JP2010218855A - Negative electrode for nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a negative electrode, sufficiently improve the volume capacity of the negative electrode to enhance the capacity and suppress decline in negative electrode characteristics, in a nonaqueous electrolyte secondary battery using an alloy having the La<SB>3</SB>Co<SB>2</SB>Sn<SB>7</SB>type crystal structure for a negative-electrode active material in the negative electrode. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes a positive electrode 12, the negative electrode 11 and nonaqueous electrolytic solution 14. For the negative electrode, the negative-electrode active material including alloy powder having the La<SB>3</SB>Co<SB>2</SB>Sn<SB>7</SB>type crystal structure and graphite powder is used. In application of a negative electrode material including the negative-electrode active material on a negative electrode current collector, a filling factor of the negative electrode material is set to be ≥59% and ≤73%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a negative electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery using such a negative electrode for a nonaqueous electrolyte secondary battery. In particular, the negative electrode in the non-aqueous electrolyte secondary battery is improved, and the volume capacity in the negative electrode is sufficiently improved to obtain a high-capacity non-aqueous electrolyte secondary battery, and the load in the non-aqueous electrolyte secondary battery It is characterized in that the characteristic is prevented from deteriorating.

  In recent years, non-aqueous electrolyte secondary batteries that use non-aqueous electrolyte and charge and discharge by moving lithium ions between the positive and negative electrodes have been used as power sources for portable electronic devices and power storage. Has been.

  In such a nonaqueous electrolyte secondary battery, a graphite material is widely used as a negative electrode active material in the negative electrode.

  Here, in the case of a graphite material, the discharge potential is flat and the lithium ions are inserted and desorbed between the graphite crystal layers to be charged / discharged. There is an advantage that the volume change is small.

  On the other hand, in recent years, mobile devices such as mobile phones, notebook computers, and PDAs have been remarkably reduced in size and weight, and power consumption has increased with the increase in functionality. In non-aqueous electrolyte secondary batteries, demands for weight reduction and capacity increase are increasing.

  However, when a graphite material is used for the negative electrode active material, the capacity of the graphite material is not necessarily sufficient, and there is a problem that it is not possible to sufficiently meet the above demands.

  Therefore, in recent years, it has been studied to use a material that forms an alloy with lithium, such as silicon, germanium, and tin, as a high-capacity negative electrode active material.

  However, when these materials that form an alloy with lithium are used as the negative electrode active material, the volume change accompanying the insertion and removal of lithium is large, and repeated charge and discharge repeatedly destroys the particle structure and makes the particles finer. As a result, the current collecting property inside the electrode is lowered, the battery capacity is remarkably deteriorated, and the charge / discharge cycle characteristics are greatly reduced as compared with those using graphite.

Therefore, in recent years, as disclosed in Patent Document 1, less expansion due to insertion and elimination reactions of lithium, as a negative electrode active material capable of high capacity, La ₃ Co ₂ Sn ₇ type crystal structure It has been proposed to use an alloy having

However, when an alloy having a La ₃ Co ₂ Sn ₇ type crystal structure is used as the negative electrode active material, when the negative electrode material containing the alloy powder is pressed to produce the negative electrode, the packing density of the negative electrode material is increased. There is a problem that it is difficult to increase the volume capacity and to increase the capacity.

Further, in a non-aqueous electrolyte secondary battery using an alloy having a La ₃ Co ₂ Sn ₇ type crystal structure as a negative electrode active material, the initial charge / discharge efficiency is poor, the discharge capacity is lowered, and the volume capacity is sufficiently increased. There is also a problem that it is difficult to increase the capacity and it is difficult to increase the capacity.

JP-A-2005-310739

An object of the present invention is to solve the above-mentioned problems in a non-aqueous electrolyte secondary battery, and in particular, an alloy having a La ₃ Co ₂ Sn ₇ type crystal structure is used as a negative electrode active material. The negative electrode in the non-aqueous electrolyte secondary battery is improved, and the volume capacity in the negative electrode is sufficiently improved to obtain a high-capacity non-aqueous electrolyte secondary battery, and the load characteristics in the non-aqueous electrolyte secondary battery are It is an object to suppress the decrease.

