JP2013182706A - Precursor for negative electrode, manufacturing method of precursor for negative electrode, production method of material for negative electrode, electrode and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precursor for negative electrode which can be used suitably in manufacturing of a high capacity lithium ion secondary battery having superior cycle performance and charge/discharge efficiency.SOLUTION: The precursor for negative electrode is used for manufacturing the negative electrode of a lithium ion secondary battery, and has active material particles, a first resin layer covering the active material particles, and a second resin layer covering the first resin layer. The first resin composing the first resin layer has a residual carbon rate lower than that of the second resin composing the second resin layer, when subjected to calcination.

Description

  The present invention relates to a negative electrode precursor, a method for manufacturing a negative electrode precursor, a method for manufacturing a negative electrode material, an electrode, and a lithium ion secondary battery.

  As a negative electrode of a lithium ion secondary battery, one made of a material containing a carbon material and an active material is widely used. This is because even if the charge / discharge cycle proceeds, dendritic lithium is hardly deposited on the negative electrode using the carbon material, and safety is guaranteed.

  Such a negative electrode has been manufactured by applying a paste containing a particulate carbon material, a particulate active material, and a dispersion medium on a current collector, and removing the dispersion medium (for example, Patent Document 1). reference).

  However, when the negative electrode manufactured as described above is applied, there is a problem that the cycle performance (capacity maintenance ratio when charging and discharging are repeatedly performed) cannot be sufficiently improved.

  Further, conventionally, there has been a problem that the charge / discharge capacity and the charge / discharge efficiency cannot be made sufficiently excellent.

JP 2005-347147 A

  An object of the present invention is to provide a precursor for a negative electrode that can be suitably used for the production of a lithium ion secondary battery that is excellent in cycleability, and has a high capacity and excellent charge / discharge efficiency. Providing a method for producing a negative electrode precursor that can be produced efficiently, having excellent cycleability, and capable of being suitably used for producing a lithium ion secondary battery having high capacity and excellent charge / discharge efficiency Providing a method for producing a negative electrode material capable of efficiently producing a material, and providing an electrode suitable for use in a lithium ion secondary battery having excellent cycleability, high capacity and excellent charge / discharge efficiency It is another object of the present invention to provide a lithium ion secondary battery that has excellent cycle performance, high capacity, and excellent charge / discharge efficiency.

Such an object is achieved by the present invention described in the following (1) to (14).
(1) A negative electrode precursor used for manufacturing a negative electrode of a lithium ion secondary battery,
Active material particles,
A first resin layer covering the active material particles;
A second resin layer covering the first resin layer,
The first resin constituting the first resin layer is characterized in that the residual carbon ratio when subjected to the firing treatment is lower than that of the second resin constituting the second resin layer. A negative electrode precursor.

  (2) The negative electrode precursor according to (1), wherein the active material particles are composed of Si or an oxide thereof.

  (3) The said 1st resin is a precursor for negative electrodes as described in said (1) or (2) whose residual carbon ratio measured according to JISK6910 is 20 mass% or less.

  (4) The negative electrode precursor according to any one of (1) to (3), wherein the second resin is a resin having a residual carbon ratio measured in accordance with JIS K6910 of 30% by mass or more.

  (5) The negative electrode precursor according to any one of (1) to (4), wherein the average thickness of the first resin layer is 1 nm or more and 10 μm or less.

  (6) The negative electrode precursor according to any one of (1) to (5), wherein an average particle diameter of the active material particles is 1 nm or more and 3 μm or less.

(7) When the content of the active material particles in the negative electrode precursor is X ₀ [mass%] and the content of the first resin in the negative electrode precursor is X ₁ [mass%], 0 The precursor for negative electrodes according to any one of (1) to (6), which satisfies a relationship of .05 ≦ X ₀ / X ₁ ≦ 500.

(8) When the content of the active material particles in the negative electrode precursor is X ₀ [% by mass] and the content of the second resin in the negative electrode precursor is X ₂ [% by mass], 0 The precursor for negative electrodes according to any one of the above (1) to (7), which satisfies the relationship of .01 ≦ X ₀ / X ₂ ≦ 10.

(9) The negative electrode precursor is in the form of particles,
The negative electrode precursor according to any one of (1) to (8), wherein the negative electrode is manufactured using a plurality of negative electrode precursors.

(10) A method for manufacturing a precursor for a negative electrode used for manufacturing a negative electrode of a lithium ion secondary battery,
A first coating step of coating the surface of the active material particles with a first resin layer composed of a first resin;
A second coating step of coating the surface of the first resin layer with a second resin layer composed of a second resin;
The method for producing a precursor for a negative electrode, wherein the first resin has a carbon residue rate lower than that of the second resin when subjected to a firing treatment.

(11) A method for producing a negative electrode material used for producing a negative electrode of a lithium ion secondary battery,
A first coating step of coating the surface of the active material particles with a first resin layer composed of a first resin;
A second coating step of coating the surface of the first resin layer with a second resin layer composed of a second resin to obtain a negative electrode precursor;
A firing step of firing the negative electrode precursor,
The method for producing a negative electrode material, wherein the first resin has a carbon residue rate lower than that of the second resin when the firing step is performed.

  (12) The said baking process is a manufacturing method of the material for negative electrodes as described in said (11) which performs heat processing 800 degreeC or more and 1500 degrees C or less for 30 minutes or more and 12 hours or less under inert gas atmosphere.

  (13) An electrode produced using the negative electrode precursor according to any one of (1) to (9).

  (14) A lithium ion secondary battery comprising the electrode according to (13).

