JP2001167801A - Method of transporting lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of safely transporting a lithium secondary cell that suppresses maximum rising temperature of the cell to prevent a disaster in case that the temperature of the cell is raised by accident during transportation of the cell. SOLUTION: The lithium secondary cell comprises an electrode body 1, of which positive or negative plates 2, 3, are wound or laminated through a separator 4 and uses non-aqueous electrolyte. When energy per unit mass accumulated in the cell is E (J/g), specific heat is Cp (J/ deg.C.g), normal transporting temperature is T1 ( deg.C), maximum rising temperature is T2 ( deg.C), and minimum temperature of the cell that brings about unsafe state of the cell by heating is t ( deg.C), the cell is transported in state that satisfies a relation of E/Cp+T1=T2<t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safe lithium secondary battery that limits the maximum temperature of the battery so as not to cause a disaster even if the battery temperature rises due to an accident or the like during transportation. Transportation method.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as power batteries for portable electronic devices such as mobile phones, VTRs, and notebook computers. In addition, the lithium secondary battery has a unit cell voltage of about 4 V, which is higher than that of a conventional secondary battery such as a lead storage battery, and has a higher energy density. Against this background, electric vehicles (E
V) or a motor drive power source for a hybrid electric vehicle (HEV).

In general, a lithium secondary battery includes a non-aqueous electrolyte in which a lithium transition metal composite oxide is used as a positive electrode active material, a carbonaceous material is used as a negative electrode active material, and a Li ion electrolyte is dissolved in an organic solvent as an electrolyte. Liquid is used. There are various types of electrodes such as a sandwich type, a wound type, and a laminated type as an electrode body which is a part for performing a battery reaction, and each structure has a structure in which a positive electrode plate and a negative electrode plate are separated by a separator. I have.

[0004] Here, an EV / HEV battery requires a large power to drive a motor or the like, and therefore requires a certain amount of capacity per battery. Therefore, it is preferable to use a wound type or a laminated type for such applications, and to form these electrode bodies,
Generally, an electrode plate (which indicates a positive electrode plate and a negative electrode plate) in which an electrode active material layer is formed on a surface of a current collecting substrate made of metal is used.

When an internal short-circuit, an external short-circuit, an overcharge, or the like occurs in a lithium secondary battery using such a wound or stacked electrode body, the lithium secondary battery may be damaged by the internal resistance of the electrode body. The generated Joule heat causes the battery temperature to rise. At this time, when a large current suddenly flows through the electrode body, the temperature rise naturally becomes remarkable, and there is a risk that the battery may explode or develop into a disaster.

[0006] Here, an internal cause and an external cause can be considered as the temperature rise of the battery. For example, it is considered that the internal cause is, for example, a case where there is a damaged portion such as a break in the separator, a case where metal dust, which is a good electrical conductor, enters during the production of the wound body and penetrates the separator, and the like. However, since a short circuit occurs between the electrode plates in the battery, a large current flows. The Joule heat generated at this time heats and evaporates the non-aqueous electrolyte, so that the internal pressure of the battery increases, and there is a danger that the battery may burst or explode.

On the other hand, as an external cause, it is conceivable that an electric good conductor such as a nail penetrates the inside of the battery. In this case, a phenomenon similar to an internal short circuit occurs. Further, it is assumed that the positive and negative terminals of the battery are short-circuited. In this case, the degree of heat generation differs depending on the magnitude of the load (resistance) at the time of external short-circuit. Other possible cases include a case where overcharging occurs due to a failure of the charging device, a case where the charging device is placed near a heating device such as an engine and heated.

[0008] The inventors have studied the causes of the temperature rise of such various batteries, and found the Journal of Power Sources
81-82 (1999) 887-890, 2
Regarding lithium secondary batteries having a capacity of 5 Ah, the results of examining temperature changes of batteries when performing nail penetration tests, external short-circuit tests, overcharge tests, and external heating tests are published. Among them, the one with the largest temperature rise is the nail penetration test, that is, the case where an internal short circuit has occurred, and the temperature rise to about 400 ° C. has been confirmed.

[0009]

The lithium secondary battery having such a large capacity is provided with a pressure relief valve for releasing the internal pressure of the battery to an external pressure at a predetermined pressure when the internal pressure of the battery increases. And prevents explosion due to battery temperature rise. However, explosion of the battery is inevitable when the internal pressure of the battery rapidly rises and the pressure release cannot keep up, or when the operation of the pressure relief valve is defective. Further, the battery once the pressure relief valve has been activated cannot be used basically thereafter.

