JP4638453B2 - Nonaqueous electrolyte secondary battery operation method - Google Patents

Description

  The present invention relates to a method for operating a nonaqueous electrolyte secondary battery excellent in energy density and cycle characteristics.

Conventionally, a non-aqueous solution using a layered compound LiCoO ₂ or LiNiO ₂ , which is a lithium-containing composite oxide capable of 4V discharge, as a positive electrode active material, and spinel type LiMn ₂ O _4, and graphite as a carbon material as a negative electrode active material. An electrolyte secondary battery is known. The charge / discharge reaction of this nonaqueous electrolyte secondary battery is as shown in the following formulas (1) to (4). Equations (1) to (3) are charge / discharge reactions of LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ , respectively, and Equation (4) is a charge / discharge reaction of graphite.

In the reactions represented by the formulas (1) to (3), Li ⁺ (lithium ions) are desorbed from predetermined sites in the crystal of the lithium-containing composite oxide during charging, and lithium ions are discharged from the lithium-containing composite oxide during discharge. Inserted into a predetermined site in the crystal. By the way, the charge / discharge reaction shown in the equations (1) to (3) occurs in a potential range of 3.6 to 4.4 V (. Vs. Li / Li ⁺ ), that is, a so-called 4 V discharge region. The site of the lithium-containing composite oxide that inserts and desorbs lithium ions by the reaction is called a site in the 4 V discharge region.

  In a conventional non-aqueous electrolyte secondary battery, a reductive decomposition reaction of the non-aqueous electrolyte occurs on the surface of the carbon material that is the negative electrode active material at the time of the initial charge. ˜20% is consumed by the negative electrode, which causes a problem that the amount of lithium ions related to the charge / discharge reaction, that is, the amount of lithium ions that fill sites in the 4V discharge region of the lithium-containing composite oxide decreases.

In addition, in the spinel type lithium manganese composite oxide, in addition to the sites in the 4V discharge region, lithium ions are present in a potential range (so-called 3V discharge region) of 3.6V (.vs. Li / Li ⁺ ) or less. The existence of sites that can be inserted and removed is known. If the site in the 3V discharge region can be used for the charge / discharge reaction, it can be expected that the energy density of the nonaqueous electrolyte secondary battery will be significantly improved.

  However, in a conventional nonaqueous electrolyte secondary battery using a lithium manganese composite oxide, the lithium contained in the system is only lithium contained in the lithium manganese composite oxide, and these lithiums are sites in the 4 V discharge region. Since it does not insert into or desorb from the site in the 3V discharge region, it cannot use the site in the 3V discharge region of the lithium manganese composite oxide as the battery capacity. There was a problem.

  The present invention has been made in view of the above problems, and by controlling the electrical characteristics of a cable that transmits high-frequency power, the occurrence of a phase difference between the high-frequency power is suppressed and the film thickness distribution characteristics are made uniform. It aims to provide a way to do.

  As described above, the lithium-containing composite oxide of the nonaqueous electrolyte secondary battery has a considerable amount of unused capacity (latent capacity) due to the absence of lithium ions. Therefore, if a technique for adding lithium ions in an amount corresponding to the unused capacity in the battery can be established, it can be expected to increase the energy density of the nonaqueous electrolyte secondary battery.

  This invention is made | formed in view of the said situation, Comprising: It aims at providing the operating method of a non-aqueous electrolyte secondary battery with a high energy density.

In order to achieve the above object, the present invention employs the following configuration.
The method for operating the non-aqueous electrolyte secondary battery of the present invention includes a positive electrode composed of a positive electrode mixture formed into a plate shape or a sheet shape including at least a lithium manganese composite oxide powder represented by the following composition formula: A negative electrode mixture formed into a plate shape or a sheet shape containing at least a carbon material powder, and an amount of lithium that is bonded to the surface of the negative electrode mixture and that corresponds to an unused capacity existing in the positive electrode mixture Is a method for operating a non-aqueous electrolyte secondary battery comprising a negative electrode made of a metallic lithium foil to which is added, and a non-aqueous electrolyte, and is charged and discharged using a site in the 4 V discharge region and a site in the 3 V discharge region It is characterized by that.
LiMn _2−x M _x O ₄
However, M is at least one element of Ti, V, Cr, Fe, Co, Ni, Al, Ag, Mg, and Li, and x indicating the composition ratio is 0 ≦ x ≦ 1.0. is there.

  In such a nonaqueous electrolyte secondary battery, in addition to lithium contained in the lithium-containing composite oxide, lithium is further added in the form of a metallic lithium foil. Lithium bonded to the negative electrode as a metal lithium foil immediately diffuses into the carbon material as the negative electrode active material in contact with the electrolyte, and is subjected to a charge / discharge reaction. Thus, the amount of lithium related to the charge / discharge reaction of the battery can be increased, and the energy density of the nonaqueous electrolyte secondary battery can be increased.