  According to the present invention, the present invention provides a negative electrode precursor that can be suitably used for the production of a lithium ion secondary battery that has excellent cycleability, high capacity, and excellent charge / discharge efficiency, and the negative electrode precursor. Providing a method for producing a negative electrode precursor that can be produced efficiently, having excellent cycleability, and capable of being suitably used for producing a lithium ion secondary battery having high capacity and excellent charge / discharge efficiency Providing a method for producing a negative electrode material capable of efficiently producing a material, and providing an electrode suitable for use in a lithium ion secondary battery having excellent cycleability, high capacity and excellent charge / discharge efficiency In addition, it is possible to provide a lithium ion secondary battery that has excellent cycle performance, high capacity, and excellent charge / discharge efficiency.

It is sectional drawing which shows typically an example of the precursor for negative electrodes of this invention. It is a schematic diagram which shows typically an example of the manufacturing method of the material for negative electrodes of this invention. It is a schematic diagram of a lithium ion secondary battery. It is sectional drawing which shows typically another example of the precursor for negative electrodes of this invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.
<Precursor for negative electrode>
First, the negative electrode precursor of the present invention will be described.
FIG. 1 is a cross-sectional view schematically showing an example of the negative electrode precursor of the present invention.

  By the way, as a negative electrode of a lithium ion secondary battery, what was comprised with the material containing a carbon material and an active material is used widely. This is because even if the charge / discharge cycle proceeds, dendritic lithium is hardly deposited on the negative electrode using the carbon material, and safety is guaranteed.

  Such a negative electrode has been manufactured by applying a paste containing a particulate carbon material, a particulate active material, and a dispersion medium on a current collector, and removing the dispersion medium.

  However, when the negative electrode manufactured as described above is applied, there is a problem that the cycle performance (capacity maintenance ratio when charging and discharging are repeatedly performed) cannot be sufficiently improved.

  Further, conventionally, there has been a problem that the charge / discharge capacity and the charge / discharge efficiency cannot be made sufficiently excellent.

Therefore, the present inventor has conducted intensive research for the purpose of solving the above problems, and has reached the present invention. That is, the negative electrode precursor of the present invention is used for manufacturing a negative electrode of a lithium ion secondary battery, and includes active material particles, a first resin layer covering the active material particles, and the first resin layer. A second resin layer that covers the resin layer, and the first resin that constitutes the first resin layer has a residual carbon ratio when the firing treatment is performed. It is lower than the 2nd resin to comprise. With such a configuration, the above problems can be solved. That is, with such a configuration, a sufficient volume of voids can be reliably formed around the active material particles in the sintering process in the production of the negative electrode (negative electrode material) described in detail later. it can. This allows the voids to absorb the expansion and contraction of the active material during charging and discharging of the lithium ion secondary battery, effectively preventing the expansion and contraction of the electrode (negative electrode) of the lithium ion secondary battery. Can be suppressed. As a result, the charge / discharge efficiency and cycle performance of the lithium ion secondary battery can be made excellent. Moreover, by having a hollow that can absorb the expansion / contraction of the active material, it becomes possible to use an active material with excellent charge / discharge capacity, and the charge / discharge capacity and charge / discharge efficiency of the lithium ion secondary battery are sufficiently excellent. Can be. On the other hand, when the above conditions are not satisfied, the excellent effects as described above cannot be obtained. For example, when the resin layer that covers the active material particles is only one layer, or when the residual carbon ratio when the firing treatment is performed, the second resin layer is more than the first resin constituting the first resin layer. When the second resin constituting the battery is lower, it is difficult to form the voids as described above, and the charge / discharge efficiency and cycle performance of the lithium ion secondary battery cannot be sufficiently improved. . Moreover, the active material excellent in charge / discharge capacity cannot be used, and the charge / discharge capacity and charge / discharge efficiency of the lithium ion secondary battery cannot be sufficiently improved. . In addition, when the residual carbon ratio when the firing treatment is performed is lower in the second resin constituting the second resin layer than in the first resin constituting the first resin layer,
The remaining carbon ratio of the first resin when the firing treatment is performed (hereinafter, also simply referred to as “the remaining carbon ratio of the first resin”), and the remaining carbon ratio of the second resin when the firing treatment is performed. (Hereinafter, it is also simply referred to as “the residual carbon ratio of the second resin”) may be the residual carbon ratio when the firing treatment is performed under the same conditions, and the specific conditions of the firing treatment are not particularly limited. For example, the residual carbon ratio measured according to JIS K6910 can be adopted for each of the first resin and the second resin.

  The negative electrode precursor 10 of this embodiment shown in the figure is in the form of particles, and the surface of the active material particles 1 is covered with the first resin layer 21, and the surface of the first resin layer 21 is the second. The resin layer 22 is covered. With such a configuration, when a negative electrode of a lithium ion secondary battery is manufactured using a plurality of particulate negative electrode precursors 10, the degree of freedom in molding increases. It can respond suitably to formation of a negative electrode. In addition, in the production of the negative electrode (negative electrode material) described in detail later, a sufficient volume of voids can be formed around the active material particles 1 more reliably. This allows the voids to absorb the expansion and contraction of the active material during charging and discharging of the lithium ion secondary battery, and more effectively prevent the expansion and contraction of the electrode (negative electrode) of the lithium ion secondary battery. -It can be suppressed. As a result, the cycle performance of the lithium ion secondary battery can be made particularly excellent.

[Active material particles]
In the present invention, the active material particles constituting the negative electrode precursor is a concept including particles composed of the precursor in addition to those functioning as an active material in the negative electrode of the final lithium ion secondary battery.

  The active material particle 1 constituting the negative electrode precursor 10 is not particularly limited as long as it is a metal that forms a compound with Li, but, for example, one made of Si, Sn, Ti, or an oxide thereof is used. However, it is preferably composed of Si or its oxide. Thereby, the charge / discharge capacity of the active material particles can be further increased.

