Negative electrode active material, negative electrode, and non-aqueous electrolyte energy storage element

Abstract

To provide a negative electrode active material, high in discharge capacity in a potential range with a closed circuit potential of 0.40 V vs. Li / Li+ or more and also high in coulombic efficiency, and a negative electrode and a nonaqueous electrolyte power storage device in which such negative electrode active material is used.SOLUTION: A negative electrode active material for a nonaqueous electrolyte power storage device is a carbon material containing an element M. The element M is an element that increases the reaction potential of graphite with lithium ions when part of a carbon atom constituting the crystal structure of the graphite is substituted with the atom of the element M, in calculation results based on the first principle calculation, and the content of an oxygen element that is desorbed at an ambient temperature above 800°C is 6 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material, a negative electrode, and a non-aqueous electrolyte energy storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring charge-transporting ions between the two electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] Carbon materials such as graphite and non-graphitic carbon are widely used as negative electrode active materials in non-aqueous electrolyte energy storage elements (see Patent Documents 1 and 2). Lithium titanate is also known as another negative electrode active material (see Patent Document 3). On the other hand, copper foil is widely used as the negative electrode substrate for non-aqueous electrolyte energy storage elements. For example, a negative electrode for a non-aqueous electrolyte energy storage element is fabricated by providing a negative electrode active material layer containing graphite or the like on copper foil. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2018 / 043369 [Patent Document 2] Japanese Patent Publication No. 2013-016353 [Patent Document 3] Japanese Patent Publication No. 2015-28949 [Overview of the project] [Problems that the invention aims to solve]

[0005] From the viewpoints of cost reduction, weight reduction, and suppression of substrate component leaching during over-discharge, it is desirable to use aluminum foil instead of copper foil as the negative electrode substrate. However, in non-aqueous electrolyte energy storage elements where lithium ions are used as charge transport ions and aluminum foil as the negative electrode substrate, lithium-aluminum alloying reactions are likely to occur, so closed circuit potential 0.35V vs. Li / Li + The negative electrode needs to be operated within a potential range above a certain level. By operating the negative electrode within such a potential range, the dendrite deposition of metallic lithium on the negative electrode can be suppressed, thus enabling rapid charging.

[0006] However, for common carbon materials such as graphite and non-graphitizable carbon, the closed-circuit potential is 0.40V vs. Li / Li + The discharge capacity is small in the above potential range. Furthermore, according to the inventors' findings, graphite oxide, a carbon material containing oxygen, is used in a closed circuit at a potential of 0.40V vs. Li / Li + When used within the above potential range, the discharge capacity is large, but the ratio of discharge capacity to charge capacity, i.e., the Coulomb efficiency, is low. Furthermore, lithium titanate, a negative electrode active material that can be used with aluminum foil as the negative electrode substrate, has disadvantages such as low discharge capacity and high cost.

[0007] This invention was made based on the circumstances described above, and its purpose is to compare closed-circuit potentials of 0.40V versus Li / Li. + The objective is to provide a negative electrode active material with a large discharge capacity and high Coulomb efficiency in the above potential range, as well as a negative electrode and a non-aqueous electrolyte energy storage element using such a negative electrode active material.

[0008] In this specification, the reduction reaction in which charge transport ions (lithium ions in the case of lithium-ion non-aqueous electrolyte secondary batteries) are absorbed from the non-aqueous electrolyte to the negative electrode active material is referred to as "charging," and the oxidation reaction in which charge transport ions are released from the negative electrode active material is referred to as "discharging." [Means for solving the problem]

[0009] A negative electrode active material (A) for a non-aqueous electrolyte energy storage element according to one aspect of the present invention is a carbon material containing element M, wherein, based on calculation results from first-principles calculations, when some of the carbon atoms constituting the crystal structure of graphite are replaced with atoms of element M, the reaction potential of the graphite with lithium ions is increased, and the oxygen element content that desorbs at an ambient temperature of over 800°C is 6% by mass or less.

[0010] The negative electrode active material (B) for a non-aqueous electrolyte energy storage element according to one aspect of the present invention is a carbon material containing element M, wherein element M is at least one selected from the group consisting of beryllium, boron, aluminum, silicon, phosphorus, sulfur, titanium, and gallium, and the oxygen element content that desorbs under an ambient temperature of over 800°C is 6% by mass or less.

[0011] A negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises the above-mentioned negative electrode active material (A) or the above-mentioned negative electrode active material (B).

[0012] A non-aqueous electrolyte energy storage element according to one aspect of the present invention includes the above-mentioned negative electrode. [Effects of the Invention]

[0013] According to one aspect of the present invention, closed-circuit potential 0.40V vs. Li / Li + This invention provides a negative electrode active material with a large discharge capacity and high Coulomb efficiency in the above potential range, as well as a negative electrode and a non-aqueous electrolyte energy storage element using such a negative electrode active material. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is an external perspective view showing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing an energy storage device configured by assembling multiple non-aqueous electrolyte energy storage elements according to one embodiment of the present invention. [Figure 3]Figure 3 shows the charge-discharge curves for the first cycle of each non-aqueous electrolyte energy storage element in Example 4 and Comparative Examples 1 and 2. [Figure 4] Figure 4 shows the discharge curves (including the open-circuit voltage after discharge) for the third cycle of each non-aqueous electrolyte energy storage element in Example 4 and Comparative Examples 1 and 2. [Modes for carrying out the invention]

[0015] First, an overview of the negative electrode active material, negative electrode, and non-aqueous electrolyte energy storage element disclosed herein will be provided.

[0016] A negative electrode active material (A) for a non-aqueous electrolyte energy storage element according to one aspect of the present invention is a carbon material containing element M, wherein, based on calculation results from first-principles calculations, when some of the carbon atoms constituting the crystal structure of graphite are replaced with atoms of element M, the reaction potential of the graphite with lithium ions is increased, and the oxygen element content that desorbs at an ambient temperature of over 800°C is 6% by mass or less.

[0017] The negative electrode active material (A) has a closed-circuit potential of 0.40V vs. Li / Li + The discharge capacity is large and the Coulomb efficiency is high in the above potential range. The reason for this is not clear, but the following reason is speculated: The carbon material contains element M, which increases the reaction potential with charge transport ions (e.g., lithium ions), resulting in a closed-circuit potential of 0.40V vs. Li / Li + The discharge capacity increases in the above potential range. Furthermore, oxygen elements that desorb at ambient temperatures above 800°C, i.e., oxygen elements that do not desorb at ambient temperatures below 800°C, are oxygen elements that are strongly bonded to carbon elements in the carbon material, and it is presumed that the presence of such oxygen elements is one of the causes of the decrease in Coulomb efficiency. Therefore, if the content of oxygen elements that desorb at ambient temperatures above 800°C in the negative electrode active material, which is a carbon material, is 6 mass% or less, the closed circuit potential is 0.40V vs. Li / Li +The Coulomb efficiency in the above potential range increases. For the above reasons, it is presumed that the above effects are achieved in the negative electrode active material (A).

[0018] The method of calculation based on the first-principles calculation for specifying the element M will be described in detail later.

[0019] The measurement of the oxygen element content in the negative electrode active material (carbon material) is performed on the negative electrode active material before charge and discharge, or for the negative electrode active material incorporated in the negative electrode of the non-aqueous electrolyte storage element, on the material processed by the following procedure. First, the non-aqueous electrolyte storage element is discharged at a constant current to the discharge cut-off voltage during normal use at a current of 0.1C. Then, it is disassembled, the negative electrode is taken out, and washed with dimethyl carbonate. A test cell is assembled with the washed negative electrode as the working electrode and metallic lithium as the counter electrode. For this test cell, constant current discharge is performed at a current of 50 mA / g per mass of the negative electrode active material until the closed-circuit potential of the negative electrode becomes 2.0V vs. Li / Li + to adjust the negative electrode active material (carbon material) to a fully discharged state (a state in which the charge transport ions involved in the charge and discharge reaction have desorbed). It is disassembled again, and the negative electrode is taken out. The taken-out negative electrode is washed with dimethyl carbonate. Then, the negative electrode mixture containing the negative electrode active material is peeled off from the negative electrode substrate, and the negative electrode mixture is washed with water. The negative electrode mixture washed with water is immersed in an acid or alkali solution to remove the metal derived from the negative electrode substrate and the SEI (solid electrolyte interface) film, etc., then washed with water, and dried under reduced pressure to obtain the negative electrode active material. The disassembly operations of the non-aqueous electrolyte storage element and the test cell are performed in an argon atmosphere with a dew point of -60°C or lower. Here, "during normal use" refers to the case where the non-aqueous electrolyte storage element is used by adopting the charge and discharge conditions recommended or specified for the non-aqueous electrolyte storage element.

