JP5267976B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode for a lithium ion secondary battery for obtaining good characteristics for both initial discharge capacity and cycle characteristics after 100 cycles. <P>SOLUTION: Active material particles 4 of the anode for a lithium ion secondary battery are to be composed of at least two kinds of composite particles 4a, 4b composed of silicon 1, a silicon-intermetallic compound 2 and carbon 3, with different particle sizes from each other. Of the composite particles 4a, 4b, it is so constituted that a particle diameter D<SB>95</SB>of the first composite particle 4a having a small particle size is 2 to 30 &mu;m, and a particle diameter D<SB>5</SB>of the second composite particle 4b having a large particle size is larger than the particle diameter D<SB>95</SB>of the first composite particle, and carbon contents of the composite particles 4a, 4b having two kinds of particle sizes are to be different from each other. Further, the second composite particles 4b with large particle sizes occupy 50 parts to 80 parts by weight in ratio. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery having composite particles containing a silicon simple substance, a silicon-intermetallic compound, and carbon as a negative electrode active material, and a lithium ion secondary battery using the same.

  With the widespread use of mobile devices such as mobile phones and laptop computers, the role of secondary batteries as power sources is gaining importance. These secondary batteries are required to be small, light and have a high capacity, and to be less susceptible to deterioration of charge / discharge capacity even when charge / discharge is repeated. Currently, many lithium ion secondary batteries are used as secondary batteries satisfying such characteristics.

  As a negative electrode active material constituting a negative electrode of a lithium ion secondary battery, a structure mainly composed of a carbon material such as graphite or hard carbon (non-graphitizable carbon) has been used so far. When a negative electrode active material mainly composed of a carbon material is used, there is a feature that the discharge capacity after repetition of the charge / discharge cycle of the battery can be increased. However, lithium-ion secondary batteries using carbon materials as the negative electrode active material have already achieved improvements in charge / discharge capacity up to near the theoretical limit. Can't expect. On the other hand, since there is a strong demand for further improvement of the charge / discharge capacity of the lithium ion secondary battery, a negative electrode active material capable of realizing a higher capacity, that is, a higher energy density than that of the carbon material has been studied.

  As a negative electrode active material for a lithium ion secondary battery, the use of metallic lithium is being studied because of its high energy density and light weight. However, when metallic lithium is used, it is known that dendrites (dendritic crystals) may be deposited on the surface of the metallic lithium region during charging as the charge / discharge cycle is repeated. When dendrite is deposited, there is a problem that an internal short circuit may occur through the separator constituting the battery, which shortens the battery life. For this reason, it has been difficult to simply use metallic lithium as the negative electrode active material.

Further, as a method for increasing the energy density that can be stored in the lithium ion secondary battery, the composition formula is Li _x A (x is the Li content, A is the metal element) by reacting with lithium (Li) ions in the electrolytic solution by charging. The so-called Li storage material that forms a lithium alloy is used as a negative electrode active material. When such a negative electrode active material is used, it is expected that the capacity of the battery is increased because the amount of occlusion and release of lithium ions per unit volume is larger than that of a carbon material alone. Non-Patent Document 1 describes silicon as a negative electrode active material (non-oxidized, simple substance of silicon only. In the following description, when simply referred to as silicon, it means silicon as a simple substance and does not contain silicon oxide. Examples using Li storage materials containing

  In the negative electrode active material containing silicon described in Non-Patent Document 1, the amount of occlusion and release of lithium ions per unit volume is relatively large, and thus the capacity of the lithium ion secondary battery can be increased. However, when silicon is used as the negative electrode active material in this way, generally, when lithium ions are occluded and released, the negative electrode active material itself repeatedly expands and contracts, so that the pulverization of the negative electrode material may proceed. Is known. Due to the pulverization of the negative electrode material, there arises a problem that the irreversible capacity is increased due to charge and discharge, thereby causing a problem that cycle characteristics as a secondary battery are lowered. Here, the cycle characteristic is a rate at which the chargeable / dischargeable capacity is reduced with respect to the initial charge / discharge capacity when the secondary battery is repeatedly charged / discharged a certain number of times. When the rate of decrease in the chargeable / dischargeable capacity is large after a certain number of charge / discharge cycles, the cycle characteristics are referred to as low.

  Thus, as a countermeasure against the low cycle characteristics of the lithium ion secondary battery, Patent Document 1 proposes a method using a negative electrode active material containing silicon oxide instead of silicon as the negative electrode material. In the method in Patent Document 1, the ratio of volume expansion / contraction per unit weight of the negative electrode active material can be reduced by using silicon oxide as the negative electrode active material. As a result, it is confirmed that the cycle characteristics of the lithium ion secondary battery are improved because the pulverization of the negative electrode material can be prevented. On the other hand, in this case, since the negative electrode active material contains an oxide, the conductivity of the negative electrode is reduced, and therefore, the irreversible capacity is increased and the charge / discharge efficiency (the ratio of the discharge capacity to the charge capacity) is reduced. Had a problem.

  Further, in Patent Document 2, in order to improve the conductivity of the negative electrode when silicon oxide is used as the negative electrode active material and to improve the initial charge and discharge efficiency, in addition to silicon oxide, It has also been proposed to add iron and titanium. However, in this case, although the electrical conductivity of the negative electrode is relatively high at the beginning, simply adding these metals gradually reduces the electrical conductivity of the negative electrode containing the negative electrode active material as the charge and discharge are repeated. Had the problem. This is because the additive metal is not so high in corrosion resistance and oxidation resistance to the electrolytic solution.

  As a means for solving these problems, Patent Document 3 discloses a method in which three materials of silicon, silicon-intermetallic compound (silicon-metal alloy), and carbon (graphite in Patent Document 3) are used as the negative electrode active material. Has been. In Patent Document 3, a mixed material composed of silicon and carbon is first pulverized into a composite material, and a silicon-metal alloy such as a silicon-nickel alloy is further added to form composite particles. By combining the three, the negative electrode active material in Patent Document 3 imparts a high energy density by further adding silicon while maintaining the capacity maintenance characteristics of carbon. On top of that, by adding a silicon-metal alloy that is superior in electrical conductivity compared to silicon, a decrease in electrical conductivity due to the resistance generated between the interfaces between the different material layers ( (Increase in internal resistance) is suppressed.