[0010] Further, as the battery is in a state closer to full charge, the released energy increases, so that the temperature rise of the battery due to a short circuit or the like becomes large. Therefore,
For example, if the temperature of a manufactured battery rises for some reason while it is being transported from a manufacturing plant in one country to another place in that country or to another country in a state with a large charge capacity such as full charge, etc. Are more likely to lead to accidents and disasters.

[0011] The inventors have found that there are many causes of the battery temperature rising as described above. However, in most cases, the battery itself is heated by the energy stored in the battery. Also, paying attention to the fact that the battery temperature rises most at the time of an internal short circuit, and limiting the amount of energy stored in the battery to an amount that satisfies a predetermined condition, the rise of the battery temperature is suppressed to a certain temperature or less. The present invention has been reached by considering that the present invention can be performed.

It is needless to say that it is preferable that the manufactured battery is charged and discharged once and its characteristics are confirmed, and then shipped and transported. In this case, if the battery is shipped in a completely discharged state, the battery temperature cannot rise due to factors other than external heating, and this is considered preferable in terms of transport safety. However, in consideration of the charge / discharge characteristics, self-discharge characteristics, and the like of the lithium secondary battery, it is easily assumed that when the battery is completely discharged as described above, the battery cannot be used in actual use thereafter. Therefore, such a method cannot be adopted.

[0013]

That is, according to the present invention, there is provided a lithium secondary battery using a non-aqueous electrolyte, comprising an electrode body formed by winding or laminating each of positive and negative electrode plates via a separator. It is a transportation method, wherein the energy amount per unit weight stored in the battery is E (J / g), the specific heat of the battery is Cp (J / ° C. · g), and the normal transportation temperature of the battery is T ₁ ( C), the maximum temperature of the battery is defined as T ₂ (° C.), and the minimum temperature at which the battery becomes unsafe due to heat is defined as t (° C.).
E / Cp + T ₁ = T ₂ <t A method for transporting a lithium secondary battery is provided, wherein the transport is performed in a state where the relationship of the formula is satisfied.

In the method for transporting a lithium secondary battery according to the present invention, the maximum temperature rise T ₂ is preferably equal to or lower than the boiling point of the non-aqueous electrolyte. On the other hand, the maximum rise temperature T ₂ may be equal to or lower than the lowest temperature among the boiling points of the main components of the non-aqueous electrolyte. It is also preferable that the maximum rise temperature T ₂ be equal to or lower than the highest temperature among the melting points of the main constituent materials of the separator.

The method for transporting a lithium secondary battery of the present invention is suitably applied to transport of a battery having a battery capacity of 2 Ah or more when fully charged. Further, the present invention is applied to transport of a battery used as a power source for an electric vehicle or a hybrid electric vehicle.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A lithium secondary battery (battery) to which a transportation method of the present invention is applied includes an electrode body formed by winding or laminating positive and negative electrode plates via a separator, and a non-aqueous electrolyte. Is used. However, this does not prevent application to a coin-type battery including an electrode body in which a separator is sandwiched between one positive electrode plate and one negative electrode plate.

FIG. 1 is a perspective view showing a schematic structure of a wound electrode body (hereinafter referred to as a “wound body”) 1. Wound body 1
Has a structure in which electrode plates 2.3 (positive plates 2, negative plates 3) on which a plurality of current collecting tabs (tabs) 5 and 6 are attached are wound around the outer periphery of a core 13 via a separator 4. ing.

Here, the positive electrode plate 2 is manufactured by applying a positive electrode active material on both surfaces of a current collecting substrate to form a positive electrode active material layer. As the current collecting substrate, a metal foil having good corrosion resistance to a positive electrode electrochemical reaction, such as an aluminum foil or a titanium foil, is preferably used. In addition, a punching metal or a mesh (net) can be used instead of the foil. As the positive electrode active material, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO)
O ₂ ) and lithium transition metal composite oxides such as lithium manganate (LiMn ₂ O ₄ ) can be used.