[0020] The oxygen element content in the negative electrode active material (carbon material) is measured by the following method using an oxygen, nitrogen, and hydrogen analyzer "EMGA-930" manufactured by HORIBA. Detector for oxygen: Inert gas fusion - non-dispersive infrared absorption method (NDIR) Sample mass: 20 mg to 25 mg Gas extraction furnace power: Impulse furnace output 0 to 8.0 kW (The relationship between output and temperature should be determined in advance and adjusted according to the set temperature.) Carrier gas: Helium Calibration method: Single-point calibration using a standard sample Calculation conditions: Time calculation Time accumulated for each set temperature (1) 0 to 60 seconds (400℃) (2) 60 to 110 seconds (600℃) (3) 110 to 160 seconds (800℃) (4) 160 to 210 seconds (1000℃) (5) 210 to 260 seconds (1200℃) (6) 260 to 330 seconds (2500℃) Measurement procedure: A graphite crucible is placed in the extraction furnace and preheated at 3231°C for 30 seconds, then at 400°C for 20 seconds to remove oxygen elements from the crucible. The crucible is then removed to the atmosphere, 20 mg to 25 mg of the sample is placed inside, and it is placed back into the extraction furnace. Next, the temperature is gradually increased and heated according to the set temperatures and times from (1) to (6) above, and the amount of oxygen elements desorbed from the sample at each temperature is quantified. In addition, considering that oxygen elements may be adsorbed again on the crucible after being exposed to the atmosphere after preheating, the amount of oxygen elements desorbed from the crucible alone after being exposed to the atmosphere after preheating is also measured and removed. The "amount of oxygen element desorbed in the negative electrode active material (carbon material) under ambient temperatures exceeding 800°C (mass%)" is determined as a percentage of the total mass of oxygen element measured at set temperatures of 1000°C, 1200°C, and 2500°C (total mass of oxygen element measured between 160 and 330 seconds of cumulative time) relative to the mass of the sample (negative electrode active material) before heating in the extraction furnace, which has been measured in advance.

[0021] The negative electrode active material (B) for a non-aqueous electrolyte energy storage element according to one aspect of the present invention is a carbon material containing element M, wherein element M is at least one selected from the group consisting of beryllium, boron, aluminum, silicon, phosphorus, sulfur, titanium, and gallium, and the oxygen element content that desorbs under an ambient temperature of over 800°C is 6% by mass or less.

[0022] The negative electrode active material (B) has a closed-circuit potential of 0.40V vs. Li / Li + The discharge capacity is large and the Coulomb efficiency is high within the above potential range. Beryllium, boron, aluminum, silicon, phosphorus, sulfur, titanium, and gallium are elements that, based on first-principles calculations, increase the reaction potential of graphite with lithium ions when some of the carbon atoms constituting the crystal structure of graphite are replaced with atoms of the above element M. Therefore, for the same reasons as the above-mentioned negative electrode active material (A), it is presumed that the negative electrode active material (B) also exhibits the above effect.

[0023] The content of element M in the negative electrode active material (A) and negative electrode active material (B) is preferably 0.05% by mass or more and 15% by mass or less. When the content of element M in the carbon material negative electrode active material (A) and negative electrode active material (B) is within the above range, the closed circuit potential is 0.40V vs. Li / Li + In the above potential range, the discharge capacity becomes larger, and the Coulomb efficiency also increases.

[0024] The element M content in the negative electrode active material (carbon material) is measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The negative electrode active material (carbon material) is dissolved in an aqueous nitric acid solution by total dissolution treatment using microwave decomposition and then subjected to the above measurement. The above measurement is performed on the negative electrode active material before charging and discharging, or, in the case of negative electrode active material incorporated into the negative electrode of a non-aqueous electrolyte energy storage element, it is performed on material that has been treated in the same manner as when measuring the "oxygen element content in the negative electrode active material (carbon material)" described above.

[0025] In the negative electrode active material (A) and negative electrode active material (B), the closed-circuit potential is 0.40V vs. Li / Li + From the charged state, with a current of 50mA / g per mass of the above negative electrode active material, the closed circuit potential is 2.00V vs. Li / Li + After constant current discharge, the open-circuit potential after 10 minutes was 1.33V vs. Li / Li + The above conditions are preferable. If the open-circuit potential after discharge is high under these conditions, open-circuit potential 0.40V vs. Li / Li + The discharge capacity in the above potential range becomes larger. Furthermore, it is presumed that when some of the carbon elements in the graphene layer of the carbon material are replaced with element M, the number of storage sites where charge transport ions are inserted into the graphene layer increases in the high potential range, and the open-circuit potential after discharge increases. In other words, the high open-circuit potential after discharge as described above means that some of the carbon elements in the graphene layer of the carbon material have been sufficiently replaced with element M, and as a result, the open-circuit potential of 0.40V vs. Li / Li + It is presumed that this will result in a greater discharge capacity within the above potential range.

[0026] The open-circuit potential measurement described above is performed at a temperature of 25°C using a test battery assembled with metallic lithium as the counter electrode. For the working electrode of the test battery, either the negative electrode before charging and discharging is used, or, if it is incorporated into a non-aqueous electrolyte energy storage element, the non-aqueous electrolyte energy storage element is disassembled using the same procedure as for measuring the "oxygen content in the negative electrode active material (carbon material)" described above, and the negative electrode is washed with dimethyl carbonate. The electrolyte of the test battery is a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35, with a concentration of 1 mol / dm³. 3 A solution of LiPF6 dissolved at the specified concentration is used. For the test battery, a closed-circuit potential of 0.40V is measured with a current of 50mA / g per mass of negative electrode active material vs. Li / Li + Constant current and constant voltage charging is performed until the voltage reaches 0.40V vs. Li / Li. +This is assumed to be 12 hours after reaching the target. Subsequently, a closed-circuit potential of 2.00V vs. Li / Li is applied with a current of 50 mA / g per mass of the negative electrode active material. + The circuit is discharged at a constant current until a certain point is reached, and the open-circuit potential is measured 10 minutes later. Note that when the counter electrode is metallic lithium, the dissolution and deposition reaction resistance of metallic lithium at the counter electrode is extremely low, so the voltage between the working electrode and the counter electrode during charging and discharging can be considered to be approximately equal to the potential of the working electrode relative to the oxidation-reduction potential of metallic lithium.

[0027] A negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode active material (A) or a negative electrode active material (B) according to one aspect of the present invention. The negative electrode has a closed-circuit potential of 0.40V vs. Li / Li + The discharge capacity is large and the Coulomb efficiency is high within the above potential range.

[0028] The negative electrode preferably further comprises a negative electrode substrate mainly composed of aluminum. The negative electrode comprising a negative electrode substrate mainly composed of aluminum may have a closed-circuit potential of 0.40V vs. Li / Li + Even when used within the above potential range, the discharge capacity is large and the Coulomb efficiency is high, and by using it within the above potential range, the alloying reaction between the metal and aluminum, in which charge transport ions such as lithium-aluminum alloying reactions are reduced, can be suppressed. Furthermore, by incorporating an anode substrate mainly composed of aluminum, the anode can be made lighter and less expensive, and the leaching of components from the anode substrate during over-discharge can also be suppressed.

