y ≦ 4, 3 ≦ z ≦ 7) is synthesized.

Thereafter, the obtained ramsdellite-type lithium titanate Li _x Ti _y O _z is used as an atmospheric condition for predetermined post-annealing conditions, and an inert gas atmosphere (for example, nitrogen gas or argon (Ar) gas) containing no oxygen is used. The post-annealing process is performed inside. The post-annealing treatment is performed at any temperature within a temperature range of 100 to 400 ° C. (for example, 250 ° C.) as a temperature condition and a processing time condition of predetermined post-annealing conditions, and at least 3 hours or more. It is desirable to carry out for a period of time (for example, 15 hours).

  Through such a procedure, a negative electrode material for a lithium secondary battery having a small irreversible capacity, excellent charge / discharge cycle characteristics, and a large discharge capacity can be obtained.

  The negative electrode material for a lithium secondary battery according to the present invention is formed in either a pellet shape or a sheet shape obtained by mixing and rolling with carbon and a binder, as in the case of a conventional negative electrode material. By combining a positive electrode material such as lithium cobaltate and a known organic electrolyte, various types of lithium secondary batteries such as a coin shape, a cylindrical shape, a square shape, and a sheet shape can be produced.

(Example)
Examples of a negative electrode material for a lithium secondary battery, a method for producing a negative electrode material for a lithium secondary battery, and a secondary battery using the negative electrode material according to the present invention will be described in detail below. In addition, this invention is not limited only to the Example demonstrated below, In the range which does not change the summary, it cannot be overemphasized that it can change suitably and can implement.

Example 1
First, as Example 1, the result of evaluating the temperature condition among the post-annealing conditions when performing the post-annealing process will be described.

(1) Method for producing ramsdelite-type lithium titanate as negative electrode material In Example 1, ramsdelite-type lithium titanate, which is a negative electrode material for lithium secondary batteries, was subjected to a two-step solid-phase reaction shown in the following chemical formula. Synthesized.

Li2CO3 + TiO2 → Li2TiO3 + CO2 + H2O (1)
(1/2) Li2TiO3 + (5/4) TiO2 + (1/4) Ti
→ LixTiyOz (2)
First, as shown in the above reaction formula (1), lithium carbonate (Li 2 CO 3) and titanium oxide (TiO 2) are mixed and subjected to a heat treatment at 700 ° C. for 5 hours, whereby a non-tunneled lithium titanate ( Li2TiO3) was obtained.

  Next, as shown in the above reaction formula (2), the obtained non-tunneled lithium titanate (Li 2 TiO 3) is mixed with titanium oxide and titanium metal and subjected to heat treatment at 1200 ° C. for 10 hours. As a result, lithium titanate (LixTiyOz) having a three-dimensional tunnel crystal structure was obtained (where 0.75 ≦ x ≦ 2.66, 1.33 ≦ y ≦ 4, 3 ≦ z ≦). 7).

  Note that all heat treatments were performed in a nitrogen gas atmosphere not containing oxygen.

  Furthermore, as post-annealing conditions for performing the post-annealing treatment, 75 ° C., 90 ° C., 100 ° C., 125 ° C., 150 ° C., 250 ° C. in a nitrogen gas atmosphere with respect to the powdered ramsdellite type lithium titanate. , 350 ° C., 400 ° C., 425 ° C., 450 ° C., and 550 ° C., respectively, for 5 hours.

(2) Evaluation of crystal structure according to temperature during post-annealing treatment Next, evaluation of the crystal structure according to temperature during post-annealing treatment in the above-described method for producing ramsdelite type lithium titanate was performed using an XRD pattern (X-Ray Diffraction: X The results obtained based on (line diffraction) will be described. FIG. 1 is a characteristic diagram showing XRD patterns of ramsdellite-type lithium titanate subjected to post-annealing treatment at various temperatures for 5 hours in the method for manufacturing a negative electrode material for a lithium secondary battery according to the present invention. The horizontal axis in FIG. 1 is the diffraction angle (2θ: twice the Bragg angle), and the vertical axis shows the X-ray intensity in an arbitrary relative unit for each temperature during each post-annealing process.

  In FIG. 1, (b), (c), (d), (e), (g), (h), and (i) show the ramsdelite type lithium titanate prepared in Example 1. The XRD pattern of the sample which performed the post-annealing process for 5 hours at each temperature of 90 degreeC, 100 degreeC, 125 degreeC, 400 degreeC, 425 degreeC, 450 degreeC, and 550 degreeC is shown, respectively. FIG. 1A also shows an XRD pattern without post-annealing as a reference.

  As shown in FIGS. 1 (b), (c), (d) and (e), as in the case without post-annealing in FIG. Also for the sample of Fig. 1 (f), the ramsdelite type titanate having a three-dimensional tunnel structure which matches the XRD pattern (PDF # 34-0393) of lithium titanate having the known ramsdelite type crystal structure shown in Fig. 1 (f). It was confirmed that the single phase crystal structure of lithium was maintained. That is, it was confirmed that there was no change in the crystal structure in the post-annealing process at a temperature condition of 400 ° C. or lower.

  On the other hand, as shown by the arrows in FIGS. 1 (g), (h), and (i), when the post-annealing treatment is performed under a temperature condition exceeding 400 ° C., a new peak appears in the XRD pattern of the sample around 20 ° or It occurred around 30 °, and it was confirmed that the ramsdellite type crystal structure collapsed.

(3) Evaluation of electrode characteristics: Evaluation by a charge / discharge test of a lithium secondary battery Next, a ramsdelite type lithium titanate prepared by performing post-annealing treatment under each temperature condition described above was used as a working electrode, and metallic lithium was A test cell having a size of 2320 (diameter: 23 mm, width: 2 mm) was prepared as a counter electrode, and the electrode characteristics were evaluated.

