KR101457267B1 - Secondary battery - Google Patents

Abstract

Disclosure of the Invention A problem to be solved by the present invention is to provide a secondary battery that performs charge / discharge efficiently during rapid charging / discharging.
The secondary battery is a secondary battery composed of a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolytic solution. The positive electrode active material has a charge potential different from that of the negative electrode active material, Particles and at least second active material particles.

Description

Secondary Battery {SECONDARY BATTERY}

The present invention relates to a secondary battery.

BACKGROUND ART [0002] In recent years, electric vehicles such as electric vehicles and plug-in hybrid vehicles have been put to practical use. A rechargeable secondary battery is used as the driving battery mounted on such electric vehicle.

In the secondary battery, for example, graphite is used as the negative electrode active material, and metal oxide capable of storing and storing lithium as the positive electrode active material is used. The metal oxide, which is a positive electrode active material, is mainly contained in the positive electrode active material layer as particles. In this case, a lithium ion battery using a plurality of types of positive electrode active material having different particle diameter distributions is known (for example, see Patent Document 1) in order to obtain high safety at the time of overcharging and high initial capacity.

Japanese Patent Application Laid-Open No. 2010-176996 (claim 1, summary, etc.)

The lithium ion battery described above has high safety at the time of overcharging and has a large initial capacity, but the following problems arise when the lithium ion battery is mounted on an electric vehicle or the like. For example, at the time of rapid charging such as descent of a hill road or a regenerative braking operation in which a rapid brake is applied while driving, an excessively large charging current flows into the secondary battery at the time of normal charging. However, Therefore, there is a problem that charging can not be performed efficiently. This problem also applies not only to rapid charging but also to rapid discharging of a secondary battery mounted in a camera, for example, flash.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the problems of the prior art, and to provide a secondary battery that performs charge / discharge efficiently during rapid charging / discharging.

The secondary battery of the present invention is a secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolytic solution, wherein the positive electrode active material has a charge potential different from that of the negative electrode active material, And at least the first active material particles and the second active material particles that are different from each other. By including the first active material particles and the second active material particles having different charge potentials and different average particle diameters, the charging / discharging responsiveness can be enhanced, and the charging and discharging can be efficiently performed at the time of rapid charging and discharging.

It is preferable that the second active material particle of the positive electrode active material has an average particle diameter smaller than that of the first active material particle and that the charging potential with respect to the negative electrode active material is higher than that of the first active material particle. With such a configuration, the charging responsiveness can be enhanced, and the charging at the time of rapid charging can be performed efficiently.

Wherein the positive electrode comprises a current collecting foil and a positive electrode active material layer formed on the current collecting foil and containing the positive electrode active material and the positive electrode active material layer is formed such that the first active material particle is, It is preferable that the first electrode is formed to be larger than the first electrode. With this configuration, the charging responsiveness can be further improved, and the charging at the time of rapid charging can be performed efficiently.

It is preferable that the average particle size of the first active material particles is 1 to 50 탆 and the average particle size of the second active material particles is 20 nm to 1 탆. With this range, slurry can be easily formed at the time of production, and charging / discharging at the time of rapid charging / discharging can be efficiently performed.

According to the secondary battery of the present invention, it is possible to exhibit an excellent effect that charge / discharge can be efficiently performed at the time of rapid charge / discharge.

1 is a schematic view for explaining a vehicle equipped with a secondary battery according to the present embodiment.
2 is a schematic view for explaining a secondary battery of the present embodiment.
Fig. 3 is a schematic diagram (a) for explaining the configuration of the electrode of this embodiment, and Fig.
4 is a schematic view for explaining the movement of lithium ions during discharging of the present embodiment.
Fig. 5 is a schematic view for explaining the movement of lithium ions during discharging according to the embodiment. Fig.
6 is a schematic view for explaining the movement of lithium ions during charging according to the present embodiment.
7 is a schematic view for explaining the movement of lithium ions during the conventional rapid charging.
8 is a schematic diagram for explaining the movement of lithium ions during rapid charging according to the present embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings.

