BR102017019288B1 - ELECTRODE, SECONDARY BATTERY, BATTERY PACK AND VEHICLE - Google Patents

Abstract

ACCORDING TO AN EMBODIMENT, AN ELECTRODE INCLUDING PARTICLES OF ACTIVE MATERIAL IS PROVIDED. THE ACTIVE MATERIAL PARTICLES CONTAIN MONOCLINICAL NIOBIO-TITANIUM COMPOSITE OXIDE PARTICLES AND AN AMORPHOUS CARBON BODY. THE AMORPHOUS CARBON BODY COVERS AT LEAST A PART OF THE SURFACES OF THE MONOCLINICAL NIOBIO-TITANIUM COMPOSITE OXIDE PARTICLES. A RATIO OF S2/S1 BETWEEN A CONCENTRATION OF CARBON ATOM S2 AND A CONCENTRATION OF NIOBIUM ATOM S1 ON AN ELECTRODE SURFACE, ACCORDING TO X-RAY PHOTOELECTRON SPECTROSCOPY, IS 5 TO 100.

Description

FIELD

[001] The embodiments described in this document generally refer to an electrode, a secondary battery, a battery pack and a vehicle.

BACKGROUND

[002] In recent years, a secondary battery such as a lithium-ion secondary battery or a non-aqueous electrolyte secondary battery has been developed as a battery that has a high energy density. The battery is expected to be used as a power supply for vehicles such as a hybrid automobile and an electric automobile, or as a large-sized power supply for power storage. When the secondary battery is used as the power source for vehicles, it is required that the secondary battery achieves fast charge and discharge performance and long-term reliability or the like in addition to high energy density.

[003] Lithium ions and electrons move quickly through an electrolyte and an external circuit respectively between a positive electrode and a negative electrode that can insert and extract lithium ions and electrons, to allow charging and fast downloads. A battery capable of rapid charging and discharging has the advantage that charging time is considerably short. When the battery capable of rapid charging and discharging is used as the power source for vehicles, the motor performances of the automobile can be improved and the regenerative power energy can be recovered efficiently.

[004] A carbon-based negative electrode that uses a carbonaceous material such as graphite as a negative electrode active material is used as a negative electrode with the ability to insert and extract lithium ions and electrons. However, when rapid charging and discharging is repeated in a battery that includes the carbon-based negative electrode, lithium metal dendrites may precipitate on the negative electrode. Lithium metal dendrites can cause an internal short circuit. Therefore, when rapid charging and discharging is repeated on the battery that includes the carbon-based negative electrode, a concern is raised that heat generation and ignition may occur.

[005] Therefore, a battery that includes a negative electrode that uses a metallic composite oxide as the negative electrode active material in place of the carbonaceous material has been developed. In particular, in a battery that uses a composite metal oxide titanium oxide as the negative electrode active material, the lithium metal dendrites are less likely to precipitate even when rapid charge and discharge are repeated compared to those in the battery. which includes the carbon-based negative electrode. A battery that uses titanium oxide has a more stable rapid charge and discharge and a longer life than that of a battery that includes a carbon-based negative electrode.

[006] However, titanium oxide has a higher (more noble) potential compared to lithium metal compared to carbonaceous material. In addition, titanium oxide has a lower theoretical capacity per unit mass compared to carbonaceous material. For this, there is a problem that the battery that includes a negative electrode that uses titanium oxide as the negative electrode active material has a lower energy density compared to the battery that includes the carbon-based negative electrode.

[007] For example, the potential relative to lithium metal of a lithium-titanium oxide composite such as Li4Ti5O12 is about 1.5 V (versus Li+/Li) or more. On the other hand, the potential with respect to graphite lithium metal is about 0.1 V (versus Li+/Li) or more. In the present context, the lithium metal potential of titanium oxide is caused by an oxidation-reduction reaction that occurs between trivalent titanium ions and tetravalent titanium ions when lithium ions are electrochemically inserted and extracted. That is, the potential in relation to the lithium metal of titanium oxide is inherent to titanium oxide and the reduction in potential is limited electrochemically. Therefore, it is substantially difficult to reduce the potential relative to lithium metal of titanium oxide to improve energy density. Since the potential of titanium oxide relative to lithium metal is high, a battery that includes a negative electrode containing titanium oxide secondaryly allows stable rapid charging and discharging.

[008] The theoretical capacity per unit mass of lithium-titanium oxide composite such as Li4Ti5O12 is 175 mAh/g. On the other hand, the theoretical capacity per unit mass of graphite is 372 mAh/g. Furthermore, titanium oxide has fewer sites capable of inserting lithium ions into its crystal structure compared to carbonaceous material, and lithium ions are likely to stabilize in its crystal structure. Therefore, the ratio between the actual capacity of titanium oxide and its theoretical capacity is lower than the ratio of the actual capacity of the carbonaceous material to its theoretical capacity.

[009] From the above, the energy density of the battery that includes the negative electrode containing titanium oxide is markedly lower compared to the battery that has the carbon-based negative electrode.

[010] In view of the above, a new electrode material containing titanium and niobium was studied. In particular, in a monocyclic niobium-titanium composite oxide represented by TiNb2O7, tetravalent titanium ions are reduced to trivalent titanium ions and pentavalent niobium ions are reduced to trivalent niobium ions when lithium ions were inserted. Therefore, this monocyclic niobium-titanium composite oxide can maintain the electrical neutrality of a crystal structure even when many lithium ions are inserted, compared with titanium oxide. As a result, the monocyclic Nb-Ti composite oxide represented by TiNb2O7 has a high theoretical capacity of 387 mAh/g.

BRIEF DESCRIPTION OF THE DRAWINGS

[011] Figure 1 is a cross-sectional view that schematically shows an example of a layer containing negative electrode active material of a secondary battery according to a first embodiment;

[012] Figure 2 is a schematic view showing an example of the crystal structure of a monocyclic niobium-titanium composite oxide;

[013] Figure 3 is a schematic view of the crystal structure shown in Figure 2 as seen from the other direction;

[014] Figure 4 is a cross-sectional view that schematically shows an example of the secondary battery according to the first embodiment;

[015] Figure 5 is an enlarged cross-sectional view of a portion A of the secondary battery shown in Figure 4;

[016] Figure 6 is a partially cropped perspective view that schematically shows another example of the secondary battery according to the first embodiment;

[017] Figure 7 is an enlarged cross-sectional view of a portion B of the secondary battery shown in Figure 6;

[018] Figure 8 is a perspective view that schematically shows an example of a battery module according to a second embodiment;

[019] Figure 9 shows an exploded perspective view showing an example of a battery pack according to a third embodiment;

[020] Figure 10 is a block diagram showing an example of an electrical circuit of the battery pack shown in Figure 9;

[021] Figure 11 is a cross-sectional view that schematically shows an example of a vehicle according to a fourth embodiment;

[022] Figure 12 schematically shows another example of the vehicle according to the fourth embodiment;

[023] Figure 13 is a graph showing a Raman spectrum according to Example 1;

[024] Figure 14 is a graph showing a Raman spectrum according to Comparative Example 6;

[025] Figure 15 is a graph showing a narrow scan spectrum of Nb3d according to Example 1;

[026] Figure 16 is a graph showing a narrow scan spectrum of C1s according to Example 1;

[027] Figure 17 is a graph showing a narrow scan spectrum of P2p according to Example 1;

[028] Figure 18 is a graph showing a narrow scan spectrum of C1s shown in Figure 16 after peak separation;

[029] Figure 19 is a graph showing a narrow scan spectrum of P2p shown in Figure 17 after peak separation;

[030] Figure 20 is a graph showing a narrow scan spectrum of Nb3d according to Example 3;

[031] Figure 21 is a graph showing a narrow scan spectrum of C1s according to Example 3;

[032] Figure 22 is a graph showing a narrow scan spectrum of P2p according to Example 3;

[033] Figure 23 is a graph showing a narrow scan spectrum of C1s shown in Figure 21 after peak separation;

[034] Figure 24 is a graph showing a narrow scan spectrum of P2p shown in Figure 22 after peak separation;

[035] Figure 25 is a graph showing a narrow scan spectrum of Nb3d according to Example 23;

[036] Figure 26 is a graph showing a narrow scan spectrum of C1s according to Example 23;

[037] Figure 27 is a graph showing a narrow scan spectrum of P2p according to Example 23;

[038] Figure 28 is a graph showing a narrow scan spectrum of C1s shown in Figure 26 after peak separation;

[039] Figure 29 is a graph showing a narrow scan spectrum of P2p shown in Figure 27 after peak separation;

[040] Figure 30 is a graph showing a narrow scan spectrum of Nb3d according to Comparative Example 1;

[041] Figure 31 is a graph showing a narrow scan spectrum of C1s according to Comparative Example 1;

[042] Figure 32 is a graph showing a narrow-scan spectrum of P2p according to Comparative Example 1;

[043] Figure 33 is a graph showing a narrow scan spectrum of C1s shown in Figure 31 after peak separation; It is

[044] Figure 34 is a graph showing a narrow-scan spectrum of P2p shown in Figure 32 after peak separation.

DETAILED DESCRIPTION

[045] According to one embodiment, an electrode that includes particles of active material is provided. The active material particles contain monoclinic niobium-titanium composite oxide particles and an amorphous carbon body. The amorphous carbon body covers at least a portion of the surfaces of the monoclinic niobium-titanium composite oxide particles. A ratio of S2/S1 between a carbon atom concentration S2 and a niobium atom concentration S1 on an electrode surface, according to X-ray photoelectron spectroscopy, is 5 to 100. The S2/S1 atom concentration niobium S1 is an area intensity for an Nb3s-related peak. The S2 carbon atom concentration is a total of area intensities for C1s-related peaks. The peaks related to C1s are within a range of 286 eV to 294 eV. Peaks related to C1s include a peak assigned to a C-O bond, a peak assigned to a C=O bond, a peak assigned to a C(=O)-O bond, and a peak assigned to a CO32- bond.

[046] According to another embodiment, a second battery is provided. The second battery includes a negative electrode, a positive electrode and an electrolyte. The negative electrode is the electrode according to the modality.

[047] According to yet another embodiment, a battery pack is provided. The battery pack includes a secondary battery depending on the embodiment.

[048] According to another embodiment, a vehicle is provided. The vehicle includes a battery pack depending on the embodiment.

[049] During the initial charge of a secondary battery such as a lithium-ion secondary battery or a non-aqueous electrolyte secondary battery, lithium ions are inserted between layers of a negative electrode active material on a negative electrode. At the same time, electrons move to the negative electrode through an external circuit. As a result, the negative electrode active material is reduced and a negative electrode potential with respect to the negative electrode lithium metal (from this point on herein referred to simply as a potential) is reduced. In contrast, lithium ions and electrons are emitted from a positive electrode. As a result, a positive electrode active material is oxidized and a positive electrode potential is increased.

[050] The difference between the negative electrode potential and the positive electrode potential in the fully charged state is the voltage of the secondary battery. One of the methods of increasing voltage is a method of reducing the negative electrode potential in the state of full charge.

[051] In a negative electrode using a carbonaceous material such as graphite, the lowest limiting value of a negative electrode potential during charging is about 0 V (versus Li+/Li) and is very low. A coating film referred to as a solid electrolyte interface (SEI) is considered to be formed on at least a portion of the main surface of such a negative electrode. This SEI is generated on the surface of the negative electrode during the initial charge of the battery. Specifically, when the negative electrode potential drops to about 1.0 V (versus Li+/Li) by charging, at least one of a salt of electrolyte and non-aqueous solvent contained in a non-aqueous electrolyte is decomposed by reduction at the negative electrode . A decomposition product generated by decomposition is deposited on the surface of the negative electrode. By stacking the deposit, the SEI is formed.

[052] Graphite has a structure in which a plurality of graphene sheets are stacked. This graphene sheet is composed of carbon atoms covalently bonded by an sp2 hybridized orbital. The plurality of graphene sheets are held together by the van der Waals force. The bond provided by the van der Waals force is weaker than the covalent bond. Therefore, when graphite is used as the negative electrode active material, solvated lithium ions are inserted between the graphene sheets during initial charging. That is, the non-aqueous solvent of the non-aqueous electrolyte is co-inserted together with lithium ions between the graphene sheets. The solvent inserted between the graphene sheets is decomposed by reduction between the graphene sheets. This decomposition product contributes to the formation of SEI between the graphene sheets.

[053] From the above, in the negative electrode containing the graphite, the SEI is considered to be generated on the surface of the negative electrode and generated between the graphene sheets in the graphite structure. SEI plays a passive role and further suppresses the decomposition of the non-aqueous electrolyte at the negative electrode. SEI has lithium-ion conductivity but no electron conductivity. Therefore, the negative electrode on which the SEI is formed can stably insert lithium ions.

[054] However, lithium ions are used together with the non-aqueous electrolyte in order to generate the SEI. When lithium ions permeate the SEI during charging and discharging, resistance occurs. Therefore, when the SEI film thickness is increased, lithium ions are reduced and the internal resistance is increased, which tends to reduce the capacity of the negative electrode.

[055] In the negative electrode using monocyclic niobium-titanium composite oxide, the lowest limiting value of the negative electrode potential during charging is about 1.4 V (versus Li+/Li), which is relatively high. Since the negative electrode potential is not reduced to about 1.0 V (versus Li+/Li) in the fully charged state at such a negative electrode, reductive decomposition of the non-aqueous electrolyte is less likely to occur and is also less likely to occur. for the SEI to be generated. Therefore, since the reduction of lithium ions and the increase in internal resistance are less likely to occur in the case of using such a negative electrode, charging and discharging can be carried out stably.

[056] For example, by overcharging, the lower threshold value of the negative electrode potential of about 1.4 V (versus Li+/Li) can be reduced to, for example, the range of about 1.0 V ( against Li+/Li) up to 1.2 V (against Li+/Li) on the negative electrode using monocyclic niobium-titanium composite oxide. And then the battery voltage is increased, which can increase the charging and discharging capacity of the battery. However, when the lower threshold value of the negative electrode potential during charging is set within this range, reductive decomposition of the non-aqueous electrolyte is likely to occur. Furthermore, when the lower threshold value of the negative electrode potential during charging is within this range, the coating film such as the SEI described above is less likely to be generated, which makes it difficult to further suppress the reductive decomposition of the non-aqueous electrolyte. . Therefore, the battery in which the lower threshold value of the negative electrode potential during charging is within a range of 1.0 V (versus Li+/Li) to 1.2 V (versus Li+/Li) tends to have a density of higher energy and a shorter life than those of a battery in which the lower limiting value of the negative electrode potential during full charge is about 1.4 V (versus Li+/Li).

[057] When the lower limit value of the negative electrode potential of the negative electrode using the monocyclic niobium-titanium oxide composite during charging is set to lower than 1.0 V (versus Li+/Li), the battery voltage can be increased and the battery capacity can be increased. It is considered that when the lower threshold value of the negative electrode potential during charging is set to lower than 1.0 V (versus Li+/Li), reductive decomposition of the non-aqueous electrolyte occurs as with the negative electrode containing graphite and the coating film like SEI is formed on the surface of the negative electrode. The generation of the SEI is considered to allow further reductive decomposition of the non-aqueous electrolyte at the negative electrode to be suppressed.

[058] However, the crystal structure of monocyclic niobium-titanium composite oxide is widely different from the crystal structure of graphite. That is, in monocyclic niobium-titanium composite oxide, a portion of skeleton structure is formed by the covalent bonding of oxide ions. Therefore, it is considered that lithium ions are inserted into an empty portion which is the lithium ion insertion site of the monocyclic niobium-titanium composite oxide, but the non-aqueous electrolyte solvent is not inserted into the empty portion. Most of the dangling bonds on the surface of monocyclic niobium-titanium composite oxide are terminated with hydroxyl groups. On the other hand, most of the dangling bonds on the graphite surface are not terminated with functional groups or similar and π electrons are present.

