JP6315998B2 - Negative electrode and non-aqueous electrolyte battery - Google Patents

Description

  Embodiments described herein relate generally to a negative electrode and a nonaqueous electrolyte battery.

  In recent years, non-aqueous electrolyte batteries that are charged and discharged by moving Li ions between a negative electrode and a positive electrode have been developed from the viewpoints of energy problems and environmental problems, such as electric vehicles (EV), hybrid vehicles (HEV), solar It is expected as a large power storage device for stationary power generation systems such as photovoltaic power generation.

  Such non-aqueous electrolyte batteries are more resistant to long-term use than non-aqueous electrolyte batteries used in small mobile phones, laptop computers, etc., and are less likely to ignite or explode in the event of an accident. Properties are required.

In a nonaqueous electrolyte battery using a carbon-based negative electrode, it is known that metallic lithium, so-called dendrite, is deposited on the negative electrode during operation at a low temperature or deterioration due to long-term use. This is because the lithium occlusion and release potential of the carbon negative electrode is in the vicinity of 0.1 V vs Li / Li ⁺ , which is close to the lithium deposition potential. The dendrite has a needle shape. Therefore, the dendrite may penetrate the separator and cause an internal short circuit. Such an internal short circuit may cause abnormal heat generation of the battery and is dangerous.

On the other hand, the precipitation of dendrites can be suppressed by using a negative electrode active material that has a higher lithium insertion and release potential than the carbon negative electrode. Examples of such an active material include a metal oxide negative electrode (for example, lithium titanium composite oxide), an alloy-based negative electrode (for example, tin), and the like. Among these, lithium titanate, particularly Li ₄ Ti ₅ O _12, is known as a material having extremely high cycle stability because the size and structure of the crystal lattice hardly change during insertion and desorption of Li ions. However, the theoretical capacity of Li ₄ Ti ₅ O ₁₂ is 175 mAh / g, which is about half that of 336 mAh / g of the carbon negative electrode. Therefore, when Li ₄ Ti ₅ O ₁₂ is used, there is a problem that the energy density of the battery is lower than that of the carbon-based negative electrode.

JP 2012-099287 A Japanese Patent Laid-Open No. 2005-135872 Japanese Patent No. 4597666 JP2013-84601A

  An object of this invention is to provide the negative electrode which can implement | achieve the nonaqueous electrolyte battery excellent in a lifetime characteristic and a rate characteristic, and the nonaqueous electrolyte battery which can show the outstanding lifetime characteristic and a rate characteristic.

According to a first embodiment, a negative electrode is provided. The negative electrode includes a negative electrode material layer. The negative electrode material layer includes a plurality of negative electrode active material particles and a second conductive additive. Each of the plurality of negative electrode active material particles includes secondary particles and a first conductive additive in contact with at least a part of the surface of the secondary particles . The secondary particles are formed by aggregation of a plurality of primary particles of monoclinic niobium titanium composite oxide. The second conductive auxiliary agent is in contact with the first conductive auxiliary agent. The second conductive additive is disposed between the negative electrode active material particles. The first conductive additive, in the Raman spectrum obtained by Raman spectroscopy of the negative electrode layer, and the D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, the frequency of 1550 cm ^-1 1650 cm ^-1 G band appearing in the region. In the Raman spectrum of the first conductive additive, the ratio of the peak intensity of the G band to the peak intensity of the D band is in the range of 0.5 to 1.3. The second conductive additive, in the Raman spectrum obtained by Raman spectroscopy of the negative electrode layer, and the D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, the frequency of 1550 cm ^-1 1650 cm ^-1 G band appearing in the region. In the Raman spectrum, the ratio of the G band peak intensity to the D band peak intensity is in the range of 1.5 to 10.

  According to the second embodiment, a nonaqueous electrolyte battery is provided. The nonaqueous electrolyte battery includes a negative electrode, a positive electrode, and a nonaqueous electrolyte. The negative electrode is a negative electrode according to the first embodiment.

FIG. 1 shows a Raman spectrum of a part of an example negative electrode according to the first embodiment. FIG. 2 is a schematic cross-sectional view of a part of the negative electrode material layer of the negative electrode of the example according to the first embodiment. FIG. 3 is a schematic cross-sectional view of an example nonaqueous electrolyte battery according to the second embodiment. 4 is an enlarged cross-sectional view of part A of the nonaqueous electrolyte battery shown in FIG. FIG. 5 is a micro Raman image of a part of the negative electrode of Example 1. FIG. 6 is a Raman spectrum for the segment indicated by B in FIG. FIG. 7 is a Raman spectrum for the segment indicated by C in FIG.

  Hereinafter, embodiments will be described with reference to the drawings. In addition, the same code | symbol shall be attached | subjected to a common structure through embodiment, and the overlapping description is abbreviate | omitted. Each figure is a schematic diagram for promoting explanation and understanding of the embodiment, and its shape, dimensions, ratio, etc. are different from the actual device, but these are the following explanations and known techniques. The design can be changed as appropriate.

(First embodiment)
According to a first embodiment, a negative electrode is provided. The negative electrode includes a negative electrode material layer. The negative electrode material layer includes a plurality of negative electrode active material particles and a second conductive additive. Each of the plurality of negative electrode active material particles includes monoclinic niobium titanium composite oxide particles and a first conductive auxiliary agent in contact with at least a part of the surface of the monoclinic niobium titanium composite oxide particles. The second conductive auxiliary agent is in contact with the first conductive auxiliary agent. The second conductive additive is disposed between the negative electrode active material particles. The first conductive additive, in the Raman spectrum obtained by Raman spectroscopy of the negative electrode layer, and the D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, the frequency of 1550 cm ^-1 1650 cm ^-1 G band appearing in the region. In the Raman spectrum of the first conductive additive, the ratio of the peak intensity of the G band to the peak intensity of the D band is in the range of 0.5 to 1.3. The second conductive additive, in the Raman spectrum obtained by Raman spectroscopy of the negative electrode layer, and the D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, the frequency of 1550 cm ^-1 1650 cm ^-1 G band appearing in the region. In the Raman spectrum, the ratio of the G band peak intensity to the D band peak intensity is in the range of 1.5 to 10.

Recently, as a material having a potential and a high charge-discharge capacity can be suppressed precipitation of lithium dendrites, niobium composite capable general formula _{Li x M (1-y)} Nb y Nb 2 O (7 + δ) represents e.g. Oxide (wherein M is at least one selected from the group consisting of Ti and Zr, and x, y and δ are 0 ≦ x ≦ 6, 0 ≦ y ≦ 1 and −1 ≦ δ ≦ 1 respectively. A battery active material is reported. In particular, a monoclinic niobium titanium composite oxide represented by TiNb ₂ O ₇ can insert and desorb lithium in a wider potential range than Li ₄ Ti ₅ O ₁₂ . In addition, there are many spaces into which lithium ions can be inserted. Furthermore, with the insertion of lithium ions, the Nb ions in the crystal are reduced from pentavalent to trivalent, so, for example, more lithium ions are inserted compared to Ti that is reduced from tetravalent to trivalent. However, the electrical neutrality can be maintained. For the above reasons, the monoclinic niobium titanium composite oxide can exhibit a high charge / discharge capacity.

  However, as a result of intensive studies, the inventors have found that monoclinic niobium titanium composite oxide can cause an increase in battery resistance and battery expansion.

The monoclinic niobium titanium composite oxide can insert and desorb Li at a lower potential than Li ₄ Ti ₅ O ₁₂ , for example, Li can be inserted to a potential in the vicinity of 1 V (vs. Li / Li ⁺ ). can do. In such a high charge state, that is, in a state where the negative electrode potential is low, Ti and Nb in the monoclinic niobium titanium composite oxide become very active and promote the decomposition reaction of the nonaqueous electrolyte. The decomposition of the non-aqueous electrolyte can cause an increase in battery resistance and battery expansion.

  As a result of diligent research based on such knowledge, the inventors have arranged the first conductive aid having a low crystallinity so as to be in contact with at least part of the surface of the monoclinic niobium titanium composite oxide particles. By arranging the second conductive additive having a high degree of crystallinity between the negative electrode active material particles, an increase in resistance due to decomposition of the nonaqueous electrolyte and expansion of the battery can be suppressed, and a low resistance can be achieved. I found it.

  The first conductive auxiliary agent can impart electron conductivity to the monoclinic niobium titanium composite oxide particles and can form a stable coating on the surface of the monoclinic niobium titanium composite oxide particles. .

