Electrodes, batteries, and battery packs

Abstract

The present invention provides an electrode capable of suppressing corrosion of a current collector, a battery equipped with this electrode, and a battery pack. [Solution] According to the embodiment, an electrode 400 is provided which includes a current collector 401 and an active material-containing layer 402 supported on the current collector 401. The active material-containing layer 402 includes an active material, a conductive agent including a carbon material, and a water-soluble binder. The first carbon ratio based on backscattered electron images measured by a scanning electron microscope from the current collector 401 to 1 μm in the active material-containing layer 402 is lower than the second carbon ratio based on backscattered electron images measured by a scanning electron microscope at a position corresponding to 50% of the thickness of the active material-containing layer 402.

Description

Technical Field

[0001] Embodiments of the present invention relate to electrodes, batteries, and battery packs.

Background Art

[0002] As an electrode for a secondary battery, there is known one produced by applying a slurry containing an active material to a current collector such as an Al foil, drying it, and pressing it. For example, when water is used as a dispersion medium of the slurry, the current collector corrodes. Suppression of this corrosion has been demanded.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide an electrode capable of suppressing corrosion of a current collector, a battery including this electrode, and a battery pack.

Means for Solving the Problems

[0005] According to an embodiment, an electrode including a current collector and an active material-containing layer supported on the current collector is provided. The active material-containing layer contains an active material, a conductive agent including a carbon material, and a water-soluble binder. A first carbon ratio based on a backscattered electron image measured by a scanning electron microscope up to 1 μm from the current collector in the active material-containing layer is lower than a second carbon ratio based on a backscattered electron image measured by a scanning electron microscope at a position corresponding to 50% of the thickness of the active material-containing layer.

[0006] According to one embodiment, a battery is provided that has electrodes according to the embodiment.

[0007] Furthermore, according to the embodiment, a battery pack including the battery of the embodiment is provided. [Brief explanation of the drawing]

[0008] [Figure 1] A plan view showing an example of an electrode in an embodiment. [Figure 2] A cross-sectional view of the electrode shown in Figure 1, cut along the line II-II. [Figure 3] A cross-sectional view of the electrode shown in Figure 1, cut along the line III-III. [Figure 4] A cross-sectional view showing a magnified portion of the cross-section shown in Figure 2. [Figure 5] A partially cutaway cross-sectional view of a secondary battery according to an embodiment. [Figure 6] Side view of the battery in Figure 5. [Figure 7] A cross-sectional view of the secondary battery of the embodiment, cut in a direction perpendicular to the terminal extension direction. [Figure 8] Enlarged cross-sectional view of section A in Figure 7. [Figure 9] A perspective view showing an example of a battery pack including a secondary battery of an embodiment. [Figure 10] An exploded perspective view of the battery pack of the embodiment. [Figure 11] Figure 10 is a block diagram showing the electrical circuit of the battery pack. [Modes for carrying out the invention]

[0009] The causes of corrosion in aluminum-containing current collectors are presumed to be as follows: The slurry applied to the current collector is prepared by dispersing components such as active material, binder, and conductive agent in an aqueous solvent. A water-soluble binder is used as the binder. Carbon material is used as the conductive agent. Water-soluble binders have high hygroscopicity and water retention properties. Therefore, even if the electrodes are stored in a low-humidity environment, a small amount of moisture is mixed into and retained within the electrodes. As a result, corrosion occurs in the aluminum-containing current collector. If the active material contains alkaline components derived from the raw materials, the alkaline components dissolve in the small amount of moisture. This exposes the aluminum-containing current collector to an alkaline environment, causing the corrosion reaction to progress.

[0010] Furthermore, when moisture enters the electrode, the carbon material within the electrode reduces oxygen, generating an alkaline aqueous solution. This alkaline aqueous solution, along with the Al current collector and the conductive agent or active material, constitutes a local cell (Al / alkaline aqueous solution / conductive agent or active material). It is believed that this local cell formation leads to the progression of galvanic corrosion. Therefore, the Al / alkaline aqueous solution / conductive agent local cell is considered to be the main factor accelerating Al corrosion.

[0011] To suppress corrosion of aluminum-containing current collectors, methods such as using pH adjusters to change the slurry from alkaline to neutral, removing excess lithium contained in the active material, and applying a protective layer of polymer or other material to the aluminum-containing current collector have been considered. However, using pH adjusters may cause undesirable reactions such as proton exchange with the lithium contained in the active material. Removing excess lithium and forming a protective layer result in high material or process costs. Moreover, these methods do not sufficiently suppress corrosion.

[0012] Through diligent research, the inventors have discovered for the first time that corrosion can be suppressed by reducing the contact points between the Al-containing current collector and the carbon material. Furthermore, the inventors have also discovered that corrosion can be suppressed by reducing the contact points between the current collector and the carbon material in current collectors containing materials other than Al, such as stainless steel, Cu, Zn, Ni, Sn, or Pb. Embodiments will be described below. First, the electrode of the first embodiment will be described. <First Embodiment> The electrode of the first embodiment includes a current collector and an active material-containing layer. The active material-containing layer is supported on one or both sides of the current collector. The active material-containing layer includes an active material, a conductive agent containing a carbon material, and a water-soluble binder. The first carbon ratio, based on backscattered electron images measured by a scanning electron microscope in the portion of the active material-containing layer up to 1 μm from the current collector, is lower than the second carbon ratio, based on backscattered electron images measured by a scanning electron microscope at a position corresponding to 50% of the thickness of the active material-containing layer.

[0013] The electrode of the first embodiment will be described with reference to Figures 1 to 3. In Figures 1 to 3, the z-axis direction is assumed to be parallel to the thickness direction of the electrode. The x-axis direction intersects perpendicularly with the z-axis direction. The x-axis direction is assumed to be parallel to the short side direction of the electrode. The y-axis direction intersects perpendicularly with both the x-axis and z-axis directions. The y-axis direction is assumed to be parallel to the long side direction of the electrode.

[0014] The electrode 400 includes a current collector 401 and an active material-containing layer 402. The current collector 401 is strip-shaped or rectangular. The active material-containing layer 402 is supported on both sides (both main surfaces) of the current collector 401, except for one end 403 in the short-side direction x. The active material-containing layer 402 contains an active material, a conductive agent containing carbon material, and a water-soluble binder. In the active material-containing layer 402, the first carbon content A in the range up to a distance of 1 μm parallel to the thickness direction z from one main surface of the current collector 401 is measured from backscattered electron images measured by a scanning electron microscope. In addition, in the active material-containing layer 402, the second carbon content B at a position corresponding to 50% of the thickness T of the active material-containing layer from the same main surface of the current collector 401 is measured from backscattered electron images measured by a scanning electron microscope. The first carbon content A is lower than the second carbon content B. Furthermore, one end 403 of the current collector 401 in the short-side direction does not support the active material-containing layer 402 and can function as a current-collecting tab. The position of the current-collecting tab is not limited to one end of the current collector 401 in the short-side direction, but may be at both ends of the current collector 401 in the short-side direction, for example. Alternatively, the current-collecting tab may extend from one or more locations on the long side of the current collector 401.