  The average particle diameter of the active material particles 1 constituting the negative electrode precursor 10 is preferably 1 nm or more and 3 μm or less, and more preferably 1 nm or more and 1 μm or less. When the average particle diameter of the active material particles 1 constituting the negative electrode precursor 10 is a value within the above range, it is possible to more effectively suppress a decrease in cycle performance due to particle cracking due to volume expansion.

  The shape of the active material particles 1 constituting the negative electrode precursor 10 may be any shape such as, for example, a spherical shape, a spindle shape, a scale shape, or a needle shape, but preferably has a spherical shape. . As a result, a more uniform coating can be achieved, and a particularly excellent cycle performance can be obtained by improving the conductivity.

[First resin layer]
The negative electrode precursor 10 is made of a material containing a first resin, and includes a first resin layer 21 that covers the active material particles 1.

  The first resin constituting the first resin layer 21 satisfies the following relationship with the second resin constituting the second resin layer 22 described in detail later. That is, the first resin has a lower carbon residue rate than that of the second resin when the firing treatment is performed. Due to such a difference in the remaining carbon ratio, in the sintering process in the production of the negative electrode (negative electrode material) as will be described in detail later, the carbon produced by the carbonization of the resin at the site corresponding to the second resin layer 22 While the material layer is formed, a gap is formed in a portion corresponding to the first resin layer 21. Therefore, the gap can absorb the expansion / contraction of the active material during charging / discharging of the finally obtained lithium ion secondary battery, and the expansion / contraction of the electrode (negative electrode) of the lithium ion secondary battery is prevented. -It can be suppressed. As a result, the cycle performance of the lithium ion secondary battery can be made excellent. In general, shrinkage occurs during the sintering process (for example, when the negative electrode precursor 10 having a particle shape as illustrated is sintered to obtain a granular negative electrode material, the particle size of the negative electrode material is: For example, the part of the second resin layer 22 and the part of the carbon material layer 3 do not completely coincide with each other for reasons such as being smaller than the particle diameter of the negative electrode precursor 10 before sintering.

  The remaining carbon ratio of the first resin may be lower than the remaining carbon ratio of the second resin when the firing treatment is performed under the same conditions, but for each of the first resin and the second resin. The difference between the residual carbon ratio of the second resin and the residual carbon ratio of the first resin measured according to JIS K6910 is preferably 5% by mass to 60% by mass, and more preferably 20% by mass to 50%. It is more preferable that the amount is not more than mass%. As a result, it is possible to more reliably form a void having a volume that can sufficiently absorb expansion / contraction of the active material during charging / discharging of the lithium ion secondary battery, and the volume of the void is larger than necessary. Can be prevented. As a result, the cycle performance, charge / discharge capacity, and charge / discharge efficiency of the lithium ion secondary battery can be made particularly excellent.

  The residual carbon ratio of the first resin measured in accordance with JIS K6910 is preferably 20% by mass or less, and more preferably 1% by mass or more and 15% by mass or less. Thereby, the space | gap of the volume which can fully absorb the expansion | swelling and shrinkage | contraction of an active material at the time of charging / discharging of a lithium ion secondary battery can be formed more reliably. As a result, the cycle performance of the lithium ion secondary battery can be made particularly excellent. In addition, the charge / discharge capacity and charge / discharge efficiency of the lithium ion secondary battery can be particularly excellent.

  As the first resin, for example, various thermosetting resins and various thermoplastic resins can be used, and thermosetting resins are preferable. By using the thermosetting resin, the stability of the shape of the negative electrode precursor in the sintering process described in detail later can be made particularly excellent, and the negative electrode material produced using the negative electrode precursor Can be controlled more suitably.

  The thermosetting resin is not particularly limited, and examples thereof include phenolic resins such as novolac type phenolic resin and resol type phenolic resin, epoxy resins such as bisphenol type epoxy resin and novolac type epoxy resin, melamine resin, urea resin, and aniline resin. , Cyanate resin, furan resin, ketone resin, unsaturated polyester resin, urethane resin and the like. In addition, modified products obtained by modifying these with various components can also be used.

  The thermoplastic resin is not particularly limited, and examples thereof include polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate. , Polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, polyphthalamide and the like. Moreover, these copolymers or these mixtures can also be used.

  Among these, epoxy resin, styrene butadiene rubber, polyvinyl alcohol and a mixture thereof are particularly preferable. Thereby, volume expansion is absorbed more effectively and particularly excellent cycle characteristics are obtained.

  The first resin may contain a nitrogen-containing resin as a main component resin. By carbonizing such a resin, a carbon material layer composed of hard carbon containing nitrogen can be obtained. When nitrogen is contained in the hard carbon constituting the carbon material layer, suitable electrical characteristics can be imparted to the carbon material layer due to the electronegativity of nitrogen. Thereby, occlusion and discharge | release of lithium ion can be accelerated | stimulated and a high charging / discharging characteristic can be provided.

Here, the following can be illustrated as nitrogen-containing resin.
That is, examples of thermosetting resins as nitrogen-containing resins include melamine resins, urea resins, aniline resins, cyanate resins, urethane resins, phenol resins modified with nitrogen-containing components such as amines, and epoxy resins. Examples of the thermoplastic resin as the nitrogen-containing resin include polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide, polyetherimide, polyamideimide, polyimide, polyphthalamide, and the like. Is mentioned.