  Here, the negative electrode active material composed of particles composed of silicon, a silicon-metal alloy, and carbon is charged and discharged repeatedly by a battery using the material, so that silicon absorbs and discharges lithium. Expansion and contraction are repeated, whereby the negative electrode as a whole expands gradually. It is known that due to the expansion and contraction, the particles constituting the negative electrode active material are separated from each other, so that contact between the particles is lost, and contact between the particles of the negative electrode active material and the current collector is lost. ing. Here, when the battery is repeatedly charged and discharged, the inside of the negative electrode, and consequently the internal resistance of the battery, increases, and the discharge capacity of the battery also decreases. The deterioration of these characteristics appears as low cycle characteristics of the battery.

  In general, when only silicon is used as the negative electrode active material of the battery, 4.4 Li (lithium) atoms are occluded per Si (silicon) atom during charging, and the expansion coefficient due to volume expansion at that time is It is said that the maximum is 300%. When particles consisting of carbon, silicon, and silicon-metal alloy are used as the negative electrode active material, the proportion of silicon is relatively low, and the electrical conductivity of the negative electrode when the carbon and silicon-metal alloy are expanded Acts to maintain. However, the effect is not always sufficient. Therefore, it is possible to suppress the expansion of Li atoms during occlusion, and accordingly, development of particles of a negative electrode active material capable of suppressing the deterioration of the cycle characteristics of the battery has been demanded. .

  Of course, if the ratio of the silicon content of the battery is greatly reduced, it is possible to suppress a decrease in cycle characteristics. However, in this case, the charge / discharge capacity of the battery is reduced, which is not realistic. The necessary conditions for a lithium ion secondary battery are that the charge / discharge capacity of the battery per unit volume (first time discharge capacity if focusing on the electric energy that can be taken out from the battery) is large and good cycle characteristics. It is to make it compatible.

  In order to suppress expansion during lithium occlusion in the particles of the negative electrode active material, in Patent Document 3, heat treatment is performed on the composite particles including the three of silicon, silicon-metal alloy, and graphite at the time of production. Thereby, the carbon content inside is deposited on the surface of the composite particle. The precipitated carbon component forms an amorphous carbon layer (carbon layer) on the outermost periphery of the composite particle. By the heat treatment, the composite particles become a composite particle having a three-layer structure having a silicon and graphite layer inside, a silicon-metal alloy layer on the outside, and a carbon layer on the outermost layer. In a battery using a negative electrode active material composed of these particles, the outermost carbon layer plays a role of tightening the composite particles from the outside, and this occurs when the negative electrode active material of the battery occludes Li atoms. Expansion of silicon inside can be suppressed. For the above reason, in the lithium ion secondary battery having the negative electrode active material described in Patent Document 3, it is possible to improve the cycle characteristics.

Japanese Patent No. 2999741 Japanese Patent No. 3010226 JP 2007-87956 A Hong Li, Xuejie Huang, Liquan Chen, Zhengang Wu, Yong Liang, “A High Capacity Nano-Si Composite Anode Material for Lithium Rechargeable Batteries” Electrochemical and Solid-State Letters, Volume 2, Issue 11, pp.547-549, ( (November 1999)

  As described in Patent Document 3, reduction in internal resistance and cycle characteristics of the lithium ion secondary battery is performed by subjecting the composite particles composed of silicon, silicon-intermetallic compound, and carbon to heat treatment at a constant temperature and time. It has a certain effect on improvement. According to Patent Document 3, the heat treatment performed on the composite particles is performed in an argon (Ar) atmosphere or the like, preferably at a temperature of 800 to 1000 ° C. for about 1 to 4 hours. However, the existence of such a long temperature raising step increases the processing time required for the production process of the composite particles, which may lead to an increase in production cost. In addition, in order to deposit a carbon layer having an appropriate thickness on the surface of the composite particle, it is required to control the size and shape of the composite particle fairly strictly. Specifically, it may be required to perform management that requires classifying the composite particles before heat treatment, performing heat treatment while finely changing the conditions for each particle size, and mixing again after heat treatment. Such complicated handling also leads to an increase in the manufacturing cost of the composite particles, and becomes a big problem particularly when the composite particles are industrially mass-produced.

  Further, in the method of Patent Document 3, a carbon layer is coated around the composite particles. However, it is difficult to uniformly coat the carbon layer because the shape of the composite particles is non-uniform. Need to thicken the carbon layer. However, when this carbon layer is thick, there is a possibility that the action of silicon to occlude Li atoms during battery charging may be hindered. In addition, the presence of a thick carbon layer inevitably reduces the silicon content in the composite particles. These are considered to appear as a decrease in the charge / discharge capacity of the battery, which is supported by the fact that the values of the initial discharge capacity are generally lower than those of the comparative examples in each example of Patent Document 3. To alleviate this decrease in charge / discharge capacity, the thickness of the outer carbon layer of the composite particle can be reduced, but in that case, the effect of tightening the composite particle from the outside by the carbon layer will be reduced. Thus, the effect intended in Patent Document 3 for improving the cycle characteristics of the battery cannot be obtained.

  Although the present invention adopts a composite particle configuration consisting of silicon, silicon-intermetallic compound, and carbon as a negative electrode active material of a lithium ion secondary battery, it does not carry out a long-time heat treatment on the composite particle. In order to solve the problem. That is, the present invention provides a negative electrode for a lithium ion secondary battery in which the charge / discharge capacity of the battery is large and a good cycle characteristic is obtained by a method different from Patent Document 3, and a lithium ion secondary battery using the same A battery is proposed.

  In the present invention, the negative electrode active material is composed of composite particles having conductivity, consisting of silicon, a silicon-intermetallic compound, and carbon. In this case, two or more types having different particle sizes are used. Composite particles belonging to the particle group are prepared and mixed at a predetermined ratio to obtain a negative electrode active material. Here, by using composite particles composed of a plurality of particle groups having different particle sizes, the following effects can be obtained in the negative electrode active material. That is, by mixing and using two or more kinds of particles having a particle size, particles having a small particle size enter the space between the particles having a large particle size, and the particles having each particle size are densely packed in the negative electrode active material. Since it fills, the density of an electrode improves and the contact location between each particle | grains which comprise a negative electrode active material increases. In addition, since the increase in the contact location between this particle | grain brings about the improvement of the electrical conductivity in a negative electrode, the secondary effect that the internal resistance in a battery falls is also acquired.