[059] Furthermore, in a state in which the lower limit of the negative electrode potential during charging is defined as lower than 1.0 V (versus Li+/Li), lithium ions are considered to be inserted in excess into the portion void of monocyclic niobium-titanium composite oxide. As a result of the insertion of excess lithium ions, the reduction reaction of the monocyclic niobium-titanium composite oxide during charging becomes unstable, which may cause a change in the crystal structure of the monocyclic niobium-titanium composite oxide.

[060] In view of the above, when the lower limit value of the negative electrode potential of the negative electrode using the monocyclic niobium-titanium composite oxide during charging is set to lower than 1.0 V (versus Li+/Li) , it is difficult to form an SEI that exhibits the same effect as that of the negative electrode that contains graphite on the surface of the negative electrode.

FIRST MODE

[061] An electrode according to a first embodiment contains active material particles. The active material particles contain monoclinic niobium-titanium composite oxide particles and an amorphous carbon body covering at least a portion of the surfaces of the niobium-titanium composite oxide particles. The S2/S1 ratio between a carbon atom concentration S2 and a niobium atom concentration S1 on the electrode surface, obtained by X-ray photoelectron spectroscopy, is 5 to 100. The niobium atom concentration S1 is calculated from an intensity of an area for a peak related to Nb3d. The S2 carbon atom concentration is calculated from the total area intensities for peaks related to C1s, with the peaks related to C1s appearing within a range of 286 eV to 294 eV and comprising a peak attributed to a bond of C-O, a peak assigned to a C=O bond, a peak assigned to a C(=O)-O bond, and a peak assigned to a CO32- bond.

[062] The electrode according to the first embodiment will be described below together with an embodiment of a secondary battery. The secondary battery includes the electrode according to the first embodiment as a negative electrode. The secondary battery comprises a negative electrode containing negative electrode active material particles, a positive electrode and an electrolyte. The negative electrode active material particles contain monoclinic niobium-titanium composite oxide particles and an amorphous carbon body covering at least a portion of the surfaces of the niobium-titanium composite oxide particles. The ratio of S2/S1 between the concentration of carbon atom S2 and the concentration of niobium atom S1 on the surface of the negative electrode, obtained by X-ray photoelectron spectroscopy, is 5 to 100. The concentration of niobium atom S1 is calculated from an intensity of an area for a peak related to Nb3d. The S2 carbon atom concentration is calculated from the total area intensities for peaks related to C1s, with the peaks related to C1s appearing within a range of 286 eV to 294 eV and comprising a peak attributed to a bond of C-O, a peak assigned to a C=O bond, a peak assigned to a C(=O)-O bond, and a peak assigned to a CO32- bond.

[063] In the secondary battery according to the first embodiment, a coating film generated by the reductive decomposition of the electrolyte is provided on the surface of the negative electrode. This coating film has the same role as that of an SEI provided on the surface of the negative electrode mentioned above that contains the graphite. Specifically, the S2/S1 ratio between the carbon atom concentration S2 and the niobium atom concentration S1 on the surface of the negative electrode, obtained by X-ray photoelectron spectroscopy, is 5 to 100. On the surfaces of the Negative electrode active material contained in the negative electrode, a favorable coating film which further suppresses the reductive decomposition of the electrolyte and which has low internal resistance is provided.

[064] Therefore, such a negative electrode can further suppress the reductive decomposition of a non-aqueous electrolyte even if the lower threshold value of a negative electrode potential during charging is set to lower than 1.0 V (versus Li+/Li ). Therefore, the non-aqueous electrolyte secondary battery according to the first embodiment including the negative electrode can achieve high energy density and excellent cycle characteristics.

[065] The secondary battery according to the first embodiment includes a negative electrode, a positive electrode and an electrolyte.

[066] The secondary battery according to the first embodiment may additionally include a separator arranged between the positive electrode and the negative electrode. The positive electrode, the negative electrode and the separator can constitute an electrode group. The electrolyte can be kept in the electrode group.

[067] The secondary battery according to the first embodiment may additionally include a container member that houses the electrode group and the electrolyte.

[068] Furthermore, the secondary battery according to the first embodiment may additionally include a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode.

[069] From this point on in this document, the negative electrode, the positive electrode, the electrolyte, the separator, the container member, the positive electrode terminal and the negative electrode terminal will be described in detail.

1) NEGATIVE ELECTRODE

[070] In the secondary battery according to the first embodiment, the negative electrode is placed so as to face the positive electrode. The negative electrode includes a negative electrode current collector and a layer containing negative electrode active material. The layer containing negative electrode active material is provided on at least one main surface of the negative electrode current collector. At least a portion of the negative electrode current collector faces a positive electrode current collector with the layer containing negative electrode active material interposed therebetween.

[071] Figure 1 is a cross-sectional view that schematically shows an example of the layer containing negative electrode active material of the secondary battery according to the first embodiment; Figure 1 is an enlarged cross-sectional view of a portion of the surface of a layer containing negative electrode active material 500 facing the positive electrode. The layer containing negative electrode active material 500 contains particles of negative electrode active material 50, a conductive agent 51, a binder 52, and a coating film SEI. The negative electrode active material particles 50 contain monocyclic niobium-titanium composite oxide particles 501 and an amorphous carbon body 502.

NEGATIVE ELECTRODE ACTIVE MATERIAL

[072] The negative electrode active material particles 50 are composed of single primary particles, secondary particles formed by the aggregation of a plurality of primary particles, or a mixture thereof.

[073] The primary particle size of the negative electrode active material particles 50 is preferably 0.1 μm to 5 μm. Setting the primary particle size of the negative electrode active material particles 50 in this range makes it possible to improve productivity in the production of an electrode and obtain a negative electrode that has favorable performance. When the primary particle size of the negative electrode active material particles 50 is more than 5 μm, the diffusion distance of lithium ions in solid is increased and the overvoltage during charging and discharging is increased. Therefore, the use of the negative electrode in which the primary particle size of the negative electrode active material particles 50 is more than 5 μm may cause the decline in the input/output characteristics of the battery. On the other hand, the use of the negative electrode in which the primary particle size of the negative electrode active material particles 50 is less than 0.1 μm causes a charge and discharge curve that has an abrupt change shape, which may cause a reduction in battery energy density.

[074] The secondary particle size of the negative electrode active material particles 50 is preferably 1 μm to 50 μm. When the secondary particle size of the negative electrode active material particles 50 is within this range, productivity during electrode production can be improved and a negative electrode that has favorable performance can be obtained. The secondary particle size of negative electrode active material particles 50 of less than 1 μm causes decline in the coating ability of a slurry produced during electrode production, or makes it necessary to excessively add a conductive auxiliary agent in order to to sufficiently maintain a conductive path, which is not preferential. On the other hand, the secondary particle size of the negative electrode active material particles 50 of more than 50 μm makes it impossible to sufficiently maintain the conductive trajectory in the secondary particles of the negative electrode active material particles 50, which may cause decay in battery life performance.

[075] Primary particle size and secondary particle size mean a particle size in which a volume integrated value is 50% in a particle size distribution obtained by a particle size distribution measuring apparatus of the laser diffraction type. As a sample when particle size distribution measurement is performed, a dispersion solution is used, which is obtained by diluting the negative electrode active material particles 50 with N-methyl-2-pyrrolidone so that the concentration of negative electrode active material particles 50 is defined from 0.1% by mass to 1% by mass.

[076] The BET specific surface area of the negative electrode active material particles 50 is desirably 1 m2/g to 30 m2/g. By definition, the specific surface area of the negative electrode active material particles 50 to 1 m2/g or more, a contact area between the negative electrode active material particles 50 and the non-aqueous electrolyte can be guaranteed enough. Therefore, it is likely that the battery including the negative electrode containing such negative electrode active material particles 50 will have favorable discharge rate characteristics and may shorten a charging time. Setting the specific surface area of the negative electrode active material particles 50 to 30 m2/g or less makes it possible to suppress the reactivity between the negative electrode and the non-aqueous electrolyte from being increased excessively. The use of the negative electrode containing such negative electrode active material particles 50 makes it possible to improve the battery life characteristics. The use of such negative electrode active material particles 50 makes it possible to improve the coating ability of the slurry containing the negative electrode active material particles 50 in a negative electrode production process to be described later.

[077] This BET specific surface area means a specific surface area determined by a nitrogen BET method (Brunauer, Emmet and Teller). The specific surface area based on nitrogen BET method can be obtained by the following method.

[078] First, the nitrogen gas adsorption content (ml/g) of the negative electrode active material particles 50 is measured at each pressure P while a nitrogen gas pressure P (mmHg) is gradually increased in the nitrogen gas. nitrogen at 77 K (nitrogen boiling point). Then, an adsorption isotherm is obtained by plotting the nitrogen gas adsorption content against each relative pressure P/P0. The relative pressure P/P0 is obtained by dividing the pressure P (mmHg) by a saturated vapor pressure P0 (mmHg) of the nitrogen gas. Then, a BET plot is calculated from the nitrogen adsorption isotherm and the BET equation and a specific surface area is obtained using the BET plot. For the calculation of the BET plot, a multiple BET point method is used.

MONOCYCLIC NIOBIUM-TITANIUM COMPOSITE OXIDE

[079] Monocyclic niobium-titanium composite oxide particles 501 are composed of single primary particles, secondary particles formed by aggregation of a plurality of primary particles or a mixture thereof.

[080] Figure 2 is a schematic view showing an example of the crystal structure of a monocyclic niobium-titanium composite oxide. Figure 3 is a schematic view of the crystal structure shown in Figure 2 as viewed from the other direction. Figures 2 and 3 show the crystal structure of Nb2TiO7 as an example of the monocyclic niobium-titanium composite oxide.

[081] As shown in Figures 2 and 3, the crystal structure of Nb2TiO7 has a configuration in which metal ions 101 and oxide ions 102 constitute a portion of backbone structure 103. In each metal ion 101, niobium ions (Nb) and titanium (Ti) ions are arranged at a ratio of Nb to Ti of 2:1 in a random manner. The skeletal structure portions 103 are alternatively arranged in a three-dimensional manner. Empty portions 104 are provided between backbone portions 103. Empty portions 104 are hosts for lithium ions. The empty portions 104 occupy a large portion of the entire crystal structure as shown in Figure 2. In addition, the empty portions 104 can maintain a structure stably even if lithium ions are inserted.

[082] Regions 105 and 106 shown in Figures 2 and 3 each have two-dimensional channels in a [100] direction and a [010] direction. As shown in Figure 3, the crystal structure of Nb2TiO7 has 107 empty portions. The 107 empty portion has a tunnel structure that is suitable for conducting lithium ions. The empty portion 107 is connected to region 105 and region 106 as a conductive path in the [001] direction. The presence of the conductive path allows the lithium ions to move back and forth between region 105 and region 106.

[083] The crystal structure of the monocyclic niobium-titanium composite oxide shown in Figures 2 and 3 has a large space into which lithium ions are inserted in an equivalent manner and has industrial stability. Furthermore, the crystal structure includes regions that have two-dimensional channels into which lithium ion rapidly diffuses and a conductive path in the [001] direction that connects the regions. Therefore, in the crystal structure of monocyclic niobium-titanium composite oxide, the insertion properties of lithium ions to the insertion space and the extraction properties of lithium ions from the insertion space are improved, and the insertion and extraction space for lithium ions is effectively increased. This makes it possible to provide high capacity and high rate performance.

[084] Furthermore, in the crystal structure mentioned above, when a lithium ion is inserted into the empty portion 104, the metal ion 101 that constitutes the backbone structure portion 103 is reduced to trivalent, which thereby maintains the electrical neutrality of the crystal. In monocyclic niobium-titanium composite oxide, not only the Ti ion is reduced from tetravalent to trivalent, but also the Nb ion is reduced from pentavalent to trivalent. For this, a large amount of reduced valences per weight of active material is required. Therefore, even when a large amount of lithium ions is inserted, the electrical neutrality of the crystal can be maintained. To achieve this, monocyclic niobium-titanium composite oxide has a higher energy density compared to a compound such as titanium oxide that contains only one tetravalent cation. Specifically, the theoretical capacity of monocyclic niobium-titanium composite oxide is about 387 mAh/g, which is more than twice the value of a titanium oxide that has a spinel structure.

[085] The crystal structure of the monocyclic niobium-titanium composite oxide can be confirmed by X-ray diffraction (XRD).

[086] The monocyclic niobium-titanium composite oxide is represented by the general formula Ti1-xM1xNb2-yM2yO7. In the general formula, 0 < x < 1 and 0 < y < 1 are defined. Elements M1 and M2 are at least one selected from the group consisting of V, Ta, Fe, Bi, Sb, As, P, Cr, Mo, W, B, Na, Mg, Al and Si.

[087] Like element M1, it is preferred to use at least one element from Fe and Al. These elements are trivalent elements. Therefore, the use of these elements as the M1 element makes it possible to improve the electron conductivity of monocyclic niobium-titanium composite oxide. Therefore, the use of these elements as the M1 element makes it possible to improve the capacity and fast charge performance of the negative electrode.

[088] From the point of view of improving electron conductivity, it is more preferable to use at least one element selected from the group consisting of V, Ta, Bi, Sb, As and P as the M1 element. Since these elements are pentavalent elements, the electron conductivity of monocyclic niobium-titanium composite oxide can be further improved.

[089] Like element M1, it is preferred to use at least one element selected from the group consisting of B, Na, Mg and Si. The atomic weights of these elements are less than the atomic weight of Ti. Therefore, the use of these elements like the M1 element make it possible to increase the capacity of the negative electrode.

[090] As element M2, it is preferred to use at least one element selected from the group consisting of Cr, Mo and W. Since these elements are hexavalent elements, the electron conductivity of monocyclic niobium-titanium composite oxide can be improved.

[091] The use of Ta as the M2 element makes it possible to obtain a monocyclic niobium-titanium composite oxide that has the same performance as in the case of using Nb as the M2 element. This is considered to be due to the fact that Nb and Ta have the same physical, chemical and electrical properties.

[092] Like elements M1 and M2, at least one element selected from the group consisting of Mo, W and V can be used. These elements exhibit an effect as a sintering auxiliary agent. Therefore, the use of these elements as at least one of M1 and M2 makes it possible to reduce a firing temperature in the production of monocyclic niobium-titanium composite oxide.

[093] Monocyclic niobium-titanium composite oxide can also be represented by the general formula Tii-xMxNb2O7 (0 < x < 1). M in the general formula is the same as the M1 described above.

[094] The content of elements M1 and M2 in the compound represented by the general formula Ti1-xM1xNb2-yM2yO7 and the content of element M in the compound represented by the general formula Ti1-xMxNb2O7 can be quantified, for example, by ICP spectroscopic analysis.

[095] The monocyclic niobium-titanium composite oxide may contain an oxide that has a composition that is beyond a stoichiometric ratio represented by the general formula Ti1-xM1xNb2M2yO7 (0 < x < 1, 0 < y < 1). The oxide can be represented by the general formula Tii-xM1xNb2-yM2yθ7+δ (0^x < 1, 0^y < 1, -0.3^δ^0.3).