This first conductive additive has a low crystallinity. Specifically, the first conductive additive is a ratio of the peak intensity of the G band to the peak intensity of the D band in the Raman spectrum obtained from the negative electrode material layer by Raman spectroscopy (hereinafter referred to as intensity ratio I _G / _ID ). Called) in the range of 0.5 to 1.3. The first conductive assistant is, for example, a carbon material having a low crystallinity.

Here, D band in the Raman spectrum is a band that appears in the frequency region of 1300cm ^-1 ~1400cm ^-1. The G band is a band that appears in the frequency region of 1550 cm ^{−1 to} 1650 cm ⁻¹ . The peak of the D band is a peak caused by defects in amorphous carbon or graphite. The peak of the G band is a peak caused by graphite (exactly, vibration in a hexagonal lattice of carbon atoms). Therefore, the greater the intensity ratio I _G / _{ID, the} higher the crystallinity, and the smaller the intensity ratio I _G / _ID , the lower the crystallinity.

The first conductive additive intensity ratio I _G / I _D is within a range of 0.5 to 1.3 is arranged so as to be in contact with at least a portion of the surface of the monoclinic niobium titanium composite oxide particles Thus, it is possible to form a stable coating from the product produced by the decomposition of the nonaqueous electrolyte by the monoclinic niobium titanium composite oxide particles in a highly charged state, and to form this coating on the surface of the composite oxide particles. it can. The film formed in this way can prevent further decomposition of the nonaqueous electrolyte by the monoclinic niobium titanium composite oxide particles.

  On the other hand, in the negative electrode material layer, when the first conductive additive is not in contact with the surface of the monoclinic niobium titanium composite oxide particles and is disposed away from the composite oxide particles, Although the decomposition of the non-aqueous electrolyte by the niobium titanium composite oxide particles is promoted, a stable film cannot be formed on the surface of the composite oxide particles. As a result, the decomposition of the non-aqueous electrolyte further proceeds, and the resistance increases and the battery expands more easily.

The first conductive additive intensity ratio I _G / I _D is within a range of 0.5 to 1.3 is excellent in electrical conductivity, sufficient electron conductivity in the monoclinic niobium titanium composite oxide particles Can give sex.

When the strength ratio I _G / _{ID of} the first conductive aid is less than 0.5, the conductivity is lowered, and the conductivity cannot be imparted to the active material. On the other hand, when the strength ratio I _G / _{ID of} the first conductive additive is larger than 1.3, a stable film cannot be formed after decomposing the non-aqueous electrolyte solvent on the active material surface.

  The second conductive auxiliary agent can form a conductive network between the negative electrode active material particles, and can suppress a gas generation reaction due to a side reaction with impurities or a solvent of the nonaqueous electrolyte.

This second conductive additive has a high degree of crystallinity. Specifically, in the second conductive additive, the ratio of the peak intensity of the G band to the peak intensity of the D band in the Raman spectrum obtained by Raman spectroscopy from the negative electrode material layer, that is, the intensity ratio I _G / _ID is 1. Within the range of 5-10. Here, the D band and the G band are as described above.

When the strength ratio I _G / _{ID of} the second conductive auxiliary agent is less than 1.5, decomposition of the nonaqueous electrolyte is promoted, but no film is formed at the active material interface, and gas generation occurs. In other words, the resistance of the battery may increase and the battery may expand. This is the same phenomenon as the case where the first conductive auxiliary agent is arranged away from the surface of the monoclinic niobium titanium composite oxide particles. On the other hand, when the strength ratio I _G / _{ID of} the first conductive auxiliary agent is larger than 10, the dispersibility to the electrode and the binding property to the active material particles are lowered, so that it is difficult to arrange between the particles. Become.

As described above, the first conductive aid having a low degree of crystallinity is disposed so as to be in contact with at least a part of the surface of the monoclinic niobium titanium composite oxide particles. This is because the monoclinic niobium titanium composite oxide in a high potential state can decompose the non-aqueous electrolyte due to a phenomenon specific to the material. For example, Li ₄ Ti ₅ O ₁₂ hardly causes a charge / discharge reaction at a potential in the vicinity of 1 V (vs. Li / Li ⁺ ) at which the activities of Ti and Nb increase. Even if the decomposition reaction of the nonaqueous electrolyte by Li ₄ Ti ₅ O ₁₂ occurs, it immediately converges, so that the conductive auxiliary agent in contact with Li ₄ Ti ₅ O ₁₂ is hardly involved in the reaction. In other words, the decomposition reaction of the nonaqueous electrolyte by Li ₄ Ti ₅ O ₁₂ does not depend much on the crystallinity of the conductive additive in contact with the surface.

  In contrast, the negative electrode according to the first embodiment has a low degree of crystallinity so as to be in contact with at least part of the surface of the monoclinic niobium titanium composite oxide particles in the negative electrode material layer, as described above. By disposing the conductive assistant 1, the decomposition of the non-aqueous electrolyte, which is a unique phenomenon caused by the monoclinic niobium titanium composite oxide, is used, and the coating obtained as a result of the decomposition of the non-aqueous electrolyte Further decomposition of the nonaqueous electrolyte can be suppressed.

  Thus, when the negative electrode according to the first embodiment is used in a nonaqueous electrolyte battery, decomposition of the nonaqueous electrolyte can be suppressed. In addition, when the negative electrode according to the first embodiment is used in a nonaqueous electrolyte battery, an increase in resistance can be suppressed and the conductivity of the first conductive auxiliary and the second conductive auxiliary is fully utilized. be able to. Thanks to these, the negative electrode according to the first embodiment can realize a nonaqueous electrolyte battery having excellent life characteristics and rate characteristics.

  Next, the negative electrode according to the first embodiment will be described in more detail.

  The negative electrode according to the first embodiment includes a negative electrode material layer. The negative electrode according to the first embodiment can further include a negative electrode current collector. The negative electrode material layer can be formed on the negative electrode current collector.

  As described above, the negative electrode material layer includes a plurality of negative electrode active material particles and a second conductive additive. Each of the negative electrode active material particles includes monoclinic niobium titanium composite oxide particles and a first conductive additive.

  The negative electrode active material particles may be primary particles of monoclinic niobium titanium composite oxide. In this case, the first conductive additive is in contact with at least a part of the surface of the negative electrode active material particles.

  Alternatively, the negative electrode active material particles may be secondary particles formed by aggregation of primary particles of monoclinic niobium titanium composite oxide. In this case, the first conductive additive is present on at least a part of the surface of the negative electrode active material particles. For example, the negative electrode active material particles are secondary particles formed by agglomerating primary particles of a plurality of monoclinic niobium titanium composite oxides, and the first conductive auxiliary agent is in contact with the surface of each primary particle. Good. Alternatively, the negative electrode active material particles are secondary particles formed by agglomerating primary particles of a plurality of monoclinic niobium titanium composite oxides, and the first conductive auxiliary agent is present on at least a part of the surface of the secondary particles. It may be in contact.

  The negative electrode active material particles are secondary particles formed by agglomerating primary particles of a plurality of monoclinic niobium titanium composite oxides, and the first conductive auxiliary agent is in contact with the surface of each primary particle. Is more preferable. In such negative electrode active material particles, not only the non-aqueous electrolyte is easily retained in the secondary particles, but also the first conductive auxiliary agent in contact with the surfaces of the adjacent primary particles is each monoclinic niobium titanium. Formation of a stable film that suppresses decomposition of the nonaqueous electrolyte on the surface of the primary particle of the composite oxide can be promoted.

  The primary particles of the monoclinic niobium titanium composite oxide preferably have an average particle size of 0.01 μm or more and 10 μm or less.

The negative electrode active material particles preferably have an average particle diameter of 1 μm or less and a specific surface area in the range of 5 to 50 m ² / g according to the BET method by N ₂ gas adsorption. The negative electrode active material particles having such an average particle diameter and specific surface area can increase the utilization factor and increase the substantial capacity.

The monoclinic niobium titanium composite oxide contained in the negative electrode active material particles is a compound that can be represented by, for example, the general formula Li _x Nb ₂ TiO ₇ . Here, the subscript x is a number within the range of 0 ≦ x ≦ 6, and changes depending on the state of charge of the monoclinic niobium titanium composite oxide. Strictly speaking, monoclinic niobium-titanium composite oxide does not contain lithium element. However, when this composite oxide is used in a non-aqueous electrolyte battery, Li is inserted, and even when subjected to discharge, Li is not completely released. Sometimes. Compound represented by the general formula Li _x Nb ₂ TiO ₇ also includes compounds represented by the general formula general formula _{Li x Nb 2 TiO 7 ± δ} . Here, the subscript δ is a number within the range of 0 ≦ δ ≦ 0.3, and is a variable depending on various factors such as oxygen deficiency due to the manufacturing process.