  Here, when silicon absorbs and releases Li atoms for charging and discharging of the battery, there are many contact points between the particles. This brings about the effect that the continuous connection is maintained. Moreover, when the large particle | grains occlude Li atom inside the negative electrode active material and the volume expand | swells, the space | gap between them also expands simultaneously. At that time, the small particles with a small particle size filling the voids may be densely packed. When the volume expansion is performed, the small particle size slightly changes the relative position of the particles at the contact site. It is thought that following the volume expansion by causing a movement similar to plastic deformation as a whole, such as changing to. Furthermore, it has been found that the role of the carbon region contained in the small particle size is large in this deformation action, and as a result, the carbon region is considered to suppress the volume change of the negative electrode active material to some extent. . In addition, the carbon region changes its shape following the deformation of the particles accompanying the volume change of the negative electrode active material, thereby contributing to the maintenance of electrical and physical contact between the particles when the particles are deformed. It is thought that there is.

  Therefore, by mixing and using two or more kinds of particles having different particle diameters, the particles having small particle diameters are displaced or deformed during the expansion and contraction of Li atoms by occlusion and release by silicon. While maintaining mutual contact with large particles, it is possible to flexibly respond to changes in the volume. In addition, the presence of particles having a small particle size also acts to absorb the volume expansion of the negative electrode active material to some extent. As a result, even if volume expansion occurs in the negative electrode active material, the contact between the large particle size and the small particle size continues to be maintained. In addition, even when Li atoms are released by the discharge of the battery and the volume of the negative electrode active material contracts conversely, the above-described slippage and change in position due to the small particle size occur in the same manner, and the negative electrode active material The internal structure only returns to its original state. Therefore, the expansion and contraction of the negative electrode active material are suppressed and smoothly proceeded by these actions, and the occurrence of pulverization is also suppressed. Therefore, even if the charge and discharge of the lithium ion secondary battery is repeated, good cycle characteristics Can be obtained.

  By the way, in the lithium ion secondary battery of the present invention, it is mainly particles having a large particle size that are responsible for insertion and extraction of Li atoms by silicon. On the other hand, particles having a small particle size have a relatively small contribution to the insertion and extraction of Li atoms, and play a role in the role of electrical conduction to electrically connect particles having a large particle size. Here, since it is mainly carbon that contributes to electrical conduction in the negative electrode active material, in the lithium ion secondary battery of the present invention, the carbon content in the particles having a small particle size is increased, and Conversely, the carbon content in the large-diameter particles is decreased, and the silicon content is increased accordingly. Thereby, the charge / discharge capacity of the battery can be sufficiently increased while maintaining the electrical conductivity in the negative electrode active material. In this case, since the carbon region in the particles having a small particle size increases, the followability to the volume change of the particles having a large particle size at the time of occlusion and release of Li atoms is improved. It is also effective in suppressing pulverization of particles having a large particle diameter when repeated. Therefore, it contributes to the improvement of the cycle characteristics of the lithium ion secondary battery.

  It should be noted that since a large volume change is actually caused during the insertion and extraction of Li atoms, and the pulverization is mainly a large particle size, all the negative electrode active materials of the lithium ion secondary battery are used. If it is composed only of particles having a small particle diameter, it appears that the anode active material can be prevented from being pulverized and the cycle characteristics of the battery can be prevented from deteriorating. However, in this case, it is known that the charge / discharge capacity of the battery is small, and the electrical characteristics required for the lithium ion secondary battery are not satisfied. A silicon-nickel alloy is particularly preferably used as the silicon-intermetallic compound contained in the composite particles.

  That is, the present invention is a negative electrode used in a lithium ion secondary battery having a lithium ion conductive nonaqueous electrolyte, wherein the negative electrode has a current collector and a negative electrode active material, and the negative electrode active material is The composite particle includes any of silicon, silicon-intermetallic compound, and carbon, and the composite particle includes at least a first particle group and a second particle group, and the first particle In the particle size distribution of the composite particles belonging to the group, the remainder belonging to the first particle group excluding the composite particles in the range of 5% by volume from the side where the average particle diameter measured by the laser diffraction / scattering method is large The range of the average particle diameter of the composite particles is 2 μm to 30 μm, and in the particle size distribution of the composite particles belonging to the second particle group, the volume ratio is 95 in terms of the volume ratio from the side where the average particle diameter measured by the method increases. Percent The average particle diameter of the remaining composite particles belonging to the second particle group excluding the surrounding composite particles is larger than the average particle diameter of the remaining composite particles belonging to the first particle group. It is the negative electrode for lithium ion secondary batteries characterized.

  Further, in the present invention, the carbon content in the composite particles belonging to the first particle group is 30 to 80 parts by weight with respect to 100 parts by weight of the composite particles belonging to the first particle group. 2. The lithium ion secondary battery characterized in that the carbon content in the composite particles belonging to 2 particle groups is 5 to 30 parts by weight with respect to 100 parts by weight of the composite particles belonging to the second particle group. It is a negative electrode.

  Further, in the present invention, the total of composite particles belonging to the second particle group among the composite particles is 50 parts by weight to 80 parts by weight with respect to 100 parts by weight of the composite particles. It is a negative electrode for an ion secondary battery.

  Further, according to the present invention, the negative electrode active material includes a mixture of the composite particles and a thermosetting resin, and the composite particles and the current collector are disposed between the composite particles and the thermosetting resin. The negative electrode for a lithium ion secondary battery is characterized by being bound to each other.

  Furthermore, the present invention is the negative electrode for a lithium ion secondary battery, wherein the silicon-intermetallic compound contains at least a silicon-transition metal compound.

  Furthermore, the present invention is the negative electrode for a lithium ion secondary battery, wherein the silicon-transition metal compound contains at least a silicon-nickel compound.

  Furthermore, the present invention is a lithium ion secondary battery comprising the negative electrode.

