JP5740708B2 - Non-aqueous electrolyte secondary battery positive electrode, non-aqueous electrolyte secondary battery, and battery module - Google Patents

Description

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a battery module.

In recent years, non-aqueous electrolyte secondary batteries containing olivine-type lithium composite compound particles as positive electrode active materials have been proposed and put into practical use as batteries expected to be reduced in size, weight, and capacity (for example, (See Patent Documents 1 and 2).
This non-aqueous electrolyte secondary battery uses a positive electrode using a lithium-containing phosphate compound having an olivine structure, and a lithium-containing metal oxide having a property capable of reversibly removing and inserting lithium ions such as carbon-based materials. And a non-aqueous electrolyte.
In this positive electrode, a metal foil referred to as a current collector is an electrode material mixture containing olivine type lithium composite compound particles such as lithium iron phosphate (LiFePO ₄ ) particles whose surfaces are coated with a carbonaceous film, and a binder. It is formed by applying to the surface.

  Such non-aqueous electrolyte secondary batteries are lighter and smaller than conventional secondary batteries such as lead batteries, nickel cadmium batteries, and nickel metal hydride batteries, and have high energy. It is used as a power source for portable electronic devices such as telephones and notebook personal computers. In recent years, non-aqueous electrolyte secondary batteries have also been studied as high-output power sources for electric vehicles, hybrid vehicles, electric tools, etc., and batteries used as these high-output power sources have high-speed charge / discharge characteristics. Is required.

JP 2009-48958 A JP 2009-206085 A

By the way, in the positive electrode material of the conventional non-aqueous electrolyte secondary battery, the surface of the olivine-type lithium composite compound particles is not sufficiently covered with the carbonaceous film, so that lithium ions are taken in and released from the olivine-type lithium composite compound. Since the speed is low, that is, the charge transfer resistance is high, there is a problem that the overvoltage of the positive electrode becomes high.
When the overvoltage of the positive electrode becomes high, the electrode resistance at the time of charging / discharging also becomes high. As a result, the charge / discharge speed of the secondary battery becomes slow, resulting in a problem that the charge / discharge characteristics deteriorate. It will be.

  The present invention has been made in order to solve the above-described problems, and by increasing the lithium ion intake / release rate in the olivine-type lithium composite compound particles, the charge / discharge rate of the positive electrode is increased, and thus the secondary Positive electrode for non-aqueous electrolyte secondary battery with increased charge / discharge rate of battery, non-aqueous electrolyte secondary battery provided with positive electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery It aims at providing the battery module provided with the battery.

  As a result of intensive studies to solve the above problems, the present inventors have found that a non-aqueous electrolyte secondary solution containing olivine-type lithium composite compound particles having a carbonaceous film formed on the surface as a positive electrode active material In the positive electrode for a battery, if the coverage of the carbonaceous film with respect to the surface area of the olivine-type lithium composite compound particles is 95% or more, the lithium ion intake / release rate in the olivine-type lithium composite compound can be increased. It has been found that the charge / discharge rate of the positive electrode can be increased, and as a result, the charge / discharge rate of the secondary battery can be increased, and the present invention has been completed.

That is, the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention is a positive electrode for a non-aqueous electrolyte secondary battery comprising olivine-type lithium composite compound particles having a carbonaceous film formed on the surface as a positive electrode active material. the olivine-type lithium composite compound coverage of the carbonaceous coating to the surface area of the particles Ri der least 95%, packing density of the olivine-type lithium composite compound particles in the non-aqueous electrolyte secondary battery positive electrode, 0 characterized in that .90g / cm ³ or more and is 1.09 g / cm ³ or less.

The nonaqueous electrolyte secondary battery of the present invention includes the positive electrode for a nonaqueous electrolyte secondary battery of the present invention.
The battery module of the present invention includes the nonaqueous electrolyte secondary battery of the present invention.

  According to the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, since the coverage of the carbonaceous film with respect to the surface area of the olivine-type lithium composite compound particles having a carbonaceous film formed on the surface is 95% or more, The lithium ion intake / release rate in the olivine-type lithium composite compound can be increased, and the charge / discharge rate of the positive electrode can be increased. As a result, the charge / discharge rate of a secondary battery using the positive electrode for a non-aqueous electrolyte secondary battery can be increased.

  According to the non-aqueous electrolyte secondary battery of the present invention, since the positive electrode for the non-aqueous electrolyte secondary battery of the present invention is provided, the charge / discharge rate of the positive electrode can be improved. Therefore, the charge / discharge characteristics of the secondary battery can be improved.