[0015] By making the first carbon ratio A lower than the second carbon ratio B, the contact points between the current collector 401 and the conductive carbon material can be reduced. As a result, localized battery formation can be prevented, and corrosion of the current collector due to pitting corrosion, etc., can be suppressed. When corrosion of the current collector is suppressed, the decrease in the peel strength of the electrode 400 can be suppressed, and the decrease in the contact area between the current collector 401 and the active material-containing layer 402 that occurs with the use of the electrode can be suppressed. Therefore, even if the contact points between the current collector 401 and the carbon material are reduced, the resistance remains low, and the increase in sheet resistance that occurs with the use of the electrode can be suppressed. This can improve the rate characteristics of the battery.

[0016] The electrodes should preferably satisfy the following equation (1).

[0017] A / B ≤ 0.5 (1) However, A represents the first carbon content, and B represents the second carbon content.

[0018] By satisfying equation (1), the corrosion suppression effect can be enhanced by reducing the contact points between the current collector and the carbon material. Therefore, it becomes possible to suppress the increase in electrode sheet resistance over a long period of time.

[0019] A more preferable range is 0.02 ≤ A / B ≤ 0.5. By setting A / B to between 0.02 and 0.5, a high corrosion suppression effect can be obtained while ensuring the conductivity of the active material-containing layer.

[0020] On the surface of the carbon material in contact with the current collector, it is desirable that the ratio of β to α (β / α), where α is the oxygen content (at%) and β is the carbon content (at%), be 0.6 or greater. It is desirable that the carbon material in contact with the current collector is located within 0.5 μm of the current collector surface, parallel to the thickness direction z. The oxygen content α (at%) is presumed to originate from the binder. By setting the ratio (β / α) within the above range, the carbon material coated with a binder can be located near the current collector. This is expected to reduce contact between the carbon material and the current collector. As a result, an electrode with excellent rate performance and charge / discharge cycle life can be realized.

[0021] The following provides a detailed explanation of the current collector and the active material-containing layer.

[0022] The current collector is not particularly limited as long as it is formed from a conductive material. Examples of current collectors include those containing one or more conductive materials selected from the group consisting of Al, stainless steel, Cu, Zn, Ni, Sn, and Pb. In addition to the above types of conductive materials, the current collector may contain unavoidable impurities. A preferred current collector is one containing Al.

[0023] Al may be a pure metal or an alloy. Current collectors containing Al may also contain elements other than Al. Examples of elements other than Al include Si, Fe, Mn, Mg, Cu, Cr, Zn, Ga, V, Ni, B, Zr, and Ti. The types of elements other than Al can be one or more. It is desirable that the content of elements other than Al in an Al-containing current collector be 0.75 wt% or less.

[0024] The form of the current collector can be foil, plate, sheet, etc.

[0025] The thickness of the current collector can be 20 μm or less. More preferably, it can be 15 μm or less.

[0026] The active material is not particularly limited as long as it is capable of intercalating and deintercalating alkali metal ions such as lithium ions. The active material can consist of one or more types.

[0027] An active material is desirable in which the pH of the aqueous dispersion containing 40 wt% of the active material is between 5 and 9. The aqueous dispersion is a slurry in which the active material is dispersed in water so that its proportion to the total weight is 40 wt%. An active material with an aqueous dispersion pH between 5 and 9 may contain alkaline impurities such as alkaline components derived from the raw materials. This active material can suppress the rise in pH when moisture is introduced into the electrode. Active materials that contain Li from the time of synthesis will have an aqueous dispersion pH outside the range of 5 to 9.

[0028] The pH of the aqueous dispersion is as follows: An aqueous dispersion containing 40 wt% of the active material is placed in a sealed container and allowed to stand at 80°C for 24 hours. After that, the active material is removed using filter paper, and the pH of the solution is measured. For pH measurement, for example, the glass electrode method is used.

[0029] Examples of active materials whose aqueous dispersion has a pH of 5 to 9 include water-insoluble metal oxides, alloys, and alkali metal phosphate compounds. Examples of water-insoluble metal oxides include oxides of one or more elements selected from the group consisting of Si, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Nb, Sn, and Sb (referred to as the first element), hydroxides of the first element, fluorides of the first element, and solid solutions of the first element. Examples of alloys include those containing one or more elements selected from the group consisting of Si, P, S, Zn, Sn, and Bi (referred to as the second element). Examples of alkali metal phosphate compounds include manganese phosphate, nickel phosphate, substances consisting of cobalt phosphate and alkali metals, lithium iron phosphate, solid solutions thereof, and partial fluorides.

[0030] A more desirable active material is one whose aqueous dispersion has a pH in the range of 6 to 8. This active material is preferably a compound that does not contain alkali metals such as Li. Examples of such active materials include oxides of the first element, hydroxides of the first element, solid solutions of the first element, and alloys containing the second element.

[0031] Further desirable active materials are niobium-containing oxides, titanium-containing oxides, and lithium iron phosphate.

[0032] Examples of titanium-containing oxides include orthorhombic titanium oxide, monoclinic titanium oxide, rutile titanium oxide, anatase titanium oxide, and orthorhombic titanium-containing oxide. For each crystal structure of titanium oxide, the composition before charging is TiO2, and the composition after charging is Li x It can be represented as TiO2 (where x is 0 ≤ x ≤ 1). Furthermore, the pre-charge structure of monoclinic titanium oxide can be represented as TiO2(B).

[0033] Examples of niobium-containing oxides include niobium oxide, niobium-titanium-containing oxide, niobium-tungsten-containing oxide, and niobium-titanium-molybdenum-containing oxide.

[0034] Examples of niobium oxides include Nb2O5.

[0035] Examples of niobium-titanium-containing oxides include monoclinic niobium-titanium-containing oxides, Ti2Nb2O9, and Ti2Nb 10 O 29 TiNb 14 O 37 TiNb 24 O 62 This includes substituted niobium titanium composite oxides in which at least a portion of Nb and / or Ti is substituted with a different element. Examples of substituted elements include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, and Al. A substituted niobium titanium composite oxide may contain one substituted element or two or more substituted elements.