The application of these various positive electrode active materials to a current collecting substrate (metal foil) is performed by applying a slurry or paste prepared by adding a solvent, a binder, or the like to the positive electrode active material powder, using a doctor blade method, a roll coater method, or the like. The method is performed by coating and drying the current collecting substrate using the method described above. In forming the positive electrode active material layer, fine carbon powder such as acetylene black or carbon black is added to the positive electrode active material powder as a conductive additive.

The negative electrode plate 3 can be manufactured in the same manner as the positive electrode plate 2. As the current collecting substrate of the negative electrode plate 3, a metal foil having good corrosion resistance to a negative electrode electrochemical reaction such as a copper foil or a nickel foil is suitably used. Of course, punching metal or mesh may be used. As the negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon, or a highly graphitized carbonaceous powder such as artificial graphite or natural graphite is used.

As the separator 4, a Li ion-permeable polyethylene film having micropores (PE
Film) having a three-layer structure sandwiched between porous Li ion-permeable polypropylene films (PP films) is preferably used. This is because when the temperature of the wound body 1 rises, the PE film softens at about 130 ° C., the micropores are crushed, and also serves as a safety mechanism for suppressing the movement of Li ions, that is, the battery reaction. And this PE
By sandwiching the film with a PP film having a higher softening temperature, even when the PE film is softened, the PP film retains its shape and retains the positive electrode plate 2 and the negative electrode plate 3.
This prevents contact and short-circuit of the battery and ensures reliable suppression of battery reaction and secures safety.

The electrode plates 2 and 3 and the separator 4 are
At the time of the winding work, tabs 5 and 6 are attached to portions of the electrode plates 2 and 3 where the current collecting substrate not coated with the electrode active material is exposed. For this reason, it is preferable that the electrode plates 2 and 3 have a stripe structure in which the active material layer is not formed at least at one end in the width direction of the current collecting base material. The core 13 can be made of various materials such as metal, resin and ceramic. When a conductive material is used, it is necessary to ensure insulation from the electrode plates 2 and 3.

As the tabs 5 and 6, foil-like ones made of the same material as the current collecting substrate of each of the electrode plates 2 and 3 are preferably used. The tabs 5 and 6 can be attached to the electrode plates 2 and 3 using ultrasonic welding, spot welding, or the like. At this time, as shown in FIG. 1, the tabs 5 and 6 are arranged such that the tab of one electrode is arranged on one end surface of the wound body 1.
It is preferable to attach each of them to prevent contact between the tabs 5 and 6, which is preferable.

In assembling a battery using the wound body 1 manufactured as described above, first, while ensuring continuity between the positive and negative electrode terminals for extracting current to the outside and the tabs 5 and 6, respectively. Then, the manufactured wound body 1 is inserted into the battery case and held at a stable position. After that, the battery case can be sealed by impregnating with a non-aqueous electrolyte and then sealing the battery case. In the present invention, the shape and structure of the battery case, or the tabs 5 and 6 in the wound body 1 are used.
Needless to say, there is no limitation on the form of connection between the terminal and the positive and negative terminals.

As the non-aqueous electrolyte, lithium hexafluoride
Lithium phosphate (LiPF ₆) Or lithium borofluoride (L
iBF_Four) And other lithium complex fluorine compounds or persalts
Lithium citrate (LiClO_Four) Such as lithium halide
Of one or more types selected from oxides
The quality is ethylene carbonate (EC), diethyl carbonate
Nate (DEC), dimethyl carbonate (DMC),
Carbonic esters such as propylene carbonate (PC)
Solvent, γ-butyrolactone, tetrahydrofuran,
Dissolved in a single solvent such as cetonitrile or a mixed solvent
Are preferably used.

Next, FIG. 2 shows a perspective view of a laminated electrode body (hereinafter, referred to as “laminated body”) 7. The laminate 7 has a structure in which a positive electrode plate 8 and a negative electrode plate 9 are alternately laminated with a separator 10 interposed therebetween, and tabs 11 and 12 are attached to each of the electrode plates 8 and 9. I have. In FIG. 2, the surface shapes of the electrode plates 8 and 9 are square, but may be various shapes such as a circle and an ellipse.

The electrode plates 8 and 9 can be manufactured by the same method as the electrode plates 2 and 3 used for the above-described wound body 1. In addition, it goes without saying that there is no limitation on the shape of the battery case, the terminal position of the battery, and the outer shape of the battery that house the stacked body 7, and the separator and the non-aqueous electrolyte are also different from the case where the wound body 1 is used. Similar ones can be used.

