JP2010080285A - Flat nonaqueous electrolyte secondary battery and method of manufacturing the same - Google Patents

Abstract

A flat non-aqueous electrolyte secondary battery that suppresses capacity reduction during a charge / discharge cycle and a method for manufacturing the same are provided.
In the nonaqueous electrolyte secondary battery of the present invention, the negative electrode is a negative electrode molded body 6 including negative electrode active material particles capable of occluding lithium. The negative electrode active material particles contain silicon. In the element molar ratio of lithium and silicon obtained by X-ray photoelectron spectroscopic analysis of the surface of the negative electrode molded body 6, when the element molar ratio on the large side is H and the element molar ratio on the small side is L, lithium is formed into the negative electrode. The H / L in the initial fully charged state stored in the body 6 is set to 3.0 or less.
[Selection] Figure 1

Description

  The present invention relates to a flat non-aqueous electrolyte secondary battery and a method for manufacturing the same.

  Conventionally, flat type non-aqueous electrolyte secondary batteries with high electromotive force and high energy density have been used as main power sources for electronic devices such as mobile communication devices and portable devices, and as power sources for memory backup. It has increased. With the remarkable development of electronic devices, non-aqueous electrolyte secondary batteries having a high capacity and excellent cycle characteristics are strongly demanded from the viewpoints of miniaturization, high performance, and maintenance-free electronic devices.

  Lithium manganese oxide is often used as the positive electrode material, and lithium aluminum alloy is used as the negative electrode material. However, the lithium aluminum alloy collapses during the charge / discharge cycle, and the battery characteristics deteriorate.

Therefore, in order to suppress the collapse of the negative electrode material during the charge / discharge cycle, it has been proposed to form a negative electrode with a mixture molding containing a lithium-containing silicon oxide and use glass fibers for the separator (for example, Patent Documents). 1).
Japanese Patent No. 3466045

  When a battery is configured using the negative electrode described in Patent Document 1, a relatively good cycle characteristic is exhibited in a charge / discharge cycle at about 50% of the nominal capacity. However, there is a problem that the capacity is rapidly reduced during the charge / discharge cycle at the same capacity as the nominal capacity, that is, at a depth of 100%. When lithium is occluded and diffused in silicon oxide, which is a negative electrode active material, the active material expands and contracts. In particular, the expansion is not uniform in the negative electrode mixture molded body during the first charge. Therefore, when a part of the molded body is damaged and charging / discharging is performed deeply, the current collecting property in the thickness direction of the molded body is remarkably lowered due to the damage. This is considered to cause a rapid capacity drop.

  The present invention solves the above-described problems of the prior art by reducing the non-uniformity in the thickness direction during the first occlusion of lithium into the negative electrode molded body, and suppressing the decrease in capacity during the charge / discharge cycle. An object is to provide a water electrolyte secondary battery. Furthermore, it aims at providing the manufacturing method of the flat type nonaqueous electrolyte secondary battery which suppressed the capacity | capacitance fall at the time of a charge / discharge cycle.

  In order to achieve the above object, the flat non-aqueous electrolyte secondary battery of the present invention has an element molar ratio of H on the larger side and an element molar ratio on the smaller side of the element molar ratio of lithium and silicon on the top and bottom surfaces of the molded negative electrode. When the element molar ratio is L, H / L in the first fully charged state in which lithium is occluded into the negative electrode molded body is 3.0 or less. Thereby, in a flat type nonaqueous electrolyte secondary battery, the capacity | capacitance fall at the time of a charge / discharge cycle can be suppressed. As a specific method thereof, metallic lithium is disposed on both the upper surface and the bottom surface of the negative electrode molded body during battery assembly, and after the battery is assembled, lithium is inserted from the metal lithium into the negative electrode molded body. Alternatively, the assembled battery is stored at 50 ° C. or more and 80 ° C. or less under a condition selected from a combination of a period of 1 day or more and 7 days or less, so that lithium is occluded from the metal lithium into the negative electrode molded body. Alternatively, at least one of vinylene carbonate and vinyl ethylene carbonate is contained in the electrolytic solution in an amount of 0.1% by weight to 20% by weight.