In the present invention, in order to solve the above problems, in the negative electrode for a nonaqueous electrolyte secondary battery in which a negative electrode material containing a negative electrode active material is provided on a negative electrode current collector, In addition to including an alloy powder having a La ₃ Co ₂ Sn ₇ type crystal structure and a graphite-based powder, the filling rate of the negative electrode material is set to 59% or more and 73% or less.

Then, in the non-aqueous electrolyte secondary battery negative electrode, the alloy having the above _La 3 _Co 2 Sn ₇ type crystal structure, it is preferable to use a high volume capacity _La 3 _Ni 2 Sn ₇ alloy.

In addition, in the negative electrode for a non-aqueous electrolyte secondary battery, when using an alloy powder having a La ₃ Co ₂ Sn ₇ type crystal structure and a graphite-based powder as the negative electrode active material, such a negative electrode active material is used. In order to increase the packing density of the negative electrode material using and improve the initial charge and discharge efficiency, the proportion of the graphite-based powder in the negative electrode active material is preferably 50% by mass to 90% by mass, and more preferably Is 70 mass% or more and 90 mass% or less.

  As the graphite powder, various graphite-based materials such as natural graphite, artificial graphite, and graphite particles whose surfaces are coated with amorphous carbon can be used. In particular, mesocarbon microbeads are used. It is preferable. The mesocarbon microbeads are obtained by graphitizing spherical carbon fine particles obtained by separating and purifying mesofuse microspheres generated by heat treatment of coal tar.

Here, the mesocarbon microbead has a higher filling property than the powder of the alloy having the La ₃ Co ₂ Sn ₇ type crystal structure, and has a higher hardness in the graphite-based powder. Cracking is prevented. For this reason, when the negative electrode material is filled and applied on the negative electrode current collector, voids remain in the negative electrode material, and the nonaqueous electrolyte solution can be used even if the packing density of the negative electrode material is increased. Is appropriately impregnated in the negative electrode material, and the rate of Li ion delivery is not reduced, and high volume capacity and load characteristics can be obtained.

  In addition, in this negative electrode for non-aqueous electrolyte secondary battery, the negative electrode material has a filling rate of not less than 59% and not more than 73%. If the filling rate is less than 59%, the volume capacity decreases. As a result, when the filling rate is higher than 73%, the non-aqueous electrolyte is not properly penetrated into the negative electrode material, and the initial charge / discharge efficiency is lowered and the load characteristic is also lowered. Because.

Further, if the particle size of the alloy powder having the La ₃ Co ₂ Sn ₇ type crystal structure is too small, the compressibility is lowered and the filling property is deteriorated, whereas the particle size of the particle is large. When it becomes too much, the contact points between the alloy particles described above are reduced, the electron conductivity is lowered, and the load characteristics are lowered. Therefore, it is preferable to use a powder of an alloy having the La ₃ Co ₂ Sn ₇ type crystal structure having a median diameter (D50) in the range of 1 μm to 20 μm, more preferably about 5 μm. To use.

  In addition, if the particle size of the graphite powder becomes too small, the reactivity with the non-aqueous electrolyte becomes too high, and side reactions occur during the first charge / discharge, and the first charge / discharge efficiency decreases. On the other hand, if the particle size of the particles becomes too large, the particles are easily broken, or the contact points between the particles are reduced, leading to a decrease in electron conductivity. For this reason, it is preferable to use a graphite powder having a median diameter (D50) in the range of 5 to 30 μm.

  In the nonaqueous electrolyte secondary battery of the present invention, the negative electrode for a nonaqueous electrolyte secondary battery as described above is used as the negative electrode in a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte. I did it.

