JP2018073611A - Negative electrode for electric device and electric device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for an electric device with improved charge/discharge efficiency and cycle durability, and to provide an electric device using the same.SOLUTION: A negative electrode (10) for an electric device includes: a silicon-containing alloy (1) containing silicon and tin; a carbon coating layer (2) which is formed by a carbon-based material and coats the silicon-containing alloy (1); a conductive assistant (3) for the negative electrode; and a binder (4) for the negative electrode. A ratio of a specific surface area of the carbon-based material to the specific surface area of the conductive assistant for the negative electrode is 7 or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a negative electrode for an electric device and an electric device using the same. Specifically, the present invention relates to a negative electrode for an electric device having improved charge / discharge efficiency and cycle durability, and an electric device using the same.

  2. Description of the Related Art In recent years, electrical devices having excellent cycle durability that do not deteriorate in performance even when repeatedly charged and discharged have been promoted as drive power sources for electronic equipment and vehicle travel.

  For example, Patent Document 1 discloses an electrode material for a lithium secondary battery made of particles of a solid state alloy containing silicon as a main component. In this electrode material, particles of the alloy in a solid state are dispersed in microcrystalline silicon or amorphous silicon, and microcrystalline or amorphous materials made of elements other than silicon are dispersed. Therefore, according to Patent Document 1, it is said that an electrode material for a high capacity lithium secondary battery having a low resistance and a high charge / discharge efficiency can be provided.

JP 2004-311429 A

  However, an electric device including a lithium secondary battery is desired to have higher charge / discharge efficiency and cycle durability, and an electrode material such as that in Patent Document 1 cannot be said to be sufficient.

  The present invention has been made in view of the problems of such conventional techniques. And the objective of this invention is providing the negative electrode for electric devices by which charging / discharging efficiency and cycling durability were improved, and an electric device using the same.

  A negative electrode for an electric device according to an aspect of the present invention includes a carbon coating layer that is formed of a carbon-based material and covers a silicon-containing alloy, a negative electrode conductive additive, and a negative electrode binder. The ratio of the specific surface area of the carbon-based material to the specific surface area is within a predetermined range.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode for electric devices by which charging / discharging efficiency and cycling durability were improved, and an electric device using the same can be provided.

FIG. 1 is a schematic diagram illustrating an example of a negative electrode for an electric device according to the present embodiment. FIG. 2 is a cross-sectional view schematically showing an example of the electric device according to the present embodiment.

  Hereinafter, the negative electrode for an electric device and the electric device using the same according to the present embodiment will be described in detail with reference to the drawings. In addition, the dimension ratio of drawing is exaggerated on account of description, and may differ from an actual ratio.

[Negative Electrode 10 for Electric Devices]
As shown in FIG. 1, a negative electrode 10 for an electric device of the present embodiment includes a silicon-containing alloy 1 containing silicon and tin, a carbon coating layer 2 formed of a carbon-based material and covering the silicon-containing alloy 1, and a negative electrode A conductive auxiliary agent 3 and a negative electrode binder 4. When the negative electrode 10 for an electric device includes such a carbon coating layer 2, an area in which the electrolytic solution forming the electrolyte layer 30 of the electric device 100 is in direct contact with the silicon-containing alloy 1 is reduced. Therefore, depletion of the electrolyte solution and excessive decomposition reaction of the electrolyte solution can be suppressed. Moreover, it can suppress that the side reaction material which prevents the electroconductivity in a negative electrode by the excessive decomposition | disassembly of this electrolyte solution produces | generates. Moreover, when the negative electrode 10 for electric devices is equipped with such a carbon coating layer 2, the conductivity of the surface of the silicon-containing alloy 1 can be made uniform. Therefore, when the negative electrode 10 for an electric device of the present embodiment is used in an electric device 100 such as a lithium ion secondary battery, lithium ions are inserted into a local portion of the silicon-containing alloy 1, and the silicon-containing alloy 1 Can be prevented from deteriorating.

  Furthermore, in this embodiment, the ratio of the specific surface area of the carbonaceous material to the specific surface area of the conductive auxiliary agent 3 for negative electrode is 7 or more. By setting the specific surface area ratio of the conductive auxiliary agent 3 for the negative electrode and the carbon-based material in such a range, a wide range of the silicon-containing alloy 1 can be covered with the carbon-based material. Therefore, the contact between the silicon-containing alloy 1 and the electrolytic solution can be further reduced, and the conductivity of the surface of the silicon-containing alloy 1 can be made more uniform. Further, by setting the specific surface area ratio between the negative electrode conductive additive 3 and the carbonaceous material in such a range, the ratio of the negative electrode conductive additive 3 bonded to the negative electrode binder 4 tends to decrease. Therefore, a decrease in the binder function of the negative electrode binder 4 can be suppressed and the strength of the electric device negative electrode 10 can be maintained. As a result, the charge / discharge efficiency and cycle durability of the electric device can be improved. In addition, since the said mechanism is based on estimation, this embodiment is not limited to the said mechanism.

(Silicon-containing alloy 1)
The negative electrode 10 for an electric device of this embodiment includes a silicon-containing alloy 1 containing silicon and tin. The silicon-containing alloy 1 functions as a negative electrode active material and is a material capable of occluding and releasing lithium. In the present embodiment, by using such a silicon-containing alloy 1, volume change due to alloying of silicon and lithium ions during charging and discharging can be suppressed, and the discharge capacity and cycle durability of the electric device 100 can be increased. it can.

  The silicon content of the silicon-containing alloy 1 is preferably 20% by mass or more based on the entire silicon-containing alloy 1. By setting the silicon content of the silicon-containing alloy 1 in such a range, the amorphous-crystal phase transition can be suppressed, and the cycle durability of the electric device 100 can be improved. The silicon-containing alloy 1 can be produced by, for example, a mechanical alloy method, an arc plasma melting method, or the like.

  In the present embodiment, the silicon-containing alloy 1 includes Si, Sn, and M elements, and M is at least one element selected from the group consisting of transition elements, B, C, Mg, Al, and Zn. Is preferred. The transition element refers to an element between the Group 3 element and the Group 11 element. By using such a silicon-containing alloy 1, the discharge capacity and cycle durability of the electric device 100 can be increased.

  M is at least one element selected from the group consisting of B, C, Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, and Ta. More preferably. M is more preferably at least one element selected from the group consisting of C, Al, Ti, V, and Zn. Furthermore, it is most preferable that it is at least any one of Al or Ti. By including such an element in the silicon-containing alloy 1, it is possible to improve cycle durability while maintaining the discharge capacity of the electric device 100.