The vehicle 1 is an electric vehicle. The in-vehicle battery pack 3 in which a plurality of secondary batteries 2 are mounted is mounted on the bottom (under the floor) of the vehicle 1, for example, an electric car. And supplies electric power to the traveling motor of the vehicle 1 from each secondary battery 2. [

The secondary battery 2 will be described below with reference to the drawings.

As shown in FIG. 2, the secondary battery 2 has a battery case 11. In the battery case 11, the electrode portion 12 is insulated from the battery case 11 by the insulating plate 13 and accommodated. The inside of the battery case 11 is filled with the electrolyte solution 14 and the battery case 11 is sealed by the lid portion 15.

The electrode unit 12 is provided with a negative electrode tab 16 and a positive electrode tab 17 and is connected to a negative electrode member and a positive electrode member of the electrode unit 12, The negative electrode tab 16 is connected to the negative electrode terminal 18 provided on the lid portion 15 and the positive electrode tab 17 is connected to the positive electrode terminal 19 provided on the lid portion 15.

As shown in Fig. 3, the electrode section 12 is formed by winding an electrode plate comprising a positive electrode 22 and a negative electrode 23 provided with a separator 21 interposed therebetween. The positive electrode 22 is composed of a positive electrode active material layer 25 provided on both surfaces of the positive electrode collector foil 24 and the positive electrode collector foil 24 and containing a positive electrode active material. The negative electrode 23 is formed on both surfaces of the negative electrode current collecting foil 26 and the negative electrode current collecting foil 26 and is made of the negative electrode active material layer 27 containing the negative electrode active material.

The positive electrode active material layer 25 of the positive electrode 22 of the electrode portion 12 contains the first active material particles and the second active material particles as the positive electrode active material. The second active material particle has a charging potential higher than that of the first active material particle, that is, an attraction force of lithium ions higher than that of the first active material particle, and an average particle diameter smaller than that of the first active material particle. In addition, the fact that the charge potential is low means that the electronegativity is low.

In the present embodiment, the second active material particles having a high lithium ion adsorption capacity and a small particle diameter are mixed as the positive electrode active material without forming the positive electrode active material only with the normally used first active material particles, so that the charge response Thereby forming a secondary battery having high performance. This point will be described below.

First, the normal discharge in the present embodiment will be described with reference to Figs. 4 and 5. Fig. 4, the graph shows the battery voltage versus the SOC (charge state), and a schematic diagram showing the state of the positive electrode and the negative electrode at the time of SOC indicated by O is also shown.

First, as shown in the graph of Fig. 4, the secondary battery of the present embodiment changes such that the battery voltage of the secondary battery becomes higher in a state where the voltage for SOC is 80% of SOC. This is because the positive active material contains the second active material particles 32 having high lithium ion adsorption capability. That is, in the secondary battery of this embodiment, the second active material particle 32 is made to be 20% of the second active material particle 32 with respect to 80% of the first active material particle 31, as the positive electrode active material, And the first active material particles 31 are mixed.

Fig. 4 (a) shows a fully charged state. That is, in the positive electrode, the lithium ions 30 are not stored in the first active material particles 31 and the second active material particles 32, and all the lithium ions 30 are inserted into the negative electrode active material 33 . When the discharge starts, the lithium ions 30 are discharged from the negative electrode active material 33, and the lithium ions 30 move to the positive electrode active material. In this case, among the positive electrode active materials, the lithium ions 30 are first stored in the second active material particles 32 having a large lithium ion adsorption capacity.

As shown in FIG. 4 (b), when the SOC of the secondary battery reaches 80% due to the progress of the discharge, the abnormal lithium ions 30 are not occluded in the second active material particles 32. As shown in FIG. 4 (b), when the lithium ions 30 can not be further received in the second active material particles 32, the first active material particles 31, The lithium ion 30 is occluded. 5 (b), when the discharge progresses thereafter, the lithium ions 30 are completely occluded in the first active material particles 31, and the lithium ions 30 are separated from the negative electrode (Fully discharged state).

That is, in the secondary battery of the present embodiment, at the time of discharging, lithium ions 30 are stored in the second active material particles 32 when the SOC is 100 to 80%, and when the SOC is less than 80 to 0% Lithium ions are intercalated in the active material particles 31.

