Electrochemical device

Abstract

This electrochemical device includes a positive electrode, a negative electrode, a separator, and a lithium-ion conductive electrolyte. The positive electrode includes a positive electrode active material for reversibly doping anions. The negative electrode is provided with a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector, wherein the negative electrode mixture layer includes a negative electrode active material for reversibly doping lithium-ions, and the negative electrode active material includes non-graphitizable carbon. The specific surface area of the negative electrode mixture layer is 10 m2 / g to 70 m2 / g. The separator includes an olefin-based resin.

Description

Electrochemical Devices

[0001] The present invention relates to an electrochemical device.

[0002] In recent years, electrochemical devices that combine the energy storage principles of lithium-ion secondary batteries and electric double-layer capacitors have attracted attention. Such electrochemical devices typically use a polarizable electrode as the positive electrode and a non-polarizable electrode as the negative electrode. As a result, electrochemical devices are expected to combine the high energy density of lithium-ion secondary batteries with the high output characteristics of electric double-layer capacitors.

[0003] Patent Document 1 proposes an electricity storage device in which an electrolytic solution and an electricity storage device element formed by stacking positive and negative electrodes with a separator interposed therebetween are housed inside an exterior body, and the electricity storage device is provided with a positive electrode terminal and a negative electrode terminal inside the exterior body that are electrically connected to the positive electrode and negative electrode that constitute the electricity storage device, respectively, and are provided so as to protrude to the outside from the exterior body, and the electricity storage device element is provided with an insulating first fixing member that fixes the positive electrode, negative electrode, and separator that constitute the electricity storage device element and that is released from the fixation at a temperature of 90°C or higher and 160°C or lower.

[0004] JP 2014-123699 A

[0005] Generally, a cellulose-based nonwoven fabric (hereinafter also referred to as a cellulose-based separator) is used as a separator for an electrochemical device. Although a cellulose-based separator is inexpensive, it easily absorbs moisture, which easily causes deterioration of the negative electrode due to the moisture, and the deterioration of the negative electrode easily increases the internal resistance of the electrochemical device.

[0006] One aspect of the present invention is a battery including a positive electrode, a negative electrode, a separator, and a lithium ion conductive electrolyte, wherein the positive electrode includes a positive electrode active material that is reversibly doped with anions, and the negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the negative electrode current collector, wherein the negative electrode mixture layer includes a negative electrode active material that is reversibly doped with lithium ions, the negative electrode active material includes non-graphitizable carbon, and the specific surface area of ​​the negative electrode mixture layer is 10 m ２ / g or more, 70m ２ / g or less, and the separator contains an olefin-based resin.

[0007] According to the present invention, an increase in the internal resistance of an electrochemical device is suppressed.

[0008] 1 is a longitudinal sectional view showing the configuration of an electrochemical device according to one embodiment of the present invention.

[0009] An electrochemical device according to one embodiment of the present invention includes a positive electrode, a negative electrode, a separator, and a lithium ion conductive electrolyte. The positive electrode includes a positive electrode active material that is reversibly doped with anions. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the negative electrode current collector. The negative electrode mixture layer includes a negative electrode active material that is reversibly doped with lithium ions, and the negative electrode active material includes non-graphitizable carbon. The specific surface area of ​​the negative electrode mixture layer is 10 m ２ / g or more, 70m ２ / g or less. The separator contains an olefin-based resin. Hereinafter, a separator containing an olefin-based resin will also be referred to as an "olefin-based separator."

[0010] Olefin-based separators have a lower moisture content than cellulose-based separators, which suppresses deterioration of the negative electrode due to moisture in the separator and thus suppresses the increase in internal resistance of the electrochemical device associated with negative electrode deterioration. Furthermore, olefin-based separators are more stable with respect to electrolytes containing lithium ions (or metallic lithium attached to the negative electrode surface in the pre-doping process) than cellulose-based separators, and are therefore less susceptible to deterioration. Therefore, by using olefin-based separators, low internal resistance can be maintained for a long period of time. As a result, the reliability of the electrochemical device is improved.

[0011] The negative electrode active material contains non-graphitizable carbon, and the specific surface area of ​​the negative electrode mixture layer is 10 m ２ / g or more, the resistance of the negative electrode is significantly reduced, and as a result, the internal resistance of the electrochemical device is significantly reduced. In this case, the reactivity of the negative electrode is increased, and the above-mentioned deterioration of the negative electrode is likely to progress, so the effect of suppressing the deterioration of the negative electrode by using an olefin-based separator is significantly obtained. However, if the specific surface area of ​​the negative electrode mixture layer is 70 m ２If it is larger than 1 / g, the reactivity of the negative electrode is so high that the above-mentioned deterioration of the negative electrode may not be suppressed.

[0012] From the viewpoint of suppressing the deterioration of the negative electrode, the specific surface area of ​​the negative electrode mixture layer is set to 10 m ２ / g or more, 50m ２ / g or less is preferable.

[0013] The non-graphitizable carbon exhibits capacity through a Faraday reaction in which lithium ions are reversibly absorbed and released. The doping of lithium ions into the negative electrode active material is a concept that includes at least the phenomenon of lithium ions being absorbed into the negative electrode active material, and may also include the adsorption of lithium ions into the negative electrode active material and chemical interactions between the negative electrode active material and lithium ions.

[0014] The negative electrode potential is, for example, a lithium reference (vs. Li / Li ＋ ) is 0.2 V or less. The above negative electrode potential is the negative electrode potential (25 °C) at the completion of pre-doping (or during charging) described below. Lithium ions are pre-doped into the negative electrode mixture layer in advance. This reduces the potential of the negative electrode, increases the potential difference (i.e., voltage) between the positive electrode and the negative electrode, and improves the energy density of the electrochemical device. The amount of lithium to be pre-doped is set so that the negative electrode potential in the electrolyte after pre-doping is 0.2 V or less relative to metallic lithium. The amount of lithium to be pre-doped may be, for example, about 50% to 95% of the maximum amount that can be occluded in the negative electrode mixture layer.

[0015] The specific surface area of ​​the negative electrode mixture layer is the BET specific surface area determined using a measuring device conforming to JIS Z8830 (e.g., a Tristar II 3020 manufactured by Shimadzu Corporation). Specifically, the electrochemical device is disassembled, and the negative electrode is removed. A half cell is assembled using this negative electrode as the working electrode and Li metal foil as the counter electrode, and Li in the negative electrode is dedoped until the negative electrode potential reaches 1.5 V. Next, the negative electrode from which Li has been dedoped is washed with dimethyl carbonate (DMC) and dried. Thereafter, the negative electrode mixture layer is peeled off from the negative electrode current collector, and approximately 0.5 g of a sample of the negative electrode mixture layer is collected.