In the nonaqueous electrolyte secondary battery of the present invention, as the lithium-containing composite oxide, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or those obtained by substituting a part of the transition metal of these composite oxides with a different element is used. Moreover, what mixed these 2 or more types may be used.

  Further, the non-aqueous electrolyte secondary battery of the present invention is the non-aqueous electrolyte secondary battery described above, wherein a plurality of metallic lithium foils are spaced apart from each other on the surface of the negative electrode mixture and uniformly distributed. -It is characterized by having a joined negative electrode. In particular, the distance between the foils is preferably 31 mm or less.

  In such a non-aqueous electrolyte secondary battery, a plurality of metallic lithium foils are uniformly dispersed on the surface of the negative electrode mixture, so that lithium easily diffuses into the carbon material during the charge / discharge reaction, and the metallic lithium foil Part of it will not remain.

The above LiMn _2−x M _x O ₄ is a so-called spinel type lithium manganese composite oxide, and is lithium in the potential range of 3.6 to 4.4 V (.vs. Li / Li ⁺ ) in the crystal. In addition to sites where ions are inserted / desorbed (hereinafter referred to as sites in the 4V discharge region), sites where lithium ions are inserted / desorbed at 3.6V (.vs. Li / Li ⁺ ) or lower (hereinafter referred to as 3V). (Referred to as discharge area site). The lithium contained in this LiMn _2−x M _x O ₄ fills the 4V discharge region site, and the 3V discharge region site is vacant. If lithium is further added to the non-aqueous electrolyte secondary battery having LiMn _2−x M _x O ₄ in the form of a metallic lithium foil, it becomes possible to use the site in the 3V discharge region, and the non-aqueous electrolyte secondary battery can be used. The energy density of the secondary battery can be further improved.

Further, it is preferable to add at least one element of Ti, V, Cr, Fe, Co, Ni, Al, Ag, Mg, and Li as the element M, and among these, Cr, Fe, Co, Ni It is preferable to add at least one of Li and Li. When these elements are added, the transition of the crystal structure due to the yarn-Teller effect caused by LiMn _2−x M _x O ₄ due to the progress of discharge can be suppressed, and the discharge capacity of the battery as the charge / discharge cycle progresses. It is possible to suppress the decrease. In particular, in the case of the non-aqueous electrolyte secondary battery of the present invention, since the discharge is performed until the battery voltage becomes 3 V or less in order to use the site of the LiMn _{2 -x} M _x O ₄ 3 V discharge region, the element M is added. Addition and prevention of the transition of the crystal structure of LiMn _2−x M _x O ₄ is extremely effective for suppressing the decrease in the discharge capacity of the battery.

In particular, as the positive electrode active material (lithium manganese composite oxide) of the nonaqueous electrolyte secondary battery, it is preferable to use a lithium manganese composite oxide having a surface coated with a conductive polymer. When lithium manganese composite oxide coated with a conductive polymer is used, the internal resistance of the positive electrode can be reduced due to the conductivity of the conductive polymer, so it is possible to suppress a decrease in discharge capacity in the 3V discharge region. It becomes. In particular, in the case of the non-aqueous electrolyte secondary battery of the present invention, since the discharge is performed until the battery voltage becomes 3 V or less in order to use the site of the LiMn _2−x M _x O ₄ 3 V discharge region, Reducing the internal resistance of the positive electrode by molecular coating is extremely effective for suppressing a decrease in the discharge capacity of the battery.

In the above non-aqueous electrolyte secondary battery, the weight of the metal lithium foil is Lim, and the weight of lithium that satisfies the 3V discharge region site of LiMn _2−x M _x O ₄ is Li3V. When the weight of lithium consumed in the reduction reaction of the non-aqueous electrolyte that occurs on the surface of the carbon material during the initial charge of the secondary battery is Li1c, the weight of the metal lithium foil satisfies the relationship Lim ≧ Li3V + Li1c. preferable. Li3V and Li1c can be obtained from the test results obtained by conducting a charge / discharge test using the positive electrode mixture and the negative electrode mixture as working electrodes and lithium as a counter electrode.

  In particular, it is more preferable that the amount of the metal lithium foil is in the range of 3 wt% to 10 wt% with respect to the carbon material.

  In the non-aqueous electrolyte secondary battery of the present invention, as the carbon material, natural graphite, artificial graphite, amorphous carbon, or the like can be used, or a mixture of two or more of these may be used.