  In the present invention, as the negative electrode active material of the lithium ion secondary battery, mixed particles of at least two kinds of particle sizes composed of silicon, silicon-intermetallic compound, and carbon and having different particle size distributions are mixed. And use. As a result, the gaps between the large particles are closely packed with the small particles, and the number of contact points between the particles increases, and the mutual contact between the particles is the insertion and extraction of Li atoms. It is maintained even after the volume change accompanying. Further, the configuration of the negative electrode active material suppresses the volume expansion of the negative electrode active material to some extent. For the above reasons, by mixing and using particles having a plurality of particle sizes, the cycle characteristics can be improved without reducing the charge / discharge capacity (or initial discharge capacity) of the lithium ion secondary battery.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of composite particles contained in a negative electrode active material that constitute the negative electrode for a lithium ion secondary battery of the present invention. In FIG. 1, the active material particles 4 of the negative electrode are composed of three types of compositions of fine particles of silicon 1 and silicon-intermetallic compound 2 and carbon 3 filling the periphery of the particles, and each has a particle size. Is an aggregate of composite particles 4a and composite particles 4b having different values. This carbon 3 is graphite or amorphous carbon. The proportion of the carbon content of the composite particle 4a having a relatively small particle size needs to be at least the same as or higher than that of the composite particle 4b having a large particle size.

Silicon 1 which is a granular body of a single silicon contained in the negative electrode active material particles 4 in FIG. 1 occludes or releases Li atoms during charge / discharge of a lithium ion secondary battery. On the other hand, the silicon-intermetallic compound 2 serves to alleviate, although somewhat, the expansion and contraction that occurs when the negative electrode active material is repeatedly charged and discharged, and to ensure conductivity between the particles of silicon 1 that is the active material. There is. Here, the silicon-intermetallic compound 2 is preferably a silicon-transition metal compound such as nickel silicide or cobalt silicide. In general, it is known that transition metal forms metal silicide (M-Si _x , M is a transition metal element, and x is the number of atoms) by an operation such as heating with silicon. This intermetallic compound is often formed of a compound of transition metal 1 atom and silicon 2 atom, such as M-Si ₂ . Among these, a silicon-nickel alloy, which is a compound of silicon and nickel, is particularly suitable, has high conductivity, and has a small amount of expansion / contraction during the insertion and extraction of Li atoms. Have

By the way, even when a transition metal other than nickel is used as the metal silicide, generally good characteristics can be obtained, but in the case of a silicon-iron compound, it is easy to form an alloy containing a large proportion of silicon, such as Fe ₃ Si _7. Therefore, the ratio of the silicon simple substance contained in the negative electrode active material is relatively decreased, and the discharge capacity may be slightly reduced. In addition, the silicon-cobalt compound may cause a reaction in which cobalt elutes in the electrolytic solution, although it is slightly during charging and discharging. In addition, since the silicon-titanium compound has a high affinity with oxygen for titanium, an oxidation reaction is likely to occur. Therefore, the resistance value in the negative electrode is slightly high, which is somewhat disadvantageous in a long-term reliability test such as a cycle test. There is a case.

On the other hand, when a metal material other than a transition metal, such as aluminum or magnesium, is used, metal silicide (M-Si _x ) is not formed between these metals and silicon. However, it exists as a fine granular material in the composite particle as a simple substance. For this reason, as compared with the silicon-transition metal compound, surface oxidation in the granular body and reaction with the electrolyte solution of the battery are very likely to occur, which appears as a significant deterioration in cycle characteristics. Therefore, it is necessary to limit the use of the metal added to silicon to a metal that forms an intermetallic compound with silicon.

  FIG. 2 is a cross-sectional view of a lithium ion secondary battery having a negative electrode according to the present invention. In FIG. 2, the lithium ion secondary battery of the present invention includes a negative electrode current collector 6 such as a copper foil and a negative electrode 7 composed of a negative electrode active material 5 formed on the surface thereof, a positive electrode current collector 9 such as aluminum and the like. And a positive electrode 10 made of a positive electrode active material 8 formed on the surface. The negative electrode active material 5 and the positive electrode active material 8 are disposed to face each other with a separator 11 interposed therebetween. The separator 11 is made of a porous film made of a polyolefin such as polypropylene or polyethylene, or a fluororesin, and is impregnated with a non-aqueous electrolyte solution. A negative electrode lead tab 13 and a positive electrode lead tab 14 are connected to the negative electrode 7 and the positive electrode 10, respectively, for taking out the electrode, and the negative electrode 7, the separator 11 and the positive electrode 10 are sealed with an exterior film 12 such as a laminate film. ing. The tip portions of the negative electrode lead tab 13 and the positive electrode lead tab 14 are drawn to the outside of the exterior film 12, and serve as electrode terminals for the negative electrode and the positive electrode, respectively.

  Generally, the larger the relative weight (weight ratio) of silicon in the negative electrode active material, the larger the capacity of the battery per volume, but when the weight ratio of silicon is large, the expansion of the volume due to repeated charge and discharge accordingly. Shrinkage also increases, and this is a result of a decrease in capacity due to volume change, that is, low cycle characteristics of the battery. For this reason, in order to limit the content of silicon (single substance) contained in the composite particles of the negative electrode active material to a certain range, the weight ratio of the silicon-intermetallic compound contained in the composite particles is 5% or more and less than 50%. In this case, preferable characteristics can be obtained, but the present invention is not limited to this range. Similarly to the silicon-intermetallic compound, carbon also has a role of relieving expansion and contraction of the negative electrode active material due to repeated charge and discharge, and improving electrical conductivity with respect to the active silicon particles. When this silicon-intermetallic compound and carbon coexist, good cycle characteristics can be obtained.

  The present invention is characterized in that at least two kinds of composite particles having different particle size distributions are mixed and used as composite particles composed of silicon, silicon-intermetallic compound and carbon used as the negative electrode active material. Of the at least two types of composite particles, the first composite particles having a small particle size must be in the following range. That is, among the first composite particles, the remaining 95% composite particles excluding particles in the range of 5% by volume from the side where the average particle diameter (diameter) measured by the laser diffraction / scattering method is large are excluded. The average particle diameter is in the range of 2 μm to 30 μm. More desirably, this range is 10 μm to 20 μm. On the other hand, the particle size of the second composite particles having a large particle size is 95% by volume from the side where the average particle diameter (diameter) measured by the laser diffraction / scattering method is the same among the second composite particles. The average particle size of the remaining 5% of the composite particles excluding the particles in the range of 1 is required to be larger than the average particle size of the first composite particles having a small particle size.

