JP6167943B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

JP 2013-077421 (Patent Document 1) discloses a non-aqueous electrolyte 2 containing carbon-coated LiFePO ₄ in a first active material of a positive electrode and lithium nickel composite oxide in a second active material of a positive electrode. A secondary battery is disclosed.

JP 2013-077421 A

  Plug-in hybrid vehicles (PHV) having the advantages of hybrid vehicles (HV) and electric vehicles (EV) have been put into practical use.

  The PHV can exhibit high fuel efficiency by switching the driving mode according to the state of charge (SOC) of the battery. In other words, in a state where the remaining battery level is sufficient (high SOC range), the vehicle uses only electric power (EV mode), and in a state where the remaining battery level is low (low SOC range), the engine and motor Run in combination (HV mode).

  In consideration of such usage, non-aqueous electrolyte secondary batteries are desired to improve the output in the low SOC region while maintaining the capacity in the high SOC region.

As means for improving the output characteristics of the low SOC region, as disclosed in Patent Document 1, for example, a 4V class positive electrode active material (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ or the like) and a 3V class positive electrode active material (LiFePO 4). ₄ ) and the like are effective. That is, the capacity of the high SOC region is secured by the 4V class positive electrode active material, and the output in the low SOC region is improved by the 3V class positive electrode active material.

  However, when the present inventor fabricated a nonaqueous electrolyte secondary battery using a mixed positive electrode containing two types of positive electrode active materials having different operating potentials and investigated its performance in detail, the intended performance was initially low. Although obtained, a new problem has been found that the battery performance is remarkably lowered after cycle endurance and after charge storage endurance.

  The present invention has been made in view of the above-mentioned problems, and its object is to provide a non-aqueous electrolyte secondary battery excellent in output characteristics in a low SOC region and excellent in cycle durability and charge storage durability. Is to provide.

  The present inventor conducted intensive studies to solve the above problems, and in a non-aqueous electrolyte secondary battery using a mixed positive electrode containing two types of positive electrode active material particles having different operating potentials, The positive electrode active material particles with the lower operating potential are exposed to a potential higher than the original operating potential, so that the positive electrode active material particles expand and contract rapidly due to charge / discharge, which disrupts the conductive network in the electrode. I found out that The present inventor has not limited to this, and through further research, has found an electrode configuration capable of efficiently mitigating expansion / contraction of the positive electrode active material particles accompanying charge / discharge, and has completed the present invention. It was. That is, the nonaqueous electrolyte secondary battery of the present invention has the following configuration.

  (1) A nonaqueous electrolyte secondary battery includes composite particles including a hollow body and first positive electrode active material particles supported on an outer shell of the hollow body.

  Since the hollow body has a cavity inside, the expansion of the first positive electrode active material particles supported on the outer shell of the hollow body can be absorbed and relaxed in the cavity. Thereby, even if the first positive electrode active material particles are used at a higher potential than the original operating potential and the expansion thereof becomes excessive, the conductive network in the electrode can be maintained.

  Therefore, even if the positive electrode active material represented by a mixed positive electrode has an electrode configuration exposed to a high potential, the nonaqueous electrolyte secondary battery can be excellent in cycle durability and charge storage durability.

(2) The hollow body preferably has an opening in the outer shell that communicates with the internal cavity.
According to the inventor's research, excessive expansion / contraction of the positive electrode active material particles not only causes disconnection of the conductive network, but also induces depletion of the electrolyte solution (also referred to as “liquid depletion”) in the electrode. . That is, the expanded positive electrode active material particles press the voids in the electrode, and the electrolytic solution to be held in the electrode is discharged out of the electrode. In particular, during cycle endurance, repeated expansion and contraction of the positive electrode active material particles act as if they were a pump, and the liquid withering progresses at an accelerated rate. And with the expansion of the positive electrode active material particles and the discharge of the electrolyte, the voids in the electrode are gradually crushed and the porosity of the electrode is lowered. Thereby, the ion movement in the electrode is hindered and the output characteristics are deteriorated.

  The decrease in porosity accompanying the charge / discharge cycle can be alleviated to some extent by increasing the amount of the resin component (typically the binder) in the electrode. However, an increase in the resin component means an increase in the resistance component, resulting in a decrease in output characteristics.

  As described above, in the conventional technology, even if the mixed positive electrode includes positive electrode active material particles having excellent output characteristics in the low SOC region, sufficient output characteristics are exhibited after cycle endurance and after charge storage endurance. I can't.

  On the other hand, when the hollow body has an opening as described above, the electrolyte can flow into the cavity through the opening, and the electrolyte can be held in the cavity. The electrolyte held in the cavity is once released from the cavity when the first positive electrode active material particles expand and the hollow volume of the hollow body contracts, but the first positive electrode active material particles contract and the hollow body When the volume of the cavity is restored, it is occluded by the cavity again. Therefore, even when the charge / discharge cycle is repeated, the porosity of the electrode is maintained, and liquid drainage can be prevented. Thereby, the output characteristics after cycle endurance and after charge storage endurance can be secured.

(3) The outer shell of the hollow body preferably contains an acrylic resin.
Since the acrylic resin can exhibit suitable elasticity, the hollow body can flexibly follow the expansion / contraction of the first positive electrode active material particles by including the acrylic resin in the outer shell. Further, the outer shell is easily elastically deformed, and more electrolyte can be occluded in the cavity when the first positive electrode active material particles contract.

  Moreover, since acrylic resin is excellent in various mechanical strengths, it can maintain a shape stably over a long period of time. Furthermore, the acrylic resin is resistant to the organic solvent contained in the electrolytic solution, and is excellent in dispersibility in the binder solution used when slurrying the positive electrode mixture.

(4) The first positive electrode active material particles preferably have a conductive layer on the surface thereof.
Thereby, conductivity is imparted to the first positive electrode active material particles and the composite particles, thereby improving the output characteristics.

  (5) The nonaqueous electrolyte secondary battery further includes second positive electrode active material particles, and the lithium-based average discharge potential of the first positive electrode active material particles is greater than the lithium-based average discharge potential of the second positive electrode active material particles. Is preferably low.

  Thus, by using two types of positive electrode active materials having different Li-based average discharge potentials (that is, operating potentials), output characteristics in the low SOC region can be improved. In general, the first positive electrode active material particles having a low operating potential are exposed to a high potential every time charging / discharging is performed, so that the conductive network is severed by excessive expansion / contraction, and output characteristics after cycle endurance deteriorate. However, since the first positive electrode active material particles are supported on the hollow body as described above, output characteristics can be ensured even after cycle durability.

Here, the “Li-based average discharge potential” is one of indices indicating the operating potential of the positive electrode active material. The average discharge potential based on Li can be measured by a conventionally known method. For example, using a general tripolar cell and a charge / discharge device, the counter electrode and the reference electrode are made of metal Li, and in the range of about 4.2 to 2.5 V (vs. Li / Li ⁺ ), 0.1 to The discharge capacity of the working electrode composed of the positive electrode active material (compound density: about 2.5 to 3.5 g / cm ³ ) was measured at a current density of about 1.0 mA / cm ² and obtained at the time of discharge. The average discharge potential can be calculated by dividing the total power amount by the discharge capacity.