  As the non-aqueous electrolyte, non-aqueous electrolytes in which various lithium salts are dissolved in an aprotic solvent alone or in a mixed solvent of two or more aprotic solvents can be used. Further, instead of the non-aqueous electrolyte solution, a gel electrolyte obtained by mixing the non-aqueous electrolyte solution and the polymer material to be gelled, or a solid electrolyte in which the electrolyte is dispersed in the polymer material may be used.

  In addition, when using a non-aqueous electrolyte as the non-aqueous electrolyte, the separator used to separate the positive electrode and the negative electrode is a porous polyolefin film such as a commonly used porous polypropylene film or porous polyethylene film. can do.

  The shape of the nonaqueous electrolyte secondary battery of the present invention may be any of a cylindrical shape, a square shape, a coin shape, a sheet shape, and the like.

  As described above in detail, the nonaqueous electrolyte secondary battery of the present invention includes a negative electrode in which a metal lithium foil is bonded to the surface of a negative electrode mixture containing a carbon material powder, and contains lithium. In addition to lithium contained in the composite oxide, lithium is further added to the battery system in the form of a metal lithium foil, so that the amount of lithium involved in the charge / discharge reaction can be increased, and the non-aqueous electrolyte secondary battery The energy density of can be increased.

  In addition, since a plurality of metallic lithium foils are joined to the surface of the negative electrode mixture so as to be separated from each other, lithium easily diffuses into the carbon material during the charge / discharge reaction, and a part of the metallic lithium foil The energy density of the nonaqueous electrolyte secondary battery can be increased without remaining. In particular, when metal lithium foils are spaced apart and uniformly distributed, if the distance between the foils is 31 mm or less, the diffusion of metal lithium into the negative electrode becomes easier and good cycle characteristics can be obtained. .

Furthermore, the lithium-containing composite oxide, a lithium-manganese composite oxide represented by the formula LiMn _{2-x M} x _{O 4,} in the non-aqueous electrolyte secondary battery having the LiMn _{2-x M} x _{O 4} If lithium is further added in the form of a metallic lithium foil, the LiLiMn _2−x M _x O ₄ 3 V discharge region site can be used, and the energy density of the nonaqueous electrolyte secondary battery can be further improved. Can do. In particular, in the case of the non-aqueous electrolyte secondary battery of the present invention, since the discharge is performed until the battery voltage becomes 3 V or less in order to use the site of the LiMn _{2 -x} M _x O ₄ 3 V discharge region, the element M is added. Addition and prevention of the transition of the crystal structure of LiMn _2−x M _x O ₄ is extremely effective for suppressing the decrease in the discharge capacity of the battery.

In the non-aqueous electrolyte secondary battery of the present invention, the weight of the metal lithium foil is Lim, the weight of lithium satisfying the 3V discharge region site of LiMn _2−x M _x O ₄ is Li 3V, and the non-aqueous electrolyte secondary battery is When the weight of lithium consumed in the reduction reaction of the non-aqueous electrolyte that occurs on the surface of the carbon material during the initial charge of the secondary battery is Li1c, the weight of the metal lithium foil satisfies Lim ≧ Li3V + Li1c. The energy density of the nonaqueous electrolyte secondary battery can be increased. In particular, the energy density of the nonaqueous electrolyte secondary battery can be further increased by setting the amount of the metal lithium foil in the range of 3 wt% to 10 wt% with respect to the carbon material.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the nonaqueous electrolyte secondary battery of the present invention is not limited to the embodiments shown in the following drawings. In FIG. 1, an example of the nonaqueous electrolyte secondary battery which is embodiment of this invention is shown. This non-aqueous electrolyte secondary battery is a so-called coin-type battery, and is a disk-shaped positive electrode mixture (positive electrode) 4 containing at least a lithium composite oxide and a disk-like material containing at least a carbon material. The negative electrode 3, the separator 6 disposed between the positive electrode mixture 4 and the negative electrode 3, and a non-aqueous electrolyte are mainly configured.

  The non-aqueous electrolyte secondary battery includes a substantially flat cylindrical battery case 1 made of stainless steel or the like and a sealing plate 2 made of stainless steel or the like. The separator 6 and the disc-shaped positive electrode mixture 4 are sequentially laminated, and the sealing plate 2 is disposed thereon. An annular gasket 7 made of polypropylene is interposed between the battery case 1 and the sealing plate 2. Glass wool filter papers 5 and 5 are inserted between the separator 6 and the positive electrode mixture 4 and the negative electrode 3, respectively. The non-aqueous electrolyte is impregnated in the positive electrode mixture 4, the negative electrode 3, the separator 6, and the glass wool filter papers 5 and 5.

  The positive electrode mixture 4 is formed by forming a lithium-containing composite oxide powder and a conductive additive made of graphite powder or the like into a disk shape with a binder made of polyvinylidene fluoride resin or the like.

