JP2019021585A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a nonaqueous electrolyte secondary battery with trilithium phosphate added to a positive electrode mixture layer, which can be manufactured with a small resistance at a high productivity.SOLUTION: A nonaqueous electrolyte secondary battery herein disclosed comprises: a positive electrode with a positive electrode mixture layer formed on a positive electrode current collector; a negative electrode; and a nonaqueous electrolyte solution. The positive electrode mixture layer includes at least a positive electrode active material and trilithium phosphate particles. The product of a maximum diameter (μm) of the trilithium phosphate particles and a collapse force (mN) of the trilithium phosphate particles is 1.2 or more and 3150 or less.SELECTED DRAWING: Figure 1

Description

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

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries (lithium secondary batteries) are lighter and have higher energy density than existing batteries. It is used as a driving power source. The positive electrode of such a nonaqueous electrolyte secondary battery is configured, for example, by applying a positive electrode mixture layer to the surface of a positive electrode current collector that is a conductive foil.

In the above non-aqueous electrolyte secondary battery, in order to suppress various problems that occur when a high voltage state is reached, an inorganic material such as trilithium phosphate (Li ₃ PO ₄ ) has been conventionally used for the positive electrode mixture layer. A technique for adding a phosphoric acid compound has been proposed (see, for example, Patent Document 1). Such an inorganic phosphoric acid compound is formed by adsorbing an acid (for example, hydrogen fluoride (HF)) generated by the decomposition of the non-aqueous electrolyte to the particle surface when the battery is in a high voltage state, thereby causing the inorganic phosphoric acid compound to separate from the positive electrode active material. This prevents the transition metal from eluting and suppresses the deterioration of the non-aqueous electrolyte secondary battery.

JP 2014-103098 A

  In recent years, with the spread of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, further higher performance (for example, small battery resistance) is desired. Moreover, it is desired that it can be manufactured with high productivity.

  The present invention has been made in view of the above points, and an object thereof is a non-aqueous electrolyte secondary battery in which trilithium phosphate is added to a positive electrode mixture layer, which has low resistance and high productivity. A non-aqueous electrolyte secondary battery that can be manufactured is provided.

  In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary battery having the following configuration.

  The non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode having a positive electrode mixture layer formed on a positive electrode current collector, a negative electrode, and a non-aqueous electrolyte. The positive electrode mixture layer contains at least a positive electrode active material and trilithium phosphate particles. The product of the maximum diameter (μm) of the trilithium phosphate particles and the crushing force (mN) of the trilithium phosphate particles is 1.2 or more and 3150 or less.

When the product is 1.2 or more, the resistance of the nonaqueous electrolyte secondary battery can be sufficiently reduced. On the other hand, when the above product is 3150 or less, clogging of the filter can be suppressed during manufacturing (especially in the impurity removal step before the positive electrode mixture coating step), and the non-aqueous electrolyte secondary battery is high. Can be manufactured with productivity.
Therefore, according to such a configuration, the non-aqueous electrolyte secondary battery in which trilithium phosphate is added to the positive electrode mixture layer has a low resistance and can be manufactured with high productivity. A secondary battery can be provided.

It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a perspective view which shows typically the electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a graph which shows the evaluation result of the resistance increase ratio in a test example. It is a graph which shows the evaluation result of the filter trap rate in a test example.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, members / parts having the same action are denoted by the same reference numerals. In addition, the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. In addition, matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, general techniques relating to the construction of non-aqueous electrolyte secondary batteries) It can be grasped as a design matter of those skilled in the art based on the prior art.

  Hereinafter, a lithium ion secondary battery will be described as an example of the nonaqueous electrolyte secondary battery disclosed herein. FIG. 1 is a perspective view schematically showing an outer shape of a lithium ion secondary battery according to this embodiment, and FIG. 2 is a perspective view schematically showing an electrode body of the lithium ion secondary battery according to this embodiment. . The lithium ion secondary battery 100 is configured by housing an electrode body 80 shown in FIG. 2 inside a rectangular battery case 50 shown in FIG.

(1) Battery Case The battery case 50 includes a flat case body 52 having an open upper end, and a lid 54 that closes an opening at the upper end. The lid 54 is provided with a positive terminal 70 and a negative terminal 72. Although not shown, the positive electrode terminal 70 is electrically connected to the positive electrode 10 of the electrode body 80 accommodated in the battery case 50, and the negative electrode terminal 72 is electrically connected to the negative electrode 20. The battery case 50 is made of, for example, aluminum.