  The silicon-containing alloy 1 containing Si, Sn, and M elements may contain inevitable impurities. An inevitable impurity means what exists in a raw material or is inevitably mixed in a manufacturing process. Inevitable impurities are essentially unnecessary impurities, but are insignificant and do not affect the characteristics of the silicon-containing alloy 1, and thus are allowed impurities. The content of inevitable impurities is preferably less than 0.5% by mass, more preferably less than 0.1% by mass, and less than 0.01% by mass with respect to the entire silicon-containing alloy 1. Further preferred.

  The general formula of the silicon-containing alloy 1 is preferably Si—Sn—M, and more preferably Si—Sn—Ti or Si—Sn—Ti—Al. Here, in the general formula Si-Sn-Ti, the Sn content is 7% by mass or more and 30% by mass or less, the Ti content is more than 0% by mass and 37% by mass or less, and the balance is Si and inevitable impurities. preferable. Or in general formula Si-Sn-Ti, it is preferable that Sn content is 30 mass% or more and 51 mass% or less, Ti content exceeds 0 mass% and 35 mass% or less, and the remainder is Si and inevitable impurities. . In the general formula Si-Sn-Ti, it is more preferable that the Sn content is 7% by mass or more and 30% by mass or less, Ti is more than 7% by mass and 37% by mass or less, and the balance is Si and inevitable impurities. Alternatively, it is more preferable that the Sn content is 30% by mass or more and 51% by mass or less, the Ti content is more than 7% by mass and 35% by mass or less, and the balance is Si and inevitable impurities. Further, in the general formula Si—Sn—Ti, the Sn content is 7% by mass to 30% by mass, the Ti content is 18% by mass to 37% by mass, and the balance is Si and inevitable impurities. preferable. Or, in the general formula Si-Sn-Ti, the Sn content is 30% by mass or more and 51% by mass or less, the Ti content is more than 7% by mass and 20% by mass or less, and the balance is Si and inevitable impurities. preferable. Furthermore, in the general formula Si—Sn—Ti, the Sn content is 7% by mass or more and 21% by mass or less, the Ti content is 24% by mass or more and 37% by mass or less, and the remainder is Si and inevitable impurities. preferable. By setting the content of each element within the above range, a lithium ion battery excellent in cycle characteristics can be provided.

  In the general formula Si-Sn-Ti-Al, the Sn content is 2 mass% to 10 mass%, the Ti content is 25 mass% to 35 mass%, and the Al content is 0.3 mass%. It is preferable that the content is 3% by mass or less and the balance is Si and inevitable impurities. By setting the content of each element within the above range, the cycle characteristics of the electric device can be improved. In addition, as for content of Sn, 3 mass% or more is more preferable. Further, the Sn content is more preferably 9% by mass or less, and even more preferably 8.5% by mass or less. Further, the content of Ti is more preferably 28% by mass or more, and further preferably 29% by mass or more. The Ti content is more preferably 34% by mass or less, further preferably 33% by mass or less, particularly preferably 32% by mass or less, and most preferably 31% by mass or less. Further, the Al content is more preferably 0.35% by mass or more, and further preferably 0.4% by mass or more. Further, the Al content is more preferably 2.5% by mass or less, and further preferably 2.0% by mass or less. In addition, the content of Si is preferably 58% by mass or more, more preferably 58.5% by mass or more, and further preferably 59% by mass or more. 70 mass% or less is preferable, as for content of Si, 68 mass% or less is more preferable, 67 mass% or less is further more preferable, and 66 mass% or less is especially preferable.

  D50 of the silicon-containing alloy 1 is not particularly limited, but is preferably more than 0.01 μm and less than 20 μm. By setting D50 of the silicon-containing alloy 1 within such a range, the carbon coating layer 2 can be efficiently coated on the surface of the silicon-containing alloy 1. And the expansion | contraction and shrinkage | contraction of the silicon containing alloy 1 can be suppressed, and it can suppress and prevent effectively that the coat | covered carbon coating layer 2 peels from the silicon containing alloy 1 surface. Therefore, cycle durability of the electric device 100 can be increased. In addition, it is more preferable that D50 of the silicon-containing alloy 1 is 0.4 to 10 μm, and further preferably 2.5 to 7 μm. D50 represents the particle diameter when the cumulative value of the particle size distribution on a volume basis is 50%, and can be measured by, for example, a laser diffraction / scattering method.

  In the present embodiment, the negative electrode 10 for an electric device includes the silicon-containing alloy 1, but may include a negative electrode active material other than the silicon-containing alloy 1. The negative electrode active material other than the silicon-containing alloy 1 may be any material that can occlude and release lithium. Examples of the negative electrode active material other than the silicon-containing alloy 1 include carbon materials, metals such as silicon that are alloyed with lithium, alloys of silicon and other metals, and oxides containing these metals.

(Carbon coating layer 2)
The negative electrode 10 for an electric device according to this embodiment includes a carbon coating layer 2 that is formed of a carbon-based material and covers the silicon-containing alloy 1. When the negative electrode 10 for an electric device is provided with such a carbon coating layer 2, an excessive decomposition reaction of the electrolytic solution caused when the silicon-containing alloy 1 is in direct contact with the electrolytic solution of the electric device or the like, and local application to the silicon-containing alloy 1 Insertion of typical lithium ions can be suppressed. Note that coating the silicon-containing alloy 1 means that the silicon-containing alloy 1 and the carbon coating layer 2 are chemically or physically bonded.

  The ratio of the area covering the entire surface of the silicon-containing alloy 1 with the carbon coating layer 2 is preferably 90% to 100%, more preferably 95% to 100%, and 99% to 100%. More preferably. By making the ratio which the carbon coating layer 2 coat | covers in such a range, charging / discharging efficiency and cycle durability can be improved.

  The carbon-based material is not particularly limited, but preferably has low crystallinity. This is because, when the crystallinity of the carbon coating layer 2 is low, lithium ion insertion and desorption are unlikely to occur, and thus the coating state of the silicon-containing alloy 1 is easily maintained. For the carbon coating layer 2, for example, acetylene black, furnace black, carbon black, channel black, graphite or the like can be used. Of these, the carbon coating layer 2 is preferably made of acetylene black or carbon fiber having low crystallinity.

  The shape of the carbon-based material is not particularly limited, and for example, a particulate or fibrous carbon-based material can be used. From the viewpoint of ease of coating, the carbon coating layer 2 is preferably in the form of particles, and from the viewpoint of conductivity, the carbon coating layer 2 is preferably in the form of fibers.