The average discharge potentials (vs. Li ^/ Li ⁺ ) of typical positive electrode active materials are listed as follows. LiCoO ₂ (about 3.7 to 3.8 V), LiNiO ₂ (about 3.6 to 3.7 V), LiMn ₂ O ₄ (about 3.8 to 3.9 V), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (about 3.7V), LiFePO ₄ (about 3.3-3.4V).

  (6) It is preferable that the first positive electrode active material particles include a lithium-containing phosphate having an olivine structure.

  The olivine-type lithium-containing phosphate can be a 3V-grade positive electrode active material (average discharge potential: about 3.0 to 3.5 V). Therefore, when the operating voltage of the battery is designed at about 3.0 to 4.1 V, it can contribute to the improvement of output in the low SOC region.

(7) It is preferable that the second positive electrode active material particles include a lithium nickel composite oxide.
Lithium nickel composite oxides such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ can be a 4V class positive electrode active material (average discharge potential: about 3.5 to 4.0 V). Therefore, when the second positive electrode active material particles contain the lithium nickel composite oxide, the capacity of the high SOC region can be ensured.

  (8) According to another situation of this invention, the manufacturing method of a nonaqueous electrolyte secondary battery is provided. That is, the manufacturing method includes a first step of forming a conductive layer on the surface of the first positive electrode active material particles, and a second step of obtaining composite particles by supporting the first positive electrode active material particles on the outer shell of the hollow body. And a third step of obtaining a positive electrode mixture by mixing the composite particles, the second positive electrode active material particles, the conductive material, and the binder.

  Thereby, the non-aqueous electrolyte secondary battery having a large capacity in the high SOC region and excellent output characteristics in the low SOC region can be manufactured.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery which is excellent in the output characteristic in a low SOC area | region, and excellent in cycling durability and charge storage durability is provided.

It is a schematic diagram which shows an example of a structure of the composite particle concerning one Embodiment of this invention. It is a schematic diagram which shows an example of a structure of the hollow body concerning one Embodiment of this invention. It is a typical top view which shows an example of a structure of the positive electrode plate concerning one Embodiment of this invention. It is a typical top view showing an example of the composition of the negative electrode plate concerning one embodiment of the present invention. It is a schematic diagram which shows an example of a structure of the electrode body concerning one Embodiment of this invention. It is typical sectional drawing which shows an example of a structure of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is a flowchart which shows the outline of the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is a flowchart which shows the outline of the positive electrode plate preparation process concerning one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention (hereinafter, also referred to as “this embodiment”) will be described in detail, but the present embodiment is not limited thereto. In the following description, the average particle diameter is a median diameter (so-called d50) measured by a laser diffraction / scattering method.

[Nonaqueous electrolyte secondary battery]
FIG. 6 is a schematic cross-sectional view showing an example of the configuration of the nonaqueous electrolyte secondary battery of the present embodiment. Referring to FIG. 6, a battery 1000 includes an electrode body 400 and an electrolytic solution (not shown) inside a rectangular outer package 500. The exterior body 500 is, for example, an aluminum casing, and may include a pressure type current interrupt device (CID) that interrupts a current path in response to an increase in pressure inside the battery.

  The electrode body 400 includes a positive electrode plate 100, a negative electrode plate 200, and a separator 300. 3 and 4, each of positive electrode plate 100 and negative electrode plate 200 is a long belt-like sheet member, and the current collector core material is continuously exposed on one side in the lateral direction (width direction). The non-mixed material part

  Referring to FIG. 5, electrode body 400 is wound so that positive electrode plate 100 and negative electrode plate 200 face each other with separator 300 interposed therebetween. As shown in FIG. 5, the non-mixed portions of the positive electrode plate 100 and the negative electrode plate 200 are exposed from different directions on the winding axis AW of the electrode body 400.

  Referring again to FIG. 6, in electrode body 400, the non-composite portion (positive electrode current collector core material 100 a) of positive electrode plate 100 is connected to positive electrode terminal 104 through positive electrode current collector plate 102, and The mixture part (negative electrode current collector core material 200 a) is connected to the negative electrode terminal 204 via the negative electrode current collector plate 202.

Hereinafter, each member constituting the battery 1000 will be described.
<Positive electrode plate>
With reference to FIG. 3, the positive electrode plate 100 is a long strip-shaped sheet member, and includes a positive electrode current collector core material 100a and a positive electrode mixture portion 100b formed on the positive electrode current collector core material 100a. The positive electrode current collector core material 100a is, for example, an Al foil.

The positive electrode mixture portion 100b is formed by fixing a positive electrode mixture containing the composite particles 10, a conductive material, and a binder on the positive electrode current collector core material 100a. As long as the positive electrode mixture portion 100b includes the composite particles 10, the positive electrode mixture portion 100b may include other components. For example, the positive electrode mixture portion 100b may include second positive electrode active material particles. The positive electrode mixture density of the positive electrode mixture portion 100b is, for example, about 2.0 to 4.0 g / cm ³ .

(Composite particles)
Referring to FIG. 1, composite particle 10 includes a hollow body 12 and first positive electrode active material particles 14 supported on outer shell SH of hollow body 12. The composite particle 10 can absorb the expansion of the first positive electrode active material particle 14 by the cavity HL. Therefore, even if the first positive electrode active material particles 14 are materials that are particularly large in expansion / contraction due to charge / discharge, it is possible to suppress the disconnection of the conductive network in the positive electrode mixture portion 100b.

(Hollow body)
The hollow body 12 has, for example, an outer shell SH made of a resin material and a cavity HL. The hollow body 12 can have any outer shape such as a spherical shape, an ellipsoidal shape, a cylindrical shape, and a rectangular parallelepiped shape, but the outer shape is preferably close to a spherical shape from the viewpoint of filling properties in the electrode. In the hollow body 12, the number of cavities HL is not limited to one, and a plurality of cavities HL may be provided.

  As shown in FIG. 1, the hollow body 12 can have one or more openings OP communicating with the cavity HL in the outer shell SH. As a result, the electrolytic solution flows into the cavity HL through the opening OP, and the electrolytic solution can be held in the cavity HL. As the first positive electrode active material particles 14 expand and contract, the hollow body 12 occludes / releases the electrolytic solution, so that it is possible to prevent the progress of liquid drainage in the electrode.

  The hollow body 12 having the opening OP can be prepared as follows, for example. First, a microcapsule including an outer shell containing a thermoplastic resin and an inclusion containing an expanding agent is prepared. As the expansion agent, a substance having a large expansion coefficient such as hydrocarbon can be used. In general, such microcapsules are commercially available.

  Next, the microcapsule is heated. As a result, the outer shell softens, the expansion agent starts to gasify, the internal pressure rises, and the microcapsules expand. At this time, in the microcapsule, the internal pressure and the tension of the outer shell are balanced to maintain the expanded state. As the heating continues further, small cracks are generated in various parts of the thinned outer shell. That is, this crack becomes the opening OP.

(shell)
The outer shell is preferably composed of a thermoplastic resin as described above. Here, considering the resistance to the electrolytic solution, an acrylic resin, a styrene resin, a fluorine resin, or the like is preferable as the material of the outer shell. Among these, acrylic resins are particularly preferable because they exhibit suitable elasticity and excellent mechanical strength. In addition, the acrylic resin is dispersible in a binder solution [for example, a solution in which polyvinylidene fluoride (PVdF) is dissolved in N-methyl-2-pyrrolidone (NMP)] used when the positive electrode mixture is slurried. Is good.