[096] That is, during the preparation of the monocyclic niobium-titanium composite oxide, oxygen defects may occur in a raw material or an intermediate product. The unavoidable impurities contained in the raw material as well as impurities mixed in it during preparation may be present in the composite oxide. Due to the inevitable factor, a monocyclic niobium-titanium composite oxide containing an oxide having a composition beyond a stoichiometric ratio can be prepared in some cases. The oxide having a composition beyond a stoichiometric ratio has excellent lithium ion insertion stability as with an oxide having a composition having a stoichiometric ratio. Therefore, even when the monocyclic niobium-titanium composite oxide contains the oxide having a composition beyond a stoichiometric ratio, the influence on the lithium ion insertion capacity is small.

[097] The monocyclic niobium-titanium composite oxide can contain different phases with different Nb/Ti ratios. Examples of the different phases include TiO2, Nb24TiO62, Nb14TiO37 and Nb10Ti2O29 of the Rutile type.

[098] As monocyclic niobium-titanium composite oxide particles 501, only one type of monocyclic niobium-titanium composite oxide particles can be used and mixtures of a plurality of types of monocyclic niobium-titanium composite oxide particles can be used .

AMORPHOUS CARBON BODY

[099] The amorphous carbon body 502 covers at least a portion of the surfaces of the monoclinic niobium-titanium composite oxide particles 501. It is preferred that the amorphous carbon body 502 uniformly coats all surfaces of the composite niobium-titanium oxide particles. monocyclic niobium-titanium 501. The amorphous carbon body 502 may have a film shape or a particle shape.

[100] The amorphous carbon body 502 is a porous body capable of forming lithium ions and a non-aqueous solvent contained in a non-aqueous electrolyte permeate. The electron conductivity of the amorphous carbon body 502 is higher than the electron conductivity of the monocyclic niobium-titanium composite oxide particles 501. Therefore, the amorphous carbon body 502 promotes the generation of a coating film SEI on the surfaces of negative electrode active material particles 50 during initial battery charging.

[101] That is, the coating film SEI provided on the amorphous carbon body 502 supported on the surfaces of the monocyclic niobium-titanium composite oxide particles 501 tends to have a greater film thickness and a higher film thickness uniformity. than those of the coating film provided on the surfaces of the negative electrode active material particles 50 that do not support the amorphous carbon body 502.

[102] The thickness of the amorphous carbon body 502 is preferably 1 nm to 10 nm, and more preferably 2 nm to 10 nm. The excessively thick amorphous carbon body 502 tends to inhibit the diffusion of lithium ions, which tend to increase the internal resistance of the negative electrode. The excessively thin amorphous carbon body 502 tends to be less likely to form the coating film SEI. Therefore, the use of a negative electrode that has an excessively thick or excessively thin 502 amorphous carbon body tends to cause a decline in the cycling characteristics of the battery.

[103] The state and thickness of the amorphous carbon body 502 can be confirmed with transmission electron microscopy (TEM) observation. Specifically, first, ruthenium is adsorbed on the surfaces of negative electrode active material particles 50 by an evaporation method. Then, the negative electrode active material particles 50 are embedded in a resin and the resin is thinned by ion milling cutter using DualMill 600 manufactured by GATAN. Then, primary particles of arbitrary negative electrode active material particles 50 are subjected to TEM observation. This observation allows the dispersibility of the amorphous carbon body 502 in the negative electrode active material particles 50 to be understood. 10 or more particles are subjected to observation and the average value of the thickness of the amorphous carbon body 502 is calculated as the thickness of the amorphous carbon body 502. As a TEM apparatus, for example, H-9000UHR III manufactured by Hitachi, Ltd .Can be used. In this measurement, an accelerating voltage is set at 300 kV and an image magnification is set at a magnification of 2,000,000 times.

[104] The amorphous carbon body 502 is made by carbon that has low crystallinity. The amorphous carbon body 502 may contain a graphite crystal structure. The crystallinity of the amorphous carbon body 502 can be understood by Raman spectroscopy analysis. That is, the IG/ID ratio of IG peak intensity of a G band and ID peak intensity of a D band for negative electrode active material particles 50 obtained by Raman spectroscopy measurement is preferably 1. 2 or less, more preferably 1.1 or less, and even more preferably 1.0 or less.

[105] In the present context, the G band is a peak found within a range of 1530 cm-1 to 1630 cm-1 in the Raman spectrum. The G band is derived from the graphite structure of the amorphous carbon body 502. The D band is a peak found within a range of 1280 cm-1 to 1380 cm-1 in the Raman spectrum. The D band is derived from the amorphous structure of the amorphous carbon body 502. In this Raman spectrum, a peak derived from the monocyclic niobium-titanium composite oxide particles 501 does not appear substantially at the positions of the G band and the D band.

[106] Therefore, the low IG/ID ratio of the negative electrode active material particles 50 obtained by Raman spectrometry means that the crystallinity of the amorphous carbon body 502 is low. The lower limit value of the IG/ID ratio is not particularly limited, but is, for example, 0.8 or more.

[107] This Raman spectrum can be obtained by subjecting negative electrode active material particles 50 to microscopic Raman spectroscopy. As a measuring device, for example, Nicolet Almega (registered trademark) manufactured by Thermo Fisher Scientific can be used. In measurement, for example, the wavelength of a light measuring source is set to 532 nm; a slit size is set at 25 μm; laser intensity is set to 10%; an exposure time is set to 5 seconds; and the accumulated amount is set to 10. The obtained Raman spectrum is subjected to peak fitting according to a last squares method within a measurement range of 1100 cm-1 to 2000 cm-1. As a fitting function, a Gauss-Lorentz function is used.

[108] The layer containing negative electrode active material 500 may contain other oxides as a negative electrode active material other than the negative electrode active material particles 50 containing the monocyclic niobium-titanium composite oxide particles 501 and the amorphous carbon body 502.

[109] Examples of the other oxides include a titanium oxide that has a monocyclic structure, a titanium oxide that has a rutile structure, and a titanium oxide that has an anatase structure. The titanium oxide that has each crystal structure can be represented by TiO2 as an uncharged composition and LixTiO2 (x is 0 < x < 1) as a charged composition. The uncharged structure of titanium oxide which has a monocyclic structure can be represented as TiO2(B).

[110] Examples of the other oxides include a lithium-titanium oxide that has a spinel structure (e.g., the general formula LÍ4+XTÍ5O12 (-1 < x < 3)), a lithium-titanium oxide that has a ramsdellite structure (e.g. LÍ2+xTÍ3O7 (-1 < x < 3), Lii+xTÍ2O4 (0 < x < 1), Lii,i+xTii,8θ4 (0 < x < 1), Li1.07+xTi1 .86O4 (0 < x < 1) and LixTiO2 (0 < x < 1). Examples of lithium titanium oxide include a lithium titanium oxide composite in which the dopant is introduced into the lithium titanium oxide which has a spinel structure or a ramsdellite structure.

[111] Examples of the other oxides include an orthorhombic Na-containing niobium-titanium composite oxide represented by the general formula Li2+vNa2-wM1xTi6-y-zNbyM2zOi4+δ (0 < v < 4, 0 < w < 2, 0 < x < 2, 0 < y < 6, 0 < z < 3, y + z < 6, - 0.5 < δ < 0.5; M1 contains at least one selected from Cs, K, Sr, Ba and Ca; and M2 contains at least one selected from Zr, Sn, V, Ta, Mo, W, Fe, Co, Mn and Al).

COATING FILM

[112] The coating film SEI covers at least a portion of the surface of the negative electrode. It is preferred that the coating film SEI covers at least a portion of the surface of the layer containing negative electrode active material 500. It is more preferred that the coating film SEI covers at least a portion of the surface of the amorphous carbon body 502 of the negative electrode active material particles 50. The coating film SEI may cover at least a portion of the surface of the negative electrode active material particles 50 on which the amorphous carbon body 502 is not supported.

[113] The coating film SEI is a porous body that makes lithium ions permeate and is less likely to make the non-aqueous solvent of the non-aqueous electrolyte permeate. This coating film SEI has the same role as the SEI provided on the surface of the negative electrode mentioned above which contains the graphite. That is, the coating film SEI plays a passive role and further suppresses the decomposition of the non-aqueous electrolyte at the negative electrode.

[114] The coating film SEI contains a decomposition product of at least one of an electrolyte salt and a non-aqueous solvent. This decomposition product contains an organic compound. The organic compound is mainly produced by the decomposition of a non-aqueous solvent. Examples of the organic compound include (CH2OCO2Li)2, lithium alkyl carbonate (ROCO2Li), lithium carbonate (Li2CO3), or mixtures thereof. In the present context, R is a hydrocarbon group.

[115] The thickness and uniformity of the coating film SEI can be understood by the ratio S2/S1 between the carbon atom concentration S2 and the niobium atom concentration S1 obtained by subjecting the surface of the negative electrode to spectroscopy. X-ray photoelectron (XPS).

[116] That is, in the spectrum of the negative electrode surface obtained by XPS, a peak related to Nb3d is derived from niobium contained in the monocyclic niobium-titanium composite oxide. The Nb3d-related peak is observed within a range of 204 eV to 212 eV. A niobium atom concentration S1 calculated from the intensity of the peak area related to Nb3d is considered to correlate with the surface area of the layer containing negative electrode active material 500 that is not covered with the amorphous carbon body 502 and the SEI of coating film.

[117] The niobium S1 atom concentration obtained by XPS analysis, for example, is 3 atm% or less, preferably 2.5 atm% or less, and more preferably 1.5 atm% or less . The lower limit value of niobium atom concentration S1 is not particularly limited, but is 0.1 atm% or more as an example.

[118] In the spectrum of the negative electrode surface obtained by XPS, a peak assigned to a C-O bond, a peak assigned to a C=O bond, a peak assigned to a C(=O)-O bond, and a peak assigned to a CO32- bond are related to C1s and appear within a range of 286 eV to 294 eV. The peaks related to C1s are derived from the carbon contained in the coating film SEI.

[119] The peak attributed to the C-O bond appears within a range of 286 eV to 287.5 eV. The peak attributed to the C=O bond appears within a range of 287.5 eV to 289 eV and appears at a higher binding energy position compared to the peak attributed to the C–O bond. The peak attributed to the C(=O)-O bond appears within a range of 289 eV to 290 eV and appears at a higher binding energy position compared to the peak attributed to the C=O bond. The peak attributed to the CO32- bond appears within a range of 290 eV to 292 eV and appears at a higher binding energy position compared to the peak attributed to the C(=O)-O bond. Two peaks attributed to the CO32− bond can be detected within a range of the above binding energy. In this case, the total of the intensities of the two peak areas is taken as the peak attributed to the CO32- bond.

[120] A carbon atom concentration S2 calculated from the total of the intensities of these peak areas is considered to be correlated to the area and thickness of the coating film SEI on the surface of the negative electrode.

[121] The S2 carbon atom concentration obtained by XPS analysis, for example, is 9 atm% to 25 atm%, preferably 10 atm% to 22 atm%, and more preferably 13 atm% at 22 atm%.

[122] The large ratio S2/S1 between the carbon atom concentration S2 and the niobium atom concentration S1 means that the SEI of coating film formed on the surfaces of the negative electrode active material particles 50 is thick or the SEI of coating film covers most of the surfaces of the negative electrode active material particles 50. The small S2/S1 ratio means that the SEI of coating film formed on the surfaces of the negative electrode active material particles 50 is thin or the SEI coating film covers only a part of the surfaces of the negative electrode active material particles 50.

[123] In the battery according to the first embodiment, the S2/S1 is from 5 to 100. In the vicinity of the surface of the negative electrode in which the S2/S1 ratio is within this range, the SEI of coating film having a Film thickness sufficient to further suppress the reductive decomposition of the non-aqueous electrolyte can be considered to be provided relatively uniformly on the surfaces of the negative electrode active material particles 50. Therefore, at the negative electrode at which the S2/S1 ratio is within In this range, further reductive decomposition of the non-aqueous electrolyte is less likely to occur and internal resistance tends to be small. The S2/S1 ratio is preferably 10 to 100 and more preferably 20 to 100.

[124] The coating film SEI preferably additionally contains an inorganic compound in addition to the organic compound. This inorganic compound is mainly generated by the decomposition of electrolyte salt. When the coating film SEI additionally contains the inorganic compound, further reductive decomposition of the non-aqueous electrolyte is less likely to occur. When the coating film SEI contains the inorganic compound, the coating film SEI may be a composite of an organic compound and an inorganic compound. The inorganic compound has a bond represented by PFxOy. In the present context, 0 < x < 1 and 0 < y < 1 are defined.

[125] The content of inorganic compound in the SEI of coating film can be understood by XPS. That is, in the spectrum of the negative electrode surface obtained by X-ray photoelectron spectroscopy, a peak related to P2p, which appears within a range of 133 eV to 137 eV and attributed to a PFxOy bond is derived from the phosphorus contained in the SEI coating film.

[126] The peak attributed to the PFxOy bond can appear within a range of 132 eV to 136 eV. The concentration of phosphorus atom S3 calculated from a peak area intensity is considered to be correlated with the content of the inorganic compound contained in the SEI of coating film provided on the surface of the negative electrode.

[127] A plural of peaks attributed to the PFxOy bond can be detected within a range of 132 eV to 136 eV. In this case, the S3 phosphorus atom concentration can be calculated from the total intensities of the plural of peak areas detected within a range of 132 eV to 136 eV.

[128] The S3 phosphorus atom concentration obtained by XPS analysis, for example, is 0.4 atm% to 3 atm% and, preferably, 0.5 atm% to 3 atm%.

[129] The S3/S1 ratio between the phosphorus atom concentration S3 and the niobium atom concentration S1 is preferably 0.3 to 20. The SEI of coating film which has a high quenching effect is still further reductive decomposition of the electrolyte can be considered to be provided on at least a part of the surface of the negative electrode in which the ratio S3/S1 is within this range. This S3/S1 ratio is most preferably 0.4 to 10.

[130] This XPS analysis can be performed by the following method.

[131] First, a secondary battery is placed in a fully discharged state. In the present context, the state of complete discharge means a state in which lithium ions are completely released from a negative electrode active material. Specifically, the battery is discharged at a discharge rate of 0.2 C and placed into an overdischarge state. A clipped voltage is set at 1.0 V. Then, in an argon-filled glove box, the battery is disassembled, and a negative electrode is removed.

[132] XPS analysis is preferably performed on batteries at the initial shipping stage. That is, in a repeatedly charged and discharged battery, a coating film SEI may be formed in excess on the surface of a negative electrode, or an element derived from a positive electrode active material eluted in an electrolyte by a side reaction may be contained in the SEI coating film on the surface of the negative electrode. Therefore, in order to accurately understand the SEI state of coating film on the negative electrode surface, XPS analysis is preferably performed on batteries with a smaller number of charge and discharge cycles in the initial shipping stage. . Therefore, XPS analysis is most preferably carried out in a state where a battery immediately after production, for example a battery subjected to degassing treatment and then released, is disassembled.

[133] Next, the removed negative electrode is thoroughly washed with a non-aqueous solvent such as ethyl methyl carbonate, to remove lithium ions that remain on the negative electrode. When lithium ions remain on the negative electrode, lithium ions can react with the electrolyte to generate lithium carbonate and lithium fluoride or the like. When these impurities are contained in the coating film SEI, the composition of the coating film SEI can be changed. Therefore, it is preferred to completely remove the lithium ions at the negative electrode. In this series of operations, the negative electrode is not exposed to air.

[134] Next, two test pieces are cut out from the surface of the washed negative electrode. The shape of the test piece is, for example, a square that has a side length of 2 cm. Then, one of the test pieces is used as a negative electrode to form a half cell. As a counter electrode and the reference electrode of the half cell, a lithium metal is used. Then, in the half cell, a negative electrode potential with reference to the reference electrode is measured. It is confirmed that the negative electrode potential with reference to the reference electrode is 2.0 V (versus Li+/Li) or more, that is, the negative electrode active material is completely discharged.