  The size of the carbon-based material is not particularly limited. For example, when the carbon-based material is particulate, the average particle diameter (D50) is preferably 10 to 200 nm, and more preferably 20 to 150 nm. By setting the size of the carbon-based material in such a range, the surface of the silicon-containing alloy 1 can be easily coated, and the carbon coating layer 2 can be uniformly coated on the surface of the silicon-containing alloy 1. D50 represents the particle diameter when the cumulative value of the particle size distribution on the volume basis is 50%, and can be measured by, for example, a laser diffraction / scattering method.

  For example, when the carbonaceous material is fibrous, the length is preferably 5 to 20 μm, and more preferably 8 to 15 μm. For example, when the carbonaceous material is fibrous, the diameter is preferably 20 to 500 nm, and more preferably 50 to 300 nm. By setting the size of the carbon-based material in such a range, the surface of the silicon-containing alloy 1 can be easily coated, and the carbon coating layer 2 can be uniformly coated on the surface of the silicon-containing alloy 1. The length and diameter of the fibrous carbon-based material can be an average value of several to several tens of pieces actually measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

The specific surface area of the carbonaceous material is not particularly ^limited, is preferably from 7.7m ² / g~206m 2 / ^g, more preferably from ^{13.1m 2 / g~206m 2 / g,} 133m 2 More preferably, it is / g-206m < ² > / g. By setting the specific surface area of the carbon-based material in such a range, a wide range of the silicon-containing alloy 1 can be covered with the carbon coating layer 2. Therefore, the contact between the silicon-containing alloy 1 and the electrolytic solution can be further reduced, and the conductivity of the surface of the silicon-containing alloy 1 can be made more uniform. The specific surface area of the carbon coating layer 2 can be measured by a BET method by adsorbing nitrogen gas.

  The method for chemically or physically bonding the carbon-based material to the surface of the silicon-containing alloy 1 is not particularly limited. For example, a method of embedding at least a part of the carbon coating layer 2 in the silicon-containing alloy 1 by shearing and physically bonding it, a method of chemically bonding the silicon-containing alloy 1 and the carbon coating layer 2 through functional groups, etc. Is mentioned. Specific examples of the method for chemically or physically bonding the carbon-based material to the surface of the silicon-containing alloy 1 include a mechanochemical method, a liquid phase method, a sintering method, and a vapor deposition (CVD) method. For example, when the mechanochemical method is used, the rotation speed (treatment rotation speed) is preferably 3000 to 8000 rpm, and more preferably 4000 to 7000 rpm. Moreover, 200-400W is preferable and, as for load power, 250-300W is more preferable. The treatment time is preferably 10 to 60 minutes, more preferably 20 to 50 minutes. By setting the mechanochemical method to such conditions, the carbon-based material can be uniformly coated on the surface of the silicon-containing alloy 1.

  The mixing ratio of the silicon-containing alloy 1 and the carbon coating layer 2 when the carbon-based material is coated on the silicon-containing alloy 1 is not particularly limited. However, the content of the carbon-based material is preferably 0.1 to 5% by mass and more preferably 0.5 to 3% by mass with respect to a total of 100% by mass of the silicon-containing alloy 1 and the carbon-based material. By setting the content of the carbon-based material in such a range, the coverage of the silicon-containing alloy 1 with the carbon coating layer 2 can be easily controlled within the preferable range as described above.

(Electroconductive aid 3 for negative electrode)
The negative electrode 10 for an electrical device includes a negative electrode conductive additive 3. The negative electrode conductive additive 3 can effectively form an electronic network inside the negative electrode active material layer 11 and increase the discharge capacity of the electric device. Examples of the material for forming the negative electrode conductive additive 3 of the negative electrode 10 for an electrical device include carbon black such as acetylene black, and carbon materials such as graphite and carbon fiber. These conductive auxiliary agents 3 for negative electrodes may be used independently and may use 2 or more types together. By including the negative electrode active material layer 11 in the negative electrode active material layer 11, an electronic network inside the negative electrode active material layer 11 is effectively formed, and the discharge capacity of the lithium ion battery can be improved. 1-10 mass% is preferable with respect to the whole negative electrode active material layer 11, and, as for content of the conductive support agent 3 for negative electrodes, 2-6 mass% is more preferable. By setting the content of the conductive auxiliary agent 3 for the negative electrode in such a range, the conductivity of the negative electrode active material layer 11 can be improved.

The specific surface area of the negative electrode conductive additive 3 is not particularly ^limited, is preferably 1m ² / g~100m 2 / ^g, more preferably ^{1m 2 / g~50m 2 / g,} 3m 2 / More preferably, it is g-10m < ² > / g. By setting the specific surface area of the negative electrode conductive auxiliary agent 3 in such a range, the ratio of the negative electrode conductive auxiliary agent 3 bonded to the negative electrode binder 4 tends to decrease. A fall can be suppressed and the intensity | strength of the negative electrode 10 for electrical devices can be maintained. In addition, the specific surface area of the conductive auxiliary agent 3 for negative electrodes can be measured by a BET method by adsorbing nitrogen gas.

  The ratio of the specific surface area of the carbonaceous material to the specific surface area of the conductive additive 3 for the negative electrode is 7 or more. By setting the specific surface area ratio in such a range, it is possible to maintain the strength of the negative electrode 10 for an electric device that can make the conductivity of the surface of the silicon-containing alloy 1 more uniform. Therefore, the charge / discharge efficiency and cycle durability of the electric device can be improved. In addition, the ratio of the specific surface area of the carbonaceous material to the specific surface area of the conductive auxiliary agent 3 for the negative electrode is preferably 10 or more, more preferably 15 or more, further preferably 18 or more, and 26 or more. Most preferably it is. Further, the ratio of the specific surface area of the carbon-based material to the specific surface area of the conductive auxiliary agent 3 for the negative electrode is preferably 40 or less, more preferably 35 or less, further preferably 30 or less, and most preferably 27 or less.

  The negative electrode 10 for an electric device can include a negative electrode current collector 12 and a negative electrode active material layer 11 disposed on at least one surface of the negative electrode current collector 12. The silicon-containing alloy 1, the negative electrode conductive additive 3 and the negative electrode binder 4 described above are added with a solvent to form a negative electrode slurry, which is applied to the negative electrode current collector 12 and dried to form the negative electrode active material layer 11. be able to. That is, the negative electrode active material layer 11 includes the silicon-containing alloy 1, the negative electrode conductive additive 3, the negative electrode binder 4, and the like.

