JPH01134875A - Lithium battery - Google Patents

Abstract

PURPOSE:To improve discharging characteristics, charging and discharging efficiency, charging and discharging capacity, and a cyclic lifetime by providing a negative electrode via the formation of a lithium metal layer at the rear side of the deposited separator of a negative electrode active material. CONSTITUTION:A negative electrode active material 6 of an aluminum or an aluminum alloy is formed on the sheet shaped active material 3 of a positive electrode 1 via a separator 4, and a lithium metal layer 7 is adhered to the rear side of the separator 4 adhered to the negative electrode active material 6, thereby forming a negative electrode 5. According to the aforesaid construction, the potential of the negative electrode 5 can be lowered, compared with the potential of a positive electrode and battery voltage can be raised. Moreover, the capacity of the negative electrode 5 can be enlarged, compared with the capacity of the positive electrode. Consequently, a lithium ion can be discharged not only from the negative electrode active material of an aluminum-lithium alloy, but also from a lithium metal layer at the time of discharging. And charging and discharging efficiency can be neared to 100% and high potential can be maintained until the finish of discharging.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in lithium batteries.

[Prior art] Conventionally, metallic lithium has been used alone in the negative electrode of lithium batteries, but the precipitated lithium during charging is extremely active and may react with the electrolyte or cause dendrite growth of the precipitated lithium. Therefore, there were problems such as internal short circuits and a decrease in capacity.

As an improvement thereof, it has been proposed to use a lithium-aluminum alloy for the negative electrode. For example, JP-A-61-66
No. 369 and US Pat. No. 4,002,492 disclose that lithium is diffused into aluminum by an electrochemical alloying reaction between lithium and aluminum during charging,
Techniques have been disclosed that attempt to suppress the reaction of precipitated lithium with an electrolytic solution and the growth of dendrites. However, the release reaction of sodium from the lithium-aluminum alloy during discharge is not fast enough, and therefore sufficient discharge characteristics are not necessarily obtained.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems and provides a lithium battery with improved discharge characteristics, charge/discharge efficiency, charge/discharge capacity, cycle tfQ, and maximum discharge current by increasing the rate of lithium release from the negative electrode. The purpose is to provide

[Means for Solving the Problems] The lithium battery of the present invention includes a positive electrode integrally formed with a sheet-like active material in close contact with a current collecting electrode, and an aluminum cathode in close contact with the sheet-like active material through a separator. Alternatively, it is characterized by having a negative electrode active material made of at least 1Fli of an aluminum alloy, and a negative electrode having a lithium metal layer connected to the back side of the surface where the separator is in close contact with the negative electrode active material.

[Operations and Effects of the Invention] The lithium battery of the present invention has a negative electrode active material made of aluminum or an aluminum-lithium alloy, and a lithium metal layer provided on the W surface side of the negative electrode active material on which the separator is in close contact. It is something. By having such a structure, f! The electrode potential can be lowered relative to the positive electrode and the battery voltage can be increased. Moreover, the capacity of the negative electrode in which the negative electrode active material and the lithium gold Ji layer are integrated can be made larger than that of the positive electrode.

Therefore, during discharging, lithium ions can be released not only from the aluminum-lithium alloy negative electrode active material but also from the lithium metal layer, making it possible to approach charge and discharge efficiency to 100% and maintain a high potential until the end of discharge. be able to.

Furthermore, during charging, lithium undergoes an alloying reaction on the surface of the negative electrode active material near the positive electrode and is not deposited on the lithium metal layer, so problems such as dendrite growth and reaction between precipitated lithium and electrolyte solution do not occur.

[Example] The present invention will be explained below with reference to Examples.

FIG. 1 shows a perspective view showing the configuration of this embodiment.

This lithium battery consists of a positive electrode 1 in which a collective i-electrode 2 and a sheet-like active material 3 are closely contacted and integrally formed, and a separator 4 is interposed between the positive electrode 1 and the sheet-like active material 3 made of aluminum or an aluminum alloy. A lithium metal layer 7 is closely adhered to the negative electrode active material 6 and the back side of the negative electrode active material 6 to which the separator 4 is in close contact, forming the negative electrode 5 . The separator 4 is mainly impregnated with an electrolytic solution (not shown). A positive terminal 8 made of 5US304 is connected to the current collector electrode 2, and an n-pole terminal 9 made of aluminum is connected to the negative electrode active material 6, and they are sealed by the P1-sealing method to prevent liquid from leaking into the plastic film case 10. It is formed by

<Example 1> The current collecting electrode 2 is an expanded metal made of 5US304 (5
0x50x0.2mm).