[135] Next, the other test piece is set in an XPS apparatus so that it is not exposed to air. Then, the test piece is subjected to XPS measurement to obtain an XPS spectrum. As the XPS apparatus, for example, Quantera (registered trademark) SXM manufactured by ULVAC-PHI can be used. For the measurement, for example, monochromated Al Kα1,2 rays are used as excited X-rays; an X-ray irradiation diameter is set at 200 μm; and a photoelectron escape angle is 45 degrees. As the analysis software, PHI Multipak can be used. For data processing, 9-point smoothing is performed and the horizontal axis correction reference value is set to 458.8 eV. The reference value is a peak position related to Ti2p derived from TiO2. For the spectrum to fit, a Gauss-Lorents function is used as a fitting function; a Shirley method is used as a background processing method; and a last squares method is used as an adjustment method.

[136] Next, the XPS spectrum is subjected to wide-scan analysis and the elements contained in a measuring region are confirmed. Examples of the elements observed by wide-scan analysis include Li, P, F, O, C, Nb, and Ti. Then, all elements observed by wide-scan analysis are subjected to narrow-scan analysis to obtain a broad-scan spectrum closely related to each element. Then, the narrow-scan spectrum of each element is subjected to adjustment to obtain the areal intensity of each element. The atomic concentration of each element can be calculated by multiplying the area intensity of the element by a relative sensitivity coefficient that corresponds to each element.

[137] Next, the niobium atom concentration S1 is calculated by dividing the atomic concentration of the niobium element obtained in this way by the total atomic concentrations of the respective elements.

[138] Next, a narrow-scan spectrum related to C1s is subjected to peak separation. The C1s-related narrow-scan spectrum may additionally include a peak derived from at least one of the conducting agent 51 and the binder 52 in addition to the coating film SEI-derived peak described above. Examples of the peak derived from at least one of the conducting agent 51 and the binder 52 include a C-C bond and a CHx bond. The peak attributed to the C–C bond appears within a range of 286 eV to 282 eV and appears at a lower binding energy position compared to the peak attributed to the C–O bond. The peak attributed to the CHx bond appears within the same range as the peak attributed to the C-C bond.

[139] Among all the C1s-related peaks observed in this way, only the above-mentioned peak derived from the coating film SEI is extracted. The concentration of carbon atom S2 derived from the organic compound contained in the coating film SEI is calculated from the total intensities of the peak areas derived from the coating film SEI and the relative carbon sensitivity coefficient.

[140] Next, a narrow-scan spectrum related to P2p is subjected to peak separation. From the intensity of the peak area attributed to a PFxOy bond and the relative sensitivity coefficient of phosphorus, the concentration of phosphorus atom S3 derived from the inorganic compound contained in the coating film SEI is calculated.

[141] By the above method, the ratios S2/S1 and S3/S1 can be obtained.

[142] The film thickness of the coating film SEI is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. When the film thickness of the coating film SEI is large, the suppression effect of electrolyte decomposition on the negative electrode is improved and the cycle characteristics of the battery tend to be improved.

[143] The film thickness of the coating film SEI is preferably 150 nm or less, more preferably 120 nm or less, and even more preferably 90 nm or less. When the film thickness of the coating film SEI is small, the diffusion capacity of lithium ions in the negative electrode tends to be improved and the internal resistance tends to be reduced.

[144] The SEI film thickness of coating film can be obtained by XPS depth direction analysis.

[145] Specifically, first, a negative electrode is taken from a battery in the same way as described in the XPS spectrum measurement method above to obtain a test piece. Then, this test piece is set in an XPS apparatus, an argon (Ar) ion etched and the XPS measurement are repeated alternately. In this measurement, Li1s, C1s, F1s, P2p and Nb3d are set as measurement targets; an etch rate is set at 7 nm/min with respect to silicon oxide (SiO2); and XPS measurement is performed per minute. Then, the spectrum obtained is subjected to adjustment to obtain the area intensity of each element. Then, the atomic concentration of the element is calculated from the area intensity of the element and the relative sensitivity coefficient of the element. Then, for each spectrum, the atomic concentration of Li1s in the total atomic concentration of Li1s, C1s, F1s, P2p and Nb3d is calculated. Then, within these spectra, a spectrum is confirmed, in which the atomic concentration related to Li1s is close to 1 atm% and higher than 1 atm% and which is obtained at the deepest position. Then, a recording depth is calculated from a recording time and rate when the spectrum is obtained. The depth calculated in this way can be considered as the film thickness of the coating film SEI.

[146] That is, as described above, the coating film SEI contains the decomposition products of the electrolyte salt and solvent contained in the electrolyte. These decomposition products contain lithium. As described above, in the negative electrode taken out in a state of complete discharge, lithium ions are completely separated from the negative electrode active material. Therefore, the Li1s-related peak detected by XPS depth direction analysis can be considered to be derived from the coating film SEI. From the above, it can be considered that the SEI of coating film exists up to a position where a peak indicating that the atomic concentration related to Li1s is higher than 1 atm% is obtained. Therefore, it can be considered that the coating film SEI is provided up to the limit between a depth at which a spectrum having a Li1s-related atomic concentration of more than 1 atm% is obtained and a depth at which a spectrum having a Li1s-related atomic concentration of 1 atm% or less is obtained. Therefore, a depth at which a spectrum having a Li1s-related atomic concentration of close to 1 atm% and higher than 1 atm% and obtained at the deepest position is obtained can be considered as the film thickness of the Li1s film SEI. coating.

[147] The conductive agent 51 is blended to improve the current collection performance and to suppress the contact resistance between the negative electrode active material particles 50 and the current collector. Examples of conductive agent 51 include carbonaceous materials such as steam grown carbon fiber (VGCF), acetylene black, carbon black, and graphite. One of these may be used as the conductive agent 51, or two or more thereof may be used in combination as the conductive agent 51. Alternatively, in lieu of using the conductive agent 51, a carbon coating or a material coating Electron-conducting inorganic agent can be applied to the surfaces of the negative electrode active material particles 50. The conducting agent 51 can be omitted.

[148] The binder 52 is mixed to fill the gaps of the negative electrode active material particles 50 dispersed with the binder 52 and also to bind the negative electrode active material particles 50 and the negative electrode current collector. Examples of binder 52 include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluoride-containing rubber, styrene-butadiene rubber, a polyacrylic acid compound, and an imide compound. One of these may be used as the binder 52, or two or more thereof may be used in combination as the binder 52.

[149] From the point of view of improving cycle characteristics, it is preferred to use carboxymethyl cellulose, a polyacrylic acid compound, or a mixture thereof as the binder 52. Carboxymethyl cellulose and the polyacrylic acid compound polyacrylic acid have high ability to coat the surfaces of the negative electrode active material particles 50. Therefore, the use of carboxymethyl cellulose and polyacrylic acid compound as the binder 52 makes it possible to suppress the decomposition of the electrolyte on the surfaces of the material particles active negative electrode 50 that are not covered with the amorphous carbon body 502. The binder 52 can be omitted.

[150] It is preferred that the negative electrode active material particles 50, the conductive agent 51 and the binder 52 are mixed respectively at rates of 68% by mass to 96% by mass, 2% by mass to 30% by mass and from 2% by mass to 30% by mass, in the layer containing negative electrode active material. The conductive agent 51 content of 2% by mass or more makes it possible to improve the current collection performance of the layer containing negative electrode active material. The binder 52 content of 2 mass % or more provides sufficient binding property between the layer containing negative electrode active material and the negative electrode current collector, which can provide promising excellent cycle performance. On the other hand, the contents of the conducting agent 51 and the binder 52 are preferably 28% by mass or less, which thereby increases the capacity.

[151] The negative electrode current collector is a material that is electrochemically stable at the insertion and extraction potentials of lithium ions from the negative electrode active material. The negative electrode current collector is preferably made of copper, nickel, stainless steel, aluminum, or an aluminum alloy containing 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 to 20 μm. The negative electrode current collector having such a thickness can achieve a balance between the resistance and the reduction in the weight of the negative electrode.

[152] The density of the layer containing negative electrode active material (which does not include the current collector) is preferably 1.8 g/cm3 to 2.8 g/cm3. The negative electrode in which the density of the layer containing negative electrode active material is within this range has an excellent energy density and retention property of the non-aqueous electrolyte. The density of the layer containing negative electrode active material is more preferably 2.1 g/cm3 to 2.6 g/cm3.

[153] Next, an example of a method of producing a secondary battery that includes the negative electrode will be described.

[154] First, negative electrode active material particles 50 are prepared. Specifically, first, monocyclic niobium-titanium composite oxide particles 501 are prepared. Examples of a method of producing the monocyclic niobium-titanium composite oxide particles 501 include a solid phase method, a hydrothermal method, a sol-gel method and a coprecipitation synthesis method.

[155] Next, monocyclic niobium-titanium composite oxide particles 501, a carbon source and pure water are mixed and thoroughly mixed to prepare a dispersion solution.

[156] As the carbon source, sugars such as sucrose, maltose and glucose, polyolefins, nitriles, alcohols such as polyvinyl alcohol (PVA), organic compounds containing a benzene ring, aromatic hydrocarbons such as pyrene, naphthalene and chrysene or mixtures thereof same can be used. As the carbon source, PVA is preferably used. The use of PVA as the carbon source tends to provide an improvement in the dispersibility of the amorphous carbon body 502 on the surfaces of the monocyclic niobium-titanium composite oxide particles 501.

[157] From the point of view of improving the cycle characteristics of the battery, the addition content of the carbon source is preferably 1.0 parts by mass or more, and more preferably 2.0 parts by weight. mass or more relative to 100 parts by mass of the monocyclic niobium-titanium composite oxide particles 501. When the addition content of the carbon source is increased, the film thickness of the amorphous carbon body 502 is increased, which tends to cause an increase in the SEI film thickness of the coating film.

[158] From the point of view of reducing the internal resistance of the negative electrode, the addition content of the carbon source is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less in relative to 100 parts by mass of the monocyclic niobium-titanium composite oxide particles 501. When the addition content of the carbon source is reduced, the film thickness of the amorphous carbon body 502 is reduced, which tends to cause a reduction in SEI film thickness of coating film.

[159] Then, the dispersion solution is subjected to spray drying to obtain a powder sample. Then, the obtained powder sample is further dried at a temperature of 70°C to 200°C for 1 minute to 1 hour. In this way, the monocyclic niobium-titanium composite oxide particles 501 supporting the unfired amorphous carbon body 502 are obtained.

[160] Then, the composite oxide particles are fired under an inert atmosphere to carry out a carbonization treatment. As the gas for the inert atmosphere, for example, nitrogen gas, carbon dioxide gas or argon gas or the like can be used. A trigger time is set, for example, from 1 hour to 5 hours.

[161] From the point of view of reducing the internal resistance of the negative electrode, a trigger temperature is preferably 650°C or more, and more preferably 700°C or more. When the firing temperature is elevated, the crystallinity of the amorphous carbon body 502 is improved, which tends to provide an improvement in the electron conductivity of the negative electrode active material particles 50.

[162] From the point of view of improving the cycle characteristics of the battery, the firing temperature is preferably 850°C or lower, and more preferably 800°C or lower. When the firing temperature is reduced, the crystallinity of the amorphous carbon body 502 is reduced, which tends to provide an improvement in the electrolyte decomposition suppression effect of the coating film SEI.

[163] In this way, the negative electrode active material particles 50 can be obtained, which contains the monocyclic niobium-titanium composite oxide particles 501 having a surface of which at least a part is covered with the carbon body amorphous 502.

[164] Next, a negative electrode is produced using the negative electrode active material particles 50 obtained in this way. Specifically, first, particles of negative electrode active material 50, a conductive agent 51 and a binder 52 are suspended in a solvent to prepare a slurry. This slurry is then applied to one surface or both surfaces of a negative electrode current collector. Then, the applied slurry is dried to obtain a laminate of the negative electrode current collector and the layer containing negative electrode active material. From there, the laminate is pressed. In this way, the negative electrode can be obtained.

[165] The negative electrode can be produced by the following method. First, negative electrode active material particles 50, a conductive agent 51 and a binder 52 are mixed to obtain a mixture. Then, the mixture is formed into a pellet shape. Then, by placing the pellets in a negative electrode current collector, the negative electrode can be obtained.

[166] Next, a method of providing a coating film SEI on the surface of a negative electrode will be described. Coating film SEI can be provided on the surface of the negative electrode, for example, by a method that includes initial charging of a secondary battery and aging after initial charging.

[167] Specifically, first, a secondary battery that includes the negative electrode obtained by the method described above is produced. So, this battery is initially charged. During initial charging, a negative electrode potential is defined as lower than 1.0 V (versus Li+/Li). By the initial charge, a coating film SEI is formed on the surface of the negative electrode. The negative electrode potential during initial charge is preferably set at 0.8 V (against Li+/Li) or less, and more preferably at 0.7 V (against Li+/Li) or less. When the negative electrode potential during initial charging is low, the film thickness of the coating film SEI tends to be increased. The lower threshold value of the negative electrode potential during initial charging is not particularly limited and an example of the same is 0.6 V (versus Li+/Li). During initial charging, the negative electrode potential is maintained at less than 1.0 V (versus Li+/Li), for example, for 8 to 48 hours.

[168] Then, the initially charged battery is subjected to aging. By aging, the SEI of coating film on the surface of the negative electrode grows. An aging temperature is preferably set at 25°C to 60°C. An aging time is preferably set from 8 hours to 48 hours. When the aging temperature is high or the aging time is long, the coating film SEI formed on the surface of the negative electrode is likely to grow, and the film thickness of the coating film SEI tends to be increased.

[169] The aged battery can be discharged, followed by degassing treatment.

2) POSITIVE ELECTRODE

[170] The positive electrode may include a positive electrode current collector and a layer containing positive electrode active material. The layer containing positive electrode active material may be formed on one surface or both reverse surfaces of the positive electrode current collector. The layer containing positive electrode active material may include a positive electrode active material and, optionally, an electroconductive agent and a binder.

[171] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may include one type of positive electrode active material, or alternatively, include two or more types of positive electrode active materials. Examples of oxide and sulfide include compounds with the ability to have Li (lithium) and Li ions be inserted and extracted.

[172] Examples of such compounds include manganese dioxides (MnO2), iron oxides, copper oxides, nickel oxides, lithium-manganese composite oxides (e.g., LixMn2O4 or LixMnO2; 0 < x < 1), oxides lithium-nickel composites (e.g. LixNiO2; 0 < x < 1), lithium-cobalt oxide composites (e.g. LixCoO2; 0 < x < 1), lithium-nickel-cobalt oxide composites (e.g. LixNii —yCθyθ2; 0 < x < 1, 0 < y < 1), lithium-manganese-cobalt composite oxides (e.g. LixMnyCoi—yO2; 0 < x < 1, 0 < y < 1), lithium-manganese composite oxides manganese-nickel that has a spinel structure (e.g., LixMn2—yNiyO4; 0 < x < 1, 0 < y < 2), lithium phosphates that have an olivine structure (e.g., LixFePO4; 0 < x < 1 , LixFei-yMnyPO4; 0 < x < 1, 0 < y < 1 and LixCoPO4; 0 < x < 1), iron sulfides [Fe2(SO4)3], vanadium oxides (e.g. V2O5) and composite oxides of lithium-nickel-cobalt-manganese (LiNi1-x-yCoxMnyO2; 0 < x < 1, 0 < y < 1, x + y < 1). As the active material, one of these compounds can be used singly, or plural compounds can be used in combination.

