JP2955323B2 - Battery - Google Patents

Description

The present invention relates to a primary battery and a secondary battery, and more particularly to a battery having excellent separator safety.

[Conventional technology]

In recent years, the capacity and output of electric energy storage devices such as primary batteries, secondary batteries, capacitors, and capacitors have been increasing. Along with this, particularly in batteries, safety problems occurring at the time of abnormalities such as short circuits have been greatly highlighted.

For example, in the case of a lithium battery whose usage has been increasing remarkably in recent years, when a short circuit occurs inside and outside the battery, the battery temperature rises sharply, which causes the battery contents to erupt and further cause an explosion.

In order to solve such a problem, it has been attempted to add various devices to a separator for separating a positive electrode and a negative electrode.

For example, JP-A-60-23954 proposes to use a synthetic resin film having fine pores as a separator. According to such a method, when an external short circuit occurs in a single cell as compared with the conventional nonwoven fabric separator, a certain effect is actually found, but an internal short circuit or an external short circuit in two or more single cells connected in series is caused. For a short circuit under more severe conditions such as a short circuit, it has not been effective to use a synthetic resin film having micropores as a separator.

JP-A-1-186751 describes, as a further improvement, that a low-melting-point wax is partially applied to the above-mentioned synthetic resin film having fine pores. In this case, the applied part has no ion permeability and has low temperature,
That is, the internal resistance is increased in the actual use temperature range, which is not preferable. In addition, the basic performance is deteriorated even at around room temperature by being covered with the wax-like insulating film, which is not preferable.

On the other hand, Japanese Patent Application Laid-Open No. Sho 60-52 proposes a separator in which polyethylene powder particles are adhered to the surface of a polypropylene nonwoven fabric. Japanese Patent Application Laid-Open No. Sho 61-232560 discloses a separator having a high melting point material and a low melting point material. The use of a nonwoven fabric made of a composite fiber having a heavy structure as a separator has been proposed, but the pore size is large because the nonwoven fabric is used as a base material,
It takes a long time for the resin to melt and close the pores, and the closure is not perfect, which is not preferable.

Also, Japanese Patent Application Laid-Open No. 1-283585 proposes that a microporous film made of a low-melting resin and a nonwoven fabric are used in a superposed manner, and the safety is improved. It is not enough for a short circuit under severe conditions.

Furthermore, as long as the nonwoven fabric is used, the film thickness is large and the volume is inevitably increased, which is a problem that goes against the trend of reducing the size and weight of the battery.

[Problems to be solved by the invention]

The above-mentioned conventional improvement means partially exhibited the effect of the improvement, but were insufficient in the following points.

For example, in the case of an external short circuit, the conventional improvement can prevent troubles such as rupture or explosion, but short circuit under more severe conditions, for example, a battery pack in which many cells are connected in parallel or series. Short circuit.

 Internal short circuit with red heat.

 Short circuit at high temperature.

Short circuit due to instantaneous destruction such as nail sticking or crushing.

 Short circuit when separator deteriorates.

 Dend light short circuit.

 Short circuit due to internal contact between positive and negative tabs.

When such a severe short circuit as described above occurs, a phenomenon such as rupture or explosion also occurs, and there is a problem that peripheral equipment, a building, or even a human body is damaged.

Particularly, in recent years, accidents due to such causes have occurred frequently, and it has become an urgent social need to ensure safety under more severe conditions than before. For that purpose, further improvement of the separator is necessary.

The present inventors previously, in order to solve these problems, by using a separator coated with a resin porous powder aggregate having a softening temperature of 95 ° C or more and 160 ° C or less on a synthetic resin microporous membrane, remarkable. I found an improvement.

However, at a high temperature exceeding 180 ° C., the separator is torn or cut, and further improvement is required in order to obtain more reliable safety.

An object of the present invention is to solve the above-mentioned problems and to provide a battery that can maintain safety even in abnormal situations by using a separator having excellent safety.

[Means for solving the problem]

The present inventors have studied in detail phenomena that occur in abnormalities such as short circuits in order to achieve the above-mentioned object, and by using a separator having a specific thermal deformation behavior, even in the event of an abnormality under severe conditions, It has been found that a battery that can maintain safety can be obtained.

