HK1189714A - Improved adhesion of active electrode materials to metal electrode substrates - Google Patents

Description

Improved adhesion between active electrode materials and metal electrode substrates

Technical Field

The present invention relates to a method for improving the adhesion between active cathode and anode materials and metal substrates, particularly for lithium ion secondary batteries.

Background

High performance lithium ion secondary batteries with high energy density, fast charge/discharge cycles, and long cycle life have become increasingly important to the hybrid and electric automobile industries. In addition, large lithium ion batteries also play an important role in energy storage for regenerative power generation and valley power generation.

A lithium ion secondary battery generally comprises two electrodes (a cathode and an anode), with a porous separator and a liquid electrolyte material between the two electrodes. At least one electrode, typically a cathode, comprises a metal substrate (acting as a current collector) and an electrode material applied by coating onto the metal substrate. The cathode material is formed by a mixture comprising a lithium-containing compound, a binder, a solvent, and a conductive particulate material, wherein the lithium-containing compound provides a source of lithium ions in the battery. The anode material typically comprises a lithium-intercalatable carbon or graphite-type compound, a binder, a solvent, and a conductive particulate material. Aluminum metal is typically the substrate for the cathode material. Copper metal is typically the substrate for the anode material.

The lithium-containing compound in the electrode material may be, for example, a lithium iron phosphate material (LFP), LiMXO₄(M: Fe, Mn, Co, Ni, etc. and mixtures of these elements; X: P, Si, V, etc. and mixtures of these elements), Li₂FePO₄F、LiCoO₂、LiCo_1/3Ni_1/3Mn_1/3O₂、LiMn₂O₄、Li₂MnO₃-LiMO₂(M：Mn、Ni、Co)、Li₂SO₄Lithium vanadium oxide, lithium vanadium phosphate, lithium titanate, other lithium ion intercalation compounds, and/or mixtures and composites of any of the foregoing materials. The lithium-containing compound in the electrode material may provide lithium ions to the electrolyte and may receive lithium ions from the electrolyte during charge and discharge cycles.

Although lithium-containing compounds have a higher electrical energy density during discharge and also have a large number of charge cycles, they have the disadvantage of having a lower electrical conductivity. To overcome this difficulty, the electrode material is usually provided with a conductive particulate material, for example conductive carbon black. The carbon black provides increased electrical conductivity to the coating. In other electrode coatings, lithium-containing compounds (typically in the form of solid particles) may be coated with graphite layers to provide increased electrical conductivity.

The preparation of electrodes for lithium batteries generally involves coating a metal substrate with a layer of electrode material. Manufacturing techniques have been developed to allow rapid application of coatings of electrode materials. These techniques require that the coating include a solvent. A common solvent is N-methyl-2-pyrrolidone (NMP). A binder, typically polyvinylidene fluoride (PVDF), is also included.

To form the electrodes, electrode materials are typically provided in the form of inks or liquid compositions, which may be applied to the metal substrate by techniques similar to printing techniques. After the electrode material is applied to the substrate, the coating is subjected to a calendering process to compress and heat the coating, which increases the density of the coating.

Two aspects of achieving high performance in these cells are good internal ionic and electronic conductivity. In the case of electronic conductivity, it is important to have a low electrical resistance at the interface between the active cathode material and the metal electrode substrate. This is achieved by ensuring complete adhesion between the cathode and the metal substrate.

The adhesion between the coating and the substrate is generally carried out by one or more of the following three mechanisms:

-a surface roughness;

-a chemical bond; and/or

Interfacial reaction or recombination.

Due to the surface roughness, the mechanical interlock between their rough interfaces ensures good contact between the coating and the substrate, although the compounds constituting the substrate and the coating do not need to establish chemical bonds.

Due to chemical bonding, the coating must contain a component or composition capable of establishing a molecular bond with the substrate. This is desirable in most binders, such as those used in battery cathode ink formulations.

Through interfacial reactions, a new compound(s) is typically formed at the interface and may acquire characteristics that promote one or both of the two aforementioned adhesion mechanisms, surface roughness and chemical bonding.

In the case of lithium ion secondary batteries, there is a significant problem in achieving good adhesion at the interface between the electrode material and the metal substrate. This type of coated electrode needs to maintain its electrical conductivity while also being flexible enough to be wound or rolled into the final cell shape. Thus, the lithium-containing cathode material is mixed with a binder, conductive carbon particles, and a solvent to make an ink that can be cast on a continuous roll of sheet metal, such as aluminum, which can then be cut to the appropriate length and rolled with the other components to make a battery. Further, when good adhesion is achieved between the cathode and the current collector substrate, higher pressure is applied during the process, which may be referred to as calendering. The additional pressure, in turn, improves electrical contact between the particles and increases packing density, both of which are desirable for performance improvement. Fig. 1 shows the gradual decrease in resistance of pressed pellets of a conventional LFP powder without additional particles Super P (Super P is a trade name for carbon black materials commonly used in lithium battery production) or binder. As the contact between the particles increases, the conductivity increases.

As described above, a typical cathode ink composition may contain lithium metal oxide as a source of lithium ions, polyvinylidene fluoride (PVDF) or PVDF copolymer resin as a binder, N-methyl-2-pyrrolidone (NMP) as a binder solvent, and carbon black as a source of conductive particles. Factors such as surface charge, reaction between components, and final ink pH can result in little or no adhesion between the mixture and the metal electrode substrate. In particular, it is desirable to obtain a good mixing and distribution of the conductive carbon particles in order to ensure a good electrical contact over the whole area and a good cathode coating thickness.