[173] Most preferred examples of the positive electrode active material include lithium-manganese composite oxides that have a spinel structure (e.g., LixMn2O4; 0 < x < 1), lithium-nickel composite oxides (e.g., LixNiO2 ; 0 < x < 1), composite lithium-cobalt oxides (e.g., LixCoO2; 0 < x < 1), composite lithium-nickel-cobalt oxides (e.g., LiNi1-yCoyO2; 0 < x < 1), lithium-manganese-nickel composite oxides that have a spinel structure (e.g., LixMn2-yNiyO4; 0 < x < 1, 0 < y < 2), lithium-manganese-cobalt composite oxides (e.g., LixMnyCo1-yO2 ; 0 < x < 1, 0 < y < 1), lithium-iron phosphates (e.g. LixFePO4; 0 < x < 1) and lithium-nickel-cobalt-manganese composite oxides (LiNi1-x-yCoxMnyO2; 0 < x < 1, 0 < y < 1, x + y < 1). The positive electrode potential can be made high by using these positive electrode active materials.

[174] The primary particle size of the positive electrode active material is preferably within a range of 100 nm to 1 μm. Positive electrode active material that has a primary particle size of 100 nm or more is easy to handle during industrial production. In the positive electrode active material having a primary particle size of 1 μm or less, the diffusion of lithium ions into the solid can proceed smoothly.

[175] The specific surface area of the positive electrode active material is preferably within a range of 0.1 m2/g to 10 m2/g. The positive electrode active material that has a specific surface area of 0.1 m2/g or more can ensure sufficient sites for inserting and extracting Li ions. The positive electrode active material that has a specific surface area of 10 m2 /g or less is easy to deal with during industrial production and can ensure good charging and discharging cycle performance.

[176] The binder is added to fill gaps between the dispersed positive electrode active material and also to bind the positive electrode active material with the positive electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluoride rubber, polyacrylate compounds, and imide compounds. One of these may be used as the binder, or two or more may be used in combination as the binder.

[177] The electroconductive agent is added to improve current collection performance and to suppress contact resistance between the positive electrode active material and the positive electrode current collector. Examples of the electroconductive agent include carbonaceous substances such as steam grown carbon fiber (VGCF), acetylene black, carbon black, and graphite. One of these may be used as the electroconductive agent or two or more may be used in combination with the electroconductive agent. The electroconductive agent can be omitted.

[178] In the layer containing the positive electrode active material, the positive electrode active material and binder are preferably mixed in proportions within ranges of 80% by mass to 98% by mass and from 2% by mass to 20% by mass, respectively.

[179] When the binder content is 2% by mass or more, sufficient electrode resistance can be achieved. When the binder content is 20% by mass or less, the insulator content in the electrode is reduced and thus the internal resistance can be reduced.

[180] When an electroconductive agent is added, the positive electrode active material, binder and the electroconductive agent are preferably mixed in proportions of 77% by mass to 95% by mass, from 2% by mass to 20% by mass. mass and from 3% by mass to 15% by mass, respectively.

[181] When the content of the electroconductive agent is 3% by mass or more, the effects described above can be expressed. By definition, the electroconductive agent content is 15% by mass or less, the proportion of electroconductive agent contacting the electrolyte may be low. When this ratio is low, the decomposition of an electrolyte may be reduced during storage at high temperatures.

[182] The positive electrode current collector is preferably an aluminum sheet, or an aluminum sheet alloy containing one or more elements selected from the group consisting of Mg, Ti, Zn, Ni, Cr , Mn, Fe, Cu and Si.

[183] The thickness of the aluminum sheet or aluminum sheet alloy is preferably within a range of 5 μm to 20 μm, and more preferably 15 μm or less. The purity of the aluminum sheet is preferably 99% by mass or more. The transition metal content such as iron, copper, nickel or chromium contained in the aluminum sheet or aluminum sheet alloy is preferably 1% by mass or less.

[184] The positive electrode can be produced by the following method, for example. First, a positive electrode active material, an electroconductive agent, and a binder are suspended in a solvent to prepare a slurry. The slurry is applied to one surface or both reverse surfaces of a positive electrode current collector. Then, the applied slurry is dried to form a layered stack of the layer containing positive electrode active material and the positive electrode current collector. Then, the layered stack is subjected to pressing. The positive electrode can be produced in this way. Alternatively, the positive electrode can also be produced by the following method. First, a positive electrode active material, an electroconductive agent and a binder are mixed to obtain a mixture. Then the mixture is formed into pellets. Then the positive electrode can be obtained by arranging the pellets on the current collector of the positive electrode.

3. ELECTROLYTE

[185] As the electrolyte, for example, a non-aqueous electrolyte can be used. As the non-aqueous electrolyte, a liquid non-aqueous electrolyte or a gel non-aqueous electrolyte can be used. Liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol/L to 2.5 mol/L.

[186] Examples of the electrolyte salt include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenic (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3) , lithium-bistrifluoromethylsulfonylimide (LiTFSI; LiN(CF3SO2)2), lithium-bis(pentafluorosulfonyl)imide (LiBETI; LiN(SO2C2F5)2), lithium-bis(fluorosulfonyl)imide (LiFSI; LiN(SO2F)2), lithium- bis(oxalate)borate (LiBOB; LiC4BO8) and mixtures thereof. The electrolyte is preferably less likely to be oxidized even at high potentials and LiPF6 is most preferred.

[187] Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), or vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), or methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl-tetrahydrofuran (2-MeTHF), or dioxolane (DOX); linear ethers such as dimethoxyethane (DME) or diethoxyethane (DEE); Y—butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used singularly or as a mixed solvent.

[188] The gel-like non-aqueous electrolyte is prepared by obtaining a composite of a liquid non-aqueous electrolyte and a polymeric material. Examples of the polymeric material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO) and mixtures thereof.

[189] The non-aqueous electrolyte may additionally contain at least one compound selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC) and ethylene sulfide (ES) as an additive. The additive suppresses the decomposition of the non-aqueous electrolyte. The content of the additive in the non-aqueous electrolyte is preferably 0.1% by mass to 5% by mass.

4. SEPARATOR

[190] The separator may be made, for example, of a porous film or non-woven fabric of synthetic resin that includes polyethylene, polypropylene, cellulose or polyvinylidene fluoride (PVdF). In view of safety, a porous film made of polyethylene or polypropylene is preferred. This is due to the fact that such a porous film melts at a fixed temperature and thus has the ability to turn off the current.

5. CONTAINER MEMBER

[191] As the container member, for example, a container made of laminate film or a metal container can be used.

[192] The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[193] Like the laminate film, a multilayer film is used that includes multiple layers of resin and a metal layer sandwiched between the resin layers. The resin layer may include, for example, a polymeric material such as polypropylene (PP), polyethylene (PE), nylon or polyethylene terephthalate (PET). The metal layer is preferably made of aluminum sheet or an aluminum sheet alloy in order to reduce weight. The laminate film can be formed into the shape of a container member by heat sealing.

[194] The wall thickness of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[195] The metal casing is made, for example, of aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc or silicon. If the aluminum alloy contains a transition metal such as iron, copper, nickel or chromium, its content is preferably 1% by weight or less.

[196] The shape of the container member is not particularly limited. The shape of the container member can be, for example, flat (thin), square, cylinder, coin or button shape. Depending on the size of the battery, the container member may be, for example, a container member for compact batteries installed in mobile electronic devices, or the container member for large batteries installed in vehicles such as two- to four-wheeled automobiles, rail and similar.

6. NEGATIVE ELECTRODE TERMINAL

[197] The negative electrode terminal may be made of a material that is electrochemically stable at the potential at which Li is inserted into and extracted from the negative electrode active material described above and has electrical conductivity. Specific examples of the material for the negative electrode terminal include copper, nickel, stainless steel, aluminum and aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si. Aluminum or aluminum alloy is preferred as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

7. POSITIVE ELECTRODE TERMINAL

[198] The positive electrode terminal can be made, for example, of a material that is electrically stable in the potential range of 3 V to 5 V (versus Li/Li+) with respect to the oxidation and reduction potential of lithium, and has Electric conductivity. Examples of the material for the positive electrode terminal include aluminum and an aluminum alloy containing one or more selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, Si and the like. The positive electrode terminal is preferably made of the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[199] Next, the secondary battery according to the second embodiment will be described more specifically with reference to the drawings.

[200] Figure 4 is a cross-sectional view that schematically shows an example of a secondary battery according to the first embodiment. Figure 5 is an enlarged cross-sectional view of section A of the secondary battery shown in Figure 4.

[201] The secondary battery 100 shown in Figures 4 and 5 includes a bag-shaped container member 2 shown in Figure 4, an electrode group 1 shown in Figures 4 and 5, and an electrolyte, which is not shown. Electrode group 1 and electrolyte are housed in container member 2. Electrolyte (not shown) is held in electrode group 1.

[202] The pouch-shaped container member 2 is made of a laminate film that includes two resin layers and a metal layer sandwiched between the resin layers.

[203] As shown in Figure 4, electrode group 1 is a group of electrodes rolled into a planar shape. The group of electrodes wound 1 in a flat shape includes a negative electrode 3, a separator 4 and a positive electrode 5, as shown in Figure 5. The separator 4 is sandwiched between the negative electrode 3 and the positive electrode 5.

[204] The negative electrode 3 includes a negative electrode current collector 3a and a layer containing negative electrode active material 3b. The active material according to the first embodiment is included in the layer containing negative electrode active material 3b. In the portion of the negative electrode 3 positioned most externally between the group of coiled electrodes 1, the layer containing active material of negative electrode 3b is formed only on an inner surface of the current collector of the negative electrode 3a, as shown in Figure 4 For other portions of negative electrode 3, layers containing active material of negative electrode 3b are formed on both reverse surfaces of the current collector of negative electrode 3a.

[205] The positive electrode 5 includes a positive electrode current collector 5a and layers containing positive electrode active material 5b formed on both reverse surfaces of the positive electrode current collector 5a.

[206] As shown in Figure 4, a negative electrode terminal 6 and a positive electrode terminal 7 are positioned in the vicinity of the outer peripheral edge of the wound electrode group 1. The negative electrode terminal 6 is connected to a portion of the collector of current from the negative electrode 3a from the externally positioned negative electrode 3. The positive electrode terminal 7 is connected to the positive electrode current collector 5a of the externally positioned positive electrode 5. The negative electrode terminal 6 and the positive electrode terminal 7 extend from an opening of the pouch-shaped container member 2. The pouch-shaped container member 2 is heat-sealed by a layer of thermoplastic resin disposed inside it.

[207] The secondary battery according to the first embodiment is not limited to the secondary battery of the structure shown in Figures 4 and 5 and may be, for example, a battery of a structure as shown in Figures 6 and 7.

[208] Figure 6 is a partially cropped perspective view that schematically shows another example of a secondary battery according to the first embodiment. Figure 7 is an enlarged cross-sectional view of a portion B of the secondary battery shown in Figure 6.

[209] The secondary battery 100 shown in Figures 6 and 7 includes an electrode group 11 shown in Figures 6 and 7, a container member 12 shown in Figure 6, and an electrolyte, which is not shown. The electrode group 11 and the electrolyte are housed in the container member 12. The electrolyte is held in the electrode group 11.

[210] Container member 12 is made of a laminate film that includes two resin layers and a metal layer sandwiched between the resin layers.

[211] As shown in Figure 7, electrode group 11 is a stacked electrode group. The stacked electrode group 11 has a structure in which the positive electrodes 13 and the negative electrodes 14 are stacked alternately with the separator (or separators) 15 sandwiched between them.

[212] The electrode group 11 includes plural positive electrodes 13. Each of the plural positive electrodes 13 includes a positive electrode current collector 13a and layers containing positive electrode active material 13b supported on both reverse surfaces of the current collector of the positive electrode 13a. The electrode group 11 includes plural negative electrodes 14. Each of the plural negative electrodes 14 includes a negative electrode current collector 14a and layers containing negative electrode active material 14b supported on both reverse surfaces of the negative electrode current collector 14a. One end of the negative electrode current collector 14a of each of the negative electrodes 14 projects from the negative electrode 14. The projected negative electrode current collector 14a is electrically connected to a strip-shaped negative electrode terminal 16. The tip of the strip-shaped negative electrode terminal 16 is extended from the container member 12. Although not shown in the drawings, one end of each positive electrode current collector 13a of the positive electrodes 13, which is positioned in the side opposite the projecting end of the negative electrode current collector 14a, projects from the positive electrode 13. The positive electrode current collector 13a projects from the positive electrode 13 is electrically connected to a positive electrode terminal strip-shaped positive electrode terminal 17. The tip of the strip-shaped positive electrode terminal 17 is positioned opposite the negative electrode terminal 16 and extends from the container member 12.

[213] In the electrode and secondary battery according to the first embodiment, the S2/S1 ratio between the carbon atom concentration S2 and the niobium atom concentration S1 on the electrode surface obtained by X-ray photoelectron spectroscopy is from 5 to 100. On the surface of such an electrode, a favorable coating film is provided, which suppresses further reductive decomposition of the electrolyte and has low internal resistance.

[214] Therefore, the use of such an electrode as the negative electrode can further suppress the reductive decomposition of the electrolyte even when the lower threshold value of the negative electrode potential during full charge is set lower than 1.0 V ( against Li+/Li). Therefore, the secondary battery according to the first embodiment including such a negative electrode can achieve high energy density and excellent cycle characteristics.

SECOND MODE

[215] According to a second embodiment, a battery module is provided. The battery module according to the second embodiment includes plural secondary batteries according to the first embodiment.

[216] In the battery module according to the second embodiment, each of the single batteries can be arranged electrically connected in series, in parallel, or in a combination of series connection and parallel connection.

[217] An example of the battery module according to the second embodiment will be described below with reference to the drawings.

[218] Figure 8 is a perspective view that schematically shows an example of the battery module according to the second embodiment. A battery module 200 shown in Figure 8 includes five single batteries 100, four bus bars 21, a positive electrode-side conductor 22, and a negative electrode-side conductor 23. Each of the five single batteries 100 is a secondary battery according to the first modality.

[219] Each bus bar 21 connects a negative electrode terminal 6 of a single battery 100 and a positive electrode terminal 7 of the single battery 100 positioned adjacently. The five single batteries 100 are thus connected in series by the four bus bars 21. That is, the battery module 200 shown in Figure 8 is a battery module of the five in-series connections.

[220] As shown in Figure 8, the positive electrode terminal 7 of the single battery 100 located at one end on the left between the row of five single batteries 100 is connected to the positive electrode side conductor 22 for external connection. In addition, the negative electrode terminal 6 of the single battery 100 located at the other end on the right between the row of five single batteries 100 is connected to the negative electrode side conductor 23 for external connection.

[221] The battery module according to the second embodiment includes the secondary battery according to the first embodiment. Therefore, the battery module according to the second embodiment can achieve high energy density and excellent cycle characteristics.

THIRD MODE

[222] According to a third embodiment, a battery pack is provided. The battery pack includes a battery module according to the second embodiment. The battery pack may include a single secondary battery according to the first embodiment, in place of the battery module according to the second embodiment.

[223] The battery pack according to the third embodiment may additionally include a protective circuit. The protective circuit has a function to control the charging and discharging of the secondary battery. Alternatively, a circuit included in equipment in which the battery pack serves as a power source (e.g., electronic devices, vehicles, and the like) can be used as the protective circuit for the battery pack.

[224] Furthermore, the battery pack according to the third embodiment may additionally comprise an external power distribution terminal. The external power distribution terminal is configured to externally output current from the secondary battery and to input external current to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied through the external power distribution terminal. When the battery pack is charged, the charging current (which includes the regenerative energy from motive power of vehicles such as automobiles) is supplied to the battery pack through the external power distribution terminal.