(Negative electrode binder 4)
The negative electrode 10 for electric devices includes a negative electrode binder 4. The negative electrode binder 4 can bind the negative electrode active materials to each other or the negative electrode active material and the negative electrode conductive additive 3. Examples of the material for the negative electrode binder 4 used in the negative electrode 10 for electric devices include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), poly Ether nitrile (PEN), polyacrylonitrile (PAN), polyimide (PI), polyamide (PA), polyamideimide (PAI), carboxymethylcellulose (CMC), ethylene-vinyl acetate copolymer (EVA), polyvinyl chloride (PVC) ), Thermoplastic resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), thermosetting resins such as epoxy resins, styrene-butadiene rubber (SBR), isoprene (IR), include elastomers such as butadiene rubber (BR). These negative electrode binders 4 may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of polyimide (PI), polyamide (PA), and polyamideimide (PAI) is preferable because of excellent adhesion and heat resistance as the negative electrode binder 4. Although content of the binder 4 for negative electrodes contained in the negative electrode active material layer 11 is not specifically limited, 0.5-15 mass% is preferable with respect to the whole negative electrode active material layer 11, and 1-10 mass% is more. preferable.

(Negative electrode current collector 12)
The lithium ion battery of this embodiment can include the negative electrode active material layer 11 disposed on at least one surface of the negative electrode current collector 12. The negative electrode current collector 12 can be disposed so that electrons can be transferred between the negative electrode active material layer 11 and a negative electrode tab 63 described later. The material forming the negative electrode current collector 12 is preferably a metal such as copper (Cu), titanium (Ti), nickel (Ni), stainless steel (SUS), or the like. Among these, it is preferable to use copper (Cu) as a material for forming the negative electrode current collector 12.

  As described above, the negative electrode 10 for an electrical device includes the silicon-containing alloy 1 containing silicon and tin, the carbon coating layer 2 formed of a carbon-based material and covering the silicon-containing alloy 1, the negative electrode conductive additive 3, A negative electrode binder 4. And the ratio of the specific surface area of the carbonaceous material with respect to the specific surface area of the conductive support agent 3 for negative electrodes is 7 or more. When the negative electrode 10 for an electric device of the present embodiment is used for the electric device 100, the charge / discharge efficiency and the cycle durability can be improved.

[Electrical device 100]
The electric device 100 of this embodiment can include the negative electrode 10 for electric devices as described above. Therefore, the electrical device 100 of this embodiment can improve charging / discharging efficiency and cycle durability. Examples of the electric device 100 include a lithium ion battery and an electric double layer capacitor described later.

  The electric device 100 according to the present embodiment can include the negative electrode 10 for electric devices. Therefore, the electrical device 100 of this embodiment can improve charging / discharging efficiency and cycle durability. In addition to the negative electrode 10 for an electric device, the electric device 100 includes a positive electrode 20 for an electric device, an electrolyte layer 30, a positive electrode tab 61, a negative electrode tab 63, an outer package 65, and the like as shown in FIG. Furthermore, it can be provided. That is, the electric device 100 can include the exterior body 65 and the battery element 50 accommodated in the exterior body 65. The battery element 50 can be formed by stacking a plurality of single battery layers 40. The unit cell layer 40 can include the positive electrode 20 for an electric device, the negative electrode 10 for an electric device, and the electrolyte layer 30 disposed between the positive electrode 20 for an electric device and the negative electrode 10 for an electric device. Further, as shown in FIG. 2, a plurality of unit cell layers 40 can be stacked and electrically arranged in parallel. The positive electrode tab 61 and the negative electrode tab 63 can extract the current generated in the single battery layer 40 to the outside of the electric device 100.

  The electric device 100 is not limited to the form as shown in FIG. 2. For example, the negative electrode active material layer 11 is disposed on one surface of the current collector, and the positive electrode active material layer is disposed on the other surface of the current collector. It is good also as a bipolar battery containing the bipolar electrode like which 21 is arrange | positioned. Further, the structure of the electric device 100 is not limited to the stacked type, and may be a wound type.

(Positive electrode 20 for electrical devices)
The positive electrode for an electric device 20 can include a positive electrode current collector 22 and a positive electrode active material layer 21 disposed on at least one surface of the positive electrode current collector 22. The positive electrode 20 for an electric device has a positive electrode current collector 22 in which a material for forming a positive electrode active material layer is dispersed in a solvent to form a positive electrode slurry, and the positive electrode current collector 22 is coated with a positive electrode slurry and dried. Layer 21 can be formed. The positive electrode active material layer 21 can include a positive electrode active material, a positive electrode conductive additive, a positive electrode binder, and the like.

(Positive electrode active material)
Examples of the positive electrode active material include lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. Examples of the lithium-transition metal composite oxide include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O ₂ , Li (Li—Ni—Mn—Co) O _2, and transitions thereof. An example in which a part of the metal is substituted with another element can be given. Examples of the lithium-transition metal phosphate compound include LiFePO ₄ . Examples of the lithium-transition metal sulfate compound include Li _x Fe ₂ (SO ₄ ) ₃ .

The positive electrode active material preferably contains a solid solution lithium-containing transition metal oxide represented by the chemical formula: Li _1.5 [Ni _a Co _b Mn _c [Li] _d ] O ₃ . In the formula, Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, and O represents oxygen. In the formula, a, b, c and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = The relationship of 1.5, 1.1 ≦ a + b + c <1.4 is satisfied. By using such a positive electrode active material, the discharge capacity of the electric device 100 can be increased. Further, by using such a positive electrode active material, the charge / discharge potential of the electric device can be increased. The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In the above chemical formula, a, b, c and d are 0 <a <1.35, 0 ≦ b <1.35, 0 <c <1.35, 0.15 <d ≦ 0.35, a + b + c + d = 1 .5, 1.15 ≦ a + b + c <1.35 is preferably satisfied. In the above chemical formula, a, b, c and d are 0 <a <1.3, 0 ≦ b <1.3, 0 <c <1.3, 0.15 <d ≦ 0.35, a + b + c + d = 1.5, 1.2 ≦ a + b + c <1.3 is more preferable. By using such a positive electrode active material, the discharge capacity of the electric device can be increased.

  The average primary particle size of the positive electrode active material is preferably 50 nm to 2000 nm, more preferably 100 to 1000 nm, and further preferably 200 nm to 400 nm. By setting the average primary particle diameter of the positive electrode active material in such a range, the discharge capacity of the electric device can be increased. In addition, the average primary particle diameter of a positive electrode active material can be made into the average value of several to several dozen actually measured using the transmission electron microscope (TEM) or the scanning electron microscope (SEM).

(Conductive aid for positive electrode)
The conductive additive for positive electrode can effectively form an electronic network inside the positive electrode active material layer 21 and increase the discharge capacity of the electric device. 1-10 mass% is preferable with respect to the whole positive electrode active material layer 21, and, as for content of the conductive support agent for positive electrodes, 2-6 mass% is more preferable. By setting the content of the conductive additive for the positive electrode in such a range, the conductivity of the positive electrode active material layer 21 can be improved.