  In addition, the nonaqueous electrolyte secondary battery of the present invention is characterized in that the negative electrode for a nonaqueous electrolyte secondary battery as described above is used for the negative electrode, and for the positive electrode and the nonaqueous electrolyte, There is no particular limitation.

And in the nonaqueous electrolyte secondary battery of this invention, the well-known positive electrode active material generally used can be used as a positive electrode active material used for the positive electrode. For example, lithium cobalt complex oxides such as LiCoO _2, lithium-nickel composite oxides such as _{LiNiO 2, LiMn 2 O 4,} LiMnO lithium-manganese composite oxides such as _{2, LiNi 1-x Co x} O 2 (0 <X <1) and other lithium / nickel / cobalt composite oxides, LiMn _1-x Co _x O ₂ (0 <x <1) and other lithium / manganese / cobalt composite oxides, LiN _x Co _y Mn _z O ₂ (x + y + z = 1 ) lithium-nickel-cobalt-manganese composite oxides such _{as, LiNi x Co y Al z O} 2 (x + y + z = 1) containing lithium transition metal oxide of the lithium-nickel-cobalt-aluminum composite oxides such as Things can be used.

  Moreover, as a non-aqueous electrolyte, what melt | dissolved the electrolyte which consists of a well-known lithium salt in the well-known well-known non-aqueous solvent can be used.

  Here, examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, and chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. In particular, it is preferable to use a mixed solvent of the above cyclic carbonate and chain carbonate.

Examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C _{4 F 9 SO 2), LiC} (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Li 2 B 10 Cl 10, Li 2 B 12 Cl 12 and, of these A mixture or the like can be used. In addition to these lithium salts, it is preferable to include a lithium salt having an oxalato complex as an anion. And lithium-bis (oxalato) borate etc. can be used as a lithium salt which uses such an oxalato complex as an anion.

In the present invention, in a negative electrode for a non-aqueous electrolyte secondary battery in which a negative electrode material containing a negative electrode active material is provided on a negative electrode current collector, an alloy powder having an La ₃ Co ₂ Sn ₇ type crystal structure and graphite When using a negative electrode active material containing a base powder and the filling rate of the negative electrode material is not less than 59% and not more than 73%, so that an alloy powder having a La ₃ Co ₂ Sn ₇ type crystal structure is used alone In comparison with the above, the filling property of the negative electrode material is improved, and the negative electrode material is appropriately impregnated with the non-aqueous electrolyte.

  As a result, when the above negative electrode for a water electrolyte secondary battery is used for the negative electrode in a nonaqueous electrolyte secondary battery, the initial charge / discharge efficiency is prevented from being lowered, and the volume capacity in the negative electrode is sufficiently improved. As a result, a high-capacity non-aqueous electrolyte secondary battery can be obtained, and a decrease in load characteristics in the non-aqueous electrolyte secondary battery can be suppressed.

It is a schematic explanatory drawing of the three-electrode-type test cell which used each negative electrode of the Example and comparative example of this invention for the working electrode. In the three-electrode test cell using each negative electrode of the example of the present invention and the comparative example as a working electrode, the relationship between the filling rate of the negative electrode material and the volume discharge capacity is used for the graphite powder in the negative electrode and artificial graphite powder is used. It is the figure which showed the result compared with what was and what used the mesocarbon micro bead. In the three-electrode test cell using each negative electrode of the example of the present invention and the comparative example as a working electrode, the relationship between the filling rate of the negative electrode material and the initial charge / discharge efficiency is shown in FIG. It is the figure which showed the result compared with what used and the thing using a mesocarbon micro bead. In the three-electrode test cell using each negative electrode of the example of the present invention and the comparative example as a working electrode, the relationship between the filling rate of the negative electrode material and the load characteristics was determined using artificial graphite powder as the graphite powder in the negative electrode. It is the figure which showed the result compared with a thing and the thing using a mesocarbon micro bead.