[0029] The main component refers to a component that is present in an amount of 50% or more by mass.

[0030] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode according to one aspect of the present invention. The negative electrode potential of this non-aqueous electrolyte energy storage element is a closed-circuit potential of 0.40V vs. Li / Li + When used within the above range, it exhibits a large discharge capacity and high Coulomb efficiency.

[0031] Preferably, the non-aqueous electrolyte energy storage element further comprises a non-aqueous electrolyte containing propylene carbonate. In this case, the charge acceptance performance of the non-aqueous electrolyte energy storage element is improved, and high-speed, efficient charging can be performed.

[0032] In the non-aqueous electrolyte energy storage element, the negative electrode potential at the charging termination voltage during normal use is 0.35V vs. Li / Li + The above is preferable. The non-aqueous electrolyte energy storage element has a large discharge capacity and high Coulomb efficiency even when used in such a negative electrode potential range. Furthermore, by using the non-aqueous electrolyte energy storage element in such a negative electrode potential, a negative electrode substrate mainly composed of aluminum can be suitably applied to the negative electrode.

[0033] This document describes in detail a negative electrode active material, a negative electrode, a non-aqueous electrolyte energy storage element, an energy storage device, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments according to one embodiment of the present invention. Note that the names of the components (each element) used in each embodiment may differ from the names of the components (each element) used in the background art.

[0034] <Negative electrode active material (A)> The negative electrode active material (A) according to one embodiment of the present invention is a carbon material. This negative electrode active material is used as the negative electrode active material for a non-aqueous electrolyte energy storage element. A carbon material is a material in which the most abundant element by mass is carbon. In addition to carbon, the negative electrode active material (A) contains element M, and may further contain other elements such as hydrogen, nitrogen, and oxygen. The carbon content in the negative electrode active material (A) is preferably 70% by mass or more and 99.95% by mass or less, and more preferably 80% by mass or more and 99.9% by mass or less. The lower limit of the carbon content in the negative electrode active material (A) may be more preferably 90% by mass, 95% by mass, 97% by mass, 98% by mass, or 99.0% by mass. The upper limit of the carbon content in the negative electrode active material (A) may be more preferably 99.0% by mass, 97% by mass, or 95% by mass.

[0035] Element M is the element that, based on first-principles calculations, increases the reaction potential of graphite with lithium ions when some of the carbon atoms constituting the crystal structure of graphite are replaced with atoms of element M. Regarding the "crystal structure of graphite" mentioned above, the first-principles calculations are performed based on this crystal structure of graphite, and the negative electrode active material (A) is not limited to having a graphite crystal structure. The method for first-principles calculations to identify element M is described below.

[0036] First-principles calculations are computational methods for predicting material properties abruptly. These methods can calculate the total energy and electron energy band structure of models containing atoms with known atomic numbers and spatial coordinates. Broadly speaking, there are two types of calculation methods: "wave function theory" and "density functional theory." The calculation method used in this specification is based on density functional theory.

[0037] Using first-principles calculations, element M is identified by the following procedure. (1) Select any element A that is a candidate for element M. Create a 2×1×2 supercell by stretching the unit crystal lattice of LiC6 (space group: P6 / mmm) by twice the length in both the x and z directions. Next, create "element A-substituted graphite" C by substituting 1 / 24 of the carbon atoms with atoms of element A. 5.75 A 0.25 Total energy E1 and LiC 5.75 A 0.25 The total energy E2 is calculated by first-principles calculations. 5.75 A 0.25 The structure corresponds to the discharge state (SOC 0%), LiC 5.75 A 0.25 The structure corresponds to the theoretical charge state (SOC 100%).

[0038] (2) LiC 5.75 A 0.25The arrangement of lithium atoms in the structure of [the material] has an enormous number of possible combinations, making it impossible to evaluate all possibilities. Therefore, first-principles calculations are performed using a genetic algorithm. A genetic algorithm is a type of optimization algorithm that mimics the process of biological evolution. It is a method that can quickly find the optimal individual by repeatedly performing the process of preferentially rearranging superior genes from multiple individuals whose parameters are represented by genes. The calculation conditions for the genetic algorithm are shown below. Number of genes per individual: 1 Number of individuals generated per generation: 20 Percentage of individuals to survive each generation: 0.6 Ratio of two-point crossover: 0.4 Percentage of uniform crossover: 0.4 Number of superior individuals that are unconditionally passed on to the next generation without genetic manipulation: 3 Probability of uniform crossover occurring: 0.8 Probability of mutation occurring: 0.02 Maximum number of generations: 200 Convergence criteria: When the most stable individual has not been updated for 10 consecutive generations.

[0039] For the first-principles calculations in the genetic algorithm described in (2) above, the Vienna Ab-initio Simulation Package (VASP) software can be used. The calculation conditions are as follows: Cutoff energy of plane wave basis function: 400 eV Approximation method for exchange-correlation interaction: GGA+U Pseudopotential: PAW(PBEsol) k-point: gamma point Energy smearing: Gaussian method

[0040] (3) For the top 23 structures with high structural stability as a result of (2) above, first-principles calculations are performed again to accurately calculate the free energy value, the charge of each ion, etc., and the total energy of the most stable structure is set to E2.

[0041] For calculating the total energies E1 and E2 in (1) and (3) above, the Vienna Ab-initio Simulation Package (VASP) software can be used. The calculation conditions are as follows: The k-points are set so that the k-resolution value is approximately 1000. The k-resolution is the product of the number of atoms in the model and the k-points in the a, b, and c axes. Cutoff energy of plane wave basis function: 420 eV Approximation method for exchange-correlation interaction: GGA+U Pseudopotential: PAW(PBEsol) k point: k-resolution≒1000 Energy smearing: Gaussian method

[0042] The difference between E2 and E1 (E2-E1) is the reaction energy E with lithium ions in element A-substituted graphite. A This is calculated as the reaction energy E. A The reaction potential V is based on the oxidation-reduction potential of lithium. A Convert to this. The reaction potential that can be similarly determined when element A is carbon is the reaction potential of graphite with lithium V C The reaction potential is V. A The reaction potential is V C The element A that becomes larger is element M.

[0043] Select carbon (C), boron (B), aluminum (Al), silicon (Si), phosphorus (P), titanium (Ti), nitrogen (N), gallium (Ga), sulfur (S), and beryllium (Be) as element A, and determine the respective reaction potential V using the method described above. A The results obtained are shown in Table 1 below.

[0044] [Table 1]

[0045] Among the elements A in Table 1 above, for which first-principles calculations were performed, the reaction potential VA 0.30V vs. Li / Li + Elements with higher reaction potentials than V include B, Al, Si, P, Ti, Ga, S, and Be, which correspond to element M. A The higher the element M, the better the closed-circuit potential (0.40V) vs. Li / Li. + It is expected that the discharge capacity in the above potential range can be increased. On the other hand, the reaction potential V A As the value increases, the voltage of the non-aqueous electrolyte energy storage element decreases. Therefore, the reaction potential V obtained by the first-principles calculation above A For example, 0.50V vs. Li / Li + Above 1.60V vs. Li / Li + Preferably, the following: 0.60V vs. Li / Li + Above 1.40V vs. Li / Li + The following is more preferable. From this viewpoint, among the elements M above, B, Al, Si, P, Ga, S, and Be are preferred, and B, Al, Ga, and S are more preferred. The elements M above are preferably from groups 2 to 16, more preferably from groups 13 to 16, and even more preferably from group 13. One or more elements M can be used.

[0046] Li x C 5.75 A 0.25 Instead, Na x C 5.75 A 0.25 and K x C 5.75 A 0.25 Similarly, the reaction potential V when element A is carbon and when element A is boron. A This was determined by first-principles calculations. The results are shown in Tables 2 and 3 below.