[0016] Next, the collected sample is heated at 150°C for 12 hours under a reduced pressure of 95 kPa or less, and then nitrogen gas is adsorbed onto a sample of known mass to obtain an adsorption isotherm over a relative pressure range of 0 to 1. The surface area of ​​the sample is then calculated from the monolayer adsorption amount of gas obtained from the adsorption isotherm. Here, the specific surface area is calculated using the BET single-point method (relative pressure 0.3) using the BET formula below.

[0017] P / V (P0-P) = (1 / VmC) + {(C-1) / VmC} (P / P0)... (1)

[0018] S=kVm...(2)

[0019] P0: saturated vapor pressure P: adsorption equilibrium pressure V: adsorption amount at adsorption equilibrium pressure P Vm: monolayer adsorption amount C: parameters related to heat of adsorption, etc. S: specific surface area k: nitrogen monomolecular occupation area 0.162 nm ２

[0020] The surface portion of the negative electrode mixture layer may have a first layer containing lithium carbonate as a coating component. The first layer is mainly formed on the surface of the negative electrode active material. The larger the specific surface area of ​​the negative electrode mixture layer, the more likely the negative electrode is to deteriorate. However, by forming the first layer, deterioration of the negative electrode is significantly suppressed. However, in an environment where lithium carbonate is formed on the surface portion of the negative electrode mixture layer, cellulose-based separators tend to deteriorate rapidly. On the other hand, olefin-based separators are less likely to deteriorate even in an environment where lithium carbonate is formed on the surface portion of the negative electrode mixture layer, and a good first layer is formed, thereby maximizing the above-mentioned effects of the first layer.

[0021] The surface layer portion of the negative electrode may have a second layer containing a solid electrolyte as a component of the coating. The second layer has a different composition from the first layer and is distinguishable from the first layer. In electrochemical devices that use lithium ions, a solid electrolyte interfacial coating (i.e., an SEI coating) is formed on the negative electrode mixture layer during charge and discharge. The second layer may be formed as an SEI coating. The SEI coating plays an important role in charge and discharge reactions, but if the SEI coating is formed too thick, negative electrode deterioration will increase. In contrast, the first layer containing lithium carbonate promotes the formation of a good SEI coating and has the effect of maintaining the SEI coating in a good state during repeated charge and discharge. Therefore, by forming the first layer on the surface layer portion of the negative electrode mixture layer, negative electrode deterioration can be significantly suppressed even when the specific surface area of ​​the negative electrode mixture layer is increased to suppress an increase in low-temperature DCR.

[0022] When the coating has a first layer and a second layer, at least a portion of the second layer covers at least a portion of the surface of the negative electrode active material via the first layer. That is, at least a portion of the first layer is covered by the second layer. The first layer is interposed between the surface of the negative electrode active material and the second layer and serves as an underlayer for the second layer. By using the first layer as an underlayer, the second layer is formed as a good-condition SEI coating.

[0023] The second layer may also contain lithium carbonate. When the second layer contains lithium carbonate, the lithium carbonate content in the second layer is less than the lithium carbonate content in the first layer. Using the first layer containing a large amount of lithium carbonate as an underlayer is a necessary condition for the second layer to be formed as a good SEI coating.

[0024] The first layer is formed on the surface of the negative electrode mixture layer before assembling the electrochemical device. In an electrochemical device assembled using the negative electrode, a homogeneous, moderately thick second layer (SEI coating) is formed on the surface of the negative electrode active material through subsequent charge and discharge. The SEI coating is formed, for example, by a reaction between an electrolyte and a negative electrode in an electrochemical device. Because the electrolyte can pass through not only the second layer but also the first layer, the entire surface including the first and second layers may be referred to as the SEI coating. However, for convenience, the second layer will be referred to as the SEI coating in this specification to distinguish it from the first layer.

[0025] The presence of a region containing lithium carbonate such as the first layer can be confirmed by analyzing the surface layer by, for example, X-ray photoelectron spectroscopy (XPS), although the analysis method is not limited to XPS.

[0026] The thickness of the first layer may be, for example, 1 nm or more, 5 nm or more if a longer-term effect is expected, or 10 nm or more if a more reliable effect is expected. However, if the thickness of the first layer exceeds 50 nm, the first layer itself may become a resistance component. Therefore, the thickness of the first layer may be 50 nm or less, or may be 30 nm or less. The thickness of the first layer is, for example, 1 nm to 50 nm.

[0027] The thickness of the second layer may be, for example, 1 nm or more, or may be 3 nm or more, or 5 nm or more is sufficient. However, if the thickness of the second layer exceeds 20 nm, the second layer itself may become a resistance component. Therefore, the thickness of the second layer may be 20 nm or less, or may be 10 nm or less.

[0028] The ratio A / B of the thickness A of the first layer to the thickness B of the second layer is preferably 1 or less from the viewpoint of reducing the initial low-temperature DCR. In this case, the thickness of the second layer is preferably 20 nm or less, and may be 10 nm or less. However, from the viewpoint of forming a second layer in good condition, it is desirable that the A / B ratio be 0.1 or more, and for example, the A / B ratio may be 0.2 or more.

[0029] The thicknesses of the first and second layers are measured by analyzing the surface portion of the negative electrode mixture layer at multiple locations (at least five locations). The average thickness of the first or second layer measured at multiple locations is then used as the thickness of the first or second layer. The negative electrode mixture layer used as the measurement sample may be peeled off from the negative electrode current collector. In this case, the coating formed on the surface of the negative electrode active material that constituted the vicinity of the surface portion of the negative electrode mixture layer may be analyzed. Specifically, the negative electrode active material covered with the coating may be collected from the region of the negative electrode mixture layer that was disposed on the side opposite to the surface that was bonded to the negative electrode current collector and used for analysis.

[0030] XPS analysis of the surface portion of the negative electrode mixture layer is performed, for example, by irradiating an argon beam onto the surface portion or a coating formed on the surface of the negative electrode active material in the chamber of an X-ray photoelectron spectrometer, and observing and recording changes in the spectra attributable to C1s, O1s electrons, etc. with respect to irradiation time. In this case, the spectrum of the outermost surface of the surface portion may be ignored to avoid analytical errors. The thickness of the region where peaks attributable to lithium carbonate are stably observed corresponds to the thickness of the first layer.