The monoclinic niobium titanium composite oxide contained in the negative electrode active material particles may be a compound other than the compound represented by the general formula Li _x Nb ₂ TiO ₇ . For example, a general formula Nb ₂ Ti _1-x M _x O _{7 in} which a part of titanium is substituted with another metal (where 0 <x <1 and the element M is Nb, V, Ta, Bi, Sb, As , P, Cr, Mo, W, B, Na, Mg, Al, and Si.

  The negative electrode material layer can also include one or more types of negative electrode active material particles other than the plurality of negative electrode active material particles including monoclinic niobium titanium composite oxide particles.

  As described above, the first conductive additive is in contact with at least a part of the surface of the monoclinic niobium titanium composite oxide particles. The first conductive additive is preferably in contact with the entire surface of the monoclinic niobium titanium composite oxide particles. The first conductive additive in contact with the entire surface of the monoclinic niobium titanium composite oxide particles has a stable coating that suppresses the progress of the decomposition of the non-aqueous electrolyte, and the monoclinic niobium titanium composite oxide particles It can be formed on the surface. As a result, more excellent life characteristics and rate characteristics can be achieved. When in contact with the entire surface of the monoclinic niobium titanium composite oxide particles, the thickness of the first conductive aid is preferably in the range of 0.01 μm to 0.5 μm.

Intensity ratio I _G / I _D as the first conductive additive is in the range of 0.5 to 1.3, for example, carbonizing the carbon source on the surface of the monoclinic niobium titanium composite oxide particles Can be mentioned. As the carbon source, a gas obtained by vaporizing a hydrocarbon gas such as methane, ethane, propane, ethylene or propylene, or a liquid hydrocarbon such as toluene, benzene, xylene or mesitylene can be used. The strength ratio I _G / _ID of the first conductive aid can be controlled, for example, by adjusting the formation conditions.

For example, at least one selected from the group consisting of graphite, carbon nanotubes, and carbon nanofibers is used as the second conductive additive having an intensity ratio I _G / _ID in the range of 1.5 to 10. Can do. In theory, pure graphite has no Raman activity corresponding to the D band, so the intensity ratio I _G / I _D is infinite. However, in reality, these materials included in the negative electrode material layer have a Raman activity corresponding to the D band because a diamond-like impurity layer and the like are mixed. Therefore, the second conductive additive containing at least one of the above materials can have an intensity ratio I _G / _ID in the range of 1.5-10.

  The negative electrode material layer can further include a binder. The binder can be used as necessary to bind the negative electrode active material particles and the second conductive additive in the negative electrode material layer and the negative electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, and styrene butadiene rubber.

  The negative electrode material layer described above can be formed on both sides or one side of the negative electrode current collector. In addition, the negative electrode current collector can include a non-supported portion of the negative electrode material layer on which no negative electrode material layer is formed. This non-supported portion of the negative electrode material layer can serve as a negative electrode current collecting tab.

  The negative electrode current collector is preferably formed from a material that is electrochemically stable in a potential range where lithium ion insertion and extraction occurs in the negative electrode active material particles. Examples of such materials include copper, nickel, stainless steel, aluminum, and aluminum alloys. The aluminum alloy preferably contains one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si.

  The thickness of the negative electrode current collector is preferably 5 μm or more and 20 μm or less. Thereby, it can reduce in weight, maintaining the intensity | strength of a negative electrode.

  The negative electrode according to the first embodiment can be manufactured, for example, by the following method.

  First, monoclinic niobium titanium composite oxide particles are prepared.

First, an oxide or salt containing Ti and an oxide or salt containing Nb are mixed at a molar ratio so as to form a monoclinic complex oxide represented by the general formula TiNb ₂ O ₇ . The salt is preferably a salt such as carbonate and nitrate that decomposes at a relatively low temperature to produce an oxide. These raw material compounds are pulverized until the average particle size is 5 μm or less, and mixed so as to be as uniform as possible.

  Next, the obtained mixture is calcined at 800 to 1200 ° C. to obtain a calcined product, and then calcined. Firing is performed in a temperature range of 1100 to 1500 ° C. over a total time of 5 to 30 hours. After firing, monoclinic niobium titanium composite oxide particles are obtained.

  Lithium ions are inserted into the monoclinic niobium titanium composite oxide synthesized as described above by charging. Alternatively, a monoclinic complex oxide containing lithium can be obtained in advance by using a compound containing lithium such as lithium carbonate as a synthetic raw material.

  Next, the first conductive additive is disposed so as to contact the surface of the monoclinic niobium titanium composite oxide particles. For example, the first conductive auxiliary agent can be disposed by heating monoclinic niobium titanium composite oxide particles in a gas phase together with a hydrocarbon-based gas as a carbon source. As the carbon source, a gas obtained by vaporizing a hydrocarbon gas such as methane, ethane, propane, ethylene or propylene, or a liquid hydrocarbon such as toluene, benzene, xylene or mesitylene can be used.

Specifically, the first conductive auxiliary agent can be formed as follows, for example. First, monoclinic niobium titanium composite oxide particles are heated. Next, the above carbon source is introduced into the heated composite oxide particles and further heated in a reducing atmosphere. Thereby, the carbon source is carbonized on the surface of the composite oxide particle, and the first conductive additive is generated. According to this method, it is possible to form the first conductive additive in contact with the entire surface of the monoclinic niobium titanium composite oxide particles. The intensity ratio I _G / _ID and the thickness in the Raman spectrum of the first conductive additive can be controlled by, for example, the treatment time, the amount introduced, the thermal decomposition temperature and the heating temperature of the hydrocarbon serving as the carbon source. . Although the treatment time varies depending on the surface area of the monoclinic niobium titanium composite oxide particles, it is usually preferably about 10 minutes to 5 hours.

  After forming the first conductive auxiliary agent, the monoclinic niobium titanium composite oxide particles can be subjected to further pulverization treatment so as to have an arbitrary particle form.

  Next, the monoclinic niobium titanium composite oxide particles having the first conductive auxiliary agent disposed on the surface can be aggregated into secondary particles. Thus, negative active material particles are obtained which are primary particles of monoclinic niobium titanium composite oxide particles having the first conductive aid arranged on the surface or secondary particles formed by agglomerating the primary particles.

  Next, the second conductive assistant is arranged between the negative electrode active material particles thus obtained by the following procedure.

  First, the second conductive additive and the binder are mixed and dispersed in an appropriate solvent. As the second conductive auxiliary agent and binder, those described above can be used. For example, NMP can be used as the solvent. At this time, it is desirable to uniformly and finely disperse the conductive assistant in the solvent. As a dispersion method, a ball mill, a bead mill, a jet mill, an SC mill, an attritor, and other known methods can be used. The dispersion state can be controlled by, for example, the second conductive auxiliary agent amount, the binder agent amount, the solvent amount, and the dispersion strength. A part of the binder can be dispersed first, and the rest can be mixed after the negative electrode active material particles are added.

  Subsequently, the previously obtained negative electrode active material particles are put into a solvent in which the second conductive auxiliary agent and the binder are dispersed and dispersed therein. When mixing the negative electrode active material particles with the second conductive additive and the binder, it is desirable to disperse the negative electrode active material particles without destroying the form of the negative electrode active material particles. As such a dispersion method, feather stirring, a rotation / revolution mixer, a planetary mixer, and other known methods are used. By the above method, a slurry for preparing a negative electrode can be produced.

  When preparing the slurry for preparing the negative electrode, the negative electrode active material, the conductive auxiliary (total of the first conductive auxiliary and the second conductive auxiliary) and the binder are 70% by weight or more and 96% by weight or less, It is preferable to blend at a ratio of 2% to 28% by weight and 2% to 28% by weight. When the content of the conductive auxiliary is 2% by weight or more, the current collecting performance of the negative electrode material layer can be improved. Further, when the content of the binder is 2% by weight or more, the binding property between the negative electrode material layer and the current collector can be sufficiently obtained. Therefore, according to the above formulation, cycle characteristics can be further improved. On the other hand, from the viewpoint of increasing the capacity, it is preferable that the conductive aid and the binder are each 28% by weight or less.

  Next, the negative electrode preparation slurry thus prepared is applied to the surface of the negative electrode current collector. Under the present circumstances, the negative electrode material layer unsupported part demonstrated previously can be made by making the part which does not apply | coat the slurry for negative electrode preparation to a negative electrode collector.