[0036] Examples of monoclinic niobium titanium-containing oxides include those represented by the general formula Li c TiNb d O7 (0 ≦ c ≦ 5, 1 ≦ d ≦ 4). A more preferred composition is TiNb2O7.

[0037] Examples of monoclinic niobium titanium-containing oxides include compounds represented by Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. Each subscript in the composition formula is 0 ≦ x ≦ 5, 0 ≦ y < 1, 0 ≦ z < 2, -0.3 ≦ δ ≦ 0.3.

[0038] Other examples of monoclinic niobium titanium-containing oxides include compounds represented by Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula is 0 ≦ y < 1, 0 ≦ z < 2, -0.3 ≦ δ ≦ 0.3.

[0039] Examples of niobium tungsten-containing oxides include Nb 14 W3O 44 , Nb 16 W5O 55 , Nb 18 W8O 69 and the like.

[0040] Examples of niobium titanium molybdenum-containing oxides include those represented by the general formula Li a Ti b Nb 2-2d Mo c+2d O 2b+5+3c(It is preferable that the subscripts a, b, c, and d are respectively within the ranges of 0 ≦ a ≦ b + 4 + 3c, 0.3 ≦ b ≦ 1.6, 0.3 ≦ c < 1.6, and 0 ≦ d < 0.4) A cubic titanium-niobium-molybdenum composite oxide represented by the general formula Li a M b NbMo c O d where M is any one or more selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y, and Si, and 0 ≦ a ≦ b + 2 + 3c, 0 ≦ b ≦ 1.4, 0 ≦ c ≦ 0.5, and 2.33 ≦ d / (1 + b + c) ≦ 2.50, and the composite oxide is included, etc.

[0041] Examples of lithium iron phosphate include Li x FePO4 (0 < x ≦ 1.1), Li x Fe 1-y Mn y PO4 (0 < x ≦ 1.1, 0 ≦ y ≦ 1), etc.

[0042] The active material particles may be in the form of primary particles or secondary particles in which the primary particles are aggregated. Also, the primary particles and secondary particles may be mixed.

[0043] The content of the active material in the active material-containing layer can be 85 wt% or more and 97 wt% or less.

[0044] The conductive agent includes a carbon material. Examples of the carbon material include carbon nanotubes, acetylene black, carbon black, coke (it is desirable that the average particle diameter is 10 μm or less and the heat treatment temperature is 800 °C to 2000 °C), carbon fiber, graphite, etc. The conductive agent may consist only of a carbon material or may include a conductive agent other than the carbon material. Examples of the conductive agent other than the carbon material include metal compound powders such as TiO, TiC, TiN, etc., and metal powders such as Al, Ni, Cu, Fe, etc. The type of the conductive agent can be one kind or two or more kinds.

[0045] The conductive agent can be in the form of, for example, granules, flakes, fibers, etc.

[0046] The content of the conductive agent in the active material-containing layer can be between 0.2 wt% and 5 wt%.

[0047] The binder includes a water-soluble binder. Examples of water-soluble binders include carboxymethylcellulose, carboxymethylcellulose salts (e.g., sodium carboxymethylcellulose, lithium carboxymethylcellulose), polyacrylic acid, sodium polyacrylate, polyacrylonitrile, polytetrafluoroethylene, and copolymers thereof. The presence of a water-soluble binder in the electrode can be confirmed by infrared spectroscopy (IR). The binder may also contain binders other than water-soluble binders (e.g., hydrophobic binders). There may be one or more types of binders.

[0048] The binder content in the active material-containing layer can be between 1 wt% and 5 wt%.

[0049] The electrodes can be fabricated, for example, by the first method or the second method.

[0050] The first method is described below. An active material, conductive agent, and binder are suspended in a solvent to obtain a first slurry in which the proportion of carbon material is 0.1 wt% to 5 wt%. A second slurry is obtained in which the proportion of carbon material is 0.2 wt% to 10 wt% by suspending the active material, conductive agent, and binder in a solvent. For example, water is used as the solvent for each slurry. After applying the first slurry to the current collector, the second slurry is applied on top of the first slurry. The resulting laminate is dried at a rate that removes the solvent as quickly as possible. Rapid drying allows the binder and carbon material in the slurry to diffuse onto the electrode surface, thus forming a concentration gradient. The drying rate should preferably be within a range that does not cause cracks in the active material-containing layer due to stress concentration, or cause the active material-containing layer to peel off from the current collector. Drying can be performed, for example, by leaving the laminate in a drying oven at 120°C or higher for 0.5 minutes or more. After drying, the laminate is pressed to obtain the electrode.

[0051] Next, the second method will be described. The active material, conductive agent, and binder are suspended in a solvent to obtain a slurry in which the weight ratio of the binder to the weight of the carbon material (weight of binder / weight of carbon material) is 3 or less. For example, water is used as the solvent for the slurry. The slurry is applied to a current collector. The resulting laminate is dried. The drying rate can be carried out under the same conditions as described in the first method. As a result, the binder and carbon material in the slurry diffuse to the electrode surface, so that a concentration gradient can be formed. The electrode is obtained by pressing the dried laminate.

[0052] In both the first and second methods, the electrodes may be cut as needed to achieve the desired size. Cutting can be done after drying or after pressing.

[0053] Next, we will explain the methods for measuring the primary carbon content A, the secondary carbon content B, the atomic weight ratio of oxygen to carbon, and the composition of the active material in the electrode.

[0054] The first carbon fraction A and the second carbon fraction B are measured from backscattered electron images obtained by scanning electron microscopy. On the other hand, the atomic weight ratio of oxygen to carbon is measured by scanning electron microscope-energy dispersive X-ray spectrometry (SEM-EDX).

[0055] If the electrode to be measured is integrated into the battery, remove the electrode (positive or negative) from the battery using the method described below.

[0056] The battery is disassembled under an argon atmosphere, and the electrode (positive or negative electrode) to be measured is removed. The electrode is washed two or three times with a solvent consisting of dimethyl carbonate under an argon atmosphere. Then, after vacuum drying at 100°C, the measurement is performed using the method described below.