  ADVANTAGE OF THE INVENTION According to this invention, the flat type nonaqueous electrolyte secondary battery which suppressed the capacity | capacitance fall at the time of a charge / discharge cycle can be provided. Furthermore, the manufacturing method of the flat type nonaqueous electrolyte secondary battery can be provided.

  1st invention in this invention is a flat type nonaqueous electrolyte secondary battery which has a positive electrode, a negative electrode, the separator interposed between a positive electrode and a negative electrode, and a nonaqueous electrolyte. The negative electrode is a flat molded body including negative electrode active material particles capable of occluding lithium. The negative electrode active material particles contain silicon. Furthermore, in the element molar ratio of lithium and silicon determined by X-ray photoelectron spectroscopy analysis on the top and bottom surfaces of the molded negative electrode, H is the element molar ratio on the large side, and L is the element molar ratio on the small side. H / L is 3.0 or less in the first fully charged state in which is stored in the negative electrode molded body. Thus, by reducing the non-uniformity in the thickness direction during the first lithium occlusion, it is possible to suppress a decrease in capacity during the charge / discharge cycle.

  According to a second aspect of the present invention, in the first aspect, the non-aqueous electrolyte contains at least one of vinylene carbonate and vinyl ethylene carbonate in an amount of 0.1% by weight to 20% by weight. It is a non-aqueous electrolyte secondary battery. These additives are known to have an effect of suppressing the formation of a film that inhibits the movement of lithium ions on the surface of a molded negative electrode containing lithium. Although the reason is not clear, it is considered that this effect promotes diffusion of lithium occluded in the negative electrode active material particles from the lithium foil pressure-bonded to one surface of the negative electrode molded body.

  According to a third invention of the present invention, in the first or second invention, the negative electrode active material particles are an alloy containing at least a silicon phase and a titanium disilicide phase, and the crystallite size of the silicon phase and the titanium disilicide phase is A flat nonaqueous electrolyte secondary battery having a thickness of 50 nm or less. Silicon alone has a large expansion and contraction during charging and discharging, and there is a slight difficulty in maintaining the shape of the molded negative electrode. In silicon oxide, oxygen forms lithium oxide and causes irreversible capacity, so the battery capacity decreases. On the other hand, an alloy of transition metal and silicon is preferable because it solves these problems and has higher electron conductivity. Of the transition metals, titanium is particularly preferable. This is because titanium disilicide, which is an alloy with silicon, has high electron conductivity.

  The fourth invention in the present invention is another method for producing the flat type non-aqueous electrolyte secondary battery in the first invention. In this method, metallic lithium is disposed on both sides of the upper surface and the bottom surface of the molded negative electrode during battery assembly. Then, after assembling the battery, lithium is absorbed from the metal lithium into the negative electrode active material particles in the negative electrode molded body. Thereby, in the element molar ratio of lithium and silicon obtained by X-ray photoelectron spectroscopic analysis of the top and bottom surfaces of the molded negative electrode, H is the element molar ratio on the large side and L is the element molar ratio on the small side. The H / L in the first fully charged state in which lithium is occluded from the metal lithium into the negative electrode molded body is set to 3.0 or less. Also by such a method, H / L can be made 3.0 or less, and as a result, the capacity | capacitance fall at the time of a charging / discharging cycle can be suppressed.