[0047] [Table 2]

[0048] [Table 3]

[0049] As shown in Tables 2 and 3, when sodium ions or potassium ions are absorbed and released into the carbon material as charge transport ions, the reaction potential V is similarly reduced by substituting some of the carbon elements with boron elements. A The calculation results showed an increase in the negative electrode active material (A). When applied to sodium ion energy storage elements and potassium ion energy storage elements, the closed-circuit potential was 0.40V vs. Li / Li. + It is presumed that this results in a large discharge capacity and high Coulomb efficiency within the above potential range.

[0050] The content of element M in the negative electrode active material (A) (carbon material) is preferably 0.05% by mass or more and 15% by mass or less, and more preferably 0.1% by mass or more and 10% by mass or less. The lower limit of the content of element M may be more preferably 0.15% by mass, 0.5% by mass, 1% by mass, 3% by mass, or 5% by mass. The upper limit of the content of element M may be more preferably 5% by mass, 3% by mass, 2% by mass, 1.5% by mass, or 1.0% by mass. By having the content of element M in the negative electrode active material (A) within the above range, the closed circuit potential is 0.40V vs. Li / Li + In the above potential range, the discharge capacity becomes larger, and the Coulomb efficiency also increases.

[0051] In one embodiment of the present invention, it is preferable that the carbon material has a graphene layer, and that some of the carbon elements constituting this graphene layer are replaced with aluminum elements. It is preferable that the carbon material has a layered crystalline structure in at least a portion of it.

[0052] The negative electrode active material (A) is preferably a carbon material in which a (002) plane diffraction peak is observed in X-ray diffraction (XRD) measurements using CuKα rays. Furthermore, the negative electrode active material (A) has an average lattice plane spacing (d) of the (002) plane determined by the X-ray diffraction method. 002 It may be preferable that the carbon material has an average lattice plane spacing (d) of 0.33 nm or more and less than 0.42 nm, and the above average lattice plane spacing (d002 It may be more preferable that the carbon material has a n-scale of 0.34 nm to 0.38 nm. The above XRD measurement is performed on the negative electrode active material before charging and discharging or in the fully discharged state described above. The XRD measurement is performed by the following method.

[0053] The powder X-ray diffraction pattern of the sample is acquired using an X-ray diffractometer (Rigaku, model: MiniFlex II). The radiation source is CuKα, the tube voltage is 30kV, and the tube current is 15mA. The diffracted X-rays pass through a 30μm thick Kβ filter and are detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width is 0.02°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13mm (OPEN), and the scattering slit width is 8mm. The obtained pattern is fitted to the peak shape by optimization using the integrated powder X-ray analysis software PDXL, and the position and full width at half maximum of each diffraction peak are obtained. Typically, diffraction peaks that can be attributed to the (002) plane are observed between 2θ = 24.5° and 26.5°.

[0054] The upper limit of the oxygen element content that desorbs in the negative electrode active material (A) at an ambient temperature exceeding 800°C is 6% by mass, preferably 3% by mass, and more preferably 2% by mass, 1% by mass, 0.3% by mass, 0.1% by mass, or 0.01% by mass. When the oxygen element content that desorbs in the negative electrode active material (A) at an ambient temperature exceeding 800°C is less than or equal to the above upper limit, the closed-circuit potential is 0.40V vs. Li / Li + In the above potential range, the charge-discharge hysteresis tends to decrease, and the Coulomb efficiency tends to increase. The lower limit of the oxygen element content that desorbs in the negative electrode active material (A) under ambient temperatures exceeding 800°C may be 0% by mass, 0.001% by mass, or 0.01% by mass. The oxygen element content can be above any of the lower limits and below any of the upper limits.

[0055] In the negative electrode active material (A), the closed-circuit potential is 0.40V vs. Li / Li+ From the charged state, with a current of 50mA / g per mass of the above negative electrode active material, the closed circuit potential is 2.00V vs. Li / Li + After constant current discharge, the lower limit of the open-circuit potential after 10 minutes is 1.33V vs. Li / Li + Preferably, 1.35V vs. Li / Li + More preferable is 1.37V vs. Li / Li + More preferably, 1.40V vs. Li / Li + Even more preferable is 1.50V vs. Li / Li + 1.60V vs. Li / Li + 1.70V vs. Li / Li + 1.80V vs. Li / Li + Or 1.90V vs. Li / Li + In some cases, this is even more preferable. If the open-circuit potential 10 minutes after discharge is above the lower limit, the closed-circuit potential is 0.40V vs. Li / Li + The discharge capacity becomes larger in the above potential range. The upper limit of the open-circuit potential is, for example, 2.00V vs. Li / Li + Even if it is 1.99V vs. Li / Li + Even if it is 1.90V vs. Li / Li + 1.80V vs. Li / Li + 1.70V vs. Li / Li + 1.60V vs. Li / Li + 1.50V vs. Li / Li + Or 1.45V vs. Li / Li + Even if it is 1.43V vs. Li / Li + The above open-circuit potential may be the above upper limit (preferably 1.43V vs. Li / Li). + If the values ​​are less than or equal to the specified limit, it is possible to achieve both a large discharge capacity and a small difference between the open-circuit voltage and the average discharge voltage. The open-circuit potential can be set to be above or below the lower limit and below the upper limit of the specified limit.

[0056] In the C1s spectrum of the negative electrode active material (A) obtained by X-ray photoelectron spectroscopy (XPS), the integrated intensity in the range of 282.5 eV to 283.5 eV is preferably 3 eV or more and 80 eV or less, and more preferably 5 eV or more and 60 eV or less. The lower limit of this integrated intensity may be more preferably 7 eV, 10 eV or 20 eV. In the C1s spectrum by XPS, a peak derived from the bond between the carbon element and the element M is presumed to appear in the range of 282.5 eV to 283.5 eV. Therefore, when the integrated intensity in the range of 282.5 eV to 283.5 eV in the above C1s spectrum is within the above range, it is considered that the element M is sufficiently chemically bonded to the carbon element, and the open circuit potential is 0.40 V vs. Li / Li + The discharge capacity in the above potential range becomes larger, and the Coulomb efficiency becomes higher.

[0057] The XPS measurement is performed on the negative electrode active material before charge and discharge or on the negative electrode active material incorporated in the negative electrode of the non-aqueous electrolyte storage element by the following method for the material treated in the same procedure as when measuring the "content of oxygen element in the negative electrode active material (carbon material)" described above. Attach carbon tape on the sample holder and place the sample thereon. Introduce the sample holder into the sample chamber of "AXIS NOVA" manufactured by KRATOS ANALYTICAL, which is an XPS device, and acquire the XPS spectrum. The XPS measurement is performed under a reduced pressure of 5×10 -5 Pa or less. To measure the C1s spectrum, perform a narrow scan by integrating 10 times at 272 eV to 300 eV respectively. Correct the energy value of the C1s spectrum so that the energy value showing the maximum intensity of the C1s peak becomes 284.8 eV. AlKα is used as the X-ray source, with an emission of 10 mA and an anode HT of 15 kV. During measurement, a neutralizing gun is used, with a filament current of 2 A, a charge balance of 3.5 V, and a filament bias of 1.2 V. For narrow scans, the step size is 0.1 eV and the dwell time is 250 ms. The analyzer settings are as follows: analyzer mode "Spectrum", lens mode "Field of View 1: Survey", energy resolution "Pass Energy 40", and analysis area "slot". Using the method described above, the C1s spectrum, with its energy values ​​corrected, is then subjected to background removal using the linear method. Specifically, a linear function passing through the points where the minimum value is observed in the range of 280 eV to 284 eV and the points where the minimum value is observed in the range of 292 eV to 300 eV is removed as background. For the C1s spectrum with the background removed, the intensity at 284.8 eV is normalized to 100, and the integrated intensity in the range of 282.5 eV to 283.5 eV is calculated.

[0058] The negative electrode active material (A) is usually in powder form. The negative electrode active material (A) may be used in combination with other negative electrode active materials, for example, but a preferred form is to use the negative electrode active material (A) as a powder alone.