  The conductive additive for positive electrode preferably contains a fibrous conductive aid and a granular conductive aid. Due to the synergistic effect of using a plurality of conductive additives for positive electrodes, the cycle characteristics are improved and the voltage of the electrical device at a low potential is improved compared to the case where a fibrous conductive additive or a granular conductive additive is used alone. This is to contribute to the reduction of the descent.

That is, it is preferable that the electric device 100 of the present embodiment includes the negative electrode 10 for electric devices and the positive electrode 20 for electric devices. The positive electrode 20 for an electric device includes a positive electrode active material containing a solid solution lithium-containing transition metal oxide represented by a chemical formula: Li _1.5 [Ni _a Co _b Mn _c [Li] _d ] O ₃ , and a fibrous form It is preferable to provide a conductive auxiliary and a granular conductive auxiliary. In the formula, Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, and O represents oxygen. A, b, c and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = 1.5. 1.1 ≦ a + b + c <1.4 is satisfied. Therefore, compared with the case where a fibrous conductive support agent or a granular conductive support agent is used independently, it can contribute to the improvement of cycle characteristics and the reduction of the voltage drop of the electric device at a low potential.

  The fibrous conductive auxiliary means a conductive auxiliary having a fiber-like shape. The fiber shape includes, for example, an elongated shape such as a column shape, and the shape such as a straight line shape or a curved shape is not particularly limited. Further, the fiber shape may be a tube shape having a hollow inside as long as it has a fiber-like shape. In the present embodiment, by using such a fibrous conductive additive, a three-dimensional electronic network is formed, so that the conductivity between the positive electrode active materials can be improved.

  As the fibrous conductive additive, for example, carbon fibers such as carbon nanotubes, carbon nanohorns, carbon nanofibers, carbon nanofilaments, carbon fibrils, and vapor grown carbon fibers can be used.

  The fiber diameter of the fibrous conductive additive is preferably 5 nm or more and 50 nm or less. In addition, the fiber diameter of the fibrous conductive additive is more preferably 7 nm or more and 20 nm or less, and further preferably 8 nm or more and 15 nm or less. By setting the fiber diameter of the fibrous conductive additive in such a range, the voltage drop of the electric device at a low potential can be more effectively suppressed. In addition, the fiber diameter of a fibrous conductive support agent can be made into the average value of several to several dozen fiber diameters measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

  The fiber length of the fibrous conductive additive is preferably 50 nm or more and 50 μm or less, and more preferably 500 nm or more and 20 μm or less. By setting the fiber length of the fibrous conductive additive in such a range, the conductivity between the positive electrode active materials can be improved and the cycle characteristics can be improved. In addition, the fiber length of a fibrous conductive support agent can be made into the average value of several to several dozen fiber length measured using the transmission electron microscope (TEM) or the scanning electron microscope (SEM).

  The aspect ratio of the fibrous conductive additive is preferably 10 or more. By setting the aspect ratio of the fibrous conductive additive in such a range, the conductivity between the positive electrode active materials can be improved, and the cycle characteristics can be improved. Further, the aspect ratio of the fibrous conductive additive is more preferably 10 or more and 1000 or less, and further preferably 20 or more and 1000 or less.

  The fiber diameter of the fibrous conductive assistant is preferably 5 nm to 50 nm, and the aspect ratio of the fibrous conductive assistant is preferably 10 or more. By setting the fiber diameter and aspect ratio of the fibrous conductive additive in such a range, the conductivity between the positive electrode active materials can be improved, and the cycle characteristics can be improved.

The specific surface area of the fibrous conductive additive is preferably ^{10 m} 2 / g or more 300 meters ² / g or less, more preferably less 100 m ² / g or more 250 meters ² / g, more preferably 170m ² / g or more 210 m ² / g or less. By setting the specific surface area of the fibrous conductive additive in such a range, the conductivity between the positive electrode active materials can be improved, and the cycle characteristics can be improved. In addition, the BET specific surface area of a fibrous conductive support agent can be measured by BET method by adsorbing nitrogen gas.

  The granular conductive auxiliary means a conductive auxiliary having a grain-like shape, and the long diameter of the granular conductive auxiliary is smaller than the long diameter of the fibrous conductive auxiliary. The granular form includes, for example, shapes such as a spherical shape, a hemispherical shape, an ellipsoid, a short chain shape, a scale shape, a cylindrical shape, and a polygonal column shape, and may be linear or curved. Moreover, the inside of a granular form may be hollow as long as it has a shape like a grain. By using such a granular conductive additive, the surface of the positive electrode active material is uniformly covered with the granular conductive additive, and the reaction overvoltage at low potential peculiar to the solid solution lithium-containing transition metal oxide can be reduced. It is done. Therefore, it is considered that the voltage drop of the electric device at a low potential can be reduced.

  As the particulate conductive additive, for example, carbon powder such as carbon black or graphite can be used. Examples of carbon black include acetylene black, furnace black, channel black, and thermal black. Examples of graphite include natural graphite and artificial graphite.

  The average primary particle diameter of the granular conductive aid is preferably 45 nm or less. By setting the average primary particle diameter of the granular conductive auxiliary to such a range, the surface of the positive electrode active material is uniformly covered with the granular conductive auxiliary, and thus a voltage drop at a low potential can be effectively suppressed. . The average primary particle size of the granular conductive aid is more preferably from 0.1 nm to 35 nm, and further preferably from 1 nm to 30 nm. Moreover, the average primary particle diameter of a granular conductive support agent can be made into the average value of several to several dozen actually measured using the transmission electron microscope (TEM) or the scanning electron microscope (SEM).

The specific surface area of the granular conductive aid is preferably 110 m ² / g or more. By setting the specific surface area of the granular conductive additive in such a range, the contact area between the granular conductive auxiliary and the positive electrode active material can be increased, so that a voltage drop at a low potential can be effectively suppressed. . Incidentally, more preferably the specific surface area of the particulate conductive additive is 150 meters ² / g or more, and still more preferably 170m ² / g or more. Further, it is preferred that the specific surface area of the particulate conductive additive is less than 300 meters ² / g, more preferably at 250 meters ² / g or less, still more preferably not more than 210 m ² / g. In addition, the BET specific surface area of a granular conductive support agent can be measured by a BET method by adsorbing nitrogen gas.