  The fifth invention in the present invention is yet another method for producing the flat type nonaqueous electrolyte secondary battery in the first invention. In this method, metallic lithium is arranged on the surface of the molded negative electrode during battery assembly. Then, after assembling the battery, lithium is absorbed from the metal lithium into the negative electrode active material particles in the negative electrode molded body. At this time, the assembled battery is stored at a predetermined temperature for a predetermined period. The predetermined temperature and the predetermined period are represented by a point A (50, 5), a point B (50, 7), a point C (60, 7), a point D (70) in the graph where Y is the number of days and X is the temperature. , 3), point E (80, 1), point F (70, 1), point G (60, 1) are connected in order, and finally, on the polygonal line formed by connecting point G and point A It is the combination which exists in. By applying such storage conditions, in the element molar ratio of lithium and silicon determined by X-ray photoelectron spectroscopic analysis on the top and bottom surfaces of the molded negative electrode, the larger element molar ratio is H, and the smaller element molar ratio is H. When the element molar ratio is L, H / L in the first fully charged state in which lithium is occluded from metallic lithium into the negative electrode molded body is set to 3.0 or less. Also by such a method, H / L can be made 3.0 or less, and as a result, the capacity | capacitance fall at the time of a charging / discharging cycle can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to this embodiment.

(Embodiment)
FIG. 1 is a cross-sectional view of a flat non-aqueous electrolyte secondary battery (hereinafter also referred to as a flat battery) according to an embodiment of the present invention. This battery includes a positive electrode can 1, a negative electrode can 2, a gasket 3, a positive electrode 4, a negative electrode molded body 6 that is a negative electrode, and a non-aqueous electrolyte (not shown). The positive electrode 4 includes a positive electrode active material, a conductive agent, and a binder. The flat negative electrode molded body 6 includes negative electrode active material particles, a conductive agent, and a binder. The negative electrode active material particles capable of occluding lithium contain silicon. The separator 5 and the non-aqueous electrolyte are interposed between the positive electrode 4 and the negative electrode molded body 6. The separator 5 is configured by punching a resin nonwoven fabric or a microporous film into a circle. At the opening of the metal positive electrode can 1, a resin gasket 3 that is injection-molded in an annular shape is disposed. The battery is hermetically sealed by disposing a metal negative electrode can 2 via a gasket 3 and bending the upper end of the positive electrode can 1 inward to crimp the positive electrode can 1. In order to alloy the negative electrode active material particles contained in the molded negative electrode 6 with lithium, a lithium foil is pressure-bonded to the surface of the molded negative electrode 6 at the time of assembling the battery, and electrochemically lithium in the presence of a non-aqueous electrolyte. Occlude.

  The present inventors diligently studied a flat type nonaqueous electrolyte secondary battery. As a result, it is possible to suppress the decrease in capacity during the charge / discharge cycle by alleviating non-uniformity in the thickness direction at the time of the first occlusion, in particular, occlusion / diffusion of lithium into the molded negative electrode 6. I found it.

  That is, the molded negative electrode 6 includes active material particles containing silicon. Examples of such active material particles include silicon, silicon-containing alloys, and silicon compounds such as silicon oxide. And in the element molar ratio of lithium and silicon calculated | required by the X-ray photoelectron spectroscopy analysis of the surface of the negative electrode molded object 6, the element molar ratio of a large side is set to H, and the element molar ratio of a small side is set to L. At this time, when H / L of the first full charge state which occluded lithium in the negative electrode molded object 6 satisfy | fills 3.0 or less, it discovered that the capacity | capacitance fall at the time of a charging / discharging cycle was suppressed.

  H / L is obtained from a measurement result based on an X-ray photoelectron spectroscopy (hereinafter referred to as XPS) analysis method after etching the molded negative electrode 100 to 100 nm in terms of silicon dioxide. This is because an accurate elemental molar ratio between lithium and silicon cannot be obtained because a film is present on the outermost surface. After etching 100 nm in terms of silicon dioxide, the H / L obtained from XPS analysis should be 3.0 or less. H / L is more preferably 2.5 or less.