  Hereinafter, the non-aqueous electrolyte secondary battery negative electrode according to the present invention will be specifically described with reference to examples, and in the non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery negative electrode of the examples, It will be clarified by giving a comparative example that the volume capacity in the negative electrode is improved and the load characteristic is suppressed from being lowered. The negative electrode for a non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery of the present invention are not limited to those shown in the following examples, and can be implemented with appropriate modifications within the scope not changing the gist thereof. Is.

(Example A1)
In Example A1, in preparing the negative electrode, as the graphite powder, the lattice spacing (d002) measured by X-ray diffraction was 0.336 nm, the median diameter (D50) was 20 μm, and the true density was 2.26 g / A non-oriented artificial graphite powder of cm ³ is used, and an alloy powder having a crystal structure of La ₃ Co ₂ Sn ₇ type has a median diameter (D50) of 5 μm and a true density of 7.68 g / cm ³ . A certain La ₃ Ni ₂ Sn ₇ alloy powder was used.

Then, using a negative electrode active material in which the above La ₃ Ni ₂ Sn ₇ alloy powder and artificial graphite powder are mixed at a mass ratio of 5: 5, a carboxy as a thickener having a true density of 1.35 g / cm ³ is used. In an aqueous solution in which methylcellulose is dissolved in water, the negative electrode active material described above and a styrene-butadiene rubber as a binder having a true density of 0.91 g / cm ³ , and a negative electrode active material, a binder, and a thickener are combined in 97. It added and knead | mixed so that it might become mass ratio of 5: 1.5: 1.0, and the negative mix slurry was produced.

  Next, the negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector made of copper foil, dried, and then rolled using a roller press, cut into a size of 2 cm × 2 cm, and the negative electrode Was made.

Then, the negative electrode thus produced, along with determining the packing density of the negative electrode material has been applied onto the negative electrode current collector, the true density of the above La ₃ Ni ₂ Sn ₇ alloy powder and artificial graphite powder and a binder The true density of the calculated negative electrode material was determined, and the filling rate of the negative electrode material was determined by the following formula.

Filling rate (%) = (filling density ÷ true density of negative electrode material) × 100
As a result, the true density of the negative electrode material was 4.87 g / cm ³ , and the filling rate of the negative electrode material was 65.1%.

(Example A2)
In Example A2, the negative electrode active material obtained by mixing the La ₃ Ni ₂ Sn ₇ alloy powder and the artificial graphite powder in a mass ratio of 2: 8 in the production of the negative electrode in Example A1 was used. Except for the above, a negative electrode was produced in the same manner as in Example A1.

  And about the negative electrode produced in this way, it carried out similarly to said Example A1, and calculated | required the true density and filling rate of negative electrode material.

As a result, the true density of the negative electrode material was 3.29 g / cm ³ , and the filling rate of the negative electrode material was 67.5%.

(Example A3)
In Example A3, the negative electrode active material obtained by mixing the La ₃ Ni ₂ Sn ₇ alloy powder and the artificial graphite powder at a mass ratio of 1: 9 in the preparation of the negative electrode in Example A1 was used. Except for the above, a negative electrode was produced in the same manner as in Example A1.

  And about the negative electrode produced in this way, it carried out similarly to said Example A1, and calculated | required the true density and filling rate of negative electrode material.

As a result, the true density of the negative electrode material was 2.76 g / cm ³ , and the filling rate of the negative electrode material was 68.3%.

(Comparative Example a1)
In Comparative Example a1, in the production of the negative electrode in Example A1 above, only the above La ₃ Ni ₂ Sn ₇ alloy powder was used as the negative electrode active material, and the negative electrode was otherwise processed in the same manner as in Example A1. Was made.

  And about the negative electrode produced in this way, it carried out similarly to said Example A1, and calculated | required the true density and filling rate of negative electrode material.

As a result, the true density of the negative electrode material was 7.52 g / cm ³ and the filling rate of the negative electrode material was 63.2%.