When the content of the active material particles 1 in the negative electrode precursor 10 is X ₀ [mass%] and the content of the first resin in the negative electrode precursor 10 is X ₁ [mass%], 0.05 It is preferable that the relationship of ≦ X ₀ / X ₁ ≦ 500 is satisfied, and it is more preferable that the relationship of 0.1 ≦ X ₀ / X ₁ ≦ 10 is satisfied. By satisfying such a relationship, it is possible to more reliably form a void having a volume that can sufficiently absorb expansion / contraction of the active material during charging / discharging of the lithium ion secondary battery, and the void Can be prevented from becoming unnecessarily large. As a result, the cycle performance, charge / discharge capacity, and charge / discharge efficiency of the lithium ion secondary battery can be made particularly excellent.

  The first resin layer 21 may contain the first resin as a main component and also contain a curing agent, an additive, and the like.

  The curing agent is not particularly limited. For example, in the case of a novolak type phenol resin, hexamethylenetetramine, resol type phenol resin, polyacetal, paraform, and the like can be used. In the case of epoxy resins, known as epoxy resins such as polyamine compounds such as aliphatic polyamines and aromatic polyamines, acid anhydrides, imidazole compounds, dicyandiamide, novolac-type phenol resins, bisphenol-type phenol resins, and resol-type phenol resins. Can be used.

  Further, the additive contained in the first resin layer is not particularly limited, for example, metal, pigment, lubricant, antistatic agent, antioxidant, organic acid, inorganic acid, nitrogen-containing compound, oxygen-containing compound, An aromatic compound, a nonferrous metal element, etc. can be mentioned.

  The thickness of the first resin layer 21 is preferably 1 nm or more and 10 μm or less, and more preferably 1 nm or more and 1000 nm or less. As a result, it is possible to more reliably form a void having a volume that can sufficiently absorb expansion / contraction of the active material during charging / discharging of the lithium ion secondary battery, and the volume of the void is larger than necessary. Can be prevented. As a result, the cycle performance, charge / discharge capacity, and charge / discharge efficiency of the lithium ion secondary battery can be made particularly excellent.

[Second resin layer]
The negative electrode precursor 10 is made of a material containing a second resin, and includes a second resin layer 22 that covers the first resin layer 21.

  The second resin that constitutes the second resin layer 22 satisfies the following relationship with the first resin that constitutes the first resin layer 21 described above. That is, the second resin has a carbon residue rate higher than that of the first resin when the firing treatment is performed.

  The residual carbon ratio of the second resin measured according to JIS K6910 is preferably 30% by mass or more, and more preferably 35% by mass or more and 95% by mass or less. Thereby, volume expansion is suppressed more effectively and particularly excellent cycle characteristics are obtained.

  As the second resin, for example, various thermosetting resins and various thermoplastic resins can be used, and thermosetting resins are preferable. By using the thermosetting resin, the stability of the shape of the negative electrode precursor in the sintering process described in detail later can be made particularly excellent, and the negative electrode material produced using the negative electrode precursor Can be controlled more suitably.

  The thermosetting resin is not particularly limited, and examples thereof include phenolic resins such as novolac type phenolic resin and resol type phenolic resin, epoxy resins such as bisphenol type epoxy resin and novolac type epoxy resin, melamine resin, urea resin, and aniline resin. , Cyanate resin, furan resin, ketone resin, unsaturated polyester resin, urethane resin and the like. In addition, modified products obtained by modifying these with various components can also be used.

  The thermoplastic resin is not particularly limited, and examples thereof include polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate. , Polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, polyphthalamide and the like.

  Among these, a phenol resin is particularly preferable. Thereby, volume expansion is suppressed more effectively and particularly excellent cycle characteristics are obtained.

  The second resin may contain a nitrogen-containing resin as a main component resin. By carbonizing such a resin, a carbon material layer composed of hard carbon containing nitrogen can be obtained. When nitrogen is contained in the hard carbon constituting the carbon material layer, suitable electrical characteristics can be imparted to the carbon material layer due to the electronegativity of nitrogen. Thereby, occlusion and discharge | release of lithium ion can be accelerated | stimulated and a high charging / discharging characteristic can be provided.

Here, the following can be illustrated as nitrogen-containing resin.
That is, examples of thermosetting resins as nitrogen-containing resins include melamine resins, urea resins, aniline resins, cyanate resins, urethane resins, phenol resins modified with nitrogen-containing components such as amines, and epoxy resins. Examples of the thermoplastic resin as the nitrogen-containing resin include polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide, polyetherimide, polyamideimide, polyimide, polyphthalamide, and the like. Is mentioned.

When the content of the active material particles 1 in the negative electrode precursor 10 is X ₀ [% by mass] and the content of the second resin in the negative electrode precursor 10 is X ₂ [% by mass], 0.01 It is preferable that the relationship of ≦ X ₀ / X ₂ ≦ 10 is satisfied, and it is more preferable that the relationship of 0.25 ≦ X ₀ / X ₂ ≦ 4 is satisfied. By satisfying such a relationship, a high charge / discharge capacity and excellent cycle performance can be achieved at a higher level.

  Further, the second resin layer 22 may contain the second resin as a main component and also contain a curing agent, an additive, and the like.

  The curing agent is not particularly limited. For example, in the case of a novolak type phenol resin, hexamethylenetetramine, resol type phenol resin, polyacetal, paraform, and the like can be used. In the case of epoxy resins, known as epoxy resins such as polyamine compounds such as aliphatic polyamines and aromatic polyamines, acid anhydrides, imidazole compounds, dicyandiamide, novolac-type phenol resins, bisphenol-type phenol resins, and resol-type phenol resins. Can be used.

  Further, the additive contained in the second resin layer is not particularly limited, for example, metal, pigment, lubricant, antistatic agent, antioxidant, organic acid, inorganic acid, nitrogen-containing compound, oxygen-containing compound, An aromatic compound, a nonferrous metal element, etc. can be mentioned.