Now, when the battery manufactured by using the above-described wound body 1 or the laminated body 7 is shipped from a manufacturing plant and transported to a predetermined place, in the present invention, the battery has the following formula: E / Cp + T ₁ = T ₂ <t formula where E (J / g): accumulated energy per unit weight, Cp (J / ° C. · g): specific heat of battery, T ₁ (° C.): normal transport temperature , T ₂ (° C.): maximum temperature rise t (° C.): minimum temperature at which the battery becomes unsafe due to heat

Here, the stored energy amount per unit weight E (J / g) refers to the energy amount actually charged into the battery at the time of transportation, and the energy amount per unit weight when the battery is fully charged. Is E ₀ (J / g), the relationship of E ≦ E ₀ holds. Battery specific heat Cp (J /
° C · g) indicates the specific heat of the whole battery, not the specific heat of only the electrode body. It is apparent that the equation holds similarly even when the energy amount E ′ (J) of the entire battery is used instead of E and the heat capacity C (J / ° C.) of the entire battery is used instead of Cp. The amount of energy stored in the battery is
It is also the charge capacity (dischargeable capacity) of the battery.

The specific heat Cp of the battery is obtained by dropping a battery, which is kept at a predetermined temperature inside the battery by placing it in a dryer or the like, into water stored in a Dewar bottle,
It can be obtained by measuring the rising water temperature. In addition, if the heat loss due to the heat radiation from the Dewar bottle is obtained in advance by using a mass of material having a known specific heat, a more accurate specific heat of the battery can be measured.

Usually, the transport temperature T ₁ (° C.) is room temperature, but in consideration of differences in transport means such as when using an aircraft or when using a ship, the transport route (sea route) is taken into consideration. In consideration of the climatic region of, for example, a tropical region or a cold region, it is also possible to appropriately determine an appropriate value.

As is apparent from the equation, the maximum temperature T ₂ (° C.) depends on the energy stored in the battery.
It refers to the battery temperature reached when the battery itself is warmed.
In addition, the minimum temperature t at which the battery becomes unsafe due to heat
The term (° C.) refers to, for example, a temperature at which the non-aqueous electrolyte evaporates and the internal pressure of the battery increases to operate the pressure relief valve, and a temperature at which the reaction rapidly starts due to an exothermic reaction of the battery components. . The boiling point of the non-aqueous electrolyte varies depending on the type and mixing ratio of the solvent forming the non-aqueous electrolyte, and since the set opening pressure of the pressure relief valve and the pressure resistance of the container (battery case) can be arbitrarily set, t differs depending on the design of the battery (structure, materials used, etc.).

Therefore, as a method of using the equation, first, t is determined according to the battery design, and then T ₂ is determined. Since T ₁ can be determined by a transportation method or the like, and Cp can be obtained in advance by a separate measurement, E can be uniquely determined for T ₂ thus determined.

Next, a specific mode of use of the above-described formula will be described with an example. The first mode of use of the equation, the maximum temperature increase T _2, is to set the boiling point of the non-aqueous electrolyte. For example, the boiling point of the solvent used for the non-aqueous electrolyte is 241 ° C. for the aforementioned PC and 2 ° C. for the EC.
48 ° C., 127 ° C. in DEC, and 90 ° C. in DMC. When such a solvent is mixed, the boiling point may increase due to intermolecular interaction, but each component may start to evaporate at the boiling point.

That is, the boiling point of the non-aqueous electrolyte defined in the present invention refers to a temperature at which at least one component of the non-aqueous electrolyte starts to evaporate from the non-aqueous electrolyte. The boiling point changes depending on the external pressure. In this case, the external pressure is the internal pressure of the battery,
Usually, it is 1 atm. However, it may vary depending on the temperature outside the battery, the pressure of the inert gas when the battery is sealed, and the like.

Therefore, it is also preferable that the maximum rise temperature T ₂ be equal to or lower than the lowest temperature among the boiling points of the main components of the non-aqueous electrolyte. What are the major components of the non-aqueous electrolyte?
It does not refer to the components contained above. For example,
It goes without saying that in a mixture of equal amounts of the solvent A and the solvent B, both solvents A and B are the main components. Even if the solvent A is 20%, the solvent A can be considered as a main component.
On the other hand, in a mixed solvent in which the solvent A is 98% and the solvent B is 2%, the main component can be considered to be only the solvent A. Regarding whether or not it is a main component, a component containing only 1/20 or less of the content relative to any other component is regarded as not a main component, and this condition can be used as a criterion. .