[0031] In the case of a negative electrode removed from a completed electrochemical device after a predetermined aging process or at least one charge / discharge cycle, the surface portion of the negative electrode mixture layer has an SEI coating (i.e., a second layer) containing a solid electrolyte. The thickness of the region where peaks attributable to bonds possessed by compounds contained in the SEI coating are stably observed corresponds to the thickness of the SEI coating (i.e., the thickness of the second layer).

[0032] The compound contained in the SEI coating is selected to contain an element that can be a label for the second layer. The element that can be a label for the second layer may be, for example, an element (e.g., F) that is contained in the electrolyte and is substantially not contained in the first layer. LiF, for example, may be selected as the compound that contains the element that can be a label for the second layer.

[0033] When the second layer contains LiF, a substantial F1s peak attributed to LiF bonds is observed when the second layer is measured by X-ray photoelectron spectroscopy. In this case, the thickness of the region where the peak attributed to LiF bonds is stably observed corresponds to the thickness of the second layer.

[0034] On the other hand, the first layer usually does not contain LiF, and when the first layer is measured by X-ray photoelectron spectroscopy, a substantial F1s peak attributed to the LiF bond is not observed. Therefore, the thickness of the region where a peak attributed to the LiF bond is not stably observed may be defined as the thickness of the first layer.

[0035] An O1s peak attributed to lithium carbonate can also be observed in the SEI coating. However, the SEI coating formed in the electrochemical device has a different composition from the first layer formed in advance, so the two can be distinguished. For example, in an XPS analysis of the SEI coating, an F1s peak attributed to LiF bonds is observed, but a substantial F1s peak attributed to LiF bonds is not observed in the first layer. Furthermore, the amount of lithium carbonate contained in the SEI coating is small. The Li1s peak can be observed, for example, in ROCO ２ Peaks derived from compounds such as Li and ROLi can be detected.

[0036] When the first layer is analyzed by XPS, in addition to the first peak of O1s attributed to the C=O bond, a second peak of O1s attributed to the Li-O bond may be observed. The region of the coating present near the surface of the negative electrode active material contains a small amount of LiOH or Li ２ It may contain O.

[0037] Specifically, when the first layer constituting the surface layer portion of the negative electrode mixture layer is analyzed in the depth direction, a first region in which a first peak (O1s attributable to a C═O bond) and a second peak (O1s attributable to a Li—O bond) are observed, and the first peak intensity is greater than the second peak intensity, and a second region in which the first peak and the second peak are observed and the second peak intensity is greater than the first peak intensity may be observed, in order of increasing distance from the outermost surface of the surface layer portion. Furthermore, a third region may also be present that is closer to the outermost surface of the surface layer portion than the first region, and in which the first peak is observed but the second peak is not observed. The third region is likely to be observed when the thickness of the lithium carbonate-containing region is large.

[0038] The magnitude of the peak intensity can be determined by the height of the peak from the baseline.

[0039] At the center in the thickness direction of the first layer, the C1s peak attributed to a C—C bond is generally not observed, or even if observed, its intensity is half or less of the peak intensity attributed to a C═O bond.

[0040] Next, a method for forming the first layer containing lithium carbonate on the surface layer portion of the negative electrode mixture layer will be described. The step of forming the first layer can be performed by, for example, a vapor phase method, a coating method, or a transfer method.

[0041] Examples of the gas phase method include chemical vapor deposition, physical vapor deposition, and sputtering. For example, lithium carbonate may be deposited on the surface of the negative electrode mixture layer using a vacuum deposition device. The pressure in the chamber of the device during deposition is, for example, 10 －２ ~10 －５ The temperature of the lithium carbonate evaporation source may be 400 to 600°C, and the temperature of the negative electrode mixture layer may be -20 to 80°C.

[0042] As a coating method, a solution or dispersion containing lithium carbonate can be applied to the surface of the negative electrode using, for example, a microgravure coater, followed by drying to form the first layer. The lithium carbonate content in the solution or dispersion is, for example, 0.3 to 2 mass %, and when a solution is used, the concentration may be equal to or lower than the solubility (for example, about 0.9 to 1.3 mass % in the case of an aqueous solution at room temperature).

[0043] Furthermore, a step of forming a second layer containing a solid electrolyte so as to cover at least a portion of the first layer is carried out to obtain a negative electrode. The surface layer portion of the obtained negative electrode mixture layer has a first layer and a second layer. The second layer is formed so that at least a portion of it covers at least a portion (preferably the entire) of the surface of the negative electrode active material through the first layer (i.e., with the first layer as a base layer).

[0044] The step of forming the second layer is performed in a state where the negative electrode mixture layer is in contact with the electrolyte, and therefore may also serve as at least a part of a step of pre-doping lithium ions into the negative electrode mixture layer. For example, metallic lithium may be used as a source of the pre-doped lithium ions.

[0045] The metallic lithium may be attached to the surface of the negative electrode mixture layer. Note that, for example, a first layer containing lithium carbonate and having a thickness of 1 nm or more and 50 nm or less can also be formed by exposing a negative electrode having a negative electrode mixture layer to which metallic lithium is attached to a carbon dioxide gas atmosphere.

[0046] The step of attaching metallic lithium to the surface of the negative electrode mixture layer can be carried out by, for example, a vapor phase method, transfer, or the like. Examples of the vapor phase method include chemical vapor deposition, physical vapor deposition, and sputtering. For example, metallic lithium may be formed in the form of a film on the surface of the negative electrode mixture layer using a vacuum deposition device. The pressure in the chamber of the device during deposition is, for example, 10 －２ ~10 －５ The temperature of the lithium evaporation source may be 400 to 600°C, and the temperature of the negative electrode mixture layer may be -20 to 80°C.

[0047] The carbon dioxide gas atmosphere is preferably a dry atmosphere containing no moisture, and may have a dew point of, for example, -40°C or lower or -50°C or lower. The carbon dioxide gas atmosphere may contain gases other than carbon dioxide, but the molar fraction of carbon dioxide is preferably 80% or higher, and more preferably 95% or higher. It is preferable that the atmosphere does not contain any oxidizing gases, and the molar fraction of oxygen should be 0.1% or lower.

[0048] To form a thicker first layer, the partial pressure of carbon dioxide is set to, for example, 0.5 atmospheres (5.05×10 ４ It is efficient if the pressure is greater than 1 atmosphere (1.01 x 10 ５ Pa) or more.