  The thickness of the second resin layer 22 is preferably 1 nm or more and 100 μm or less, and more preferably 1 nm or more and 1 μm or less. Thereby, high charge / discharge capacity and excellent cycleability can be achieved at a higher level.

  As shown in the figure, when the negative electrode precursor is in the form of particles, the average particle diameter of the negative electrode precursor 10 is preferably 100 nm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. . When the average particle size of the negative electrode precursor 10 is a value within the above range, high charge / discharge capacity and excellent cycle performance can be achieved at a higher level.

<< Method for Producing Negative Electrode Precursor, Method for Producing Negative Electrode Material >>
Next, the manufacturing method of the precursor for negative electrodes of this invention and the manufacturing method of the material for negative electrodes are demonstrated.
FIG. 2 is a schematic view schematically showing an example of the method for producing a negative electrode material of the present invention.

  The method for producing a negative electrode precursor of the present invention includes a first coating step (1a) in which the surface of an active material particle is coated with a first resin layer composed of a first resin, and the first resin. And a second coating step (1b) for coating the surface of the layer with a second resin layer composed of a second resin, and the method for producing a negative electrode material of the present invention further comprises a negative electrode A firing step (1c) for firing the precursor for use. Thereby, while being excellent in cycling property, the precursor for negative electrodes and the material for negative electrodes which can be used suitably for manufacture of the lithium ion secondary battery which is high capacity | capacitance and is excellent also in charging / discharging efficiency can be manufactured efficiently.

[First coating step]
As shown in FIG. 2, in the first coating step, the surface of the active material particles 1 is coated with a first resin layer 21 made of a first resin (1a).

  In forming the first resin layer 21, a composition (resin composition) composed only of the first resin may be used, or a composition (resin containing other components in addition to the first resin). Composition) may be used. For example, the formation of the first resin layer 21 includes the first resin and a liquid medium (a liquid that functions as a solvent and / or a dispersion medium) in which the first resin is dissolved and / or dispersed. May be. Thereby, the 1st resin layer 21 can be formed in the surface of the active material particle 1 easily and reliably. Moreover, the thickness of the 1st resin layer 21 can be controlled easily and reliably by adjusting the dilution rate by a liquid medium.

  Examples of the liquid medium include water, ketones such as toluene, acetone and methyl ethyl ketone, ethers such as diethyl ether and ethylene glycol monomethyl ether, alcohols such as methanol, ethanol and propanol, amides such as dimethylformamide and the like. Can be used.

  This step can be performed, for example, by mixing and stirring the active material particles 1 and a composition (resin composition) containing the first resin. When performing melt mixing, for example, a kneading apparatus such as a kneading roll, a single screw or a twin screw kneader can be used. Moreover, when performing melt | dissolution mixing, mixing apparatuses, such as a Henschel mixer and a disperser, can be used, for example. The resin composition thus obtained may be one obtained by physically mixing a plurality of types of components, or is applied during mixing (stirring, kneading, etc.) during preparation of the resin composition. A part of the material may be chemically reacted with mechanical energy and thermal energy converted from the mechanical energy. Specifically, a mechanochemical reaction using mechanical energy or a chemical reaction using thermal energy may be performed.

[Second coating step]
As shown in FIG. 2, in the second covering step, the surface of the first resin layer 21 is covered with a second resin layer 22 made of the second resin (1b). Thereby, the precursor 10 for negative electrodes is obtained.

  In forming the second resin layer 22, a composition (resin composition) composed only of the second resin may be used, or a composition (resin) containing other components in addition to the second resin. Composition) may be used. For example, the formation of the second resin layer 22 includes a second resin and a liquid medium (a liquid that functions as a solvent and / or a dispersion medium) in which the second resin is dissolved and / or dispersed. May be. Thereby, the second resin layer 22 can be easily and reliably formed on the surface of the first resin layer 21. Further, the thickness of the second resin layer 22 can be easily and reliably controlled by adjusting the dilution ratio with the liquid medium.

  Examples of the liquid medium include water, ketones such as toluene, acetone and methyl ethyl ketone, ethers such as diethyl ether and ethylene glycol monomethyl ether, alcohols such as methanol, ethanol and propanol, amides such as dimethylformamide and the like. Can be used.

  This step can be performed, for example, by mixing and stirring the active material particles 1 provided with the first resin layer 21 and the composition (resin composition) containing the second resin. When performing melt mixing, for example, a kneading apparatus such as a kneading roll, a single screw or a twin screw kneader can be used. Moreover, when performing melt | dissolution mixing, mixing apparatuses, such as a Henschel mixer and a disperser, can be used, for example. The resin composition thus obtained may be one obtained by physically mixing a plurality of types of components, or is applied during mixing (stirring, kneading, etc.) during preparation of the resin composition. A part of the material may be chemically reacted with mechanical energy and thermal energy converted from the mechanical energy. Specifically, a mechanochemical reaction using mechanical energy or a chemical reaction using thermal energy may be performed.

[Baking process]
In this step, the carbon material layer 3 is formed by firing (1c). That is, the carbon material layer 3 is formed by carbonizing the layers (the first resin layer 21 and the second resin layer 22) made of a material containing resin. Thereby, the negative electrode material 100 is obtained. The negative electrode material 100 is usually used as an electrode (negative electrode) of a lithium ion secondary battery by mixing and molding with other components.