Aluminum is generally a substrate for cathode materials and is known to have a nanoscale oxide surface layer. Alkaline and strongly acidic solutions dissolve the oxide layer, however, the reoxidation rate after exposure to air at room temperature is known to be very fast, on the order of microseconds for the first few nanometers of alumina coating to reform. The oxide layer is expected to change the surface properties of the substrate and to some extent provide electrical insulation.

The aluminum substrate may be cleaned with alkaline and acidic solutions to remove the aluminum oxide layer from the substrate surface. However, this step is not a viable processing step in the preparation of the electrode, not only because it introduces an additional step, but primarily because the oxide layer is rapidly reformed prior to the final electrode material coating step. In addition, KOH is known to undergo a somewhat violent exothermic reaction with aluminum, producing hydrogen. Therefore, it is difficult to perform the reaction on a large scale.

Finally, in order to achieve good adhesion, in addition to introducing one of the above adhesion mechanisms, it is necessary to obtain good mixing and distribution of the particulate conductive material, such as conductive carbon, in order to ensure good electrical contact over the entire area and a good coating thickness.

Various methods have been used to overcome the adhesion problem. These methods include pre-coating the metal electrode with an interfacial layer, pre-treating the metal surface with an acid wash to increase surface roughness, and adding functional groups that enhance crosslinking of the monomer and PVDF copolymer binder.

Several prior art attempts to improve the coating of electrode materials on metal substrates in battery preparation are listed below.

US patent application US2009/0263718a1 discloses that the addition of two different size ranges of particulate conductive carbon (one having an average particle size of 3-10 microns and the other having an average particle size of1 micron or less) helps to improve adhesion during the pressing step and prevents the formation of defects such as detachment.

U.S. patent application US2009/0155689A1 discloses the use of LiMPO as a catalyst for the preparation of a catalyst for the reaction of olefins₄A multimodal particle size distribution is used in the (M: Fe or Mn) active cathode material, comprising at least one fraction of micron-sized particles and at least one fraction of sub-micron-sized particles, to increase the packing density and optimize porosity. Two different methods are generally used to obtain materials with different particle size distributions. Although attention is paid to improving energy density and dynamic performance, similar to patent application US2009/02673718a1, it is expected that adhesion will beIs improved.

US patent application US2004/0234858a1 discloses that when a surface roughness of at least 0.1 micron is used in the current collector, the adhesion between the mixed layer and the current collector is greatly improved.

Us patent 5,399,447 discloses a method for reducing the acidity of an adhesion promoter layer consisting of carbon and polyacrylic acid by treating it with LiOH. Furthermore, there is a risk that H + ions replace Li + in the cathode material, thus decreasing the battery capacity.

International patent application WO00/49103 describes a method for bonding a vinylidene fluoride resin to a metal substrate, characterized in that when bonding polyvinylidene fluoride to a metal substrate, at least one resin (b) selected from acrylic polymers and methacrylic polymers or containing the polymers and at least one organic compound (c) selected from mercapto, thioether, carboxylic acid or carboxylic anhydride groups are added and mixed to the vinylidene fluoride resin (a).

Methods of making electrodes for use in electrochemical devices are disclosed in U.S. patent application US2006/0153972A 1. In this patent, the adhesive is provided by a conductive adhesive prepared by mixing particulate rubber with particulate conductive carbon. The effect of too little or too much rubber is emphasized depending on the proportions.

While the above prior art teaches methods of improving adhesion, many of these methods add additional processing steps to the preparation of the battery cathode, adding complexity and cost. Most battery manufacturers are reluctant to significantly alter their manufacturing processes. Therefore, it is desirable to enhance the adhesion between the electrode material and the metal substrate without adding an additional step in the electrode preparation process. It is desirable, especially for powders of various particle characteristics and morphologies, to obtain improved adhesion of electrode materials without any further changes in the coating preparation steps and without pretreatment of the current collector/substrate in the lithium ion secondary battery manufacturing industry.

In this specification, the term "comprising" and its grammatical equivalents are to be taken in an inclusive sense unless otherwise indicated.

The applicant does not consider the prior art discussed in this specification to be common knowledge in australia or elsewhere.

Summary of The Invention

In a first aspect, the present invention provides a composition for forming a battery electrode for a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

-organic materials with high alkalinity.

In certain aspects, the organic material may be dissolved in an organic solvent. Accordingly, in a second aspect, the present invention provides a composition for forming a battery electrode for a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

-organic materials soluble in organic solvents with high basicity.

In a third aspect, the present invention provides a composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

-organic materials having imino and aminoacetal groups.

In a fourth aspect, the present invention provides a composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

organic materials that chelate or bond with active ingredients in the metal substrate and/or the electrode layer. The active ingredient that may be chelated or bonded to the organic material may comprise a conductive particulate material. The conductive particulate material may be a carbonaceous material. In embodiments where the organic material is chelated with the metal substrate or with the active ingredient, the organic material can be strongly chelated with the metal substrate or the active ingredient.