[0049] The temperature of the negative electrode exposed to the carbon dioxide gas atmosphere may be, for example, in the range of 15° C. to 120° C. The higher the temperature, the thicker the first layer becomes.

[0050] The thickness of the first layer can be easily controlled by changing the time for which the negative electrode is exposed to the carbon dioxide gas atmosphere. The exposure time may be, for example, 12 hours or more and less than 10 days.

[0051] The step of forming the first layer is preferably carried out before constructing the electrode body, but may be carried out after constructing the electrode body. That is, a positive electrode may be prepared, a negative electrode having a negative electrode mixture layer to which metallic lithium is attached may be prepared, a separator may be interposed between the positive electrode and the negative electrode to form an electrode body, and the electrode body may be exposed to a carbon dioxide gas atmosphere to form the first layer on the surface portion of the negative electrode mixture layer.

[0052] The pre-doping process of lithium ions into the negative electrode mixture layer proceeds further, for example, by subsequently contacting the negative electrode mixture layer with an electrolyte and then leaving it for a predetermined time, and is completed. Such a process may be a process of forming a second layer so as to cover at least a portion of the first layer. For example, by performing at least one charge / discharge cycle on the electrochemical device, the second layer is formed in the negative electrode mixture layer and the pre-doping of lithium ions into the negative electrode can be completed. Furthermore, for example, the pre-doping of lithium ions into the negative electrode can also be completed by applying a predetermined charging voltage (e.g., 3.4 to 4.0 V) between the terminals of the positive electrode and the negative electrode for a predetermined time (e.g., 1 to 75 hours).

[0053] (Olefin-based separator) Commonly used cellulose-based separators have many functional groups, such as OH groups, that easily react with lithium ions, and also contain a relatively large amount of water, making them susceptible to damage due to side reactions. Furthermore, the reaction of metallic lithium with the separator can reduce the amount of lithium pre-doped into the negative electrode. The main reason for the common use of cellulose-based separators is their excellent electrolyte permeability, which facilitates pre-doping.

[0054] For example, when pre-doping lithium ions in a wound body formed by winding a positive electrode and a negative electrode with a separator interposed between the positive electrode and the negative electrode, it is difficult to use an olefin-based separator because the lithium ions eluted from the metallic lithium introduced for pre-doping are difficult to diffuse throughout the wound body. In other words, when the metallic lithium for pre-doping is directly immersed in the electrolyte, it is essential to use a cellulose-based separator.

[0055] In contrast, the electrochemical device according to this embodiment uses an olefin-based separator. Because the olefin-based separator has low reactivity with metallic lithium, it is possible to suppress separator degradation and improve the reliability of the electrochemical device. Additionally, the olefin-based separator has high strength, and even when thinned, it can maintain a sufficiently high strength. Therefore, by tightly winding the positive and negative electrodes, a wound body with high surface pressure can be used, improving the performance of the electrochemical device, such as the capacity.

[0056] The olefin resin contained in the separator preferably includes at least one selected from the group consisting of polypropylene (PP) and polyethylene (PE). PP separators and PE separators have high strength and are stable against electrolytes containing lithium ions, and are therefore suitable for use in electrochemical devices in which the first and second layers are formed on the surface of the negative electrode mixture layer.

[0057] On the other hand, olefin-based separators have a higher air resistance than cellulose-based separators, and the lithium ion passage rate through the separator is slow. While the high air resistance of olefin-based separators does not pose a problem in the charge and discharge of ordinary electrochemical devices, the pre-doping process of lithium ions may require a long time due to the slow lithium ion passage rate. In this regard, it is preferable to adopt a method in which lithium ions are not supplied to the negative electrode through the separator in the pre-doping process. For example, as described below, pre-doping can be performed without requiring a long time by contacting a negative electrode in which metallic lithium has been previously attached to the entire surface of the negative electrode mixture layer with an electrolyte.

[0058] The separator preferably has an air permeability resistance of 70 sec / 100 mL or more and 500 sec / 100 mL or less. When the air permeability resistance is in this range, it is possible to achieve both a reduction in the internal resistance of the electrochemical device and an improvement in reliability. More preferably, the separator has an air permeability resistance of 70 sec / 100 mL or more and 300 sec / 100 mL or less, and even more preferably, 70 sec / 100 mL or more and 230 sec / 100 mL or less (or 180 sec / 100 mL or more and 230 sec / 100 mL or less).

[0059] Here, the air permeation resistance is an index showing the time (seconds) required for a predetermined volume (100 mL) of air to permeate per unit area of ​​the separator when a predetermined pressure difference is applied between both sides of the separator. Based on JIS P8117:2009, the air permeation resistance is calculated by setting the separator area (permeation area) to 6.42 cm. ２ The resistance is measured by the Gurley tester method with the inner cylinder weight set to 567 g.

[0060] The thickness of the separator is preferably 12 μm or more and 30 μm or less in terms of allowing easy permeation of lithium ions and having sufficient strength.

[0061] FIG. 1 schematically illustrates the configuration of an electrochemical device 200 according to one embodiment of the present invention. The electrochemical device 200 includes an electrode assembly 100, a nonaqueous electrolyte (not shown), a metal cell case 210 with a bottom that accommodates the electrode assembly 100 and the nonaqueous electrolyte, and a sealing plate 220 that seals the opening of the cell case 210. The electrode assembly 100 is formed by winding a strip-shaped positive electrode 10 and a strip-shaped negative electrode 20 together with a separator 30 interposed between the positive electrode 10 and the negative electrode 20 to form a columnar wound body. A gasket 221 is disposed around the periphery of the sealing plate 220, and the interior of the cell case 210 is sealed by crimping the open end of the cell case 210 to the gasket 221. A positive electrode current collector 13 having a central through-hole 13h is welded to the exposed positive electrode core material portion 11x. One end of the tab lead 15 is connected to the positive current collector plate 13, and the other end is connected to the inner surface of the sealing plate 220. Therefore, the sealing plate 220 functions as an external positive electrode terminal. On the other hand, the negative current collector plate 23 is welded to the negative electrode core material exposed portion 21x. The negative current collector plate 23 is directly welded to a welding member provided on the inner bottom surface of the cell case 210. Therefore, the cell case 210 functions as an external negative electrode terminal.

[0062] The electrochemical device is not limited to the wound type electrochemical device shown in Fig. 1. For example, it may be a stacked type electrochemical device. That is, the electrode assembly may be configured as a stacked body by stacking sheet-like positive and negative electrodes with a separator interposed between the positive and negative electrodes.

