JPS5873968A - Electrode unit, battery cell and method of improving inversion thereof - 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] The present invention relates to an electrode unit having a structure that applies compressive force to the electrode, a battery having such an electrode unit, and a method for improving the reversibility of the battery. .

The number of times a metal electrode, such as an alkali metal cathode (ie, negative electrode), of an electrolytically decomposable cell (battery) can be repeatedly charged and discharged usually determines the reversibility of the battery. Assuming there is sufficient electrolyte, the reversibility (
R) is the number of complete charges and discharges obtained from the cell;
and the ratio of the amount of metal contained in the electrode to the stoichiometric amount of metal required for complete reaction at the opposite electrode ((1)). It is given in the form of a product (wholesale n = aT). One complete peeling from the metal electrode (one reversal at the end) is one complete peeling from the metal electrode (one reversal at
In general, this process cannot be repeated ad infinitum, as corrosion or physical isolation of the metal in the electrode structure makes debonding increasingly difficult. Can not. Sometimes the metal cannot reach exfoliation and becomes electrochemically inert. To compensate for the loss of active metal available for stripping, it is temporarily necessary to contain more metal in the electrode than is required for a complete reaction by the active ingredient of the battery km. Therefore, reversibility is generally a function of the method of stripping, the amount of metal obtained in the electrode, the amount of electrolyte obtained, etc.

For example, when using a lithium electrode in a free state (no pressing force is applied), K I in polyethylene carbonate
If the electrolyte contains M Lim F6 or I M Lie104, the maximum number of times the battery can be reversed is 1.6~
It ranks 2.5. It would be very desirable if the reversibility of such electrodes and knots could be improved.

This invention seeks to significantly increase the number of inversions for electrodes that form porosity or outer coalescent deposits on themselves.

That is, the electrode unit of the present invention includes an electrode that forms a porous outer coalescence material on itself, and a mechanism that applies compressive force to the electrode so that the formed material can be easily peeled off from the outer surface of the electrode unit. It includes the following.

The battery of the present invention also comprises an anode, a cathode, and an electrolyte, the cathode forming a porous outer coalesced seed on itself, and the formed seed forming a porous outer seed on its outer surface. It includes a mechanism that applies compressive force to the electrode so that it can be easily peeled off from the electrode. As the electrode, for example, an alkali metal cathode such as a lithium cathode is used. Further, it is preferable that the pressing force be applied continuously at least during recharging.

Furthermore, this invention attempts to improve the reversibility of the battery by increasing the number of times the cell electrodes are reversed. 11 The method of the present invention is to form an electrolyte cell having an anode and a cathode forming a porous outer coalescent material on itself, and an electrolyte. A compressive force is applied to this cathode as described above. In this case as well, the electrode is preferably an alkali metal cathode such as a lithium cathode, and it is desirable that the charging and discharging pressures be applied continuously.

According to the electrode unit, battery, and method of the present invention, very remarkable effects can be obtained. By applying a compressive force, the coalescing seed particles on the electrodes are brought closer together. As discussed in more detail below, this reduces the interparticle electrical resistance and counteracts the increased resistance to metal ion migration from the particles through the porous seed. Therefore, according to the present invention, the peeling of metal from the outer surface of the electrode (that is, from the front surface of the seed) is promoted.

In one embodiment of the invention, an electrolyte cell (battery) includes at least one anode, an alkali metal cathode, at least one separator between the anode and cathode, and a non-liquid electrolyte. A mechanism is used to apply a compressive force that exceeds the compressive strength of the coalesced seeds on the cathode.The compressive force compresses the seeds and brings the particles closer together to reduce the interparticle electrical resistance. This compressive force is preferably such that it exceeds the compressive strength of the substrate on which the seeds are plated and physically deforms the substrate.This compressive force causes the seeds to coalesce. In the front WJ (between the cathode and the separator), the peeling off of the alkali metal from the electrolyte alkali metal particles is promoted, and the reversibility of the battery is significantly improved.

This invention is particularly effective when applied to lithium electrodes. At a critical pressure above which the lithium electrode deforms, the plating structure is noticeably different from that obtained at low pressures.

When scanned with an electron microscope, the plated seeds obtained using lithium under low pressure are highly porous, with particles in the shape of loose platelets or flats. All plated seeds obtained above the critical pressure are non-porous. The particles are cylindrical, with their axes oriented perpendicular to the substrate. These cylinders are gathered close to each other, and the end faces of the cylinders form non-porous smooth surfaces parallel to the base surface.