  Next, the coated film is dried to obtain a negative electrode material layer. By pressing this negative electrode material layer, the negative electrode according to the first embodiment can be obtained. Next, a method for confirming the positional relationship among the monoclinic niobium titanium composite oxide particles, the first conductive auxiliary agent, and the second conductive auxiliary agent, and the first conductive auxiliary agent and the second conductive auxiliary agent. A method for confirming the crystallinity of the agent will be described.

  The positional relationship between the monoclinic niobium titanium composite oxide particles, the first conductive aid, and the second conductive aid, and the crystallinity of the first conductive aid and the second conductive aid are: For example, it can be confirmed by micro Raman spectroscopy.

  In the microscopic Raman spectroscopic measurement, the spectrum can be acquired by dividing the target visual field. Therefore, in the micro Raman spectroscopy measurement, the Raman spectrum of the target measurement location can be determined.

  Further, in micro Raman spectroscopy, surface composition fluctuations can be measured in the depth direction while adjusting the laser intensity. For example, if the surface of the negative electrode active material particles is carbon coated, increasing the laser intensity will cause the spectrum of the active material under the coat to appear and visually check the state of the coat. Can do.

  Furthermore, a Raman spectrum can be acquired by selecting an arbitrary range from the electrode surface image with a microscope. As a result, spectral information by location such as between primary particles of monoclinic niobium titanium composite oxide particles in the negative electrode and between the negative electrode active material particles can be obtained, and the relationship between carbon crystallinity and arrangement can be confirmed. it can.

  The first conductive agent in contact with the surface of the monoclinic niobium titanium composite oxide particles in the negative electrode provided in the nonaqueous electrolyte battery and the second conductive agent disposed between the negative electrode active material particles are, for example, It can be measured by the method.

  First, a non-aqueous electrolyte battery to be inspected is prepared. The state of charge of the target nonaqueous electrolyte battery may be any state.

  Next, the battery is disassembled in an inert gas atmosphere, and a part of the negative electrode is collected. For example, in a glove box in an argon gas atmosphere, the battery is disassembled, the electrolytic solution is extracted, and the negative electrode in the electrode group is cut out.

  Next, the cut negative electrode is washed with a solvent. As the solvent, chain carbonate (dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc.) or acetonitrile can be used. After cleaning, a vacuum state is maintained while maintaining an inert gas atmosphere, and the negative electrode is dried. The negative electrode can be dried, for example, under a vacuum of 50 ° C. for 10 hours.

  Next, the dried negative electrode is set in a microscopic Raman spectroscopic measurement device (for example, inVia Raman microscope manufactured by Renishaw), and a Raman spectrum is measured. Specifically, the surface image is obtained by operating the microscope and performing the measurement within the observation range, for example, within a 50 μm square field of view. From the surface image thus obtained, the presence of the negative electrode active material particles can be visually confirmed.

  Next, the observation range is divided by arbitrary steps to generate segments, and a Raman spectrum is collected for each segment. The Raman spectrum can be acquired by irradiating a YAG laser having a wavelength of 532 nm, for example. The laser intensity is preferably in the range of 0.1% to 20% of the irradiation intensity. It is preferable to irradiate the measurement field with a laser and measure the Raman spectrum for about 1 to 30 seconds.

  When microscopic Raman spectroscopy is performed on the negative electrode material layer of the negative electrode according to the first embodiment, the following results are obtained.

  First, the attribution of each peak that can appear on the Raman spectrum obtained by performing microscopic Raman spectroscopic measurement on the negative electrode material layer of the negative electrode according to the first embodiment will be described.

The resulting peaks appearing in the frequency domain (G band) of 1550 cm ^-1 1650 cm ^-1 on the Raman spectra, as described above, the graphite (to be exact hexagonal lattice in the vibration of carbon atoms) due to the It is a peak. Further, the peak appearing in the frequency region (D band) of 1300 cm ^{−1 to} 1400 cm ⁻¹ is a peak due to amorphous carbon or graphite defects as described above. Here, the peak intensity of the peak of G-band and I _G, the peak intensity of the peak of the D band and I _D. The intensity ratio I _G / _ID is obtained by dividing the intensity I _G by the intensity I _D. When the intensity ratio I _G / _ID is in the range of 0.5 to 1.3, the peak of the D band and the G band is attributed to the peak derived from the first conductive aid. When the intensity ratio I _G / _ID is in the range of 1.5 to 10, the peak of the D band and the G band is attributed to the peak derived from the second conductive additive. When the first conductive assistant and the second conductive assistant coexist at the place where the Raman spectrum was measured, the first coexistence spectrum is analyzed by multivariate analysis based on the spectrum information of each simple substance. It can be separated into a peak derived from the second conductive assistant and a peak derived from the second conductive assistant.

Also, of the Raman spectrum, 100cm ^-1 ~200cm ^-1, attributed the peak derived from TiNb ₂ O ₇ a plurality of peaks appearing in the frequency domain of the 250cm ^-1 ~300cm ^-1 and 600cm ^-1 ~700cm ^-1 .

Now, confirming the presence of the negative electrode active material particles from the surface image obtained by micro-Raman spectroscopy on the negative electrode material layer of the negative electrode according to the first embodiment, and acquiring a Raman spectrum in the vicinity of the negative electrode active material particles, for example, The plurality of peaks attributed to the monoclinic complex oxide represented by the general formula TiNb ₂ O ₇ and the peaks of the G band and the D band attributed to the first conductive additive appear simultaneously. .

Further, by changing the laser intensity, the peak attributed to TiNb ₂ O ₇ and the peak attributed to the first conductive additive change relatively. Examples thereof will be described in detail below.

On the other hand, when the Raman spectrum of the part located between the negative electrode active material particles is acquired, the peak of the G band and the D band attributed to the second conductive additive can be detected. For example, the peak is represented by Nb ₂ TiO ₇ . The peak attributed to the monoclinic complex oxide is not detected. In addition, the 2nd conductive support agent does not need to exist in all between negative electrode active material particles. Therefore, it is necessary to acquire the Raman spectrum of the part located between negative electrode active material particles about several places.

  Thus, by performing microscopic Raman spectroscopic measurement on the negative electrode, it is possible to grasp the positional relationship among the monoclinic complex oxide, the first conductive auxiliary agent, and the second conductive auxiliary agent of the negative electrode.

  Here, an example of a Raman spectrum obtained from the vicinity of the negative electrode active material particles in the negative electrode material layer of the negative electrode of the example according to the first embodiment will be described.

  FIG. 1 shows a Raman spectrum of a part of the negative electrode material layer of the negative electrode of the example according to the first embodiment. The three spectra shown in FIG. 1 are spectra obtained by changing the intensity of the irradiation laser stepwise at the same location divided from the microscopic Raman surface image.

The spectrum (A) shown in the upper part of FIG. 1 is a spectrum obtained by irradiating a low intensity laser. The spectrum (A) has appeared a peak of G-band to the frequency region of 1550 cm ^-1 1650 cm ^-1, which appears a peak of D-band frequency region of 1300cm ^-1 ~1400cm ^-1. In the spectrum (A), the intensity ratio I _G / _ID is 1.2. That is, the peaks of the G band and D band in the spectrum (A) are peaks attributed to the first conductive additive. On the other hand, in the spectrum (A), no peak appears in the low frequency region of 100 to 1000 cm ⁻¹ . That is, the peak derived from TiNb ₂ O ₇ does not appear in spectrum (A).

The spectrum (B) shown in the middle of FIG. 1 is a spectrum obtained by irradiating a medium intensity laser. Also in the spectrum (B), similarly to the spectrum (A), the frequency region of 1550 cm ^-1 1650 cm ^-1 and appear a peak of G-band, D band frequency region of 1300cm ^-1 ~1400cm ^-1 The peak appears. In the spectrum (B), the intensity ratio I _G / _ID is 1.1. That is, the peaks of the G band and D band in the spectrum (B) are peaks attributed to the first conductive additive. However, the G band peak and the D band peak in the spectrum (B) are lower in intensity than those in the spectrum (A). On the other hand, in the spectrum (B), a peak derived from TiNb ₂ O ₇ appears in a low frequency region of 100 to 1000 cm ⁻¹ .

The spectrum (C) shown in the lower part of FIG. 1 is a spectrum obtained by irradiating a high-intensity laser. This spectrum (C) is also frequency region of 1550 cm ^-1 1650 cm ^-1, in the frequency region of 1300cm ^-1 ~1400cm ^-1, the peak does not appear. On the other hand, in the spectrum (C), a peak derived from TiNb ₂ O ₇ appears in the low frequency region of 100 to 1000 cm ⁻¹ , and its intensity is larger than that of the spectrum (B).