Next, the normal charging from this fully discharged state will be described with reference to Fig.

6 (a), when charging starts from the fully discharged state, the lithium ion 30 is first charged from the first active material particle 31 to the second active material particle 32 because the second active material particle 32 has a high lithium ion attracting power. It goes away. 6 (b), when the lithium ions 30 are separated from all of the first active material particles 31, the lithium ions 30 are also separated from the second active material particles 32 as well. 6 (c), when the lithium ions 30 are separated from all the second active material particles 32, they are in a fully charged state.

That is, in the secondary battery of the present embodiment, at the time of charging, lithium ions are released from the first active material particles 31 when the SOC is 0 to 80%, and when the SOC is 80 to 100%, the second active material particles The lithium ions 30 are emitted from the cathode 32.

As described above, during normal charging, lithium ions are liable to be released from the first active material particles 31 having a low lithium ion attracting power. During normal discharge, lithium ions are attracted to the second active material particles 32 having high lithium ion- .

On the other hand, at the time of rapid charging, a charging current larger than that at normal charging flows into the secondary battery in a short time by, for example, a regenerative brake, unlike the case of normal charging. This rapid charging will be described with reference to FIGS. 7 and 8. FIG.

Fig. 7 is a graph (a) and a schematic diagram (b) for explaining rapid charging in the case where one type of active material particle is present as in the prior art. The graph shows the charging voltage for the charging current. When the charge current value in the graph is I ₁ , the positive and negative electrodes are in the state of FIG. 7 (b).

At the time of normal charging (when the charging current value in the graph is I ₁ ), the lithium ions 30 stored in the first active material particles 31 are discharged as described above. However, in this case, since the first active material particle 31 has a small surface area per unit volume and it is difficult to release the lithium ions 30, the resistance is large and the charge voltage is liable to rise.

Since the charging current value is large when a large charging current is generated by the regenerative brake (when the charging current value is I _{2 in the} graph), if the magnitude of the resistance is the same as the state represented by I ₁ , It got higher and could not be charged.

On the other hand, in the present embodiment, as described below with reference to Fig. 8, by having not only the first active material particles 31 but also the second active material particles 32, the charge responsiveness is high, Voltage is not higher than the voltage, it is possible to charge efficiently at the time of rapid charging.

FIG. 8 is a schematic diagram (a), (b), and (c) for explaining rapid charging in the case of the present embodiment. The graph shows the charging voltage for the charging current. When the charging currents in the graph are I ₁ and I ₂ , the positive electrode and the negative electrode are in the state of (b) and (c) of FIG. 8, respectively.

During normal charging (in the case of I ₁ ), lithium ions 30 are discharged from the first active material particles 31 as described above. However, in this case, since the first active material particle 31 has a small surface area per unit volume and it is difficult to release the lithium ions 30, the resistance is large and the charge voltage is liable to rise. In addition, since the second active material particles 32 have high lithium ion adsorption ability, it is difficult to release lithium ions.

At the time of rapid charging by the regenerative brake or the like (in the case of I ₂ ), a large charging current flows. In this case, although the surface area per unit volume is large when the voltage generated by the large charging current flowing through the secondary battery is high, the lithium ions (Li) are generated from the second active material particles 32, 30 are easily released. That is, since the second active material particles 32 have a large surface area per unit volume, lithium ions are liable to be released when a high voltage is applied.

In this case, the resistance is lower than that in the case of discharging lithium ions from the first active material particles 31. As a result, the voltage of the battery as a whole is hard to rise with respect to the charging current. As a result, it becomes difficult to exceed the upper limit voltage at the time of rapid charging, so that charging can be performed even at rapid charging.

Even if all the lithium ions are discharged from the second active material particles 32 due to the longer regeneration time, that is, the rapid charging time is prolonged, the second active material particles 32 are more likely to be discharged than the first active material particles 31 The lithium ions existing in the first active material particles 31 move to the second active material particles 32 because of the high attraction force of lithium ions. As a result, lithium ions are immediately discharged from the second active material particles 32, and the charging current at the time of regeneration can be efficiently received and charged.