Such seeds are maintained even after several cycles of charging and discharging. In special cases where pressure fluctuates across the lithium electrode, porous types and smooth types can be used. There is a clear boundary between the cylindrical grains.This shows that the plating structure is sensitively influenced by pressure close to the critical pressure.

In other embodiments, the anode is of uniform current density, such as a Mo52 anode, and the cathode is an alkali metal substrate with a seed material on the outside that incorporates the alkali metal substrate on the inside. Each metal particle has its own properties. - For example, at the anode, is LfxMO8
A transition metal chacosinide containing 2 is used, and lithium is used for the cathode. L i x Mo! The 32 anode active material is preferably pretreated to operate in the first phase described in U.S. Pat. No. 4,224,390.

For example, electrode materials such as alkali metals such as lithium,
It is thermodynamically unstable in the presence of a conductive metal ionic electrolyte that is liquid at room temperature. For example, liquid electrolytes react violently with alkali metals to form alkali hydroxides and hydrogen gas. This reaction may become so intense that it may explode. However, some electrolytes react less vigorously with the electrode metal to form a kinetically unstable passivation film on the surface of the metal electrode. Such electrolytes can be used to form practical cells using metal shield electrodes.

For example, after cycling such a metal electrolyte cell a number of times, the two parts of the electrode can be physically separated. (1) a central, substantially non-porous, membraned metal substrate; and (2) a plated combination of porous, electrolytically active metal particles with each particle having a passivating membrane. I want seeds,
That's it.

When such a metal electrode is exposed to an electrolyte, a chemical reaction begins, which forms a passivation film on the metal surface. This passivated membrane is essentially non-porous, although it is permeable to ions. This membrane attempts to electrochemically isolate metal particles. The conductivity on the particles is too high: there is a balance between increasing the passivation reaction due to the conductivity and reducing the electrochemical activity of the particles due to the conductivity being too low. Low conductivity reduces the rate of reaction between the electrolyte and metal, but
.

Facilitates debonding of the metal from the substrate than from the inside of the particle (due to the higher contact resistance between the particles).

In order to obtain a large number of inversions (T) and to reduce the area of the metal electrode (to reduce the reaction with the electrolyte forming excess passivating metal), it is necessary to use nonporous material inside or below the seed material. It is desirable that stripping of the electrolytically active metal occur selectively on the front surface (outside) of the seed rather than on the surface of the substrate. If it does not occur at the front but at the lower base,
The front surface loses physical contact with the remaining portion of the seed and the substrate, so that the front surface becomes inert. Compressing the seed beyond its compressive strength (i.e., deforming the seed to aggregate its particles) causes selective debonding of the front surface.

There are three resistance factors that prevent the electrodes from peeling off from various parts during operation of the battery. That is, (1) electrical resistance between the particle in question and the current collector; These include the ion resistance associated with movement, and the resistance associated with (Ill) metal ions being detached from the particles and transported through the passivation membrane.

Regarding the first factor, the closer the particles are to the front of the grain, the higher the electrical storm resistance. In fact, it is reasonable to assume that the resistance is zero for particles at the surface of the substrate.

Regarding the second factor, the ionic resistance is highest for the substrate and lower for particles closer to the front of the seed. The ionic resistance is lowest at the front surface of the species, where the diffusion of ions to become active ions is shortest (and highest at the substrate where the diffusion path is longest).

Regarding the third factor, passivation resistance depends on the chemistry of the passivation film and cannot be substantially changed by changing the physical parameters of the seed.

When the seeds to be coalesced are subjected to a compressive force (preferably in an orthogonal direction) that exceeds their compressive strength, a twofold effect occurs. First of all, the porosity of the seed is reduced as the particles are brought closer together. This results in more ionic resistance to delamination at the substrate than at the front surface. At the same time, since the contact area between adjacent particles increases, the electrical resistance between the seed particles decreases. As a result, the sum of the three resistance factors becomes large near the substrate, and the sum becomes small for particles near the front of the particle, improving the reversibility of the battery as desired (the front is the electrode (For convenience, it can be considered as a relay part between the and the separator). The compressive force thus provides a smooth, non-porous surface, which makes the electrode electrically active and facilitates its peeling from the outer surface.

The invention is applicable to any type of battery, especially those having electrodes that react with the electrolyte to form a porous coalescent material on the electrodes during recharging. Cathode materials, such as alkali metals, alkaline earth metals, and transition metals such as zinc, react with certain electrolytes to form species. In the presence of a non-liquid electrolyte, such as polypropylene carbonate containing Ltolo4, an alkali metal, e.g. do.