  Here, the residual carbon ratio of the first resin is lower than the residual carbon ratio of the second resin. Therefore, the shrinkage rate when the first resin layer 21 is carbonized is larger than the shrinkage rate when the second resin layer 22 is carbonized, and voids 4 are formed around the active material particles 1. The By forming such a void 4, the void can absorb the expansion / contraction of the active material at the time of charge / discharge of the lithium ion secondary battery finally obtained, and the lithium ion secondary battery The expansion / contraction of the electrode (negative electrode) can be effectively prevented / suppressed. As a result, the cycle performance of the lithium ion secondary battery can be made excellent.

  This step is preferably performed in an inert atmosphere (eg, helium, nitrogen gas, etc.). Thereby, it can prevent reliably that the carbon atom which comprises 1st resin and 2nd resin will be removed as a carbon dioxide etc. more than necessary.

  In this step, it is preferable that the heat treatment at 800 ° C. or higher and 1500 ° C. or lower is performed for 30 minutes or longer and 12 hours or shorter in an inert gas atmosphere (eg, helium, nitrogen gas, etc.). This makes it possible to more reliably form a void having a volume that can sufficiently absorb expansion / contraction of the active material during charging / discharging of the lithium ion secondary battery, and particularly excellent in productivity of the negative electrode material. Can be.

  As described above, the heat treatment temperature in this step is preferably 800 ° C. or higher and 1500 ° C. or lower, more preferably 900 ° C. or higher and 1300 ° C. or lower. Thereby, the effects as described above are more remarkably exhibited.

  In addition, the heat treatment time in this step is preferably 30 minutes to 12 hours, more preferably 30 minutes to 6 hours. Thereby, the effects as described above are more remarkably exhibited.

<Electrode / Lithium ion secondary battery>
Next, the electrode (negative electrode) of the present invention and a lithium ion secondary battery (hereinafter simply referred to as “secondary battery”) including the same will be described.

  The electrode of the present invention is manufactured using the negative electrode precursor of the present invention as described above, and the lithium ion secondary battery of the present invention includes the electrode of the present invention. Thereby, while being excellent in cycling property, the lithium ion secondary battery which is excellent also in charge / discharge efficiency with high capacity | capacitance is obtained.

Hereinafter, preferred embodiments of the electrode (negative electrode) and the lithium ion secondary battery of the present invention will be described.
FIG. 3 is a schematic diagram showing the configuration of the embodiment of the lithium ion secondary battery.

  As illustrated in FIG. 2, the secondary battery 1000 includes a negative electrode 130, a positive electrode 210, an electrolytic solution 160, and a separator 180.

As shown in FIG. 2, the negative electrode 130 includes a negative electrode material 120 and a negative electrode current collector 140.
The negative electrode current collector 140 is made of, for example, copper foil or nickel foil.

The negative electrode material 120 is manufactured using the negative electrode precursor of the present invention as described above.
The negative electrode 130 can be manufactured as follows, for example.

  The negative electrode material according to the present invention (obtained by firing the negative electrode precursor of the present invention) is converted into an organic polymer binder (fluorine polymer containing polyethylene, polypropylene, etc., butyl rubber, butadiene rubber, etc.) And the like, etc.), a viscosity adjusting solvent (N-methyl-2-pyrrolidone, dimethylformamide, etc.), etc., mixed and kneaded to form a paste-like mixture (kneaded product) by compression molding, roll molding, etc. The negative electrode material 120 can be obtained by molding into a shape or a pellet. And the negative electrode 130 can be obtained by laminating | stacking the negative electrode material 120 and the negative electrode collector 140 which were obtained in this way.

  Further, the negative electrode material according to the present invention comprises an organic polymer binder (fluorine polymer including polyethylene, polypropylene, etc., rubbery polymer such as butyl rubber, butadiene rubber, etc.), a viscosity adjusting solvent (N-methyl). 2-pyrrolidone, dimethylformamide, etc.) and the like are mixed and kneaded to form a slurry-like mixture (kneaded material) as the negative electrode material 120, and this is applied to the negative electrode current collector 140 and molded to form the negative electrode 130 can also be manufactured.

  The mixing amount of the organic polymer binder and the organic polymer binder with respect to 100 parts by weight of the negative electrode material according to the present invention is not particularly limited, and can be, for example, 1 part by weight or more and 30 parts by weight or less. .

  The electrolyte solution 160 fills between the positive electrode 210 and the negative electrode 130, and is a layer in which lithium ions move by charge / discharge.

  As the electrolytic solution 160, a solution obtained by dissolving a lithium salt serving as an electrolyte in a non-aqueous solvent is used.

  As this non-aqueous solvent, it is possible to use a mixture of cyclic esters such as propylene carbonate, ethylene carbonate and γ-butyrolactone, chain esters such as dimethyl carbonate and diethyl carbonate, and chain ethers such as dimethoxyethane. it can.

As the electrolyte, lithium metal salts such as LiClO ₄ and LiPF ₆ , tetraalkylammonium salts, and the like can be used. Further, the above salts can be mixed with polyethylene oxide, polyacrylonitrile, etc. and used as a solid electrolyte.

  The separator 180 is not particularly limited, and for example, a porous film such as polyethylene or polypropylene, a nonwoven fabric, or the like can be used.

As shown in FIG. 2, the positive electrode 210 includes a positive electrode material 200 and a positive electrode current collector 220.
The positive electrode material 200 is not particularly limited. For example, a composite oxide such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), polyaniline, A conductive polymer such as polypyrrole can be used.

As the positive electrode current collector 220, for example, an aluminum foil can be used.
And the positive electrode 210 in this embodiment can be manufactured with the manufacturing method of the known positive electrode.

  As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.

  For example, in the above-described embodiment, the case where the negative electrode precursor has a particulate shape has been mainly described. However, the negative electrode precursor of the present invention may have a shape other than the particulate shape.