[0063] Each component of the electrochemical device according to the embodiment of the present invention will now be described in more detail.

[0064] The negative electrode comprises a negative electrode current collector and a negative electrode mixture layer supported on the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material that is reversibly doped with lithium ions, and the negative electrode active material contains non-graphitizable carbon (i.e., hard carbon). The thickness of the negative electrode mixture layer is, for example, 10 to 300 μm per side of the negative electrode current collector.

[0065] The negative electrode current collector is made of a sheet-like metal material, such as a metal foil, a porous metal, or an etched metal. Examples of the metal material include copper, a copper alloy, nickel, and stainless steel.

[0066] The negative electrode current collector is a generally disk-shaped metal plate. The material of the negative electrode current collector is, for example, copper, copper alloy, nickel, stainless steel, etc. The material of the negative electrode current collector may be the same as the material of the negative electrode current collector.

[0067] The non-graphitizable carbon may have a (002) plane spacing (i.e., the spacing between carbon layers) d002 of 3.8 Å or more as measured by X-ray diffraction. The theoretical capacity of the non-graphitizable carbon is preferably, for example, 150 mAh / g or more. The use of non-graphitizable carbon makes it easier to obtain a negative electrode with a small low-temperature DCR and small expansion and contraction during charge and discharge. The non-graphitizable carbon preferably accounts for 50% by mass or more, more preferably 80% by mass or more, and even 95% by mass or more of the negative electrode active material. Furthermore, the non-graphitizable carbon preferably accounts for 40% by mass or more, more preferably 70% by mass or more, and even 90% by mass or more of the negative electrode mixture layer.

[0068] As the negative electrode active material, non-graphitizable carbon and a material other than non-graphitizable carbon may be used in combination. Examples of materials other than non-graphitizable carbon that can be used as the negative electrode active material include graphitizable carbon (soft carbon), graphite (natural graphite, artificial graphite, etc.), lithium titanium oxide (spinel-type lithium titanium oxide, etc.), silicon oxide, silicon alloy, tin oxide, tin alloy, etc.

[0069] From the viewpoint of achieving high packing properties of the negative electrode active material in the negative electrode and easily suppressing side reactions with the electrolyte, the average particle size of the negative electrode active material (particularly non-graphitizable carbon) is preferably 1 μm to 20 μm, and more preferably 2 μm to 15 μm.

[0070] In this specification, the average particle size means the volume-based median diameter (D50) in the particle size distribution obtained by laser diffraction particle size distribution measurement.

[0071] The negative electrode mixture layer contains a negative electrode active material as an essential component, and optionally contains a conductive agent, a binder, a thickener, etc. Examples of the conductive agent include carbon black and carbon fiber. Examples of the carbon black include acetylene black (AB) and ketjen black (KB). Examples of the binder include fluororesin, acrylic resin, and rubber material. Examples of the thickener include cellulose derivatives.

[0072] The negative electrode mixture layer may contain a negative electrode active material and a conductive agent. In this case, the specific surface area of ​​the negative electrode mixture layer may reflect the specific surface areas of the negative electrode active material and the conductive agent. For example, when a conductive agent with a large specific surface area (e.g., KB) is used, the specific surface area of ​​the negative electrode mixture layer may be adjusted by changing the amount of the conductive agent added.

[0073] The negative electrode mixture layer is formed, for example, by mixing a negative electrode active material, a conductive agent, and the like together with a dispersion medium to prepare a negative electrode mixture slurry, applying the negative electrode mixture slurry to a negative electrode current collector, and then drying the slurry.

[0074] The negative electrode mixture layer is pre-doped with lithium ions. This reduces the potential of the negative electrode, increasing the potential difference (i.e., voltage) between the positive electrode and the negative electrode, thereby improving the energy density of the electrochemical device. The amount of lithium pre-doped may be, for example, approximately 50% to 95% of the maximum amount that can be occluded in the negative electrode mixture layer.

[0075] (Positive Electrode) The positive electrode contains a positive electrode active material that is reversibly doped with anions. The positive electrode active material is, for example, a carbon material or a conductive polymer. The positive electrode may include a positive electrode mixture layer that contains the positive electrode active material and a positive electrode current collector that supports the positive electrode mixture layer. The thickness of the positive electrode mixture layer is, for example, 10 to 300 μm per side of the positive electrode current collector.

[0076] The positive electrode current collector is made of a sheet-like metal material, such as a metal foil, a porous metal, or an etched metal. Examples of the metal material include aluminum, an aluminum alloy, nickel, and titanium.

[0077] The positive electrode current collector is a generally disk-shaped metal plate. A through-hole is preferably formed in the center of the positive electrode current collector to serve as a passage for the non-aqueous electrolyte. The material of the positive electrode current collector is, for example, aluminum, an aluminum alloy, titanium, stainless steel, or the like. The material of the positive electrode current collector may be the same as the material of the positive electrode current collector.

[0078] The carbon material used as the positive electrode active material is preferably a porous carbon material, such as activated carbon or the carbon materials exemplified as the negative electrode active material (e.g., non-graphitizable carbon). Examples of raw materials for activated carbon include wood, coconut shells, coal, pitch, and phenolic resin. The activated carbon is preferably activated.

[0079] The average particle size of the activated carbon is not particularly limited, but is preferably 20 μm or less, and more preferably 3 μm to 15 μm.

[0080] The specific surface area of ​​the positive electrode mixture layer generally reflects the specific surface area of ​​the positive electrode active material. ２ / g or more, 4000m ２ / g or less is sufficient, and ２ / g or more, 3000m ２ / g or less is desirable. The specific surface area of ​​the positive electrode mixture layer is the BET specific surface area determined using a measuring device conforming to JIS Z8830 (e.g., a Tristar II 3020 manufactured by Shimadzu Corporation). Specifically, the electrochemical device is disassembled, and the positive electrode is removed. Next, the positive electrode is washed with DMC and dried. Thereafter, the positive electrode mixture layer is peeled from the positive electrode current collector, and approximately 0.5 g of a sample of the positive electrode mixture layer is collected. Next, the specific surface area of ​​the collected sample is determined in accordance with the method for measuring the specific surface area of ​​the negative electrode mixture layer already described.

[0081] The activated carbon preferably accounts for 50% by mass or more, more preferably 80% by mass or more, and even 95% by mass or more of the positive electrode active material, and more preferably 40% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more of the positive electrode mixture layer.

