JPH0249364A - lithium secondary battery - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use The present invention relates to a rechargeable and dischargeable lithium secondary battery that can be used as a mobile DC power source, a backup power source, and the like.

Conventional technology Rechargeable lithium secondary batteries that use lithium as an anode (in principle, have a high energy density) have attracted attention in recent years and are being actively developed in various regions. Nosai.

Due to the dendritic and moss-like lithium dendrites that occur in the lithium negative electrode, the positive and negative electrodes become electrically conductive, causing what is called an internal short circuit in the battery, and the negative electrode itself gradually collapsing from its original shape and deteriorating. Therefore, it has been extremely difficult to achieve a long charge/discharge cycle life.

As a solution to this problem, attempts have been made to create lithium alloys that absorb and desorb lithium, but the alloys tend to collapse when a large amount of lithium is absorbed and desorbed, and sufficient effects have not always been achieved. However, improvements in the negative electrode are desired.

Problems to be Solved by the Invention As another attempt, there is a battery system in which vanadium pentoxide, which has a high potential, is used for the positive j, and is combined with a negative pole made of niobium hexoxide (Japanese Patent Publication No. 59412/1982). This niobium hexoxide is easily doped and undoped with lithium ions, and it appears that l is strong against deep charging and discharging.

However, the voltage and capacitance obtained vary depending on the configuration conditions of the positive electrode, negative electrode, etc., and the actual situation is that it has not been commercialized because sufficient characteristics cannot be obtained.

Accordingly, one object of the present invention is to provide a lithium secondary battery in this battery system with increased voltage and electric capacity and excellent over-discharge and charge/discharge cycle life.

Means for Solving the Problems In order to solve the above-mentioned problems, in the present invention, various charging and discharging characteristics of vanadium hexaoxide and niobium hexoxide were studied, and the amount of niobium hexoxide to be filled was changed in molar amount to vanadium hexaoxide. The ratio is 0.
5 or more and 1 or less, and the total amount of lithium contained in the positive electrode and negative electrode is 1.1 in molar ratio to vanadium hexaoxide.
The above is set to 2 or less, and furthermore, the molar ratio of 1 to niobium hexoxide is 2 or less.

Function: In this battery system, during discharge, lithium doped into niobium hexoxide at the negative electrode becomes lithium ions and dissolves into the light liquid, moves into the positive electrode, and is doped into vanadium hexoxide. Furthermore, during charging, the opposite transfer reaction occurs. In other words, only lithium moves between the positive and negative electrodes during charging and discharging.

Now, the charging and discharging of sR niobium on vanadium hexate is considered as follows.

- Role reaction 1 in n (near 3, f5N3V vs Li) Reaction up to the second stage 1.7 to 2 in n (2,3-V2v
(near vSLl) 2 in n (near 2 to I V vs Li) As shown in Figure 2, the charging and discharging reaction of vanadium hexoxide is as follows: when the −th stage reaction sets the potential of lithium to 0, a
The response is around 3V rather than around 5”/.

The second stage reaction is a reaction from 3v or less to around 2v. And for boat fishing, the charge/discharge cycle life of the -stage method is short, and the charge/discharge cycle life tends to decrease by a large margin when the second stage is exceeded and reaches a deep A discharge of 1 V or less. . Therefore, the charge/discharge cycle life can be maintained for a long time by limiting the charging/discharging to the -stage charging/discharging or the second stage charging/discharging as much as possible.

Furthermore, as shown in Figure 3, the discharge of niobium pentaoxide used for the negative electrode is a negative reaction only, and the reference DICNKI
KAGAKU So, & a (1982) W
b205asan Active Materia
l of' Po5itive IC1ectr
odefor Nonaqueous Lithium
As shown in 5econdary Ce1ls,
is a 2-electron reaction. From these facts, the electric capacity of the first stage reaction of vanadium hexoxide is equivalent to 0.5 mole of niobium pentoxide for 1 mole of vanadium hexoxide. It is believed that the potential of niobium oxide (Funetsuri Vc5) is similar to that of metallic lithium, and that it exhibits very stable charging and discharging characteristics if it is 1 V or more.

Therefore, in order to maximize electric capacity.

The charging capacitance of niobium hexoxide should be higher than the first stage reaction of vanadium hexoxide, and the simolar ratio should be higher than 0.5. Further, it is better to keep the molar ratio to 1 or less so that the discharge of vanadium hexaoxide does not exceed the depth of the second stage reaction at worst.