The sheet-like active material 3 is a plain woven fabric of phenolic activated carbon fibers (
50X50X0.5mm) to form a sag and collect current 82
And what is sheet-like active material 3? 9? It is integrated.

Separator 4 is polypropylene nonwoven fabric (55 x 55 x 0
．． 2mm), sheet-like active material 3d f1411
It is sandwiched by iKatsumono 6. The electrolyte impregnated into the separator 4 is 3fvILiCIO4/propylene carbonate 60%-1,2-dime(-xyethane 40% by volume)
It is a solution of

The negative electrode active material 6 is an aluminum-lithium alloy (55X5
A lithium metal layer (50X50X0.2m+) 7 is attached to the back of the fi
lfi 5 is formed.

These contents are housed in a high-barrier plastic film case 10 mainly made of polyethylene and aluminum.

The basic operation of this battery will be explained. When a voltage of 3 V is applied between the positive electrode terminal 8 and the terminal 9 of the opening 8i, ClO4- ions in the electrolytic solution gather on the sheet-like active material 3 in the positive electrode 1, giving electrons to the sheet-like active material 3. These electrons are transmitted to the external circuit via the current collecting electrode 2. ClO4- remains in the sheet-like active material-F due to electrical adsorption.

On the other hand, in the negative electrode 5, [i+ ions in the electrolyte gather on the aluminum-lithium alloy that is the negative electrode active material 6, receive electrons transmitted through the external circuit, and become lithium on the aluminum-lithium alloy negative electrode active material 6. alloying with lithium progresses. This state is charging.

In the discharge, electrons are transmitted in the opposite way to the above, and ClO4 is transferred into the electrolyte.
- ions and Li+ ions are released.

In this case, a rib-ram metal layer 7 is formed on the back side of the negative electrode active material 6.
By providing this, the potential of the negative electrode 6 can be made lower than the positive +41. That is, the voltage between the terminals immediately after the battery is manufactured is 0.0 if there is no lithium gold IiI layer 7.
Although it is about 3V, it can be increased to about 2.7V by forming the lithium metal layer 7. Therefore, this battery can maintain a high voltage until the end of discharge.

Further, due to the presence of the lithium metal layer 7, the capacity of the negative electrode 5 made of the negative trI active material 6 can be made larger than that of the positive electrode. Therefore, during discharging, [-i+ ions are released not only from the negative electrode active material 6 but also from the lithium metal layer 7. This is the charge/discharge efficiency (ratio of charge amount to 1ffl (discharge m/
Charging suspension)
This is effective in bringing it close to 0%. That is, in the absence of the lithium metal layer 7, the terminal voltage decreases at the end of discharge, making it difficult to discharge, and the L from the negative electrode active material 6 decreases.
Based on the fact that the release of i+ ions is not 100% reversible, the charging and discharging efficiency of the battery is 80-90%.
% or less. Therefore, ClO4- accumulates on the positive electrode active material, deteriorating the discharge characteristics from the next cycle onwards. However, when the lithium metal layer 7 is provided, the inter-terminal voltage is maintained high even at the end of discharge, and the lithium metal layer 7 takes over and releases l-i+ ions that were not released from the negative electrode active material. Therefore, the charging/discharging efficiency can be brought close to 100%. Therefore, the cycle life can be dramatically extended.

(Comparative Example 1) A battery of this comparative example was formed in the same manner as the battery of Example 1 except that the negative electrode active material was only a lithium aluminum alloy and the lithium metal layer was not provided.

(Evaluation) FIG. 2 shows the relationship between charge/discharge cycles and discharge capacity in Example 1 and Comparative Example 1. In the case of Example 1 in which the lithium metal layer of the present invention was provided, the discharge capacity did not deteriorate. On the other hand, in Comparative Example 1 in which no lithium metal layer was provided, the discharge capacity decreased as the number of cycles increased. This cycle test consists of 3
The graph shows the change in discharge capacity with respect to the number of cycles when the battery was charged at 3 mA for 1 hour and then discharged at 3 mA for 1 ON or until it reached 1 V.