  Examples of the acrylic resin include polymethyl methacrylate (PMMA), cross-linked PMMA, polyethyl methacrylate (PEMA), cross-linked PEMA, polybutyl methacrylate (PBMA), polyalkyl methacrylate such as cross-linked PBMA, and methacrylic acid. Examples include copolymers of acrylates or methacrylates such as methyl / styrene copolymers, crosslinked methyl methacrylate / dimethacrylate glycol copolymers, and crosslinked butyl acrylate / dimethacrylate glycol copolymers. it can.

(Average particle size)
The average particle size of the hollow body 12 is preferably 1 μm or more and 15 μm or less. When the average particle diameter is less than 1 μm, the amount of the electrolyte solution that can be held in the cavity HL decreases, and the cycle durability may decrease. On the other hand, when the average particle diameter exceeds 15 μm, it is difficult to densely arrange the first positive electrode active material particles 14 on the surface of the hollow body 12, and the conductive path may be interrupted and resistance may increase. In addition, according to the result of the experiment conducted by the inventor described later, the average particle diameter of the hollow body 12 is more preferably 3 μm or more and 12 μm or less.

(Average hollowness)
In this specification, the percentage of the value obtained by dividing the arithmetic average value (average inner diameter) of the inner diameter ID for the plurality of hollow bodies 12 by the arithmetic average value (average outer diameter) of the outer diameter OD is defined as the average hollowness.

  Here, referring to FIG. 2, the inner diameter ID indicates the constant direction diameter (Feret diameter) of the cavity HL in the cross-sectional image of the hollow body 12, and the outer diameter OD indicates the hollow body 12 in the cross-sectional image of the hollow body 12. It shall indicate the constant direction diameter of the outline.

  The average hollowness of the hollow body 12 can be measured by a conventionally known method. As a specific example, the following method can be illustrated, for example.

  First, after encapsulating a plurality of hollow bodies 12 in an epoxy resin and curing the resin, a cross-sectional sample is cut out with a microtome or the like. Next, the cross-sectional sample is observed using a transmission electron microscope (TEM) or an electron microscope (SEM). In the observation visual field, the inner diameter ID and the outer diameter OD are measured for each of the plurality of hollow bodies 12, and the average inner diameter and the average outer diameter are calculated by calculating the arithmetic average value of the results. Then, the average hollowness can be calculated by dividing the average inner diameter by the average outer diameter. At this time, from the viewpoint of measurement accuracy, the number of measured hollow bodies is, for example, 10 or more, preferably 100 or more, more preferably 1000 or more.

  In calculating the average hollowness, the average particle diameter obtained by the laser diffraction / scattering method can be used as a substitute for the average outer diameter obtained by the above-described microscopy.

  Such average hollowness is preferably 17% or more and 83% or less. When the average hollowness is less than 17%, the flexibility of the outer shell SH is lowered, and the followability to expansion / contraction of the first positive electrode active material particles 14 may be lowered. On the other hand, if the average hollowness exceeds 83%, the elasticity of the outer shell SH decreases, it becomes difficult to restore the shape after deformation, and the amount of electrolyte that can be held in the cavity HL may decrease gradually. In addition, according to the result of the experiment conducted by the inventor described later, the average hollowness is more preferably 25% or more and 75% or less.

(First positive electrode active material particles)
The first positive electrode active material particles 14 are supported on the outer shell SH. As a method for supporting the first positive electrode active material particles 14 on the outer shell SH, for example, a mechano-fusion method described later can be cited. In consideration of supporting on the surface of the hollow body 12, the first positive electrode active material particles 14 are preferably small-diameter particles. The average particle diameter of the first positive electrode active material particles 14 is, for example, about 1 to 10 μm, preferably about 1 to 5 μm, and more preferably about 2 to 4 μm.

  The first positive electrode active material particles 14 need only be supported on the outer shell SH of the hollow body 12 and do not necessarily cover the entire surface of the hollow body 12. However, from the viewpoint of ensuring the conductivity of the composite particle 10, the exposed surface of the hollow body 12 in the composite particle 10 is preferably small. Moreover, when the quantity of the hollow body 12 is too small with respect to the quantity of the 1st positive electrode active material particle 14, it may not be able to fully absorb the expansion / contraction of the 1st positive electrode active material particle. Therefore, in the composite treatment of the hollow body 12 and the first positive electrode active material particles 14, the hollow body 12 is in the range of 5 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the first positive electrode active material particles 14. It is preferable to mix in the range of 10 parts by weight or more and 50 parts by weight or less.

The 1st positive electrode active material particle 14 should just be able to act as a positive electrode active material of a nonaqueous electrolyte secondary battery. As the first positive electrode active material particles 14, for example, LiCoO ₂ , LiNiO ₂ , LiNi _a Co _b O ₂ (where a + b = 1, 0 <a <1, 0 <b <1 is satisfied), LiMnO. ₂ , LiMn ₂ O ₄ , LiNi _a Co _b Mn _c O ₂ (where a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1). Examples include metal oxides and lithium-containing phosphates such as LiMPO ₄ (wherein M is one or more elements selected from the group consisting of Co, Ni, Mn and Fe). it can. The first positive electrode active material particles 14 may contain two or more of these positive electrode active materials.

  Note that the positive electrode active material may be a material in which a different element is doped in a trace amount, or a part of a metal element may be substituted with a different element. Examples of such different elements include Mg, Al, Si, Ca, Ti, V, Cr, Zn, Ga, Zr, Nb, Mo, Sn, Hf, and W.

The first positive electrode active material particles 14 are lithium-containing phosphates having an olivine structure, that is, a general formula LiMPO ₄ (wherein M is one or more selected from the group consisting of Co, Ni, Mn and Fe). It is preferable that the compound represented by these is included. Since such a compound can be a 3V-grade positive electrode active material, when combined with a 4V-grade positive electrode active material, it is easy to increase the output in the low SOC region.

Here, in the general formula LiMPO ₄ , M in the formula is more preferably Fe. That is, it is more preferable that the first positive electrode active material particles 14 include lithium iron phosphate (LiFePO ₄ ). This is because lithium iron phosphate is particularly excellent in output characteristics in a low SOC region.

(Conductive layer)
With reference to FIG. 1, it is preferable that the 1st positive electrode active material particle 14 has the conductive layer 16 on the surface. In particular, when the first positive electrode active material particle 14 is a material having low conductivity such as lithium iron phosphate, the first positive electrode active material particle 14 desirably has a conductive layer 16. When the first positive electrode active material particles 14 have the conductive layer 16, conductivity is imparted to the first positive electrode active material particles 14 and the composite particles 10, and output characteristics are further improved.

  Here, the conductive layer 16 can be, for example, a general carbon coating layer. It can be confirmed that the first positive electrode active material particles 14 have the conductive layer 16 by using, for example, SEM observation and elemental analysis with an electron beam microanalyzer (EPMA) in combination.

  Note that the conductive layer 16 does not necessarily have to cover the entire surface of the first positive electrode active material particles 14, and may be provided at least in part. However, as shown in FIG. 1, the conductive layer 16 is preferably one that covers the substantially entire surface of the first positive electrode active material particles 14 in a thin and uniform manner. In the first positive electrode active material particles 14, the mass ratio between the positive electrode active material and the conductive layer 16 (for example, carbon) is, for example, about 98: 2 to 99: 1.