As described above, in the present embodiment, by mixing not only the first active material particles 31 but also the second active material particles 32 having a small average particle size as the positive electrode active material, an excessive charging current at the time of rapid charging is efficiently received So that charging can be performed. In this case, since the second active material particles 32 have a high lithium ion adsorption capacity, lithium ions are occluded in the second active material particles 32 in most cases, so that even if rapid charging is started at any timing, The charging current at the time of regeneration can be received and charged. Even if lithium ions are not occluded in the second active material particles 32, since the lithium ions move from the first active material particles 31 to the second active material particles 32, rapid charge can similarly be efficiently performed .

In this embodiment, the electromotive force of the battery can be made higher than when the active material layer is formed of only the first active material by mixing the second active material having higher lithium ion adsorption capacity than the first active material. In this case, similarly, if all of the active material layer is constituted by only the second active material, the problem that the responsiveness at the time of rapid charging is low is not preferable.

Further, when the particle diameters of all the positive electrode active material particles are small (for example, about 0.1 탆), it is difficult to form a slurry in the production process. However, in the present embodiment, the first active material particles 31 and the second active material particles 32 are mixed to facilitate slurry formation.

In other words, as described above, in the present embodiment, the first active material particle 31 and the second active material particle 32 are included to enhance charging responsiveness at the time of rapid charging. However, in the present embodiment, The first active material particle 31 is used as the main active material of the positive electrode and the second active material particle 32 is contained to increase the electromotive force of the battery to improve the voltage characteristics of the battery. In addition, by having the first active material particles 31 as well as the second active material particles 32, slurry formation at the time of production is facilitated.

Examples of the positive electrode active material include a commonly used active material such as a metal oxide capable of occluding and releasing lithium, for example, a layered metal oxide, a spinel metal oxide and a metal compound, and an oxide salt type metal oxide. have. As the metal oxide of a layered structure type, there may be mentioned the lithium nickel composite oxide, lithium-cobalt composite oxide, a ternary composite oxide _{(LiCo 1/3 Ni 1/} 3 Mn 1/3 O 2). Lithium nickel complex oxide is preferably lithium nickel oxide (LiNiO ₂ ). The lithium-cobalt composite oxide is preferably lithium cobalt oxide (LiCoO ₂ ). Examples of the spinel-type metal oxide include lithium manganese-based complex oxides such as lithium manganese oxide (LiMn ₂ O ₄ ). Examples of the metal oxide of an oxide salt type include iron (III) phosphate (LiFePO ₄ ), manganese phosphate lithium (LiMnPO ₄ ), and lithium silicon phosphate.

As described above, the second active material and the first active material are selected such that the first active material particle 31 has lower attraction force for lithium ions than the second active material particles 32. In this case, it is preferable that the difference in the lithium ion attraction force, that is, the charge potential difference is 0.2 to 1.0 V. If the charge potential difference is less than 0.2 V, it may be difficult to obtain the advantage of using two different kinds of active materials, and if the potential difference is larger than 1.0 V, the charge characteristics of the battery are deteriorated. Therefore, it is preferable that the ratio is within this range.

Since the second active material particle 32 receives the charging current at the time of rapid charging as described above, it is preferable that the second active material particle 32 is contained in an amount of 1 to 20% based on the capacity of the battery Do. By including in this range, for example, the charging current by the regenerative brake can be efficiently charged. More preferably, the second active material particles 32 are contained in an amount of 2 to 10% based on the capacity of the battery.

As the combination of the second active material and the first active material, for example, lithium manganese oxide (charge potential 4.1 V when the metal lithium is used for the negative electrode) is used as the second active material, and lithium nickel oxide (Charge potential 3.6 V when the negative electrode is used) or lithium cobalt oxide (charge potential 3.8 V when metal lithium is used as the negative electrode).