The average primary particle diameter of the granular conductive additive is preferably 45 nm or less, and the specific surface area of the granular conductive auxiliary is preferably 110 m ² / g or more. By setting the average primary particle diameter and specific surface area of the granular conductive aid in such a range, the surface of the positive electrode active material is uniformly covered with the granular conductive aid, and the contact area between the granular conductive aid and the positive electrode active material. Can be increased. Therefore, the voltage drop at a low potential can be more effectively suppressed.

  The ratio of the specific surface area of the fibrous conductive additive to the specific surface area of the granular conductive aid is preferably 0.6 or more and 1.3 or less. That is, the value obtained by dividing the specific surface area of the fibrous conductive assistant by the specific surface area of the granular conductive assistant is preferably 0.6 or more and 1.3 or less. By setting the ratio of the specific surface area in such a range, the cycle characteristics are high, and the voltage drop at a low potential can be reduced. The ratio of the specific surface area of the fibrous conductive additive to the granular conductive aid is more preferably 0.7 or more and 1.3 or less, and further preferably 0.8 or more and 1.2 or less.

  The ratio of the mass of the fibrous conductive additive to the mass of the granular conductive aid is preferably 0.8 or more. That is, the value obtained by dividing the mass of the fibrous conductive assistant by the mass of the granular conductive assistant is preferably 0.8 or more. By setting the mass ratio of the conductive additive for the positive electrode in such a range, cycle characteristics are high, and a voltage drop at a low potential can be reduced. In addition, it is more preferable that ratio of the mass of the fibrous conductive support agent with respect to a granular conductive support agent is 0.9 or more. Moreover, the ratio of the mass of the fibrous conductive additive to the granular conductive aid is preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 2.1 or less. In addition, it is preferable that ratio of the mass of the fibrous conductive support agent with respect to the mass of a granular conductive support agent exceeds 1, It is more preferable to exceed 1.3, It is further more preferable to exceed 1.7.

  The ratio of the average primary particle size of the positive electrode active material to the average primary particle size of the particulate conductive additive is preferably 5 to 100, more preferably 7 to 90, and even more preferably 9 to 80. . By making the ratio of the average primary particle diameter of the positive electrode active material to the average primary particle diameter of the granular conductive auxiliary in such a range, the contact area between the positive electrode active material and the granular conductive auxiliary agent can be increased. The voltage drop of the electric device at the potential can be suppressed.

  The content of the carbon material contained in the fibrous conductive auxiliary and the granular conductive auxiliary is preferably 80% by mass or more, more preferably 90% by mass, and further preferably 95% by mass or more. . Further, the content of the carbon material contained in the conductive additive for positive electrode is particularly preferably 98% by mass or more, and most preferably 100% by mass. By making content of the carbon material contained in the conductive support agent for positive electrodes into such a range, the electroconductivity between positive electrode active materials can be improved.

  0.1 mass%-5 mass% are preferable with respect to the whole positive electrode active material layer 21, and, as for content of a fibrous conductive support agent, 1 mass%-3 mass% are more preferable. Moreover, 0.1 mass%-5 mass% are preferable with respect to the whole positive electrode active material layer 21, and, as for content of a granular conductive support agent, 1 mass%-3 mass% are more preferable. By making content of a fibrous conductive support agent and granular conductive support agent into such a range, the cycling characteristics of an electrical device can be made high and the voltage drop in low potential can be made small.

(Binder for positive electrode)
The positive electrode binder used for the positive electrode active material layer 21 can be the same as the negative electrode binder 4 used for the negative electrode active material layer 11. The content of the positive electrode binder contained in the positive electrode active material layer 21 can be the same as the content of the negative electrode binder 4 used in the negative electrode active material layer 11.

(Positive electrode current collector 22)
The positive electrode current collector 22 can be arranged so that electrons can be transferred between the positive electrode active material layer 21 and a positive electrode tab 61 described later. The material forming the positive electrode current collector 22 is preferably a metal such as aluminum (Al), titanium (Ti), nickel (Ni), and stainless steel (SUS). Among these, it is preferable to use aluminum (Al) as a material for forming the positive electrode current collector 22.

(Electrolyte layer 30)
The electrical device 100 of this embodiment can further include an electrolyte layer 30 disposed between the electrical device negative electrode 10 and the electrical device positive electrode 20. The electrolyte layer 30 isolates the electrical device negative electrode 10 and the electrical device positive electrode 20 and mediates the movement of lithium ions. From the viewpoint of reducing internal resistance, the thickness of the electrolyte layer 30 is preferably 1 to 100 μm, and more preferably 5 to 50 μm. The electrolyte layer 30 includes a non-aqueous electrolyte. As the non-aqueous electrolyte, a gel or solid polymer electrolyte in which a lithium salt is dissolved in an ion conductive polymer and a liquid electrolyte in which a lithium salt is dissolved in an organic solvent can be held in a porous substrate layer and used.

  Examples of the ion conductive polymer used in the polymer electrolyte include polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), hexafluoropropylene, polyethylene glycol (PEG), polyacrylonitrile (PAN), and polymethyl. Examples include methacrylate (PMMA) and copolymers thereof.

Examples of the organic solvent used in the liquid electrolyte include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl. And carbonates such as carbonate (EMC) and methylpropyl carbonate (MPC). As the lithium salt used in the liquid _{electrolyte, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF ₃ SO ₃ etc. are mentioned.

  The material for forming the porous substrate layer is not particularly limited, but it is preferable to use a thermoplastic resin such as polyethylene, polypropylene, or ethylene-propylene copolymer. The porosity of the porous substrate layer is not particularly limited, but is preferably 40 to 85%. When the porosity is 40% or more, sufficient ion conductivity can be obtained. On the other hand, when the porosity is 85% or less, the strength of the porous substrate layer can be maintained well.

(Positive electrode tab 61 and negative electrode tab 63)
The electric device 100 may further include a positive electrode tab 61 that electrically connects the positive electrode current collector 22 and a device external to the electric device 100. The electric device 100 may further include a negative electrode tab 63 that electrically connects the negative electrode current collector 12 and an external device of the electric device 100. The material which forms the positive electrode tab 61 and the negative electrode tab 63 is not specifically limited, For example, at least 1 selected from the group which consists of aluminum, copper, titanium, nickel can be used. The material forming the positive electrode tab 61 and the negative electrode tab 63 may be the same or different.

(Exterior body 65)
The electrical device 100 of this embodiment can further include an exterior body 65 that houses the battery element 50. Examples of the exterior body 65 include a can and a film formed by a film. The shape of the exterior body 65 is not particularly limited, and can be a cylindrical shape, a square shape, or a sheet shape. Although not particularly limited, it is preferable that the exterior body 65 is formed of a film from the viewpoint of reduction in size and weight. Among these, from the viewpoint of high output and cooling performance, the film is preferably a laminate film, and the laminate film preferably contains aluminum. Moreover, it is preferable that the electric device 100 is a flat laminated lithium ion battery. Since such a lithium ion battery can increase the discharge capacity and the heat dissipation performance, it is optimal for mounting in a vehicle. As an example of the laminate film containing aluminum, there is a three-layer laminate film of PP / aluminum / nylon.