[0057] A cross-section is cut from the electrode by ion milling. The cross-section is a section cut along the thickness direction of the electrode. From the SEM image of the cross-section, positions 0.5 μm away from the surface of the current collector, 1 μm away, and a position corresponding to 50% of the thickness of the active material-containing layer are determined, parallel to the thickness direction of the active material-containing layer. The SEM image is a backscattered electron image with a field of view of 30,000 to 50,000 times. The SEM image is acquired so that the SEM field of view fits within the thickness direction of the electrode. Also, five SEM images are acquired so that the fields of view do not overlap. The SEM image (backscattered electron image) is subjected to contrast binarization to separate the active material portion x, which appears white, from the carbon material portion y, which appears black. The active material portion is the part of the active material-containing layer other than the carbon material portion. The ratio of the carbon material portion y to the active material portion x in the region up to 1 μm from the current collector is defined as the first carbon ratio A (=y / x). Furthermore, the ratio of the carbon material portion y to the active material portion x at a position corresponding to 50% of the thickness of the active material-containing layer is defined as the second carbon ratio B (=y / x).

[0058] Here, the method for measuring the thickness of the active material-containing layer will be explained with reference to Figure 4. Figure 4 schematically shows an example of the above cross-section. For example, it can be determined by observing the cross-section exemplified in Figure 4 with a scanning electron microscope (SEM). At four locations (for example, shown by the dashed lines in Figure 4) that divide the area observed at a magnification of 1000x into five equal parts, the distance between the contact point of the active material-containing layer 402 and the current collector 401 and the surface 404 of the active material-containing layer that does not contact the current collector 401 is measured, and the average of the measured values ​​obtained at the four points is taken as the thickness of the active material-containing layer T. In Figure 4, the distance from the surface of the current collector 401 that corresponds to 50% of the thickness of the active material-containing layer T is shown as T / 2.

[0059] Secondary electron images are acquired by SEM at the same electrode cross-section from which the above SEM images (backscattered electron images with a field of view of 30,000 to 50,000x) were obtained. From the obtained secondary electron images, an arbitrary carbon material is selected from the carbon material located at a distance of 0.5 μm parallel to the electrode thickness direction z from the surface of the current collector 401. Elemental analysis by EDX is performed on five SEM images in which only the selected carbon material is included in the SEM field of view. This allows for the measurement of oxygen content α (at%) and carbon content β (at%) for each SEM image. The average values ​​of the measurement results are taken as oxygen content α (at%) and carbon content β (at%). The atomic weight ratio of oxygen to carbon is obtained by calculating oxygen content α (at%) / carbon content β (at%) × 100. <Active material> The crystal structure and elemental composition of the active material can be determined by powder X-ray diffraction (XRD) and inductively coupled plasma (ICP) emission spectroscopy.

[0060] According to the electrode of the first embodiment described above, by making the first carbon ratio A, based on the backscattered electron image measured by a scanning electron microscope, lower than the second carbon ratio B, also based on the backscattered electron image measured by a scanning electron microscope, the contact points between the current collector and the conductive carbon material can be reduced. As a result, localized battery formation can be prevented, and current collector corrosion such as pitting corrosion can be suppressed. When corrosion of the current collector is suppressed, the decrease in the peel strength of the electrode can be suppressed. Therefore, even if the contact points between the current collector and the carbon material are reduced, the resistance remains low, and the increase in sheet resistance associated with the use of the electrode can be suppressed. This makes it possible to improve the rate characteristics of the battery. <Second Embodiment> The battery of the second embodiment includes the electrode of the first embodiment as at least one of the positive or negative electrode. The battery also includes an electrolyte. The battery may further comprise a separator disposed between the positive and negative electrodes. The negative electrode, positive electrode, and separator may constitute an electrode group. The electrolyte may be held in the electrode group. The structure of the electrode group is not limited and can be, for example, a stacked type, a wound type, etc. The battery may further comprise an outer casing member that houses the electrode group and the electrolyte.

[0061] Furthermore, the battery may further include a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

[0062] The battery in question may be a rechargeable battery, for example, a lithium rechargeable battery. Furthermore, the rechargeable battery may include a non-aqueous electrolyte rechargeable battery containing a non-aqueous electrolyte.

[0063] When the electrodes of the embodiment are used as the positive or negative electrode, the electrodes described below can be used as the opposite electrode (also called the counter electrode).

[0064] The opposite electrode comprises a current collector and an active material-containing layer. The active material-containing layer is supported on one or both sides of the current collector. The active material-containing layer contains an active material and a binder, and optionally a conductive agent.

[0065] Examples of active materials used for the counter electrode include water-insoluble metal oxides (for example, oxides of one or more metals selected from the group consisting of Si, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Nb, Sn, and Sb; hydroxides of the above metals; fluorides of the above metals; and solid solutions thereof), alloy electrode materials (Si, P, S, Zn, Sn, Bi), alkali metal phosphate compounds (manganese phosphate, nickel phosphate, substances consisting of cobalt phosphate and alkali metals, and solid solutions and partial fluorides thereof). The number of active materials can be one or more.

[0066] Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0067] Examples of conductive agents include those similar to those described in the first embodiment. Note that the conductive agent may also be omitted.

[0068] In the active material-containing layer, it is preferable that the active material and the binder be blended in proportions of 80 wt% to 98 wt% and 2 wt% to 20 wt%, respectively.

[0069] The current collector can be similar to that described in the first embodiment. The current collector may also include portions on its surface where the active material-containing layer is not formed. These portions can function as current-collecting tabs.

[0070] The opposite electrode can be manufactured, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of the current collector. Next, the applied slurry is dried to obtain a laminate of the active material-containing layer and the current collector. Then, this laminate is pressed. In this way, the electrode is manufactured.

[0071] Alternatively, electrodes may be manufactured by the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, electrodes can be obtained by placing these pellets on a current collector.

[0072] The electrolyte, separator, outer casing, negative electrode terminal, and positive electrode terminal will be described in detail below.

[0073] electrolyte As the electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0074] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0075] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); and γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0076] Gel-like non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0077] Alternatively, in addition to liquid nonaqueous electrolytes and gel-type nonaqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymer solid electrolytes, and inorganic solid electrolytes may be used as nonaqueous electrolytes.

[0078] Room temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as liquids at room temperature (15°C to 25°C). Room temperature molten salts include room temperature molten salts that exist as liquids on their own, room temperature molten salts that become liquid when mixed with an electrolyte salt, room temperature molten salts that become liquid when dissolved in an organic solvent, or mixtures thereof. Generally, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. Also, organic cations generally have a quaternary ammonium skeleton.

[0079] Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and then solidifying it.

[0080] Inorganic solid electrolytes are solid materials that have lithium ion conductivity. Here, lithium ion conductivity means 1 × 10⁻⁶ at 25°C. -6 This refers to exhibiting a lithium ion conductivity of S / cm or higher. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows.

[0081] As an oxide-based solid electrolyte, it has a NASICON (Sodium (Na) Super Ionic Conductor) type structure, and its general formula is Li 1+x It is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. In the above general formula, Mα is one or more selected from the group consisting of, for example, titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is in the range of 0 ≤ x ≤ 2.