(3.1) Manufacturing Method of Lithium Secondary Battery First, a detailed manufacturing method of a test cell of a lithium secondary battery as shown in FIG. 4 used for evaluating the electrode characteristics of Example 1 will be described. FIG. 4 is a battery cross-sectional view showing an example of a cross-sectional structure of a test cell of a lithium secondary battery using the negative electrode material for a lithium secondary battery according to the present invention. For the material of the working electrode of the test cell, The ramsdelite type lithium titanate produced by performing post-annealing treatment under various temperature conditions in the procedure as described in the item (1) of Example 1 is used as a negative electrode material for a lithium secondary battery.

  First, ramsdelite-type lithium titanate powder as a negative electrode material, carbon acetylene black, and PTFE (polytetrafluoroethylene) as a binder are pulverized and mixed with a cracking machine (crusher), then rolled. The sheet was rolled to a thickness of 0.5 mm by pressing.

  Thereafter, the obtained sheet was punched out into a disk shape having a diameter of 15 mm and vacuum-dried overnight to produce a negative electrode material pellet serving as a working electrode, that is, a negative electrode active material pellet 2 shown in FIG. In addition, the composition of the negative electrode active material pellet 2 which becomes a working electrode is oxide (ramsdellite type lithium titanate powder): acetylene black: PTFE = 70: 25: 5 by weight ratio.

  Next, a titanium mesh having a diameter of 15 mm is welded to the inside of the working electrode case 1 of the test cell shown in FIG. 4, and a negative electrode active material pellet 2 serving as a working electrode is lightly pressure-bonded on the titanium mesh. The top of the pellet 2 was covered with a titanium mesh having a diameter of 17 mm, and the titanium mesh was welded to the working electrode case 1. Thereafter, the negative electrode active material pellet 2 containing ramsdellite type lithium titanate was fixed to the working electrode case 1 by further pressing.

  On the other hand, a nickel mesh is welded to the inner side of the counter electrode case 5 having a diameter of 23 mm of the test cell shown in FIG. 4, and lithium metal ions 4 can be easily inserted and extracted on the sheet-like metal lithium 4 having a diameter of 17 mm thereon. Crimping was performed as a counter electrode containing a positive electrode material, and a gasket 3 was set on the outer edge of the counter electrode case 5.

Next, a polyethylene separator 6 is placed on the working electrode case 1 to which the negative electrode active material pellet 2 is fixed, and a 1 mol / L LiPF ₆ / (EC + DMC) is obtained as an electrolyte non-aqueous electrolyte 7 having lithium ion conductivity. ) Was poured into a polyethylene separator 6, and the counter electrode case 5 on which the gasket 3 was set was covered from above the working electrode case 1, and the whole was caulked to prepare a test cell. Here, (EC + DMC) indicates a mixed solvent of ethylene carbonate and dimethyl carbonate, respectively, and a lithium salt of LiPF ₆ as an electrolyte is dissolved in the mixed solvent.

  As described above, in Example 1, acetylene black was used as the carbon mixed with the ramsdelite type lithium titanate. Other carbon blacks, activated carbons, graphites and the like may be used.

  Further, the particle diameter of carbon is not particularly limited as long as the particle diameter is suitable for ensuring sufficient conductivity between the ramsdellite-type lithium titanate particles and the battery case. However, in general, it is preferable from the viewpoint of securing a conductive path that the entire surface of the ramsdelite-type lithium titanate particles is in contact with the carbon particles, and the size of the carbon particles is larger than that of the ramsdelite-type lithium titanate. Those having a small value are desirable.

  Also, the binder is not particularly limited. In addition to polytetrafluoroethylene (PTFE) used in Example 1, ordinary lithium secondary such as polyethylene, polypropylene, and polyvinylidene fluoride (PVDF). Binders used in batteries can be used.

  Further, the non-aqueous electrolyte solution 7 having lithium ion conductivity and the separator 6 that physically separates the negative electrode active material pellet 2 and the metal lithium 4 are also non-aqueous used in ordinary lithium ion secondary batteries. An electrolytic solution or a separator can be used and is not particularly limited.

(3.2) Evaluation by Charge / Discharge Test of Lithium Secondary Battery Using a test cell of a lithium secondary battery produced by the above-described production method, a current density of 1 mA / cm ² and a voltage range of 0.5 to 3.5 V Under the conditions, a charge / discharge test was performed. FIG. 6 shows a working electrode of ramsdellite-type lithium titanate that was post-annealed in a nitrogen gas atmosphere at temperatures of 250 ° C. and 450 ° C. for 5 hours in the method for manufacturing a negative electrode material for a lithium secondary battery according to the present invention. It is a characteristic view which shows an example of the charging / discharging curve of the 10th cycle of the lithium secondary battery used as material, In the test cell of the lithium secondary battery produced by the above-mentioned manufacturing method, current density 1mA / cm < ² >, voltage range 0 10 shows a charge / discharge curve at the 10th cycle when the charge / discharge operation is repeated under the condition of 5-3.5 V together with the case without post-annealing treatment. The horizontal axis in FIG. 6 indicates the charge / discharge capacity (mAh / g), and the vertical axis indicates the voltage (V).

  In FIG. 6, three curves (A), (B), and (C) indicated as “Li ion desorption” indicate electrode characteristics during the discharge operation of the 10th cycle, and are indicated as “Li ion insertion”. The three curves (D), (E), and (F) indicate the electrode characteristics during the charging operation of the 10th cycle. Each of the three curves is shown by curves (A) and (D), in which a ramsdelite type lithium titanate subjected to a post-annealing treatment at 250 ° C. for 5 hours in a nitrogen gas atmosphere is used as an active electrode active material. Curves (B) and (E) show the case where ramsdelite type lithium titanate subjected to post-annealing treatment at 450 ° C. for 5 hours in a nitrogen gas atmosphere is used as a working electrode active material. Curves (C) and (F) show cases where ramsdellite-type lithium titanate without post-annealing treatment is used as the active electrode active material.