As the lithium-containing composite oxide, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or a material obtained by substituting a part of the transition metal of these composite oxides with a different element can be used. A mixture may be used.

In particular, it is preferable to use a lithium manganese composite oxide represented by the composition formula LiMn _2−x M _x O ₄ . Here, the element M represents at least one element of Ti, V, Cr, Fe, Co, Ni, Al, Ag, Mg, and Li, and x indicating the composition ratio is 0 ≦ x ≦ 1. 0.

LiMn _{2-x M} x _{O 4} above is called a spinel-type lithium-manganese composite oxide, lithium-ion at a potential range of 3.6~4.4V in the crystal (.vs. Li / Li ⁺⁾ Inserted and desorbed (hereinafter referred to as the 4V discharge region site) and 3.6 V (.vs. Li / Li ⁺ ) or less where lithium ions are inserted and desorbed (hereinafter referred to as the 3V discharge region site). Called a site). Moreover, the lithium contained in LiMn _2−x M _x O ₄ fills the site in the 4V discharge region, and the site in the 3V discharge region is vacant.

In this LiMn _2−x M _x O ₄ , at least one element of Ti, V, Cr, Fe, Co, Ni, Al, Ag, Mg, and Li is added as the element M. Among these, it is preferable to add one or more of Cr, Fe, Co, Ni, Al, Ag, Mg, and Li. When these elements M are added, the transition of the crystal structure due to the Yarn-Teller effect caused in LiMn _2−x M _x O ₄ by the progress of discharge can be suppressed, and the discharge capacity of the battery as the charge / discharge cycle progresses. It is possible to suppress the decrease.

  Moreover, it is preferable to use the lithium manganese composite oxide which coat | covered the conductive polymer on the surface as a lithium manganese composite oxide which is a positive electrode active material of the said nonaqueous electrolyte secondary battery. When a lithium manganese composite oxide coated with a conductive polymer is used, the internal resistance of the positive electrode can be reduced, so that a reduction in discharge capacity in the 3V discharge region can be suppressed.

  As shown in FIG. 2, the negative electrode 3 is composed of a negative electrode mixture 8 containing a carbon material and a metal lithium foil 9 bonded to the surface of the negative electrode mixture 8. The negative electrode mixture 8 is a carbon material powder formed into a disk shape by a binder made of polyvinylidene fluoride resin or the like, and a conductive additive such as graphite powder can be added as necessary.

  The metal lithium foil 9 preferably has a thickness of 50 μm or less. The metal lithium foil 9 is bonded to the negative electrode mixture 8 after the negative electrode mixture 8 is formed. 2 shows an example in which one metal lithium foil 9 is bonded to the negative electrode mixture 8. However, the present invention is not limited to this, and a plurality of metal lithium foils are separated from each other and bonded to the surface of the negative electrode mixture. You may do it. In particular, the interval between the metallic lithium foils that are spaced apart from each other and uniformly distributed is preferably 31 mm or less. Lithium added in the form of metallic lithium foil diffuses into the carbon material, which is the negative electrode active material, in contact with the electrolyte, and is subjected to a charge / discharge reaction.

Further, the weight of the metal lithium foil 9 is Lim, and the weight of lithium that fills the 3V discharge region site of LiMn _2−x M _x O ₄ is Li3V. When the nonaqueous electrolyte secondary battery is initially charged, It is preferable that the weight of the lithium metal foil 9 satisfies Lim ≧ Li3V + Li1c, where Li1c is the weight of lithium consumed in the reduction reaction of the nonaqueous electrolyte. Li3V and Li1c can be obtained from the test results obtained by conducting a charge / discharge test using the positive electrode mixture and the negative electrode mixture as working electrodes and lithium as a counter electrode. In particular, when the weight of the metal lithium foil 9 is 3 wt% or more and 10 wt% or less, more preferably 4.5 wt% or more and 10 wt% or less with respect to the weight of the carbon material contained in the negative electrode mixture 8. Good. The metal lithium foil 9 consumes lithium that fills the LiMn _2−x M _x O ₄ 3V discharge region site, and consumes lithium in the reduction reaction of the nonaqueous electrolyte that occurs on the surface of the carbon material during the first charge. Even if it is a case, it is preferable to add so that the one part may remain | survive.

  The carbon material constituting the negative electrode mixture 8 may be any material that reversibly inserts and desorbs lithium ions. For example, any one of natural graphite, artificial graphite, amorphous carbon, or the like, or these Two or more of these may be mixed.