The amount of lithium to be filled is, in principle, the same as the amount of niobium hexoxide, and is preferably between 1 equivalent and 2 equivalents -1, that is, 1 to 2 in terms of molar ratio, to vanadium pentoxide.

However, in reality, a certain amount of Iy lithium, which is involved in charging and discharging, remains in vanadium hexoxide and niobium hexoxide. Therefore, in order to cover this loss, the molar ratio should be at least 1.1 or more.

Furthermore, it is considered that the amount of lithium filled should be the same as the desired electric capacity for niobium hexoxide.

This is not necessarily necessary. In order to maximize the charge/discharge cycle life of niobium hexoxide, it is better to limit the amount of lithium charged as much as possible.

When the charging amount of lithium is equal to or more than the same electric capacity as niobium pentoxide, it is good during shallow charging and discharging, but when it comes to deep charging and discharging, all of the niobium hexoxide is utilized, so the niobium pentoxide crystals The lattice becomes easy to break and the charge/discharge cycle life becomes disadvantageous. On the other hand, if the amount of lithium charged is equal to or greater than the same electric capacity, even if deep charging/discharging is performed, all of the niobium pentoxide will not be utilized, and therefore a stable charging/discharging cycle life cannot be maintained. be.

For these reasons, it is even better to set the filling amount of lithium to 1 molar ratio of 2 or less to niobium pentoxide.

Also, with such a composition ratio, 6
Vanadium oxide is N for lithium.

It shows a potential of about 3.6v, and that of niobium hexoxide is about 1
．． Since the voltage is around 5V, a battery voltage of around 2V can be obtained.

Therefore, not only the charge/discharge characteristics are improved, but also a high voltage of around 2V can be obtained, and the energy density is improved accordingly.

On the other hand, in Japanese Patent Publication No. 62-69412, the capacity of fish cages was restricted.
However, in this case, due to the limitation of negative electrode lithium, the first stage reaction of vanadium hexoxide is also limited, and the efficiency is not necessarily maximum in terms of electric capacity. The amount of niobium filled is at least 1 molar ratio (double the electric capacity) to vanadium pentoxide, while the amount of lithium is less than 1 molar ratio to vanadium pentoxide (less than half the electric capacity of niobium pentoxide). , the amount of lithium is limited with a very large amount of niobium pentoxide, but in this case, the resulting battery voltage is around 1.5V, so it is positioned as a 1.6V battery,
The aim is completely different from the present invention.

As mentioned above, the features of the present invention are as follows! Vanadium hexachloride and niobium pentoxide are used to achieve the highest possible pressure, maximum energy density, and long charge/discharge cycle life.

The optimum composition ratio of lithium was found.

This will be explained below using examples.

Embodiment FIG. 1 is a sectional view of a lithium secondary battery according to the present invention. In the figure, 1 is a case that also serves as the positive and negative terminals.

2 is a sealing plate that also serves as a negative electrode terminal, 3 is a polypropylene gasket that insulates and seals the case and the sealing plate, 4 is a positive electrode, 90ftπ of vanadium pentoxide, 5wt% of carbon black as a conductive agent, and a binder. The aqueous dispersion of fluororesin was kneaded in terms of solid content in Swt%, dried and pulverized, formed into a pellet with a diameter of 15 ff, and vacuum dried at 1 tso° C. to dehydrate it. The filling amount of vanadium hexoxide in the positive electrode 4 was 238 fiSF (the first stage reaction from around 3.5 V, equivalent to 35 mAh in terms of electric capacity).

6 is a negative i, and 90 wt% of niobium hexoxide, carbon black SWt as a conductive agent, and 5 wt% of solid content of aqueous disvergebond as a fluororesin as a binder are kneaded,
After drying and pulverizing, it is formed into a pellet with a diameter of 15fl, and
It is a mixture obtained by vacuum drying at °C and dehydration treatment, and the desired lithium foil is closely attached to this mixture, and it is immersed in a propylene carbonate solution containing 1 mol/l of lithium perchlorate. Lithium is doped into niobium hexoxide. 6 is polypropylene microporous membrane and nonwoven fabric 2
This is a separator made of a layered laminate.

The electrolytic solution was a solvent in which propylene carbonate and 1.2 dimethoxyethane were mixed in a ratio of 1=1, with 1 mol/l of lithium perchlorate dissolved therein. The size of this battery is 2 in diameter
0Jjll thickness 2.6 shoulder thickness.