  As shown in FIG. 6, the charge / discharge voltage of these ramsdelite-type lithium titanate materials is a low voltage of 1.5 V or less with respect to the lithium counter electrode, so that it can be used as a negative electrode material for lithium secondary batteries. Is possible.

  Moreover, in FIG. 6, compared with the sample without the post-annealing treatment shown by the curves (C) and (F), the post-annealing treatment at 250 ° C. for 5 hours shown by the curves (A) and (D) was performed. For the sample, it was found that the charge / discharge capacity increased and the irreversible capacity also decreased. On the other hand, the sample subjected to the post-annealing treatment at 450 ° C. for 5 hours shown by the curves (B) and (E) changes the crystal structure as described in FIG. It was also found that the charge / discharge capacity was greatly reduced even when compared with the sample without post-annealing shown in FIG.

  The three types of samples used in the charge / discharge test of FIG. 6 were further subjected to 100 cycles of charge / discharge tests, and the results are shown in FIG. 7 as the cycle dependency of the discharge capacity. FIG. 7 is a characteristic diagram showing an example of charge / discharge cycle characteristics of a test cell of a lithium secondary battery using the negative electrode material for a lithium secondary battery according to the present invention, in a sample without a post-annealing treatment, in a nitrogen gas atmosphere Of the discharge capacity when 100 cycles of charge / discharge test were conducted for each of the sample subjected to post-annealing treatment at 250 ° C. for 5 hours and the sample subjected to post-annealing treatment at 450 ° C. for 5 hours in a nitrogen gas atmosphere. The state of change is indicated by a black circle mark (●), an upward triangle mark (△), and a downward triangle mark (▽), respectively.

  For comparison, FIG. 7 shows a change in discharge capacity of a 100-cycle charge / discharge test for a sample subjected to a 5-hour post-annealing treatment in a nitrogen gas atmosphere at a low temperature of 75 ° C. Is also shown with a cross mark (×).

  As shown in FIG. 7, it was confirmed that the sample subjected to the post-annealing process at 250 ° C. can perform a very stable charge / discharge operation up to 100 cycles as indicated by the upward triangle mark (Δ). However, in the case of a sample without post-annealing treatment, and at a temperature of 450 ° C. and 75 ° C. deviating from the temperature range of 100-400 ° C. set as a desirable temperature condition for post-annealing treatment in the present invention. In the case of samples that have been annealed, it is confirmed that the discharge capacity decreases significantly when charging and discharging are repeated, as indicated by the black circle mark (●), downward triangle mark (▽), and cross mark (x). It was.

  In addition, as post-annealing conditions, including those without post-annealing treatment, each temperature condition of 75 ° C, 90 ° C, 100 ° C, 125 ° C, 150 ° C, 250 ° C, 350 ° C, 400 ° C, 425 ° C, and 450 ° C ( The atmosphere was all nitrogen gas, and the processing time was all 5 hours). Samples prepared by post-annealing were used in the first cycle, the fifth cycle, the 10th cycle, the 50th cycle, and the 100th cycle. The results of measuring the discharge capacity, the discharge capacity maintenance rate after 100 cycles, and the irreversible capacity (the difference between the charge capacity and the discharge capacity) between the first cycle and the 100th cycle are shown in Table 1 below. In the leftmost column of Table 1, in order to facilitate understanding, not only the sample used in Example 1 but also the sample used in Example 2 and Example 3 described later are used. Indicates that.

表１に示すように、本発明において望ましいポストアニーリング処理用の温度条件として設定した１００−４００℃の温度範囲内の温度条件でポストアニーリング処理を行った場合には、不可逆容量が減少し、充放電サイクル特性の改善を図ることができることが確認された。

As shown in Table 1, when the post-annealing process is performed under a temperature condition within a temperature range of 100 to 400 ° C. set as a desirable temperature condition for the post-annealing process in the present invention, the irreversible capacity decreases and the charge is reduced. It was confirmed that the discharge cycle characteristics can be improved.

  For example, referring to Table 1, in the case of a sample subjected to post-annealing treatment at a temperature condition of 250 ° C., the discharge capacity maintenance ratio after 100 cycles shows the highest value of 95%, and 100 cycles of the sample without post-annealing treatment Compared with the discharge capacity maintenance rate after that, it was found that the discharge capacity was improved by about 25% and had excellent charge / discharge cycle characteristics. On the other hand, the sample subjected to the post-annealing treatment at a temperature condition deviating from the temperature range of 100 to 400 ° C. set as the desirable temperature condition for the post-annealing treatment in the present invention is the same as the sample without post-annealing. In either case, it was found that the discharge capacity retention rate after 100 cycles was as low as 70% or less.

  As described above, among the post-annealing conditions when performing the post-annealing process, the temperature condition should be set in advance to be any temperature within a temperature range of 100 ° C. or higher and 400 ° C. or lower. I found out.

(Example 2)
Next, as Example 2, the result of evaluating the processing time of the post-annealing process among the post-annealing conditions when performing the post-annealing process will be described. That is, in Example 2, ramsdellite-type lithium titanate was synthesized by a two-stage solid phase reaction similar to the production method described in Example 1, and the atmosphere of the post-annealing treatment was the same as in Example 1. As in the case of using nitrogen gas, the processing time of the post-annealing process is changed to various times, and the temperature condition within the temperature range of 100 to 400 ° C. set as the desired temperature condition for the post-annealing process in the present invention. Evaluation of changes in crystal structure and electrode characteristics in the case of 250 ° C. and in the case of 90 ° C. and 450 ° C. of temperature conditions deviating from the temperature range of 100-400 ° C. set as desirable post-annealing temperature conditions in the present invention did.