Non-aqueous electrolytes are propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2 methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, Non-pro such as dimethyl ether The emission of solvent or a mixed solvent obtained by mixing two or more of these _{solvents,, LiPF 6, LiBF 4,} LiSbF 6, LiAsF 6, LiClO 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiSbF 6 , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), one or more of electrolytes composed of lithium salts such as LiCl and LiI It is possible to use a solution obtained by dissolving a mixture of. Further, instead of the non-aqueous electrolyte, a gel electrolyte obtained by mixing the non-aqueous electrolyte and the polymer material to be gelled, or a solid electrolyte in which the electrolyte is dispersed in the polymer material can be used.

  The separator 6 may be a porous polyolefin film such as a commonly used porous polypropylene film or porous polyethylene film.

In this nonaqueous electrolyte secondary battery, lithium is further added in the form of a metallic lithium foil in addition to lithium contained in the lithium-containing composite oxide. During the initial charge of the non-aqueous electrolyte secondary battery, a reductive decomposition reaction of the non-aqueous electrolyte occurs on the surface of the carbon material of the negative electrode, and 10 to 20% of lithium ions released from the lithium-containing composite oxide by this reaction. Is fixed to the negative electrode, which causes a phenomenon in which the amount of lithium ions related to the charge / discharge reaction, that is, the amount of lithium ions that fill sites in the 4V discharge region of the lithium-containing composite oxide decreases. Further, the lithium manganese composite oxide LiMn _2−x M _x O ₄ has sites where lithium is inserted / extracted in the 4V discharge region and sites where lithium is inserted / extracted in the 3V discharge region. The lithium contained in LiMn _2−x M _x O ₄ is arranged at the site of the 4V discharge region, and the site of the 3V discharge region is vacant. Thus, a considerable amount of unused capacity (latent capacity) due to the absence of lithium ions is present in the lithium-containing composite oxide that is the positive electrode active material. Therefore, by adding an amount of lithium corresponding to this unused capacity to the negative electrode in the form of a metal lithium foil, it becomes possible to utilize the unused capacity of the lithium-containing composite oxide that is the positive electrode active material. The energy density of the electrolyte secondary battery can be increased.

  In this non-aqueous electrolyte secondary battery, a plurality of metallic lithium foils 9 are uniformly dispersed on the surface of the negative electrode mixture 8, so that lithium diffuses into the carbon material of the negative electrode during the charge / discharge reaction. Since all of the added lithium is utilized for the charge / discharge reaction without leaving a part of the metal lithium foil, the energy density of the nonaqueous electrolyte secondary battery can be increased.

Furthermore, this non-aqueous electrolyte secondary battery uses a lithium manganese composite oxide represented by LiMn _2−x M _x O _{4 in} which a part of Mn is substituted with an element M as a lithium composite oxide. Can suppress the transition of the crystal structure due to the Yarn-Teller effect caused by LiMn _2−x M _x O ₄ due to the progress of the discharge, and the discharge capacity of the battery is reduced as the charge / discharge cycle progresses In particular, in the case of the non-aqueous electrolyte secondary battery of the present invention, the discharge of the LiMn _2−x M _x O ₄ 3V discharge region is used until the battery voltage becomes 3V or less. Therefore, by adding the element M to prevent the transition of the crystal structure of LiMn _2−x M _x O ₄ , it is possible to extremely effectively suppress the decrease in the discharge capacity of the battery.

  Example 1 A non-aqueous electrolyte secondary battery as shown in FIG. 1 was prepared, and the influence of the addition of metal lithium foil on the cycle characteristics of the battery was investigated. First, 80 parts by weight of lithium cobalt composite oxide (LiCoO2), 5 parts by weight of graphite powder and 5 parts by weight of acetylene black powder as a conductive additive, and 10 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methyl was added to this mixture. 100 parts by weight of pyrrolidone was added and mixed well with a homomixer to obtain a slurry. After that, this slurry was applied on an Al substrate having a size of 100 mm × 140 mm and a thickness of 20 μm by a doctor blade method, preliminarily dried in air, compression-molded by a hot press, and then punched into a disk shape having a diameter of 16 mm. The positive electrode was obtained by heating and drying in vacuum.

  Next, 90 parts by weight of natural graphite powder and 10 parts by weight of polyvinylidene fluoride as a binder were mixed. Further, 200 parts by weight of N-methylpyrrolidone as a solvent was added to this mixture, and the mixture was sufficiently mixed with a homomixer to obtain a slurry. . After that, slurry was applied on a copper substrate of 100 mm × 140 mm and thickness 10 μm by the doctor blade method, pre-dried in the air, compression molded with a roll press, and then punched into a disk shape with a diameter of 16 mm. The negative electrode mixture was obtained by heating and drying in vacuum. On this negative electrode mixture, a commercially available metal lithium foil prepared separately was pressure-bonded using a roller press in a dry room (dew point of −50 ° C. or lower) to prepare a negative electrode. In addition, the negative electrode which produced 1.5 weight% of metal lithium foil with respect to the weight of the natural graphite which is a negative electrode active material was produced.