[0059] The average particle size of the negative electrode active material (A) can be, for example, 1 nm to 100 μm, and is preferably 1 μm to 100 μm. Setting the average particle size of the negative electrode active material above the lower limit makes manufacturing and handling easier. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity when the negative electrode active material layer is formed. "Average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0060] To obtain powder with a predetermined particle size, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and wind classifiers are used as needed, both dry and wet.

[0061] The method for producing the negative electrode active material (A) is not particularly limited, and it can be synthesized, for example, by chemical vapor deposition (CVD). Specifically, a raw material gas containing a gas that provides element M (also called a substitution element source gas) and a carbon source gas is introduced into a reaction vessel such as a quartz tube, and the material can be synthesized by CVD at a high temperature using an electric furnace or the like. The reaction temperature in the above synthesis can be, for example, 700°C to 1200°C.

[0062] Examples of substitution element source gases include halides of element M such as BCl3 and AlCl3. Substitution element source gases can also be obtained by sublimating a substitution element source compound that is solid at room temperature by heating. Examples of carbon source gases include hydrocarbons such as benzene, acetylene, ethylene, methane, ethane, and propane. Furthermore, it is preferable to use a carrier gas such as nitrogen in addition to the above-mentioned raw material gases.

[0063] It is preferable to reheat the carbon material precipitated in the reaction vessel by the above synthesis. For example, the precipitated carbon material is recovered and reheated in a vacuum displacement furnace. The reheating is carried out, for example, under a nitrogen atmosphere or an argon atmosphere. The treatment temperature during the reheating can be between 600°C and 1000°C. The carbon material after reheating is used as a negative electrode active material after being crushed, for example, in a mortar.

[0064] <Negative electrode active material (B)> The negative electrode active material (B) according to one embodiment of the present invention is a carbon material containing element M, wherein element M is at least one selected from the group consisting of beryllium, boron, aluminum, silicon, phosphorus, sulfur, titanium, and gallium, and the oxygen element content that desorbs under an ambient temperature of over 800°C is 6% by mass or less.

[0065] The specific form and preferred form of the negative electrode active material (B) are the same as those of the negative electrode active material (A) described above, except that element M is at least one selected from the group consisting of beryllium, boron, aluminum, silicon, phosphorus, sulfur, titanium, and gallium.

[0066] <Negative electrode> The negative electrode according to one embodiment of the present invention is a negative electrode for a non-aqueous electrolyte energy storage element, comprising the negative electrode active material (A) or negative electrode active material (B) according to one embodiment of the present invention described above. The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The negative electrode active material (A) and negative electrode active material (B) according to one embodiment of the present invention are collectively referred to as "negative electrode active material according to one embodiment of the present invention".

[0067] The negative electrode substrate is conductive. Whether or not it is conductive is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975) if it is 10 -2 The determination is made using Ω·cm as the threshold. The negative electrode substrate material can be a metal or alloy thereof, such as copper, nickel, stainless steel, nickel-plated steel, or aluminum, or a carbonaceous material. Preferably, the negative electrode substrate has aluminum as its main component. Using such a negative electrode substrate can reduce costs, reduce weight, and suppress the leaching of components from the negative electrode substrate during over-discharge. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from a cost standpoint. Therefore, aluminum foil or aluminum alloy foil is preferred as the negative electrode substrate.

[0068] Suitable materials for the negative electrode substrate include pure aluminum or aluminum alloys. "Pure aluminum" refers to aluminum with an aluminum element content of 99.00% by mass or more, for example, the 1000 series aluminum specified in JIS-H-4000 (2014). "Aluminum alloy" refers to a metal in which the most abundant element is aluminum, but the aluminum element content is less than 99.00% by mass, for example, aluminum alloys other than the 1000 series specified in the above JIS. Examples of aluminum alloys other than the 1000 series specified in the above JIS include the 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, and 7000 series aluminum alloys specified in the above JIS. The aluminum element content in the negative electrode substrate is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0069] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0070] The intermediate layer is a layer placed between the negative electrode substrate and the negative electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the negative electrode substrate and the negative electrode active material layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0071] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components.

[0072] The negative electrode active material layer includes the negative electrode active material according to the embodiment of the present invention described above. The negative electrode active material layer may further include other negative electrode active materials. The other negative electrode active materials can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials that can intercept and release lithium ions are usually used as negative electrode active materials. Examples of other negative electrode active materials include metallic lithium; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 LiTiO 2、 Examples include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and conventionally known carbon materials other than the negative electrode active material according to one embodiment of the present invention (graphite, non-graphitic carbon, etc.).

[0073] The content of the negative electrode active material according to one embodiment of the present invention relative to all negative electrode active materials in the negative electrode active material layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and may be substantially 100% by mass. In this way, by mainly using the negative electrode active material according to one embodiment of the present invention as the negative electrode active material, the closed circuit potential of 0.40V vs. Li / Li + The discharge capacity in the above potential range becomes larger, and the Coulomb efficiency becomes higher.

[0074] The total content of all negative electrode active materials in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 70% by mass or more and 95% by mass or less. By setting the content of negative electrode active materials within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer. For similar reasons, the content of negative electrode active materials in the negative electrode active material layer according to one embodiment of the present invention is preferably 60% by mass or more and 99% by mass or less, and more preferably 70% by mass or more and 95% by mass or less.

[0075] The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include non-graphite carbon and graphene-based carbon. Examples of non-graphite carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

[0076] When a conductive agent is included in the negative electrode active material layer, the content of the conductive agent in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte energy storage element can be increased. In one embodiment of the present invention, it may be preferable that the negative electrode active material layer does not contain a conductive agent.

[0077] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0078] The binder content in the negative electrode active material layer is preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 20% by mass or less. By keeping the binder content within the above range, the negative electrode active material can be stably maintained.

[0079] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like.

[0080] When a thickening agent is included in the negative electrode active material layer, the content of the thickening agent in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, it may be preferable that the negative electrode active material layer does not contain a thickening agent.

[0081] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0082] When the negative electrode active material layer contains fillers, the filler content in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, it is preferable that the negative electrode active material layer does not contain fillers.

[0083] The negative electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0084] The negative electrode can be obtained, for example, by laminating a negative electrode active material layer directly onto a negative electrode substrate or via an intermediate layer. The intermediate layer can be obtained by coating the negative electrode substrate with an intermediate layer forming material.

[0085] The above-mentioned negative electrode active material layer can be formed by coating with a negative electrode active material layer forming material (negative electrode mixture paste). The above-mentioned negative electrode active material layer forming material comprises a negative electrode active material according to one embodiment of the present invention, other components contained in the negative electrode active material layer, and a dispersion medium. As the dispersion medium, an organic solvent such as water or N-methylpyrrolidone (NMP) may be appropriately selected and used. The coating of the negative electrode active material layer forming material can be carried out by known methods. Typically, after coating, the coating film is dried to volatilize the dispersion medium. After that, it is preferable to press the coating film in the thickness direction.

[0086] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element (hereinafter also simply referred to as "energy storage element") according to one embodiment of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists in a state impregnated with the positive electrode, negative electrode, and separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0087] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from, for example, the configurations exemplified in the negative electrode.

[0088] The positive electrode substrate has conductivity. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor deposition film, mesh, porous material, etc., and foil is preferred from the viewpoint of cost. Therefore, an aluminum foil or an aluminum alloy foil is preferred as the positive electrode substrate.

[0089] The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte storage element.

[0090] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler as necessary. The optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified in the above negative electrode.

[0091] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium-ion secondary battery, a material that can occlude and release lithium ions is usually used. Examples of the positive electrode active material include a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, a lithium transition metal composite oxide having a spinel-type crystal structure, a polyanion compound, a chalcogen compound, sulfur, etc. As the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, for example, Li[Li x Ni (1-x) O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1-x) O2(0≦x<0.5), Li[Li x Niγ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1-x-γ-β) Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), etc. As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Some atoms or polyanions in these materials may be substituted with atoms or anions of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in mixture form.