In a fifth aspect, the present invention provides a composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-intercalating graphitic compound;

-a binder;

-a solvent;

-a conductive particulate material; and

-an organic material chelated or bonded to the metal substrate and/or the conductive particulate material. The conductive particulate material may be a carbonaceous material. In embodiments where the organic material is chelated with the metal substrate or with the conductive particulate material, the organic material may be strongly chelated with the metal substrate or the conductive particulate material.

The compositions of the first, second, third, fourth and fifth aspects of the present invention may also contain water. The water may be present in an amount sufficient to dissolve the organic material. It is desirable that water be present in the minimum amount necessary to dissolve the organic material to minimize the amount of water introduced into the composition.

The organic material may include carbonate ions or carbonates.

The organic material may be highly basic and may also chelate or bond with the metal substrate and/or with active ingredients in the electrode layer.

The organic material may comprise a guanidine compound. Guanidine (NHC (NH)₂)₂) Including imino groups and aminal or aminoacetal groups. The organic material may comprise guanidine carbonate. The structural formula of guanidine carbonate is (NHC (NH)₂)₂)CO3(NHC(NH₂)₂). It has high alkalinity, and when prepared as a 5% aqueous solution, has a pH of 11-12. Its solubility in water is about 40-45g per 100g of water.

The organic material may have high alkalinity when dissolved in water. In certain embodiments, the organic compound has a pH of at least 8 in 1M aqueous solution, more preferably a pH of at least 9, more preferably a pH of at least 9.3, even more preferably a pH of at least 10, or at least 11 or at least 12 in 1M aqueous solution. In other embodiments, the organic compound has a pH of at least 8 when dissolved in water, for example at 5% by weight in water, more preferably a pH of at least 9, more preferably a pH of at least 9.3, even more preferably a pH of at least 10, or at least 11 or at least 12.

Other organic materials with high alkalinity and chelating properties may include ethylenediamine, trymine, trymidine, histidine, glycine, ammonia, N-butylamine, methylamine, piperidine, triethylamine, diethanolamine, EDTA, and the like. It is also possible to combine two compounds, one of which has a high basicity and the other providing a strong chelating property.

In a sixth aspect, the present invention provides a method of forming an electrode for use in a lithium ion battery, the method comprising the steps of providing a metal substrate and coating an electrode material on the metal substrate, wherein the coating of electrode material applied to the metal substrate comprises a composition according to the first, second, third, fourth or fifth aspects of the present invention.

The organic material may be at least partially soluble in water when the coating is applied on the metal substrate.

The metal substrate may comprise an aluminum substrate or a copper substrate.

The metal substrate may comprise aluminum or an aluminum alloy. The metal substrate may comprise an aluminum sheet or a sheet made of an aluminum alloy. The metal substrate may also comprise copper or a copper alloy. The metal substrate may comprise a copper sheet or a sheet made from a copper alloy.

The electrode coating may be applied to the metal substrate by spraying or printing.

The method may further comprise subjecting the coated metal substrate to a calendering step to increase the density of the electrode material coating. The calendering step may comprise pressing or rolling, optionally under heating.

In a seventh aspect, the present invention provides a lithium battery comprising a first electrode, a second electrode and an electrolyte comprising a lithium compound, wherein at least one electrode comprises a metal substrate having coated thereon an electrode material comprising a coating formed from a composition according to any one of the first aspect of the present invention, the second aspect of the present invention, the third aspect of the present invention, the fourth aspect of the present invention or the fifth aspect of the present invention.

The inventors have found that it is often necessary to add a minimum amount of organic material to the composition to obtain good adhesion to the substrate. It is expected that a minimum amount of organic material of about 1 wt% is required to obtain good adhesion, typically at least 1.5 wt% or even at least 1.8 wt%, or even at least 2 wt%. If the organic material is present in the composition as a solution, a lesser amount may be used than if the organic material is present in the composition as a solid. The percentage of organic material added is in weight percent of electrode material/weight of the composition.

The composition of the invention can be used on a cathode or an anode. The battery electrode according to an embodiment of the present invention may be a cathode or an anode.

In another aspect, the invention provides a battery electrode for a lithium ion battery comprising an electrically conductive substrate to which an electrode layer is applied, characterised in that the electrode layer comprises an overbased organic material or an organic material which is soluble in organic solvents, or an organic material having imino and aminoacetal groups, or an organic material which chelates or bonds strongly to a metal substrate and/or chelates or bonds to an active material in the electrode layer, such as an electrically conductive particulate material (which may be a carbonaceous material).

In all aspects of the invention, the organic material may comprise an organic compound (e.g. a single organic compound) or two or more organic compounds.

It has been found that it may not be necessary to mix the organic material with the other materials of the electrode layer before applying the electrode material onto the electrode layer. In particular, satisfactory adhesion is obtained by applying the organic material to the substrate (e.g., by spraying or brushing or wiping) and then applying the electrode layer to the substrate. In another aspect, the present invention provides a method of forming an electrode for a lithium ion battery, including the step of applying an organic material having high basicity, or an organic material that can be dissolved in an organic solvent, or an organic material having an imino group and an amino acetal group, or an organic material that can strongly chelate with a metal substrate, to the substrate, and then applying an electrode material to the substrate. Here, the composition applied to the substrate may be considered to include the organic material and the other electrode material, but the composition is applied in two different steps.