The above condition for the particle diameter of the first composite particles is denoted by D ₉₅ , and the condition for the particle diameter of the second composite particles is denoted by D ₅ . In each of the above conditions, the particle size D ₉₅ of the first composite particles is in the range of 2 μm to 30 μm, and the particle size D ₅ of the second composite particles is larger than the particle size D ₉₅ of the first composite particles. That is. Here, when the particle size D ₉₅ of the first composite particle is less than 2 μm, which is the lower limit of the above conditions, agglomeration due to fine particles occurs, and the same behavior as that of a particle having a large particle size occurs. As a result, the volume change of the active material becomes large, and the negative electrode active material is cracked, resulting in poor cycle characteristics. Also, special considerations for handling fine powders are required for handling in the production process of composite particles. On the other hand, when the upper limit of 30 μm is exceeded, since the particle size is large, the discharge capacity is greatly deteriorated by repeated charge and discharge of the battery, and the cycle characteristics are also lowered. Furthermore, when the particle size D ₅ of the second composite particle is the same as or smaller than the particle size D ₉₅ of the first composite particle, a mixture of a large particle and a small particle may be used. The effect becomes poor, and in this case as well, sufficient characteristics cannot be obtained in the cycle characteristics of the battery.

  In addition, among the at least two types of composite particles having different average particle sizes, the ratio of carbon contained in the first composite particles having a small particle size is 30% or more and 80% or less by weight, and the second particle having a large particle size. The proportion of carbon contained in the composite particles needs to be 5% or more and 30% or less by weight. In general, the addition of carbon has the effect of alleviating the volume change due to the expansion and contraction of the negative electrode active material due to repeated charge and discharge, but the silicon content decreases if the weight ratio of carbon in the composite particles is too large. The required charge / discharge capacity of the battery cannot be obtained. Conversely, if the weight ratio of carbon is too small, the effect of adding carbon cannot be obtained, so that the cycle characteristics of the battery are lowered due to the volume change of the negative electrode active material.

  The range of the amount of carbon added in the present invention is different between the first composite particles and the second composite particles, and the weight of the carbon of the second composite particles having a large particle size that greatly affects the charge / discharge capacity of the battery. The ratio is kept low to secure the charge / discharge capacity of the battery, while the weight ratio of carbon in the first composite particles having a small particle size is relatively high, thereby improving the cycle characteristics. In this way, by changing the carbon content between composite particles having different particle sizes, the two electrical characteristics required for a lithium ion secondary battery, that is, ensuring the charge / discharge capacity of the battery and improving the cycle characteristics, are compatible. It is possible to make it.

  As described above, in the present invention, at least two types of composite particles, ie, the first composite particles having a small particle size and the second composite particles having a large particle size are used, and these are mixed to produce a negative electrode active material. It is characterized by that. The mixing ratio of these composite particles needs to be in the range of 50 to 80 parts by weight of the second composite particles having a large particle size with respect to 100 parts by weight of the composite particles. If the ratio of the second composite particles is less than 50 parts by weight, a sufficient charge / discharge capacity as a battery cannot be obtained. In addition, when the amount is more than 80 parts by weight, the effect of particles having a small particle size is reduced, and the effect of causing a movement similar to plastic deformation as a whole following the volume change of the negative electrode active material due to charging and discharging of the battery is reduced. Cycle characteristics will be lowered.

  Below, the example of the preparation methods of the negative electrode active material particle of a lithium ion secondary battery is described. As a production method, a method is generally used in which silicon and a silicon-intermetallic compound are first mixed to produce composite particles, and then carbon is bonded to form a three-component composite particle. You may use the method.

  First, a method for producing composite particles of silicon and a silicon-intermetallic compound will be described. In the case where the metal constituting the silicon-intermetallic compound is a transition metal, a method of producing a silicon-transition metal compound (silicon alloy) by mixing and melting silicon and the transition metal, and a transition metal on the surface of the silicon simple substance There is a method of coating by vapor deposition and alloying. As described above, nickel is particularly suitable as a metal for forming a transition metal compound with silicon by these methods, and transition metals other than nickel, such as iron, cobalt, and titanium, can also be used favorably. . These methods are also effective when producing a silicon-intermetallic compound with a metal other than a transition metal. The composite particles of silicon and silicon-intermetallic compound are prepared by mixing particles that are fine particles of the silicon-intermetallic compound thus produced and particles of silicon alone, and sintering the mixture at high temperature and reduced pressure. And

  Subsequently, carbon is combined with the produced composite particle of silicon and silicon-intermetallic compound to produce a composite particle of three parties. As this means, first, the composite particles, which are a sintered body of silicon and a silicon-intermetallic compound, are placed in a high temperature non-oxygen atmosphere, and a gas atmosphere of an organic compound is introduced therein, followed by sintering. There is a method of forming a coating of amorphous carbon around the body composite particles. There is also a method in which graphite or amorphous carbon fine powder or particles are mixed in the sintered body, and the atmosphere is controlled to perform sintering again. The former method is advantageous in improving the cycle characteristics because the amorphous and crystalline carbon layers are coated around the silicon and silicon-intermetallic particles. Regarding the charge / discharge capacity, there is a possibility that it is difficult to obtain the merit of improving the characteristics. Therefore, it is preferable to use the former method mainly for the production of the first composite particles having a small particle diameter, and the latter method for the second composite particles having a large particle diameter.

  The negative electrode active material layer constituting the negative electrode of the lithium ion secondary battery is prepared by dispersing the composite particles composed of silicon, silicon-intermetallic compound, and carbon and the binder prepared by the above method in a solvent and kneading the mixture. It is produced by coating on the surface of the electric body and drying in a high temperature atmosphere. Here, the binder is a thermosetting binder selected from polyimide, polyamide, polyamideimide, polyacrylic acid resin, and polymethacrylic acid resin, and N-methyl-2-pyrrolidone (NMP) is used as a solvent. And the like are preferred.

Carbon black or acetylene black may be mixed in the negative electrode active material layer as necessary in order to impart conductivity. The electrode density in the produced negative electrode is preferably in the range of 1.0 g / cm ³ or more and 2.0 g / cm ³ or less. When this electrode density is too low, the charge / discharge capacity is reduced, and the merit of the conventional negative electrode active material made of only a carbon material is small. On the other hand, if it is too high, it becomes difficult to impregnate the electrode including the negative electrode with the electrolytic solution, so that the charge / discharge capacity is also lowered. In addition, since the thickness of the negative electrode current collector should be a thickness that allows the strength to be maintained by itself, it is generally necessary to be in the range of 4 to 100 μm. Moreover, in order to raise the energy density, it is more preferable that it is the range of 5-30 micrometers.