  According to the battery module of the present invention, since the non-aqueous electrolyte secondary battery of the present invention is provided, the charge / discharge characteristics of the battery module can be improved.

It is a schematic sectional drawing of the vertical direction which shows the structure of the nonaqueous electrolyte secondary battery of one Embodiment of this invention. It is a schematic sectional drawing of the horizontal direction which shows the structure of the nonaqueous electrolyte secondary battery of one Embodiment of this invention. It is a perspective view which shows the electric power generation element of the nonaqueous electrolyte secondary battery of one Embodiment of this invention, (a) is a positive electrode, (b) is a negative electrode, (c) has arrange | positioned the positive electrode, the negative electrode, and the separator. Each state is shown. It is a figure which shows the charging / discharging characteristic of Example 1, 2 of this invention, and a comparative example.

The form for implementing the positive electrode for nonaqueous electrolyte secondary batteries of this invention, a nonaqueous electrolyte secondary battery, and a battery module is demonstrated.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

FIG. 1 is a schematic view in a vertical direction showing a configuration of a nonaqueous electrolyte secondary battery (hereinafter also simply referred to as “secondary battery”) including a positive electrode for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. Sectional drawing and FIG. 2 are schematic sectional drawings of the horizontal direction which shows the structure of the secondary battery.
The secondary battery 1 of the present embodiment is called a lithium ion secondary battery, and a lid member 3 is joined to an upper opening of a bottomed cylindrical case 2 made of stainless steel or the like to form a sealed structure. A power generation element 4 having a stack structure, a positive electrode connection terminal 5, a negative electrode connection terminal 6, and a nonaqueous electrolyte solution 7 are accommodated in the case 2, and the positive electrode connection terminal 5 and the negative electrode connection terminal 6 are provided with an insulator (not shown) on the lid member 3. The positive connection terminal 5 is connected to the positive external connection terminal 8, and the negative connection terminal 6 is connected to the negative external connection terminal 9.

In the power generation element 4, as shown in FIG. 3, sheet-like positive electrodes 11 and sheet-like negative electrodes 12 are alternately arranged with separators 13 interposed therebetween.
The positive electrode 11 includes a positive electrode current collector 21 and a positive electrode active material layer 22 formed on the positive electrode current collector 21. The positive electrode active material layer 22 may be formed only on one surface of the positive electrode current collector 21 or may be formed on both surfaces of the positive electrode current collector 21. These positive electrode current collectors 21 are connected to the positive electrode connection terminal 5 by bundling ends where the positive electrode active material layer 22 is not formed.

The positive electrode current collector 21 is not particularly limited as long as it has electrical conductivity and can form the positive electrode active material layer 22 on the surface. For example, a metal foil is preferable. Aluminum foil is preferred.
The positive electrode active material layer 22 adds a conductive agent such as acetylene black, a binder such as polyvinylidene fluoride (PVdF), an organic solvent such as N-methyl-2-pyrrolidinone (NMP) to the positive electrode active material, The positive electrode active material layer slurry obtained by applying the agitated and kneaded slurry for the positive electrode current collector 21 on the positive electrode current collector 21 and heating and drying is used. As the positive electrode active material, an olivine type lithium composite having a carbonaceous film formed on the surface is used. Compound particles are preferably used.

  As the olivine type lithium composite compound particles having a carbonaceous film formed on the surface, (1) the surface of the olivine type lithium composite compound particles has a carbonaceous film formed at a surface coverage of almost 100%; (2) The surface of the primary particles of the olivine type lithium composite compound is formed with a carbonaceous film having a surface coverage of almost 100%, and the primary particles are bonded to each other through the carbonaceous film to form secondary particles. Any one or both of the aggregates of the olivine-type lithium composite compound particles can be used.

The olivine-type lithium composite compound particles, lithium cobaltate, lithium nickelate, lithium manganate, lithium titanate and _{Li x A y D z PO 4} ( where, A is Co, Mn, Ni, Fe, Cu, and Cr One or more selected from the group, D is selected from the group of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, rare earth elements One or two or more selected from the group of 0 <x <2, 0 <y <1.5, and 0 ≦ z <1.5) are preferred.