Compared to Comparative Example 1, in Example 1 in which the lithium metal layer 7 was provided, the cycle life was extended by more than 10 times.

In addition, during charging, Li+ ions undergo an alloying reaction with the negative electrode active material 6-H near the positive electrode, and only a small amount of them precipitate on the lithium metal layer 7, resulting in a short circuit due to the separator's own suitability due to the growth of Puntorai 1~. Also, problems such as decomposition reactions between the precipitated lithium metal and the electrolytic solution could be avoided.

(Example 2) FIG. 3 is a perspective view illustrating the structure of a battery according to this example.

This lithium battery has a current collecting electrode 12 and a sheet-like active material 13.
and a negative electrode active material 16 formed of an aluminum-lithium alloy on the sheet-like active material 13 side of the positive electrode 11 with a separator 14 interposed therebetween.
A lithium metal layer 17 is closely attached to the back side of the negative electrode active material 16 to which the separator is attached, forming the negative electrode 15 .

This c”tViA active material 16 has a diameter of 0.1 to 0.5 m.
A calligraphy hole 18 of m is provided. The mine vinegar solution, one positive terminal, negative terminal 20, and case 21 are the same as in the first embodiment.

By providing the through holes 18 in the negative electrode active material 16, the lithium metal layer 17 on the back surface of the negative electrode active material 16 is formed during discharge.
The lithium released from the through hole 18 moves more easily to the separator side, and the discharge current is reduced to 2.
It can be made larger than that. Also, the diameter of the through hole is 1
When the thickness exceeds mm, the separator 14 and lithium gold ffF
Since there is a possibility that 117 comes into direct contact with the through hole, andrite growth of lithium occurs through the through hole during charging, causing a short circuit problem, the diameter of the through hole is preferably Q, 5 mm or less.

The width of the through hole is large, and the discharge performance is improved, but the negative electrode active material 1
Considering the mechanical strength, resistance, etc. of No. 6, 10 pieces/cm' is appropriate.

Therefore, if a through hole with a diameter of 0.1 to Q, 5n+m is provided in the negative electrode active material, the movement of lithium ions released from the lithium metal layer on the back side of the negative electrode active material into the electrolyte becomes easier, and the discharge current increases. can be made larger.

(Example 3) In this example, a satin woven fabric of phenolic activated carbon fiber was used as the sheet-like active material in Example 1, and a lithium-aluminum alloy (50x50x0.1
They are the same except that n+m> is used. As shown in the cross-sectional view of the satin weave in Fig. 5 and the organization chart in Fig. 4, its tissue point is the 7th point.
As shown in the cross-sectional view of the plain weave in the figure, the wefts are not adjacent to each other, but are intertwined at a certain interval, so that the weft or warp yarns are long and floating, creating a coarse weave. Therefore, the surface becomes smooth and 1
When it is in contact with the J electrode, the contact area is large and the current collection efficiency is considered to be high.

A battery was constructed using this sheet-like active material made of satin woven fabric.

(Comparative Example 2) In order to compare the performance of fiber cloths with different weaving methods of sheet-like active materials, a plain woven cloth shown in the plane structure diagram of FIG. 6 was used. However, the square electrode overactive material was formed from a lithium-aluminum alloy (50x50x'0.2 mm).The other separators and electrolytes were the same to form a battery.

I made plans for these two batteries.

The results of this charging/discharging cycle test are shown in FIG. 8, and the charging/discharging efficiency is shown in FIG. 9. The test method is 0. Charge with OV for 1 hour,
was discharged through a resistance of Ω.

The discharge capacity at this time is the same as in the case of plain woven fabric, but the charging /
J5 [As shown in FIG. 9, the electric efficiency was improved by about 10% in the case of satin woven fabric compared to plain woven fabric. In the case of the charge/discharge cycle test, in the case of this example, the discharge capacity did not decrease and was 0.
．． The discharge capacity of the battery of Comparative Example 2, which maintains 6 mAh, is decreased.