  Although the use of the electric device 100 is not particularly limited, as described above, the charge / discharge efficiency and the cycle durability are improved. Therefore, it can be suitably used for vehicles. Specifically, the electric device 100 of the present embodiment can be suitably used for a driving power source for a vehicle.

  Hereinafter, the present embodiment will be described in more detail with reference to Examples and Comparative Examples, but the present embodiment is not limited to these.

[Example 1]
(Preparation of positive electrode)
A 2 mol / L aqueous solution of nickel acetate, cobalt acetate and manganese acetate was prepared. Next, a predetermined amount was weighed so that the composition would be Li _1.5 [Ni _0.281 Co _0.281 Mn _0.688 [Li _0.25 ]] O ₃ to prepare a mixed solution. Then, while stirring the mixed solution with a magnetic stirrer, ammonia water was added dropwise to the mixed solution until the pH reached 7. Further, a 2 mol / L aqueous sodium carbonate solution was dropped into the mixed solution to precipitate a nickel-cobalt-manganese composite carbonate. The obtained precipitate was subjected to suction filtration, washed with water, and dried under conditions of about 120 ° C. and about 5 hours. And the obtained dried material was calcined under conditions of about 500 ° C. and about 5 hours. Lithium hydroxide was added to this so that the composition would be Li _1.5 [Ni _0.281 Co _0.281 Mn _0.688 [Li _0.25 ]] O _3, and kneaded for about 30 minutes in an automatic mortar. Furthermore, it heated at the temperature increase rate of 50 degreeC / hour in air | atmosphere, and after that, this baking was performed for about 12 hours at 750 degreeC, and the positive electrode active material was obtained.

To 94.5 parts by mass of the positive electrode active material thus obtained, 3.0 parts by mass of a conductive additive for positive electrode and 30 parts by mass of a solvent were added, and a planetary mixer (manufactured by Primics Co., Ltd., Hibismix 2P-03) was added. Type) to prepare a positive electrode conductive additive solution. In addition, 1.5 mass parts fibrous conductive support agent and 1.5 mass parts granular conductive support agent were used for the conductive support agent for positive electrodes. The solvent used was N-methylpyrrolidone (NMP). The fibrous conductive auxiliary agent had a fiber diameter of 11 nm and a specific surface area of 200 m ² / g. Moreover, the average primary particle diameter of the granular conductive aid was 25 nm, and the specific surface area was 206 m ² / g.

  A positive electrode binder solution prepared by dissolving 2.5 parts by mass of a positive electrode binder with 45.0 parts by mass of a solvent is added to the positive electrode conductive additive solution thus obtained, and the mixture is kneaded again with a planetary mixer. A slurry was prepared. Note that N-methylpyrrolidone (NMP) was used as the solvent. Moreover, the solid content concentration of the produced positive electrode slurry was 57.1% by mass.

The positive electrode slurry thus obtained was applied to one surface of the positive electrode current collector with a bar coater so that the thickness of the positive electrode active material layer after drying was 50 μm. Next, the positive electrode current collector coated with the positive electrode slurry was placed on a hot plate and dried at 120 ° C. to 130 ° C. for 10 minutes so that the residual amount of the solvent was 0.02% by mass or less. The product obtained by drying in this way is compression-molded with a roller press, and the mass of the positive electrode active material layer is about 3.5 mg / cm ² , the film thickness is about 50 μm, and the density is 2.70 g / cm ^3. Was cut as follows. As the positive electrode current collector, an aluminum foil having a thickness of 20 μm was used.

Next, the obtained cut product was placed in a vacuum dryer and decompressed (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.). Subsequently, the temperature was increased to 120 ° C. at a temperature increase rate of 10 ° C./min while flowing nitrogen gas at 100 cm ³ / min. Then, after hold | maintaining for 12 hours in the state pressure-reduced to 100 mmHg (1.33 * 10 < ⁴ > Pa) at 120 degreeC, it was made to cool to room temperature (25 degreeC). The dried product thus obtained was used as the positive electrode.

(Preparation of negative electrode)
First, metal powders were alloyed by a mechanical alloy method using a planetary ball mill (P-6, manufactured by Friitch Germany). Specifically, a metal powder prepared so as to have a mass ratio of Si: Sn: Ti = 60: 10: 30 and pulverized balls made of zirconia were put into a container made of zirconia. Then, the base which fixes the container made from zirconia was rotated at 600 rpm for 24 hours, and metal powder was alloyed. Then, the base which fixes the container made from zirconia was rotated at 400 rpm for 1 hour, and the alloyed metal powder was grind | pulverized. D50 of the obtained silicon-containing alloy was 6 μm.

Next, 80 parts by mass of a silicon-containing alloy and 0.8 parts by mass of a carbon-based material are mixed, and a composite treatment is performed using Nobilta (registered trademark) NOB-MINI manufactured by Hosokawa Micron Co., Ltd. The alloy was coated with a carbon-based material. As the carbon-based material, particulate acetylene black having a BET specific surface area of 206 m ² / g and an average particle diameter (D50) of 25 nm was used. The compounding process was performed under the conditions of a processing rotation speed of 6000 rpm, a load power of 300 W, and a processing time of 30 minutes.

Next, 80.8 parts by mass of a silicon-containing alloy coated with a carbon-based material, 4.2 parts by mass of a conductive additive for negative electrode, and 15 parts by mass of a binder for negative electrode are dispersed in 100 parts by mass of N-methylpyrrolidone. It was. These were mixed in a defoaming kneader (AR-100 manufactured by Thinky Co., Ltd.) to obtain a negative electrode slurry. The conductive auxiliary agent for the negative electrode was acetylene black having a BET specific surface area of 7.7 m ² / g, and the negative electrode binder was polyimide. Therefore, the ratio of the specific surface area of the carbonaceous material to the specific surface area of the conductive additive for negative electrode is 26.7.

  Next, a negative electrode slurry is uniformly applied on one surface of the negative electrode current collector so that the thickness of the negative electrode active material layer after drying is 30 μm, and dried in a vacuum for 24 hours. Obtained. The negative electrode current collector was a 10 μm thick copper foil.