  The negative electrode active material particles are preferably an alloy containing two or more phases of a silicon phase and a titanium disilicide phase. Silicon alone has a large expansion and contraction during charging and discharging, and there is a slight difficulty in maintaining the shape of the molded negative electrode 6. In silicon oxide, oxygen forms lithium oxide and causes irreversible capacity, so the battery capacity decreases. An alloy of transition metal and silicon is preferable because it solves the above problems and further has high electron conductivity. Of the transition metals, titanium is particularly preferable. This is because titanium disilicide, which is an alloy with silicon, has high electron conductivity. However, what actually reacts with lithium is a silicon phase dispersed in the alloy, and the weight ratio of the silicon phase to the titanium disilicide phase in the alloy is preferably in the range of 1: 9 to 9: 1. That is, the weight of the silicon phase in the total weight of the silicon phase and the titanium disilicide phase is preferably 10% or more and 90% or less. This range is when it is assumed that all titanium has formed titanium disilicide. When the weight ratio of silicon is less than 10% by weight, the obtained capacity is small. If it exceeds 90% by weight, it is difficult to maintain the shape of the molded negative electrode 6 as in the case of using silicon alone.

  The crystallite size of the silicon phase and the titanium disilicide phase is more preferably 50 nm or less. By setting the crystallite size to 50 nm or less, it is possible to suppress a decrease in electron current collection due to the collapse of the active material particles, an increase in the surface coating, and the like during the expansion and contraction due to the reaction with lithium during charging and discharging. As a result, it is possible to further suppress the capacity drop during the cycle. The crystallite size is more preferably 20 nm or less. Hereinafter, the above alloy is referred to as a Ti—Si alloy.

  As the lithium ion conductive nonaqueous electrolytic solution, for example, a solution in which a lithium salt is dissolved in a nonaqueous solvent is used. Nonaqueous solvents include, for example, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), Examples include chain ethers such as 1,2-dimethoxyethane (DME). These may be used alone or in combination of two or more.

  Next, a specific method for setting the H / L value in the initial fully charged state to 3.0 or less will be described. First, the additive is added to the non-aqueous electrolyte. That is, vinylene carbonate (VC) and vinyl ethylene carbonate (VEC) are added to the above non-aqueous solvent. These additives are known to have an effect of suppressing the formation of a film that inhibits the movement of lithium ions on the surface of the negative electrode molded body 6 containing lithium. Although the reason is not clear, it is considered that this effect promotes diffusion of lithium occluded in the negative electrode active material particles from the lithium foil pressure-bonded to one surface of the negative electrode molded body 6.

  The content of the additive in the nonaqueous electrolytic solution needs to be 0.1 wt% or more and 20 wt% or less, more preferably 1 wt% or more and 10 wt% or less. If it is less than 0.1% by weight, the formation of a coating that inhibits the movement of lithium ions cannot be sufficiently suppressed. On the other hand, if it exceeds 20% by weight, the conductivity of the nonaqueous electrolytic solution is lowered, and the rate characteristics and the low temperature characteristics are lowered.

  The bonding position of the lithium foil (lithium metal) is preferably the negative electrode can 2 side of the negative electrode molded body 6 from the viewpoint of industrial productivity, but the separator 5 of the negative electrode molded body 6 from the viewpoint of compatibility between cycle characteristics and industrial productivity. Side is desirable. However, from the viewpoint of cycle characteristics, both surfaces (the separator 5 side and the negative electrode can 2 side) of the negative electrode molded body 6 are more desirable. By adhering lithium metal to both surfaces of the molded negative electrode 6, the alloying reaction can be performed more uniformly. Thus, even when the above-mentioned additive is not used, the H / L in the initial fully charged state is set to 3.0 or less by arranging metallic lithium on both sides of the upper surface and the bottom surface of the molded negative electrode 6 at the time of battery assembly. Can do. Of course, it is more preferable to use it together with an additive.

  Alternatively, when metallic lithium is disposed on one surface of the molded negative electrode 6, the assembled battery is stored at a predetermined temperature for a predetermined period in order to set the H / L in the initial fully charged state to 3.0 or less. The combination of the predetermined temperature and the predetermined period needs to satisfy the following condition. That is, in the graph where Y is the number of days and X is the temperature, point A (50, 5), point B (50, 7), point C (60, 7), point D (70, 3), point E (80 , 1), point F (70, 1), point G (60, 1) in that order, and finally a combination on or inside a polygonal line formed by connecting point G and point A. When the temperature and the period are insufficient, the uniformization of lithium in the negative electrode molded body 6 is insufficient. On the other hand, when the temperature and period are excessive, side reactions such as film formation increase. Even when metallic lithium is disposed on both surfaces of the molded negative electrode 6, it is preferable to store the assembled battery under such conditions.