  Here, in the case of 250 ° C., which is a temperature condition within a temperature range of 100-400 ° C. set as a desirable temperature condition for the post-annealing treatment in the present invention, the processing time of the post-annealing treatment is 0.5 hours (30 Min), 0.75 hours (45 minutes), 1 hour, 3 hours, 5 hours (same as in Example 1), 10 hours, 15 hours, and 30 hours, and in the case of Example 1 Samples were synthesized by a similar two-step solid phase reaction. On the other hand, in the case of 90 ° C. and 450 ° C. that deviate from the temperature range of 100-400 ° C. set as the desirable temperature conditions for post-annealing in the present invention, the processing time of the post-annealing treatment is 0.5. Samples were synthesized by the same two-stage solid-phase reaction as in Example 1 at 5 types of time (30 minutes), 1 hour, 3 hours, 5 hours (same as in Example 1), and 10 hours. .

(1) Evaluation of crystal structure depending on temperature during post-annealing process First, at a temperature condition of 90 ° C. and 450 ° C. deviating from the temperature range of 100-400 ° C. set as a desirable temperature condition for post-annealing process in the present invention. About the sample which performed the post-earning process, the change of crystal structure was investigated by XRD pattern measurement. FIG. 2 shows characteristics of an XRD pattern of ramsdelite type lithium titanate subjected to post-annealing treatment at temperatures of 90 ° C. and 450 ° C. for various treatment times in the method for producing a negative electrode material for a lithium secondary battery according to the present invention. FIG. The horizontal axis of FIG. 2 is the diffraction angle (2θ: twice the Bragg angle), and the vertical axis is the X-ray intensity of an arbitrary relative unit at the time of each post-annealing treatment at 90 ° C. and 450 ° C. Shown for each processing time.

  As shown in FIGS. 2 (a), 2 (b), and 2 (d), in the case of a low-temperature post-annealing sample at 90 ° C., either 0.5 hour (30 minutes), 1 hour, or 10 hours In the same manner as in the case of the 5-hour post-earning treatment shown in FIG. 1B in Example 1 (in the case shown in FIG. 2C), a single-phase crystal of ramsdelite type lithium titanate was formed. I found out that

  However, as shown in FIGS. 2 (e) and 2 (f), in the case of a 450 ° C. high-temperature post-earning treatment sample, it was carried out even in the case of 0.5 hour (30 minutes) or 1 hour. As in the case of the 5-hour post-annealing treatment shown in FIG. 1 (h) in Example 1 (in the case shown in FIG. 2 (g)), the crystal structure changes, and further, a long-time heat treatment is performed. When it did, it turned out that the change of a crystal structure becomes more remarkable and it depends greatly on the processing time of a post-earning process.

  On the other hand, a sample subjected to post-annealing treatment at 250 ° C. in the temperature range of 100-400 ° C. set as a desirable temperature condition for post-annealing treatment in the present invention is also measured by XRD pattern measurement. The change of crystal structure was investigated. Although not shown, in the post-annealing process at 250 ° C., 0.5 hours (30 minutes), 0.75 hours (45 minutes), 1 hour, 3 hours, 10 hours, 15 hours, 30 hours In any treatment time, as in the case of the treatment time of 5 hours in FIG. 1D, it was confirmed that the single-phase crystal structure of ramsdellite type lithium titanate having a three-dimensional tunnel structure was confirmed.

  However, the relationship between the treatment time and the crystal growth is that the longer the treatment, the more the crystal grows and the higher the crystallinity. Even under the temperature condition of 250 ° C., the treatment time is longer than 30 hours. Then, as in the case where the post-annealing process is performed for 5 hours at a temperature of 450 ° C. or 550 ° C., the crystal structure tends to change.

(2) Evaluation of electrode characteristics: Evaluation by charge / discharge test of lithium secondary battery Next, production of Example 1 was performed using lithium titanate powder subjected to post-annealing treatment for each treatment time as described above. A negative electrode material pellet to be a working electrode is produced by a manufacturing method similar to the above method, and a test cell as shown in FIG. 4 having a working electrode using each negative electrode material pellet is produced. As in the case, the charge / discharge cycle measurement for each test cell was performed under the conditions of a current density of 1 mA / cm ² and a voltage range of 0.5 to 3.5 V.

  The post-annealing treatment is performed for 0.5 hour (30 minutes) and 1 hour at 90 ° C. and 450 ° C., respectively, deviating from the temperature range of 100 to 400 ° C. set as a desirable temperature condition for the post annealing treatment in the present invention. 3 hours, 5 hours (similar to the case of Example 1), a sample prepared by performing five kinds of time of 10 hours, and 100-400 ° C. set as a temperature condition for the post-annealing treatment desirable in the present invention The post-annealing treatment was performed at 250 ° C. under the temperature condition in the temperature range of 0.5 hour (30 minutes), 0.75 hour (45 minutes), 1 hour, 3 hours, 5 hours (as in the case of Example 1). The same) For samples prepared at 8 hours of 10 hours, 15 hours, and 30 hours, the first cycle, the fifth cycle, the 10th cycle, the 50th cycle, Table 2 shows the results of measuring the discharge capacity at each cycle, the discharge capacity retention rate after 100 cycles, and the irreversible capacity (the difference between the charge capacity and the discharge capacity) between the first cycle and the 100th cycle. Show. In the leftmost column of Table 2, as in the case of Table 2, not only in the case of the sample used in Example 2, but also in Example 1 and Example 3 described later, in order to facilitate understanding. If it is a sample to be used, this is indicated.

表２に示すように、本発明において望ましいポストアニーリング処理用の温度条件として設定した１００−４００℃の温度範囲からは逸脱した９０℃という低温処理の試料の１００サイクル後における放電容量維持率については、比較的長時間の１０時間のポストアニーリング処理を行った場合には７９％以上を実現しているものの、表１に示したポストアニーリング処理無しの場合の放電容量維持率（６９．８％）よりも約１０％の改善しか確認されなかった。さらに、５時間以下のポストアニーリング処理の試料に関しては、ポストアニーリング処理の効果が全く見られないことが分かった。

As shown in Table 2, the discharge capacity retention rate after 100 cycles of a sample at a low temperature of 90 ° C. deviating from the temperature range of 100-400 ° C. set as a desirable temperature condition for post-annealing in the present invention When a relatively long 10-hour post-annealing treatment was performed, 79% or more was achieved, but the discharge capacity retention rate without the post-annealing treatment shown in Table 1 (69.8%) Only about 10% improvement was confirmed. Furthermore, it was found that the post-annealing effect was not seen at all for the post-annealing sample of 5 hours or less.