The present inventors can improve the membrane strength of the separator by including fine particles in a predetermined particle size range in the resin porous powder aggregate, and the safety at a high temperature in particular is greatly improved. I found that.

That is, the battery of the present invention is a battery having a positive electrode, a negative electrode and a separator as basic constituent elements, wherein the separator is a synthetic resin microporous membrane, and at least one surface of the separator has a softening temperature of 95 ° C or higher and 160 ° C or lower. The resin particles that are covered with the porous powder aggregate and that constitute the resin porous powder aggregate contain 1% by weight or more and 50% by weight or less of particles having a particle size of 0.01 μm or more and 1 μm or less. Features.

[Operation] Conventionally, a large short-circuit current has flowed in the event of an abnormality such as a short-circuit.
When the internal temperature of the battery rises, the separator softens and melts, closing the pores to reduce the permeability of ions, and reducing the short-circuit current so that the temperature does not reach a certain temperature or higher. There was the idea of ensuring safety with the system. However, according to the conventional method, in the case of an abnormality such as a short circuit under severe conditions as described above, a rupture or explosion still occurs.

The present inventors have studied such a phenomenon in detail, and as a result, when a conventionally known separator is used, the phenomenon that the pores of the separator are blocked by the softening and melting of the separator as described above when the internal temperature rises. This is true, but the fact that the separator melts and flows at the same time loses the function of electrically insulating the positive and negative electrodes, resulting in a more severe short circuit. Was found.

This phenomenon is particularly remarkable when the internal temperature rise is not uniform, there is a temperature distribution, or when a local temperature rise occurs. This phenomenon has been found to be a major cause of loss of security.

As described above, the present inventors have disclosed that a synthetic resin microporous film is coated with a resin porous powder aggregate having a softening temperature of 95 ° C. or more and 160 ° C. or less, and a resin constituting the resin porous powder aggregate. The use of a separator containing 1% by weight to 50% by weight of particles having a particle size of 0.01 μm or more and 1 μm or less has found a remarkable improvement over the above problem.

In the present invention, the synthetic resin microporous membrane is not particularly limited, but, for example, a microporous membrane having a network structure composed of fine communication holes as described in JP-A-54-52167. Is mentioned.

Although the material is not particularly limited, examples thereof include polyethylene, polypropylene, polybutene, polyvinyl chloride, polyethylene terephthalate, nylon, polytetrafluoroethylene, and the like, and a mixture or copolymer thereof.

In the present invention, the resin porous powder aggregate is a continuous body in which the resin particles are single or in contact with each other, and is an aggregate having voids between the particles in a single-layer or multi-layer state.

Softening temperature of the resin porous powder aggregate in the present invention,
Glass transition temperature (Tg) and melting point (Tm) of 95 ° C or more
The temperature is 160 ° C or lower, preferably 110 ° C or higher and 150 ° C or lower, more preferably 110 ° C or higher and 145 ° C or lower.

If the softening temperature is lower than 95 ° C., it is preferable from the viewpoint of ensuring safety. However, since the internal impedance increases in a temperature range where the battery is normally used, the performance of the battery is impaired, which is not preferable.

On the other hand, if the softening temperature exceeds 160 ° C., the internal temperature of the battery rises to this temperature as described above, and safety cannot be secured, which is not preferable.

The resin having a softening point in the range of 95 to 160 ° C is not particularly limited, but examples thereof include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and polyolefin resins such as polybutene. Examples include polystyrene resins such as polystyrene and styrene-acrylonitrile copolymer, and polyacryl resins such as polyethyl methacrylate and polymethyl methacrylate. Of these, low density polyethylene, linear low density polyethylene and high density polyethylene are particularly preferred.

As described above, in order to ensure safety against abnormalities under all conditions, it is essential to use a resin porous powder aggregate having a softening temperature in the above temperature range, but it is even more important In the temperature range exceeding the softening temperature, the resin porous powder aggregate softens and melts, closes the pores of the synthetic resin microporous membrane, and increases the internal impedance of the battery and maintains high resistance. .