In all aspects of the invention it may be preferred that the organic material does not contain counter ions, such as Na or K, which cause unwanted reactions with aluminium or the electrolyte.

In the present specification, the term "composition" is used to refer to a direct mixture of components in a composition, as well as components of a composition that are present in two or more regions, layers or volumes, mixed at a boundary, or a composition having a layered composition.

In the present description, the composition may be applied to the substrate by applying a direct mixture of all the components of the composition to the substrate, or by applying one or more components to the substrate and then applying one or more components in sequence, or by applying the organic material (in solid form, in the form of an organic solution or in the form of an aqueous solution) to the substrate and then applying one or more other components in an additional one step or in additional two or more application steps.

Brief Description of Drawings

Fig. 1 is a graph of electrical resistance versus pressure for a compressed tablet of a conventional LFP powder, illustrating the gradual decrease in electrical resistance with increasing pressure;

figure 2 is a photograph of a GC solution placed in contact with NMP. GC showed immediate very fine precipitation;

FIG. 3 is a photograph of an apparatus for applying the electrode material composition to an aluminum substrate as described in example 3;

fig. 4 schematically shows the steps of assembling the test cell used in example 4;

FIG. 5 is a graph of voltage versus capacitance for an electrode material containing 1.6% GC as described in example 5;

FIG. 6 is a photograph of a test electrode prepared using an electrode composition containing 1% GC added as a solid (upper photograph), an electrode composition containing 1% GC added as a 1M solution (middle photograph), and an electrode composition containing 1.34% GC added as a 1M solution (lower photograph); and

FIG. 7 is the difference between the carbon precoat (lower photograph) and the stripped coating (upper photograph) as used in comparative example 8.

Detailed description of the invention

Preferred embodiments of the present invention will be described.

In the following description, "good adhesion" means that the coating does not show a signal that the battery cathode coating is detached from the aluminum substrate after strong press rolling or calendering.

In the experimental work conducted by the present inventors, guanidine carbonate was used as an organic material and added to the electrode material composition. It was found that the addition of guanidine carbonate significantly enhanced the adhesion of the electrode material to the aluminum substrate without negatively affecting the electrical properties of the electrode material. Furthermore, the coating is carried out by simply adding guanidine carbonate (usually in the form of an aqueous solution of guanidine carbonate) to the electrode material composition to be applied on the aluminum substrate. Therefore, no additional processing steps (steps other than the addition of guanidine carbonate solution) are required to form the electrode.

Guanidine carbonate is a fairly unique organic carbonate. It is one of the strongest basic compounds, one of which is the smaller amount needed to obtain a given high pH.

Surprisingly, the inventors have found that adding a small amount of guanidine carbonate dissolved in water (e.g., 1.6 wt% of a standard paste) to a standard cathode paste formulation improves adhesion after intensive pressing and results in a smooth surface. Surprisingly, addition of dry guanidine carbonate was not effective at lower guanidine carbonate addition levels.

Without being bound by theory, the inventors believe that guanidine carbonate has multiple effects. The high alkalinity of guanidine carbonate results in some degree of exothermic local interfacial reaction and dissolution of the surface layer of alumina present on the aluminum substrate, possibly forming surface roughness on the aluminum substrate. Furthermore, by cleaning the oxide layer (which is electrically insulating in nature) in situ and during the application of the electrode material onto the substrate, the electrical connection between the cathode material and the aluminum current collector is enhanced.

Other overbased organic compounds are expected to have a similar effect as guanidine carbonate in forming surface roughness, although higher concentrations may be required if those other overbased organic compounds are less basic than guanidine carbonate. Although one of the above prior art documents teaches away from the use of acids, this is due to H⁺Ions with Li⁺Ions compete for space, but some strongly acidic solutions are expected to work as well.

Generally, care must be taken that no undesired side reactions with the substrate or electrolyte occur, whatever the compound chosen, has the same effect as guanidine carbonate. The electrolyte is typically LiPF dissolved in a mixture of diethyl carbonate (DEC), Ethylene Carbonate (EC) and/or Propylene Carbonate (PC)₆And (3) salt. Without being limited by theory, these carbonates, which are already present in the electrolyte, indicate a possible compatibility between guanidine carbonate and the electrolyte.

Another possible reason for strong adhesion is that guanidine carbonate is characterized by its strong chelation with metals, which allows it to strongly bond to aluminum and iron in the substrate and to LFP particles, respectively.

It is also possible that guanidine carbonate, due to its chelating properties and the presence of carbonate, has some affinity for carbon particles, resulting in its functionalization and resulting in a more homogeneous mixing. Monarch1300, a functionalized granular carbon surface treated with acid, resulted in good adhesion. Unfortunately, it is not as good a conductor as Super pli (which is another carbon black material commonly used in electrode preparation for lithium ion batteries). Super P Li carbon black is particularly useful for lithium ion battery applications, and therefore, battery manufacturers often use this carbon black material.

In another embodiment of the invention, it was found that the addition of a small amount of LiOH dissolved in water to a standard cathode paste enhanced adhesion, although Li migration in electrochemical tests may eliminate good adhesion. For very similar reasons, it is generally preferred to avoid the presence of counter ions such as Na and K, which may cause other undesirable reactions with aluminum or electrolytes. Thus, in another aspect, suitably, the organic material is free of counter ions that cause undesired reactions with the aluminum or electrolyte.