  Table 2 shows the discharge capacity retention rate after 100 cycles of a sample at a high temperature of 450 ° C. deviating from the temperature range of 100-400 ° C. set as a desirable temperature condition for post-annealing in the present invention. Thus, the longer the processing time of the post-annealing process, the lower the discharge capacity maintenance rate after 100 cycles, and even with the shortest processing time of 0.5 hours (30 minutes), 62% It turned out to be quite low. In other words, as shown in FIGS. 2E, 2F, and 2G, for the sample processed at a high temperature of 450 ° C., the longer the processing time of the post-annealing process, the more the change in crystal structure proceeds. Since mixing of the layers becomes remarkable, it can be considered that the resistance at the particle interface increases and the discharge capacity rapidly decreases.

  On the other hand, discharge after 100 cycles of a sample subjected to post-annealing treatment at 250 ° C. in a temperature condition within a temperature range of 100-400 ° C. set as a desirable temperature condition for post-earning treatment in the present invention. As shown in Table 2, the capacity retention rate is as high as 86.4% even when the processing time is the shortest 0.5 hour (30 minutes). As the processing time increases to 97.1% at 15 hours, the post-annealing processing time is as high as 95.9% even if the processing time is 30 hours. The value was found to be obtained.

  In addition, for the sample having a treatment time of less than 3 hours at 250 ° C., there was hardly any significant change in the discharge capacity until the 10th cycle, but a rapid decrease in the discharge capacity was observed after the 50th cycle. On the other hand, for samples having a long processing time of 3 hours or more, the decrease in discharge capacity and the irreversible capacity from the first cycle to the 100th cycle are small, and in particular, in the case of a processing time of 15 hours, 100 cycles. The reduction of the discharge capacity to the eye and the value of the irreversible capacity were very small, and it was found that the post-annealing treatment showed the highest effect.

  In other words, the irreversible capacity at the 100th cycle is obtained by performing the post-annealing treatment for a long time of 3 hours or more at 250 ° C. in the temperature range of 100 to 400 ° C. set as a desirable temperature condition for the post-annealing treatment in the present invention. As a result, it was found that the effect of post-annealing treatment was obtained. However, when the treatment time is longer for 30 hours under the temperature condition of 250 ° C., a high characteristic improvement effect is obtained, but further improvement beyond the characteristic improvement effect at the time of 15 hours treatment may not be obtained. I understood.

  As a factor that can improve the characteristics by performing a long-time post-annealing treatment of, for example, 3 hours or more at 250 ° C. within a temperature range of 100 to 400 ° C., by performing a long-time post-annealing treatment, It is considered that the rearrangement of ions at the grain boundary occurs, the dangling bond defect is eliminated, and as a result, the insertion / extraction of lithium ions in the charge / discharge cycle proceeds more efficiently. be able to.

  As described above, among the post-annealing conditions when performing the post-annealing treatment, the treatment time condition is that the treatment is performed for at least 3 hours when the temperature is any temperature within a temperature range of 100 ° C. to 400 ° C. It turned out that time should be predetermined.

(Example 3)
Next, as Example 3, the result of evaluating the atmosphere during the post-annealing process among the post-annealing conditions when performing the post-annealing process will be described. That is, in Example 3, a ramsdellite-type lithium titanate was synthesized by a two-stage solid phase reaction similar to the production method described in Example 1, and the post-processing time was 5 hours at a temperature of 250 ° C. In the annealing process, as an atmosphere of the post-annealing process, in addition to the nitrogen (N ₂ ) gas in the first embodiment, argon (Ar) gas, hydrogen-nitrogen (H ₂ -N ₂ ) mixed gas, oxygen gas, air For each of the above, changes in crystal structure and electrode characteristics were evaluated.

(1) Evaluation of crystal structure according to atmosphere during post-annealing treatment First, post-annealing treatment at 250 ° C. for 5 hours is performed using nitrogen gas, Ar gas, H ₂ —N ₂ mixed gas, oxygen gas, air With respect to each sample performed in the atmosphere, the change in crystal structure was examined by XRD pattern measurement. FIG. 3 is a schematic view of the ramsdellite-type lithium titanate subjected to post-annealing treatment in various atmospheres at the same temperature and time (250 ° C., 5 hours) in the negative electrode material manufacturing method for lithium secondary battery according to the present invention. It is a characteristic view which shows an XRD pattern. The horizontal axis in FIG. 3 is the diffraction angle (2θ: twice the Bragg angle), and the vertical axis is the X-ray intensity of an arbitrary relative unit at the time of each post-annealing treatment at temperatures of 90 ° C. and 450 ° C. Shown for each processing time.

In FIG. 3, FIGS. 3B, 3 </ b> C, 3 </ b> D, 3 </ b> E, and 3 </ b> F show nitrogen (N ₂ ) for the sample of ramsdelite-type lithium titanate manufactured in Example 1. In the respective atmospheres of gas (same as in Example 1), argon (Ar) gas, hydrogen-nitrogen (H ₂ -N ₂ ) mixed gas, oxygen gas, and air (air), The XRD pattern of the sample which performed the post annealing process is shown, respectively. Note that FIG. 3A also shows an XRD pattern without post-annealing processing as a reference.

  As shown in FIG. 3C, when Ar gas is used as the atmosphere of the post-annealing process, the case of the nitrogen gas of Example 1 (FIG. 3B shows the case of nitrogen gas at a temperature of 250 ° C. It was confirmed that a single phase crystal of ramsdellite-type lithium titanate having a three-dimensional tunnel crystal structure was obtained as a sample after the post-annealing treatment.