(Comparative Example a2)
In Comparative Example a2, a negative electrode was produced in the same manner as in Example A1, except that only the artificial graphite powder was used as the negative electrode active material in the production of the negative electrode in Example A1.

  And about the negative electrode produced in this way, it carried out similarly to said Example A1, and calculated | required the true density and filling rate of negative electrode material.

As a result, the true density of the negative electrode material was 2.23 g / cm ³ and the filling factor of the negative electrode material was 70.1%.

  And the three-electrode type test cell 10 shown in FIG. 1 was produced using each negative electrode of Examples A1 to A3 and Comparative Examples a1 and a2 produced as described above.

Here, in the above-described three-electrode test cell 10, each of the above negative electrodes is used as the working electrode 11, metallic lithium is used for each of the counter electrode 12 and the reference electrode 13 that are positive electrodes, and the non-aqueous electrolyte solution 14 is In this non-aqueous electrolyte solution 14, a solution obtained by dissolving lithium hexafluorophosphate LiPF ₆ at a ratio of 1 mol / l in a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 3: 7 is used. The working electrode 11, the counter electrode 12, and the reference electrode 13 were immersed in the above.

Thus, each three-electrode type test cell 10 produced using each negative electrode of Examples A1 to A3 and Comparative Examples a1 and a2 as the working electrode 11 acts on the reference electrode 13 with a constant current of 1.0 mA / cm ^2. After charging until the potential of the electrode 11 becomes 0 V, and further charging until the potential of the working electrode 11 with respect to the reference electrode 13 becomes 0 V with a constant current of 0.1 mA / cm ^2, a constant current of 1.0 mA / cm ² Then, discharging was performed until the potential of the working electrode 11 with respect to the reference electrode 13 became 1 V, and the first charge / discharge was performed.

Then, the initial total charge capacity Qa charged in two stages as described above and the initial discharge capacity Qb are measured, and as the initial charge and discharge efficiency (%), as shown in the following formula (1), the first time The ratio of the initial discharge capacity Qb to the total charge capacity Qa was determined, and the discharge capacity per unit volume of the negative electrode material in each negative electrode was determined as the volume discharge capacity (mAh / cm ³ ). The results are shown in Table 1 below. It was shown to.

  Initial charge / discharge efficiency (%) = (Qb / Qa) × 100 (1)

As a result, when each negative electrode of Examples A1 to A3 using La ₃ Ni ₂ Sn ₇ alloy powder and artificial graphite powder as the negative electrode active material was used, only La ₃ Ni ₂ Sn ₇ alloy powder was used as the negative electrode active material. Compared with the case where the negative electrode of Comparative Example a1 used was used, the initial charge / discharge efficiency and the volume discharge capacity were greatly improved.

Also, when using the negative electrode of Example A1~A3 with and La ₃ Ni ₂ Sn ₇ alloy powder and artificial graphite powder in the negative electrode active material of Comparative Example a2 using only artificial graphite powder as the negative electrode active material Compared to the case where the negative electrode was used, the volume discharge capacity was high although the initial charge / discharge efficiency was lowered. In particular, when the negative electrodes of Examples A2 and A3 in which the proportion of the artificial graphite powder in the negative electrode active material is 80% by weight or more are used, the decrease in the initial charge / discharge efficiency is reduced and the volume discharge capacity is increased. It was improving.

(Example A4 and Comparative Examples a3 to a8)
In Example A4 and Comparative Examples a3 to a8, as the negative electrode active material, the La ₃ Ni ₂ Sn ₇ alloy powder and the artificial graphite powder were mixed at a mass ratio of 2: 8 as in Example A2 above. In the same manner as in Example A1, Example A4 and Comparative Examples a3 to A3 were used except that the filling rate of the negative electrode material using such a negative electrode active material was changed. Each negative electrode of a8 was produced.