[0082] A specific example of a lithium phosphate solid electrolyte having a NASICON-type structure is Li 1+x Al x Ti 2-x LATP compounds represented as (PO4)3 where 0.1 ≤ x ≤ 0.5; Li 1+x Al y Mβ 2-yA compound represented by (PO4)3, where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, 0 ≦ x ≦ 1, and 0 ≦ y ≦ 1; Li 1+x Al x Ge 2-x A compound represented by (PO4)3, where 0 ≦ x ≦ 2; and, Li 1+x Al x Zr 2-x A compound represented by (PO4)3, where 0 ≦ x ≦ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 A compound represented by, where Mγ is one or more selected from the group consisting of Ti and Ge, 0 < x ≦ 2, and 0 ≦ y < 3; Li 1+2x Zr 1-x Ca x Examples of compounds represented by (PO4)3, where 0 ≦ x < 1, can be given.

[0083] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, Li x PO y N z An amorphous LIPON compound represented by, where 2.6 ≦ x ≦ 3.5, 1.9 ≦ y ≦ 3.8, and 0.1 ≦ z ≦ 1.3 (for example, Li 2.9 PO 3.3 N 0.46 ); Garnet-type structure La 5+x A x La 3-x Mδ2O 12 A compound represented by, where A is one or more selected from the group consisting of Ca, Sr, and Ba, Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 0.5; Li3Mδ 2-x L2O 12 A compound represented by, where Mδ is one or more selected from the group consisting of Nb and Ta, L may contain Zr, and 0 ≦ x ≦ 0.5; Li 7-3x Al x A compound represented by La3Zr3O 12 where 0 ≦ x ≦ 0.5; Li 5+x La3Mδ 2-x Zr x O12 Represented by , where Mδ is 1 or more selected from the group consisting of Nb and Ta, and 0 ≤ x ≤ 2, it is an LLZ compound (e.g., Li7La3Zr2O 12 ); and having a perovskite-type structure La 2 / 3-x Li x Examples include compounds represented as TiO3 where 0.3 ≤ x ≤ 0.7.

[0084] One or more of the above compounds can be used as a solid electrolyte. Two or more of the above solid electrolytes may also be used.

[0085] Separator The separator is formed from a porous film containing, for example, polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or from a synthetic resin nonwoven fabric. From a safety standpoint, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and interrupt the electric current.

[0086] Exterior components For example, the outer packaging material can be a container made of laminate film or a metal container.

[0087] The thickness of the laminating film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[0088] As the laminate film, a multilayer film is used that includes multiple resin layers and a metal layer interposed between these resin layers. The resin layers include polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be molded into the shape of an exterior component by sealing it by heat fusion.

[0089] The thickness of the metal container wall is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0090] Metal containers are made from, for example, aluminum or aluminum alloys. Aluminum alloys preferably contain elements such as magnesium, zinc, and silicon. If aluminum alloys contain transition metals such as iron, copper, nickel, and chromium, their content is preferably 100 ppm by mass or less.

[0091] The shape of the exterior components is not particularly limited. For example, the exterior components may be flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior components can be appropriately selected according to the battery dimensions and intended use.

[0092] negative terminal The negative terminal has a potential range of 1V to 3V relative to the oxidation-reduction potential of lithium (vs.Li / Li +The negative electrode terminal can be formed from an electrically stable and conductive material. Specifically, examples of materials for the negative electrode terminal include copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use aluminum or an aluminum alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0093] Positive terminal The positive terminal has a potential range of 3V to 4.5V relative to the oxidation-reduction potential of lithium (vs.Li / Li + The positive electrode terminal can be formed from an electrically stable and conductive material. Examples of positive electrode terminal materials include aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector. An example of a secondary battery in an embodiment will be described with reference to Figures 5 to 8.

[0094] Figures 5 and 6 show an example of a secondary battery using a metal container.

[0095] The electrode group 1 is housed in a rectangular cylindrical metal container 2. The electrode group 1 has a structure in which a separator 5 is interposed between the positive electrode 3's positive electrode active material-containing layer and the negative electrode 4's negative electrode active material-containing layer, and these are wound in a spiral shape to form a flattened shape. The separator 5 covers the surface of either the positive electrode active material-containing layer or the negative electrode active material-containing layer. As shown in Figure 6, multiple strip-shaped positive electrode leads 6 are electrically connected to each of the multiple points on the end of the positive electrode 3 located at the end face of the electrode group 1. Similarly, multiple strip-shaped negative electrode leads 7 are electrically connected to each of the multiple points on the end of the negative electrode 4 located at the same end face. These multiple positive electrode leads 6 are bundled together and electrically connected to a positive electrode conductive tab 8. The positive electrode terminal is formed from the positive electrode leads 6 and the positive electrode conductive tab 8. The negative electrode leads 7 are bundled together and connected to a negative electrode conductive tab 9. The negative electrode terminal is formed from the negative electrode leads 7 and the negative electrode conductive tab 9. The metal sealing plate 10 is fixed to the opening of the metal container 2 by welding or the like. The positive electrode conductive tab 8 and the negative electrode conductive tab 9 are each pulled out to the outside through outlet holes provided in the sealing plate 10. The inner circumferential surface of each outlet hole in the sealing plate 10 is covered with an insulating member 11 to prevent short circuits caused by contact with the positive electrode conductive tab 8 and the negative electrode conductive tab 9.

[0096] Figures 7 and 8 show an example of a secondary battery using a laminate film exterior component.

[0097] As shown in Figures 7 and 8, the flat wound electrode group 1 is housed in a bag-shaped outer casing member 12 made of a laminate film with a metal layer interposed between two resin films. The flat wound electrode group 1 is formed by spirally winding a laminate consisting of a negative electrode 4, a separator 15, a positive electrode 3, and another separator 15 stacked in that order from the outside, and then press-molding this laminate. The outermost negative electrode 4 has a configuration in which a negative electrode active material-containing layer 4b containing negative electrode active material is formed on one side of the inner surface of the negative electrode current collector 4a, as shown in Figure 8. The other negative electrodes 4 are configured by forming negative electrode active material-containing layers 4b on both sides of the negative electrode current collector 4a. The positive electrode 3 is configured by forming positive electrode active material-containing layers 3b on both sides of the positive electrode current collector 3a.