When a H ₂ —N ₂ mixed gas is used, as shown in FIG. 3D, post-annealing at 425 ° C. for 5 hours in the nitrogen atmosphere shown in FIG. As in the case of the treatment, in the XRD pattern of the sample after the post-annealing treatment, a new peak was generated near the diffraction angle 2θ = 27 °, and it was confirmed that the ramsdellite type crystal structure was broken. . This is considered to be because the sample is reduced because the atmosphere of the H ₂ —N ₂ mixed gas has a strong reducing property, which means that the atmosphere used for the post-annealing process is not desirable.

Furthermore, when oxygen gas or air is used, as shown in FIGS. 3E and 3F, the XRD pattern of the sample after the post-annealing treatment is different from the XRD pattern of the ramsdellite type lithium titanate. It was confirmed that completely different peaks were generated and the crystal structure was changed. This can be attributed to the fact that titanium on the sample surface reacts with oxygen in the atmosphere to produce titania (TiO ₂ ). That is, the generated phase as shown in FIGS. 3E and 3F is an XRD pattern (PDF # 75-1757) of titanium oxide having a known Rutile type crystal structure shown in FIG. ), And the presence of oxygen in the atmosphere during the post-annealing treatment confirmed that the ramsdellite-type lithium titanate was changed to a rutile-type titanium oxide (TiO ₂ ).

(2) Evaluation of electrode characteristics: Evaluation by charge / discharge test of lithium secondary battery Next, the production method of Example 1 using lithium titanate powder subjected to post-annealing treatment in each atmosphere as described above In the case of Example 1, negative electrode material pellets serving as working electrodes were produced by the same manufacturing method as in Example 1, and a test cell having a working electrode using each negative electrode material pellet as shown in FIG. Similarly, charge / discharge cycle measurement for each test cell was performed under the conditions of a current density of 1 mA / cm ² and a voltage range of 0.5 to 3.5 V.

One cycle for a sample prepared by performing post-annealing treatment at 250 ° C. for 5 hours using each of five atmospheres of nitrogen gas, Ar gas, H ₂ —N ₂ mixed gas, oxygen gas, and air 1st, 5th cycle, 10th cycle, 50th cycle, 100th cycle, discharge capacity maintenance rate after 100th cycle, and irreversible capacity (charge capacity and discharge) in the 1st cycle and 100th cycle The results of measuring the difference in capacity are shown in Table 3 below. Note that the leftmost column of Table 3 is used not only in the case of the sample used in Example 3 but also in Example 1 and Example 2 in order to facilitate understanding, as in Table 1. In the case of a sample, this is indicated.

表３に示すように、酸素ガス、空気のように、酸素を含む雰囲気中でポストアニーリング処理を行った試料の場合、前述のように、ルチル型構造の酸化チタン（ＴｉＯ_２）を有する試料に変化しているため、１サイクル目の放電後であっても充電容量が急激に減少し、１００サイクル後における放電容量維持率は３０％以下という著しく低い値になってしまう。この要因としては、チタン酸リチウムよりも酸化チタンの結晶粒界の抵抗がより高いので、イオン導電性が低下したためであると考えることができる。

As shown in Table 3, in the case of a sample that has been post-annealed in an oxygen-containing atmosphere such as oxygen gas or air, the sample having rutile structure titanium oxide (TiO ₂ ) is used as described above. Therefore, even after the first cycle discharge, the charge capacity rapidly decreases, and the discharge capacity retention rate after 100 cycles becomes a remarkably low value of 30% or less. It can be considered that this is because the ion conductivity is reduced because the resistance of the crystal grain boundary of titanium oxide is higher than that of lithium titanate.

In addition, as described above, the ramsdellite-type crystal structure of the sample that has been subjected to the post-annealing process in the atmosphere of the H ₂ —N ₂ mixed gas is destroyed, so that the discharge capacity increases as the charge / discharge cycle proceeds. The discharge capacity retention rate after 100 cycles was greatly reduced, and further decreased from the value without the post-annealing process (69.8% as shown in Table 1), and the post-annealing process was performed. It was confirmed that no characteristic improvement effect was obtained.

  That is, as shown in Table 3, only when the Ar gas, which is an inert gas containing no oxygen, is used as the atmosphere for the post-annealing treatment, the characteristic improvement effect almost the same as that of the nitrogen gas can be obtained, and 100 cycles It was confirmed that the subsequent discharge capacity retention rate was 96% or more. From the above, it was confirmed that it was essential to use an inert gas containing no oxygen as the atmosphere during post-annealing.

As described above, among the post-annealing conditions for performing the post-annealing process, the atmospheric condition is an atmosphere of an inert gas (for example, nitrogen (N ₂ ) gas or argon (Ar) gas) that does not contain at least oxygen. I understood that it should be decided beforehand.

(Comparative Example 1)
Next, a 2320-size coin cell lithium secondary battery using the negative electrode material for a lithium secondary battery according to the present invention as a negative electrode material, and a commercially available chemical spinel type lithium titanate (spinel type LTO), which is a known material, are used. A comparison result of electrode characteristics with the 2320-size coin cell type lithium secondary battery used as the negative electrode material will be further described.

  Here, as the negative electrode material for a lithium secondary battery according to the present invention, a ramsdellite type titanic acid produced by performing a post-annealing treatment at 250 ° C. for 5 hours in a nitrogen atmosphere as described in Example 1. The case where lithium powder (LTO) is used will be described below as an example.

(1) Manufacturing method of two types of lithium secondary batteries to be compared For two types of 2320-size coin cell type lithium secondary batteries to be compared, the same positive electrode material is used as the lithium cobalt oxide (LCO). Only the material is a different material, and one is a ramsdellite-type lithium titanate powder (LTO) that has been subjected to a post-annealing treatment at 250 ° C. for 5 hours in the same nitrogen atmosphere as in Example 1. Regarding the other comparison object, a commercially available spinel type lithium titanate (spinel type LTO) is used as a negative electrode, and each of them is an LCO-LTO secondary battery and an LCO-spinel type LTO secondary battery, and a 2320 size coin cell. Type lithium secondary battery was produced.