  The positive electrode active material is not particularly limited as long as lithium can be reversibly occluded / released, but lithium manganese oxide, lithium cobalt oxide, and the like are preferable.

Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiB ₁₀ Cl _10. , Lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, imides (lithium bispentafluoroethylsulfonate imide (LiN (C ₂ F ₅ SO ₂ ) ₂ ), etc.) Can be mentioned. These may be used alone or in combination of two or more. The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 2.0 mol / L, and more preferably 0.5 to 1.5 mol / L.

  Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

  The flat battery shown in FIG. 1 was prepared according to the following procedure, and the cycle characteristics were evaluated.

(I) Production of Positive Electrode 4 An active material powder made of lithium manganese oxide, carbon black as a conductive agent, and fluororesin (polytetrafluoroethylene) as a binder have a weight ratio of 90: 6: 4. Mixing at a ratio, a positive electrode mixture was prepared. The binder was used as an aqueous dispersion. The positive electrode mixture was molded into a pellet shape having a diameter of 4.3 mm and a thickness of 1.1 mm at a pressure of 1 ton / cm ² , and the positive electrode 4 was produced. Thereafter, the positive electrode 4 was dried in the air at 250 ° C. for 10 hours.

(Ii) Production of negative electrode molded body 6 The negative electrode molded body 6 was produced by the following procedure.

  Silicon powder (purity 99.99%, particle size 75 to 150 μm) and titanium powder (purity 99.7%, particle size 150 μm or less) were mixed at a molar ratio of 85:15 to prepare a mixed powder. After 1.7 kg of this mixed powder was put into a vibrating ball mill device (model number: FV-20 type, internal volume: 64 L) manufactured by Chuo Kakki Co., Ltd., 250 kg of stainless steel balls having a diameter of 1 inch were further added. I put it in. Thereafter, the atmosphere in the apparatus was replaced with argon gas, and then pulverized (mechanical alloying) for 60 hours under the conditions of an amplitude of 8 mm and a frequency of 1200 rpm to prepare a Ti—Si alloy powder.

  This Ti—Si alloy was recovered in a vibration dryer VU30 type manufactured by Chuo Kakoki Co., Ltd. while maintaining an argon atmosphere. Then, an argon / oxygen mixed gas is intermittently introduced over 1 hour so that the temperature of the Ti—Si alloy does not exceed 100 ° C. with vibration stirring, and an oxide film is formed on the surface of the Ti—Si alloy particles. did. Then, the powder of 63 micrometers or less was taken out by classifying using a sieve, and this was made into the negative electrode active material particle.

  From the results of XRD measurement, it was confirmed that the Ti—Si alloy contains at least a silicon phase and a titanium disilicide phase. Further, the crystallite size was calculated using the peak position, the half-value width, and the Scherrer equation. As a result, it was found that the silicon phase was amorphous and the crystallite size of the titanium disilicide phase was 15 nm. The weight ratio of silicon phase to titanium disilicide phase was 50:50, assuming that all of the titanium formed titanium disilicide.

  The Ti—Si alloy as the negative electrode active material particles thus prepared, the carbon black as the conductive agent, and the polyacrylic acid as the binder were mixed in a weight ratio of 86: 7: 7 as a solid content. A negative electrode mixture was prepared. This negative electrode mixture was molded into a pellet shape having a diameter of 4 mm and a thickness of 0.3 mm, and a negative electrode molded body 6 was produced. Then, it dried in air | atmosphere for 12 hours at 190 degreeC.