Here, for A, Co, Mn, Ni, and Fe are for D, and for D, Mg, Ca, Sr, Ba, Ti, Zn, and Al are in terms of high discharge potential, abundant resources, safety, etc. preferable.
Here, the rare earth elements are 15 elements of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu which are lanthanum series.
Among these lithium composite compounds, LiFePO ₄ is preferable.

The carbonaceous film formed on the surface of the olivine-type lithium composite compound particles is obtained by firing a carbon precursor such as pitch at 1000 ° C. or less in an inert atmosphere. Amorphous carbon).
The coverage of the carbonaceous film with respect to the surface area of the olivine-type lithium composite compound particles is preferably 95% or more.
Here, when the coverage of the carbonaceous film is less than 95%, the internal resistance of the olivine-type lithium composite compound particles is increased, and as a result, the lithium ion intake / release rate in the olivine-type lithium composite compound particles is reduced, This is not preferable because the charge / discharge rate of the positive electrode decreases.

The packing density of the olivine-type lithium composite compound particles having a carbonaceous film formed on the surface in the positive electrode active material layer 22 is preferably 0.90 g / cm ³ or more and 1.09 g / cm ³ or less.
Here, when the packing density is less than 0.90 g / cm ³ , the conductive resistance increases, which is not preferable. The upper limit value of 1.09 g / cm ³ for the packing density is a limit at which the olivine-type lithium composite compound particles are packed in the positive electrode, and it is difficult to increase the packing density beyond this value. When the packing density is 1.09 g / cm ³ , the conductive resistance of the positive electrode active material layer 25 approximates the resistance of amorphous carbon.

Here, the reason why the coverage of the carbonaceous film is 95% or more will be described in more detail.
In conventional olivine-type lithium composite compound particles having a carbonaceous film formed on the surface, the lithium ion incorporation / release rate in the lithium composite compound cannot be said to be fast enough to satisfy the requirements. In particular, at the end of charging / discharging, the conductive resistance of the positive electrode tends to increase, and the charge / discharge rate decreases.

The reason for this is that since there are many portions on the surface of the olivine-type lithium composite compound particles where no carbonaceous film exists, the electrons in the olivine skeleton adjacent to the Li ion reaction site of the olivine-type lithium composite compound particles It is considered that a part that is not covered with the carbonaceous film is formed at the receiving and receiving site, and it is difficult to take in and release Li ions in that part.
The reason why there are many parts where no carbonaceous film exists on the particle surface is considered to be that the coverage of the carbonaceous film on the surface of the olivine type lithium composite compound particle is low in the first place. It is conceivable that excessive stress is applied to the particles due to stirring and kneading when the slurry for the positive electrode active material layer is produced using the olivine type lithium composite compound particles, and the carbonaceous film is peeled off.

On the other hand, in the olivine type lithium composite compound particles having the carbonaceous film formed on the surface of the present invention, the coverage of the carbonaceous film is 95% or more, and therefore adjacent to the Li ion reaction site of the olivine type lithium composite compound particles. This is probably because the portion of the olivine skeleton that is not covered with the carbonaceous film at the electron transfer site is reduced, and the region where the incorporation and release of Li ions is inhibited is reduced.
In particular, when the coverage of the carbonaceous film is 100%, most of the electron transfer sites in the olivine skeleton adjacent to the Li ion reaction site of the olivine-type lithium composite compound particles are covered with the carbonaceous film. This is considered to be because there is no possibility that the intake and release of Li ions will be hindered.

The negative electrode 12 includes a negative electrode current collector 31 and a negative electrode active material layer 32 formed on the negative electrode current collector 31.
The negative electrode current collector 31 is not particularly limited as long as it has electrical conductivity and can form the negative electrode active material layer 32 on the surface. For example, a metal foil is preferable. Copper foil is preferred.
The negative electrode active material layer 32 is obtained by adding a conductive agent such as acetylene black, a binder such as polyvinylidene fluoride (PVdF), an organic solvent such as N-methyl-2-pyrrolidinone (NMP) to the negative electrode active material, The negative electrode active material layer slurry obtained by applying the agitated and kneaded slurry for the negative electrode current collector 31 to heat drying is used. Examples of the negative electrode active material include graphite (graphite), lithium metal, tin, and titanium. Lithium acid or the like is preferably used.