In summary, and without wishing to be bound by theory, guanidine carbonate has several effects, each of which enhances the adhesion of the cathode material paste to the aluminum substrate (or the anode material paste to the copper substrate). Adhesion enhancement mechanisms obtained with very small amounts of guanidine carbonate may include cleaning of the oxide surface layer of aluminum (or copper), roughening of the interface, chemical bonding with the cathode (or anode) material particles and the substrate, and possibly functionalization of the carbon addition particles.

Spherical particles are generally expected to require significantly stronger bonding than flat particles because of the more point contact for spherical particle contact. However, if a simple method such as the one provided in the present invention is established to obtain good adhesion of spherical particles without any other binder, by suitably selecting the particle size distribution, it will become a method to optimize the packing density and porosity of the coated cathode material in a controlled manner.

Examples

In the following examples, battery cathodes were prepared by coating electrode materials on aluminum substrates.

Example 1 preparation of cathode paste formulation-use of guanidine carbonate

For a target (LFP + PVDF + Super P Li) of 10g of electrode mix in a ratio of 90:5:5(LFP: PVDF: Super P Li), the following table lists the relative amounts of the components:

PVUF	0.50g
		NMP	24g
1M guanidine carbonate solution	23 drops
		Super P Li	0．50g
LFP powder	9．00g

4 drops weight 0.1g

The method comprises the following steps:

stock solutions of1M Guanidine Carbonate (GC) were prepared by dissolving 18gGC in a volumetric flask and adding Reverse Osmosis (RO) water in an amount of 100M 1. A nearly 1M GC solution can be obtained by dissolving 18gGC in 88.66g of RO water. The resulting pH was about 11.5.

The PVDF is weighed out and then the appropriate amount of NMP is added.

The mixture was mixed at high speed using a High Speed Mixer (HSM) until the PVDF was dissolved in NMP.

1M guanidine carbonate solution was added and mixed with an Ultra Turrax (UT) set at 1 or with an equivalent dispersing device until dispersion.

Super P Li carbon black was weighed out and added to the PVDF/NMP/GC solution. HSM was used until the mixture was a homogeneous paste (approximately 5 minutes).

Weighing out the active material (e.g. LiFeP 0)₄Or other lithium-containing material) was gently ground using a mortar and pestle for several minutes to ensure that there were no large aggregates in the powder.

This powder was added to a Super P/PVDF/NMP/GC mixture. Gently mix for at least 1 hour using a flat mixer to ensure that all materials are well mixed.

Example 2 preparation of cathode paste formulation guanidine carbonate was added after obtaining a conventional paste mixture

The procedure as described in example 1 was used to a similar paste formulation except that the GC solution was post added. After a GC-free homogeneous paste was prepared, the correct amount of GC solution was added and mixed thoroughly. The amount of GC has the same ratio as in example 1 and can be determined according to the following ratio:

6g of the Super P/PVDF/NMP/active material mixture was weighed out and placed in a small beaker (50ml beaker).

0.1g of1M GC (4 drops) was added and mixed well.

The electrode coating step (using aluminum foil) was followed to obtain a cathode using the mixture.

In this case, the coating showed good adhesion, but the coating generally had a lower smooth surface than the coating obtained from the composition of example 1, depending on the degree of mixing and uniformity of the Guanidine Carbonate (GC) additive. When the GC solution droplets were contacted with NMP, very fine precipitates were immediately shown (see fig. 2). The fine precipitate was more easily dispersed uniformly in the procedure described in example 1.

Example 3 electrode coating

The electrode was coated with the electrode coating composition as follows. Fig. 3 is a photograph of an apparatus for applying the electrode material composition on an aluminum substrate:

an aluminum foil strip of appropriate size is cut.

A small amount of water/acetone was sprayed onto the glass plate and an aluminum strip was placed on top. The aluminum strip was adsorbed onto the glass plate by squeezing out the excess water/acetone from below with a folded paper towel. The edges of the aluminum strip were smoothed with a pen cap.

Micrometer of grade blade is set to 5 micrometer. Placing a sufficient amount of electrode paste on the aluminum foil; a doctor blade was placed in front of it to stabilize the continuous movement and spread the coating along the strip.

The aluminum strip was carefully removed to a glass pan and weighted at both ends to ensure that the aluminum foil did not curl when dried.

Placed in an oven at 150 ℃ for at least one hour in air.

The electrodes were pressed using a calendering machine (roller press). Once the electrodes are pressed, the steel sheets of the cell are used as a template to cut out the electrode tabs. The weight and height of each piece needs to be measured and recorded.

Before assembling the test pieces of the cells in a glove box under dry atmosphere, the pieces were placed in an oven at 150 ℃ and under vacuum for 48 hours.

The unassembled battery test elements should be preheated for at least 24 hours prior to assembly. This can be done simultaneously with the treatment of the electrodes, if possible.

Example 4-assembly procedure for battery test cells

The unassembled battery test cells and electrodes were removed from the oven into a glove box.

The separator is cut using a punch. Placed in an oven and left under vacuum at 80 ℃ for at least 24 hours.

In a glove box, an anode (lithium tape) was prepared. The strips of lithium tape were cleaned using fine sandpaper and the anode was cut using a punch.