In such a basic configuration, first, in order to compare the effects of the filling ratio of vanadium pentoxide and niobium hexoxide, the amount of vanadium pentoxide was fixed and the filling ratio of niobium pentoxide was set as shown in Table 1. At this time, the amount of lithium charged is 1 liter of niobium pentoxide in electric capacity, and 2 liters in molar ratio.
It was doubled.

Table 1 Filling ratio of niobium pentoxide The capacitance ratio in Table 1 is the capacitance ratio of niobium hexoxide when the first stage discharge reaction of vanadium pentoxide is 1, and the positive and negative reaction equation described above. Therefore, the molar ratio of niobium pentoxide is twice as high. Battery N with these formulations
is set from 1 to 5. These batteries were discharged at 500 μm and the capacitance was measured. The results are shown in FIG.

Next, leave it for 1 month at 60'C with a load resistance of 3Ω to bring it into an over-discharge state, then charge it with a SOOμm until it reaches 2.2vK'7, then discharge it with a 500μm until it reaches 1V. The time was measured. The results are shown in FIG.

As is clear from Figure 4, when the amount of niobium pentoxide in AI is 0.26 molar ratio, the reading time is the shortest, and the reading time is the shortest.
When the molar ratio is 0.6 or more, a constant value can be obtained for the duration of time to reach 1VK.

Also, from Figure 6, after overdischarge, 1.5 of 55
The molar ratio is slightly lower than the duration. This is considered to be because the discharge of 5-completed vanadium has passed its dual role due to overdischarge, and the reversibility of charging and discharging of vanadium hexaoxide has been lost.

From these results, when the filling amount of hexa-dredded niobium is at least 0.5 molar ratio and at most 1 molar ratio, a large electric capacity can be obtained and sufficient resistance to overdischarge can be obtained.

Next, the molar ratio of vanadium hexaoxide and niobium pentoxide was adjusted to 1:0.75 so that the electric capacity was 1:1.5, and the amount of lithium charged was adjusted as shown in Table 2.

For batteries with these formulations, the battery points are 6-11. Using these batteries, discharge with a constant current of SOO μm,
FIG. 6 shows the discharge characteristics, and FIG. 7 shows the emission duration up to 1V. Next, with a constant current of 500μ, 2
．． Repeat charging and discharging between 2v and 1.6v SOO times, and then.

Charge to 2.2v with SOOμm and then 500μ
Figure 8 shows the rate of change (residual rate) compared to the initial stage shown in Figure 6.

Also, in the same way, with a constant current of 6OOμ, from 221 to o
After repeating charging and discharging to V 100 times, charge to 2.2V at 500μm and then 5o.

Discharge until it reaches 1V in μm, measure its duration,
The rate of change (residual rate) compared to the initial stage in Figure 6 is shown in Figure 9.
Shown in the figure.

As is clear from FIG. 6, the higher the K and lithium ratio, the higher the discharge start voltage, which is around 2V, and conversely, when the lithium content is extremely low as in &6, it drops to around 1.5V. Also, as is clear from FIG. 7, the higher the lithium ratio, the longer the duration, and the value remains constant above 1.1. , at a lithium ratio of 1.0 with %7, lithium is 6
It is thought that when niobium oxide is doped with A, there is lithium that does not come out even when it is discharged, so the electric capacity decreases slightly.

Furthermore, even if the amount of lithium is further increased, it will not necessarily be equal to the filling electric capacity of vanadium pentoxide.

In other words, 36 mAh (approximately 70 hours at 500 μm) cannot be obtained.

This means that the reaction of vanadium hexaoxide is n
= 1, and the amount of electrolyte in the battery.
This is thought to be because the reaction efficiency of vanadium pentoxide decreases.

On the other hand, from Fig. 8, A is SOO for relatively shallow charging and discharging.
Even after cycling, there is little deterioration in capacitance, and Alo
There is also a decline in Kana, which is good and bad, and which is bad.

However, in deep charging and discharging from 2.2V to Ov shown in Figure 9, if the lithium amount is 1.6V or less in terms of electric capacity ratio, the deterioration is relatively small, but when it reaches 2.0V, the deterioration is slight. It becomes a dog, and there is considerable deterioration in Black 11's 2.6.

This is because as the lithium ratio increases, all of the niobium hexoxide is utilized through overdischarge.