In the present invention, the resin particles constituting the resin porous powder aggregate are fine particles having a particle size of 0.01 μm or more and 1 μm or less,
It is contained in an amount of 1% by weight to 50% by weight. By containing such fine particles, when the resin particles form the resin porous powder aggregate, the fine particles enter between the resin particles. For this reason, the adhesion and adhesion between the particles are improved, and the film strength of the resin porous powder aggregate is enhanced. Furthermore, the adhesion and adhesion between the synthetic resin microporous membrane and the resin porous powder aggregate are improved, and the membrane strength of the entire separator is increased.

As a result, in the temperature range exceeding the softening temperature of the resin porous powder aggregate, the resin porous powder aggregate softens and melts, closes the pores of the synthetic resin microporous membrane, and increases the internal impedance of the battery and Since high resistance can be maintained up to a higher temperature range, high safety can be ensured.

When the particle diameter of the fine particles contained in the resin particles is less than 0.01 μm, it is preferable from the viewpoint of improving the membrane strength and the safety of the battery, but is too small, so that the pores of the synthetic resin microporous membrane are too small. It is undesirably intruded inside, thereby impairing the normal function as a separator. When the particle size of the fine particles exceeds 1 μm, the fine particles are intruded between the resin particles, so that the effect is small and not preferable from the viewpoint of improving the film strength.

When the content of the above-mentioned fine particles is less than 1% by weight, the effect is too small, which is not preferable because the amount is too small.
If the content of the fine particles exceeds 50% by weight, the porosity between the particles is low when the resin particles form the resin porous powder aggregate, and the normal function as a separator is undesirably impaired.

The particle size of the remaining resin particles excluding the fine particles having the above particle size range is not particularly limited, but is preferably in the range of from 1 μm to 50 μm or less, more preferably 20 μm or less, More preferably 10μ
m or less. If the particle size exceeds 50 μm, the volume increases, which is not preferable from the viewpoint of reducing the size and weight of the battery.

In the present invention, the coating thickness of the resin porous powder aggregate,
It is 1.1 to 100 μm, preferably 1.5 to 50 μm, and more preferably 1.5 to 30 μm. When the coating thickness is less than 1.1 μm, when the resin porous powder aggregate softens and melts,
The pores of the synthetic resin microporous membrane are not sufficiently covered, and short-circuit current is reduced, temperature rise is suppressed, and safety cannot be ensured. If the coating thickness exceeds 100 μm, the volume becomes large, which is not preferable from the viewpoint of reducing the size and weight of the battery.

In the present invention, the method of coating the synthetic resin microporous membrane with the resin porous powder aggregate is not particularly limited, but, for example, using an aqueous dispersion or an oily dispersion of resin particles. A method of applying on a synthetic resin microporous membrane by various coating methods, a method of uniformly applying a resin dispersion containing a soluble substance on a synthetic resin microporous membrane and then extracting the soluble substance with an extractant, A method of uniformly applying a dry powder on a synthetic resin microporous film and fusing the powder is used.

In the former coating method, an aqueous dispersion or oil dispersion of two or more resin particles including the resin fine particles in the above-described limited range is dispersed in advance, and the synthetic resin microporous membrane is coated by various coating methods. Can be.

In the latter coating method, a dry powder of two or more kinds of resin particles including the resin fine particles in the above-described limited range is mixed in advance, and the resulting mixture is applied to coat the synthetic resin microporous film.

Further, after the application, the resin particles and the synthetic resin microporous membrane can be dried at a temperature at which the resin particles and the synthetic resin microporous film are not significantly deformed.

However, what is important is that the resin porous powder aggregate has porosity in any of the methods. For that purpose, in the drying step after the application, it must be handled at a temperature lower than the minimum film forming temperature of the resin particles. If the drying is performed at a temperature higher than the minimum film forming temperature, heat melting of the resin particles proceeds, so that a film is formed, and the porosity of the resin is lost, which is not preferable.

Therefore, the air permeability of the separator in the present invention is not particularly limited, at 25 ° C., 300 seconds / 100c
c or less, preferably 200 seconds / 100 cc or less, more preferably
150 seconds / 100cc or less.

Similarly, although not particularly limited, the lower the film resistance value (R25) at 25 ° C., the better, but it is usually
0.5~50Ω · cm ² preferably 0.5~20Ω · cm ^2, more preferably in a range of 0.5~10Ω · cm ^2.