(Second positive electrode active material particles)
In the present embodiment, the positive electrode mixture may further include second positive electrode active material particles. As the second positive electrode active material particles, those exemplified above as the first positive electrode active material particles 14 can be used. The second positive electrode active material particles may also contain two or more positive electrode active materials.

When the positive electrode mixture includes the second positive electrode active material particles, the average discharge potential (vs. Li ^/ Li ⁺ ) of the first positive electrode active material particles is lower than the average discharge potential of the second positive electrode active material particles. It is preferable to select a combination of the first positive electrode active material particles and the second positive electrode active material particles.

For example, when the combination of the first positive electrode active material particles and the second positive electrode active material particles is expressed as “first positive electrode active material particles: second positive electrode active material particles”, “LiFePO ₄ : LiNi _1/3 Co _{1 / 3} Mn _1/3 O ₂ ”,“ LiFePO ₄ : LiCoO ₂ ”,“ LiNi _1/3 Co _1/3 Mn _1/3 O ₂ : LiCoO ₂ ”and the like can be exemplified. This is because by adopting such a combination, output improvement in a low SOC region can be expected.

Further, the second positive electrode active material particles may include a general formula LiNi _a Co _b Mn _c O ₂ (wherein 0 <a <1, 0 <b <1, 0 <c <1 among lithium-containing transition metal oxides). And satisfying a + b + c = 1.) It is preferable to include a lithium nickel composite oxide represented by: Such a lithium nickel composite oxide is particularly suitable as the second positive electrode active material particle because it has a large capacity in a high SOC region and is excellent in thermal stability.

In the general formula LiNi _a Co _b Mn _c O ₂ , a, b and c in the formula are more preferably 0.2 <a <0.4, 0.2 <b <0.4, 0.2 < c <0.4 is satisfied, more preferably 0.3 <a <0.35, 0.3 <b <0.35, and 0.3 <c <0.35. This is because when the composition ratio of Ni, Co and Mn satisfies the above relationship, the balance between energy density and thermal stability is further improved.

  Further, from the viewpoint of filling property of the positive electrode mixture, the average particle diameter of the second positive electrode active material particles is, for example, about 5 to 20 μm, preferably about 5 to 15 μm, and more preferably about 6 to 10 μm.

  In the positive electrode mixture, the ratio of the total amount of the first positive electrode active material particles and the second positive electrode active material particles is, for example, about 80 to 98% by mass, preferably 85 to 96% by mass, from the viewpoint of the energy density of the battery. About 90 to 95% by mass.

  Furthermore, from the viewpoint of achieving a higher degree of compatibility between the capacity of the high SOC region and the output of the low SOC region, the ratio of the first positive electrode active material particles to the total mass of the first positive electrode active material particles and the second positive electrode active material particles Is preferably 1% by mass to 30% by mass, more preferably 3% by mass to 20% by mass, and particularly preferably 5% by mass to 15% by mass.

(Conductive material)
The conductive material contained in the positive electrode mixture is not particularly limited, and a conventionally known material can be used. For example, acetylene black (AB), ketjen black (KB), graphite, vapor grown carbon fiber (VGCF), or the like can be used. The proportion of the conductive material in the positive electrode mixture is, for example, about 1 to 10% by mass, preferably about 2 to 5% by mass, and more preferably about 3 to 5% by mass.

(Binder)
The binder contained in the positive electrode mixture is not particularly limited, and a conventionally known material can be used. For example, PVdF, polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), or the like can be used. The proportion of the binder in the positive electrode mixture is, for example, about 1 to 10% by mass, preferably about 1 to 5% by mass, and more preferably about 1 to 3% by mass.

<Negative electrode plate>
Referring to FIG. 4, the negative electrode plate 200 is a long strip-shaped sheet member, and includes a negative electrode current collector core material 200 a and a negative electrode mixture portion 200 b formed on the negative electrode current collector core material 200 a. The negative electrode current collector core material 200a is, for example, a Cu foil. Moreover, the negative electrode mixture density of the negative electrode mixture part 200b is, for example, about 0.5 to 2.5 g / cm ³ .

  The negative electrode mixture portion 200b is formed by fixing a negative electrode mixture containing a negative electrode active material and a binder on the negative electrode current collector core material 200a. The negative electrode active material is not particularly limited as long as it can act as the negative electrode active material of the nonaqueous electrolyte secondary battery. For example, a carbon-based negative electrode active material such as graphite, or an alloy-based negative electrode active material such as Si or Sn can be used. The proportion of the negative electrode active material in the negative electrode mixture is, for example, about 90 to 99% by mass.

  The binder is not particularly limited, and for example, a conventionally known material such as carboxymethyl cellulose (CMC), PTFE, styrene butadiene rubber (SBR) can be used. The proportion of the binder in the negative electrode mixture is, for example, about 1 to 10% by mass.

<Separator>
Separator 300 allows Li ⁺ to pass therethrough and prevents electrical contact between positive electrode plate 100 and negative electrode plate 200. The separator 300 is preferably a microporous film made of a polyolefin-based material from the viewpoint of mechanical strength and chemical stability. For example, a microporous film such as polyethylene (PE) or polypropylene (PP) is suitable.

  The separator 300 may be a laminate of a plurality of microporous films, or may have a heat resistant layer containing an inorganic filler (for example, alumina, magnesia, titania, etc.) on the surface thereof. The thickness of the separator 300 can be about 5-40 micrometers, for example. What is necessary is just to adjust suitably the hole diameter and porosity of the separator 300 so that the air permeability may become a desired value.

<Electrolyte>
The electrolytic solution is a liquid non-aqueous electrolyte in which a solute (Li salt) is dissolved in an aprotic solvent. Examples of the aprotic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL) and vinylene carbonate (VC), and dimethyl carbonate (DMC). ), Chain carbonates such as ethyl methyl carbonate (EMC) and diethyl carbonate (DEC). These aprotic solvents can be used in an appropriate combination of two or more from the viewpoint of electrical conductivity and electrochemical stability. In particular, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is preferably about 1: 9 to 5: 5. If a specific example is given, 3 types, EC, DMC, and EMC, can be mixed and used, for example.

Examples of the Li salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), and bis (trifluoromethanesulfonyl) imide lithium. (Li (CF ₃ SO ₂ ) ₂ N), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), or the like can be used. Moreover, you may use 2 or more types together about these solutes. The concentration of the solute in the electrolytic solution is not particularly limited, but is preferably about 0.5 to 2.0 mol / L from the viewpoint of discharge characteristics and storage characteristics. In addition, this embodiment can also be provided with a gel-like or solid nonaqueous electrolyte.

  Furthermore, in order to ensure the safety at the time of overcharge, the electrolyte solution may contain an overcharge additive. Here, the overcharge additive is a compound that reacts with the overcharged positive electrode active material to generate gas, thereby increasing the internal pressure of the battery and promoting the operation of CID. Examples of such overcharge additives include cyclohexylbenzene (CHB) and biphenyl (BP).

  As described above, in the conventional technology, the electrolyte solution is depleted in the positive electrode mixture portion during cycle durability or charge storage durability, and the contact rate between the positive electrode active material and the electrolyte solution is reduced. Therefore, in a battery after endurance, even when the electrolyte contains an overcharge additive, the amount of gas generated is small, and the CID may be difficult to operate.