  Using the positive electrode and the negative electrode prepared as described above, a coin-type non-aqueous electrolyte secondary battery as shown in FIG. 1 was prepared in a dry room. As the non-aqueous electrolyte, a solution in which LiPF6 was dissolved at a concentration of 1 mol / liter as an electrolyte in a mixed solvent of ethylene carbonate: dimethyl carbonate = 1: 2 (molar ratio) was used. The dimensions of this battery were 20 mm in diameter and 1.6 mm in total battery height.

  A potentiogalvanostat is connected to the coin-type non-aqueous electrolyte secondary battery produced as described above, and the charge / discharge current density is 100 mAh / g—the negative electrode active material weight, the charge end voltage is 4.1 V, and the discharge end voltage is 3. A constant current charge / discharge test was performed under the condition of 0V.

  (Example 2) A nonaqueous electrolyte secondary battery was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that lithium nickel composite oxide (LiNiO2) was used as the positive electrode material.

  Example 3 Similar to Example 1, except that lithium manganese composite oxide (LiMn 2 O 4) was used as the positive electrode material, and the charge / discharge conditions were changed to a charge end voltage of 4.15 V and a discharge end voltage of 2.2 V. An electrolyte secondary battery was produced and a charge / discharge test was performed.

  (Comparative Example 1) The nonaqueous electrolyte secondary was the same as in Example 1 except that the amount of metal lithium foil added to the negative electrode was 0% by weight with respect to the weight of natural graphite as the negative electrode active material. A battery was prepared and a charge / discharge test was performed.

  (Comparative Example 2) A nonaqueous electrolyte secondary, as in Example 2, except that the amount of metal lithium foil added to the negative electrode was 0% by weight with respect to the weight of natural graphite as the negative electrode active material. A battery was prepared and a charge / discharge test was performed.

  (Comparative Example 3) A non-aqueous electrolyte secondary, as in Example 3, except that the amount of metallic lithium foil added to the negative electrode was 0% by weight with respect to the weight of natural graphite as the negative electrode active material. A battery was prepared and a charge / discharge test was performed.

  FIG. 3 shows the cycle characteristics of the nonaqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3. As can be seen from FIG. 3, the addition of lithium metal not only increases the discharge capacity, but also decreases the decrease in discharge capacity accompanying an increase in the number of cycles, indicating excellent cycle characteristics. From the above, it can be considered that the addition of the metal lithium foil to the negative electrode not only improves the capacity of the battery but also improves the cycle characteristics.

  (Example 4) Next, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the relationship between the amount of metallic lithium foil added, the discharge capacity of the battery, and the cycle characteristics was investigated. First, in the same manner as in Example 3, LiMn2O4 powder, graphite powder and acetylene black powder, and polyvinylidene fluoride were mixed, and N-methylpyrrolidone was added to this mixture, which was sufficiently mixed with a homomixer to obtain a slurry. . After that, this slurry was applied on an Al substrate having a size of 100 mm × 140 mm and a thickness of 20 μm by a doctor blade method, preliminarily dried in air, compression-molded by a hot press, and then punched into a disk shape having a diameter of 16 mm. The positive electrode was obtained by heating and drying in vacuum.

  Next, in the same manner as in Example 1, natural graphite powder and polyvinylidene fluoride were mixed, N-methylpyrrolidone was further added to this mixture, and the mixture was sufficiently mixed with a homomixer to obtain a slurry. After that, slurry was applied on a copper substrate of 100 mm × 140 mm and thickness 10 μm by the doctor blade method, pre-dried in the air, compression molded with a roll press, and then punched into a disk shape with a diameter of 16 mm. The negative electrode mixture was obtained by heating and drying in vacuum. On this negative electrode mixture, a commercially available metal lithium foil prepared separately was pressure-bonded using a roller press in a dry room (dew point of −50 ° C. or lower) to prepare a negative electrode. In addition, the negative electrode which made the quantity of metal lithium foil 0, 1.5, 3.0, 4.5, 6.0, 7.5, 10 weight% with respect to the weight of the natural graphite which is a negative electrode active material. Produced.

  Using the positive electrode and the negative electrode prepared as described above, a coin-type nonaqueous electrolyte secondary battery as shown in FIG. 1 was prepared in a dry room. As the nonaqueous electrolyte, a solution obtained by dissolving LiPF6 as an electrolyte in a mixed solvent of ethylene carbonate: dimethyl carbonate = 1: 2 (molar ratio) at a concentration of 1 mol / liter was used. The dimensions of this battery were 20 mm in diameter and 1.6 mm in total battery height.