[0098] Near the outer edge of the wound electrode group 1, the negative electrode terminal 13 is connected to the negative electrode current collector 4a of the outermost negative electrode 4, and the positive electrode terminal 14 is connected to the positive electrode current collector 3a of the inner positive electrode 3. These negative electrode terminals 13 and positive electrode terminals 14 extend outward from the opening of the bag-shaped outer casing member 12. The wound electrode group 1 is sealed by heat sealing the opening of the bag-shaped outer casing member 12. When heat sealing, the negative electrode terminals 13 and positive electrode terminals 14 are sandwiched by the bag-shaped outer casing member 12 at this opening.

[0099] The battery of the embodiment described above, having electrodes as described in the embodiment, can suppress corrosion of the current collector. Therefore, the battery can suppress resistance increase over a long period of time. <Third Embodiment> The battery pack of the third embodiment includes a plurality of the batteries of the embodiment.

[0100] Examples of battery packs include those that include multiple unit cells electrically connected in series and / or parallel as constituent units, and those that include a first unit consisting of multiple unit cells electrically connected in series or a second unit consisting of multiple unit cells electrically connected in parallel. A battery pack may include at least one of these configurations.

[0101] Examples of configurations for electrically connecting multiple batteries (rechargeable batteries) in series and / or parallel include connecting multiple batteries, each equipped with an external casing, in series and / or parallel, and connecting multiple electrode groups or bipolar electrode bodies housed in a common housing in series and / or parallel. A specific example of the former is connecting the positive and negative terminals of multiple rechargeable batteries with a metal busbar (e.g., aluminum, nickel, or copper). A specific example of the latter is housing multiple electrode groups or bipolar electrode bodies in a single housing, electrochemically insulated by partitions, and electrically connecting them in series. In the case of rechargeable batteries, voltage compatibility with lead-acid batteries is improved by setting the number of batteries electrically connected in series to a range of 5 to 7. To further improve voltage compatibility with lead-acid batteries, a configuration in which 5 or 6 unit cells are connected in series is preferred.

[0102] The housing for the battery pack can be made of metal cans made of aluminum alloy, iron, stainless steel, or other materials, or plastic containers. Furthermore, the thickness of the container should preferably be 0.5 mm or more.

[0103] An example of a battery pack will be explained with reference to Figure 9. The battery pack 200 shown in Figure 9 comprises multiple rectangular secondary batteries 1001 to 1005, shown in Figure 5, as unit cells. The positive electrode conductive tab 8 of battery 1001 and the negative electrode conductive tab 9 of battery 1002 located next to it are electrically connected by leads or busbars 21. Furthermore, the positive electrode conductive tab 8 of battery 1002 and the negative electrode conductive tab 9 of battery 1003 located next to it are electrically connected by leads or busbars 21. In this way, batteries 1001 to 1005 are connected in series.

[0104] The battery pack of the embodiment described above, since it is equipped with the battery of the embodiment, can suppress resistance increase over a long period of time. <Fourth Embodiment> The battery pack according to the fourth embodiment may comprise one or more secondary batteries (single cells) according to the embodiment. Multiple secondary batteries may be electrically connected in series, parallel, or a combination of series and parallel to form a battery pack. The battery pack according to the embodiment may include multiple battery packs.

[0105] The battery pack according to this embodiment may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) can be used as the protection circuit for the battery pack.

[0106] Furthermore, the battery pack according to this embodiment may also be further equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and for inputting current to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of a vehicle such as an automobile) is supplied to the battery pack through the external terminals.

[0107] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0108] Figure 10 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. Figure 11 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 10.

[0109] The battery pack 300 shown in Figures 10 and 11 comprises a housing container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0110] The container 31 shown in Figure 10 is a bottomed rectangular container with a rectangular base. The container 31 is configured to accommodate a protective sheet 33, a battery pack 200, a printed circuit board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31, thereby housing the battery pack 200 and the other components. The container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc., although these are not shown in the figures.

[0111] The battery pack 200 comprises multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0112] At least one of the multiple single cells 100 is a secondary battery according to the embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in Figure 11. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0113] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0114] One end of the positive lead 22 is connected to the battery pack 200. One end of the positive lead 22 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 23 is connected to the battery pack 200. One end of the negative lead 23 is electrically connected to the negative terminal of one or more single cells 100.

[0115] The printed circuit board 34 is installed along one of the shorter sides of the inner surface of the housing container 31. The printed circuit board 34 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed circuit board 34 and the battery pack 200.

[0116] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0117] The thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0118] The external power supply terminal 350 is fixed to the other main surface of the printed circuit board 34. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0119] The protection circuit 346 is fixed to the other main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive side wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative side wiring 348b. The protection circuit 346 is also electrically connected to the positive side connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative side connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 35.

[0120] The protective sheet 33 is positioned on both inner surfaces in the long-side direction of the housing container 31 and on the inner surface in the short-side direction facing the printed circuit board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0121] The protection circuit 346 controls the charging and discharging of multiple single cells 100. The protection circuit 346 also disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying power to external devices, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual single cell 100 or a battery pack 200.

[0122] An example of a detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. An example of a detection signal transmitted from an individual single cell 100 or a battery pack 200 is a signal indicating that overcharging, over-discharging, or overcurrent has been detected in a single cell 100. When detecting overcharging, etc., in an individual single cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode to be used as a reference electrode is inserted into each individual single cell 100.

[0123] Furthermore, the protection circuit 346 may be a circuit included in a device that uses the battery pack 300 as a power source (for example, an electronic device, an automobile, etc.).

[0124] Furthermore, as described above, the battery pack 300 is equipped with an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device and input current from an external device to the battery pack 200 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 200 is supplied to the external device through the external terminal 350. Also, when charging the battery pack 300, charging current from an external device is supplied to the battery pack 300 through the external terminal 350. When this battery pack 300 is used as an on-board battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0125] The battery pack 300 may comprise multiple battery packs 200. In this case, the multiple battery packs 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed circuit board 34 and wiring 35 may also be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as the positive and negative terminals of the external terminals for energization, respectively.

[0126] Such battery packs are used in applications where excellent cycle performance is required, for example, when drawing high currents. Specifically, these battery packs are used as power supplies for electronic devices, stationary batteries, and on-board batteries for various vehicles (including batteries for railway vehicles). Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

[0127] The battery pack according to this embodiment comprises a battery or a battery pack according to this embodiment. Therefore, a battery pack in which resistance increase is suppressed over a long period of time can be realized. [Examples]

[0128] The embodiments of the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to the embodiments described below.

[0129] (Example 1) A first slurry was prepared by adding 96 wt% of monoclinic TiNb2O7 particles, 1 wt% of carbon nanotubes as a conductive agent, 1 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent, and stirring the mixture.