  On the other hand, in this embodiment, since the hollow body 12 suppresses depletion of the electrolyte, the CID can be reliably operated even after cycle endurance or after charge storage endurance.

[Method for producing non-aqueous electrolyte secondary battery]
The nonaqueous electrolyte secondary battery of this embodiment can be manufactured by the manufacturing method demonstrated below.

  FIG. 7 is a flowchart showing an outline of a method for manufacturing the nonaqueous electrolyte secondary battery of the present embodiment. Referring to FIG. 7, the manufacturing method includes step S100, step S200, step S300, step S400, step S500, and step S600.

Hereinafter, each step will be described.
<Process S100>
In step S100, the positive electrode plate 100 is produced. Step S100 may include a first step S101, a second step S102, and a third step S103 as follows.

(First step S101)
With reference to FIG. 8, in the first step S <b> 101, the conductive layer 16 is formed on the surface of the first positive electrode active material particles 14. For example, the carbon-containing conductive layer 16 can be formed by mixing a carbon source with the powder of the first positive electrode active material particles 14 and firing at a temperature of about 400 to 800 ° C. As the carbon source, for example, liquid organic compounds such as liquid hydrocarbons and alcohols, or saccharides such as cellulose can be used.

  In addition, when the 1st positive electrode active material particle 14 is a compound which has sufficient electroconductivity, you may abbreviate | omit 1st process S101.

(Second step S102)
In the second step S102, the composite particles 10 are obtained by supporting the first positive electrode active material particles 14 on the outer shell SH of the hollow body 12. The method for supporting the first positive electrode active material particles 14 on the outer shell SH of the hollow body 12 is not particularly limited, and can be performed using a conventionally known powder processing technique. One example is the mechanofusion method.

  Here, the mechano-fusion method refers to a method of compounding particles by applying mechanical energy such as friction and compression to powders of different materials to cause mechanochemical reaction on the particle surface and fusing the particles together. . As an apparatus capable of such a composite treatment, for example, there is a compression grinding mill “Ang Mill” manufactured by Hosokawa Micron Corporation.

  In the ong mill, powder fixed on the inner wall of a container rotating at high speed by centrifugal force is consolidated by a head (press head) of an arm rotating at the center. At this time, a mechanochemical reaction occurs between particles of different materials (that is, between the hollow body 12 and the first positive electrode active material particles 14), and the first positive electrode active material particles 14 are bonded to the outer shell SH of the hollow body 12. Can be made. What is necessary is just to change suitably the rotation speed and processing time of an arm according to batch quantity etc. FIG. For example, the rotational speed can be about 10 to 50 rpm, and the processing time can be about 60 to 180 seconds.

(Third step S103)
In the third step S103, the composite particles 10, the second positive electrode active material particles, the conductive material, and the binder are mixed to obtain a positive electrode mixture. These materials can be mixed using a general powder mixing apparatus or kneading apparatus. Note that a solution in which a binder is dissolved in a solvent is prepared in advance, and the solution may be mixed with the above materials.

  Thereafter, the positive electrode mixture is kneaded in a solvent to form a slurry, and the slurry is applied on the positive electrode collector core material 100a and dried to form the positive electrode mixture portion 100b, whereby the positive electrode plate 100 can be obtained. it can. At this time, the positive electrode plate 100 may be rolled to adjust the thickness and the density of the positive electrode mixture portion 100b.

  Alternatively, the positive electrode composite material is granulated to obtain a granulated powder, the granulated powder is rolled to obtain a sheet-like molded body, and the molded body is further pressure-bonded to the positive electrode current collector core material 100a. Thus, the positive electrode mixture portion 100b can be obtained.

<Step S200>
In step S200, the negative electrode plate 200 is produced. For example, the negative electrode active material, the thickener and the binder are kneaded in water to form a slurry, and the slurry is applied onto the negative electrode current collector core 200a and dried to form the negative electrode mixture portion 200b. The negative electrode plate 200 can be produced. At this time, the negative electrode plate 200 may be rolled to adjust the thickness and the density of the negative electrode mixture portion 200b.

<Step S300 to Step S600>
The electrode body 400 can be manufactured by winding or laminating so that the positive electrode plate 100 and the negative electrode plate 200 face each other with the separator 300 interposed therebetween (step S300). Next, the electrode body 400 is inserted into the exterior body 500 (step S400). Then, an electrolyte is injected into the outer package 500 (step S500), and the outer package 500 is sealed by a predetermined means (for example, laser welding) (step S600), whereby the nonaqueous electrolyte secondary battery of the present embodiment. (Battery 1000) can be manufactured.

  Although the present embodiment has been described above by exemplifying a prismatic battery, these descriptions are merely examples, and the present embodiment is not limited to a prismatic battery. For example, a cylindrical battery or a pouch-shaped battery (also called a laminate battery) And so on).

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to these.

  Various conditions were changed as described below to produce a positive electrode plate, a battery using the positive electrode plate was produced, and battery performance was evaluated.

<Example 1>
(Preparation of positive electrode plate: Step S100)
Referring to FIG. 3, a positive electrode plate 100 that was a long strip-shaped sheet member and had a non-mixed material portion in which the positive electrode current collector core material 100 a was continuously exposed on one side in the short direction was produced.

(First step S101)
As the first positive electrode active material particles 14, lithium iron phosphate particles (average particle diameter: 3 μm) having a conductive layer 16 on the surface were prepared. Here, the conductive layer 16 is made of carbon (C), and the mass ratio of carbon to lithium iron phosphate (LiFePO ₄ ) as a base material is LiFePO ₄ : C = 99: 1.

In the following description and Table 1, lithium iron phosphate particles having a conductive layer on the surface thereof are referred to as “LiFePO ₄ / C”.

(Second step S102)
As the hollow body 12, hollow particles (outer shell SH: acrylic resin, average particle diameter: 6 μm, average inner diameter: 3 μm, average hollowness: 50%) were prepared. The hollow body 12 has a plurality of openings OP communicating with the internal cavity HL in the outer shell SH. Here, the average hollowness and average inner diameter are arithmetic average values for 100 hollow particles. In this experiment, the average particle diameter was used instead of the average outer diameter in calculating the average hollowness.

  100 parts by mass of the first positive electrode active material particles 14 are added to 30 parts by mass of the hollow body 12, and a condition of a rotation speed of 30 rpm using a compression grinding mill (product name “Ang Mill”, manufactured by Hosokawa Micron Corporation) is used. Then, the composite processing of the particles was performed for 120 seconds to obtain composite particles 10 in which the first positive electrode active material particles 14 were supported on the outer shell SH of the hollow body 12.

(Third step S103)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (average particle diameter: 8 μm) as the second positive electrode active material particles, and AB (product name “DENKA BLACK”, manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material An NMP solution in which PVdF (product number “KF7200”, manufactured by Kureha Co., Ltd.) was dissolved was prepared as a binder.

  Then, these materials are mixed so that the mixing ratio of the positive electrode mixture is second positive electrode active material particles: composite particles: conductive material: binder = 90: 13: 4: 2 (mass ratio), Furthermore, the positive electrode mixture slurry was obtained by kneading. The breakdown of the composite particles (13 parts by mass) consists of first positive electrode active material particles (10 parts by mass) and a hollow body (3 parts by mass). Therefore, more specifically, the mixing ratio of the positive electrode mixture is as follows: second positive electrode active material particles: first positive electrode active material particles: hollow body: conductive material: binder = 90: 10: 3: 4: 2 (mass ratio) It becomes.