(Production of lithium ion battery)
In a glove box in an argon gas atmosphere, the positive electrode obtained as described above and the negative electrode of metallic lithium were punched into a circle having a diameter of 15 mm and faced each other, and an electrolyte layer was disposed therebetween. Two electrolyte layers having a thickness of 20 μm made of polypropylene were used. In addition, the positive electrode and the negative electrode used what was dried at 100 degreeC with the vacuum dryer for 2 hours before lithium ion battery preparation.

  Next, the laminate of the negative electrode, the electrolyte layer, and the positive electrode was disposed on the bottom side of a coin cell (CR2032) made of stainless steel (SUS316). Further, a gasket for maintaining insulation between the positive electrode and the negative electrode was attached, and 150 μl of the electrolyte solution was injected with a syringe. And a spring and a spacer were laminated | stacked, the upper part side of the coin cell was piled up, and it sealed by crimping, and produced the lithium ion battery. In addition, the member used for an electrolyte layer or a coin cell is previously dried at room temperature for 24 hours or more in a glove box in an argon gas atmosphere.

In addition, the following was used as electrolyte solution. First, an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC: DEC = 1: 2 was prepared. To this, lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt was dissolved so as to have a concentration of 1 mol / L to obtain an electrolytic solution.

(Activation process)
The coin cell obtained as described above was charged at a constant current of 0.1 C at room temperature (25 ° C.) until the maximum voltage reached 4.8 V, and then 0 until the minimum battery voltage reached 2.0 V. A charge / discharge cycle for constant current discharge at 1 C was performed for only one cycle to obtain a lithium ion battery.

[Example 2]
A lithium ion battery was produced in the same manner as in Example 1 except that acetylene black having a BET specific surface area of 133 m ² / g was used as the carbon-based material for forming the carbon coating layer. In addition, since the BET specific surface area of acetylene black is 133 m < ² > / g, ratio of the specific surface area of the carbonaceous material with respect to the specific surface area of the conductive support agent for negative electrodes was 17.2.

[Comparative Example 1]
A lithium ion battery was produced in the same manner as in Example 1 except that acetylene black having a BET specific surface area of 13.1 m ² / g was used as the carbon-based material for forming the carbon coating layer. In addition, since the BET specific surface area of acetylene black is 13.1 m < ² > / g, ratio of the specific surface area of the carbonaceous material with respect to the specific surface area of the conductive support agent for negative electrodes was 1.7.

[Comparative Example 2]
A lithium ion battery was produced in the same manner as in Example 1 except that the coating amount of the carbon coating layer was changed to 0% by mass.

[Evaluation]
About the lithium ion battery of an Example and a comparative example, evaluation of the Coulomb efficiency and the discharge capacity maintenance factor of the 100th cycle was implemented. The results are shown in Table 1.

(Coulomb efficiency)
The charge / discharge efficiency was evaluated by measuring the Coulomb efficiency as follows. At room temperature (25 ° C.), after charging at a constant current of 0.1 C until the maximum voltage is 4.6 V, a charge / discharge cycle is performed at a constant current of 1.0 C until the minimum voltage is 2.0 V. Cycled. And the average value of the ratio of the discharge capacity with respect to the charge capacity in each cycle was made into coulomb efficiency. The charge capacity was the electric capacity when charging from 2.0 V to 4.6 V, and the discharge capacity was the electric capacity when discharging from 4.6 V to 2.0 V.

(Discharge capacity maintenance rate at 100th cycle)
The cycle durability was evaluated by measuring the discharge capacity maintenance rate at the 100th cycle as follows. At room temperature (25 ° C.), after charging at a constant current of 0.1 C until the maximum voltage is 4.6 V, a charge / discharge cycle is performed at a constant current of 1.0 C until the minimum voltage is 2.0 V. Cycled. Then, in the first cycle and the 100th cycle, the discharge capacity when discharging from 4.6 V to 2.0 V was measured, and the ratio of the discharge capacity of the first cycle to the discharge capacity of the 100th cycle was determined as the discharge of the 100th cycle. The capacity maintenance rate was used.

  From the results of Table 1, the lithium ion secondary batteries of Example 1 and Example 2 have a specific surface area ratio of 7 or more, and therefore, compared with Comparative Example 1 and Comparative Example 2, Coulomb efficiency and 100th cycle discharge Capacity maintenance rate became high. On the other hand, although the lithium ion secondary battery of Comparative Example 1 includes a carbon coating layer, since the specific surface area ratio is 1.7, the Coulomb efficiency is slightly increased as compared with Comparative Example 2, but the 100th cycle The discharge capacity maintenance rate slightly decreased.

  Although the present invention has been described with reference to the examples and comparative examples, the present invention is not limited to these, and various modifications can be made within the scope of the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Silicon-containing alloy 2 Carbon coating layer 3 Conductive auxiliary agent for negative electrodes 4 Binder for negative electrodes 10 Negative electrodes for electric devices 20 Positive electrodes for electric devices 100 Electric devices

Claims (7)

A silicon-containing alloy comprising silicon and tin;
A carbon coating layer formed of a carbon-based material and covering the silicon-containing alloy;
A conductive additive for the negative electrode,
A negative electrode binder;
With
The negative electrode for electric devices whose ratio of the specific surface area of the said carbonaceous material with respect to the specific surface area of the said conductive support agent for negative electrodes is 7 or more.   2. The negative electrode for an electric device according to claim 1, wherein a ratio of a specific surface area of the carbonaceous material to a specific surface area of the conductive additive for the negative electrode is 18 or more. The negative electrode for an electric device according to claim 1 or 2,
An electrical device comprising a positive electrode for an electrical device,
The positive electrode for electrical devices is
Chemical formula:
_{Li 1.5 [Ni a Co b Mn} c [Li] d] O 3
(In the formula, Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, O represents oxygen, and a, b, c and d are 0 <a <1.4 and 0 ≦ b <1.4. , 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c <1.4) A positive electrode active material containing the product,
A fibrous conductive aid;
A granular conductive aid;
An electrical device comprising:   The electrical device according to claim 3, wherein the fibrous conductive assistant has a fiber diameter of 5 nm or more and 50 nm or less, and the fibrous conductive assistant has an aspect ratio of 10 or more. 5. The electrical device according to claim 3, wherein an average primary particle diameter of the particulate conductive additive is 45 nm or less, and a specific surface area of the granular conductive aid is 110 m ² / g or more.   The electric device according to claim 3, wherein a ratio of the mass of the fibrous conductive additive to the mass of the granular conductive additive is 0.8 or more.   The electrical device according to any one of claims 3 to 6, wherein a ratio of a specific surface area of the fibrous conductive additive to a specific surface area of the granular conductive additive is 0.6 or more and 1.3 or less.

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