[0130] Furthermore, 94 wt% of monoclinic TiNb2O7 particles, 3 wt% of carbon nanotubes as a conductive agent, 1 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0131] The obtained first slurry was coated onto both sides of a 20 μm thick aluminum foil current collector. The aluminum foil current collector had a purity of 99.3% or higher and may contain unavoidable impurities such as Si, Fe, Cu, Mn, Mg, Zn, and Cr. Next, the second slurry was coated onto the first slurry. The total coating thickness of the first and second slurries was 40 μm. The resulting laminate was dried by leaving it in a drying oven at 120°C for 0.5 min. Subsequently, a negative electrode was fabricated by a pressing process, in which negative electrode active material-containing layers were formed on both sides of the current collector.

[0132] (Example 2) A slurry was prepared by adding 89.5 wt% of monoclinic TiNb2O7 particles, 5 wt% of acetylene black as a conductive agent, 2 wt% of carbon nanotubes, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent, and stirring the mixture. The ratio of binder weight to carbon material weight (binder weight / carbon material weight ratio) was 0.5.

[0133] The obtained slurry was coated onto both sides of a 20 μm thick aluminum foil current collector. The slurry coating thickness was 40 μm. The resulting laminate was dried by leaving it in a 130°C drying oven for 0.5 min. Subsequently, a negative electrode was fabricated by a pressing process, in which negative electrode active material-containing layers were formed on both sides of the current collector.

[0134] (Example 3) A first slurry was prepared by adding 95.5 wt% of monoclinic TiNb2O7 particles, 1 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent, and stirring these together.

[0135] Furthermore, 90.5 wt% of TiNb2O7 particles having a monoclinic structure, 6 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0136] The negative electrode was prepared in the same manner as in Example 1, except that the compositions of the first slurry and the second slurry were changed as described above.

[0137] (Example 4) A first slurry was prepared by adding 93.5 wt% of monoclinic TiNb2O7 particles, 3 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent, and stirring these together.

[0138] Furthermore, 86.5 wt% of TiNb2O7 particles having a monoclinic structure, 10 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0139] The negative electrode was prepared in the same manner as in Example 1, except that the compositions of the first slurry and the second slurry were changed as described above.

[0140] (Example 5) A first slurry was prepared by adding 94.5 wt% of monoclinic TiNb2O7 particles, 2 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent, and stirring these together.

[0141] Furthermore, 86.5 wt% of TiNb2O7 particles having a monoclinic structure, 10 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0142] The negative electrode was prepared in the same manner as in Example 1, except that the compositions of the first slurry and the second slurry were changed as described above.

[0143] (Example 6) A first slurry was prepared by adding 95.5 wt% of monoclinic TiNb2O7 particles, 1 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent, and stirring these together.

[0144] Furthermore, 90.5 wt% of TiNb2O7 particles having a monoclinic structure, 6 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0145] The negative electrode was fabricated in the same manner as in Example 1, except that the compositions of the first and second slurries were changed as described above, and a copper foil current collector was used instead of an aluminum foil current collector.

[0146] (Example 7) A first slurry was prepared by adding 94.3 wt% of orthorhombic TiO2 particles, 2.2 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent, and stirring these together.

[0147] Furthermore, 91.5 wt% of orthorhombic TiO2 particles, 5 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0148] The obtained first slurry was coated onto both sides of a 20 μm thick aluminum foil current collector. The aluminum foil current collector was of the same type as in Example 1. Next, the second slurry was coated onto the first slurry. The total coating thickness of the first and second slurries was 40 μm. The resulting laminate was dried by leaving it in a 120°C drying oven for 0.5 min. Then, a negative electrode was fabricated by a pressing process, in which negative electrode active material-containing layers were formed on both sides of the current collector.

[0149] (Example 8) 91.5 wt% of TiNb2O7 particles having a monoclinic structure, 5 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a first slurry.

[0150] Also, 86.5 wt% of TiNb2O7 particles having a monoclinic structure, 10 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0151] A negative electrode was produced in the same manner as in Example 1, except that the compositions of the first slurry and the second slurry were changed as described above.

[0152] (Comparative Example 1) 89.5 wt% of TiNb2O7 particles having a monoclinic structure, 5 wt% of acetylene black as a conductive agent, 2 wt% of carbon nanotubes, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a slurry. The ratio of the weight of the binder to the weight of the carbon material (the ratio of the weight of the binder / the weight of the carbon material) was 0.5.

[0153] The obtained slurry was coated on both sides of an aluminum foil current collector with a thickness of 20 μm. The coating thickness of the slurry was 40 μm. The obtained laminate was dried by leaving it in a drying oven at 80°C for 2 minutes. Next, a negative electrode having a negative electrode active material-containing layer formed on both sides of the current collector was produced by passing through a pressing process.

[0154] (Comparative Example 2) 92.5 wt% of TiNb2O7 particles having a monoclinic structure, 4 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a first slurry.

[0155] Furthermore, 95.5 wt% of TiNb2O7 particles having a monoclinic structure, 1 wt% of carbon nanotubes as a conductive agent, 1.5 wt% of CMC and 2 wt% of SBR as binders, and water as a solvent were added, and these were stirred to prepare a second slurry.

[0156] The negative electrode was prepared in the same manner as in Example 1, except that the compositions of the first slurry and the second slurry were changed as described above.

[0157] The primary carbon content A, secondary carbon content B, atomic ratio of oxygen to carbon (oxygen content α (at%) / carbon content β (at%) × 100) of the electrodes in the examples and comparative examples, and the pH value of the aqueous dispersion were measured using the method described above, and the results are shown in Table 1.

[0158] Coin cells were fabricated using the electrodes from the examples and comparative examples by the following method, and their cycle performance and rate performance were evaluated.

[0159] An electrolyte was prepared by dissolving a LiPF6-supporting salt at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:2.

[0160] Coin cells were fabricated using the electrodes from the examples and comparative examples as working electrodes, Li metal as the counter electrodes and reference electrodes, and an electrolyte solution.

[0161] In this embodiment, since lithium metal is used as the counter electrode in this measurement coin cell, the electrode potential of the embodiment and comparative example is nobler than that of the counter electrode and therefore functions as the positive electrode. For this reason, the definition of charge and discharge is reversed when the electrodes of the embodiment and comparative example are used as the negative electrode. To avoid confusion, in this embodiment, the direction in which lithium ions are inserted into the electrode is called charging, and the direction in which they are removed is called discharging. Note that the electrode of this embodiment functions as a negative electrode when combined with a known positive electrode.