[225] Next, an example of a drum set according to the third embodiment will be described with reference to the drawings.

[226] Figure 9 is an exploded perspective view that schematically shows an example of the battery pack according to the third embodiment. Figure 10 is a block diagram showing an example of an electrical circuit of the battery pack shown in Figure 9.

[227] A battery pack 300 shown in Figures 9 and 10 includes a housing container 31, a lid 32, protective sheets 33, a battery module 200, a printed circuit board 34, wires 35, and an insulating plate (not shown).

[228] The housing container 31 is configured to house the protective sheets 33, the battery module 200, the printed circuit board 34 and the wires 35. The lid 32 covers the housing container 31 to house the battery module 200 and similar. Although not shown, the opening (or openings) or connection terminal (or terminals) for connecting to external device (or devices) and the like are provided in the housing container 31 and the lid 32.

[229] Protective sheets 33 are arranged on both the inner surfaces of the housing container 31 along the long-side direction and the inner surface along the short-side direction, facing the printed circuit board 34 through the battery module 200 positioned therebetween. The protective sheets 33 are made, for example, of resin or rubber.

[230] The battery module 200 includes single plural batteries 100, a positive electrode-side conductor 22, a negative electrode-side conductor 23, and an adhesive tape 24. The battery module 200 may alternatively include only one battery. only 100.

[231] A single battery 100 has a structure shown in Figures 6 and 7. At least one of the plural single batteries 100 is a secondary battery according to the second embodiment. The plural single batteries 100 are stacked so that the negative electrode terminals 6 and the positive electrode terminals 7, which extend outward, are directed in the same direction. The plural single batteries 100 are electrically connected in series, as shown in Figure 10. The plural single batteries 100 may alternatively be connected in parallel, or connected in a combination of series connection and parallel connection. If the plural single batteries 100 are connected in parallel, the battery capacity increases compared to a housing in which they are connected in series.

[232] Adhesive tape 24 secures the plural single batteries 100. The plural single batteries 100 can be attached using heat shrink tape in place of the adhesive tape 24. In this case, the protective sheets 33 are arranged to have both contact surfaces. side of the battery module 200 and the heat-shrink tape is wrapped around the battery module 200 and the protective sheets 33. Thereafter, the heat-shrink tape is heat-shrinkable to group the single plural batteries 100.

[233] One end of the positive electrode side conductor 22 is connected to the positive electrode terminal 7 of the single battery 100 located lowest in the stack of single batteries 100. One end of the negative electrode side conductor 23 is connected to the negative electrode terminal 6 of the single battery 100 located highest in the stack of single batteries 100.

[234] The printed circuit board 34 includes a positive electrode side connector 341, a negative electrode side connector 342, a thermistor 343, a protective circuit 344, wires 345 and 346, a power distribution terminal external wire 347, a plus-side (positive-side) wire 348a and a minus-side (negative-side) wire 348b. A main surface of the printed circuit board 34 faces the surface of the battery module 200 from which the negative electrode terminals 6 and the positive electrode terminals 7 extend. An insulating plate (not shown) is disposed between the printed circuit board 34 and the battery module 200.

[235] The positive electrode side connector 341 is provided with a through hole. By inserting the other end of the positive electrode side conductor 22 into the through hole, the positive electrode side connector 341 and the positive electrode side conductor 22 become electrically connected. The negative electrode side connector 342 is provided with a through hole. By inserting the other end of the negative electrode-side conductor 23 into the through hole, the negative-electrode-side connector 342 and the negative-electrode-side conductor 23 become electrically connected.

[236] The thermistor 343 is fixed to a main surface of the printed circuit board 34. The thermistor 343 detects the temperature of each single battery 100 and transmits detection signals to the protective circuit 344.

[237] The external power distribution terminal 347 is attached to the other main surface of the printed circuit board 34. The external power distribution terminal 347 is electrically connected to a device (or devices) that exists outside the assembly. battery 300.

[238] The protective circuit 344 is fixed to another main surface of the printed circuit board 34. The protective circuit 344 is connected to the external power distribution terminal 347 via the plus-side wire 348a. The protective circuit 344 is connected to the external power distribution terminal 347 via the minus-side wire 348b. In addition, the protective circuit 344 is electrically connected to the positive electrode side connector 341 via wiring 345. The protective circuit 344 is electrically connected to the negative electrode side connector 342 via wiring 346 Furthermore, the protective circuit 344 is electrically connected to each of the single plural batteries 100 via wires 35.

[239] The protective circuit 344 controls the charging and discharging of the single plural batteries 100. The protective circuit 344 is also configured to interrupt the electrical connection between the protective circuit 344 and the external power distribution terminal 347 to external devices, with based on detection signals transmitted from the thermistor 343 or detection signals transmitted from each single battery 100 or battery module 200.

[240] An example of the detection signal transmitted from the thermistor 343 is a signal indicating that the temperature of the single battery (single batteries) 100 is detected as a predetermined temperature or higher. An example of the detection signal transmitted from each single battery 100 or the battery module 200 is a signal that indicates detection of overcharge, overdischarge and overcurrent of the single battery (or single batteries) 100. When detecting over -charge or the like for each of the 100 single batteries, the battery voltage can be detected, or a positive electrode potential or a negative electrode potential can be detected. In the last housing, a lithium electrode as used as a reference electrode can be inserted into each single battery 100.

[241] It should be noted that, like the protective circuit 344, a circuit included in a device (e.g., an electronic device or an automobile) that uses the battery pack 300 as a power source can be used.

[242] As a battery pack 300 is used, for example, in applications where excellent cycle performance is required when a large current is drawn. More specifically, the battery pack 300 is used as, for example, a power source for electronic devices, a stationary battery, a built-in battery for vehicles, or a battery for rail cars. An example of electronic device is a digital camera. The battery pack 300 is used particularly favorably as a built-in battery.

[243] As described above, the battery pack 300 includes an external power distribution terminal 347. Thereafter, the battery pack 300 can output current from the battery module 200 to an external device and input current from a device external to battery module 200 via external power distribution terminal 347. In other words, when using battery pack 300 as a power source, current from battery module 200 is supplied to an external device When charging the battery pack 300, a charging current from an external device is supplied to the battery pack 300 via the external power distribution terminal 347. If the battery pack 347 300 battery pack is used as a built-in battery, the regenerative energy of a vehicle's driving force can be used as the charging current from the external device.

[244] It should be noted that the battery pack 300 may include plural battery modules 200. In this case, the plural battery modules 200 may be connected in series, in parallel, or connected in a combination of in-series connection and in-line connection. -parallel. The printed circuit board 34 and wires 35 can be omitted. In this case, the positive electrode side conductor 22 and the negative electrode side conductor 23 can be used as the external power distribution terminal.

[245] The battery pack according to the third embodiment includes the secondary battery according to the first embodiment or the battery module according to the second embodiment. From this, the battery pack can exhibit high energy density and is excellent in output performance and lifetime performance at a high temperature.

[246] The battery pack according to the third embodiment includes the secondary battery according to the first embodiment or the battery module according to the second embodiment. Therefore, the battery pack according to the third embodiment can achieve high energy density and excellent cycle characteristics.

FOURTH MODE

[247] According to a fourth embodiment, a vehicle is provided. The battery pack according to the third embodiment is installed in that vehicle.

[248] In the vehicle according to the fourth embodiment, the battery pack is configured, for example, to recover regenerative energy from the motor force of the vehicle.

[249] Examples of the vehicle according to the fourth embodiment include two- to four-wheel hybrid electric automobiles, two- to four-wheel electric automobiles, electric bicycles, and rail cars.

[250] In the vehicle according to the fourth embodiment, the installation position of the battery pack is not particularly limited. For example, the battery pack may be installed in the vehicle's engine compartment, in rear parts of the vehicle, or under seats.

[251] An example of the vehicle according to the fourth embodiment is explained below, with reference to the drawings.

[252] Figure 11 is a cross-sectional view that schematically shows an example of a vehicle according to the fourth embodiment.

[253] A vehicle 400 shown in Figure 11 includes a vehicle body 40 and a battery pack 300 in accordance with the fourth embodiment.

[254] In Figure 11, vehicle 400 is a four-wheeled automobile. As vehicle 400, for example, two- to four-wheel hybrid electric automobiles, two- to four-wheel electric automobiles, electric bicycles, and rail cars can be used.

[255] Such vehicle 400 may have plural battery packs 300 installed. In such an enclosure, the battery packs 300 may be connected in series, connected in parallel, or connected in a combination of series connection and parallel connection.

[256] The battery pack 300 is installed in an engine compartment located at the front of the vehicle body 40. The installation location of the battery pack 300 is not particularly limited. The battery pack 300 may be installed in rear sections of the vehicle body 40, or under a seat. The battery pack 300 can be used as a power source for the vehicle 400. The battery pack 300 can also recover regenerative energy from the driving force of the vehicle 400.

[257] Next, with reference to Figure 12, an aspect of vehicle operation according to the fourth embodiment is explained.

[258] Figure 12 is a view schematically showing another example of the vehicle according to the fourth embodiment. A vehicle 400, shown in Figure 12, is an electric automobile.

[259] Vehicle 400, shown in Figure 12, includes a vehicle body 40, a vehicle power supply 41, a vehicle ECU (electrical control unit) 42, which is a master controller of the vehicle power supply 41, an external terminal (an external power connection terminal) 43, an inverter 44 and a drive motor 45.

[260] Vehicle 400 includes the power supply of vehicle 41, for example, in the engine compartment, in the rear sections of the automobile body, or under a seat. In Figure 12, the position of the vehicle power supply 41 installed in the vehicle 400 is shown schematically.

[261] Vehicle power supply 41 includes plural (e.g., three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communications bus 412.

[262] The three battery packs 300a, 300b and 300c are electrically connected in series. The battery pack 300a includes a battery module 200a and a battery monitoring unit module (e.g., VTM: voltage temperature monitoring) 301a. The battery pack 300b includes a battery module 200b and a battery monitoring unit module 301b. The 300c battery pack includes a 200c battery module and a 301c battery monitoring unit module. Battery packs 300a, 300b and 300c can each be removed independently and can be exchanged for a different battery pack 300.

[263] Each of battery modules 200a to 200c includes plural single batteries connected in series. At least one of the plural single batteries is the secondary battery according to the first embodiment. Battery modules 200a to 200c each charge and discharge via a positive electrode terminal 413 and a negative electrode terminal 414.

[264] In order to collect information related to the safety of the vehicle's power supply 41, the battery management unit 411 communicates with the battery module monitoring units 301a and 301c and collects information such as voltages or temperatures of the single batteries. 100 included in 200a to 200c battery modules included in vehicle power supply 41.

[265] Communication bus 412 is connected between battery management unit 411 and battery module monitoring units 301a to 301c. The communication bus 412 is configured so that multiple nodes (i.e., the battery management unit and one or more battery module monitoring units) share a set of communication lines. Communication bus 412 is, for example, a communication bus configured based on the CAN (Control Area Network) standard.

[266] Battery module monitoring units 301a to 301c measure a voltage and a temperature of each single battery in battery modules 200a to 200c based on commands from battery management unit 411. It is possible, however, to measure temperatures only at multiple points per battery module and temperatures of all single batteries do not need to be measured.

[267] The vehicle power supply 41 may also have an electromagnetic contactor (e.g., a switching unit 415 shown in Figure 12) to switch the connection between the positive electrode terminal 413 and the negative electrode terminal 414. switching unit 415 includes a precharge switch (not shown), which is turned on when battery modules 200a to 200c are charged, and a main switch (not shown), which is turned on when the battery output is supplied to a charge. The precharge switching and main switch include a relay circuit (not shown), which is turned on or off based on a signal supplied to a coil disposed near a switching element.

[268] Inverter 44 converts an input direct current voltage to a high three-phase alternating current (AC) voltage to drive a motor. The three-phase output terminal (or terminals) of the inverter 44 is connected to each three-phase input terminal of the drive motor 45. The inverter 44 controls an output voltage based on control signals from the battery management unit 411 or of vehicle ECU 41, which controls all vehicle operation.

[269] The drive motor 45 is rotated by electrical power supplied from the inverter 44. Rotation is transferred to a drive shaft and wheels W by means of a differential gear unit, for example.

[270] Vehicle 400 also includes a regenerative braking mechanism, although not shown. The regenerative braking mechanism rotates the drive motor 45 when the vehicle 400 is braked and converts kinetic energy into regenerative energy, such as electrical energy. The regenerative energy, recovered in the regenerative braking mechanism, is fed into inverter 44 and converted into direct current. Direct current is fed into the vehicle power supply 41.

[271] One terminal of an L1 connection line is connected via a current detector (not shown) in the battery management unit 411 to the negative electrode terminal 414 of the vehicle power supply 41. The other terminal of the line connection terminal L1 is connected to a negative electrode input terminal of the inverter 44.

[272] One terminal of a connection line L2 is connected via the switching unit 415 to the positive electrode terminal 413 of the vehicle power supply 41. The other terminal of the connection line L2 is connected to a power input terminal 413. positive electrode of inverter 44.

[273] The external terminal 43 is connected to the battery management unit 411. The external terminal 43 is capable of connecting, for example, to an external power supply.

[274] The vehicle ECU 42 cooperatively controls the battery management unit 411 together with other units in response to inputs operated by a trigger or the like, which thereby performs management of the entire vehicle. Security-related data of the vehicle power supply 41, such as a remaining capacity of the vehicle power supply 41, is transferred between the battery management unit 411 and the vehicle ECU 42 via communication lines.

[275] The vehicle according to the fourth embodiment includes the battery pack according to the third embodiment. Therefore, the vehicle according to the fourth embodiment can achieve a long life and a long travel distance.

EXAMPLES

[276] Examples of the present embodiment will be described below. The present invention is not limited to the Examples described below without departing from the spirit of the present invention.

EXAMPLE 1 PREPARATION OF MONOCYCLIC NIOBIUM-TITANIUM COMPOSITE OXIDE

[277] A monocyclic niobium-titanium composite oxide was prepared by a solid phase method. Specifically, first, a titanium dioxide powder (TiO2) and a niobium pentoxide powder (Nb2O5) were mixed to obtain a mixture. In the mixture, the molar ratio between niobium and titanium was 1:1.

[278] Then, this mixture was mixed with ethanol to obtain a mixed solution. Then, this mixed solution was pulverized using a wet ball mill to obtain a primary pulverized sample.

[279] Then, the mixed solution after spraying was filtered and the filtered primary sprayed sample was dried. Then, the dried primary pulverized sample was placed in an alumina crucible and subjected to temporary firing at a temperature of 1000°C for 12 hours.

[280] Then, the powder sample obtained in this way was mixed with ethanol to obtain a mixed solution. Then, this mixed solution was pulverized using a wet ball mill to obtain a secondary pulverized sample.

[281] Then, the mixed solution after spraying was filtered and the filtered secondary sprayed sample was dried. Then, the dried secondary pulverized sample was placed in an alumina crucible and subjected to main firing at a temperature of 1100°C for 12 hours.

[282] Then, the secondary pulverized sample after the main shot was further pulverized to obtain a powder.

[283] When the powder obtained in this way was subjected to XRD measurement, the intensities and 2θ values of all peaks indicated in the XRD pattern obtained were consistent enough with the intensities and 2θ values of peaks described in PDF No. 01- 0771374. Consequently, this powder was confirmed as a monocyclic niobium-titanium composite oxide that has a single phase structure attributed to an Nb2TiO7 phase.

[284] The average particle size of the monocyclic niobium-titanium composite oxide was measured by the same method as the method of measuring the primary particle size of the negative electrode active material particles and the primary particle size (d50) thereof. was 0.6 μm.