The separator 13 is not particularly limited as long as the separator 13 is disposed between the positive electrode 11 and the negative electrode 12 and can prevent a leakage current between the positive electrode 11 and the negative electrode 12. For example, a polyolefin microporous film is used. Preferably used.
The nonaqueous electrolytic solution 7 may be a solution containing an electrolyte involved in the battery reaction of the secondary battery 1 and is not particularly limited. For example, in the case of a lithium ion secondary battery, a lithium salt is dissolved in an organic solvent. An electrolyte solution is preferably used.

Next, the manufacturing method of the positive electrode of this embodiment is demonstrated.
First, olivine type lithium composite compound particles having a carbonaceous film formed on the surface, a conductive agent such as acetylene black, a binder such as polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidinone (NMP) A positive electrode active material layer slurry is prepared by stirring and kneading an organic solvent or the like.

By controlling the stirring / kneading time, the coverage of the carbonaceous film on the surface of the olivine-type lithium composite compound particles can be maintained at 95% or more.
In addition, the following effects can be achieved.
(1) In the case where the surface of the olivine type lithium composite compound particles has a carbonaceous film formed with a surface coverage of almost 100%, the carbonaceous film in the primary particle state is controlled by controlling the stirring and kneading time. Can suppress damage.
(2) The surface of the primary particles of the olivine type lithium composite compound is formed with a carbonaceous film having a predetermined thickness at a surface coverage of almost 100%, and the primary particles are bonded to each other through the carbonaceous film. In the case of aggregates of olivine-type lithium composite compound particles that form slabs, the carbonaceous film of the primary particles on the surface of the secondary particles is damaged by controlling the stirring and kneading time, and the secondary after pressing It is possible to suppress a decrease in the coating rate of the carbonaceous film of the primary particles outside the aggregate when the particles are collapsed to be in the form of discrete primary particles.

Next, this positive electrode active material layer slurry is applied to a uniform thickness on a positive electrode current collector using a roll coater or the like, and dried by heating. Thereby, a positive electrode active material layer is formed on the positive electrode current collector. This positive electrode active material layer may be formed only on one side of the positive electrode current collector or on both sides.
Next, the positive electrode current collector on which the positive electrode active material layer is formed is pressurized using a roll press or the like, and the thickness of the positive electrode active material layer is set to an appropriate thickness, whereby the positive electrode is completed.
When pressurizing with this roll press, the positive electrode active material layer after drying can be pressed to obtain good packing density and porosity as an electrode for a non-aqueous secondary battery. In particular, in the aggregate (2), the secondary particles are collapsed into discrete primary particles, and a positive electrode active material layer having a high packing density is formed.

In the secondary battery 1 of this embodiment, the positive electrode 11 and the negative electrode 12 are alternately arranged via the separator 13 to assemble the power generation element 4, and the power generation element 4 and the nonaqueous electrolyte solution 7 are stored in the case 2. The positive electrode connection terminal 5 and the positive electrode external connection terminal 8 are connected to the positive electrode 11, the negative electrode connection terminal 6 and the negative electrode external connection terminal 9 are connected to the negative electrode 12, and the positive electrode external connection terminal 8 and the negative electrode external connection terminal 9 are connected to the lid member 3. Complete by fixing.
The battery module of the present embodiment is completed by connecting a plurality of the secondary batteries 1 of the present embodiment in series or in parallel.

  According to the positive electrode for a secondary battery of this embodiment, since the coverage of the carbonaceous film with respect to the surface area of the olivine-type lithium composite compound particles having a carbonaceous film formed on the surface is 95% or more, the olivine-type lithium The lithium ion intake / release rate in the composite compound can be increased, and the charge / discharge rate of the positive electrode can be increased. As a result, the charge / discharge rate of a secondary battery using the positive electrode for a secondary battery can be increased.

  According to the secondary battery of this embodiment, since the positive electrode of this embodiment is provided, the charge / discharge rate of the positive electrode can be improved. Therefore, the charge / discharge characteristics of the secondary battery can be improved.

  According to the battery module of this embodiment, since the secondary battery of this embodiment is provided, the charge / discharge characteristics of the battery module can be improved.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

"Example 1"
Agglomerates of LiFePO ₄ particles (manufactured by Sumitomo Osaka Cement Co., Ltd.) with a primary particle size of 100% as the positive electrode active material and a primary particle size of 0.1 to 2 μm, and acetylene black as a conductive agent are bound. Polyvinylidene fluoride (PVdF) as an agent is weighed so as to be 100: 5: 7 (parts by mass), and acetylene black and polyvinylidene fluoride (PVdF) are N-methyl-2-pyrrolidinone (NMP) in a kneader. The mixture was stirred and kneaded. Then, the resulting mixture above LiFePO ₄ particles were charged into, for 90 minutes kneading the rotational speed of the kneading machine as 100 rpm, to prepare a slurry.