[0092] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, between 0.1 μm and 20 μm. Setting the average particle size of the positive electrode active material above the lower limit facilitates the manufacturing and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When using a composite material of the positive electrode active material and other materials, the average particle size of the composite material is considered the average particle size of the positive electrode active material.

[0093] To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverizing method and powder classifying method can be selected from, for example, the methods exemplified in the negative electrode active material according to one embodiment of the present invention.

[0094] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0095] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte energy storage element can be increased.

[0096] The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the positive electrode active material can be stably maintained.

[0097] When a thickening agent is included in the positive electrode active material layer, the content of the thickening agent in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, it is preferable that the positive electrode active material layer does not contain a thickening agent.

[0098] When the positive electrode active material layer contains fillers, the filler content in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, it is preferable that the positive electrode active material layer does not contain fillers.

[0099] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0100] (Negative electrode) A negative electrode according to one embodiment of the present invention is used as the negative electrode. Details of the negative electrode are as described above.

[0101] (Separator) The separator can be appropriately selected from known separators. Examples of separators include a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer. Examples of the base layer shape of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As for the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

[0102] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass loss of less than the specified amount. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used as a mixture. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for non-aqueous electrolyte energy storage elements.

[0103] The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

[0104] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing leakage. A polymer gel may also be used in combination with a porous resin film or nonwoven fabric as described above as a separator.

[0105] (Non-aqueous electrolytes) As the non-aqueous electrolyte, it can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0106] As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

[0107] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among these, EC and PC are preferred, and PC is more preferred. When PC is included in the non-aqueous solvent, the charge acceptance of the non-aqueous electrolyte energy storage element is improved.

[0108] Examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among these, DMC and EMC are preferred.

[0109] It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and more preferable to use a combination of a cyclic carbonate and a linear carbonate. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a combination of a cyclic carbonate and a linear carbonate, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50. The total content of cyclic carbonate and linear carbonate in the non-aqueous solvent is preferably 70% by volume or more, more preferably 90% by volume or more, even more preferably 95% by volume or more, and even more preferably 99% by volume or more. The non-aqueous solvent may be substantially composed only of cyclic carbonate and linear carbonate.

[0110] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

[0111] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); and lithium salts having halogenated hydrocarbon groups such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0112] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 3 More than 2.5mol / dm 3Preferably, it is 0.3 mol / dm³ 3 More than 2.0mol / dm 3 It is more preferable that it be less than or equal to 0.5 mol / dm 3 More than 1.7mol / dm 3 It is even more preferable that the following is the case: 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0113] Non-aqueous electrolytes may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halides of the aforementioned aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, sulfurous acid Examples include dimethyl acid, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethylsulfone, dimethyl sulfoxide, diethylsulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithtrimethylsilyl titanate, lithium monofluorophosphate, and lithium difluorophosphate. These additives may be used individually or in combination of two or more.

[0114] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0115] For the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

[0116] The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (e.g., 15°C to 25°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0117] Examples of sulfide solid electrolytes in lithium-ion secondary batteries include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 These are some examples.

[0118] (Negative electrode potential, applications, etc.) The lower limit of the negative electrode potential at the charge termination voltage during normal use in the non-aqueous electrolyte energy storage element is, for example, 0.20V vs. Li / Li + Or 0.30V vs. Li / Li + This is also acceptable, but 0.35V vs. Li / Li + Preferably, 0.40V vs. Li / Li + This is more preferable. By ensuring that the negative electrode potential at the charging termination voltage during normal use is above the above lower limit, a negative electrode comprising a negative electrode substrate mainly composed of aluminum can be suitably applied. As an upper limit for the negative electrode potential at the charging termination voltage during normal use, for example, 0.80V vs. Li / Li + Preferably, 0.60V vs. Li / Li +More preferable is 0.50V vs. Li / Li + More preferably, 0.45V vs. Li / Li + This is even more preferable. By keeping the negative electrode potential at the charging termination voltage during normal use below the above upper limit, the discharge capacity can be increased. The negative electrode potential at the charging termination voltage during normal use can be above any of the lower limits and below any of the upper limits mentioned above.

[0119] Even when using a negative electrode substrate primarily composed of aluminum, this non-aqueous electrolyte energy storage element, when used within an appropriate negative electrode potential range, possesses sufficient discharge capacity and high Coulomb efficiency, and also enables rapid charging. Furthermore, by using a negative electrode substrate primarily composed of aluminum, the weight of the non-aqueous electrolyte energy storage element can be reduced. For this reason, this non-aqueous electrolyte energy storage element is particularly suitable for applications requiring weight reduction and rapid charging. Examples of such applications include power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0120] The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

[0121] Figure 1 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that the figure is a transparent view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound around a separator is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51.

[0122] <Energy storage device> The non-aqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) composed of multiple non-aqueous electrolyte energy storage elements 1 in addition to the automotive power supply described above, as well as in power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology of the present invention is applied to at least one of the non-aqueous electrolyte energy storage elements included in the energy storage unit.

[0123] Figure 2 shows an example of a power storage device 30 which is formed by further assembling power storage units 20, each of which is an assembly of two or more electrically connected non-aqueous electrolyte power storage elements 1. The power storage device 30 may include busbars (not shown) that electrically connect two or more non-aqueous electrolyte power storage elements 1, busbars (not shown) that electrically connect two or more power storage units 20, etc. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte power storage elements.

[0124] <Method for manufacturing a non-aqueous electrolyte energy storage element> The method for manufacturing the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or winding the positive electrode and the negative electrode via a separator.

[0125] The method for housing the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, when using a non-aqueous electrolyte solution, the non-aqueous electrolyte solution can be injected through an inlet formed in the container, and then the inlet can be sealed.

[0126] <Other Embodiments> Furthermore, the non-aqueous electrolyte energy storage elements of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0127] In the above embodiment, the case in which the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

[0128] In the above embodiment, an electrode body in which a positive electrode and a negative electrode are stacked with a separator in between has been described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of either the positive electrode or the negative electrode. [Examples]

[0129] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0130] [Example 1] In the quartz tube (45mm inner diameter) of the CVD apparatus "MPCVD-Powder" (manufactured by MICROPHASE), AlCl3 in an alumina boat and a graphite sheet "PF110" were placed in order from the upstream side. In addition, quartz wool was placed downstream of the graphite sheet and at the very downstream end (outlet) of the quartz tube. Under an argon gas flow, a quartz tube near a graphite sheet was heated from room temperature to 1000°C. After reaching 1000°C, argon (carrier gas) and ethylene (carbon source gas) were introduced into the quartz tube. The alumina boat containing AlCl3 was placed at the uppermost part of the quartz tube, where it was hardly heated during the heating process up to 1000°C, and was gradually moved to the heated part of the quartz tube after reaching 1000°C. Through this operation, the AlCl3 in the alumina boat inside the quartz tube was sublimated and introduced into the quartz tube as a substitution element source (aluminum source) gas. In this way, carbon material was synthesized by chemical vapor deposition (CVD) and deposited on the graphite sheet. The synthesis time was 5 hours. The flow rates of the carrier gas and carbon source gas were adjusted to 600 mL / min and 60 mL / min, respectively. The amount of AlCl3 added to the alumina boat and the heating conditions were adjusted so that the average flow rate over the 5-hour synthesis time was 20 mL / min. Subsequently, the introduction of the carrier gas and carbon source gas was stopped, and the mixture was allowed to cool from 1000°C to room temperature. The graphite sheet was removed from the quartz tube, and the carbon material adhering to the graphite sheet was recovered. This carbon material was placed in a 30 mL alumina crucible and set up in a benchtop vacuum gas displacement furnace KDF75 (manufactured by Denken Heidental). Next, under an argon atmosphere and atmospheric pressure, the temperature was raised from room temperature to 900°C at a heating rate of 5°C / min and held for 1 hour for reheat treatment. After the reheat treatment, the material was crushed in an alumina mortar to obtain the carbon material (negative electrode active material) of Example 1.