  First, a method for manufacturing an LCO-LTO secondary battery using the same Rams delite type lithium titanate as shown in FIG. 5 as the negative electrode will be described. FIG. 5 is a battery cross-sectional view showing an example of a cross-sectional structure of a coin cell of a lithium secondary battery using the negative electrode material for a lithium secondary battery according to the present invention. About the material of the negative electrode of the coin cell type lithium secondary battery As described above, the ramsdellite type lithium titanate produced by the procedure described above in Example 1 is used as the negative electrode material for the lithium secondary battery. The lithium secondary battery is manufactured by a procedure different from the case of No. 4.

  First, a negative electrode active material pellet 2 having a diameter of 15 mm containing a ramsdellite-type lithium titanate (LTO) produced by a post-annealing process (conditions: 250 ° C., 5 hours) by the same procedure as in Example 1 was produced.

  Next, a nickel mesh is welded to the inside of the negative electrode case 1 of the secondary battery, a negative electrode active material pellet 2 is placed thereon, and the negative electrode active material pellet 2 is further covered with a nickel mesh having a diameter of 17 mm. The negative electrode active material pellet 2 was fixed to the negative electrode case 1 by welding and pressure bonding the nickel mesh to the negative electrode case 1.

  Next, a gasket 3 was set on the outer edge of the negative electrode case 1.

  On the other hand, lithium cobaltate (LCO): acetylene black: PTFE = 70 in terms of weight ratio of lithium cobaltate (LCO) as a positive electrode material, carbon acetylene black and PTFE (polytetrafluoroethylene) as a binder. : After crushing and mixing with a roughing machine (crusher) so as to be 25: 5, it was rolled into a sheet shape by a roll press until the thickness became 0.5 mm. The obtained sheet was punched into a disk shape having a diameter of 15 mm and vacuum-dried to produce a positive electrode material pellet 4 containing lithium cobalt oxide (LCO).

  Next, a titanium mesh with a diameter of 15 mm was welded inside the positive electrode case 5 of the coin cell, the positive electrode material pellet 4 was placed thereon, and the positive electrode material pellet 4 was covered with a titanium mesh with a diameter of 17 mm.

  Thereafter, the covered titanium mesh was welded to the positive electrode case 5 and then subjected to pressure bonding, whereby the positive electrode material pellet 4 was fixed to the positive electrode case 5.

Next, about 2 mL of 1 mol / L LiPF ₆ / (EC + DMC) is poured into the positive electrode case 5 to which the positive electrode material pellet 4 is fixed as a non-aqueous electrolyte solution 7 of an electrolyte having lithium ion conductivity. Then, the negative electrode case 1 on which the gasket 3 was set was covered from above, and the whole was caulked to produce a coin cell type lithium secondary battery as an LCO-LTO secondary battery. Here, (EC + DMC) indicates a mixed solvent of ethylene carbonate and dimethyl carbonate, and a lithium salt of LiPF ₆ as an electrolyte is dissolved in the mixed solvent.

  Next, a method for manufacturing a comparison LCO-spinel type LTO secondary battery will be described. The manufacturing method of the LCO-spinel type LTO secondary battery using the spinel type lithium titanate (spinel type LTO), a commercially available chemical for comparison, as the negative electrode also differs only in the negative electrode material, and the LCO-LTO secondary described above. A coin cell type lithium secondary battery was produced as an LCO-spinel type LTO secondary battery by the same manufacturing method as that for the battery.

(2) Evaluation of electrode characteristics: Evaluation by a charge / discharge test of a lithium secondary battery Next, two types of 2320-size coin cell lithium secondary batteries prepared as comparison objects, that is, an LCO-LTO secondary battery and an LCO- As for the two types of coin cell type lithium secondary batteries with the spinel type LTO secondary battery, as in the case of Example 1, under the conditions of a current density of 1 mA / cm ² and a voltage range of 0.5 to 3.5 V, the charge / discharge cycle Measurements were made.

  A charge / discharge cycle test was conducted on two types of lithium secondary batteries, an LCO-LTO secondary battery and an LCO-spinel type LTO secondary battery, and the 1st cycle, 5th cycle, 10th cycle, 50th cycle, 100th cycle The results of measuring the discharge capacity in each of the eyes, the discharge capacity maintenance rate after 100 cycles, and the irreversible capacity (the difference between the charge capacity and the discharge capacity) between the first cycle and the 100th cycle will be described as Comparative Example 1. Table 4 shows.

表４に示すように、実施例１と同様のポストアニーリング処理（窒素雰囲気、２５０℃、５時間の処理条件）を行ったラムスデライト型チタン酸リチウムを負極に用いたＬＣＯ−ＬＴＯ二次電池は、１００サイクル後においても、９５％という高い放電容量維持率を示し、市販薬品のスピネル型チタン酸リチウム（スピネル型ＬＴＯ）を負極に用いたＬＣＯ−スピネル型ＬＴＯ二次電池に比し、６.５％の放電容量の改善が達成されることが確認された。

As shown in Table 4, the LCO-LTO secondary battery using Rams-delite type lithium titanate subjected to the post-annealing treatment (nitrogen atmosphere, treatment at 250 ° C. for 5 hours) similar to that in Example 1 as the negative electrode was Even after 100 cycles, it shows a high discharge capacity maintenance rate of 95%, compared with an LCO-spinel type LTO secondary battery using a commercially available chemical spinel type lithium titanate (spinel type LTO) as a negative electrode, 6. It was confirmed that a 5% improvement in discharge capacity was achieved.