(Iii) Preparation of nonaqueous electrolyte Lithium bispentafluoroethylsulfonic acid imide (LiN (C ₂ F ₅ SO ₂ ) _{2 was} added to a solvent in which PC, EC, and DME were mixed at a volume ratio of 3: 1: 3. ) Was dissolved at a concentration of 1 mol / L. Further, VEC was added so as to contain 10% by weight to prepare a nonaqueous electrolyte.

(Iv) Production of flat battery For the positive electrode can 1 which also serves as the positive electrode terminal, stainless steel having excellent corrosion resistance was used. The same stainless steel as the positive electrode can 1 was also used for the negative electrode can 2 that also served as the negative electrode terminal. Pitch was applied to the contact surface of the positive electrode can 1 with the gasket 3 and the contact surface of the negative electrode can 2 with the gasket 3. The molded negative electrode 6 was placed on the negative electrode can 2. Further, in order to alloy the negative electrode molded body 6 with lithium, a predetermined amount of lithium foil is pressure-bonded to the surface (separator 5 side) of the negative electrode molded body 6 during battery assembly, and the lithium is occluded in the presence of a non-aqueous electrolyte. To form a lithium alloy electrochemically. This is used as the negative electrode.

  A separator 5 made of a non-woven fabric made of polyethylene was placed on a negative electrode molded body 6 to which a lithium foil was pressure-bonded, and a gasket 3 made of polypropylene was placed thereon. After pouring a non-aqueous electrolyte into them, the positive electrode 4 was placed on the separator 5. Finally, the positive electrode can 1 and the negative electrode can 2 were fitted so that the separator 5 was disposed between the positive electrode 4 and the molded negative electrode 6. In this way, battery A1 (outer diameter 6.8 mm and thickness 2.1 mm) was completed. In order to alloy with lithium, it was stored at 45 ° C., which is lower than 50 ° C., for 3 days to be fully charged.

  A battery A2 was produced in the same manner as the battery A1, except that VC was added instead of VEC.

  By the same method as battery A1, except that half of the lithium foil was pressure-bonded to both surfaces (negative electrode can 2 side and separator 5 side) of the negative electrode molded body 6 at the time of battery assembly, and VEC was not added. Battery A3 was produced.

  A battery B1 was produced in the same manner as the battery A1, except that VEC was not added.

  The following evaluation tests were performed on the batteries A1 to A3 and the battery B1.

(Evaluation test)
In the thermostat set at 20 ° C., the capacity confirmation test of each battery was performed according to the following procedure. At this time, the current value is adjusted so that the current density per area on the surface where the positive electrode 4 and the negative electrode molded body 6 face each other is 0.1 mA / cm ^2, and charging is performed with a constant current until the closed circuit voltage reaches 3.5 V. did. Thereafter, the current value was adjusted so that the current density was 0.1 mA / cm ² , and discharging was performed at a constant current until the closed circuit voltage reached 2.5V. At this time, the discharge time was measured to determine the battery capacity (initial capacity). Further, charge and discharge were repeated under these conditions, and a cycle test was performed. Then, the number of cycles at which (battery capacity after cycle test) / (battery capacity before cycle test) reaches 50% or less was determined. Moreover, the integrated value of the capacity | capacitance which could be discharged by the cycle in which (battery capacity after a cycle test) / (battery capacity before a cycle test) reaches 50% or less was calculated | required as needed. The results of the evaluation test are shown in (Table 1). Further, if necessary, after charging under the same conditions as the measurement of the initial capacity in a thermostat set to 20 ° C. after the initial capacity measurement, and after leaving in a thermostat set to −20 ° C. for a predetermined time, The battery capacity was determined by discharging under the same conditions as the initial capacity measurement. This value is the initial capacity at -20 ° C.

  Battery A1 to Battery A3 exhibited higher capacity and higher cycle number than battery B1. Further, the ratio H / L of the element ratio H of the surface (mainly the separator 5 side) and the element ratio L of the small surface (mainly the negative electrode can 2 side) obtained by XPS analysis is a small value. Indicated. In particular, the batteries A1 and A2 had high capacity and a large number of cycles, and exhibited excellent cycle characteristics. These are considered to be due to the effect that the additive suppresses the formation of a film that inhibits the movement of lithium ions on the surface of the lithium-containing negative electrode. Thus, by adding VEC or VC to the non-aqueous electrolyte, the value of H / L becomes 3.0 or less, and the cycle characteristics are improved.