As mentioned above, the compressive force is such that the particles of the covering are compressed and aggregated, thereby deforming the covering. Therefore, the compressive force employed in this invention will vary depending on the nature of the electrode, electrolyte, and covering. If it is a singing metal, the compression force may be small. For example, the compressive forces at which alkali metals deform are typically small, yet all alkali metals are soft and malleable; for example, the tensile strength of lithium ranges from 60 to 80 psf. Given that the covering is porous and its internal cavities are filled with liquid electrolyte, the compressive strength (the ability of the material to deform under pressure) of the covering is less than that of pure metal.

The compression force need not be applied continuously during charging and discharging. The period of application can be short, for example, once towards the end of a recharge, or after a recharge and then before use. Yes, but it is preferable to apply continuous compression at least during recharging.

For lithium, approximately 50-500 psi of compressive force is applied continuously during recharging. As a result, a covering consisting of cylindrical particles having an axis perpendicular to the substrate is obtained.

Applying a compressive force to the electrode compresses the material that makes up the entire cell. The cell components should be soft and flexible so that the compressive forces are applied evenly. It is undesirable to use an expanded metal grid for the current collector and to use coarse-grained powders for the electrode active material. It is also desirable that the separator material be flexible. Using metal foil as a current collector,
Preferably, a phosphorescent material such as graphite or molybdenum sulfide is used for the anode. If possible, the anode should be heated to a uniform chemical flow, so that the base material can be used evenly. Separate body and Xi.

Polypropylene or a flexible, porous or semi-permeable material is preferred.

As shown in FIG. 1, a simple coil spring 10 may be used as a mechanism for applying 1 compression force to 5, and this is brought into contact with a pressure plate 12 placed on the top surface of the battery. Of course, a mechanism different from this may also be used. FIG. 2 shows a coiled battery in which the separator and am clamp 10a abut the radial cells and apply a compressive force. In either case, due to the compressive force from the spring and C-type clamp,
The porosity of the covering is reduced and the electrical resistance between the covering particles is reduced.

Returning again to FIG. 1, the electrolyte cell has a cathode 14 (with a current collector) connected to two anodes 1
6 (equipped with a current collector). An electrolyte saturation separator 1B separates the cathode 14 from the anode 16 and contains the electrolyte for the cell within the pores. The cathode, anode and separator together constitute an electrochemically active cell for the resulting current. The cathode is of such a composition that a porous, coalescent covering is formed thereon. The cells are compressed and contained within a container 20, which is preferably sealed in an inert atmosphere.

Now, as shown in Fig. 3, when forming a coiled cell, the elasticity of the two layers of separators located between the cathode and anode and on the outside are utilized to tightly wrap them around the conductor. A compressive force is applied to the desired electrode, either the cathode 14 or the anode 16.

Tension on the separator is maintained by a C-clamp 10a to provide the desired compressive force. It is preferable to use polypropylene for the separator 18.

This will be explained in more detail by referring to a busy example.

Example 1 An electrolyte cell was formed between two flat rigid pressure plates.

The anode used was a surface-treated molybdenum powder uniformly distributed on an aluminum foil substrate as described in US Pat. No. 4,251,606.

This anode provided a uniform current density to the cell. The molybdenum powder was spread at a density of 1011 I9/i, and the anode area was 5.6 scratches2.

A lithium foil of the same size and thickness of 125 microns was used as the cathode, and was sandwiched between two anodes provided with a microporous polypropylene separator (Celgard 2500 manufactured by Celanese). As an electrolyte, one containing propylene carbonate KIM LiAsF6 was used.

Propylene carbonate has a total impurity content of io
The anode and the separator were first saturated with a product that had been purified to less than 0 ppm.

The cell was assembled between two pressure plates through which a compressive force of 27 psi was applied.

The entire cell is sealed in a container filled with argon gas.
A glass-to-metal seal was employed to supply current to the negative terminal of the electrolyte cell. In which cell the anode active material is the first phase Li described in U.S. Pat. No. 4,224,590.
Processed to convert to 7M082. During this time, precautions were taken to ensure that the electrolyte did not deteriorate. The cell was repeatedly charged and discharged at a current of 2 mA with a discharge voltage of 1.3V and a charge voltage of 2.6V.