  On the other hand, as the active material contained in the positive electrode active material layer, lithium manganate, lithium cobaltate, lithium nickelate and a mixture thereof, and manganese, cobalt, nickel of the above compound are replaced with aluminum, magnesium, titanium, zinc. For example, lithium iron phosphate or the like obtained by substituting part or all of them can be used.

  Moreover, the non-aqueous electrolyte solution used for a lithium ion secondary battery mixes the 1 type (s) or 2 or more types of solvent selected from the following organic solvents, and dissolves the lithium salt melt | dissolved in these organic solvents. Used as electrolyte. Examples of organic solvents that can be used here include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). Chain carbonates such as ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, and γ-lactones such as γ-butyrolactone, , 2-Ethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran.

  Other usable organic solvents include dimethyl sulfoxide, 1,3-dioxolane, dioxolane derivatives, formamide, acetamide, dimethylformamide, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane. , Sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone And aprotic organic solvents such as

Still lithium salt used is dissolved in the organic solvent, for example _{LiPF 6, LiAsF 6, LiAlCl 4} , LiClO 4, LiBF 4, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li (CF 3 SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium lithium carbonate, chloroborane lithium, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides, and the like. Further, a polymer electrolyte may be used in place of the nonaqueous electrolytic solution using these organic solvent and lithium salt.

  Discharge end voltage value in a lithium ion secondary battery manufactured using the positive electrode and negative electrode produced by the above method, and a non-aqueous electrolyte or polymer electrolyte (the discharge is stopped as the discharge voltage during discharge decreases) Voltage) is preferably set to 1.5 V or more and 2.7 V or less. When the end-of-discharge voltage value is set lower than 1.5V, there arises a problem that the charge / discharge capacity is deteriorated due to repeated charge / discharge by the battery, that is, the cycle characteristics of the battery are lowered. In this case, the degree of difficulty in circuit design also increases. On the other hand, when the discharge end voltage value is set higher than 2.7 V, the value of the discharge capacity becomes small, so that a sufficient charge / discharge capacity as a lithium ion secondary battery cannot be obtained.

  Examples of the present invention will be described below.

Example 1
Silicon and nickel were mixed at a weight ratio of 1: 5, and melted and rapidly cooled at 1500 ° C. and 13.3 Pa to produce a silicon-nickel alloy powder which is an intermetallic compound of silicon and nickel. Next, this powder is further pulverized into fine granules, mixed with silicon alone, which is also made into fine granules, and sintered in a high-temperature and low-pressure atmosphere of 1000 ° C. and 0.01 Pa or less to produce silicon and silicon-nickel. Alloy composite particles were obtained. The composite particles were further pulverized and classified to produce particles having a relatively small particle size and particles having a large particle size. Of these, the first composite particles having a small particle size are mixed with 50 parts by weight of graphite to make 100 parts by weight, and the second composite particles having a large particle size are mixed with 10 parts by weight of graphite and similarly 100 parts by weight. The part. These mixed materials were respectively sintered in a nitrogen atmosphere at 900 ° C., and composite particles having two types of particle diameters composed of silicon, silicon-nickel alloy, and carbon were produced.

Next, of the two types of composite particles having different particle sizes, the first composite particles having a small particle size were prepared such that the particle size D ₉₅ measured by the laser diffraction / scattering method was 5 μm. Similarly, the second composite particles having a large particle size were prepared so that the particle size D ₅ measured by the laser diffraction / scattering method was 10 μm. The two types of composite particles having different particle diameters are mixed so that the weight ratio of the two is a ratio of the first composite particles: second composite particles = 20: 80, and the negative electrode active material of the lithium ion secondary battery The active material particles constituting

  Thereafter, a polyimide powder as a binder and a carbon powder (amorphous carbon powder) as a conductive agent were mixed with the active material particles, and NMP was added as a solvent to dissolve and disperse to prepare a slurry of a negative electrode material. This material was applied on the surface of a 10 μm thick copper foil as a negative electrode current collector, subjected to a drying treatment at 125 ° C. for 5 minutes in a drying furnace, and then subjected to compression molding with a roll press, and again to a drying furnace Was subjected to a drying treatment at 300 ° C. for 10 minutes to form a negative electrode active material layer. Further, the negative electrode current collector made of this copper foil and the negative electrode active material layer formed on the surface of the copper foil were punched into a 120 × 115 mm square shape to form a negative electrode. Finally, a negative electrode lead tab made of nickel for drawing out an electrode was fused to the back surface of the negative electrode active material layer forming surface of the negative electrode current collector by ultrasonic bonding.

  As for the positive electrode, active material particles made of lithium cobalt oxide were mixed with polyvinylidene fluoride as a binder, and NMP was added as a solvent to dissolve and disperse to prepare a slurry of the positive electrode material. This material was applied onto the surface of an aluminum foil having a thickness of 20 μm, which was a positive electrode current collector, and dried at 125 ° C. for 5 minutes in a drying furnace to form a positive electrode active material layer. Furthermore, a positive electrode current collector made of this aluminum foil and a positive electrode active material layer formed on the surface of the aluminum foil were punched into a 120 × 115 mm square shape to form a positive electrode. Finally, a positive electrode lead tab made of aluminum for drawing out electrodes was fused to the back surface of the positive electrode active material layer forming surface of the positive electrode current collector by ultrasonic bonding.

  Next, a 125 × 120 mm square separator made of a polypropylene porous film is prepared, and the negative electrode, the positive electrode, and the separator are opposed to each other with the separator on which the negative electrode and positive electrode active material layers are located inside each other. Were arranged and laminated. The laminate was covered with an exterior film, and an electrolytic solution was injected into the laminate, followed by sealing under vacuum. As the electrolytic solution, a solution obtained by dissolving LiPF6 at a concentration of 1 mol / l in a solvent in which EC, DEC, and EMC were mixed at a volume ratio of 3: 5: 2 was used. Note that the tips of the two negative electrodes and the positive electrode lead tab protrude from the exterior film to the outside. According to this method, a total of five laminate-type batteries were produced as Example 1.