  Furthermore, the LCO-LTO secondary battery using ramsdelite type lithium titanate as the negative electrode also obtained 195.7 mAh / g in terms of the discharge capacity at the 100th cycle, and spinel type lithium titanate (spinel type), a commercially available chemical. It was found that the discharge capacity (increase of 38.9 mAh / g) was significantly higher than that of the LCO-spinel type LTO secondary battery using (LTO) as the negative electrode.

  FIG. 7 showing the cycle characteristics regarding the discharge capacity of the test cell in Example 1 shows two types of coin cell type lithium secondary batteries in Comparative Example 1, that is, an LCO-LTO secondary battery and an LCO-spinel type. The cycle characteristics of the discharge capacity for each of the LTO secondary batteries are also indicated by a dashed square mark (dashed square mark) and a black square mark (■).

  As shown in FIG. 7, the LCO-LTO secondary battery using Ramsdelite type lithium titanate that has been post-annealed at 250 ° C. for 5 hours as a negative electrode has a dotted square mark (dashed square mark). As shown in Fig. 1, it was confirmed that a very stable charge / discharge operation was possible up to 100 cycles, but an LCO-spinel type LTO using a commercially available chemical spinel type lithium titanate (spinel type LTO) as a negative electrode. In the case of a secondary battery, when the charge / discharge cycle is repeated, the discharge capacity gradually decreases, the discharge capacity decreases significantly in the first cycle, and the post-annealing treatment is performed in the subsequent charge / discharge cycles. It has been found that the discharge capacity is reduced as compared with the LCO-LTO secondary battery using delite type lithium titanate as the negative electrode.

  As described above, the post-annealing-treated ramsdelite type lithium titanate negative electrode material according to the present invention has improved discharge capacity and theoretical capacity compared to the conventional spinel type lithium titanate negative electrode material, which is a commercially available chemical. It was confirmed that the negative electrode material was able to realize a large capacity lithium secondary battery excellent in irreversible capacity characteristics and charge / discharge cycle characteristics during charge / discharge.

DESCRIPTION OF SYMBOLS 1 ... Working electrode case (negative electrode case), 2 ... Negative electrode active material pellet, 3: Gasket, 4: Metal lithium (positive electrode material pellet), 5: Counter electrode case (positive electrode case), 6: Separator, 7: Non-aqueous electrolyte .

Claims (10)

A ramsdellite-type lithium titanate having a three-dimensional tunnel structure as a negative electrode material of lithium titanate-based _{Li x Ti y O z (0.75} ≦ x ≦ 2.66,1.33 ≦ y ≦ 4,3 ≦ z In the negative electrode material for a lithium secondary battery using ≦ 7), the Ramsdelite type lithium titanate is produced as a negative electrode material by performing post-annealing treatment under predetermined post-annealing conditions. A negative electrode material for a lithium secondary battery.   2. The negative electrode material for a lithium secondary battery according to claim 1, wherein as the atmospheric condition of the post-annealing condition, a post-annealing process is performed on the ramsdellite-type lithium titanate in an inert gas atmosphere not containing oxygen. A negative electrode material for a lithium secondary battery, wherein the negative electrode material is produced as the negative electrode material.   3. The lithium secondary battery according to claim 2, wherein either the nitrogen gas or the argon gas is used as the inert gas atmosphere as the post annealing condition. Negative electrode material.   4. The negative electrode material for a lithium secondary battery according to claim 1, wherein a temperature of 100 to 400 ° C. is used with respect to the ramsdelite type lithium titanate as a temperature condition and a treatment time condition of the post-annealing condition. A negative electrode material for a lithium secondary battery, which is produced as the negative electrode material by performing a post-annealing treatment at any temperature within the range for at least 3 hours. Li _x Ti _y O _z (0.75 ≦ x ≦ 2.66, 1.33 ≦ y ≦ 4, 3 ≦ z ≦ 7), which is a ramsdellite type lithium titanate having a three-dimensional tunnel structure, is a lithium secondary battery. A method for producing a negative electrode material for a lithium secondary battery, which is produced as a negative electrode material for a battery, wherein the ramsdellite-type lithium titanate is produced as a negative electrode material by performing a post-annealing treatment under predetermined post-annealing conditions. A method for producing a negative electrode material for a lithium secondary battery, comprising:   6. The method for producing a negative electrode material for a lithium secondary battery according to claim 5, wherein the post-annealing treatment is performed in an inert gas atmosphere containing no oxygen with respect to the ramsdellite-type lithium titanate as an atmospheric condition of the post-annealing condition. A method for producing a negative electrode material for a lithium secondary battery.   7. The method for producing a negative electrode material for a lithium secondary battery according to claim 6, wherein either the nitrogen gas or the argon gas is used as the inert gas atmosphere as the post annealing condition. A method for producing a negative electrode material for a secondary battery.   The method for producing a negative electrode material for a lithium secondary battery according to any one of claims 5 to 7, wherein a temperature condition and a treatment time condition of the post-annealing condition are 100 to 400 ° C with respect to the ramsdelite type lithium titanate. A method for producing a negative electrode material for a lithium secondary battery, comprising performing a post-annealing treatment at any temperature within the temperature range for at least 3 hours.   A negative electrode containing a lithium titanate-based material as a negative electrode material for a lithium secondary battery, and a positive electrode containing a positive electrode material capable of inserting / extracting lithium ions, and comprising an electrolyte having lithium ion conductivity The lithium secondary battery comprised by arrange | positioning between a negative electrode and the said positive electrode WHEREIN: The said negative electrode material for lithium secondary batteries contained in the said negative electrode is a lithium secondary in any one of Claim 1 thru | or 4 A lithium secondary battery comprising a battery negative electrode material.   10. The lithium secondary battery according to claim 9, wherein the negative electrode material for a lithium secondary battery is in the form of a sheet obtained by mixing a powder of the negative electrode material for a lithium secondary battery, carbon, and a binder, or is pelletized. A lithium secondary battery, wherein the lithium secondary battery is used as the negative electrode.

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