[0131] [Example 2] The carbon material (negative electrode active material) of Example 2 was obtained in the same manner as in Example 1, except that quartz wool was placed in the quartz tube, not only downstream of the graphite sheet and at the very downstream end (outlet), but also upstream and downstream of the AlCl3 placed in the alumina boat. Furthermore, by arranging the quartz wool in this manner, gas backflow was suppressed, resulting in an increase in the amount of carbon material obtained compared to Example 1.

[0132] [Examples 3 and 4] The carbon materials (negative electrode active materials) for Examples 3 and 4 were obtained in the same manner as in Example 2, except that the type of carrier gas, the type and temperature of the carbon source gas during the CVD treatment, and the atmosphere and temperature during the reheat treatment were as shown in Table 4.

[0133] [Example 5] A graphite sheet "PF110" was placed inside a quartz tube (45 mm inner diameter) of a CVD apparatus "MPCVD-Powder" (manufactured by MICROPHASE). Under a nitrogen atmosphere, the quartz tube near the graphite sheet was heated from room temperature to 1000°C at a heating rate of 10°C / min. After reaching 1000°C, nitrogen (carrier gas), ethylene (carbon source gas), and BCl3 (substitution element source gas) were introduced into the quartz tube. In this way, carbon material was synthesized by chemical vapor deposition (CVD) and deposited on the graphite sheet. The synthesis time was 5 hours. The flow rates of the carrier gas, carbon source gas, and substitution element source gas were adjusted to 600 mL / min, 45 mL / min, and 15 mL / min, respectively. Subsequently, the introduction of the carrier gas, carbon source gas, and substitution element source gas was stopped, and the mixture was allowed to cool from 1000°C to room temperature. The graphite sheet was removed from the quartz tube, and the carbon material adhering to the graphite sheet was recovered. This carbon material was placed in a 30 mL alumina crucible and set up in a tabletop vacuum gas displacement furnace KDF75 (manufactured by Denken Heidental). Next, under a nitrogen flow of 0.5 L / min and atmospheric pressure, the temperature was raised from room temperature to 900°C at a heating rate of 5°C / min, and held for 1 hour for reheat treatment. After the reheat treatment, the material was crushed in an alumina mortar to obtain the carbon material (negative electrode active material) of Example 5.

[0134] [Comparative Example 1] The non-graphitizable carbon was used directly as the carbon material (negative electrode active material) in Comparative Example 1.

[0135] [Comparative Example 2] The carbon material (negative electrode active material) of Comparative Example 2 was obtained in the same manner as in Example 3, except that AlCl3 in an alumina boat was not placed inside the quartz tube.

[0136] [Comparative Example 3] 3 g of flake graphite was immersed in 45 mL of fuming nitric acid (Wako) and stirred to form a suspension. The suspension was heated to 60°C, and 12 g of potassium chlorate (Wako) was gradually added while stirring at 300 rpm with a magnetic stirrer, and the reaction was carried out at 60°C for 3 hours. After that, the suspension was added to 750 mL of water to stop the reaction. The solid was separated from the obtained suspension by suction filtration, washed with water, and dried overnight at 60°C to obtain graphite oxide. An alumina crucible containing 4 g of the obtained graphite oxide was placed in a benchtop vacuum gas displacement furnace KDF75 (Denken Heidental). Next, under a nitrogen flow of 0.6 L / min and atmospheric pressure, the temperature was raised from room temperature to 170°C at a heating rate of 1°C / min, then further raised from 170°C to 250°C at a heating rate of 0.1°C / min, and finally raised from 250°C to 800°C at a heating rate of 1°C / min, where it was held for 5 hours to perform heat treatment. After that, it was crushed in an alumina mortar to obtain the carbon material (negative electrode active material) of Comparative Example 3.

[0137] (Measurement of the content of element M) The content of element M (aluminum or boron) was measured for each carbon material (negative electrode active material) in Examples 1 to 5 and Comparative Example 2 using the method described above. The measurement results are shown in Table 5.

[0138] (XPS measurement) XPS measurements were performed on each carbon material (negative electrode active material) of Examples 1 to 5 and Comparative Examples 1 to 3 using the method described above, and the integrated intensity in the range of 282.5 eV to 283.5 eV in the C1s spectrum was determined. The measurement results are shown in Table 5.

[0139] (XRD measurement) XRD measurements were performed on each carbon material (negative electrode active material) in Examples 1 to 4 and Comparative Examples 1 and 2 using the method described above, and the average lattice plane spacing (d) of the (002) plane was determined. 002 The following was determined. The measurement results are shown in Table 5.

[0140] (Measurement of oxygen element content) For each carbon material (negative electrode active material) in Examples 1 and 5 and Comparative Examples 1 to 3, the oxygen element content desorbed under ambient temperatures exceeding 800°C was determined using the method described above. The measurement results are shown in Table 5.

[0141] (Fabrication of the negative electrode) Each carbon material from Examples 1 to 5 and Comparative Examples 1 to 3 was used as a negative electrode active material, and a negative electrode was prepared using the following procedure. Polyvinylidene fluoride (PVDF) was used as the binder. A negative electrode mixture paste was prepared containing the above negative electrode active material and the above binder in a mass ratio of 88:12, with N-methylpyrrolidone as the dispersion medium. The negative electrode mixture paste was applied to a 20 μm thick copper foil as the negative electrode substrate, dried, and pressed to prepare a negative electrode for a non-aqueous electrolyte energy storage element in which a negative electrode active material layer was arranged on the negative electrode substrate. The electrochemical properties of the non-aqueous electrolyte energy storage element using the above negative electrode as the working electrode and metallic lithium as the counter electrode under the charge / discharge conditions described later are equivalent to the electrochemical properties of a non-aqueous electrolyte energy storage element using aluminum foil as the negative electrode substrate as the working electrode and metallic lithium as the counter electrode.

[0142] (Fabrication of non-aqueous electrolyte energy storage elements) To evaluate the performance of each obtained negative electrode, a non-aqueous electrolyte energy storage element for evaluation testing was fabricated using the above-mentioned negative electrode, in which the negative electrode active material layer was arranged in a rectangular shape with a width of 30 mm and a length of 40 mm, as the working electrode. A rectangular metallic lithium electrode with a width of 32 mm and a length of 42 mm was used as the counter electrode. A microporous polyethylene membrane was used as the separator. The non-aqueous electrolyte consisted of a mixed solvent of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35, with a concentration of 1 mol / dm³. 3 A solution of LiPF6 dissolved at the specified concentration was used. A cell was prepared by placing the working electrode and counter electrode opposite each other via the separator and injecting the non-aqueous electrolyte. This yielded the non-aqueous electrolyte energy storage elements of Examples 1 to 5 and Comparative Examples 1 to 3. Furthermore, the voltage between the working electrode and the counter electrode in each obtained non-aqueous electrolyte energy storage element can be considered to be approximately equal to the potential of the working electrode relative to the oxidation-reduction potential of metallic lithium.

[0143] (Charge / Discharge Test) Each of the non-aqueous electrolyte energy storage elements obtained in Examples 1 to 5 and Comparative Examples 1 to 3 underwent a 3-cycle charge-discharge test at 25°C under the following conditions. Charging was performed using constant current constant voltage (CCCV) charging with a charging current of 50 mA per gram of negative electrode active material and a charge termination voltage of 0.400 V, with the charge termination condition set to 12 hours after the start of constant voltage charging. Discharging was performed using constant current (CC) discharge with a discharge current of 50 mA per gram of negative electrode active material and a discharge termination voltage of 2.000 V. A 10-minute rest period was provided after both charging and discharging. The charge-discharge curves for the first cycle of each non-aqueous electrolyte energy storage element in Example 4 and Comparative Examples 1 and 2 are shown in Figure 3.

[0144] (discharge capacity) The discharge capacity of the first cycle in the above charge-discharge test was divided by the mass of the negative electrode active material to obtain the "discharge capacity [mAh / g]". The results are shown in Table 5.