  Battery A3 had a lower initial capacity but a larger number of cycles than battery A1. This is presumably because the temperature during storage promoted side reactions such as film formation on the surface of the negative electrode active material particles simultaneously with the alloying reaction between lithium and the negative electrode active material particles. However, even when the additive is not used in this way, H / L in the initial fully charged state can be made 3.0 or less by arranging metallic lithium on both sides of the upper surface and the bottom surface of the molded negative electrode 6. As a result, cycle characteristics are improved.

  Next, the evaluation result when the kind of the negative electrode active material containing silicon is changed will be described.

  A battery A4 was produced in the same manner as the battery A1, except that only the silicon powder was pulverized by a vibration mill and the crystallite size observed in the silicon phase was 15 nm.

  A battery A5 was produced in the same manner as the battery A1, except that only the silicon oxide powder was pulverized by a vibration mill and all were amorphous.

  A battery B2 was produced in the same manner as the battery A4, except that VEC was not added. A battery B3 was produced in the same manner as the battery A5 except that VEC was not added. The results of the evaluation test are shown in (Table 2).

  As apparent from (Table 2), regardless of the type of the negative electrode active material, the batteries A1, A4, and A5 to which VEC was added had a larger number of cycles than the batteries B1 to B3 to which VEC was not added. The reason why the number of cycles in the battery A4 is slightly small is considered that the electronic conductivity of the active material particles is low and the amount of expansion / contraction during charging / discharging is large. The reason why the initial capacity of the battery A5 is slightly small is considered that oxygen and lithium in the active material particles reacted to increase the irreversible capacity. Basically, when the initial capacity is small, the number of cycles reaching 50% of the initial capacity tends to increase. Therefore, when compared with the accumulated capacity up to the number of cycles that reaches 50% of the initial capacity close to the actual capacity, the batteries A1, A4, and A5 added with vinyl ethylene carbonate (VEC) have a larger accumulated capacity. I understand.

  Next, the evaluation result when the content of VEC in the non-aqueous electrolyte is changed will be described.

  A battery A6 was produced in the same manner as the battery A1, except that the addition amount of VEC was changed to 0.1% by weight. A battery A7 was produced in the same manner as the battery A1, except that the addition amount of VEC was 1% by weight. A battery A8 was produced in the same manner as the battery A1, except that the addition amount of VEC was changed to 5% by weight.

  A battery A9 was produced in the same manner as the battery A1, except that the addition amount of VEC was 20% by weight. A battery A10 was produced in the same manner as the battery A1, except that the addition amount of VEC was 25% by weight. A battery B4 was produced in the same manner as the battery A1, except that the addition amount of VEC was 0.05% by weight.

  The results of the evaluation test are shown in (Table 3).

  As is clear from (Table 3), the cycle characteristics improve as the VEC content increases. Specifically, the content is 0.10% by weight or more and the H / L value is 3.0 or less. However, when the content exceeds 20% by weight, the decrease in the initial capacity at −20 ° C. with respect to the initial capacity at room temperature increases. Since the low temperature characteristics are thus lowered, the content is set to 20% by weight or less.

  Next, the evaluation result when the storage conditions after battery assembly are changed will be described. Batteries C1 to C30 were produced in the same manner as the battery A1, except that VEC was not added and the storage conditions for alloying were 45 to 80 ° C. and 0.5 to 9 days. The results of the evaluation test are shown in (Table 4).