Next, this slurry was applied on an aluminum foil using a coater, dried, and then pressed using a press to form a positive electrode active material layer having a thickness of 100 μm on the aluminum foil. It was.
Next, a negative electrode is produced using graphite as a negative electrode active material, and a plurality of negative electrodes and the above positive electrodes are alternately arranged via separators to assemble a power generation element. The power generation element and the non-aqueous electrolyte are placed in the case. The secondary battery of Example 1 was fabricated by storing and performing electrical wiring.

"Example 2"
A positive electrode and a secondary battery of Example 2 were produced in the same manner as in Example 1 except that the kneading machine was rotated at 100 rpm for 150 minutes.

"Comparative example"
A positive electrode and a secondary battery of a comparative example were prepared in the same manner as in Example 1 except that the kneading machine was rotated at 100 rpm for 200 minutes.

"Evaluation"
(1) Coverage of carbonaceous film The coverage of the carbonaceous film of the particles in the positive electrodes of Examples 1 to 3 and Comparative Example was determined and evaluated.
Here, a part of the positive electrode is immersed in an organic solvent to dissolve the binder, or a part of the positive electrode is collapsed to take out LiFePO ₄ particles having a carbonaceous film formed on the surface. It observed using the scanning electron microscope (SEM), and the state of the carbonaceous film in the surface was confirmed.
Further, the surface of the particles was subjected to surface analysis using an energy dispersive X-ray spectrometer (EDX), and the state of the carbonaceous film on the surface was confirmed.

  As a result, the coverage of the carbonaceous film was 98 to 100% in Example 1, 95 to 98% in Example 2, and 80 to 90% in Comparative Example, and the shorter kneading time was in the positive electrode. It was found that the coverage of the carbonaceous coating on the particles was high.

(2) Charge / Discharge Characteristics The charge / discharge tests of the secondary batteries of Examples 1 to 3 and the comparative example were performed at room temperature (25 ° C.) at a constant current (1) with a cutoff voltage of 2-4.5 V and a charge / discharge rate of 1 C. 1 hour after discharge). The charge / discharge characteristics of Examples 1 and 2 and Comparative Example are shown in FIG.
As a result, it was found that the higher the coverage of the carbonaceous film of the particles in the positive electrode, the larger the capacity (%).

Thus, the capacity of the positive electrode is increased because of the high coverage of the carbonaceous film, i.e., the rate of lithium ion intake / release of the positive electrode is increased, and the overvoltage during the charge / discharge reaction of the positive electrode is increased. This is considered to be due to the decrease in electrode resistance.
In addition, the network formed by the carbonaceous film between the adjacent positive electrode active material particles is connected to a network without being cut off, so that a conductive path in the positive electrode is reliably formed, and resistance due to the connection between the positive electrode active material particles is further increased. It is thought that it decreased.
As a result, the charging speed of the positive electrode is improved, and further, side reactions unrelated to the original battery reaction such as the decomposition reaction of the electrolytic solution can be prevented. Therefore, the safety in the overcharge test etc. of the positive electrode can be prevented. And the life characteristics could be improved.

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Case 3 Lid member 4 Power generation element 5 Positive electrode connection terminal 6 Negative electrode connection terminal 7 Nonaqueous electrolyte 8 Positive electrode external connection terminal 9 Negative electrode external connection terminal 11 Positive electrode 12 Negative electrode 13 Separator 21 Positive electrode collector 22 Positive electrode active material Layer 31 Negative electrode current collector 32 Negative electrode active material layer

Claims (3)

In the positive electrode for a non-aqueous electrolyte secondary battery comprising olivine-type lithium composite compound particles having a carbonaceous film formed on the surface as a positive electrode active material,
Coverage of the carbonaceous coating to the surface area of the olivine-type lithium composite compound particles Ri der 95% or more,
The packing density of the olivine-type lithium composite compound particles in the positive electrode for a non-aqueous electrolyte secondary battery is 0.90 g / cm ³ or more and 1.09 g / cm ³ or less. Positive electrode for secondary battery. Non-aqueous electrolyte secondary battery comprising the nonaqueous electrolyte positive electrode for secondary battery according to claim 1. A battery module comprising the nonaqueous electrolyte secondary battery according to claim 2 .

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