  In the above-described embodiment, the configuration in which the first resin layer covers one active material particle is representatively described. For example, as illustrated in FIG. 4, a plurality of first resin layers are provided. The structure which coat | covers this active material particle may be sufficient. Similarly, in the present invention, the second coating layer may be configured to cover a plurality of composites (particles) in which the active material particles are coated with the first resin layer.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to this. In the examples and comparative examples, “part” indicates “part by weight” and “%” indicates “% by weight”.

[1] Measuring Method First, measuring methods in the following examples and comparative examples will be described.

1. Particle size distribution Using a laser diffraction particle size distribution measuring instrument LA-920 manufactured by Horiba, Ltd., the particle size distribution of the active material particles and the particle size distribution of the negative electrode precursor were measured by a laser explanation method. From the measurement results, the particle size (D50, average particle size) at the time of 50% accumulation from the small diameter side in the volume-based cumulative distribution was determined for the active material particles and the negative electrode precursor.

2. Residual charcoal rate About the 1st resin and 2nd resin which were used for manufacture of the precursor for negative electrodes of each example and each comparative example, the residual carbon rate was calculated | required by the measurement according to JISK6910, respectively.

3. Charging capacity, discharging capacity, charging / discharging efficiency, etc. (1) Manufacture of bipolar coin cell for secondary battery evaluation Polyvinylidene fluoride as binder for 100 parts of negative electrode material obtained in each example and each comparative example An appropriate amount of N-methyl-2-pyrrolidone as a diluent solvent was added and mixed to prepare a slurry-like negative electrode mixture. The prepared negative electrode slurry-like mixture was applied to both sides of 18 μm copper foil, and then vacuum-dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roll press. This was cut out as a circle having a diameter of 16.156 mm to produce a negative electrode.

  The positive electrode was evaluated with a bipolar coin cell using lithium metal. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of lithium perchlorate in a mixed solution of ethylene carbonate and diethyl carbonate having a volume ratio of 1: 1 was used.

(2) Evaluation of Charging Capacity and Discharging Capacity The charging condition was that charging was stopped at a constant current of 25 mA / g until it reached 1 mV, and then the charging was terminated when the current attenuated to 1.25 mA / g with 1 mV holding. The cut-off potential under discharge conditions was 1.5V.

The charge capacity was evaluated according to the following criteria.
A: Charge capacity is 1200 mAh / g or more.
○: The charge capacity is 1000 mAh / g or more and less than 1200 mAh / g.
X: Charging capacity is less than 1000 mAh / g.

The discharge capacity was evaluated according to the following criteria.
A: Discharge capacity is 1200 mAh / g or more.
A: The discharge capacity is 1000 mAh / g or more and less than 1200 mAh / g.
X: Discharge capacity is less than 1000 mAh / g.

(3) Evaluation of charge / discharge efficiency Based on the value obtained in the above (2), the charge / discharge efficiency was calculated by the following formula.

Charge / discharge efficiency (%) = [discharge capacity / charge capacity] × 100
The charge / discharge efficiency was evaluated according to the following criteria.

A: Initial charge / discharge efficiency is 80% or more.
○: Initial charge / discharge efficiency is 75% or more and less than 80%.
X: Initial charge / discharge efficiency is less than 75%.

(4) Evaluation of 60 cycle capacity retention ratio The ratio of the charge / discharge capacity obtained in (2) above and the discharge capacity after repeating charge / discharge 60 times was calculated by the following formula.

  60 cycle capacity retention rate (%) = [60th cycle discharge capacity / 1st cycle charge capacity] × 100

The second and subsequent charging / discharging conditions were defined as charging termination when the current was attenuated to 12.5 mA / g with 1 mV holding after charging at a constant current of 250 mA / g until reaching 1 mV. The cut-off potential under discharge conditions was 1.5V.
The 60 cycle capacity maintenance rate was evaluated according to the following criteria.

A: The 60-cycle capacity retention rate is 90% or more.
A: 60 cycle capacity maintenance rate is 80% or more and less than 90%.
(Triangle | delta): 60 cycle capacity maintenance rate is 60% or more and less than 80%.
X: 60 cycle capacity maintenance rate is less than 60%.

[2] Production of negative electrode material (Example 1)
First, Si (average particle diameter: 1 μm) as active material particles was prepared.

  Next, using a theta composer (manufactured by Tokuju Kogakusha Co., Ltd.), the active material particles and an epoxy resin as a first resin (YX4000, biphenyl type epoxy resin, melting point 105 ° C., epoxy equivalent 180-192 g / eq, (Mitsubishi Chemical Corporation) was mixed and kneaded. Thereby, particles (composite particles) in which the surfaces of the active material particles were coated with the first resin layer were obtained (first coating step).

  Next, the composite particles and a phenol resin (PR-217, manufactured by Sumitomo Bakelite Co., Ltd.) as the second resin were mixed and kneaded using theta composer (manufactured by Tokuju Kogakusha Co., Ltd.). As a result, a particulate negative electrode precursor in which the surface of the first resin layer was coated with the second resin was obtained (second coating step).

  Next, the negative electrode precursor obtained as described above was subjected to heat treatment at 1200 ° C. for 5 hours in a nitrogen gas atmosphere (firing step). Thereby, a large number of particulate negative electrode materials were obtained. The particulate negative electrode material thus obtained has active material particles and a carbon material layer as observed with a transmission electron microscope (TEM), and is between the active material particles and the carbon material layer. In addition, it was confirmed to have voids.

(Examples 2 to 7)
A negative electrode was produced in the same manner as in Example 1 except that the type of active material particles, the first resin, and the second resin were changed, and the constitution of the negative electrode precursor was changed as shown in Table 1. Material was obtained. The particulate negative electrode materials obtained in Examples 1 to 7 each have an active material particle and a carbon material layer as observed by a transmission electron microscope (TEM). It was confirmed that there was a gap between the material layer.