  A potentiogalvanostat is connected to the coin-type non-aqueous electrolyte secondary battery produced as described above, and the charge / discharge current density is 100 mAh / g-negative electrode carbon weight, the charge end voltage is 4.15 V, and the discharge end voltage is 2.2 V. The constant current charge / discharge test was conducted under the following conditions. The results are shown in FIGS.

  FIG. 4 shows the relationship between the weight of the metal lithium foil of the nonaqueous electrolyte secondary battery and the initial discharge capacity when LiMn2O4 is used as the positive electrode material. It can be seen that the discharge capacity increases as lithium is added, and the discharge capacity increases with the amount of lithium added up to 4.5% by weight, but the discharge capacity becomes constant when it exceeds 4.5% by weight. FIG. 5 shows the cycle characteristics of the nonaqueous electrolyte secondary battery when LiMn2O4 is used as the positive electrode material. When the amount of metallic lithium added is 1.5% by weight or less, a decrease in discharge capacity is observed with an increase in the number of cycles. Very little and shows excellent cycle characteristics. From the above, it is considered that the addition amount of the metallic lithium foil is at least 3% by weight or more, preferably 4.5 to 10% by weight. In addition, even if it added 10 weight% or more, the effect of the increase in discharge capacity or the improvement of cycling characteristics was not seen.

  (Example 5) Next, the cycle characteristics of the nonaqueous electrolyte secondary battery when the shape and arrangement of the metal lithium foil were variously changed were investigated using an electrolytic cell for battery performance measurement as shown in FIG. . First, in the same manner as in Example 3, LiMn2O4 powder, graphite powder and acetylene black powder, and polyvinylidene fluoride were mixed, N-methylpyrrolidone was added to this mixture, and the mixture was mixed with a homomixer to obtain a slurry of 100 mm. This slurry was applied onto an Al substrate 21 with a thickness of 140 mm and a thickness of 20 μm by the doctor blade method, preliminarily dried in air, compression-molded with a hot press, and then heated and dried in a vacuum. In this way, the positive electrode mixture 22 was fixed on the Al substrate 21. And the positive electrode terminal 18 was welded to the Al substrate 21, and the positive electrode 13 was created.

  Next, in the same manner as in Example 1, natural graphite powder and polyvinylidene fluoride were mixed, N-methylpyrrolidone was further added to this mixture, and the mixture was mixed with a homomixer to form a slurry. This slurry was 100 mm × 140 mm in thickness. It was coated on a 10 μm thick Cu substrate 19 by a doctor blade method, pre-dried in air, compression-molded with a roll press, and then heat-dried in a vacuum. In this way, the negative electrode mixture 20 was fixed on the Cu substrate 19. And the negative electrode terminal 17 was welded to Cu substrate, and the negative electrode 14a as shown in FIG. 7 was produced.

  Next, a metal lithium foil was joined to the surface of the negative electrode 14a using a roll press. At this time, the metal lithium foil was bonded onto the negative electrode 14a in three patterns. First, as shown in FIG. 8, one metal lithium foil 24 having a length of 81 mm, a width of 58 mm, and a thickness of 0.025 mm is arranged at the center of the negative electrode mixture 20 (sample 1), and then as shown in FIG. 6 metal lithium foils 25 of length 40 mm, width 19 mm, thickness 0.025 mm are uniformly arranged on the surface of the negative electrode mixture 20 (sample 2), and as shown in FIG. This is a sample (sample 3) in which three metallic lithium foils 26 of 100 mm and a thickness of 0.025 mm are uniformly arranged on the surface of the negative electrode mixture 20. In this way, three types of negative electrodes 14 (14b to 14d) were produced.

  The weights of the metal lithium foils of Samples 1 to 3 are almost the same, but the size and number of the foils themselves are different. When comparing the outer peripheries of the metal lithium foils of Samples 1 to 3, Sample 1: Sample 2 : Sample 3 = 1: 2.6: 2.2.

  And the electrolytic cell for battery performance measurement as shown in FIG. 7 was assembled using said positive electrode 13 and the negative electrode 14 (14b-14d) shown in FIGS. 8-10. First, a porous polypropylene separator 15 was sandwiched between a positive electrode 13 and a negative electrode 14 (14a 14c), which were further sandwiched between a pair of polypropylene spacers 12 and 12, and stored in a stainless steel battery container 11. Then, a non-aqueous electrolyte solution in which LiPF 6 as an electrolyte was dissolved in a mixed solvent of ethylene carbonate: dimethyl carbonate = 1: 2 (molar ratio) at a concentration of 1 mol / liter was poured into the battery container 11. By sealing the part with a sealing plate 23 via an O-ring 16, an electrolytic cell for battery performance measurement was produced. The positive electrode terminal 18 and the negative electrode terminal 17 penetrated the sealing plate 23 and were exposed to the outside of the battery performance measurement electrolytic cell. The positive electrode terminal 18 and the negative electrode terminal 17 are connected to a potentiogalvanostat, and a constant current charge / discharge test is performed under the conditions of a charge / discharge current density of 100 mAh / g-C, a charge end voltage of 4.15 V, and a discharge end voltage of 2.2 V. It was. The results are shown in FIG.