  Next, the positive electrode mixture slurry was applied to both main surfaces of an Al foil (positive electrode current collector core material 100a) having a thickness of 20 μm using a die coater and dried to form the positive electrode mixture portion 100b. And the positive electrode compound material part 100b was rolled using the roll mill, and the positive electrode plate 100 (thickness: 170 micrometers) was obtained.

  At this time, with reference to FIG. 3, the length dimension L1 of the positive electrode plate 100 was 4500 mm, and the width dimension W1 of the positive electrode mixture portion 100b was 94 mm.

(Preparation of negative electrode plate: Step S200)
Referring to FIG. 4, a negative electrode plate 200 having a long band-like sheet member and having a non-mixed material portion in which the negative electrode current collector core material 200a is continuously exposed on one side in the short-side direction was manufactured.

  First, graphite powder (negative electrode active material), CMC as a thickener (variety “BSH-6”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and SBR (binder) are mixed with negative electrode active material: thickener. The mixture was mixed so that the material: binder = 100: 1: 0.8 (mass ratio), and kneaded in water to obtain a negative electrode mixture slurry.

  Next, the negative electrode mixture slurry was coated on both main surfaces of a 14 μm thick Cu foil (negative electrode current collector core material 200a) using a die coater and dried to form a negative electrode mixture portion 200b. And the negative electrode mixture part 200b was rolled using the roll mill, and the negative electrode plate 200 (thickness: 150 micrometers) was obtained.

  At this time, with reference to FIG. 4, the length dimension L2 of the negative electrode plate 200 was 4700 mm, and the width dimension W2 of the negative electrode mixture portion 200b was 100 mm.

(Preparation of separator)
First, a separator base material (thickness: 25 μm) having a three-layer structure of PP / PE / PP was prepared. Next, alumina particles (96 parts by mass), which are inorganic fillers, an acrylic resin binder (4 parts by mass), and a solvent (ion exchange water) are used with CLEARMIX (M Technique Co., Ltd.). To obtain a slurry to be a heat-resistant layer. And using the gravure coater, this slurry was apply | coated on the separator base material, and it dried and formed the heat resistant layer on the base material. Thereby, the separator 300 was obtained.

(Preparation of electrolyte)
EC, DMC, and EMC were mixed so that EC: DMC: EMC = 3: 4: 3 (volume ratio) to obtain a mixed solvent. Next, an electrolytic solution was prepared by dissolving LiPF ₆ (1.0 mol / L), CHB (1% by mass), and BP (1% by mass) in the mixed solvent.

(Assembly: Step S300 to Step S600)
Referring to FIG. 5, winding was performed so that positive electrode plate 100 and negative electrode plate 200 face each other through separator 300 to obtain an elliptical wound body. Subsequently, an electrode body 400 was obtained by pressing an elliptical wound body into a flat shape at normal temperature (surface pressure: 4 kN / cm ² , time: 2 minutes) using a flat plate press (Step S300). ).

  The exterior body 500 provided with CID (not shown) was prepared. Referring to FIG. 6, positive electrode current collector plate 102 is welded to positive electrode current collector core material 100 a exposed at one end on winding axis AW of electrode body 400, and negative electrode current collector exposed at the other end. The negative electrode current collector plate 202 was welded to the core material 200a. Next, the positive electrode terminal 104 and the positive electrode current collector plate 102 provided on the outer package 500 were welded, and the negative electrode terminal 204 and the negative electrode current collector plate 202 were welded. Furthermore, the electrode body 400 was inserted into the exterior body 500 (step S400), and the electrolytic solution (125 g) prepared above was injected (step S500). Then, by sealing the outer package 500 (step S600), a rectangular nonaqueous electrolyte secondary battery having a rated capacity of 24 Ah was obtained.

<Example 2>
As shown in Table 1, a nonaqueous electrolyte secondary battery according to Example 2 was obtained in the same manner as in Example 1 except that hollow particles having an average particle diameter of 3 μm were used as the hollow body 12. .

<Example 3>
As shown in Table 1, a nonaqueous electrolyte secondary battery according to Example 3 was obtained in the same manner as in Example 1 except that hollow particles having an average particle diameter of 12 μm were used as the hollow body 12. .

<Example 4>
In the composite processing of the particles, 100 parts by mass of the first positive electrode active material particles 14 are added to 10 parts by mass of the hollow body 12 to obtain the composite particles 10, and the mixture of the positive electrode mixture is mixed with the second positive electrode active material. Material particle: first positive electrode active material particle: hollow body: conductive material: binder = 90: 10: 1: 4: 2 (mass ratio) A nonaqueous electrolyte secondary battery according to Example 4 was obtained.

<Example 5>
In the composite processing of the particles, 100 parts by mass of the first positive electrode active material particles 14 are added to 50 parts by mass of the hollow body 12 to obtain the composite particles 10, and the mixture of the positive electrode mixture is mixed with the second positive electrode active material. Material particle: first positive electrode active material particle: hollow body: conductive material: binder = 90: 10: 5: 4: 2 (mass ratio) A nonaqueous electrolyte secondary battery according to Example 5 was obtained.

<Example 6>
As shown in Table 1, as the hollow body 12, Example 1 except that hollow particles having an average particle diameter of 6 μm and an average inner diameter of 1.5 μm (average hollowness: 25%) are used. Similarly, a nonaqueous electrolyte secondary battery according to Example 6 was obtained.

<Example 7>
As shown in Table 1, as the hollow body 12, Example 1 is used except that hollow particles having an average particle diameter of 6 μm and an average inner diameter of 4.5 μm (average hollowness: 75%) are used. In the same manner, a nonaqueous electrolyte secondary battery according to Example 7 was obtained.

<Example 8>
As shown in Table 1, a nonaqueous electrolyte secondary battery according to Example 8 is obtained in the same manner as in Example 1 except that hollow particles having an average particle diameter of 1 μm are used as the hollow body 12. It was.

<Example 9>
As shown in Table 1, a nonaqueous electrolyte secondary battery according to Example 9 is obtained in the same manner as in Example 1 except that hollow particles having an average particle diameter of 15 μm are used as the hollow body 12. It was.

<Example 10>
In the composite treatment of the particles, 100 parts by mass of the first positive electrode active material particles 14 are added to 5 parts by mass of the hollow body 12 to obtain the composite particles 10, and the mixture of the positive electrode mixture is mixed with the second positive electrode active material. Material particles: first positive electrode active material particles: hollow body: conductive material: binder = 90: 10: 0.5: 4: 2 (mass ratio) A nonaqueous electrolyte secondary battery according to Example 10 was obtained.

<Example 11>
In the composite processing of particles, 100 parts by mass of the first positive electrode active material particles 14 are added to 70 parts by mass of the hollow body 12 to obtain the composite particles 10, and the mixture of the positive electrode mixture is mixed with the second positive electrode active material. Material particle: first positive electrode active material particle: hollow body: conductive material: binder = 90: 10: 7: 4: 2 (mass ratio) A nonaqueous electrolyte secondary battery according to Example 11 was obtained.

<Example 12>
As shown in Table 1, the hollow body 12 was the same as in Example 1 except that hollow particles having an average particle diameter of 6 μm and an average inner diameter of 1 μm were used (average hollowness: 17%). Thus, a nonaqueous electrolyte secondary battery according to Example 12 was obtained.