The thickness of the separator is not particularly limited, but is usually in the range of 10 to 100 μm, preferably 15 to 80 μm, and more preferably 15 to 50 μm. If the thickness is less than 10 μm, the insulating function is unduly too thin, which is not preferable.
If it exceeds 100 μm, the volume becomes large, which is not preferable from the viewpoint of reducing the size and weight of the battery.

Although the porosity is not particularly limited, it is 35 to 85%, preferably 45 to 80%, and more preferably 50 to 80%.

The battery in the present invention is not particularly limited, but examples thereof include primary batteries such as lithium batteries, manganese-zinc batteries, silver-zinc batteries, nickel-cadmium batteries, nickel-zinc batteries. And secondary batteries such as batteries, nickel-hydrogen batteries, polymer batteries, lithium secondary batteries and carbon secondary batteries.

By using a separator that satisfies the requirements of the present invention, the safety of the battery is dramatically improved, and rupture or explosion can occur even under abnormal conditions such as short circuit, reverse charge or overcharge under severe conditions. Disappears.

〔Example〕

Hereinafter, examples will be described in order to explain the present invention in detail, but the present invention is not particularly limited to the following examples.

 In addition, various physical properties were measured by the following measuring methods.

<Film Resistance> FIG. 1 shows a film resistance measuring device defined in the present invention.
The film resistance of the separator is measured using this measuring device. In FIG. 1 (A), 1A and 1B are Ni foils having a thickness of 10 μm, which are connected to the impedance measuring device 7.
As shown in FIG. 1 (C), the Ni foil 1A is 15 mm long, 10 mm wide.
The Teflon tape 6 is masked leaving a rectangle of mm. Reference numeral 3 denotes a separator impregnated with a prescribed electrolyte, which is disposed between 1A and 1B, and four sides of which are fixed with Teflon tape. Reference numeral 5 denotes a thermocouple for measuring temperature, which is attached to the glass plate 2B with a Teflon tape. A specified electrolytic solution is filled between the glass plates 2A and 2B.

Ni foil 1A and 1B, glass plates 2A and 2B, separator 3
The thermocouple 5 is housed in a case 4 shown in FIG. Reference numeral 8 denotes a recording device for recording the temperature and the measured impedance.

A 1M lithium borofluoride / propylene carbonate solution is used as an electrolyte. Measurement is 25 ° C and measurement frequency is 1k
Hz, and the film resistance R25 at 25 ° C. is obtained by the following equation.

R25 = measured value (Ω) × 1 cm × 1.5 cm (unit: Ω · cm ² ) In the measurement of the change in the film resistance shown in FIG. 3, the impedance is continuously measured using the film resistance measuring device shown in FIG. While heating, the temperature of the battery is raised in an oven set at a rate of 2 ° C./min from 25 ° C. to 175 ° C.

<Porosity> The porosity is calculated by the following equation.

<Air permeability> As shown in FIG. 2, the air permeability measurement sample in which the separator 9 was set in the Teflon holder 10 was heated in an oven set at a rate of 2 ° C./min to reach each temperature. At this point, the sample is taken out and the air permeability is measured at 25 ° C. by the following method.

Measured according to ASTM D-726 Method A. Unit is seconds / 100
cc.

Note that 5000 seconds / 100
cc-sheets or more shall be regarded as infinity (∞).

Example 1 This example shows a production example of a separator.

Celgard K-878, a polyethylene microporous membrane
Chemipearl M200 (average particle size: 6 μm, manufactured by Mitsui Petrochemical Co.) and Chemipearl S200 (average particle size: 0.5 μm) which are low-density polyethylene dispersions
m, manufactured by Mitsui Petrochemical Co., Ltd.) in the following mixing ratio (when dry) was applied by a bar coater method using a No. 12 wire bar.

Mixing ratio (when dry) Chemipearl M200 90% by weight Chemipearl S200 10% by weight After coating, hot air drying was performed at 80 ° C to obtain a separator having the properties shown in Table 1. The temperature change of the film resistance when the temperature of the separator is raised is shown by a curve A in FIG.

Example 2 This example shows a production example of a separator.

Chemipearl W500 low-density polyethylene dispersion (average particle size 2.5 μm, manufactured by Mitsui Petrochemical Co.) and Chemipearl WF low-density polyethylene dispersion
Example 1 except that a liquid prepared by dispersing 640 (average particle size: 1 μm, manufactured by Mitsui Petrochemical Co., Ltd.) in the following mixing ratio (when dry) was used.
The same operation as described above was performed.