In addition to the satin woven fabric, the same effect can be obtained by using a diagonal woven fabric (twill woven fabric) (FIG. 11 shows a knitting can diagram, and FIG. 12 shows a sectional view). By making the surface of the sheet-like active material smooth in this manner, it is possible to suppress a decrease in discharge capacity due to an increase in the number of cycles, more than in the case of a plain woven cloth.

In this way, when a sheet-like active material of the positive electrode is used with a highly smooth surface such as a satin woven fabric of phenolic activated carbon fibers, the charge/discharge efficiency can be further improved.

<Example 4> This example is the same as Example 3 except that J3 was used as the sheet-like active material, and an activated carbon fiber cloth made of acrylic fibers was used. That is, a plain woven fabric made of acrylic activated carbon 4 was used. The result of this charging cycle test is shown in FIG.

In the case of acrylic activated carbon fibers, the amount of lightning melt did not decrease after charging at 0.4V for 1 hour and discharging through a resistance of 1Ω for 60 times. The discharge capacity decreases due to repeated cycles,
I could only repeat it about 20 times. Charging and discharging J'l when charged for 1 hour at 0.4 V and discharged through a resistance of 1Ω is shown in Figure 9. In the case of the plain weave phenolic activated carbon fiber cloth of Comparative Example 2, the charge/discharge efficiency was 75%, but in the case of the acrylic type, it improved to 80 to 90%. The charging/discharging cycle test results are shown in FIG. 10. This is because the crystal structure of the phenolic activated carbon fiber cloth is Alf7.
Because it is in the form of a silica, it is easy to trap electrolyte ions and difficult to release them, whereas in the case of acrylic activated carbon 11M,
This is thought to be because the activated carbon fiber has good crystallinity and contains 2 to 10% nitrogen element in its molecular structure, making it easy to trap and release electrolyzed ions. In this case, there is almost no decrease in discharge capacity.

Therefore, if acrylic activated carbon fiber is used, the charge/discharge f
By increasing the IJ rate, it is possible to create a battery whose discharge capacity does not decrease even when the number of J cycles is increased.

In other words, the conductive polymer polyaniline has a molecular structure in which benzene rings are connected using nitrogen atoms as bonds. When this polyaniline is doped with ClO4- etc., the dopant ClO4- is formed using the nitrogen atom as an active center.
is localized and doped, but the polymer chain is stable. On the other hand, in cases where the polymer chain is formed by conjugated double bonds between atoms, such as in polyacetylene, doping delocalizes the dopant and easily breaks the double bonds between carbons. It reacts with the polymer chain/
+5 [Capacity decreases. Inferring from these facts, it is the reactivity of this dopant (ClO4-) and the bonded chains of the activated carbon fibers that determines the charging and discharging efficiency of the activated carbon fiber cloth.
ff is a bonded chain in which the nitrogen atom of the nitrile group forms at least a cyclic heterocycle, localizing the dopant;
This is thought to be because it does not react with the main bond chain. In the case of rayon-based activated carbon fibers, the above analogy is considered to be correct since they are similar to phenol-based fibers and both do not contain nitrogen atoms.

The current electrode is a part that collects electrons generated in the sheet-like active material and relays them to an external terminal, and is made of a highly conductive metal.

Further, in order to increase the efficiency, needle-like protrusions formed on the incoming electrode may be inserted into the sheet-like active material. As this electrode, stainless steel material such as 5US304, expanded metal, mesh metal, punched metal, etc. can be used.

The sheet-like active material can be a cloth-like, paper-like, or felt-like material made of activated carbon fibers or conductive polymer fibers. The activated carbon fibers may be phenolic activated carbon Jli H, or activated carbon fibers such as PAN (acrylic), rayon, pitch, and the like. Alternatively, acrylic lut, rayon fiber, pitch, or the like may be directly fired and activated to form activated carbon.

Further, when using a phenolic activated carbon fiber cloth, if a satin woven cloth is used, the contact area between the electrodes is increased compared to the case of flat 1a cloth, and the internal resistance of the battery is lowered, resulting in a battery with better battery characteristics. Furthermore, in the case of an acrylic activated carbon fiber set in which acrylic carbon fibers are activated, even if a plain woven fabric is used, even better battery characteristics can be exhibited due to the characteristics of the activated carbon fiber itself.

A polypyroprene nonwoven fabric is used as the separator, and other porous sheets such as glass fiber and ceramic fiber can also be used.