It is preferable that such second active material particles 32 have an average particle diameter as small as possible, but in order to easily form a slurry, the average particle diameter d (50) is preferably 20 nm to 1 탆, 50 to 500 nm. The first active material particles 31 have an average particle diameter of 1 to 50 mu m, more preferably 2 to 20 mu m. The average particle diameter referred to here is a value (d (50)) of the particle diameter at a volume fraction based on the integral fraction of 50%. As a method of measuring the average particle diameter, for example, laser diffraction or scattering can be used. Since the first active material particle 31 and the second active material particle 32 are in these ranges, the slurry can be easily formed and the charging current can be efficiently charged.

Examples of the negative electrode active material include carbon materials such as metal lithium, lithium alloys, metal oxides, metal sulfides, metal nitrides and graphites, which are commonly used. Examples of the metal oxide include those having an irreversible capacity such as tin oxide or silicon oxide. As the graphite as the carbon-based material, either artificial graphite or natural graphite may be used. In this embodiment, graphite is used as the active material of the negative electrode.

As the binder, a commonly used binder such as polyvinylidene fluoride may be used. Further, the active material layer may contain a conductivity enhancer such as acetylene black, and an electrolyte (for example, a lithium salt (supporting electrolyte), an ion conductive polymer, etc.). When an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may be included.

As the negative electrode current collecting foil 26, for example, aluminum or copper is used.

As the electrolyte, LiPF ₆ is dissolved in a mixed solvent of a commonly used electrolyte, for example, ethylene carbonate or propylene carbonate, which is a cyclic carbonate ester, or dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate, which is a chain carbonate ester, Organic electrolytic solution.

In the present embodiment, the positive active material layer contains a second active material having a high charging potential and a small particle diameter, thereby enhancing charging responsiveness in rapid charging, but the present invention is not limited thereto. For example, a positive electrode active material layer having a low charging potential, that is, an active material having a low lithium ion adsorption capacity and a small particle diameter and an active material having a high charging potential, that is, a high lithium ion adsorption capacity and a large particle diameter may be provided. In this case, the response to the discharge current at the time of rapid discharge is good. That is, at the time of rapid discharging, since lithium ions are likely to be received in the active material having a small particle diameter, the discharge current can be efficiently taken and discharge can be performed, and a secondary battery having high responsiveness upon discharging can be formed.

Further, as in the present embodiment, the positive electrode active material mainly composed of two kinds of active materials having high lithium ion adsorption power and small particle diameter, low lithium ion adsorption power, and large particle diameter, and also has low lithium ion adsorption capacity and small particle diameter And an active material having a high lithium ion attraction force and a large particle diameter. In this case, all responsiveness to the charging current and the discharging current at the time of rapid charging / discharging can be improved.

A method of manufacturing the electrode portion in the secondary battery of the present embodiment will be described below.

The electrode of the electrode portion is formed from the slurry forming step and the coating construction drying step.

A conductive material and the like are mixed, the dispersion liquid is mixed, and after drying, a composite conductive material powder is obtained. Then, the positive electrode active material and the binder are mixed with the obtained composite conductive material powder so as to have a desired solid content concentration to obtain a slurry (slurry forming step). Subsequently, the slurry obtained for the current collector foil is applied and dried to form an electrode layer (coating and drying step). Each of the obtained electrodes is laminated on a separator to form an electrode plate. Finally, the laminated sheet is wound in the longitudinal direction to manufacture an electrode portion.

In the case of forming the electrode layer, in order to improve the current collecting property in the electrode layer, the slurry may be formed so that the concentration of the second active material particles is different to form each layer. Particularly, it is preferable that the positive electrode active material layer is formed such that the first active material particles 31 are formed so as to be larger than the second active material particles 32 toward the current collecting foil side. When formed in this way, the current collecting characteristics can be further improved.

Hereinafter, the present invention will be further described with reference to Examples.

[Example]

As a first embodiment, a secondary battery was produced as follows. A composite conductive agent powder containing acetylene black as a conductive material and lithium manganese oxide powder (average particle diameter 0.2 mu m) as a first positive electrode active material and lithium nickel oxide powder (average particle diameter 5 mu m) and a second positive electrode active material And the second positive electrode active material was mixed so that the battery capacity became 2%. Further, polyvinylidene fluoride as a binder was mixed to prepare a positive electrode active material slurry. The obtained positive electrode active material slurry was coated on both sides of a current collecting foil made of aluminum and dried to form a positive electrode.