[0082] The positive electrode mixture layer contains a positive electrode active material as an essential component, and optionally contains a conductive agent, a binder, a thickener, etc. Examples of the conductive agent include carbon black and carbon fiber. Examples of the binder include fluororesin, acrylic resin, and rubber material. Examples of the thickener include cellulose derivatives.

[0083] The positive electrode mixture layer is formed, for example, by mixing a positive electrode active material, a conductive agent, and the like together with a dispersion medium to prepare a positive electrode mixture slurry, applying the positive electrode mixture slurry to a positive electrode current collector, and then drying the applied slurry.

[0084] The conductive polymer used as the positive electrode active material is preferably a π-conjugated polymer. Examples of π-conjugated polymers that can be used include polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, polypyridine, and derivatives thereof. These may be used alone or in combination of two or more. The weight-average molecular weight of the conductive polymer is, for example, 1,000 to 100,000. The derivative of a π-conjugated polymer refers to a polymer having a π-conjugated polymer skeleton such as polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, or polypyridine. For example, polythiophene derivatives include poly(3,4-ethylenedioxythiophene) (PEDOT).

[0085] Conductive polymers are formed, for example, by immersing a positive electrode current collector with a carbon layer in a reaction solution containing raw material monomers of the conductive polymer and electrolytically polymerizing the raw material monomers in the presence of the positive electrode current collector. In electrolytic polymerization, a positive electrode current collector and a counter electrode are immersed in a reaction solution containing the raw material monomers, and a current is passed between them using the positive electrode current collector as the anode. Conductive polymers may also be formed by methods other than electrolytic polymerization. For example, a conductive polymer may be formed by chemical polymerization of raw material monomers. In chemical polymerization, raw material monomers are polymerized using an oxidizing agent or the like in the presence of the positive electrode current collector.

[0086] The raw material monomer used in electropolymerization or chemical polymerization may be any polymerizable compound capable of producing a conductive polymer by polymerization. The raw material monomer may include an oligomer. Examples of the raw material monomer include aniline, pyrrole, thiophene, furan, thiophene vinylene, pyridine, or derivatives thereof. These may be used alone or in combination of two or more. Among these, aniline is particularly easy to grow on the surface of the carbon layer by electropolymerization.

[0087] Electropolymerization or chemical polymerization can be carried out using a reaction solution containing an anion (dopant). By doping a π-electron conjugated polymer with a dopant, excellent conductivity can be achieved. Examples of dopants include sulfate ions, nitrate ions, phosphate ions, borate ions, benzenesulfonate ions, naphthalenesulfonate ions, toluenesulfonate ions, methanesulfonate ions, perchlorate ions, tetrafluoroborate ions, hexafluorophosphate ions, and fluorosulfate ions. The dopant may also be a polymeric ion. Examples of polymeric ions include ions of polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, and polyacrylic acid.

[0088] (Separator) The separator contains an olefin-based resin. An olefin-based resin refers to a resin containing olefin units as a main component. The olefin-based resin contains, for example, 50% by mass or more, or even 70% by mass or more, of olefin units. An olefin unit refers to a monomer unit derived from an olefin (alkene) such as ethylene, propylene, or butene. Here, the divalent group (diyl group) formed by polymerization of a monomer is referred to as the "unit" of that monomer. At least a portion of the olefin may be a derivative thereof. The olefin-based resin may be a homopolymer or a copolymer synthesized from multiple olefins. Some of the hydrogen atoms of the olefin may be substituted with halogen atoms. Examples of olefin-based resins include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), chlorinated polyethylene (CPE), ethylene-vinyl acetate copolymer (EVA), and ethylene-ethyl acrylate copolymer (EEA).

[0089] Examples of separators containing olefin-based resins that can be used include polyolefin microporous membranes, woven fabrics, and nonwoven fabrics. The thickness of the separator is, for example, 8 to 40 μm, preferably 12 to 30 μm, and more preferably 14 to 25 μm or 16 to 25 μm. Among microporous membranes, woven fabrics, and nonwoven fabrics, microporous membranes, which are non-fibrous porous films, are preferred because they have particularly high strength and are suitable for thinning.

[0090] (Electrolyte) The electrolyte has lithium ion conductivity and contains a lithium salt and a solvent that dissolves the lithium salt. The anions of the lithium salt are reversibly doped and dedoped into the positive electrode. The lithium ions derived from the lithium salt are reversibly absorbed into and released from the negative electrode.

[0091] Examples of lithium salts include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiFSO ３ , LiCF ３CO ２ , LiAsF ６ , LiB １０ Cl １０ , LiCl, LiBr, LiI, LiBCl ４ , LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ These may be used alone or in combination of two or more. The lithium salt is preferably a salt having a fluorine-containing anion, since it has a high degree of dissociation, can provide an electrolyte solution with low viscosity, and can improve the withstand voltage characteristics of an electrochemical device.

[0092] The electrolyte preferably includes an imide-based electrolyte. The imide-based electrolyte includes an imide-based anion as the anion of the lithium salt. The imide-based anion may be an anion containing fluorine and sulfur, and in particular, lithium bis(fluorosulfonyl)imide, i.e., LiN(SO ２ F) ２ It is preferable to use LiFSI. For example, 80 mass % or more of the lithium salt may be LiFSI.

[0093] LiFSI is believed to have the effect of reducing the degradation of the positive electrode active material and the negative electrode active material. Among salts having fluorine-containing anions, the FSI anion is highly stable, and therefore is less likely to produce by-products, contributing to smooth charge and discharge without damaging the surface of the active material. Furthermore, the SEI coating formed on the surface of the negative electrode mixture layer by LiFSI contains a large amount of lithium fluoride and a small amount of lithium carbonate. This allows a stable coating (second layer) primarily composed of lithium fluoride to be formed over the first layer primarily composed of lithium carbonate.

[0094] The concentration of the lithium salt in the non-aqueous electrolyte in a charged state (state of charge (SOC) 90 to 100%) is, for example, 0.2 to 5 mol / L.

[0095] Examples of solvents that can be used include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, and ethyl propionate, lactones such as γ-butyrolactone and γ-valerolactone, chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, trimethoxymethane, sulfolane, methyl sulfolane, and 1,3-propane sultone. These may be used alone or in combination of two or more.

[0096] The electrolyte may contain various additives as needed. For example, unsaturated carbonates such as vinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate may be added as additives that form a lithium ion conductive coating on the surface of the negative electrode.