From the three Raman spectra (A) to (C) shown in FIG. 1, the first conductive assistant is formed on the surface of the monoclinic niobium titanium composite oxide TiNb ₂ O ₇ particles at the places where these spectra are obtained. It can be seen that the agent is in contact.

  The composition of the monoclinic niobium titanium composite oxide contained in the negative electrode active material particles can be confirmed by the Raman spectroscopy described above. For example, induced emission plasma spectroscopy (ICP) or X-ray diffraction method It can also be confirmed by (XRD).

The specific surface area of the negative electrode active material particles can be measured using, for example, Micromeritex ASPA-2010 manufactured by Shimadzu Corporation and using N ₂ as an adsorbed gas.

  The average particle diameter of the negative electrode active material particles can be measured, for example, by a laser diffraction particle size distribution measurement method. When the negative electrode active material particles are secondary particles composed of primary particles of monoclinic niobium titanium composite oxide, the average particle size of the primary particles is 100 to 1000 by observing a scanning electron microscope (SEM) image. It can be measured by counting the particle diameter of the above primary particles and calculating the average.

  When the first conductive auxiliary agent is in contact with the entire surface of the monoclinic niobium titanium composite oxide particles, the thickness of the first conductive auxiliary agent is determined by, for example, a transmission electron microscope (TEM) image. Can be measured.

  Next, an example of the negative electrode material layer included in the negative electrode according to the first embodiment will be described with reference to the drawings.

  FIG. 2 is a schematic cross-sectional view showing a positional relationship among the niobium titanium composite oxide particles, the first conductive auxiliary agent, and the second conductive auxiliary agent included in the negative electrode material layer of the example according to the first embodiment. is there.

  A negative electrode material layer 5 b, part of which is shown in FIG. 2, includes a plurality of negative electrode active material particles 53. Each negative electrode active material particle 53 is a secondary particle formed by agglomerating primary particles of monoclinic niobium titanium composite oxide particles 50. The first conductive auxiliary agent 51 is in contact with each surface of the monoclinic niobium titanium composite oxide particles 50. Specifically, the first conductive additive 51 is in contact with the entire surface of the monoclinic niobium titanium composite oxide particles 50. That is, the negative electrode active material particles 53 shown in FIG. 2 are secondary particles formed by agglomeration of primary particles of monoclinic niobium titanium composite oxide particles 50 including the first conductive auxiliary agent 51 in contact with the entire surface. In the form of particles.

  As shown in FIG. 2, a second conductive auxiliary agent 52 is disposed between the negative electrode active material particles 53. Further, as shown in FIG. 2, the second conductive auxiliary agent 52 is in contact with the first conductive auxiliary agent 51.

  According to a first embodiment, a negative electrode is provided. In the negative electrode material layer of the negative electrode, the first conductive additive having a low crystallinity is in contact with at least a part of the surface of the monoclinic niobium titanium composite oxide particles. A second conductive additive having a high degree of crystallinity is disposed between the negative electrode active material particles containing monoclinic niobium titanium composite oxide particles. Thanks to this, when used in a nonaqueous electrolyte battery, the negative electrode according to the first embodiment can suppress decomposition of the nonaqueous electrolyte and achieve low resistance. As a result, the negative electrode according to the first embodiment can realize a nonaqueous electrolyte battery having excellent life characteristics and rate characteristics.

(Second Embodiment)
According to the second embodiment, a nonaqueous electrolyte battery is provided. The nonaqueous electrolyte battery includes a negative electrode, a positive electrode, and a nonaqueous electrolyte. The negative electrode is a negative electrode according to the first embodiment.

  Hereinafter, the nonaqueous electrolyte battery according to the second embodiment will be described in detail.

  The nonaqueous electrolyte battery according to the second embodiment includes the negative electrode according to the first embodiment, a positive electrode, and a nonaqueous electrolyte.

  The positive electrode can include a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector. The positive electrode material layer may be formed on both sides of the positive electrode current collector, or may be formed on one side.

  The positive electrode material layer can include a positive electrode active material and optionally a conductive agent and a binder.

  The positive electrode current collector can include a non-supported portion of the positive electrode material layer in which the positive electrode material layer is not formed on the surface. The portion not carrying the positive electrode material layer can serve as a positive electrode current collecting tab.

  The positive electrode and the negative electrode can be arranged such that the positive electrode material layer and the negative electrode material layer face each other to constitute an electrode group. Between the positive electrode material layer and the negative electrode material layer, a member that transmits lithium ions but does not conduct electricity, such as a separator, can be disposed.

  The electrode group can have various structures. The electrode group may have a stacked structure or a wound structure. The stack type structure has, for example, a structure in which a plurality of negative electrodes and a plurality of positive electrodes are stacked with a separator interposed between the negative electrode and the positive electrode. The electrode group having a wound structure may be, for example, a can-type structure in which a negative electrode and a positive electrode are laminated with a separator interposed therebetween, or by pressing the can-type structure. The resulting flat structure may be used.

  The positive electrode current collecting tab can be electrically connected to the positive electrode terminal. Similarly, the negative electrode current collecting tab can be electrically connected to the negative electrode terminal. The positive electrode terminal and the negative electrode terminal can extend from the electrode group.

  The electrode group can be housed in the exterior member. The exterior member may have a structure that allows the positive electrode terminal and the negative electrode terminal to extend outward. Alternatively, the exterior member may include two external terminals, each of which is electrically connected to each of the positive terminal and the negative terminal.

  The nonaqueous electrolyte can be housed in the exterior member and impregnated in the electrode group.

  Hereinafter, the material of each member that can be used in the nonaqueous electrolyte battery according to the second embodiment will be described.

1. As each material of the negative electrode, those described in the description of the first embodiment can be used.

2. Positive electrode As a positive electrode active material, an oxide, sulfide, or a polymer can be used, for example. Examples of oxides and sulfides include manganese dioxide (MnO ₂ ) that occludes lithium, iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (eg, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ). , Lithium nickel composite oxide (for example, Li _x NiO ₂ ), lithium cobalt composite oxide (for example, Li _x CoO ₂ ), lithium nickel cobalt composite oxide (for example, LiNi _1-y Co _y O ₂ ), lithium manganese cobalt composite oxide _{(e.g., Li x Mn y Co 1-} y O 2), lithium manganese nickel complex oxide having a spinel structure _{(e.g., Li x Mn 2-y Ni} y O 4), lithium phosphorus having an olivine structure oxides _{(e.g., Li x FePO 4, Li x} Fe 1-y Mn y PO 4, Li x CoPO 4), iron sulfate _{[Fe 2 (SO 4) 3} ], vanadium Oxides (e.g., V ₂ O _5), and includes a lithium-nickel-cobalt-manganese composite oxide. Here, 0 <x ≦ 1 and 0 <y ≦ 1. As the active material, these compounds may be used alone, or a plurality of compounds may be used in combination.

  Examples of the polymer include conductive polymer materials such as polyaniline and polypyrrole, or disulfide-based polymer materials.

  Also, sulfur (S) or carbon fluoride can be used as the positive electrode active material.

Examples of more preferable positive electrode active materials include lithium manganese composite oxide (Li _x Mn ₂ O ₄ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium cobalt composite oxide (Li _x CoO ₂ ) having a high positive electrode voltage. ), Lithium nickel cobalt composite oxide (LiNi _1-y Co _y O ₂ ), lithium manganese nickel composite oxide having a spinel structure (Li _x Mn _2-y Ni _y O ₄ ), lithium manganese cobalt composite oxide (Li _{x Mn y Co 1-y O} 2), lithium iron phosphate (Li _x FePO _4), and includes a lithium-nickel-cobalt-manganese composite oxide. Here, 0 <x ≦ 1 and 0 <y ≦ 1.

Examples of preferable positive electrode active materials when a room temperature molten salt is used as a nonaqueous electrolyte of a nonaqueous electrolyte battery include lithium iron phosphate, Li _x VPO ₄ F (0 ≦ x ≦ 1), lithium manganese composite oxide, lithium A nickel composite oxide and a lithium nickel cobalt composite oxide are mentioned. Since these compounds have low reactivity with the room temperature molten salt, the cycle characteristics of the nonaqueous electrolyte battery can be improved.

The specific surface area of the positive electrode active material is preferably in the range of 0.1 m ² / g to 10 m ² / g. A positive electrode active material having a specific surface area of 0.1 m ² / g or more can sufficiently ensure the occlusion and release sites of lithium ions. The positive electrode active material having a specific surface area of 10 m ² / g or less is easy to handle in industrial production and can ensure good charge / discharge cycle performance.