  As shown in FIG. 11, among the samples 1 to 3, the best cycle characteristics are the negative electrode 14c of the sample 2, the next best is the negative electrode 14d of the sample 3, and finally the negative electrode of the sample 1. 14b. This order coincides with the order of the ratio of the outer peripheral length of the metal lithium foil. This is presumably because the metal lithium foil was uniformly dispersed on the negative electrode, so that the metal lithium was easily diffused into the natural graphite as the negative electrode active material, and the cycle characteristics were improved. Accordingly, a non-aqueous electrolyte secondary battery having a high energy density with improved cycle characteristics by arranging a plurality of metallic lithiums spaced apart and uniformly distributed on the negative electrode so as to lengthen the outer periphery of the metallic lithium foil. It turns out that can be obtained. In particular, if the distance between the foils is set to 31 mm or less, it is considered that diffusion of metallic lithium into the negative electrode becomes easier and good cycle characteristics can be obtained.

It is sectional drawing of the coin-type nonaqueous electrolyte secondary battery which is embodiment of this invention. It is a perspective view of the negative electrode of the nonaqueous electrolyte secondary battery shown in FIG. It is a graph which shows the cycling characteristics of the nonaqueous electrolyte secondary battery of Examples 1-3 and Comparative Examples 1-3. 6 is a graph showing the relationship between the amount of metallic lithium added to the nonaqueous electrolyte secondary battery of Example 4 and the initial discharge capacity. 6 is a graph showing cycle characteristics of the nonaqueous electrolyte secondary battery of Example 4. It is a cross-sectional schematic diagram which shows the structure of the electrolytic cell for battery performance measurement. It is a top view of a negative electrode. 2 is a plan view of a negative electrode of Sample 1. FIG. 3 is a plan view of a negative electrode of Sample 2. FIG. 4 is a plan view of a negative electrode of Sample 3. FIG. It is a graph which shows the cycle characteristic of the electrolytic cell for battery performance measurement using the negative electrode of samples 1-3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Negative electrode 4 Positive electrode compound material (positive electrode)
6 Separator 8 Negative electrode composite 9 Metal lithium foil

Claims (6)

A positive electrode comprising a positive electrode mixture formed into a plate shape or a sheet shape containing at least a powder of a lithium manganese composite oxide represented by the following composition formula;
A negative electrode composite material containing at least a carbon material powder and formed into a plate shape or a sheet shape, and an amount of lithium that is bonded to the surface of the negative electrode composite material and that corresponds to the unused capacity existing in the positive electrode composite material. A negative electrode comprising a metallic lithium foil to be added;
A non-aqueous electrolyte secondary battery operating method comprising a non-aqueous electrolyte,
A method for operating a non-aqueous electrolyte secondary battery, wherein charging and discharging are performed using a site in a 4 V discharge region and a site in a 3 V discharge region.
LiMn _2−x M _x O ₄
However, M is at least one element of Ti, V, Cr, Fe, Co, Ni, Al, Ag, Mg, and Li, and x indicating the composition ratio is 0 ≦ x ≦ 1.0. is there.   The method for operating a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode uses a lithium manganese composite oxide having a surface coated with a conductive polymer.   The operation of the non-aqueous electrolyte secondary battery according to claim 1, wherein a plurality of metallic lithium foils are provided with negative electrodes that are spaced apart from each other and uniformly distributed and bonded to the surface of the negative electrode mixture. Method.   4. The method of operating a non-aqueous electrolyte secondary battery according to claim 3, wherein an interval between a plurality of metallic lithium foils that are separated from each other and joined in the negative electrode is 31 mm or less.   The weight of the metallic lithium foil is Lim, the weight of lithium that fills the 3 V discharge region of the lithium manganese composite oxide is Li3V, and non-aqueous water is generated on the surface of the carbon material when the non-aqueous electrolyte secondary battery is charged for the first time. The weight of the lithium metal foil satisfies the relationship Lim ≧ Li3V + Li1c, where Li1c is the weight of lithium consumed in the reduction reaction of the electrolyte, according to any one of claims 1 to 4. A method for operating a non-aqueous electrolyte secondary battery.   6. The nonaqueous electrolyte according to claim 1, wherein the weight of the metal lithium foil is in the range of 3% by weight to 10% by weight with respect to the weight of the carbon material. Secondary battery operation method.

Images