Because the crystal lattice was partially broken and a large number of lithium ions entered and exited, expansion and contraction were large, and as a result, some of the niobium 5-phthalate mixture was detached, resulting in a decrease in charging and discharging efficiency.
It is thought that , and for black 11, the positive electrode is the second
It appears that the deterioration of the cathode characteristics was also caused by the failure to hold back the intended reaction.

From these facts, it is better to set the filling ratio of lithium to vanadium hexoxide at a molar ratio of 1.1 to 2, and furthermore, to niobium hexaoxide at a molar ratio of 2 or more.
, is even more preferable.

To summarize the above.

x=Nb205/”1205 y=　　Li　　/V2O5 The composition ratio is good.

Among these, especially 0.5≦X≦1.0 (molar ratio) 1.1≦y≦2.0 (tt) 2≦2.0 (molar ratio) z=　　Li　/　Nb2O5 is good.

Expressing these in weight ratio.

0.73≦X≦1.46 0.042≦y≦0.076 and further 2≦0.052 It is.

In addition, when the superposition of vanadium hexoxide is set to 1.

The weight ratios of niobium hexaoxide and lithium are shown in FIG. 10. The shaded area is the scope of the present invention, M+B is the area defined in claim 1, and B is the area defined in claim 2.

The area indicated by the broken line is still the area described in Japanese Patent Publication No. 62-59412.

The present invention is essentially different from the content described in Japanese Patent Publication No. 62-59412, and as a result of various studies, the optimum composition ratio for this battery system was found for the first time, and this is the area of the present invention. By.

It achieves a battery voltage of around 2V, has a high energy density, has a long charge/discharge cycle life, and satisfies overdischarge resistance.

In the examples, the electrolytic solution used was a mixture of propylene carbonate and 1,2 dimethoxyethane at a volume ratio of 1:1, and 1 mol/a of lithium perchlorate dissolved therein, but ethylene was used as the solvent. carbonate, butylene carbonate, ethoxymethoxyethane, 1.2 diethoxyethane.

2-methyltetrahydrocran and the like can also be used. Further, as the solute, lithium fluoroborate, lithium arsenide hexafluoride, lithium hexafluoride phosphate, lithium trifluorometa/sulfonate, etc. can also be used.

Furthermore, although a coin shape is selected as the battery shape in the embodiment, it can also be applied to 1 yen@cedar, 1 shape, etc.

Note that the amount of lithium in the battery can be determined by chemical analysis of lithium present as a lithium compound in the positive electrode and the negative electrode.

Effects of the Invention The present invention makes it possible to provide a lithium secondary battery that has a voltage around 2V, has a good charge/discharge cycle life, and has an excellent melt over discharge tK.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of a coin-shaped lithium secondary battery that can be charged and discharged according to the present invention, Figure 2 is a discharge characteristic diagram of 5-completed vanadium, Figure 3 is a discharge characteristic diagram of niobium hexoxide, and Figure 4 is a diagram of discharge characteristics of niobium hexoxide. Figure, Figure 6, Figure 6, Figure 7: Figure. Fig. 8 and Fig. 9 are special ratio diagrams of the present invention, and Fig. 1° is a composition ratio diagram of the present invention. 1... Main case, 2... Sealing plate, 3...
...Gasket, 4...Positive electrode, 5...
Negative electrode, 6... sehalator. Name of agent: Patent attorney Shigetaka Awano and one other person
When the enemy is used 1--Kazumasa pattern red-also 2--one stroke T31 column 3--ge input/to 4-11 positive brutality 5- sudden contact Chichishun [1 key listen to Hiroshi'r+ Figure 10: NbqOr/20 (Seru hit)

Claims (3)

[Claims] (1) Using an organic solvent in which lithium salt is dissolved as an electrolyte, in a charged state, using vanadium pentoxide as the positive electrode and a compound of lithium and niobium pentoxide as the negative electrode, change the filling amount of the niobium pentoxide to vanadium pentoxide. On the other hand, the molar ratio is 0.5 or more 1
The total amount of lithium contained in the positive and negative electrodes is 5.
A lithium secondary battery characterized in that the molar ratio to vanadium oxide is 1.1 or more and 2 or less. (2) The lithium secondary battery according to claim 1, wherein the molar ratio of lithium to niobium pentoxide is 2 or less. (3) Claim 1, characterized in that the molar ratio of lithium to niobium pentoxide is greater than 2.
Lithium secondary battery as described in section.