  The conductive agent is blended as necessary in order to enhance the current collecting performance and suppress the contact resistance between the positive electrode active material and the positive electrode current collector. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, and graphite.

  The binder has a function of binding the positive electrode active material and the positive electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

  The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

  The thickness of the aluminum foil or aluminum alloy foil is desirably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by weight or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by weight or less.

  For the positive electrode, for example, a positive electrode active material, a binder, and a conductive agent blended as necessary are suspended in an appropriate solvent to prepare a slurry for preparing a positive electrode, and this slurry is applied to a positive electrode current collector and dried. Then, after forming the positive electrode material layer, it is produced by pressing. Moreover, a positive electrode can also be produced by forming an active material, a binder, and a conductive agent blended as necessary into a pellet shape to form a positive electrode material layer, and forming this on a current collector.

  In preparing the positive electrode preparation slurry, the positive electrode active material and the binder are preferably blended in a proportion of 80% by weight to 98% by weight and 2% by weight to 20% by weight, respectively. Sufficient electrode strength can be obtained by setting the binder to an amount of 2% by weight or more. Moreover, the compounding quantity of the insulator of an electrode can be reduced by setting it as 20 weight% or less, and, thereby, the internal resistance of a nonaqueous electrolyte battery can be reduced.

  When a conductive agent is added, the positive electrode active material, the binder, and the conductive agent are in a proportion of 77% to 95% by weight, 2% to 20% by weight, and 3% to 15% by weight, respectively. It is preferable to mix. The conductive agent can exert the above-described effects by setting the amount to 3% by weight or more. Moreover, by setting it as 15 weight% or less, decomposition | disassembly of the nonaqueous electrolyte on the surface of the positive electrode conductive agent under high temperature storage can be reduced.

3. Separator The separator may be formed of, for example, a porous film containing polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. A porous film formed from polyethylene or polypropylene can be melted at a constant temperature to interrupt the current. Therefore, the nonaqueous electrolyte battery using those films can further improve safety.

4). Exterior Member A laminate film container or a metal container can be used as the exterior member. The shape of the exterior member may be a flat type (thin type), a square type, a cylindrical type, a coin type, a button type, a sheet type, or a laminated type. The shape and size of the exterior member can be arbitrarily designed according to the battery size. For example, a small battery exterior member loaded on a portable electronic device or a large battery exterior member loaded on a two-wheel or four-wheel automobile or the like is used.

  The laminate film is a multilayer film composed of a metal layer and a resin layer covering the metal layer. The metal layer is preferably an aluminum foil or an aluminum alloy foil. Thereby, the weight of the battery can be reduced. The resin layer can reinforce the metal layer. The resin layer may be formed of a polymer such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The thickness of the laminate film forming the exterior member is preferably 0.5 mm or less, and more preferably 0.2 mm or less. The laminate film can be formed into a desired shape by heat-sealing.

  The metal container may be formed from aluminum or an aluminum alloy. The aluminum alloy preferably contains an element such as Mg, Zn, or Si. When a transition metal such as Fe, Cu, Ni or Cr is contained in the alloy, the content is preferably 1% by weight or less. Thereby, long-term reliability and heat dissipation in a high temperature environment can be dramatically improved. The thickness of the metal plate forming the metal container is preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

5. Negative electrode terminal The negative electrode terminal can be formed from aluminum or an aluminum alloy containing at least one element selected from Mg, Ti, Zn, Mn, Fe, Cu, or Si. In order to reduce the contact resistance with the negative electrode current collector, the negative electrode terminal is preferably formed from the same material as the negative electrode current collector.

6). Positive electrode terminal The positive electrode terminal is preferably formed of aluminum or an aluminum alloy containing at least one element selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, or Si. In order to reduce the contact resistance with the positive electrode current collector, the positive electrode terminal is preferably formed of the same material as the positive electrode current collector.

7). Nonaqueous electrolyte As the nonaqueous electrolyte, a liquid nonaqueous electrolyte or a gelled nonaqueous electrolyte can be used. The liquid non-aqueous electrolyte is prepared by dissolving the electrolyte in a non-aqueous solvent. The gel-like nonaqueous electrolyte is prepared by combining a liquid electrolyte and a polymer material.

  Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), cyclic carbonate such as vinylene carbonate; chain such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC). Cyclic carbonates; cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). The non-aqueous solvent can contain these organic solvents alone or in combination.

  The concentration of the electrolyte in the liquid non-aqueous electrolyte is preferably 0.5 mol / L or more and 2.5 mol / L or less.

Examples of the electrolyte include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), tri Lithium salts such as lithium fluorometasulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ] and mixtures thereof are included.

  Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

  Next, an example of the nonaqueous electrolyte battery according to the second embodiment will be described in more detail with reference to the drawings.

  FIG. 3 is a cross-sectional view of an example nonaqueous electrolyte battery according to the second embodiment. 4 is an enlarged cross-sectional view of a portion A in FIG.

  As shown in FIG. 3, the battery 1 includes an exterior member 2 and an electrode group 3 accommodated in the exterior member 2. Here, a wound electrode group is used as the electrode group 3. The exterior member 2 has a bag shape. The exterior member 2 further includes a nonaqueous electrolyte (not shown). The nonaqueous electrolyte is impregnated in the electrode group 3.

  As shown in FIG. 4, the electrode group 3 includes a positive electrode 4, a negative electrode 5, and a plurality of separators 6. The electrode group 3 has a configuration in which the laminated body is wound in a spiral shape. This laminate has a configuration in which a separator 6, a positive electrode 4, a separator 6, and a negative electrode 5 are stacked in this order. The flat wound electrode group 3 is produced by winding such a laminated body in a spiral shape so that the negative electrode is located on the outermost periphery, and then pressing it while heating.

  The positive electrode 4 includes a positive electrode current collector 4a and a positive electrode material layer 4b formed on both surfaces of the positive electrode current collector 4a. The positive electrode material layer 4b includes a positive electrode active material, a binder, and a conductive agent.

  The negative electrode 5 includes a negative electrode current collector 5a and a negative electrode material layer 5b formed on both surfaces of the negative electrode current collector 5a. However, in the portion located on the outermost periphery of the electrode group 3, as shown in FIG. 4, the negative electrode material layer 5b is formed only on the inner surface side of the negative electrode current collector 5a.

  As shown in FIG. 3, in the vicinity of the outer peripheral end of the electrode group 3, the positive electrode terminal 7 is connected to the positive electrode current collector 4a. Further, on the outermost periphery of the electrode group 3, the negative electrode terminal 8 is connected to the negative electrode current collector 5a. Each of the positive electrode terminal 7 and the negative electrode terminal 8 extends outward from the opening of the exterior member 2.

  The nonaqueous electrolyte battery according to the second embodiment includes the negative electrode according to the first embodiment. Therefore, the nonaqueous electrolyte battery according to the second embodiment can exhibit excellent life characteristics and rate characteristics.

[Example]
Hereinafter, based on an Example, the said embodiment is described in detail.

Example 1
In Example 1, the nonaqueous electrolyte battery 1 shown in FIGS. 3 and 4 was manufactured as follows.

<Preparation of negative electrode 5>
First, among monoclinic complex oxides represented by the general formula Li _x M1M2 ₂ O _{7 ± δ} (0 ≦ x ≦ 5, 0 ≦ δ ≦ 0.3), x = 0, M1 = Ti, M2 = Nb TiNb ₂ O ₇ was synthesized.

As starting materials, commercially available oxide reagents Nb ₂ O ₅ and TiO ₂ were used. These raw material oxides were weighed to a molar ratio of 1: 1 and mixed in a mortar. Next, it was placed in an electric furnace, calcined at 800 ° C. for 12 hours, and then fired at 1400 ° C. for a total of 20 hours. After firing, product particles 50 were obtained.

The composition of the product particles was analyzed by the ICP method, and it was confirmed that the target monoclinic niobium titanium complex oxide TiNb ₂ O ₇ was obtained.

  It was confirmed by laser diffraction particle size distribution measurement and SEM observation that the obtained monoclinic niobium titanium composite oxide was composed of primary particles having an average particle size of 0.5 μm and secondary particles having an average particle size of 20 μm.

The TiNb ₂ O ₇ secondary particles 50 synthesized above were placed in a rotary kiln furnace capable of controlling the atmosphere, and propane gas was introduced at 100 mL / min while rotating the furnace.

Heating was performed for 2 hours at a baking temperature of 700 ° C. Carbon 51 obtained by carbonizing propane gas by pyrolysis was coated on the surface and inside of the TiNb ₂ O ₇ secondary particles 50. In this way, by pyrolysis gravimetric method to obtain a negative electrode active material particles 53, the content of carbon 51 in the anode active material particles 53, relative to 100 parts by weight of TiNb ₂ O ₇ particles 50, 3.4 parts of It was confirmed that.