Further, a negative electrode active material slurry containing graphite was prepared. This composition was coated on both sides of a current collecting foil made of copper and dried to form a negative electrode.

The obtained positive electrode and negative electrode were laminated together with a separator made of a porous polyethylene sheet, and the laminated sheet was wound in the longitudinal direction to form an electrode section. This electrode part was housed in an external case together with ethylene carbonate which is a non-aqueous electrolyte, to prepare a secondary battery.

As the second embodiment, lithium cobalt oxide (average particle diameter 0.2 mu m) was used instead of lithium manganese oxide as the second active material particles 32 so that the second positive electrode active material was 10% of the cell capacity based on SOC.

As a comparative example, a secondary battery was manufactured under the same conditions except that the second active material particles 32 were not provided.

If an electric vehicle with a weight of 1000 kg of a vehicle traveling at a speed of 30 m per second stops with a rapid braking force of 0.5 G, it takes six seconds to stop. At that time, the power generated by the regenerative brakes was estimated to be 150 kW maximum and the power amount 450 kJ (= 125 Wh). Since the charging power at normal rapid charging is 50 kW or less, the power received by the battery pack by the regenerative braking is three times or more the charging power at this normal time.

When the secondary batteries produced in the first and second embodiments and the secondary batteries manufactured in the comparative example were charged at 150 kW and 125 Wh in the entire vehicle (that is, the whole battery pack), charging And the charging was performed corresponding to the amount of electric power and the amount of electric power. In each of the secondary batteries obtained in the first and second embodiments, charging was performed. However, in the secondary battery obtained in the comparative example, the upper limit voltage of the battery was exceeded on the way (overvoltage) and charging could not be performed. Further, in a general electric vehicle, since one battery pack is composed of about 100 secondary batteries, the amount of electric power received by each battery is about 1/100 of the whole vehicle.

These Examples and Comparative Examples show that by containing not only the first active material particles 31 but also the second active material particles 32 having an average particle diameter smaller than that of the first active material particles 31 and having a high lithium ion attracting ability, It was found that the charging current can be efficiently received and charged.

In the present embodiment, the secondary battery is used in an electric vehicle, but it is not limited thereto. It can be used for an electric vehicle, for example, a hybrid vehicle. When used in a hybrid vehicle, it is preferable that the second active material particles 32 are contained in an amount of 1 to 30% based on the capacity of the battery. And more preferably 5 to 25%. With this range, the charging current by rapid charging can be efficiently charged even in a hybrid vehicle.

The secondary battery of the present invention can efficiently perform charging at the time of rapid charging. Such a secondary battery can be mounted on a vehicle, for example, and thus can be used in the field of vehicle manufacturing industry.

1: vehicle
2: secondary battery
3: Battery pack
11: Battery case
12:
13: insulating plate
14: electrolyte
15:
16: Negative electrode tab
17: Positive electrode tab
18: Negative terminal
19: positive terminal
21: Separator
22: positive
23: Negative electrode
24: positive current collector foil
25: positive electrode active material layer
26: Negative current collector foil
27: Negative electrode active material layer
30: Lithium ion
31: First active material particle
32: second active material particle
33: Negative electrode active material

Claims (4)

A secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolytic solution,
Wherein the positive electrode active material includes at least first and second active material particles having different charge potentials for the negative electrode active material and having different average particle diameters,
The second active material particle of the positive electrode active material has an average particle diameter smaller than that of the first active material particle and a charging potential higher than that of the first active material particle with respect to the negative electrode active material,
Wherein the positive electrode comprises a current collecting foil and a positive electrode active material layer formed on the current collecting foil and containing the positive electrode active material and the positive electrode active material layer is formed such that the first active material particle Wherein the first electrode and the second electrode are formed to increase in number. delete delete The secondary battery according to claim 1, wherein the first active material particles have an average particle diameter of 1 to 50 占 퐉 and the second active material particles have an average particle diameter of 20 nm to 1 占 퐉.

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