(2) Electrode body Next, the electrode body 80 accommodated in the battery case 50 described above will be described. As shown in FIG. 2, the electrode body 80 in this embodiment is a wound electrode body produced by laminating and winding a long sheet-like positive electrode 10 and a negative electrode 20 together with a long sheet-like separator 40. It is. In addition, the electrode body used for the non-aqueous electrolyte secondary battery disclosed here is not limited to the wound electrode body as shown in FIG. 2, for example, a plurality of positive electrodes and negative electrodes are interposed via a separator. It may be a laminated electrode body laminated alternately.

(A) Positive Electrode In the positive electrode 10 in FIG. 2, a positive electrode mixture layer 14 is formed on both surfaces of a long sheet-like positive electrode current collector 12. A positive electrode mixture layer non-formation portion 16 that is not coated with the positive electrode mixture layer 14 is formed on one side edge in the width direction of the positive electrode 10, and the positive electrode mixture layer non-formation portion 16 is formed. Is electrically connected to the positive electrode terminal 70 (see FIG. 1) described above.

The positive electrode mixture layer 14 contains a positive electrode active material as a main component and trilithium phosphate (Li ₃ PO ₄ ) particles.
The positive electrode active material is a compound capable of reversibly occluding and releasing lithium ions, and is composed of an oxide containing at least lithium (lithium composite oxide). In the present embodiment, the type of the positive electrode active material is not particularly limited, and the same positive electrode active material as that of a general lithium ion secondary battery can be used. Specific examples of such a positive electrode active material include lithium nickel composite oxide, lithium nickel cobalt composite oxide, lithium nickel cobalt manganese composite oxide, and the like. As the positive electrode active material, the working potential is preferably less than 4.3 V (vs. Li ^/ Li ⁺ ) because the effect of the present invention is particularly high, and is preferably 4.25 V (vs. Li ^/ Li ⁺ ) or less. More preferable is 4.2V (vs. Li ^/ Li ⁺ ) or less.
Although there is no restriction | limiting in particular in the average particle diameter of trilithium phosphate, For example, they are 0.2 micrometer or more and 75 micrometers or less. The average particle diameter of trilithium phosphate can be determined by measurement according to a known method. For example, it can be determined by a laser diffraction / scattering method.
The content of trilithium phosphate in the positive electrode mixture layer 14 is, for example, 0.5% by mass or more and 10% by mass or less, preferably 1% by mass or more and 8% by mass or less, and more preferably 1.5% by mass. % To 6% by mass.
In addition, the positive electrode mixture layer 14 may contain additives such as a conductive agent and a binder, as in a general lithium ion secondary battery. As the conductive agent, for example, a carbon material such as carbon black can be used. As the binder, for example, polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO) and the like can be preferably used.
Further, the positive electrode mixture layer 14 may contain a metal element such as Si, Na, K, Cl, Fe, Cu, Zn, Pb, Ni, Co, and Cr. These metal elements are contained in the trilithium phosphate powder when the paste-like positive electrode mixture is prepared, and these metal elements are contained in the positive electrode mixture layer 14. However, heat generation during overcharge and elution of metal elements can be suitably suppressed, and problems that may occur due to the addition of trilithium phosphate, such as reduced productivity and increased reaction resistance, are prevented. be able to.

  The positive electrode, for example, after preparing a paste-like positive electrode mixture containing a positive electrode active material, trilithium phosphate, etc., and removing impurities by filtration using a filter having a predetermined opening (for example, 50 μm or less), The positive electrode mixture can be produced by coating the positive electrode current collector 12 on the positive electrode current collector 12 and drying it, followed by appropriate press treatment.

(B) Negative Electrode Similarly to the positive electrode 10, the negative electrode 20 has a negative electrode mixture layer 24 mainly composed of a negative electrode active material on both surfaces of a long sheet-like negative electrode current collector 22. A negative electrode mixture layer non-formed portion 26 is formed at one side edge in the width direction of the negative electrode 20, and the negative electrode mixture layer non-formed portion 26 is electrically connected to the negative electrode terminal 72 (see FIG. 1). Connected.