Now, it is also preferable that the criterion of the maximum rise temperature T ₂ is lower than the highest temperature among the melting points of the main constituent materials of the separator. For example, a separator made of a PP / PE / PP film having a three-layer structure described above has a high melting point, and when the PP film forming the skeleton of the separator is melted, the risk of direct contact between the positive electrode plate and the negative electrode plate increases. Therefore, it is preferable that T ₂ be equal to or lower than the melting temperature of the PP film because the safety of the battery is ensured.

The equation assumes that the battery is in an adiabatic state. However, in reality, when the battery temperature rises, heat is released from the battery surface to the outside. be heated cell itself by energy, to reach the maximum rising temperature T ₂ the temperature of the battery is set it may be said that reality can not occur. Conversely, this indicates that the temperature rise of the battery can be suppressed to a temperature lower than T ₂ , so that the condition satisfying the condition of the equation can enhance the safety of the battery. It means that it is in a state where it is in a closed state.

The above-described transport method of the present invention is suitably used for a large-capacity battery having a battery capacity of 2 Ah or more, particularly 5 Ah or more when fully charged. However, in view of the object of the present invention that the battery is transported safely. Of course, it can be used for a battery having a capacity of 2 Ah or less. It goes without saying that the use of the transported battery is not limited, but the present invention can be suitably used for transporting a large-capacity battery used as a power source for an electric vehicle or a hybrid electric vehicle.

[0040]

As described above, according to the method for transporting a lithium secondary battery of the present invention, even when self-heating occurs due to a short-circuit accident or the like, the stored energy, that is, the charge amount is limited, so that the battery temperature is limited. Since the temperature of the battery does not rise to a predetermined temperature or higher, and the explosion of the battery is avoided, an excellent effect of ensuring safety during battery transportation can be obtained. On the other hand, since the battery is charged at a fixed capacity, even if the battery is self-discharged over time, no trouble is caused in actual use, and the battery characteristics are not deteriorated. If the safety of the lithium secondary battery itself is ensured, containers and the like used for transportation can be simplified and reduced in weight, so that the present invention also contributes to improvement of transportation efficiency. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic structure of a wound electrode body.

FIG. 2 is a perspective view showing a schematic structure of a stacked electrode body.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wound electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 * ... Tab, 7 ... Laminated electrode body, 8 ... Positive electrode plate, 9 ... Negative electrode plate, 10 ... Separator, 11 -12: tab, 13: winding core.

Claims (6)

[Claims] 1. A method for transporting a lithium secondary battery using a non-aqueous electrolyte, comprising an electrode body formed by winding or laminating each of positive and negative electrode plates with a separator interposed therebetween. The energy amount per unit weight is E (J / g), the specific heat of the battery is Cp (J / ° C. · g),
When the normal transport temperature of the battery is T ₁ (° C.), the maximum temperature of the battery is T ₂ (° C.), and the minimum temperature at which the battery is unsafe due to heat is t (° C.). A method for transporting a lithium secondary battery, wherein the battery is transported in a state in which a relationship represented by the following formula: E / Cp + T ₁ = T ₂ <t is satisfied. 2. The method for transporting a lithium secondary battery according to claim 1, wherein the maximum temperature rise T ₂ is lower than the boiling point of the non-aqueous electrolyte. 3. The method for transporting a lithium secondary battery according to claim 1, wherein the maximum rising temperature T ₂ is set to be equal to or lower than the lowest temperature among the boiling points of the main components of the non-aqueous electrolyte. 4. The lithium secondary battery according to claim 1, wherein the maximum temperature rise T ₂ is not more than the highest temperature among the melting points of the main constituent materials of the separator. How to transport batteries. 5. The method for transporting a lithium secondary battery according to claim 1, wherein the method is applied to a battery having a battery capacity of 2 Ah or more when fully charged. 6. The method for transporting a lithium secondary battery according to claim 1, wherein the method is applied to a battery used as a power source for an electric vehicle or a hybrid electric vehicle.