A small amount of electrolyte (LiPF) was added to the beaker₆In EC/DEC). The first electrode was immersed in a beaker for about 5 minutes before the following assembly steps were carried out.

The device is assembled without tightening the nut as follows (first as per 1-6 as described in figure 4).

The impregnated electrode was placed on the bottom of the device.

The separator is immersed in the electrolyte and then placed on top of the cathode.

The Teflon support was pushed into position over the spacer and cathode.

The anode was placed in a Teflon holder, secured over the spacer.

The steel disc was inserted on the anode and pushed down gently.

Using a microtube, 200. mu.l of electrolyte was added along the outside of the Teflon stent. Fresh electrolyte was used in a second beaker.

The upper plate is placed on the cell and the wing nuts are tightened.

The remaining devices are assembled without immediately screwing the nuts.

Once all device assemblies are complete, wait 1 hour.

The positive and negative leads are attached to the battery device and the nuts are tightened.

The current at the desired charge rate is calculated and the program is entered. The cycle for that channel is started and then the other channels are repeated.

When the cycle is over, the data is stored and the capacity to charge and discharge (mAh/g) is calculated for all cycles.

Once the cycle is complete, the device is removed from the glove box. The device was cleaned and prepared for the next experiment.

Remarking: in handling the electrolyte, 2 sets of vinyl gloves were used.

Example 5-cathode Performance of the cell

Test cells are typically tested with Li metal as the anode in what is referred to as a half-cell configuration. The voltage was swept between 2.5V and 4.2V. During the charge and discharge cycles, the current was constant and evaluated as C/10, C/5, C/2, C, 2C, 4C, 8C, 10C, 12C, 16C, etc., based on the load of the active material. In most cases, although it is possible to charge at a fixed current (typically C/2 or C/5) and discharge at different multiples of C (C = capacitance), the charge and discharge remain at the same current for a complete cycle. The results are shown in table 5 for electrode compositions comprising 1.6% GC.

Comparative example 1 preparation of standard cathode paste formulation-guanidine non-carbonate

A similar procedure was followed for the paste formulation as described in example 1, except that the guanidine carbonate additive was not included. The electrode coating procedure was then followed as described in example 3. At this time, the coating layer showed poor adhesion.

As a hint, reference to adhesion generally refers to the results obtained after strong pressing or calendering. As indicated above, a simple dry coating can adhere and have a smooth surface. Although slight or no calendering results in a clearly uniform and smooth coating, which often breaks away in the later assembly of the test cells, the tape density can be very low, which is undesirable for the application.

Comparative example 2 preparation of standard cathode paste formulation-addition of Water droplets

A similar procedure to the paste formulation described in example 1 was followed except that pure water droplets were used instead of the guanidine carbonate solution. The electrode coating procedure was then followed as described in example 3. At this time, the coating layer has no adhesiveness.

Comparative example 3 preparation of cathode paste formulation-Using dried guanidine carbonate-

A similar procedure to the paste formulation described in example 1 was followed except that guanidine carbonate in solid form without water was added instead of the GC solution. The electrode coating procedure was then followed as described in example 3. At this time, 1.3% by weight of the added solid had no adhesiveness (see fig. 6). However, improved adhesion can be obtained when the weight percent of dry GC is significantly increased. FIG. 6 shows photographs of test electrodes prepared using 1% GC added as a solid (upper photograph), 1% GC added as a 1M solution (middle photograph), and 1.34% GC added as a 1M solution (lower photograph). It was found that the use of 1.34% GC as a 1M solution had the best adhesion, followed by 1% GC as a 1M solution and then 1% GC as a solid.

Comparative example 4 preparation of cathode paste formulation with lower content of guanidine carbonate

Similar procedure to the paste formulation described in example 1 was followed except that a lower level of guanidine carbonate was used. The electrode coating procedure was then followed as described in example 3. At this time, the lower content of GC (less than about 1 wt%) showed decreased adhesion, substantially proportional to the decrease in the amount of GC (see fig. 6).

Comparative example 5 preparation of cathode paste formulation-addition of LiOH-

A similar procedure to the paste formulation described in example 1 was followed except that LiOH solution was used instead of guanidine carbonate solution. The amount of LiOH was estimated to form a pH similar to that obtained by GC. The electrode coating procedure was then followed as described in example 3. At this time, the sample showed good adhesion.

Comparative example 6 preparation of cathode paste formulation-addition of KOH-

A similar procedure to that described in comparative example 5 was followed for the paste formulation, except that KOH solution was used instead of LiOH solution. The electrode coating procedure was then followed as described in example 3. At this time, the sample did not show good adhesion.

Comparative example 7 preparation of cathode paste formulation-without guanidine carbonate but with Monarch1300 instead of Super PLi

The procedure of a paste formulation similar to that described in comparative example 1 was followed except that Monarch1300 was used as the conductive carbon additive instead of Super P Li. The electrode coating procedure was then followed as described in example 3. At this time, good adhesion was obtained using Monarch1300, however, electrical and electrochemical properties were degraded.

Comparative example 8-preparation of carbon precoat on aluminum substrate

The following solutions were prepared:

solution A

AM-30 suspension 10g Sigma420875-4L

(colloidal silica)

Solution B

0.56g of potassium hydroxide

10g of water

Solution C

5g of water

85%H₃PO₄1g

Will be provided withSolution AAdding intoSolution BIn (1).