PREPARATION OF NEGATIVE ELECTRODE ACTIVE MATERIAL

[285] Next, a negative electrode active material was prepared. Specifically, first, the monocyclic niobium-titanium composite oxide powder obtained by the method described above, sucrose and pure water were mixed to obtain a dispersion. In this dispersion, the concentration of a solute obtained by combining the monocyclic niobium-titanium composite oxide powder and sucrose was 10% by mass. The sucrose addition content was 3.5 parts by mass relative to 100 parts by mass of the monocyclic niobium-titanium oxide composite.

[286] Then, this dispersion was subjected to spray drying to obtain a powder sample. Then, the obtained powder sample was dried at a temperature of 100°C for 12 hours to sufficiently volatilize a solvent. In this way, monocyclic niobium-titanium composite oxide particles supporting an unfired amorphous carbon body were obtained.

[287] Then, this composite oxide was fired under an inert atmosphere at a temperature of 700°C for 1 hour to perform a carbonization treatment. In this way, the negative electrode active material particles containing the film-shaped amorphous carbon body were obtained.

NEGATIVE ELECTRODE PRODUCTION

[288] First, the negative electrode active material particles obtained by the method described above, graphite, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and pure water were mixed to obtain a slurry. This mass ratio of negative electrode active material particles, graphite, CMC and SBR in this slurry was 100:10:5:5.

[289] Then, the slurry was applied to both surfaces of an aluminum sheet. The thickness of the aluminum sheet was 12 μm. Then, the applied slurry was dried to form a layer containing negative electrode active material in a negative electrode current collector. From there, it was pressed to obtain a negative electrode. In this negative electrode, the negative electrode current collector includes a portion that does not support the layer containing negative electrode active material, i.e., a current collector flap.

POSITIVE ELECTRODE PRODUCTION

[290] First, a powder of LiNi0.5Co0.2Mn0.3O2, acetylene black, a carbon nanofiber, polyvinylidene fluoride (PVdF) and N-methylpyrrolidone (NMP) were mixed to obtain a slurry. The mass ratio of LiNi0.5Co0.2Mn0.3O2 powder, acetylene black, carbon nanofiber and PVdF in this slurry was 100:10:10:10.

[291] Then, the slurry was applied to both surfaces of an aluminum sheet. The thickness of the aluminum sheet was 12 μm. Then, the applied slurry was dried to form a layer containing positive electrode active material in a positive electrode current collector. From there, it was pressed to obtain a positive electrode. In this positive electrode, the positive electrode current collector includes a portion that does not support the layer containing positive electrode active material, i.e., a current collector flap.

ELECTRODE GROUP PRODUCTION

[292] First, the negative electrode and positive electrode obtained by the method described above and a strip-shaped separator were prepared. As a separator, a cellulose separator was used. So, I fold this separator in a zigzag pattern. Then, the negative electrode was stacked on the topmost layer of the zigzag-folded separator. Then, the positive electrodes and negative electrodes are alternatively inserted into spaces formed by the zigzag fold of the separator, to obtain a laminate that includes the separator, the negative electrode and the positive electrode. During this stacking, the positive electrode flap of the positive electrode current collector and the negative electrode flap of the negative electrode current collector were arranged so as to project from a side surface of the laminate and so as not to overlap in the stacking direction. Then, a negative electrode terminal was connected to the negative electrode tab protruding from the side surface of the laminate by welding. Then, a positive electrode terminal was connected to the positive electrode tab protruding from the side surface of the laminate by welding. In this way, a group of electrodes was obtained.

PREPARATION OF NON-AQUEOUS ELECTROLYTE

[293] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed to obtain a mixed solvent. The volume ratio of EC and DEC in this mixed solvent was 1:2. Then, lithium hexafluorophosphate (LiPF6) was dissolved in this mixed solvent to prepare a non-aqueous electrolyte. The molar concentration of LiPF6 in this non-aqueous electrolyte was 1 mol/m3.

SECONDARY BATTERY PRODUCTION

[294] Then, the electrode group obtained by the method described above was housed in a container member made of a laminate film. In this case, the negative electrode terminal and the positive electrode terminal were extended to the outside of the container member. Then, the circumference of the laminate film was fused together, except for a part of the circumference. Then, a non-aqueous electrolyte was injected from an unsealed portion of the laminate film, i.e., from an injection hole. Then, the injection hole was fused together to obtain a secondary battery. The discharge capacity of this battery was 3.0 Ah.

COATING FILM FORMATION

[295] The non-aqueous electrolyte secondary battery obtained by the method described above was placed in a thermostat at 25°C. Then, these batteries were subjected to initial charging at a rate of 0.2 C until the battery voltages reached 3.5 V. After the voltage reached 3.5 V, the voltage was maintained for 10 hours. A negative electrode potential when the voltage was 3.5 V was 0.7 V (versus Li+/Li).

[296] Then, the charged battery was subjected to aging. During aging, an aging temperature was set at 25°C and the aging time was set at 24 hours.

[297] Then, the aged battery was discharged at a rate of 0.2 C until the battery voltage reached 1.5 V. Then, a portion of the container member was opened and the pressure was reduced to remove the gas from the inside the container member. The opening was then sealed again. In this way, a non-aqueous electrolyte secondary battery in which the coating film was formed on the surface of the negative electrode active material existing in the vicinity of the negative electrode surface was obtained.

EXAMPLE 2

[298] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that an aging time was changed from 24 hours to 48 hours.

EXAMPLE 3

[299] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that an aging temperature was changed from 25°C to 45°C and an aging time was changed from 24 hours to 12 hours .

EXAMPLE 4

[300] A non-aqueous electrolyte secondary battery was obtained in the same way as that in Example 1 except that an aging temperature was changed from 25°C to 45°C.

EXAMPLE 5

[301] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that an aging temperature was changed from 25°C to 60°C and an aging time was changed from 24 hours to 8 hours .

EXAMPLE 6

[302] A non-aqueous electrolyte secondary battery was prepared in the same way as that described in Example 1 except that an aging temperature was changed from 25°C to 60°C and an aging time was changed from 24 hours to 12 hours .

EXAMPLE 7

[303] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that a negative electrode potential in the fully charged state was changed from 0.7 V (versus Li+/Li) to 0.8 V (versus Li+/Li).

EXAMPLE 8

[304] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that a negative electrode potential in the fully charged state was changed from 0.7 V (versus Li+/Li) to 0.6 V (versus Li+/Li).

EXAMPLE 9

[305] A negative electrode active material was obtained in the same way as that described in Example 1 except that the sucrose addition content was changed from 3.5 parts by mass to 3.6 parts by mass and a treatment temperature of carbonization was changed from 700°C to 750°C.

[306] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

EXAMPLE 10

[307] A negative electrode active material was obtained in the same way as that described in Example 1 except that the sucrose addition content was changed from 3.5 parts by mass to 3.6 parts by mass and a treatment temperature of carbonization was changed from 700°C to 800°C.

[308] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

EXAMPLE 11

[309] A negative electrode active material was obtained in the same way as that described in Example 1 except that the sucrose addition content was changed from 3.5 parts by mass to 3.6 parts by mass and a treatment temperature of carbonization was changed from 700°C to 850°C.

[310] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

EXAMPLE 12

[311] A negative electrode active material was obtained in the same manner as that described in Example 1 except that the carbon source was changed from 3.5 parts by mass of sucrose to 1.1 parts by mass of polyvinyl alcohol (PVA ) and a carbonization treatment temperature was changed from 700°C to 850°C.

[312] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

EXAMPLE 13

[313] A negative electrode active material was obtained in the same manner as that described in Example 1 except that the carbon source was changed from 3.5 parts by mass of sucrose to 5.8 parts by mass of PVA and a temperature of carbonization treatment was changed from 700°C to 850°C.

[314] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

EXAMPLE 14

[315] A negative electrode active material was obtained in the same way as that described in Example 1 except that the carbon source was changed from 3.5 parts by mass of sucrose to 9.1 parts by mass of PVA and a temperature of carbonization treatment was changed from 700°C to 850°C.

[316] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

EXAMPLE 15

[317] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that the type of an electrolyte was changed from LiPF6 to lithium tetrafluoroborate (LiBF4).

EXAMPLE 16

[318] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that LiBF4 was added to a non-aqueous electrolyte. The molar concentration of LiBF4 in the non-aqueous electrolyte was 0.2 mol/m3.

[319] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 17

[320] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that lithium bistrifluoromethylsulfonylimide (LiTFSI; LiN(CF3SO2)2) was added to a non-aqueous electrolyte. The molar concentration of LiTFSI in the non-aqueous electrolyte was 0.2 mol/m3.

[321] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 18

[322] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that lithium bis(pentafluoroethanesulfonyl)imide (LiBETI; LiN (SO2C2F5)2) was added to a non-aqueous electrolyte. The molar concentration of LiBETI in the non-aqueous electrolyte was 0.2 mol/m3.

[323] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 19

[324] The non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that lithium bis(fluorosulfonyl)imide (LiFSI; LiN(SO2F)2) was added to a non-aqueous electrolyte. The molar concentration of LiFSI in the non-aqueous electrolyte was 0.2 mol/m3.

[325] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 20

[326] The non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that lithium bis(oxalate)borate (LiBOB; LiC4BO8) was added to a non-aqueous electrolyte. The molar concentration of LiBOB in the non-aqueous electrolyte was 0.2 mol/m3.

[327] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 21

[328] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that a solvent of a non-aqueous electrolyte was changed from a mixed solvent of EC and DEC to a mixed solvent of EC and methyl ethyl carbonate ( MEC). The volume ratio of EC and MEC in this mixed solvent was 1:2.

[329] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 22

[330] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that a solvent of a non-aqueous electrolyte was changed from a mixed solvent of EC and DEC to a mixed solvent of EC and dimethyl carbonate (DMC) . The volume ratio of EC and DMC in this mixed solvent was 1:2.

[331] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 23

[332] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that vinylene carbonate (VC) was added as an additive to a non-aqueous electrolyte. The VC concentration in this non-aqueous electrolyte was 1% by mass.

[333] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 24

[334] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that fluoroethylene carbonate (FEC) was added as an additive to a non-aqueous electrolyte. The concentration of FEC in this non-aqueous electrolyte was 1% by mass.

[335] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 25

[336] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that ethylene sulfide (ES) was added as an additive to a non-aqueous electrolyte. The concentration of ES in this non-aqueous electrolyte was 1% by mass.

[337] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 26

[338] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that a solvent of a non-aqueous electrolyte was changed from a mixed solvent of EC and DEC to a mixed solvent of propylene carbonate (PC) and DEC , and VC was added as an additive. The volume ratio of PC and DEC in this mixed solvent was 1:2. The VC concentration in this non-aqueous electrolyte was 1% by mass.

[339] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 27

[340] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that a solvent of a non-aqueous electrolyte was changed from a mixed solvent of EC and DEC to a mixed solvent of PC and DEC, and FEC was added as an additive. The volume ratio of PC and DEC in this mixed solvent was 1:2. The concentration of FEC in this non-aqueous electrolyte was 1% by mass.

[341] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

EXAMPLE 28

[342] A non-aqueous electrolyte was obtained in the same way as that described in Example 1 except that a solvent of a non-aqueous electrolyte was changed from a mixed solvent of EC and DEC to a mixed solvent of PC and DEC, and ES was added as an additive. The volume ratio of PC and DEC in this mixed solvent was 1:2. The concentration of ES in this non-aqueous electrolyte was 1% by mass.

[343] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this non-aqueous electrolyte was used.

COMPARATIVE EXAMPLE 1

[344] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that a negative electrode potential during charging was changed from 0.7 V (versus Li+/Li) to 1.0 V ( against Li+/Li).

COMPARATIVE EXAMPLE 2

[345] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that an aging time was changed from 24 hours to 72 hours.

COMPARATIVE EXAMPLE 3

[346] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that an aging temperature was changed from 25°C to 45°C and an aging time was changed from 24 hours to 72 hours .

COMPARATIVE EXAMPLE 4

[347] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that an aging temperature was changed from 25°C to 60°C and an aging time was changed from 24 hours to 72 hours .

COMPARATIVE EXAMPLE 5

[348] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that aging was omitted.

COMPARATIVE EXAMPLE 6

[349] A negative electrode active material was obtained in the same way as that described in Example 1 except that a carbonization treatment temperature was changed from 700°C to 900°C.

[350] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

COMPARATIVE EXAMPLE 7

[351] A negative electrode active material was obtained in the same way as that described in Example 1 except that the sucrose addition content was changed from 3.5 parts by mass to 15.1 parts by mass.

[352] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

COMPARATIVE EXAMPLE 8

[353] A negative electrode active material was obtained in the same way as that described in Example 1 except that the sucrose addition content was changed from 3.5 parts by mass to 1 part by mass.

[354] A non-aqueous electrolyte secondary battery was obtained in the same way as that described in Example 1 except that this negative electrode active material was used.

EVALUATION METHODS SECONDARY PARTICLE SIZE MEASUREMENT

[355] The secondary particle size of the negative electrode active material particles obtained by each of the methods described in Example 1, Examples 9 to 14 and Comparative Examples 6 to 8 was measured by the method described above. As a result, the secondary particle size (d50) was 5.0 μm in any example.

OBSERVATION BY TRANSMISSION ELECTRON MICROSCOPE

[356] The surface state of the negative electrode active material obtained by each of the methods described in Example 1, Examples 9 to 14 and Comparative Examples 6 to 8 was confirmed using a transmission electron microscope (TEM) . As a result, in the negative electrode active material particles obtained by each of the methods described in Example 1, Examples 9 to 11 and Comparative Examples 6 to 8, a portion not covered with the amorphous carbon body was observed in a portion of the surfaces of monocyclic niobium-titanium composite oxide particles. In contrast, in the negative electrode active material particles obtained by each of the methods described in Examples 12 to 14, all surfaces of the monocyclic niobium-titanium composite oxide particles were uniformly coated with the amorphous carbon body. The results are shown in Table 1.

AMORPHOUS CARBON BODY THICKNESS MEASUREMENT

[357] The thickness of the amorphous carbon body contained in the negative electrode active material obtained by each of the methods described in Example 1, Examples 9 to 14 and Comparative Examples 6 to 8 was measured by the method described above. The results are shown in Table 1.

CALCULATION OF RAMAN G-BAND TO RAMAN D-BAND RATIO

[358] The Raman spectrum of the negative electrode active material obtained by each of the methods described in Example 1, Examples 9 to 14 and Comparative Examples 6 to 8 was measured by the method mentioned above, to calculate the IG/ID ratio between the IG peak intensity of a G band and the ID peak intensity of a D band. The results are shown in Table 1.

[359] In the present context, Figure 13 is a graph showing a Raman spectrum according to Example 1. Figure 14 is a graph showing a Raman spectrum according to Comparative Example 6. In Figures 13 and 14, a horizontal axis represents Raman switching and a vertical axis represents scattering intensity. In both spectra shown in Figures 13 and 14, a G band and a D band were detected.

BET-SPECIFIC SURFACE AREA MEASUREMENT

[360] The BET specific surface area of the negative electrode active material obtained by each of the methods described in Example 1, Examples 9 to 14 and Comparative Examples 6 to 8 was measured by the method described above. The results are shown in Table 1.

FILM THICKNESS MEASUREMENT OF COATING FILM

[361] The film thickness of the coating film present on the surface of the negative electrode of each of the non-aqueous electrolyte secondary batteries according to Examples 1 to 28 and Comparative Examples 1 to 8, specifically, on the surface of the layer which contains negative electrode active material was measured by the above method. The results are shown in Table 3.