(Evaluation of initial discharge capacity and cycle characteristics)
The five laminated lithium ion secondary batteries of Example 1 were first fully charged to the rated 4.2 V, then discharged to 2.7 V, and the discharge capacity at this time Was measured. This discharge capacity is the initial discharge capacity in the battery of Example 1, that is, the charge / discharge capacity. Each battery was then charged to 4.2 V and charged and discharged 100 times at a 1 C rate of discharge to 2.7 V, and the discharge capacity after 100 cycles was measured. The 1C rate is a charging / discharging method in which charging and discharging are performed for 1 hour each at a rated current of the battery. Therefore, in the case of 1C rate, it takes 2 hours to charge and discharge in one cycle. Here, the ratio of the discharge capacity after 100 cycles to the initial discharge capacity was calculated and used as the cycle characteristics. Table 1 shows the average values of the evaluation results of the initial discharge capacity and the cycle characteristics in these five batteries of Example 1.

(Comparative Examples 1 and 2)
As a comparative example, without using a negative electrode active material composed of silicon, silicon-intermetallic compound, and carbon, only graphite (carbon) and only silicon are used as the negative electrode active material, and the same dimensions as in Example 1 5 lithium ion secondary batteries were prepared and used as Comparative Example 1 and Comparative Example 2, respectively. Table 1 shows the average values of the evaluation results of the initial discharge capacity and the cycle characteristics in each of the five batteries of Comparative Examples 1 and 2. In the lithium ion secondary battery using only carbon as the negative electrode active material as in Comparative Example 1, good cycle characteristics can be obtained because the volume change of the negative electrode active material due to insertion and extraction of Li atoms is small. The discharge capacity is reduced. On the other hand, when only silicon is used as the negative electrode active material as in Comparative Example 2, the reverse characteristics are obtained, and although the initial discharge capacity is sufficiently large, the cycle characteristics are extremely low. In Comparative Examples 1 and 2, there is no first composite particle having a small particle diameter, and the particle diameter D ₅ of the second composite particle is 10 μm.

  The lithium ion secondary battery of the present invention is expected to exhibit characteristic values that are equivalent to or superior to those of the batteries of Comparative Examples 1 and 2 in Table 1. In other words, the initial discharge capacity is much larger than 354 mAh in Comparative Example 1 in Table 1, and it is necessary to have a discharge capacity approaching 661 mAh in Comparative Example 2, so that the case of 600 mAh or more was determined to be superior. . Similarly, since it is expected that the cycle characteristics at 100 cycles are equal to or higher than 74% in Comparative Example 1 shown in Table 1, it is determined that the cycle characteristics are 75% or more as superior. did. According to Table 1, in the case of Example 1, both the initial discharge capacity and the cycle characteristics satisfy the conditions of 600 mAh or more and 75% or more, respectively. Therefore, it is determined that this case is superior to the prior art. Is done.

(Examples 2-5, Comparative Examples 3-6)
A lithium ion secondary battery was produced by changing the particle diameters (average particle diameters) of two types of composite particles having different particle diameters, which are active material particles constituting the negative electrode active material of Example 1, and each of Examples 2 To 5 and Comparative Examples 3 to 6. The number of batteries produced is 5 for each of the examples and comparative examples. Among these, in Examples 2, 1, and 3 to 5 including the Example 1, the particle diameter D ₉₅ of the first composite particles having a small particle diameter is 2 μm, 5 μm, 10 μm, 20 μm, and 30 μm in order, the particle diameter D ₅ each 4μm in the order of the large second composite particles having a particle size, 10μm, 20μm, 40μm, a 40 [mu] m. On the other hand, in Comparative Examples 3 to 6, the particle size D ₉₅ of the first composite particles having a small particle size is 1.2 μm, 40 μm, 10 μm, and 15 μm in order, respectively. The particle diameter D ₅ is 1.5 μm, 60 μm, 10 μm, and 10 μm in order. Conditions other than the particle size of the negative electrode active material are the same as those in Example 1. The same evaluation as Example 1 was performed about each produced battery. Table 1 shows the average values of the evaluation results of the initial discharge capacity and the cycle characteristics in each of the five batteries of Examples 2 to 5 and Comparative Examples 3 to 6.

(Examples 6 to 10, Comparative Examples 7 to 10)
Next, a lithium ion secondary battery was produced by changing the carbon content of two types of composite particles having different particle diameters, which were active material particles constituting the negative electrode active material of Example 1, and each of Examples 6-10. And Comparative Examples 7 to 10. The number of batteries produced is 5 for each of the examples and comparative examples. Among them, in Comparative Example 7, Examples 6, 1, 7, and Comparative Example 8 including Example 1, the carbon content of the first composite particles having a small particle diameter is 20% and 30% in order by weight ratio, respectively. %, 50%, 80%, and 90%, and the carbon content of the second composite particles having a large particle diameter is constant at a ratio of 10% by weight. On the other hand, in Comparative Example 9, Examples 8, 1, 9, 10, and Comparative Example 10 including Example 1, the carbon content of the first composite particles having a small particle diameter is 50% by weight. The carbon content of the second composite particles having a constant ratio and a large particle diameter is 3%, 5%, 10%, 20%, 30%, and 40% in order by weight. The same evaluation as Example 1 was performed about each produced battery. Table 1 shows the average values of the evaluation results of the initial discharge capacity and the cycle characteristics in each of the five batteries of Examples 6 to 10 and Comparative Examples 7 to 10.

(Examples 11-13, Comparative Examples 11-18)
Furthermore, lithium ion secondary batteries were produced by changing the contents of two kinds of composite particles having different particle diameters, which are active material particles constituting the negative electrode active material of Example 1, and Examples 11 to 13 and Comparative Examples were respectively compared. It was set as Examples 11-18. The number of batteries produced is 5 for each of the examples and comparative examples. Among these, in Comparative Examples 11 to 15, including Example 1, Examples 11 to 13, 1, and Comparative Examples 16 to 18, the ratio of the first composite particles having a small particle diameter is 100% in order by weight ratio. 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 0%, and the ratio of the second composite particles having a large particle size is the weight The ratios are 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, and 100%, respectively. The total content of the first composite particles and the second composite particles in each sample is 100%. The same evaluation as Example 1 was performed about each produced battery. Table 1 shows the average values of the initial discharge capacity and the evaluation results of the cycle characteristics in each of the five batteries of Examples 11 to 13 and Comparative Examples 11 to 18.