Stirred for 1 minute and then slowly added with 85% H dropwise₃PO₄In each dropWait 2 minutes in between and add 11 drops. The pH was measured.

Remarking: this should reduce the pH to about 10.4-10.6.

At this time, the solution C was used so that the pH was slowly reached to 9.6-10 (there was no fear of time in this portion). After a few minutes, the solution gels. Ensure that the final pH is recorded. Note that: efforts were made to stabilize the pH at about 10 prior to solution gelation, otherwise pH measurements may not be accurate.

Then, 12g of water was added, mixed well, and then 1g of Super P Li was added.

The colloid was broken up and mixed with a high speed mixer (setting 3) for about 5 minutes to fully disperse.

To form a thin coating, the blade is set to 5-10 microns on a micron.

A small amount of water was sprayed onto the glass plate and the aluminum strip was placed on top. The aluminum strip was adsorbed to the glass plate by squeezing out excess water from below with a folded piece of paper towel. The edges of the aluminum strip were smoothed with a pen cap.

Then, placing sufficient pre-coat material on one end of the aluminum strip; a doctor blade was placed in front of it to stabilize the continuous movement and spread the coating along the strip.

The wet precoat was air dried and then placed in an oven at 150 ℃ for at least one hour.

The two ends of the aluminum strip are fixed with adhesive tapes, and then the adhesive tapes are adhered to the coated surface and pressed downwards with force.

The tape was removed to remove loose and excess carbon. This was done twice. The aluminum strip can now be used to coat the battery material.

FIG. 7 shows the difference between the initial carbon precoat (lower photograph) and the stripped coating (upper photograph).

Comparative example 9-electrode coating on carbon-precoated aluminum substrate

An electrode coating procedure similar to that described in example 3 was followed except that carbon pre-coated aluminum was used instead of pure aluminum.

When Super P Li is used in the precoat and cathode paste formulations, almost as good performance as the process of the invention is obtained. However, the reproducibility of the GC process is better, since the carbon pre-coat is somewhat sensitive to the detachment of loose particles. The carbon precoat typically has a small amount of local non-uniformity, which may be due to mixing difficulties once the intermediate carbon precoat paste has gelatinized.

Comparative example 10-electrode coating on carbon-precoated aluminum substrate

To test the effect on performance, several compositions of Monarch1300 and Super P Li in carbon precoat and paste formulations were prepared as described in comparative example 9 using the corresponding types of carbon. The results are summarized in the following table:

watch (A)

Comparative example 11: anode preparation without guanidine carbonate

In this example, Super P Li (0.2g) was mixed into NMP (15.82g) using a high speed mixer for 1 minute. Cpreme graphite G5(9.2G) was then mixed into the solution also using a high speed mixer for 1 minute. This mixture was then added to a slurry of NMP (5.25g) + PVDF (0.6g) which had been mixed for 1 minute at high speed. The final slurry was mixed for 20 minutes using a flat mixer. The electrodes were then coated on a copper sheet substrate using a doctor blade method at different settings and dried on a hot bench at 105 ℃.

After pressing the electrodes using a roll press, all electrodes delaminated and failed.

Example 12: preparation of an anode with 1.74 wt% guanidine carbonate

In this example, PVDF (0.6g) was dissolved in NMP (21g) using a high-speed mixer. Super P Li (0.2g) was then added to the solution and mixed at high speed for 1 minute. Cpreme G5Graphite (9.2G) was then added using a flat-bed mixer for 1 hour. 1M guanidine carbonate (0.51g) was then added to the final solution and mixed in a flat plate for another hour. The electrodes were then coated on a copper sheet substrate using a doctor blade method at different settings and dried on a hot bench at 110 ℃.

The adhesion of the material to the copper sheet after pressing the electrodes using a roll press is significantly improved over comparative example 11.

Example 13: preparation of cathode with 1.74 wt% guanidine carbonate using reduced mixing time

In this example, PVDF (0.5g) was dissolved in NMP (21g) using a high-speed mixer. Super P (0.5g) was then added to the solution and mixed at high speed for 1 minute. The active material (9.0g) was then added using a flat mixer for 5 minutes. 1.74% by weight of1M guanidine carbonate (0.54g) was then added to the final solution and mixed flat for an additional 5 minutes. The electrodes were then coated on a copper sheet substrate using a doctor blade method at different settings and dried in an oven at 120 ℃ under slow warming (approximately 1 hour → 120 ℃, 30 minutes at 120 ℃).

After roll pressing, good adhesion on the electrode was observed.

Example 14: preparation of cathode with 1.74 wt% guanidine carbonate using reduced mixing time

In this example, PVDF (0.5g) was dissolved in NMP (21g) using a high-speed mixer. Super P Li (0.5g) was then added to the solution and mixed at high speed for 1 minute. The active material (9.0g) was then added using a flat mixer for 2 hours. 1.74% by weight of1M guanidine carbonate (0.54g) was then added to the final solution and mixed flat for an additional 5 minutes. The electrodes were then coated on a copper sheet substrate using a doctor blade method at different settings and dried in an oven at 120 ℃ under slow warming (approximately 1 hour → 120 ℃, 30 minutes at 120 ℃).

After roll pressing, good adhesion on the electrode was observed.