  Next, with respect to the weight 100 of the negative electrode active material particles 53, 10% by weight of scaly graphite was weighed as the second conductive additive 52, and 5% by weight of polyvinylidene fluoride (PVdF) was weighed as the binder.

  Weighed graphite and PVdF were added to N-methylpyrrolidone (NMP) and dispersed using a bead mill. The rotation was performed at 2000 rpm, and dispersion was performed at a flow rate of 50 mL / min so that the residence time was 5 minutes.

  Negative electrode active material particles 53 were put into a dispersion of graphite and PVdF obtained by the above dispersion and dispersed by feather diffusion to prepare a slurry for preparing a negative electrode.

  This negative electrode preparation slurry was applied to an aluminum foil (negative electrode current collector 5a) having a thickness of 15 μm. At this time, a portion of the negative electrode current collector 5a where the negative electrode preparation slurry was not applied was left on the surface. Next, the negative electrode current collector 5a coated with the negative electrode preparation slurry was dried, and then subjected to press treatment. Thus, the negative electrode 5 including the negative electrode current collector 5a and the negative electrode material layer 5b formed on the negative electrode current collector 5a was obtained.

  Next, the negative electrode terminal 8 was connected to the portion of the negative electrode 5 obtained in this way where the negative electrode material layer 5b was not formed on the surface.

<Preparation of positive electrode 4>
Lithium nickel cobalt oxide (LiNi _0.8 Co _0.2 O ₂ ) powder was used as the positive electrode active material. A positive electrode composite containing 91% by weight of this positive electrode active material, 2.5% by weight of acetylene black and 3% by weight of graphite and 3.5% by weight of polyvinylidene fluoride (PVdF). An agent was prepared. This positive electrode mixture was added to NMP to prepare a slurry for preparing a positive electrode.

  This positive electrode preparation slurry was applied to an aluminum foil (positive electrode current collector 4a) having a thickness of 15 μm. At this time, a portion of the positive electrode current collector 4a where the positive electrode preparation slurry was not applied was left on the surface. Next, the positive electrode current collector 4a coated with the positive electrode preparation slurry was dried, and then subjected to press treatment. Thus, the positive electrode 4 including the positive electrode current collector 4a and the positive electrode material layer 4b formed on the positive electrode current collector 4a was obtained.

  Next, the positive electrode terminal 7 was connected to the portion of the positive electrode 4 obtained in this manner where the positive electrode material layer 4b was not formed on the surface.

<Preparation of electrode group 3>
The positive electrode 4 produced as described above, a separator 6 made of a polyethylene porous film having a thickness of 20 μm, the negative electrode 5 produced as described above, and another separator 6 were laminated in this order, A laminate was obtained. At this time, as shown in FIG. 2, the positive electrode material layer 4 a of the positive electrode 4 and the negative electrode material layer 5 a of the negative electrode 5 were laminated so as to face each other with the separator 6 interposed therebetween. This laminated body was wound in a spiral shape so that the negative electrode 5 was located on the outermost periphery, thereby preparing an electrode assembly. The flat electrode group 3 having a width of 38 mm, a height of 78 mm, and a thickness of 2.0 mm as shown in FIG.

<Accommodation in exterior member 2>
Next, an exterior member 2 made of a laminate film was prepared. The laminate film was composed of an aluminum foil having a thickness of 40 μm and a polypropylene layer formed on both sides thereof, and the thickness was 0.1 mm.

  The electrode group 3 obtained as described above was accommodated in the exterior member 2. At this time, the positive electrode terminal 7 and the negative electrode terminal 8 were extended to the outside from the opening of the exterior member 2. After housing, the inside of the exterior member 2 was vacuum dried at 80 ° C. for 24 hours.

<Preparation of non-aqueous electrolyte>
Ethylene carbonate (EC) and methyl ethyl carbonate solvent (EMC) were mixed at a volume ratio of 1: 2 to prepare a mixed solvent.

Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the non-aqueous solvent thus prepared at a concentration of 1.0 mol / L to obtain a non-aqueous electrolyte.

<Injection of non-aqueous electrolyte>
The non-aqueous electrolyte prepared as described above was injected and sealed in the exterior member 2 that accommodated the electrode group 3. Thus, the battery unit 1 was produced.

<Measurement of initial charge / discharge capacity and charge / discharge efficiency>
The battery unit 1 was charged at a 0.2 C rate until the battery voltage became 3.2 V, and left as it was at 3.2 V for 3 hours. The charging rate of the battery unit 1 in this state is 100%, that is, full charge. The charging capacity at that time was defined as the initial charging capacity. Thereafter, the nonaqueous electrolyte battery 1 was discharged at a 0.2 C rate until the battery voltage became 1.2V. The discharge capacity at this time was defined as the initial discharge capacity. Further, the initial charge capacity divided by the initial charge capacity was defined as the initial charge / discharge efficiency. Then, it charged again and the charge rate was adjusted to 50%, and the nonaqueous electrolyte battery 1 was completed.

<Rate characteristics evaluation>
After measuring the initial discharge capacity, the nonaqueous electrolyte battery 1 was charged in a 30 ° C. environment until it was fully charged. The battery was left for 30 minutes and discharged to 1.2V at a 5C rate. The rate characteristic was obtained by dividing the discharge capacity at this time by the initial discharge capacity.

<Life test>
After evaluating the rate characteristics, the nonaqueous electrolyte battery 1 was repeatedly charged and discharged in a 30 ° C. environment to measure cycle characteristics. The battery was charged at a 1C rate until it reached 3.2 V, and was left as it was at 3.2 V for 1 hour. Thereafter, the battery was left for 30 minutes, and discharged at a 1C rate until the battery voltage became 1.2V. The battery was left for 30 minutes and charged again. After repeating the above charging and discharging 50 times, the battery was charged again at a rate of 0.2 C until the battery voltage became 3.2 V, and left as it was at 3.2 V for 3 hours. Thereafter, the nonaqueous electrolyte battery 1 was discharged at a 0.2 C rate until the battery voltage became 1.2V. The capacity retention rate after the cycle was obtained by dividing the discharge capacity at this time by the initial discharge capacity.

<Measurement of Raman spectrum>
As described above, the negative electrode 5 was taken out from the nonaqueous electrolyte battery 1 of Example 1.

  Raman spectrum measurement was performed on the extracted negative electrode 5 by the following procedure.

  First, the taken-out negative electrode 5 was cut out to 5 cm square, and it was set as the sample, and this sample was set in the apparatus. From the image observed by magnifying the sample 100 times with a CCD camera, a portion where the negative electrode active material particles 53 can be visually recognized was determined as a measurement visual field. The image determined as the measurement field is shown in FIG.

  Next, the measurement visual field was set to be divided into 40 parts in the vertical and horizontal directions, and the Raman spectrum measured using a YAG laser with a wavelength of 532 nm was measured for each segment. Peak assignment was performed as previously described.

  In the segment indicated by B in FIG. 5, the presence of the negative electrode active material particles 53 can be visually recognized. FIG. 6 shows the Raman spectrum for this segment indicated by B in FIG.

As is clear from FIG. 6, in the Raman spectrum obtained from the segment B in FIG. 5, the peak in the frequency region attributed to TiNb ₂ O ₇ and the G and D band peaks attributed to carbon. And appear. The intensity ratio I _G / _ID calculated in the spectrum shown in FIG. 6 was 1.2.

  In the segment indicated by C in FIG. 5, the presence of the negative electrode active material particles 53 could not be visually recognized. FIG. 7 shows the Raman spectrum for this segment indicated by C in FIG.

As is clear from FIG. 7, in the Raman spectrum obtained from the segment C in FIG. 5, the peaks of the G band and D band attributed to carbon appear, but the vibrations attributed to TiNb ₂ O _7. There are no peaks in several regions. The intensity ratio I _G / _ID calculated in the spectrum shown in FIG. 7 was 1.8.

(Example 2)
In Example 2, a nonaqueous electrolyte battery 1 was produced in the same manner as in Example 1 except that carbon nanotubes were used as the second conductive auxiliary agent 52.

(Example 3)
In Example 3, a nonaqueous electrolyte battery 1 was produced in the same manner as in Example 1 except that the firing temperature was changed to 850 ° C. when performing carbon coating on TiNb ₂ O ₇ particles.

(Comparative Example 1)
In Comparative Example 1, a nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that carbon black was used as the second conductive additive.