[0097] EXAMPLES The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0098] Electrochemical Devices A1-A5, B1-B10 (Preparation of Positive Electrode) A 30 μm thick aluminum foil (positive electrode current collector) was prepared. 88 parts by weight of activated carbon (average particle size 5.5 μm) as the positive electrode active material, 6 parts by weight of acetylene black (AB) as the conductive agent, 4 parts by weight of carboxymethyl cellulose (CMC) as the thickener, and 2 parts by weight of polytetrafluoroethylene (PTFE) as the binder were dispersed in water to prepare a positive electrode mixture slurry. The resulting positive electrode mixture slurry was applied to both sides of aluminum foil, and the coating was dried and rolled to form a positive electrode mixture layer, resulting in a positive electrode. A 10 mm wide positive electrode current collector exposed portion was formed at the longitudinal end of the positive electrode current collector.

[0099] (Preparation of Negative Electrode) A 10 μm thick copper foil (negative electrode current collector) was prepared. A total of 90 parts by mass of the negative electrode active material and conductive agent, 4 parts by mass of carboxymethyl cellulose (CMC) as a thickener, and 6 parts by mass of styrene butadiene rubber (SBR) as a binder were dispersed in water to prepare a negative electrode mixture slurry. The resulting negative electrode mixture slurry was applied to both sides of copper foil, and the coating was dried and rolled to form a negative electrode mixture layer, resulting in a negative electrode. Non-graphitizable carbon (average particle size 5 μm) or graphite (average particle size 5 μm) was used as the negative electrode active material. Ketjen Black (KB) was used as the conductive agent. The compounding ratio of the negative electrode active material to the conductive agent was set to the value shown in Table 1. By changing the compounding ratio of the negative electrode active material to the conductive agent, the specific surface area of ​​the negative electrode mixture layer was adjusted to the value shown in Table 1.

[0100] Thereafter, a thin film of metallic lithium for pre-doping was formed on the entire surface of the negative electrode mixture layer by vacuum deposition. The amount of lithium to be pre-doped was set so that the negative electrode potential in the non-aqueous electrolyte after pre-doping was 0.2 V or less relative to metallic lithium.

[0101] Thereafter, the chamber of the device was purged with carbon dioxide to create a carbon dioxide gas atmosphere, thereby forming a first layer containing lithium carbonate on the surface of the negative electrode mixture layer. The dew point of the carbon dioxide gas atmosphere was −40° C., the molar fraction of carbon dioxide was 100%, and the pressure in the chamber was 1 atmosphere (1.01×10 ５ The temperature of the negative electrode exposed to the carbon dioxide gas atmosphere at 1 atmosphere was 25°C. The time for exposing the negative electrode to the carbon dioxide gas atmosphere was 22 hours. The first layer did not substantially contain F (or LiF).

[0102] (Preparation of electrode assembly) The separator used was a single-layer microporous polypropylene (PP) separator (thickness 25 μm), which is an olefin-based separator, or a nonwoven cellulose separator (thickness 25 μm), which is a cellulose-based separator. The air resistance of the separator was the value shown in Table 1.

[0103] The positive electrode and negative electrode were wound with a separator interposed therebetween into a cylindrical shape to form an electrode assembly. The exposed positive electrode core material protruded from one end face of the wound assembly, and the exposed negative electrode core material protruded from the other end face of the electrode assembly. A disk-shaped positive electrode current collector and a disk-shaped negative electrode current collector were welded to the exposed positive electrode core material and the exposed negative electrode core material, respectively.

[0104] (Preparation of non-aqueous electrolyte) A non-aqueous electrolyte was prepared by dissolving LiFSI as a lithium salt in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (volume ratio: 3:5:2). The concentration of LiFSI in the non-aqueous electrolyte was 1.2 mol / L.

[0105] (Assembly of electrochemical device) The electrode assembly was housed in a bottomed cell case with an opening, a tab lead connected to the positive electrode current collector was connected to the inner surface of the sealing plate, and a negative electrode current collector was welded to the inner bottom surface of the cell case. After placing a non-aqueous electrolyte in the cell case, the opening of the cell case was sealed with a sealing plate to assemble an electrochemical device as shown in Figure 1. In Table 1, A1 to A5 are electrochemical devices of examples, and B1 to B10 are electrochemical devices of comparative examples.

[0106] Thereafter, aging was performed at 60° C. while a charging voltage of 3.8 V was applied between the terminals of the positive electrode and the negative electrode to complete pre-doping of lithium ions into the negative electrode.

[0107] The electrochemical devices of the examples and comparative examples were evaluated as follows.

[0108] [Evaluation 1: Measurement of Internal Resistance of Electrochemical Device] The electrochemical device immediately after aging was subjected to a current of 2 mA / cm per positive electrode area in an environment of −30° C. until the voltage reached 3.8 V. ２ After that, the battery was charged at a constant current density of 2 mA / cm per positive electrode area in an environment of −30° C. until the voltage reached 2.2 V. ２ A constant current discharge was carried out at a current density of .

[0109] Using the discharge curve (vertical axis: discharge voltage, horizontal axis: discharge time) obtained in the above discharge, a linear approximation line was calculated for the range of 0.5 to 2 seconds after the start of discharge of the discharge curve, and the voltage VS at the intercept of the approximation line was calculated. The value (V0-VS) obtained by subtracting the voltage VS from the voltage VO at the start of discharge (0 seconds after the start of discharge) was calculated as ΔV. ΔV (V) and the current value during discharge (current density per positive electrode area 2 mA / cm ２ The internal resistance (DCR) R1 (Ω) of the electrochemical device was calculated using the following formula (A) and the surface area (area) of the positive electrode (Id). This was defined as the initial DCR.

[0110] Internal resistance R1=ΔV / Id (A)

[0111] [Evaluation 2: Reliability evaluation of electrochemical device] Next, the electrochemical device was maintained for a long period of time in an environment at 85°C with a constant voltage of 3.8 V applied. After 1000 hours had elapsed, the electrochemical device was removed and placed in an environment at -30°C, and the internal resistance (DCR) R2 (Ω) of the electrochemical device was determined in the same manner as in Evaluation 1. The ratio of R2 to R1: R2 / R1 was determined as the rate of change (deterioration rate). The smaller the rate of change, the more the increase in internal resistance was suppressed, and the higher the reliability.