Example 15

Good adhesion of the active material paste can be obtained by air brushing the GC solution onto the aluminum substrate according to the following steps:

a GC solution of a specified concentration (e.g., 1M) was added to a gravity fed air brush.

Atomization was optimized to make the solution beads as small as possible when sprayed on aluminum flakes.

The single layer GC solution was sprayed onto the aluminum sheet substrate.

The active material paste was then immediately knife-coated onto the wet GC film.

The film was dried according to the usual procedure.

It will be appreciated by persons skilled in the art that the present invention may be susceptible to variations and modifications other than those specifically described. It is to be understood that the present invention includes all changes or modifications that fall within its scope. The invention also extends to all combinations of features described herein.

Claims (30)

1. A composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

-organic materials with high alkalinity.

2. A composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

-an organic material soluble in an organic solvent.

3. A composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

-organic materials having imino and aminoacetal groups.

4. A composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-containing compound providing a source of lithium ions in the cell;

-a binder;

-a solvent;

-a conductive particulate material; and

organic materials that are chelated or bonded to the metal substrate or to the active material in the electrode layer.

5. A composition for forming a battery electrode of a lithium ion battery, the composition comprising:

-a lithium-intercalating graphitic compound;

-a binder;

-a solvent;

-a conductive particulate material; and

organic materials strongly chelated or bonded to the metal substrate and/or the conductive particulate material.

6. The composition of any one of claims 1-5, further comprising water.

7. The composition of claim 6, wherein water is present in an amount sufficient to dissolve the organic material.

8. A composition as claimed in any preceding claim, wherein the organic material comprises carbonate ions or carbonate species.

9. A composition as claimed in any one of the preceding claims, wherein the organic material comprises a guanidine compound.

10. A composition as claimed in any one of the preceding claims, wherein the organic material comprises guanidine carbonate.

11. A method of forming an electrode for use in a lithium ion battery, the method comprising the steps of providing a metal substrate and applying a coating of electrode material on the metal substrate, wherein the coating of electrode material applied on the metal substrate comprises the composition of any preceding claim.

12. The method of claim 11, wherein the organic material is at least partially dissolved in water when the coating is applied to the metal substrate.

13. The method of claim 11 or 12, wherein the metal substrate comprises aluminum or an aluminum alloy.

14. A method according to any one of claims 11 to 13, wherein the electrode coating is applied to the metal substrate by spraying or printing or using a doctor blade.

15. A method according to any one of claims 11 to 14, further comprising the step of subjecting the coated metal substrate to a calendering step or a pressing step or a rolling step to increase the density of the electrode material coating.

16. The method of claim 15, wherein the calendering step, pressing step, or rolling step comprises heating.

17. A lithium ion battery comprising a first electrode, a second electrode, and an electrolyte comprising a lithium compound, wherein at least one of the electrodes comprises a metal substrate having coated thereon an electrode material comprising a coating formed from the composition of any of claims 1-10.

18. The composition of any of claims 1-10, further comprising an organic solvent.

19. A battery electrode for a lithium ion battery comprising a conductive substrate to which an electrode layer is applied, characterized in that the electrode layer comprises an organic material having high basicity, or an organic material that can be dissolved in an organic solvent, or an organic material having imino and aminoacetal groups, or an organic material that chelates or bonds with a metal substrate or with an active material in the electrode layer.

20. The composition of any of claims 1-10, wherein the organic material comprises one organic compound, or wherein the organic material comprises two or more organic compounds.

21. The composition of any one of claims 1-10, wherein the organic compound is selected from ethylenediamine, trymine, trymidine, histidine, glycine, ammonia, N-butylamine, methylamine, piperidine, triethylamine, diethanolamine, guanidine carbonate, EDTA, or a mixture of two or more thereof.

22. A battery electrode as claimed in claim 19 wherein the electrode comprises a cathode.

23. A battery electrode as claimed in claim 19 wherein the electrode comprises an anode.

24. A method of forming an electrode for a lithium ion battery, comprising the steps of: an organic material having high basicity, or an organic material that can be dissolved in an organic solvent, or an organic material having an imino group and an aminoacetal group, or an organic material that chelates or bonds with a metal substrate, or an organic material that chelates or bonds with an active material in an electrode material is applied to a substrate, and then the electrode material is applied to the substrate.

25. The method of claim 24, wherein the organic material comprises guanidine carbonate.

26. The method of claim 24, wherein the organic material comprises one organic compound, or wherein the organic material comprises two or more organic compounds.

27. The method of claim 26, wherein the organic compound is selected from ethylenediamine, trymine, trymidine, histidine, glycine, ammonia, N-butylamine, methylamine, piperidine, triethylamine, diethanolamine, guanidine carbonate, EDTA, or a mixture of two or more thereof.

28. The composition of claim 4, wherein the organic material is chelated or bonded to particulate conductive material in the electrode layer.

29. The composition of any of claims 1-10, 17, or 27, wherein the particulate conductive material comprises a carbonaceous material.

30. A battery electrode for a lithium ion battery, the composition comprising:

-an electrically conductive substrate applied with an electrode layer comprising:

-a lithium-intercalating graphitic compound;

-a binder;

-a solvent;

-a conductive particulate material; and

organic materials strongly chelated or bonded to the metal substrate and/or to the conductive particulate material.