(Comparative Example 1)
A negative electrode material was obtained in the same manner as in Example 1 except that the first coating step was omitted. The negative electrode material thus obtained has active material particles and a carbon material layer as observed with a transmission electron microscope (TEM), but there are voids between the active material particles and the carbon material layer. It was confirmed that it does not have.

(Comparative Example 2)
A negative electrode material was obtained in the same manner as in Example 1 except that the second coating step was omitted. The negative electrode material thus obtained has active material particles and a carbon material layer as observed with a transmission electron microscope (TEM), but there are voids between the active material particles and the carbon material layer. It was confirmed that it does not have.

(Comparative Example 3)
A phenol resin (PR-217, manufactured by Sumitomo Bakelite Co., Ltd.) is used as a resin material in the first coating step, and an epoxy resin (YX4000, biphenyl type epoxy resin, melting point 105 ° C., epoxy resin as a resin material in the second coating step. A negative electrode material was obtained in the same manner as in Example 1 except that an equivalent weight of 180 to 192 g / eq (manufactured by Mitsubishi Chemical Corporation) was used. The negative electrode material thus obtained has active material particles and a carbon material layer as observed with a transmission electron microscope (TEM), but there are voids between the active material particles and the carbon material layer. It was confirmed that it does not have.

[3] Results Table 1 shows the configurations of the negative electrode precursor and the negative electrode material of each of the above Examples and Comparative Examples.

  In addition, Table 2 shows the charge capacity, discharge capacity, charge / discharge efficiency, etc. when the electrode manufactured using the negative electrode material obtained in each Example and each Comparative Example was used as the negative electrode.

  As is apparent from the table, excellent results were obtained with the present invention, whereas satisfactory results were not obtained with the comparative examples.

  In addition, the negative electrode precursor and the negative electrode are the same as described above except that the heat treatment temperature in the firing step is changed in the range of 800 to 1500 ° C. and the heat treatment time is changed in the range of 30 minutes to 12 hours. When materials were manufactured and evaluated in the same manner as described above, results similar to the above were obtained.

DESCRIPTION OF SYMBOLS 1 Active material particle 21 1st resin layer 22 2nd resin layer 3 Carbon material layer 4 Cavity 10 Negative electrode precursor 100 Negative electrode material 120 Negative electrode material 140 Negative electrode current collector 130 Negative electrode 200 Positive electrode material 220 Positive electrode current collector 210 Positive electrode 160 Electrolytic solution 180 Separator 1000 Secondary battery

Claims (14)

A negative electrode precursor used for manufacturing a negative electrode of a lithium ion secondary battery,
Active material particles,
A first resin layer covering the active material particles;
A second resin layer covering the first resin layer,
The first resin constituting the first resin layer is characterized in that the residual carbon ratio when subjected to the firing treatment is lower than that of the second resin constituting the second resin layer. A negative electrode precursor.   The negative electrode precursor according to claim 1, wherein the active material particles are composed of Si or an oxide thereof.   The precursor for a negative electrode according to claim 1 or 2, wherein the first resin is a resin having a residual carbon ratio measured in accordance with JIS K6910 of 20% by mass or less.   The precursor for a negative electrode according to any one of claims 1 to 3, wherein the second resin is a resin having a residual carbon ratio measured in accordance with JIS K6910 of 30% by mass or more.   The negative electrode precursor according to claim 1, wherein an average thickness of the first resin layer is 1 nm or more and 10 μm or less.   The negative electrode precursor according to claim 1, wherein an average particle diameter of the active material particles is 1 nm or more and 3 μm or less. When the content of the active material particles in the negative electrode precursor is X ₀ [mass%] and the content of the first resin in the negative electrode precursor is X ₁ [mass%], 0.05 ≦ The negative electrode precursor according to claim 1, wherein the negative electrode precursor satisfies the relationship of X ₀ / X ₁ ≦ 500. When the content of the active material particles in the negative electrode precursor is X ₀ [% by mass] and the content of the second resin in the negative electrode precursor is X ₂ [% by mass], 0.01 ≦ The negative electrode precursor according to claim 1, wherein the negative electrode precursor satisfies the relationship of X ₀ / X ₂ ≦ 10. The negative electrode precursor is in the form of particles,
The negative electrode precursor according to claim 1, wherein the negative electrode is produced using a plurality of negative electrode precursors. A method for producing a negative electrode precursor used for producing a negative electrode of a lithium ion secondary battery,
A first coating step of coating the surface of the active material particles with a first resin layer composed of a first resin;
A second coating step of coating the surface of the first resin layer with a second resin layer composed of a second resin;
The method for producing a precursor for a negative electrode, wherein the first resin has a carbon residue rate lower than that of the second resin when subjected to a firing treatment. A method for producing a negative electrode material used for producing a negative electrode of a lithium ion secondary battery,
A first coating step of coating the surface of the active material particles with a first resin layer composed of a first resin;
A second coating step of coating the surface of the first resin layer with a second resin layer composed of a second resin to obtain a negative electrode precursor;
A firing step of firing the negative electrode precursor,
The method for producing a negative electrode material, wherein the first resin has a carbon residue rate lower than that of the second resin when the firing step is performed.   12. The method for producing a negative electrode material according to claim 11, wherein in the firing step, heat treatment at 800 ° C. to 1500 ° C. is performed in an inert gas atmosphere for 30 minutes to 12 hours.   An electrode manufactured using the negative electrode precursor according to claim 1.   A lithium ion secondary battery comprising the electrode according to claim 13.

Images