Mixing ratio (when dry) Chemipearl W500 80% by weight Chemipearl WF640 20% by weight Table 1 shows the properties of the obtained separator. Curve B in FIG. 3 shows the temperature change of the film resistance when the temperature of the separator rises.

Example 3 This example shows a production example of a separator.

The same operation as in Example 1 was performed except that Hypore 4030U (manufactured by Asahi Kasei Kogyo), which is a polyethylene microporous membrane, was used. Table 1 shows the properties of the obtained separator. The temperature change of the film resistance when the temperature of the separator is raised is shown by a curve C in FIG.

Next, comparative examples for confirming the characteristics of the films obtained in Examples 1, 2 and 3 will be described.

Comparative Example 1 The same Chemipearl M200 as used in Example 1 was coated on a polyethylene microporous membrane Celgard K-878 (manufactured by Celanese) using a bar coater method using a No. 12 wire bar. went. After coating, dry with hot air at 80 ° C.
As a result, a separator having the same characteristics as in Example 1 was obtained.

Comparative Example 2 The same operation as in Example 1 was performed, except that a dispersion liquid having the same blending ratio of Chemipearl M200 and Chemipearl S200 as used in Example 1 was used as described below.

Mixing ratio (when dry) Chemipearl M200 99.8% by weight Chemipearl S200 0.2% by weight Table 1 shows the properties of the obtained separator.

Comparative Example 3 The same operation as in Example 1 was performed except that a dispersion liquid having the same compounding ratio of Chemipearl M200 and Chemipearl S200 as used in Example 1 was used as described below.

Mixing ratio (when dry) Chemipearl M200 40% by weight Chemipearl S200 60% by weight Table 1 shows the properties of the obtained separator.

Comparative Example 4 The same Chemipearl M200 as used in Example 1 was applied to a polypropylene nonwoven fabric (manufactured by Nippon Vilene Co., Ltd.) by a dipping coater method, and dried with hot air at 80 ° C. to obtain the properties shown in Table 1. The separator shown was obtained.

Example 4 Manganese dioxide was used as a positive electrode active material, graphite and acetylene black were used as conductive agents, and ethylene tetrafluoride was used as a binder. Manganese dioxide: graphite: acetylene black: ethylene tetrafluoride = 85: 5: 5: The mixture obtained at a weight ratio of 5 was used as a water paste, a sheet coated and dried on a stainless steel lath plate was used as a positive electrode, and a lithium metal foil was used as a negative electrode. FIG. 4 is a half sectional view of a spiral wound battery. Where 11
Is a positive electrode, 12 is a separator, 13 is a negative electrode, 14 is an insulating plate, 15 is a negative electrode lead, 16 is a positive electrode lead, and 17 is a gasket.

As the separator 12, the membrane obtained in Example 1 was used, and a liquid obtained by adjusting lithium perchlorate to a concentration of 1.0 M in a mixed solvent of propylene carbonate and dimethoxyethane (volume ratio 1: 1) as an electrolyte was used. Was used. Table 2 shows the results of various test evaluations of this battery.

Example 5 LiCoO ₂ was used as a positive electrode active material, graphite and acetylene black were used as conductive agents, and fluororubber was used as a binder. LiCoO ₂ : graphite: acetylene black: fluororubber was used in a weight ratio of 88: 7.5: 2.5: 2. The mixture was used as a dimethylformamide paste, a sheet coated and dried on an Al foil was used as a positive electrode, needle coke powder was used as a negative electrode active material, and fluoro rubber was used as a binder. Needle coke: fluoro rubber = 95: 5 weight ratio The resulting mixture was applied to a Cu foil as a dimethylformamide paste and dried, and the sheet was used as a negative electrode to produce a C2 type battery shown in FIG.

Note that the membrane obtained in Example 1 was used as the separator 12, and a liquid prepared by adjusting lithium borofluoride to a concentration of 1.0 M in a mixed solvent of propylene carbonate and butyrolactone (volume ratio = 1: 1) was used as an electrolytic solution. Was. This battery was charged at a constant voltage of 4.2 V for 5 hours. Table 2 shows the results of various test evaluations of this battery.