  Here, as shown in the following Table 2, the filling rate of the negative electrode material in each negative electrode of Example A4 and Comparative Examples a3 to a8 is 63.1% in Example A4 and 30.2% in Comparative Example a3. In Comparative Example a4, it is 41.7%, in Comparative Example a5 is 42.2%, in Comparative Example a6 is 47.0%, in Comparative Example a7 is 51.1%, and in Comparative Example a8 is 74.5%. It was.

  Then, each of the negative electrodes of Example A4 and Comparative Examples a3 to a8 was used as the working electrode 11 to produce each three-electrode test cell 10 as described above.

Further, using each of the three-electrode test cells 10 thus produced, the initial charge / discharge efficiency (%) and the volume discharge capacity (mAh / cm ³ ) were determined in the same manner as described above. Are shown in Table 2 below together with the results of Example A2.

Furthermore, for each of the three-electrode test cells 10 using the negative electrodes of Examples A2 and A4 and Comparative Examples a3 to a8, charging at the time of charging at a constant current of 1.0 mA / cm ² at the time of initial charging, respectively. The capacity Qa1 is measured, and as the load characteristic (%), as shown in the following formula (2), the charge capacity when charging at a constant current of 1.0 mA / cm ² with respect to the initial total charge capacity Qa The ratio of Qa1 was determined, and the results are shown in Table 2 below.

  Load characteristics (%) = (Qa1 / Qa) × 100 (2)

As a result, in each of the negative electrodes of Examples A2 and A4 and Comparative Examples a3 to a8 used for the negative electrode active material in which La ₃ Ni ₂ Sn ₇ alloy powder and artificial graphite powder were mixed at a ratio of 2: 8 mass, When each negative electrode of Examples A2 and A4 in which the filling rate of the material is 59% or more and 73% or less is used, and each negative electrode of Comparative Examples a3 to a7 in which the filling rate of the negative electrode material is less than 59% is used Compared to the above, the volume discharge capacity was greatly increased in spite of the decrease in the initial charge / discharge efficiency and load characteristics. Moreover, compared with the case where the negative electrode of the comparative example a8 in which the filling rate of the negative electrode material exceeded 73% was used, the initial charge / discharge efficiency and load characteristics were improved, and the volume discharge capacity was increased. In particular, when the negative electrode of Example A4 in which the filling ratio of the negative electrode material was about 63% was used, the volume discharge capacity was increased, and the initial charge / discharge efficiency and load characteristics were not decreased.

(Example B1)
In Example B1, in preparing the negative electrode, as the graphite powder, the lattice spacing (d002) measured by X-ray diffraction was 0.336 nm, the median diameter (D50) was 20 μm, and the true density was 2.26 g / The mesocarbon microbeads (MCMB) of cm ³ and the alloy powder having the La ₃ Co ₂ Sn ₇ type crystal structure have a median diameter (D50) of 5 μm and a true density of 7 μm as in Example A1. A La ₃ Ni ₂ Sn ₇ alloy powder of .68 g / cm ³ was used.

Then, in the same manner as in Example A1, except that a negative electrode active material obtained by mixing the La ₃ Ni ₂ Sn ₇ alloy powder and mesocarbon microbeads (MCMB) at a mass ratio of 2: 8 is used. Thus, a negative electrode was produced.

Then, the negative electrode thus produced, along with determining the packing density of the negative electrode material has been applied onto the negative electrode current collector, said La ₃ Ni ₂ Sn ₇ alloy powder and mesocarbon microbeads (MCMB) and a binder The true density of the negative electrode material calculated from the true density was obtained, and the filling rate of the negative electrode material was obtained.

As a result, the true density of the negative electrode material was 3.29 g / cm ³ , and the filling factor of the negative electrode material was 59.0%.

(Examples B2 to B5 and Comparative Examples b1 to b4)
In Examples B2 to B5 and Comparative Examples b1 to b4, the same La ₃ Ni ₂ Sn ₇ alloy powder and mesocarbon microbeads (MCMB) were used as the negative electrode active material, as in Example B1. In the same manner as in the case of Example B1 above, the mixture ratio of the negative electrode material using such a negative electrode active material was changed. Each negative electrode of B2-B5 and comparative examples b1-b4 was produced.