The negative electrode mixture layer 24 contains a negative electrode active material.
As the negative electrode active material, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotube, or a combination of these can be used. . From the viewpoint of energy density, it is preferable to use graphite-based materials (natural graphite (graphite), artificial graphite, etc.) among these carbon materials. The content of the negative electrode active material in the negative electrode mixture layer 24 is, for example, 85% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more.
The negative electrode mixture layer 24 may contain other additives (such as a binder and a thickener). Examples of the binder include styrene butadiene rubber (SBR). Examples of the thickener include carboxymethyl cellulose (CMC).

(C) Separator A strip-shaped sheet material having a predetermined width and having a plurality of minute holes is used for the separator 40. The separator 40 can be the same as that used in a general lithium ion secondary battery, and for example, a sheet material made of a porous polyolefin resin or the like can be used.

(3) Nonaqueous Electrolyte The battery case 50 of the lithium ion secondary battery 100 according to this embodiment contains (fills) the nonaqueous electrolyte together with the wound electrode body 80 described above. As such a non-aqueous electrolyte, typically, a non-aqueous solvent such as carbonates containing a supporting salt is used. For example, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate ( A mixed solvent with EMC) (for example, volume ratio 3: 4: 3) containing a supporting salt at a predetermined concentration (for example, about 1 mol / L) can be used. As the supporting salt, a lithium compound containing fluorine is typically used, and examples thereof include LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3, and the} like.

(4) Product of maximum diameter of trilithium phosphate particles and crushing force of trilithium phosphate particles In the lithium ion secondary battery 100 according to this embodiment, the maximum diameter (μm) of trilithium phosphate particles, The product of the trilithium phosphate particles and the crushing force (mN) is 1.2 or more and 3150 or less.
When the above product is less than 1.2, the particles become minute, the specific surface area of the particles increases, and the resistance increases. Therefore, when the above product is 1.2 or more, the resistance of the lithium ion secondary battery 100 (particularly, the resistance in the low SOC region) can be sufficiently reduced. Moreover, when the product is less than 1.2, an excessive increase in viscosity of the paste-like positive electrode mixture can be suppressed.
On the other hand, when forming the positive electrode mixture layer 14, a paste-like positive electrode mixture containing a positive electrode active material, trilithium phosphate, or the like is applied onto the positive electrode current collector 12. Prior to coating, filtration is performed to remove impurities from the positive electrode mixture. However, if the product exceeds 3150, the filter used for filtration is likely to be clogged, and productivity is reduced. . Therefore, when the product is 3150 or less, the lithium ion secondary battery 100 can be manufactured with high productivity.
Therefore, when the above product is 1.2 or more and 3150 or less, it is possible to achieve both low battery resistance and high productivity.

The maximum particle size of the trilithium phosphate particles can be determined by measurement according to a known method. For example, it can be determined by a laser diffraction / scattering method.
The crushing force of the trilithium phosphate particles is a crushing force of one particle, and can be determined by measuring according to a known method. For example, it can be measured using a known fine particle crushing force measuring device.

  The lithium ion secondary battery 100 configured as described above can be used for various applications. Suitable applications include driving power sources mounted on vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). The lithium ion secondary battery 100 can also be used in the form of a battery pack typically formed by connecting a plurality of lithium ion secondary batteries 100 in series and / or in parallel.

In the above-described embodiment, the lithium ion secondary battery has been described as an example of the non-aqueous electrolyte secondary battery disclosed herein. However, the description is intended to limit the application target of the present invention. Instead, the present invention can also be applied to non-aqueous electrolyte secondary batteries other than lithium ion secondary batteries. However, as described above, a lithium ion secondary battery (4V class battery) using a positive electrode active material (for example, lithium nickel cobalt manganese composite oxide) having an operating potential of less than 4.3 V (vs. Li ^/ Li ⁺ ) Is particularly preferable as an application target of the present invention because it has a property of generating a large amount of heat when it is in an overcharged state and can exhibit the effects of the present invention more remarkably.

[Test example]
Hereinafter, although the test example regarding this invention is demonstrated, description of the said test example is not intended to limit this invention.