(Examples 14-16, Comparative Examples 19-20)
Further, a lithium ion secondary battery was manufactured by changing the metal constituting the silicon-intermetallic compound contained in two kinds of composite particles having different particle diameters, which are active material particles constituting the negative electrode active material of Example 1. And Examples 14 to 16 and Comparative Examples 19 and 20, respectively. The number of batteries produced is 5 for each of the examples and comparative examples. Of these, in Examples 1, 14 to 16 including Comparative Example 1 and Comparative Examples 19 to 20, the metal forming the intermetallic compound with silicon was nickel (Ni), iron (Fe), cobalt ( Co), titanium (Ti), aluminum (Al), and magnesium (Mg). The same evaluation as Example 1 was performed about each produced battery. Table 1 shows the average values of the initial discharge capacity and the evaluation results of the cycle characteristics in each of the five batteries of Examples 14 to 16 and Comparative Examples 19 and 20.

According to the evaluation results of Examples 1 to 5 and Comparative Examples 3 to 6 in Table 1, the results are as follows. That is, when the active material particles that are the negative electrode active material of the lithium ion secondary battery are composed of two types of composite particles having different particle sizes, the particle size D ₉₅ of the first composite particles having a small particle size is a to no 2 [mu] m 30 [mu] m, and when the particle diameter D ₅ of the large second composite particles having a particle size greater than the particle diameter D ₉₅ of the first composite particles, good in both initial discharge capacity and the cycle characteristics Characteristics can be obtained. In this case, the initial discharge capacity of 600 mAh or more and the cycle characteristics after 100 cycles of 75% or more can be obtained at the same time, but these values can be obtained by the configuration of the negative electrode active material of the conventional lithium ion secondary battery. That was not possible.

  Moreover, according to the evaluation results of Examples 1, 6 to 10 and Comparative Examples 7 to 10 in Table 1, the results are as follows. That is, when the active material particles, which are the negative electrode active material of the lithium ion secondary battery, are composed of two types of composite particles having different particle sizes, the carbon content of the first composite particles having a small particle size is the weight. When the carbon content of the second composite particles having a large particle diameter is 30% to 80% by weight and the weight ratio is 5% to 30%, the initial discharge capacity is 600 mAh or more, Good characteristics with a cycle characteristic of 75% or more after 100 cycles can be obtained simultaneously. These values cannot be obtained with the structure of the negative electrode active material of the conventional lithium ion secondary battery.

  Furthermore, according to the evaluation results of Examples 1, 11 to 13 and Comparative Examples 11 to 18 in Table 1, it is as follows. That is, when the active material particles, which are the negative electrode active material of the lithium ion secondary battery, are composed of two types of composite particles having different particle sizes, the second composite particles having a large particle size are 50% by weight. When the ratio is from 80% to 80%, in other words, when the first composite particles having a small particle diameter are from 50% to 20% by weight, the initial discharge capacity is 600 mAh or more, and the cycle characteristics after 100 cycles are Good characteristics of 75% or more can be obtained at the same time. These values cannot be obtained with the structure of the negative electrode active material of the conventional lithium ion secondary battery.

  Furthermore, according to the evaluation results of Examples 1, 14 to 16 and Comparative Examples 19 and 20 in Table 1, the results are as follows. That is, when the active material particles, which are the negative electrode active material of the lithium ion secondary battery, are composed of two kinds of composite particles having different particle diameters, the silicon-metal interface contained in each of the two kinds of particle diameters. When transition metals such as Ni, Fe, Co, and Ti are used as the metal constituting the compound, it is possible to simultaneously obtain good characteristics with an initial discharge capacity of 600 mAh or more and a cycle characteristic after 100 cycles of 75% or more. it can. These values cannot be obtained with the structure of the negative electrode active material of the conventional lithium ion secondary battery.

  As described above, based on the embodiment of the present invention, the negative electrode active material of the lithium ion secondary battery is composed of at least two kinds of composite particles composed of silicon, silicon-intermetallic compound, and carbon, and having different particle sizes from each other. By including the mixture, it is possible to obtain characteristics superior to conventional lithium ion secondary batteries in both the initial discharge capacity and the cycle characteristics after 100 cycles. Further, the above description is for explaining the effect in the case of the embodiment of the present invention, and is not intended to limit the invention described in the claims or to reduce the scope of the claims. Absent. Moreover, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim.

The schematic cross section of the composite particle which comprises the negative electrode for lithium ion secondary batteries of this invention. Sectional drawing of the lithium ion secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon 2 Silicon-intermetallic compound 3 Carbon 4 Negative electrode active material particle 4a, 4b Composite particle 5 Negative electrode active material 6 Negative electrode collector 7 Negative electrode 8 Positive electrode active material 9 Positive electrode collector 10 Positive electrode 11 Separator 12 Exterior film 13 Negative electrode Lead tab 14 Positive lead tab

Claims (4)

A negative electrode used in a lithium ion secondary battery having a lithium ion conductive nonaqueous electrolyte,
The negative electrode has a current collector and a negative electrode active material,
The negative electrode active material has composite particles containing any of silicon, silicon- transition metal compound, and carbon,
The composite particles have at least a first particle group and a second particle group,
In the particle size distribution of the composite particles belonging to the first particle group, the composite particles having a volume ratio of 5% from the side where the average particle diameter measured by the laser diffraction / scattering method is larger are excluded. The range of the average particle diameter of the remaining composite particles belonging to the particle group is 2 μm to 30 μm,
In the particle size distribution of the composite particles belonging to the second particle group, the composite particles in the range of 95% by volume ratio from the side where the average particle diameter measured by the method is larger are excluded from the second particle group. the average particle diameter of belonging residual composite particles, Ri Oh at greater than the average particle diameter of the composite particles of the residual belonging to the first group of particles,
The carbon content in the composite particles belonging to the first particle group is 30 to 80 parts by weight with respect to 100 parts by weight of the composite particles belonging to the first particle group,
The carbon content in the composite particles belonging to the second particle group is 5 to 30 parts by weight with respect to 100 parts by weight of the composite particles belonging to the second particle group,
A negative electrode for a lithium ion secondary battery , wherein a total of composite particles belonging to the second particle group among the composite particles is 50 to 80 parts by weight with respect to 100 parts by weight of the composite particles . The negative electrode active material includes a mixture of the composite particles and a thermosetting resin, and the composite particles are bound to each other and the composite particles and the current collector are bound to each other by the thermosetting resin. The negative electrode for a lithium ion secondary battery according to claim 1, wherein : Wherein the silicon - transition metal compound Cliff Lee arsenide - a negative electrode for a lithium ion secondary battery according to claim 1 or 2, characterized in that a nickel compound. A lithium ion secondary battery comprising the negative electrode according to any one of claims 1 to 3 .

Images