  Here, as shown in Table 3 below, the filling rate of the negative electrode material in each of the negative electrodes of Examples B2 to B5 and Comparative Examples b1 to b4 was 59.3% in Example B2, and 62.3% in Example B3. 9%, 64.3% in Example B4, 73.0% in Example B5, 53.0% in Comparative Example b1, 54.2% in Comparative Example b2, and 56.3% in Comparative Example b3. 3% and 56.9% in Comparative Example b4.

Then, each of the negative electrodes of Examples B1 to B5 and Comparative Examples b1 to b4 prepared as described above was used as the working electrode 11 to prepare each three-electrode test cell 10 as described above. using each three-electrode test cell 10, in the same manner as in the above, the initial charge and discharge efficiency (%), calculated as volume discharge capacity (mAh / cm ^3), and load characteristics (%), as a result Is shown in Table 3 below.

As a result, each of Examples B2 to B5 and Comparative Examples b1 to b4 used for the negative electrode active material in which La ₃ Ni ₂ Sn ₇ alloy powder and mesocarbon microbeads (MCMB) were mixed at a ratio of 2: 8 mass. In the negative electrode, when each negative electrode of Examples B2 to B5 in which the filling rate of the negative electrode material is 59% or more and 73% or less is used, each negative electrode of Comparative Examples b1 to b4 in which the filling rate of the negative electrode material is less than 59% Compared with the case of using, the initial charge / discharge efficiency and load characteristics were slightly reduced, but the volume discharge capacity was greatly increased. In particular, when the negative electrodes of Examples B4 and B5 in which the filling rate of the negative electrode material is about 62 to 65% are used, the volume discharge capacity is increased, and the initial charge / discharge efficiency and the load characteristics are not decreased. It was.

  In addition, a graph comparing the relationship between the filling rate of the negative electrode material and the volume discharge capacity between the graphite-based powder using the artificial graphite powder and the mesocarbon microbead (MCMB). FIG. 3 shows a comparison between the negative electrode material filling rate and the initial charge / discharge efficiency, and FIG. 4 shows a comparison between the negative electrode material filling rate and load characteristics.

  As a result, when the graphite powder used artificial graphite powder and mesocarbon microbeads (MCMB) were compared, those using mesocarbon microbeads (MCMB) Compared to the one used, the decrease in the initial charge / discharge efficiency and load characteristics when the filling rate of the negative electrode material was increased was small.

10 Three-electrode test cell 11 Working electrode (negative electrode)
12 Counter electrode (positive electrode)
13 Reference electrode 14 Non-aqueous electrolyte

Claims (5)

In a negative electrode for a non-aqueous electrolyte secondary battery in which a negative electrode material containing a negative electrode active material is provided on a negative electrode current collector, an alloy powder having a La ₃ Co ₂ Sn ₇ type crystal structure as the negative electrode active material And a negative electrode for a non-aqueous electrolyte secondary battery, wherein the negative electrode material has a filling rate of 59% or more and 73% or less. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the alloy having a La ₃ Co ₂ Sn ₇ type crystal structure is a La ₃ Ni ₂ Sn ₇ alloy. Negative electrode for secondary battery.   The non-aqueous electrolyte secondary battery negative electrode according to claim 1 or 2, wherein a ratio of the graphite-based powder in the negative electrode active material is 50% by mass or more and 90% by mass or less. Negative electrode for electrolyte secondary battery.   4. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the graphite powder is mesocarbon microbeads. 5. .   In the nonaqueous electrolyte secondary battery provided with the positive electrode, the negative electrode, and the nonaqueous electrolyte, the negative electrode for nonaqueous electrolyte secondary batteries of any one of Claims 1-4 was used for the negative electrode. A non-aqueous electrolyte secondary battery.

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