In addition to the aluminum-lithium alloy, the negative electrode active material may include aluminum, aluminum-carbon aluminum-magnesium, aluminum-copper, aluminum-silicon-lithium, aluminum-magnesium-lithium, aluminum-copper-lithium alloy, etc. can.

Further, the negative electrode active material can be formed with six holes having a pore diameter of 0.5IllIl or less in a number of 10 turns/C1112 or less.

This through hole can facilitate the movement of metallic lithium released from the lithium metal layer provided on the back side into the electrolytic solution. Therefore, the discharge current can be increased.

The lithium metal layer is connected to the negative electrode active material and usually has a thickness of about 1 m. The connection method is to bring the lithium metal layer and the f1 electrode active material into close contact, or to sandwich a metal that does not react with lithium metal, such as nickel or stainless steel, between them, or to use an insulating plastic sheet, such as polypropylene nonwoven fabric, etc. It is difficult to connect the negative electrode active material and the lithium metal layer with a metal that does not react with lithium metal, such as nickel or stainless steel. This lithium metal layer (T11) releases Li+ ions into the electrolyte in the same way as the negative electrode active material. Therefore, compared to the case of only the negative electrode active material, it is possible to assist the release reaction and bring the discharge efficiency closer to 100%. Furthermore, the reason why the lithium metal layer is connected to the back side of the negative electrode active material v1 relative to the positive electrode surface side is to prevent dendrites, which do not occur when a conventional rhidium square rod active material is used.

A non-aqueous solvent that dissolves the electrolyte is used as the electrolytic solution, and propylene carbonate, 1,2-dimeth4-thiecune, T-butyrolactone, te-1-rahydrofuran, dimedylformamide, 1,3-dioxolane, aretonitrile, etc. are used alone. Or a mixture thereof can be used. The electrolytes used are LiCl Oa, L i r' Fe
, L i A S F s , L i CF 3SO3
, Li[3Fa, etc. can be used.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional perspective view explaining the structure of the lithium battery of Example 1, FIG. 2 is a graph showing changes in the discharge-to-dark cycle of the battery of Example 2, and FIG. 3 is a graph of the lithium battery of Example 2. Cross-sectional perspective views explaining the configuration, FIGS. 4 to 7, and 11
Figure 12 shows the texture of the sheet-like active material woven fabric, Figure 4 shows the organization diagram of vermilion Fj81, Figure 5 shows the sectional view of satin fabric, Figure 6 shows the organization diagram of plain weave, and Figure 7 shows the organization diagram of the woven fabric of sheet-like active material. The figure is a cross-sectional view of the plain weave, FIG. 11 is a tissue diagram of the oblique weave, FIG. 12 is a cross-sectional view of the oblique weave, and FIG. 8 is a graph showing +1 cycle change in discharge capacity of Example 3.
FIG. 9 is a graph showing the charging efficiency of Example 3 and Example 4,
FIG. 10 is a graph showing cycle changes in charge capacity in Example 4. 1.11...Positive electrode 2.12...Collecting electrode 0.
13...Sheet-like active material 5.15...Negative electrode 6.16...Negative electrode active material 7
．． 17 Lithium metal layer 18...through hole Patent applicant Nippondenso Co., Ltd. Agent Hiroshi Okawa Figure 1 Figure 3 Figure 2 Figure 4 Figure 6 Figure 7 Figure 8 Figure 10 Cycle (cycle) ) Figure 9 Figure 11 Figure 12

Claims (4)

[Claims] (1) a positive electrode formed integrally with a sheet-like active material in close contact with a current collecting electrode; a negative electrode active material made of at least one of aluminum or an aluminum alloy, and in close contact with the sheet-like active material through a separator; A lithium battery comprising a negative electrode having a lithium metal layer closely attached to the back side of the surface to which the separator is closely attached to the negative electrode active material. (2) 10 through holes of 0.5 mm or less are formed in the negative electrode active material.
The lithium battery according to claim 1, wherein the lithium battery is formed in an amount of not more than 2 pieces/cm^2. (3) The lithium battery according to claim 1, wherein the sheet-like active material is made of phenolic activated carbon fibers formed into a satin weave. (4) The lithium battery according to claim 1, wherein the sheet-like active material is formed of acrylic activated carbon fiber.