(Comparative Example 2)
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that the carbon coating was not performed on the TiNb ₂ O ₇ particles.

(Comparative Example 3)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that lithium titanate Li ₄ Ti ₅ O ₁₂ was used as the negative electrode active material particles. In Comparative Example 3, the size of the flat electrode group 3 was adjusted to be the same as that in Example 1.

(Comparative Example 4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Comparative Example 3 except that carbon coating was not performed on the lithium titanate particles.

<Evaluation>
For the nonaqueous electrolyte batteries of Examples 2 and 3 and Comparative Examples 1 to 3, in the same manner as the nonaqueous electrolyte battery of Example 1, measurement of initial discharge capacity, initial charge / discharge efficiency measurement, life test, rate characteristics Evaluation and measurement of Raman spectra were performed. The results are shown in Table 1 below together with the results of Example 1.

In Table 1, 1.6 is written in the strength ratio I _G / _ID of the first conductive aid of Comparative Example 2, but this is not the strength ratio of the first conductive aid but TiNb. The strength ratio I _G / _ID of the second conductive additive in contact with the ₂ O ₇ particles.

  As is clear from the results shown in Table 1, the nonaqueous electrolyte batteries 1 of Examples 1 to 3 were compared with the nonaqueous electrolytes of Comparative Examples 1 and 2 in the initial discharge capacity, initial charge / discharge efficiency, and after 50 cycles. It can be seen that the capacity retention rate and the rate characteristics are excellent.

From the results of Examples 1 and 2, the intensity ratio I _G / _{ID of the} D band and G band attributed to the second conductive auxiliary agent 52 is 1 even though the type of the second conductive auxiliary agent 52 is different. If it exists in the range of 5-10, it turns out that the nonaqueous electrolyte battery which shows the outstanding characteristic is realizable.

Further, from the results of Examples 1 and 3, the intensity ratio I _G / I _D of D band and G band attributed to a first conductive additive 51 if in the range of 0.5 to 1.3, It turns out that the nonaqueous electrolyte battery which shows the outstanding characteristic is realizable.

On the other hand, in the nonaqueous electrolyte battery of Comparative Example 1, as shown in Table 1, the capacity retention rate after 50 cycles was reduced, and expansion of the cell volume due to gas generation was confirmed. This is because the electrolytic solution was decomposed in the vicinity of carbon black having a small strength ratio I _G / _ID mixed as the second conductive additive, that is, low crystallinity, resulting in gas generation, resulting in a deterioration in capacity. it is conceivable that.

  In the nonaqueous electrolyte battery of Comparative Example 2, since the first conductive aid was not in contact with the vicinity of the active material, it was considered that the conductivity required for charging / discharging could not be ensured and the rate characteristics were deteriorated. . On the other hand, in the nonaqueous electrolyte battery of Comparative Example 2, gas generation could be suppressed by using carbon having a high degree of crystallinity as the second conductive additive. However, in the nonaqueous electrolyte battery of Comparative Example 2, since the first conductive auxiliary agent in contact with the surface of the negative electrode active material particles did not exist, side reactions were suppressed at the interface between the negative electrode active material particles and the nonaqueous electrolyte. It is considered that the capacity deterioration was increased because the coating film to be formed could not be formed and the decomposition reaction of the nonaqueous electrolyte had progressed.

  The nonaqueous electrolyte battery of Comparative Example 3 was significantly inferior in initial discharge capacity as compared with the nonaqueous electrolyte batteries of Examples 1 to 3 and Comparative Examples 1 and 2. This is because the energy density of the negative electrode active material itself is small, and the capacity of the nonaqueous electrolyte battery per volume is reduced.

  Moreover, when the results of Comparative Example 3 and Comparative Example 4 were compared, there was no significant change in the capacity retention rate after 50 cycles. From this result, it can be seen that the life characteristics of the nonaqueous electrolyte battery using lithium titanate particles as the negative electrode active material do not depend much on the crystallinity of the conductive additive in contact with the surface of the lithium titanate particles.

  According to at least one embodiment and example described above, a negative electrode is provided. In the negative electrode material layer of the negative electrode, the first conductive additive having a low crystallinity is in contact with at least a part of the surface of the monoclinic niobium titanium composite oxide particles. A second conductive additive having a high degree of crystallinity is disposed between the negative electrode active material particles containing monoclinic niobium titanium composite oxide particles. Thanks to this, when this negative electrode is used in a non-aqueous electrolyte battery, it can suppress decomposition of the non-aqueous electrolyte and achieve low resistance. As a result, the negative electrode according to the first embodiment can realize a nonaqueous electrolyte battery having excellent life characteristics and rate characteristics.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.
The invention described in the claims at the beginning of the filing of the present application will be appended.
[1] A plurality of negative electrode active material particles, each of which is monoclinic niobium titanium composite oxide particles and a first conductive material in contact with at least part of the surface of the monoclinic niobium titanium composite oxide particles. A negative electrode material layer comprising negative active material particles containing an auxiliary agent and a second conductive auxiliary agent in contact with the first conductive auxiliary agent and disposed between the negative electrode active material particles; conductive auxiliary agent, the Raman spectrum obtained from the negative electrode material layer by Raman spectroscopy, the D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, the frequency region of 1550 cm ^-1 1650 cm ^-1 And the ratio of the peak intensity of the G band to the peak intensity of the D band is in the range of 0.5 to 1.3, and the second conductive additive is the negative electrode. Raman spectroscopy from material layers In a more resulting Raman spectrum has a D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, and a G band appearing at frequency region of 1550 cm ^-1 1650 cm ^-1, of the G-band A negative electrode having a ratio of peak intensity to peak intensity of the D band in a range of 1.5 to 10.
[2] The negative electrode according to [1], wherein the first conductive additive is in contact with the entire surface of the monoclinic niobium titanium composite oxide particles.
[3] The negative electrode according to [2], wherein the second conductive additive includes at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphite.
[4] Each of the plurality of negative electrode active material particles is a secondary particle obtained by agglomerating the plurality of monoclinic niobium titanium composite oxide particles, and at least a surface of each of the plurality of negative electrode active material particles. [1] The negative electrode according to [1], wherein the first conductive additive is partially present.
[5] A nonaqueous electrolyte battery comprising the negative electrode according to [2], a positive electrode, and a nonaqueous electrolyte.

  DESCRIPTION OF SYMBOLS 1 ... Battery, 2 ... Exterior member, 3 ... Electrode group, 4 ... Positive electrode, 4a ... Positive electrode collector, 4b ... Positive electrode active material containing layer (positive electrode material layer), 5 ... Negative electrode, 5a ... Negative electrode collector, 5b ... negative electrode active material-containing layer (negative electrode material layer), 6 ... separator, 7 ... positive electrode terminal, 8 ... negative electrode terminal, 50 ... monoclinic niobium titanium complex oxide particles, 51 ... first conductive additive, 52 ... first 2 conductive auxiliary agent, 53 ... negative electrode active material particle.

Claims (5)

A plurality of negative electrode active material particles, each of which is a secondary particle formed by agglomerating a plurality of primary particles of monoclinic niobium titanium composite oxide, and a second particle in contact with at least a part of the surface of the secondary particle. Negative electrode active material particles comprising one conductive additive;
A negative electrode material layer comprising a second conductive auxiliary agent in contact with the first conductive auxiliary agent and disposed between the negative electrode active material particles;
Said first conductive additive, wherein in the Raman spectrum obtained from the negative electrode material layer by Raman spectroscopy, the D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, of 1550 cm ^-1 1650 cm ^-1 A G band appearing in the frequency region, and a ratio of a peak intensity of the G band to a peak intensity of the D band is in a range of 0.5 to 1.3;
Said second conductive additive, wherein in the Raman spectrum obtained from the negative electrode material layer by Raman spectroscopy, the D band appearing in the frequency region of 1300cm ^-1 ~1400cm ^-1, of 1550 cm ^-1 1650 cm ^-1 A negative electrode having a G band appearing in a frequency region and a ratio of a peak intensity of the G band to a peak intensity of the D band being in a range of 1.5 to 10.   The negative electrode according to claim 1, wherein the first conductive additive is in contact with the entire surface of each of the plurality of primary particles.   3. The negative electrode according to claim 1, wherein the second conductive additive contains at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphite. Negative electrode according to any one of claims 1 to 3, the ratio to the peak intensity of the D band peak intensity of the G band of the first conductive additive is in the range of 1.0 to 1.3 . The negative electrode according to any one of claims 1 to 4,
A positive electrode;
A non-aqueous electrolyte battery comprising a non-aqueous electrolyte.