<Example 13>
As shown in Table 1, the hollow body 12 was the same as in Example 1 except that hollow particles having an average particle diameter of 6 μm and an average inner diameter of 5 μm (average hollowness: 83%) were used. Thus, a nonaqueous electrolyte secondary battery according to Example 13 was obtained.

<Comparative Example 1>
Without mixing the hollow body 12 and the first positive electrode active material particles 14, by simply mixing only the first positive electrode active material particles 14 with the positive electrode mixture, Second positive electrode active material particle: first positive electrode active material particle: hollow body: conductive material: binder = 90: 10: 0: 4: 2 (mass ratio) The same as in Example 1 Thus, a nonaqueous electrolyte secondary battery according to Comparative Example 1 was obtained.

<Comparative example 2>
Without compounding the hollow body 12 and the first positive electrode active material particles 14, these are simply mixed with the positive electrode mixture, thereby mixing the positive electrode mixture into the second positive electrode active material particles: Comparative Example 2 is the same as Example 1 except that the first positive electrode active material particle: hollow body: conductive material: binder = 90: 10: 3: 4: 2 (mass ratio). Such a non-aqueous electrolyte secondary battery was obtained.

<Comparative Example 3>
Without compounding the hollow body 12 and the first positive electrode active material particles 14, only the hollow body 12 is simply mixed with the positive electrode mixture, thereby mixing the positive electrode mixture into the second positive electrode active material. Material particle: 1st positive electrode active material particle: Hollow body: Conductive material: Binder = 100: 0: 3: 4: 2 (mass ratio) A nonaqueous electrolyte secondary battery according to Example 2 was obtained.

＜評価＞
以上のようにして得られた各電池の性能を以下のようにして評価した。なお、以下の説明において電流値の単位「Ｃ」は電池の定格容量を１時間で放電する電流値を示すものとする。また「ＣＣ」は定電流を、「ＣＶ」は定電圧を、「ＣＰ」は定電力をそれぞれ示すものとする。

<Evaluation>
The performance of each battery obtained as described above was evaluated as follows. In the following description, the unit of current value “C” represents the current value for discharging the rated capacity of the battery in one hour. “CC” represents a constant current, “CV” represents a constant voltage, and “CP” represents a constant power.

(Measurement of initial capacity)
First, in a normal temperature (about 25 ° C.) environment, the battery was charged to 4.1 V at a current value of 1 C (24 A), then rested for 5 minutes, and further discharged to 3.0 V at a current value of 1 C, and then rested for 5 minutes.

  Next, CC-CV charge (CC current value: 1C, CV voltage: 4.1V, end current: 0.1C) and CC-CV discharge (CC current value: 1C, CV voltage: 3.0V, end current) : 0.1 C) and the initial capacity (discharge capacity) was measured.

(Capacity maintenance rate after cycle endurance)
Charge / discharge cycle with CC charge (current value: 2C, end voltage: 4.1V) and CC discharge (current value: 2C, end voltage: 3.0V) as one cycle in a thermostat set to 50 ° C Was executed 1000 cycles.

  After 1000 cycles, the capacity after the cycle was measured again under the same conditions as the “measurement of the initial capacity”, and the percentage of the value obtained by dividing the capacity after the cycle by the initial capacity was defined as the capacity maintenance ratio after the cycle endurance. The results are shown in Table 2. The numerical values shown in the column “Capacity maintenance ratio after cycle endurance” in Table 2 are arithmetic average values for five batteries.

(IV resistance value)
In a 25 ° C. environment, the SOC of the battery was adjusted to 60%, a current value of 10 C (240 A) was applied, and pulse discharge was performed for 10 seconds to measure the amount of voltage drop. The IV resistance value was calculated from the relationship between the current value and the voltage drop amount. The results are shown in Table 2. In addition, the numerical value shown in the column of “IV resistance value” in Table 2 is an arithmetic average value for 10 batteries.

(Constant power output value in low SOC range)
In a thermostatic chamber set at 25 ° C., after charging to 4.1 V with a current value of 0.2 C (4.8 A), pause for 5 minutes and then discharge to 3.0 V with a current value of 0.2 C. To confirm the capacity. And based on the confirmed capacity | capacitance, the electric charge equivalent to SOC20% was provided to the battery.

  Next, after leaving the battery in a thermostat set at −15 ° C. for 4 hours, CP discharge is performed for 8 to 12 seconds, and a constant power output value that reaches 2.5 V in 10 seconds is obtained. It was measured. The results are shown in Table 2. In addition, the numerical value shown in the column of “low SOC constant power output value” in Table 2 is an arithmetic average value for 10 batteries.

(Capacity maintenance rate after charging and storage durability)
The SOC of the battery was adjusted to 100% in a 25 ° C. environment. And the battery was preserve | saved for 100 days in the thermostat set to 60 degreeC. After 100 days, the battery was taken out, and the capacity after storage was measured under the same conditions as in “Measurement of initial capacity”. And the percentage of the value obtained by dividing the capacity after storage by the initial capacity was taken as the capacity maintenance ratio after the charge storage durability. The results are shown in Table 2. In addition, the numerical value shown in the column of “Capacity maintenance ratio after charge storage durability” in Table 2 is an arithmetic average value for 50 batteries.

(CID operation rate in overcharge test after charge storage durability)
An overcharge test was performed under the following conditions using a battery that had been charged and stored under the same conditions as the above "capacity maintenance ratio after charge storage durability". And the presence or absence of the action | operation of CID was confirmed by measuring the voltage of the battery after a test. The results are shown in Table 2. In Table 2, the numerical value shown in the column “CID operation rate in overcharge test after endurance of charge storage” indicates the number of batteries in which CID is operated out of 10 batteries.

Charging current: 1C (24A)
Charging upper limit voltage: 20V
Environmental temperature: 25 ° C.

＜結果と考察＞
（ｉ）複合粒子について
比較例１は、中空体を有さず、従来技術の如く、第１正極活物質粒子（ＬｉＦｅＰＯ₄／Ｃ）と第２正極活物質粒子（ＬｉＮｉ_1/3Ｃｏ_1/3Ｍｎ_1/3Ｏ₂）とを含む混合正極を備えるものである。比較例１は、初期においては低ＳＯＣ領域での出力特性に優れるものの、サイクル耐久後および充電保存耐久後における容量維持率が低く、さらには充電保存耐久後におけるＣＩＤ作動率が低い。この理由は、第１正極活物質粒子（ＬｉＦｅＰＯ₄／Ｃ）が本来の作動電位よりも高い電位で使用されるため、当該粒子の膨張・収縮量が大きくなり、電極内の導電ネットワークが寸断されるとともに、電極から電解液が吐出されて、液枯れを来すからであると考えられる。

<Results and discussion>
(I) Composite Particles Comparative Example 1 does not have a hollow body, and as in the prior art, the first positive electrode active material particles (LiFePO ₄ / C) and the second positive electrode active material particles (LiNi _1/3 Co _{1 / 3} Mn _1/3 O ₂ ). Although Comparative Example 1 is excellent in output characteristics in the low SOC region in the initial stage, the capacity retention rate after cycle endurance and after charge storage endurance is low, and further, the CID operation rate after charge storage endurance is low. This is because the first positive electrode active material particles (LiFePO ₄ / C) are used at a potential higher than the original operating potential, so that the amount of expansion / contraction of the particles increases and the conductive network in the electrode is cut off. In addition, it is considered that the electrolyte solution is discharged from the electrode, resulting in liquid drainage.