[0145] (Coulomb efficiency) The percentage of the discharge capacity in the first cycle relative to the charge capacity in the first cycle of the above charge-discharge test was defined as "Coulomb efficiency (%)". The results are shown in Table 5.

[0146] (Open circuit voltage) The open-circuit voltage was measured 10 minutes after the completion of the third discharge cycle in the above charge-discharge test. Note that the above open-circuit voltage can be considered to be approximately equal to the open-circuit potential of the working electrode relative to the oxidation-reduction potential of metallic lithium. The results are shown in Table 5. Figure 4 shows the discharge curves (including the open-circuit voltage after discharge) for the third cycle of each non-aqueous electrolyte energy storage element in Example 4 and Comparative Examples 1 and 2.

[0147] (Average discharge voltage) The average closed-circuit voltage during the third discharge cycle of the above charge-discharge test was calculated and used as the average discharge voltage. The results are shown in Table 5.

[0148] (Difference between open-circuit voltage and average discharge voltage) The difference between the open-circuit voltage 10 minutes after the completion of the third discharge cycle of the above charge-discharge test and the average closed-circuit voltage (average discharge voltage) during the third discharge cycle of the above charge-discharge test was calculated. The results are shown in Table 5.

[0149] (Charge-discharge hysteresis) The difference between the average closed-circuit voltage during charging and the average closed-circuit voltage during discharging in the third cycle of the above charge-discharge test was calculated and defined as the charge-discharge hysteresis. The results are shown in Table 5.

[0150] [Table 4]

[0151] [Table 5]

[0152] As shown in Table 5, the non-aqueous electrolyte energy storage elements using the negative electrode active materials of Comparative Example 1, which is a non-graphitizable carbon that does not contain element M, and Comparative Example 2, which was synthesized in the same manner as in each example except that a substituted element source gas was not used, exhibited voltages from 0.400V to 2.000V (0.400V vs. Li / Li + From 2,000V vs. Li / Li + The discharge capacity during charging and discharging in the negative electrode closed-circuit potential range was small. Furthermore, the non-aqueous electrolyte energy storage element using the negative electrode active material of Comparative Example 3, which is graphite oxide that does not contain element M, had a large discharge capacity during charging and discharging in the above voltage range, but low Coulomb efficiency. In contrast, the non-aqueous electrolyte energy storage elements using the negative electrode active materials of Examples 1 to 5, which are carbon materials containing element M, either aluminum or boron, exhibited large discharge capacity and high Coulomb efficiency during charging and discharging within the above voltage range. Furthermore, the open-circuit voltage after discharge of the non-aqueous electrolyte energy storage elements using the negative electrode active materials of Examples 1 to 5 was higher than the open-circuit voltage after discharge of the non-aqueous electrolyte energy storage elements using the negative electrode active materials of Comparative Examples 1 and 2. It is believed that the inclusion of element M increases the number of lithium ion storage sites inserted between the graphene layers in a high potential range, resulting in a higher open-circuit voltage after discharge. For example, the negative electrode active materials of Examples 1 to 5 have a closed-circuit potential of 0.40V vs. Li / Li + It can be seen that these materials are useful as negative electrode active materials for non-aqueous electrolyte energy storage elements used within the above potential range. Furthermore, among Examples 1 to 5, it can be seen that the non-aqueous electrolyte energy storage elements using the negative electrode active materials of Examples 1 to 3, where the open-circuit voltage after discharge is 1.43V or less, exhibit a small difference between the open-circuit voltage and the average discharge voltage.

[0153] [Examples 6 and 7] The non-aqueous electrolyte energy storage elements of Examples 6 and 7 were obtained in the same manner as in Example 1, except that a non-aqueous electrolyte with the composition described in Table 6 was used.

[0154] (Charge / Discharge Test) Each of the non-aqueous electrolyte energy storage elements obtained in Examples 6 and 7 was subjected to charge-discharge tests at 25°C under the following conditions. [Charge / discharge cycle 1] Charging was performed using CCCV charging with a charging current of 50 mA per gram of negative electrode active material and a charging termination voltage of 0.400 V. Charging termination was defined as 12 hours after the start of constant voltage charging. Discharging was performed using CC discharge with a discharge current of 50 mA per gram of negative electrode active material and a discharge termination voltage of 2.000 V. [Charging and discharging at a charging current of 50mA / g] Next, the following charging and discharging procedures were performed. Charging was performed using CC charging with a charging current of 50 mA per gram of negative electrode active material and a charging termination voltage of 0.400 V. Discharging was performed using CC discharge with a discharge current of 50 mA per gram of negative electrode active material and a discharge termination voltage of 2.000 V. [Charging and discharging at a charging current of 250mA / g] Next, the following charging and discharging procedures were performed. Charging was performed using CC charging with a charging current of 250 mA per gram of negative electrode active material and a charging termination voltage of 0.400 V. Discharging was performed using CC discharge with a discharge current of 50 mA per gram of negative electrode active material and a discharge termination voltage of 2.000 V. In both cases, a 10-minute rest period was provided after charging and after discharging.

[0155] (Coulomb efficiency) The percentage of discharge capacity to charge capacity during the "first cycle discharge" in the above charge-discharge test was defined as "Coulomb efficiency (%)". The results are shown in Table 6.

[0156] (Charge capacity ratio of each rate) The "Ratio of Charge Capacity at Each Rate (%)" was defined as the percentage of the charge capacity at "Charge / Discharge at a Charging Current of 250 mA / g" to the charge capacity at "Charge / Discharge at a Charging Current of 50 mA / g" in the above charge / discharge test. The results are shown in Table 6.

[0157] [Table 6]

[0158] As shown in Table 6, the non-aqueous electrolyte energy storage element of Example 7, which includes a non-aqueous electrolyte containing PC, exhibits a high ratio of charge capacity per charge and excellent charge acceptance. Furthermore, the Coulomb efficiency of the non-aqueous electrolyte energy storage element of Example 6 and the non-aqueous electrolyte energy storage element of Example 7 are equivalent, suggesting that no side reactions occurred due to the use of PC instead of EC. [Industrial applicability]

[0159] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as automobiles and the like. [Explanation of Symbols]

[0160] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage units 30 Energy storage devices

Claims

1. It is a carbon material containing element M, The element M, as determined by first-principles calculations, is an element that increases the reaction potential of graphite with lithium ions when some of the carbon atoms constituting the crystal structure of graphite are replaced with atoms of element M. In the above carbon material, some of the carbon elements are replaced with aluminum elements. A negative electrode active material for a non-aqueous electrolyte energy storage element, having an oxygen element content of 6% by mass or less that desorbs under ambient temperatures exceeding 800°C.

2. It is a carbon material containing element M, The element M mentioned above is aluminum. A negative electrode active material for a non-aqueous electrolyte energy storage element, having an oxygen element content of 6% by mass or less that desorbs under ambient temperatures exceeding 800°C.

3. The negative electrode active material according to claim 1 or claim 2, wherein the content of element M is 0.05% by mass or more and 15% by mass or less.

4. Closed circuit potential 0.40V vs. Li / Li ＋ From the charged state, with a current of 50 mA / g per mass of the above negative electrode active material, the closed-circuit potential is 2.00 V vs. Li / Li ＋ After constant current discharge, the open-circuit potential at 10 minutes afterward is 1.33V vs. Li / Li ＋ The negative electrode active material according to claim 1 or claim 2.

5. A negative electrode for a non-aqueous electrolyte energy storage element, comprising the negative electrode active material described in claim 1 or claim 2.

6. The negative electrode according to claim 5, further comprising a negative electrode substrate mainly composed of aluminum element.

7. A non-aqueous electrolyte energy storage element comprising the negative electrode described in claim 5.

8. The non-aqueous electrolyte energy storage element according to claim 7, further comprising a non-aqueous electrolyte containing propylene carbonate.

9. The negative electrode potential at the charging termination voltage during normal use is 0.35V vs. Li / Li ＋ The non-aqueous electrolyte energy storage element described in claim 7.

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