[0112] The evaluation results are shown in Table 1. In Tables 1 and 2, HC represents non-graphitizable carbon, and the internal resistance R1 is expressed as an index when the internal resistance R1 of electrochemical device A2 is set to 100. In Table 1, the rate of change (R2 / R1) is expressed as an index when the rate of change (R2 / R1) of electrochemical device A2 is set to 100.

[0113]

[0114] Electrochemical devices B1 to B10 showed an increase in initial DCR and / or a decrease in reliability. Electrochemical devices A1 to A5 showed a small initial DCR and good reliability. Compared to devices using graphite as the negative electrode active material, devices using HC as the negative electrode active material showed smaller initial DCR and rate of change (A2, B7).

[0115] When the negative electrode active material is HC and the separator is cellulose-based, the specific surface area of ​​the negative electrode mixture layer is 10 m ２ / g, the rate of change was small, but ２ On the other hand, when the negative electrode active material was HC and the separator was an olefin-based material, the rate of change increased when the specific surface area of ​​the negative electrode mixture layer was 10 m / g or more (B3, B5, B8, B9). ２ / g, the rate of change is small, and the specific surface area of ​​the negative electrode mixture layer is ２ / g or more, the rate of change was kept small (B4, A1 to A5). ２ / g or more, and in electrochemical devices in which the negative electrode active material was HC, reliability was significantly improved by changing the cellulose-based separator to an olefin-based separator (B5 → A1, B8 → A2, B9 → A4).

[0116] Electrochemical devices A6 to A10 were fabricated and evaluated in the same manner as electrochemical device A4, except that the olefin-based separator was a microporous polypropylene (PP) membrane separator having the thickness and air resistance values ​​shown in Table 2. Devices A6 to A10 in Table 2 are electrochemical devices of the examples. The evaluation results are shown in Table 2 together with those of electrochemical device A4.

[0117]

[0118] All of the devices had a small initial DCR and showed good reliability. The initial DCR was further reduced in electrochemical devices A4 and A7 to A10.

[0119] The negative electrodes of the electrochemical devices A1 to A5 were evaluated as follows.

[0120] [Evaluation 3: XPS analysis of the surface portion of the negative electrode mixture layer] The surface portion of the negative electrode mixture layer after exposure to a carbon dioxide gas atmosphere was analyzed by XPS for C1s spectrum, O1s spectrum, and Li1s spectrum. For the analysis, an X-ray photoelectron spectrometer (trade name: Model 5600, manufactured by ULVAC-PHI, Inc.) was used. The measurement conditions are shown below.

[0121] X-ray source: Al-mono (1486.6 eV) 14 kV / 200 W Measurement diameter: 800 μmφ Photoelectron take-off angle: 45° Etching conditions: Acceleration voltage 3 kV, etching rate approximately 3.1 nm / min (SiO ２ Conversion), raster area 3.1mm x 3.4mm

[0122] As a result of analysis of the C1s spectrum, O1s spectrum, and Li1s spectrum, it was confirmed that the thickness of the first layer was approximately 18 nm. Specifically, peaks such as C-C bonds, which are presumed to be impurity carbon, were observed on the outermost surface, but they rapidly decreased around 1 to 2 nm deep in the first layer. Meanwhile, a first peak attributed to C=O bonds was observed from the outermost surface to a depth of 18 nm in the surface layer portion. A peak attributed to Li-O bonds was also observed from a depth of around 18 nm. Furthermore, the steady presence of Li was confirmed from the outermost surface to a depth of 18 nm in the surface layer portion. No peaks attributed to LiF were observed.

[0123] The surface of the negative electrode mixture layer of the negative electrode removed from the electrochemical device was subjected to XPS analysis in the same manner as above. It was confirmed that a 10 nm thick SEI coating (second layer) was formed, which had a different composition from the first layer and was distinct from the first layer. In addition, a peak attributed to LiF was observed.

[0124] The electrochemical device according to the present invention is suitable for use in a vehicle, for example.

[0125] 100: Electrode body 10: Positive electrode 11x: Positive electrode core material exposed portion 13: Positive electrode current collector plate 15: Tab lead 20: Negative electrode 21x: Negative electrode core material exposed portion 23: Negative electrode current collector plate 30: Separator 200: Electrochemical device 210: Cell case 220: Sealing plate 221: Gasket

Claims

1. The battery includes a positive electrode, a negative electrode, a separator, and a lithium ion conductive electrolyte, The positive electrode includes a positive electrode active material that is reversibly doped with anions, The negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the negative electrode current collector, the negative electrode mixture layer contains a negative electrode active material that is reversibly doped with lithium ions, The negative electrode active material contains non-graphitizable carbon, The specific surface area of ​​the negative electrode mixture layer is 10 m ２ / g or more, 70m ２ / g or less, The electrochemical device, wherein the separator comprises an olefin-based resin.

2. 2. The electrochemical device according to claim 1, wherein the potential of the negative electrode is 0.2 V or less versus lithium.

3. The specific surface area of ​​the negative electrode mixture layer is 10 m ２ / g or more, 50m ２ The electrochemical device according to claim 1 or 2, wherein the surface area of ​​the electrochemical device is 0.1 μm or less.

4. 3. The electrochemical device according to claim 1, wherein the separator has an air resistance of 70 sec / 100 mL or more and 500 sec / 100 mL or less.

5. 5. The electrochemical device according to claim 4, wherein the separator has an air resistance of 70 sec / 100 mL or more and 300 sec / 100 mL or less.

6. The lithium ion conductive electrolyte is lithium bis(fluorosulfonyl)imide: LiN(SO ２ F) ２ The electrochemical device of claim 1 or 2, comprising:

7. The electrochemical device according to claim 1 , wherein a surface layer portion of the negative electrode mixture layer has a first layer containing lithium carbonate.

8. a surface layer portion of the negative electrode mixture layer has a second layer including a solid electrolyte, The electrochemical device according to claim 7 , wherein at least a portion of the second layer covers at least a portion of a surface of the negative electrode mixture layer via the first layer.

9. the second layer contains lithium carbonate; The electrochemical device according to claim 8 , wherein a content of the lithium carbonate contained in the second layer is less than a content of the lithium carbonate contained in the first layer.

10. The electrochemical device according to claim 7 , wherein the first layer has a thickness of at least 1 nm and not more than 50 nm.

11. When the first layer is measured by X-ray photoelectron spectroscopy, a substantial F1s peak attributable to a LiF bond is not observed; 9. The electrochemical device according to claim 8, wherein a substantial F1s peak attributable to a LiF bond is observed when the second layer is measured by X-ray photoelectron spectroscopy.