(1) Production of Lithium Ion Secondary Batteries of Test Examples 1 to 13 Lithium nickel cobalt manganese composite oxide as a positive electrode active material, trilithium phosphate (Li ₃ PO ₄ ) particles, and conductive material (AB) : Acetylene black) and a binder (PVDF) were dispersed in a dispersion medium (NMP: N methylpyrrolidone) to prepare a paste-like positive electrode mixture. At this time, trilithium phosphate particles having the maximum particle diameter (μm) and crushing force (mN) shown in Table 1 were used. The crushing force was measured with a commercially available fine particle crushing force measuring device. The prepared positive electrode mixture was filtered with a filter having an opening of 50 μm, and then applied to both surfaces of the positive electrode current collector (aluminum foil). Then, it dried and produced the sheet-like positive electrode by pressing at a predetermined pressure.

  Next, a negative electrode active material (graphite), a binder (SBR: styrene butadiene rubber), and a thickener (CMC) were mixed in a dispersion medium (water) to prepare a paste-like negative electrode mixture. Then, the prepared negative electrode mixture was applied to both surfaces of a sheet-like negative electrode current collector (copper foil), dried, and then pressed to prepare a sheet-like negative electrode.

And after laminating | stacking a positive electrode and a negative electrode through a separator, a winding electrode body is produced by winding this laminated body, and this winding electrode body is accommodated in a battery case with a nonaqueous electrolyte solution, and is sealed. Thus, lithium ion secondary batteries of Test Example 1 to Test Example 13 were produced. These lithium ion secondary batteries are 4V class lithium ion secondary batteries. The non-aqueous electrolyte includes a mixed solvent containing EC, DMC, and EMC at a volume ratio of 3: 4: 3, and a supporting salt (LiPF ₆ ) at a concentration of about 1 mol / liter. It was used.

(2) Evaluation test (a) Battery resistance evaluation The 4V class lithium ion secondary battery of each test example was adjusted to the state of SOC20% in the temperature environment of 25 degreeC. Next, under a temperature environment of 25 ° C., the battery was subjected to constant current discharge at a rate of 125 A for 10 seconds, and the amount of voltage drop was measured. Next, the IV resistance was calculated by dividing the voltage drop by the discharge current value. For the IV resistance obtained for each battery, a ratio was calculated when a predetermined reference value was set to 100. The results are shown in Table 1 and FIG.

(B) Filter trap rate When the prepared positive electrode mixture was filtered with a filter having an opening of 50 µm, the frequency (ratio) at which the filter clogged was calculated. The results are shown in Table 1 and FIG.

(3) Test results As shown in Table 1 and FIG. 3, the product of the maximum particle size (μm) and the crushing force (mN) of the trilithium phosphate particles is 1.2 or more. It can be seen that the resistance of the secondary battery 100 can be sufficiently reduced. On the other hand, as the results of Table 1 and FIG. 4 show, the product of the maximum particle diameter (μm) and the crushing force (mN) of the trilithium phosphate particles is 3150 or less, which means It can be seen that the clogging of the filter is suppressed and the lithium ion secondary battery 100 can be manufactured with high productivity (in the impurity removal step before the processing step).
Accordingly, the product of the product of the maximum particle size (μm) and the crushing force (mN) of the trilithium phosphate particles is 1.2 or more and 3150 or less, so that both low battery resistance and high productivity can be achieved. I understand.

  As mentioned above, although this invention was demonstrated in detail, above-described embodiment is only an illustration and what changed and modified the above-mentioned specific example is contained in the invention disclosed here.

DESCRIPTION OF SYMBOLS 10 Positive electrode 12 Positive electrode collector 14 Positive electrode mixture layer 16 Positive electrode mixture layer non-formation part 20 Negative electrode 22 Negative electrode collector 24 Negative electrode mixture layer 26 Negative electrode mixture layer non-formation part 40 Separator 50 Battery case 52 Case main body 54 Cover Body 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Lithium ion secondary battery

Claims (1)

A positive electrode in which a positive electrode mixture layer is formed on the positive electrode current collector;
A negative electrode,
A non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising:
The positive electrode mixture layer contains at least a positive electrode active material and trilithium phosphate particles,
The product of the maximum diameter (μm) of the trilithium phosphate particles and the crushing force (mN) of the trilithium phosphate particles is 1.2 or more and 3150 or less.
Non-aqueous electrolyte secondary battery.

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