This cycle was repeated (repeated) until the charge capacity on discharge dropped to 50% of the charge capacity at the end of the 10th cycle.The charge accumulation value for the entire cycle was 210 a+AH. When calculated by taking the ratio of this value to the theoretical charge value assuming that discharge was performed once, the number of inversions of the lithium cathode was 5.

Example 2 An electrolyte cell identical to that of Example 1 except that the compression force was 50 psi was cycled under the same conditions.
The number of times the lithium cathode was inverted was 8.

Example 3 Similarly, only the compressive force was changed by 100 psi K and cycles were performed under the same conditions, resulting in 19 reversals.

Leverage Example 4 Similarly, when only the compression force was changed to 170 pHi and cycles were performed under the same conditions, the number of inversions was 11.

Example 5 Same conditions as Example 4 except for electrolyte (%, o, s).

From these examples, it is clear that compressive force plays a major role in determining the number of reversals. The number of inversions varies depending on the electrolyte, but compressive force is applied to the cell.
In particular, the number of inversions obtained always leaves the cell free.
This is greater than the number of reversals that can be obtained in the case of Nishishin.

[Brief explanation of the drawing]

Fig. 1 is a side explanatory view showing the tree of the present invention (Fig. 2 is a side explanatory view showing the tree of the present invention, which is also coiled), and Figure 3 is an explanatory view showing the method of forming the tree of the present invention. 10... Coil spring 12... Pressure plate 14...
・Cathode 16... Anode 1B... Separator Patent applicant Mori Energy Limited Patent application agent Patent attorney Sugawara - Engraving of drawings (no changes to content) FIG, 1 Procedural amendment C method) t Case Indication Patent Application No. 11C/140918/2 Title of Invention 11C & Unit, Battery Cell and Method for Improving Its Reversibility & Relationship with the Case of Person Who Makes Amendment Patent Applicant Place: Canada Buoy 5C 4G 2 Burnaby, Pritish Columbia , Miltlestree)
4010 Name Mori Energy Limited Representative James Nee: Earl Stiles: 1 Nationality Canada 4 Address of agent 1-58-9-5 Kitasenzoku, Ota-ku, Tokyo Date of amended order 1982 November 12, 2018 (Shipped on November 50, 2016) 6
, Target of correction/Drawing Z Contents of correction Engraving of drawing (no change in content) As attached 1 Stomach・-289

Claims (1)

[Claims] [1] Electrodes (14, 16) forming a porous coalesced deposit on the outside of themselves, and compressive force applied to these electrodes to compress said deposit and remove it from its surface. an electrode unit comprising: a mechanism for promoting peeling of the electrode unit; A unit according to claim 0, wherein said electrode comprises an alkali metal cathode (14). [5] The unit according to claim 1 or 0, wherein the electrode (14) contains lithium. [4] The unit according to claim 1, 1, (2) or 6, wherein the mechanism continuously applies a compressive force. [6] A unit according to any one of claims [1] to [4], which includes electrolyte metal particles having the following properties. [7] A battery comprising the electrode unit according to any one of claims [1] to [6]. 0 The electrode unit comprises a cathode (14) on which a deposit is formed, an anode (16), and a non-liquid electrolyte in contact with both. ] The bacterial cell described in [2] A separator (
1B). The battery cell according to claim It #I (7) or [. [Japanese] The battery cell according to claim 7, (8) or 0, wherein the alkali metal is lithium. [11] Said electrode (14) further comprises a substrate for lithium, and said mechanism continuously applies a compressive force during recharging to cause this K
A battery according to claim 10, wherein the deposit formed on the recharging electrode comprises cylindrical particles having an axis perpendicular to the substrate. [12] The battery cell according to claim [11], wherein the compressive force is 50 to 500 psi. [15] Any of claims (7) to [:12], such that the anode (16) is a transition metal chalcosinide anode containing LixMO82, and the cathode (14) is a lithium electrode. (14) In a battery comprising a cathode and an anode, at least one of which forms a porous deposit thereon, and an electrolyte, a compressive force is applied to the electrodes. A method for improving the reversibility of a battery cell, such as compressing a deposit to promote its peeling. θ5] The method according to claim 14, in which the pole is lithium. lithium, and the compressive force is continuously applied during recharging.
15]. [17] The method according to claim [16], wherein the compressive force is in the range of 50 to 500 psi. 00 anode is LixMO82. The method according to any one of claims [14] to [17]. [19] The method according to claim [18], wherein the anode is pretreated to function in the first box. (3) The method according to any one of claims [14] to [19], wherein the compressive force is applied continuously during discharging and recharging.