  From Table 4, the H / L value tends to decrease as the alloying temperature is increased or the period is increased. From the viewpoint of integrated capacity up to the number of cycles reaching 50% of the initial capacity, it is necessary to set 5 to 7 days at 50 ° C, 1 to 7 days at 60 ° C, 1 to 3 days at 70 ° C, and 1 day at 80 ° C. I understand that there is. It is obvious that the storage period in the case of storing at a temperature between any two of these temperatures needs to be set between the appropriate periods at both temperatures. However, if an appropriate temperature and period are not selected, the integrated capacity decreases. This is thought to be due to the fact that the homogenization of the alloying is insufficient when the temperature and the period are insufficient, but side reactions such as film formation also increase when the temperature and the period are excessive.

  In the above description, a coin-shaped flat battery has been described as an example. However, the present invention can be applied to a battery in which electrodes are stacked, for example, a battery in which an electrode stack is sealed with a laminate material.

  The flat type nonaqueous electrolyte secondary battery of the present invention is suitably used as a main power source for electronic equipment such as a digital still camera and a power source for memory backup.

Sectional drawing of the flat type nonaqueous electrolyte secondary battery in embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Negative electrode can 3 Gasket 4 Positive electrode 5 Separator 6 Negative electrode molding (negative electrode)

Claims (5)

A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte,
The negative electrode is a flat negative electrode molded body containing negative electrode active material particles capable of occluding lithium, and the negative electrode active material particles contain silicon,
In the element molar ratio of lithium and silicon obtained by X-ray photoelectron spectroscopy analysis on the upper surface and the bottom surface of the molded negative electrode, H is the element molar ratio on the large side, and L is the element molar ratio on the small side. A flat non-aqueous electrolyte secondary battery having an H / L of 3.0 or less in a first fully charged state in which is stored in the molded negative electrode. The flat type nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolytic solution contains at least one of vinylene carbonate and vinylethylene carbonate in an amount of 0.1 wt% to 20 wt%. The negative electrode active material particles are an alloy containing at least a silicon phase and a titanium disilicide phase, and the crystallite size of the silicon phase and the titanium disilicide phase is 50 nm or less. The flat-type nonaqueous electrolyte secondary battery as described. A flat negative electrode molded body including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode includes negative electrode active material particles capable of occluding lithium. And a method for producing a flat non-aqueous electrolyte secondary battery in which the negative electrode active material particles contain silicon,
A first step of disposing metallic lithium on both sides of the upper surface and the bottom surface of the molded negative electrode during battery assembly;
After battery assembly, lithium from the metal lithium is occluded in the negative electrode active material particles in the negative electrode molded body, and the element molar ratio of lithium and silicon determined by X-ray photoelectron spectroscopic analysis of the top and bottom surfaces of the negative electrode molded body In the above, when the element molar ratio on the large side is H and the element molar ratio on the small side is L, the H / L in the initial fully charged state in which lithium is occluded from the metallic lithium into the molded negative electrode is 3.0 or less. A method for producing a flat type nonaqueous electrolyte secondary battery. A flat-type negative electrode molded body comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, and including negative electrode active material particles capable of occluding the negative electrode lithium, A method for producing a flat non-aqueous electrolyte secondary battery in which negative electrode active material particles contain silicon,
A first step of disposing metallic lithium on the surface of the negative electrode molded body during battery assembly;
After battery assembly, lithium from metal lithium is occluded in the negative electrode active material particles in the negative electrode molded body, and the element molar ratio of lithium and silicon determined by X-ray photoelectron spectroscopic analysis of the top and bottom surfaces of the negative electrode molded body When the element molar ratio on the large side is H and the element molar ratio on the small side is L, the H / L in the initial fully charged state in which lithium is occluded from the metal lithium into the negative electrode molded body is 3.0 or less. And a second step,
In the second step, the assembled battery is stored at a predetermined temperature for a predetermined period, and in the graph where Y is the number of days and X is the temperature during the predetermined temperature and the predetermined period, point A (50, 5) , Point B (50, 7), point C (60, 7), point D (70, 3), point E (80, 1), point F (70, 1), point G (60, 1) in this order A method for producing a flat type non-aqueous electrolyte secondary battery, characterized by being a combination on or inside a polygonal line formed by connecting points G and A at the end.

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