[0162] The fabricated coin cells were charged and discharged within a potential range of 1.0V to 3.0V relative to the metallic lithium electrode. To investigate the rate performance, after confirming the 0.2C discharge capacity, the cells were charged again with a charging current of 0.2C, and the 5C discharge capacity was confirmed at room temperature. The discharge capacity retention rate (%) was then calculated by dividing the 5C discharge capacity by the 0.2C discharge capacity and multiplying by 100. The 5C / 0.2C discharge capacity retention rate (%) serves as an indicator for evaluating rate performance.

[0163] Furthermore, the coin cells of the examples and comparative examples were subjected to a life test at 25°C, repeatedly charging and discharging at 0.2C within a potential range of 1.0V to 3.0V relative to the metallic lithium electrode. Under these conditions, 1000 charge-discharge cycles were performed (one cycle consisted of charging and discharging), and the discharge capacity retention rate after 1000 cycles was investigated. To confirm the discharge capacity retention rate after 1000 cycles, charging and discharging were performed at 0.2C (time discharge rate), and the discharge capacity after 1000 cycles was divided by the initial discharge capacity and multiplied by 100 to calculate the cycle capacity retention rate (%), with the initial discharge capacity set to 100%. The discharge capacity retention rate after 1000 cycles serves as an indicator for evaluating the cycle life characteristics. The results are summarized in Table 2.

[0164] [Table 1]

[0165] [Table 2]

[0166] Examples 1-8, where the primary carbon content A was less than the secondary carbon content B, exhibited superior rate performance compared to Comparative Examples 1 and 2. Furthermore, comparing Examples 1-8, Example 1-7, where the atomic weight ratio of oxygen to carbon was 0.6 or higher, exhibited superior cycle performance compared to Example 8, where the atomic weight ratio of oxygen to carbon was less than 0.6. Therefore, Example 1-7 demonstrated superior performance in both rate performance and cycle performance.

[0167] Although Comparative Examples 1 and 2 had an atomic weight ratio of oxygen to carbon of 0.6 or higher, their rate performance was inferior because the primary carbon content A was the same as or greater than the secondary carbon content B.

[0168] According to the electrode of at least one embodiment or example described above, corrosion of the current collector can be suppressed by making the first carbon ratio lower than the second carbon ratio. When corrosion is suppressed, the decrease in the peel strength of the electrode can be suppressed. Therefore, the increase in the sheet resistance of the electrode can be suppressed. This makes it possible to improve the rate characteristics of the battery.

[0169] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0170] The invention of the embodiment is described below.

[0171] <1> The current collector comprises a current collector and an active material-containing layer supported on the current collector, which includes an active material, a conductive agent containing a carbon material, and a water-soluble binder. An electrode in which the first carbon ratio, based on a backscattered electron image measured by a scanning electron microscope from the current collector up to 1 μm in the active material-containing layer, is lower than the second carbon ratio, based on the backscattered electron image at a position corresponding to 50% of the thickness of the active material-containing layer. <2> The following equation (1) is satisfied: <1> The electrodes described above.

[0172] A / B ≤ 0.5 (1) However, A is the first carbon ratio and B is the second carbon ratio. <3> On the surface of the carbon material in contact with the current collector, the atomic weight ratio of oxygen to carbon is 0.6 or higher. <1> or <2> The electrodes described above. <4> The current collector includes one or more materials selected from the group consisting of Al, stainless steel, Cu, Zn, Ni, Sn, and Pb. <1> from <3> An electrode as described in any of the following. <5> The active material is such that the pH of an aqueous dispersion containing 40 wt% of the active material is between 5 and 9. <1> from <4> An electrode as described in any of the following. <6> The active material comprises one or more selected from the group consisting of water-insoluble metal oxides, alloys, and alkali metal phosphate compounds. <1> from <5> An electrode as described in any of the following. <7> <1> ~ <6> A battery comprising electrodes as described in any one of the items. <8> <7> A battery pack containing the batteries listed. <9> External terminals for power supply, Protection circuit and It further comprises <8> The battery pack described above. <10> The device comprises multiple of the aforementioned batteries, The batteries are electrically connected in series, parallel, or a combination of series and parallel. <8> or <9> The battery pack described above. [Explanation of Symbols]

[0173] 1…Electrode group, 2…Container (outer material), 3…Positive electrode, 3a…Positive electrode current collector, 3b…Positive electrode active material containing layer, 4…Negative electrode, 4a…Negative electrode current collector, 4b…Negative electrode active material containing layer, 5…Separator, 6…Positive electrode lead, 7…Negative electrode lead, 8…Positive electrode conductive tab, 9…Negative electrode conductive tab, 10…Sealing plate, 11…Insulating material, 12…Outer material, 13…Negative electrode terminal, 14…Positive electrode terminal, 20 0...Battery pack, 1001~1005...Secondary battery, 21...Lead (busbar), 300...Battery pack, 100...Unit cell, 200...Battery pack, 34...Printed circuit board, 345...Thermistor, 346...Protection circuit, 350...External terminal for current supply, 400...Electrode, 401...Current collector, 402...Active material-containing layer, 403...Current collector tab, 404...Surface of active material-containing layer.

Claims

1. The current collector comprises a current collector and an active material-containing layer supported on the current collector, which includes an active material, a conductive agent containing a carbon material, and a water-soluble binder. An electrode in which the first carbon ratio, based on a backscattered electron image measured by a scanning electron microscope from the current collector up to 1 μm in the active material-containing layer, is lower than the second carbon ratio, based on the backscattered electron image at a position corresponding to 50% of the thickness of the active material-containing layer.

2. The electrode according to claim 1, satisfying the following equation (1). A / B≦0.5 (1) However, A is the first carbon ratio and B is the second carbon ratio.

3. The electrode according to claim 1, wherein the atomic weight ratio of oxygen to carbon on the surface of the carbon material in contact with the current collector is 0.6 or more.

4. The electrode according to claim 1, wherein the current collector comprises one or more selected from the group consisting of Al, stainless steel, Cu, Zn, Ni, Sn, and Pb.

5. The electrode according to claim 1, wherein the active material is an aqueous dispersion containing 40 wt% of the active material, the pH of which is 5 or more and 9 or less.

6. The electrode according to claim 1, wherein the active material comprises one or more selected from the group consisting of water-insoluble metal oxides, alloys, and alkali metal phosphate compounds.

7. A battery comprising the electrode described in any one of claims 1 to 6.

8. A battery pack comprising the battery described in claim 7.

9. External terminals for power supply, Protection circuit and The battery pack according to claim 8, further comprising the above.

10. The device comprises multiple of the aforementioned batteries, The battery pack according to claim 9, wherein the batteries are electrically connected in series, parallel, or a combination of series and parallel.

Images