Although the comparative example 2 has a hollow body, the improvement effect of the capacity retention rate after cycle endurance and after charge storage endurance is limited. Although Comparative Example 2 includes the hollow body and the first positive electrode active material particles, these are simply mixed with the positive electrode mixture and do not form composite particles. Therefore, it is considered that excessive expansion / contraction of the first positive electrode active material particles (LiFeO ₄ / C), which is the basis of output deterioration, cannot be efficiently absorbed.

In contrast to these comparative examples, in the examples provided with composite particles including the hollow body and the first positive electrode active material particles supported on the outer shell of the hollow body, the output characteristics in the low SOC region are excellent and after durability It can be confirmed that the capacity maintenance rate of the is high. The reason for this is that the hollow body forming the composite particles efficiently absorbs the excessive expansion / contraction of the first positive electrode active material particles (LiFeO ₄ / C), and retains the electrolyte so that the liquid withering proceeds. This is thought to be because it hinders.

(Ii) About average particle diameter of hollow body When Examples 1, 2, and 8 having different average particle diameters of hollow bodies are compared, Example 1 and 2 both show excellent performance, while Example 8 shows As a result, the capacity retention rate after charge storage durability was inferior. The reason for this is considered that Example 8 had a small average particle diameter of the hollow body, and therefore the amount of electrolyte solution that could be held inside the hollow body was reduced. Therefore, from these results, the average particle diameter of the hollow body is preferably 1 μm or more, more preferably 3 μm or more.

  When Examples 1, 3 and 9 were compared, Examples 1 and 3 both showed excellent performance, while Example 9 was inferior in capacity retention after cycle endurance compared to these. This is because in Example 9, since the average particle diameter of the hollow body is large, the surface of the hollow body cannot be sufficiently covered with the first positive electrode active material particles, and the conductivity of the composite particles is reduced, resulting in resistance. It is thought that this is because of the increase. Therefore, from these results, the average particle diameter of the hollow body is preferably 15 μm or less, more preferably 12 μm or less.

(Iii) About the compounding quantity of a hollow body When Example 1, 4 and 10 from which the compounding quantity of the hollow body in a compounding process differs is compared, Example 1 and 4 show the outstanding performance, Example 10 is The result after the endurance was inferior. The reason for this is considered that Example 10 could not sufficiently relax the expansion and contraction of the first positive electrode active material particles because the amount of the hollow body was small. Therefore, from these results, the hollow body is preferably blended in the range of 5 parts by mass or more, more preferably in the range of 10 parts by mass or more, with respect to 100 parts by mass of the first positive electrode active material particles.

  Further, when Examples 1, 5 and 11 were compared, Examples 1 and 5 both showed excellent performance, while Example 11 resulted in inferior IV resistance and output characteristics in a low SOC region. The reason for this is considered that Example 11 has an increased resistance due to the large amount of hollow body (resin component) in the electrode. Therefore, from these results, the hollow body is preferably blended in the range of 70 parts by mass or less and more preferably in the range of 50 parts by mass or less with respect to 100 parts by mass of the first positive electrode active material particles.

(Iv) About average hollowness of hollow body When Examples 1, 6 and 12 having different average hollowness of hollow bodies are compared, Examples 1 and 6 both show excellent performance, while Example 12 shows cycle durability. The result was inferior in performance after and after charging and storage durability. The reason for this is considered that Example 12 has a low average hollowness, so that the flexibility of the hollow body is lowered, and the followability to expansion / contraction of the first positive electrode active material particles is lowered. Therefore, from these results, the average hollowness of the hollow body is preferably 17% or more, more preferably 25% or more.

  Further, when Examples 1, 7 and 13 were compared, Examples 1 and 7 both showed excellent performance, while Example 13 resulted in inferior performance after cycle endurance and after charge storage endurance. The reason for this is thought to be that Example 13 has a high average hollowness, so that the elasticity of the hollow body is reduced, it becomes difficult to restore the shape after deformation, and the amount of electrolyte that can be held inside the hollow body is gradually reduced. It is done. Therefore, from these results, the average hollowness of the hollow body is preferably 83% or less, and more preferably 75% or less.

(V) About Comparative Example 3 The second positive electrode active material particles (LiNi _1/3 ) which are not provided with the first positive electrode active material particles (LiFePO ₄ / C) which are 3V class positive electrode active materials and which are 4V class positive electrode active materials. In Comparative Example 3 including only Co _1/3 Mn _1/3 O ₂ ), the constant power output value in the low SOC region is not sufficient. Therefore, from the viewpoint of expanding the low SOC region, it can be said that the non-aqueous electrolyte secondary battery preferably includes two or more positive electrode active materials having different operating potentials.

From the above experimental results, it can be said that the following items were proved.
(1) The non-aqueous electrolyte secondary battery includes composite particles including a hollow body and first positive electrode active material particles supported on the outer shell of the hollow body, thereby improving cycle durability and charge storage durability. To do.

  (2) The nonaqueous electrolyte secondary battery further includes second positive electrode active material particles, and the Li-based average discharge potential of the first positive electrode active material particles is greater than the Li-based average discharge potential of the second positive electrode active material particles. By adopting a low configuration, the output characteristics of the low SOC region can be improved while maintaining the capacity of the high SOC region. And the said nonaqueous electrolyte secondary battery is a battery with little fall of an output characteristic after durability.

  Although the present embodiment and examples have been described above, the embodiments and examples disclosed this time are illustrative in all points and are not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Composite particle, 12 Hollow body, 14 1st positive electrode active material particle, 16 Conductive layer, 100 Positive electrode plate, 100a Positive electrode current collection core material, 100b Positive electrode compound material part, 102 Positive electrode current collection plate, 104 Positive electrode terminal, 200 Negative electrode plate , 200a Negative electrode current collector core, 200b Negative electrode mixture part, 202 Negative electrode current collector plate, 204 Negative electrode terminal, 300 Separator, 400 Electrode body, 500 Exterior body, 1000 Battery, SH outer shell, HL cavity, OP opening, OD Outer diameter, ID inner diameter, AW winding axis L1, L2 Longitudinal length dimension, W1, W2 Short dimension length dimension.

Claims (7)

Composite particles comprising a hollow body and first positive electrode active material particles carried on the outer shell of the hollow body ;
For example Bei an electrolytic solution and,
The outer shell of the hollow body is made of a resin material,
The non-aqueous electrolyte secondary battery , wherein the resin material has elasticity and has resistance to the electrolytic solution .   The nonaqueous electrolyte secondary battery according to claim 1, wherein the hollow body has an opening communicating with an internal cavity in the outer shell. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the resin material is an acrylic resin, a styrene resin, or a fluorine resin .   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the first positive electrode active material particles have a conductive layer on a surface thereof. The non-aqueous electrolyte secondary battery further includes second positive electrode active material particles,
The lithium-based average discharge potential of the first positive electrode active material particles is lower than the lithium-based average discharge potential of the second positive electrode active material particles, according to any one of claims 1 to 4. Water electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the first positive electrode active material particles include a lithium-containing phosphate having an olivine structure.   The nonaqueous electrolyte secondary battery according to claim 5, wherein the second positive electrode active material particles include a lithium nickel composite oxide.

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