Example 6 The same operation as in Example 4 was performed except that the membrane obtained in Example 2 was used as a separator. Table 2 shows the results of various test evaluations of this battery.

Example 7 The same operation as in Example 5 was performed except that the membrane obtained in Example 3 was used as a separator. Table 2 shows the results of various test evaluations of this battery.

The following comparative examples are for confirming the performance of the batteries manufactured in the respective examples.

Comparative Example 5 The same operation as in Example 4 was performed except that the membrane obtained in Comparative Example 1 was used as a separator. Table 2 shows the results of various test evaluations of this battery.

Comparative Example 6 The same operation as in Example 5 was performed except that the membrane obtained in Comparative Example 1 was used as a separator. Table 2 shows the results of various test evaluations of this battery.

Comparative Example 7 The same operation as in Example 5 was performed, except that the membrane obtained in Comparative Example 2 was used as a separator. Table 2 shows the results of various test evaluations of this battery.

Comparative Example 8 The same operation as in Example 5 was performed except that the membrane obtained in Comparative Example 4 was used as a separator. Table 2 shows the results of various test evaluations of this battery.

Table 2 shows that the batteries using the separators produced in Comparative Examples 1 to 4 were weak to heating.

Examples 8 to 13 and Comparative Examples 5 and 6 The same operation as in Example 1 was performed except that the kind and the mixing ratio of the aqueous dispersion used in Example 1 were changed as shown in Table-3. Evaluation of the obtained coated body (separator): adhesion and air permeability (25 ° C) between the resin porous powder aggregate as the coating layer and the synthetic resin microporous membrane as the base material
Table 3 also shows the measurement results.

As shown in Table 3, the mixing ratio of the fine particles having a particle size of 0.01 to 1 μm among the resin particles, which is composed of the resin porous powder aggregate, was 20% by weight in Example 8 and 10% by weight in Example 9. 45% by weight in Example 10, 10% by weight in Example 11, 25% in Example 12,
Example 13 was 30% by weight, Comparative Example 5 was 100%, and Comparative Example 6 was 0%.
%.

The air permeability in Comparative Example 5 is 1000 seconds / 100 cc or more, which indicates that fine particles have entered the pores of the synthetic resin microporous membrane. The poor adhesion between the resin porous powder aggregate and the synthetic resin microporous membrane in Comparative Example 6 is due to the fact that the resin porous powder aggregate has a particle size of 0.01 to 1
This is because no fine particles of μm are contained.

[Effects of the Invention] As described above, the battery limited by the present invention does not cause phenomena such as rupture or explosion even under abnormal conditions such as short circuit under severe conditions, and is excellent in safety and reliability. There is an effect that the improved performance can be exhibited.

[Brief description of the drawings]

FIG. 1 is a diagram showing a film resistance measuring device defined in the present invention, FIG. 2 is a diagram showing a sample for measuring air permeability in an example of the present invention and a comparative example, and FIG. 3 is a diagram in an example of the present invention. FIG. 4 is a diagram showing a change in the film resistance value when the temperature of the separator is raised. FIG. 4 is a half sectional view of a spiral wound battery according to an example of the present invention and a comparative example. 1A, 1B: Ni foil, 2A, 2B: Glass plate, 3, 9, 12, ... Separator, 4: Case, 5: Thermocouple, 6: Teflon tape, 7: Impedance measuring device, 8 …… Recorder, 10… Teflon holder, 11… Positive electrode, 13 …… Negative electrode, 14 …… Insulating plate, 15 …… Negative electrode lead, 16 …… Positive electrode lead, 17 …… Gasket.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-77108 (JP, A) JP-A-1-167948 (JP, A) JP-A-3-283259 (JP, A) JP-A-2- 77108 (JP, A) JP-A-1-167948 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 2/16

Claims (1)

(57) [Claims] 1. A battery comprising a positive electrode, a negative electrode and a separator as basic components, wherein the separator is a microporous synthetic resin membrane, and at least one surface of the separator has a softening temperature of 95 ° C. or higher and 160 ° C. or lower. The resin particles which are coated with the powder aggregate and which constitute the resin porous powder aggregate contain 1% by weight or more and 50% by weight or less of particles having a particle size of 0.01 μm or more and 1 μm or less. Battery.