X-RAY PHOTOELECTRON SPECTROMETRY

[362] The battery obtained by each of the methods described in Examples 1 to 28 and Comparative Examples 1 to 8 was subjected to X-ray photoelectron spectroscopy. That is, the surface of the negative electrode included in each of these batteries was subjected to X-ray photoelectron spectrometry by the method described above to calculate a niobium atom concentration S1, a carbon atom concentration S2, and an atom concentration of S3 phosphorus. The results are shown in Table 3.

[363] In the present context, Figure 15 is a graph showing a narrow-scan spectrum of Nb3d according to Example 1. Figure 16 is a graph showing a narrow-scan spectrum of C1s according to Example 1 Figure 17 is a graph showing a narrow-scan spectrum of P2p according to Example 1. Figure 18 is a graph showing the narrow-scan spectrum of C1s shown in Figure 16 after peak separation. Figure 19 is a graph showing the narrow-scan spectrum of P2p shown in Figure 17 after peak separation. In these Figures, a horizontal geometric axis represents the photoelectron binding energy and a vertical geometric axis represents the number of photoelectrons observed per unit time.

[364] As shown in Figure 18, seven peaks were detected in the C1s spectrum according to Example 1. The seven peaks were detected at the positions of 284.20 eV, 285.23 eV, 286.87 eV, 288.23 eV, 289.43 eV, 290.16 eV and 291.58 eV. The five peaks detected at the positions of 286.87 eV, 288.23 eV, 289.43 eV, 290.16 eV, and 291.58 eV were used as peaks to calculate the S2 carbon atom concentration.

[365] As shown in Figure 19, two peaks were detected in the spectrum of P2p according to Example 1. The two peaks were detected at the positions of 134.50 eV and 137.44 eV. The peak detected at the position of 134.50 eV was used as the peak to calculate the S3 phosphorus atom concentration.

[366] In the present context, Figure 20 is a graph showing a narrow-scan spectrum of Nb3d according to Example 3. Figure 21 is a graph showing a narrow-scan spectrum of C1s according to Example 3 Figure 22 is a graph showing a narrow-scan spectrum of P2p according to Example 3. Figure 23 is a graph showing the narrow-scan spectrum of C1s shown in Figure 21 after peak separation. Figure 24 is a graph showing the narrow-scan spectrum of P2p shown in Figure 22 after peak separation. In these Figures, a horizontal geometric axis represents the photoelectron binding energy and a vertical geometric axis represents the number of photoelectrons observed per unit time.

[367] As shown in Figure 23, seven peaks were detected in the C1s spectrum according to Example 3. The seven peaks were detected at the positions of 283.98 eV, 285.07 eV, 286.76 eV, 288.07 eV, 289.27 eV, 290.34 eV and 291.70 eV. The five peaks detected at the positions of 286.76 eV, 288.07 eV, 289.27 eV, 290.34 eV, and 291.70 eV were used as peaks to calculate the S2 carbon atom concentration.

[368] As shown in Figure 24, three peaks were detected in the spectrum of P2p according to Example 3. The three peaks were detected at the positions of 134.68 eV, 136.30 eV and 137.58 eV. The two peaks detected at positions 134.68 eV and 136.30 eV were used as peaks to calculate the S3 phosphorus atom concentration.

[369] In the present context, Figure 25 is a graph showing a narrow-scan spectrum of Nb3d according to Example 23. Figure 26 is a graph showing a narrow-scan spectrum of C1s according to Example 23 Figure 27 is a graph showing a narrow-scan spectrum of P2p according to Example 23. Figure 28 is a graph showing the narrow-scan spectrum of C1s shown in Figure 26 after peak separation. Figure 29 is a graph showing the narrow-scan spectrum of P2p shown in Figure 27 after peak separation. In these Figures, a horizontal geometric axis represents the photoelectron binding energy and a vertical geometric axis represents the number of photoelectrons observed per unit time.

[370] As shown in Figure 28, seven peaks were detected in the C1s spectrum according to Example 23. The seven peaks were detected at the positions of 284.33 eV, 285.22 eV, 287.02 eV, 288.22 eV, 289.42 eV, 290.23 eV and 291.38 eV. The five peaks detected at the positions of 287.02 eV, 288.22 eV, 289.42 eV, 290.23 eV, and 291.38 eV were used as peaks to calculate the S2 carbon atom concentration.

[371] As shown in Figure 29, two peaks were detected in the spectrum of P2p according to Example 23. The two peaks were detected at the positions of 134.66 eV and 137.45 eV. The peak detected at the position of 134.66 eV was used as the peak to calculate the S3 phosphorus atom concentration.

[372] In the present context, Figure 30 is a graph showing a narrow-scan spectrum of Nb3d according to Comparative Example 1. Figure 31 is a graph showing a narrow-scan spectrum of C1s according to Example Comparative 1. Figure 32 is a graph showing a narrow-scan spectrum of P2p according to Comparative Example 1. Figure 33 is a graph showing the narrow-scan spectrum of C1s shown in Figure 31 after peak separation . Figure 34 is a graph showing the narrow-scan spectrum of P2p shown in Figure 32 after peak separation. In these Figures, a horizontal geometric axis represents the photoelectron binding energy and a vertical geometric axis represents the number of photoelectrons observed per unit time.

[373] As shown in Figure 33, seven peaks were detected in the C1s spectrum according to Comparative Example 1. The seven peaks were detected at the positions of 284.19 eV, 285.21 eV, 286.73 eV, 288, 21 eV, 289.41 eV, 290.60 eV and 291.59 eV. The five peaks detected at the positions of 286.73 eV, 288.21 eV, 289.41 eV, 290.60 eV, and 291.59 eV were used as peaks to calculate the S2 carbon atom concentration.

[374] As shown in Figure 34, two peaks were detected in a spectrum of P2p according to Comparative Example 1. The two peaks were detected at the positions of 134.54 eV and 137.24 eV. The peak detected at the position of 134.54 eV was used as the peak to calculate the S3 phosphorus atom concentration.

ENERGY DENSITY MEASUREMENT

[375] The energy density of the secondary battery obtained by each of the methods described in Examples 1 to 28 and Comparative Examples 1 to 8 was measured. Specifically, first, a battery was placed in a thermostat set at 25°C. Then, the battery was discharged until the battery voltage reached 3.5 V at a rate of 0.2 C. After the voltage reached 3.5 V, the battery was left on standby with that voltage maintained. The total time of constant current charging and constant voltage charging was 10 hours. Then, the battery was discharged at a rate of 0.2 C until the battery voltage reached 1.5 V to obtain a battery discharge curve. In this discharge curve, a horizontal geometric axis represented a discharge capacity (Ah) and a vertical geometric axis represented a battery voltage (V).

[376] Then, from the discharge curve, the electrical power (Wh) of the battery was calculated. Then, by dividing the electrical power by the discharge capacity, the average operating voltage (V) of the battery was obtained. The volume energy density of the battery was calculated from the average operating voltage obtained in this way, the discharge capacity and the volume of the battery. The results are shown in Table 3.

CYCLE TEST

[377] The non-aqueous electrolyte battery according to each of Examples 1 to 28 and Comparative Examples 1 to 8 was subjected to a cycle test. Specifically, first, a battery was placed in a thermostat set at 45°C. Then, the battery was charged until the battery voltage reached 3.0 V at a rate of 1 C. After the voltage reached 3.0 V, this voltage was maintained until the current value reached 0.05 C. Then, the battery was discharged at a rate of 5 C until the battery voltage reached 1.5 V. Constant current charging, constant voltage charging, and constant current discharging were repeated as a cycle. Between cycles, an interval of 10 minutes was set. This cycle was repeated until the retention ratio of battery discharge capacity to battery discharge capacity after 1 cycle was 80%. The results are shown in Table 3.

[378] The data in Examples 1 to 28 and Comparative Examples 1 to 8 have been summarized in Tables 1 to 3 below. TABLE 1

[379] In Table 1 above, in a column labeled "Carbon Source", between columns under the heading "Amorphous Carbon Body Preparation Method", the type of carbon source used as the carbon body raw material amorphous is described. In a column labeled “Carbon source addition content (parts by mass)”, the carbon source addition content in relation to 100 parts by mass of the monocyclic niobium-titanium oxide composite is described. In a column labeled "carbonization treatment temperature (°C)", a temperature during a carbonization treatment is described.

[380] In Table 1 above, the thickness of the amorphous carbon body is described in a column labeled "Thickness (nm)" in columns below the heading "Amorphous carbon body".

[381] Furthermore, in Table 1 above, in a column labeled "IG/ID" in the columns below the heading "Negative Electrode Active Material", the ratio of a Raman G band to a Raman D band obtained by spectrometry of Raman is described. In a column labeled "TEM observation", the results obtained by observation using a transmission electron microscope are described. An "uncoated portion" means that a portion not covered with the amorphous carbon body is present on a part of the surface of the monocyclic niobium-titanium oxide composite. The term "favorable uniformity" means that the amorphous carbon body is sustained in a dispersed state uniformly on the surfaces of the monocyclic niobium-titanium composite oxide particles. In a column labeled "Specific surface area (m2/g)", the specific surface area of the negative electrode active material is described. TABLE 2

[382] In Table 2 above, in a column labeled "electrolyte salt" between columns under the heading "Non-aqueous electrolyte", the type of the electrolyte salt is described. In a column labeled "Non-aqueous solvent", the type of non-aqueous solvent is described. In a column labeled "Additive", the type of additive is described.

[383] In Table 2 above, in a column labeled “Negative electrode potential (V versus Li+/Li)” between columns under the heading "Aging condition", a negative electrode potential (versus Li+/Li) during aging is described. In a column labeled "Temperature (°C)", an aging temperature is described. In a column labeled "time", an aging time is described.

[384] In Table 2 above, the thickness of the coating film provided on the surface of the negative electrode is described in a column under the heading "film thickness (nm)". TABLE 3

[385] In Table 3 above, in a column labeled "S1 (atm%)" between columns under the heading “XPS measurement result”, the niobium atom concentration S1 obtained by the method described above is described. column labeled "S2 (atm%)", the carbon atom concentration S2 obtained by the method described above is described. In a column labeled "S3 (atm%)", the phosphorus atom concentration S3 obtained by the method described above is described. above is described. In a column labeled "S2/S1", the ratio between the carbon atom concentration S2 and the niobium atom concentration S1 is described. In a column labeled "S3/S1", the ratio between the phosphorus atom concentration S3 and the niobium atom concentration S1 are described.

[386] In Table 3 above, the number of cycles when the capacity retention ratio obtained in the above cycle test reaches 80% is described in a column below the heading "Cycle Characteristics (number)". In a column below the heading "Energy density (Wh/L)", the electrical power per unit volume of the battery is described.

[387] As shown in Table 3, the cycle characteristics of the battery according to each of Examples 1 to 28 in which the S2/S1 ratio between the carbon atom concentration S2 and the niobium atom concentration S1 was 5 to 100 was more excellent compared to those of the battery according to each of Comparative Examples 1 and 5 to 8 in which the S2/S1 ratio was lower than 5 and in Comparative Examples 2 to 4 in which the S2/S1 ratio was higher than 100. This is considered as the reason why a favorable coating film that functions as a passive state is formed on the surfaces of the negative electrode active material particles positioned on the negative electrode surface.

[388] Therefore, the battery according to each of Examples 1 to 28 in which the S2/S1 ratio was 5 to 100 could achieve high energy density and excellent cycle characteristics.

[389] As is apparent from Example 1 and Examples 24 to 26 in which only the presence or absence of the additive differed between experimental examples shown in Tables 2 and 3, by adding the additive to the non-aqueous electrolyte, the characteristics battery cycle time can be improved.

[390] As shown in Tables 1 and 3, even when the raw material of the amorphous carbon body, that is, the carbon source was changed, excellent cycle characteristics could be measured.

[391] As shown in Tables 2 and 3, even when the type of electrolyte salt or non-aqueous solvent was changed, excellent cycle characteristics could be achieved.

[392] In the electrode and secondary battery according to at least one embodiment described above, the S2/S1 ratio between the carbon atom concentration S2 and the niobium atom concentration S1 on the electrode surface obtained by photoelectron spectroscopy of X-ray is from 5 to 100. On the surface of such an electrode, a favorable coating film which suppresses further reductive decomposition of the non-aqueous electrolyte and has low internal resistance is provided.

[393] Therefore, the use of such an electrode as the negative electrode can further suppress the reductive decomposition of the electrolyte even if the lower threshold value of the negative electrode potential during charging is set lower than 1.0 V (contra Li+/Li). Therefore, the secondary battery according to at least one embodiment including such a negative electrode can achieve high energy density and excellent cycle characteristics.

[394] Although certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the inventions. In fact, the innovative methods and systems described in this document can be incorporated in a variety of other ways; Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying drawings and their equivalents are intended to cover such forms or modifications as falling within the scope and spirit of the inventions.

Claims (11)

1. Electrode characterized by the fact that it comprises particles of active material, wherein: the particles of active material contain monoclinic niobium-titanium composite oxide particles and an amorphous carbon body covering at least a part of the surfaces of the oxide particles monoclinic niobium-titanium composite; at least a part of the surface of the amorphous carbon body is covered with a carbon-containing coating film, the coating film having a thickness of 10 nm to 150 nm; a ratio of S2/S1 between a carbon atom concentration S2 and a niobium atom concentration S1 on an electrode surface, according to X-ray photoelectron spectroscopy, is 5 to 100; the niobium atom concentration S1 is an area intensity for an Nb3d-related peak; and the S2 carbon atom concentration is a total of area intensities for peaks related to C1s within a range of 286 eV to 294 eV and the peaks comprising a peak attributed to a C-O bond, a peak attributed to a of C=O, a peak attributed to a C(=O)- O bond, and a peak attributed to a CO32- bond. 2. Electrode, according to claim 1, characterized by the fact that: the surface of the electrode additionally comprises a phosphorus atom, and a ratio of S3/S1 between a concentration S3 of the phosphorus atom and the concentration of niobium atom S1 on the electrode surface, according to X-ray photoelectron spectroscopy, is 0.3 to 20; the S3 concentration of the phosphorus atom is an area intensity for a P2p-related peak within a range of 133 eV to 137 eV and attributed to a PFxOy bond; x is from 0 to 1; and y is more than 0 and 1 or less. 3. Electrode according to claim 1 or 2, characterized in that a thickness of the amorphous carbon body is 1 nm to 10 nm. 4. Electrode according to any one of claims 1 to 3, characterized by the fact that: a Raman spectrum of the active material particles in accordance with Raman spectroscopy has a G band within a range of 1,530 cm-1 to 1,630 cm-1 and a D band within a range of 1,280 cm-1 to 1,380 cm-1; and an IG/ID ratio between the G-band IG peak intensity and the D-band ID peak intensity is 1.2 or less. 5. Secondary battery characterized by the fact that it comprises: the electrode, as defined in any one of claims 1 to 4, as a negative electrode; a positive electrode; and an electrolyte. 6. Secondary battery according to claim 5, characterized by the fact that the electrolyte contains at least one compound selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC) and ethylene sulfite ( ES). 7. Battery assembly characterized by the fact that it comprises the secondary battery, as defined in claim 5 or 6. 8. Battery assembly according to claim 7, characterized in that it additionally comprises: an external power distribution terminal; and a protective circuit. 9. Battery pack according to claim 7 or 8, characterized in that: the battery pack includes a plurality of secondary batteries; and the plurality of secondary batteries are electrically connected in series, in parallel, or in combination of series and parallel. 10. Vehicle characterized by the fact that it comprises the battery assembly, as defined in any one of claims 7 to 9. 11. Vehicle, according to claim 10, characterized by the fact that it comprises a mechanism configured to convert the vehicle's kinetic energy into regenerative energy.