Dispersant

Abstract

The present invention relates to a dispersant comprising a polyester derived from multiple poly(carbonyl alkylene oxy) chains (and optionally a fatty acid) and an amine, wherein the dispersant has an acid number of less than 15 mg KOH / g. The dispersants described herein provide desirable viscosity profiles during use. More particularly, some embodiments provide improved compatibility with certain solvents in the dispersion and / or are particularly suitable for use in battery systems.

Description

Technical Field

[0001] The present invention relates to a dispersant comprising a polyester and an amine derived from a plurality of poly(carbonylalkyleneoxy) chains (and optionally a fatty acid), wherein the acid value of the dispersant is less than 15 mgKOH / g. The dispersants described herein have an improved viscosity profile in use. More particularly, some embodiments result in improved compatibility with certain solvents in a dispersion and / or are particularly suitable for use in battery systems.

Background Art

[0002] Conductive carbon is a common component of battery systems, among other applications. Conductive carbon is available in various forms, and in particular, spherical and nanotube forms are used in battery systems. However, there is a problem with using conductive carbon in battery systems because it is difficult to obtain a uniform dispersion of this material necessary to achieve sufficient battery energy density and an acceptable rate of electrode wear. One way to improve the uniformity of a dispersion of conductive carbon is to use a dispersant. However, conductive carbon is particularly difficult to disperse compared to pigment carbon. This is because conductive carbon is not functionalized, and functionalization (as is evident in the case of pigment carbon) enables the dispersant to readily adhere to the carbon material, enhancing dispersibility. Thus, as one proposed approach to improving the dispersibility of conductive carbon, functionalization of conductive carbon has been carried out, but such functionalization results in loss of conductivity, which is not desirable.

[0003] In addition to conductive carbon, other materials may need to be dispersed in the battery system. Such other materials to be dispersed include, but are not limited to, lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium nickel manganese cobalt oxide (NMC), lithium manganese oxide (LMO), and lithium nickel cobalt aluminum oxide (NCA). The materials described above are those dispersed in conventional battery systems. Currently, alternative battery materials are being sought, and materials based on magnesium and sodium oxides and salts have been proposed, but these materials also need to be dispersed in the battery system.

[0004] Selecting a dispersant suitable for use in a battery system has been shown to be difficult, although a wide variety of dispersants are known for other applications. This may be due to the need for the flow of materials and / or current through the battery system, and such flow is not achievable with all types of dispersants. Furthermore, some dispersants are only suitable for use with certain types and grades of conductive carbon materials, and as a result, undesirably, the formulation of the battery system is restricted. Polyvinylpyrrolidone (PVP) is a known dispersant commonly used in battery systems, but even PVP has limitations in this application area, and thus, alternative dispersants are preferably sought.

[0005] In current battery systems, generally, particulate active materials (including conductive carbon) are dispersed in a solvent-based continuous phase, so any dispersant should be compatible with the selected solvent. At present, n-methyl-2-pyrrolidone (NMP) is a common solvent for lithium-ion battery systems. However, NMP is associated with environmental concerns, so it is desirable to replace its use with an alternative solvent system. Thus, it is also desirable to provide alternative dispersants that work well across a variety of solvent systems.

[0006] A class of dispersants containing poly(carbonylalkyleneoxy) chains in an amine carrier is known and described in European Patent Application Publication No. 0158406. However, the materials disclosed therein have an insufficient viscosity profile when used in some applications and further cause problems associated with the precipitation of crystals from some solvents when the ambient temperature is below. Dispersants prepared according to the teachings of this document contain undesirable salts because the manufacturing method of the material promotes the formation of salts. According to the present invention, the presence of salts in the dispersant has been found to be a major contributing factor to the undesirable increase in viscosity encountered when such dispersants are used for the dispersion of conductive carbon, as described in more detail below. Therefore, the dispersants of the teachings of this prior art are not very suitable for use in battery systems (and other applications) where an increase in the viscosity or thickening of the dispersion system is not tolerated or desirable.

Summary of the Invention

Problems to be Solved by the Invention

[0007] It is currently common to use PVP as a dispersant for battery systems. However, the use of PVP in battery systems has certain drawbacks that the present invention seeks to overcome. PVP is a material that limits the achievable energy density in battery systems because its use has an undesirable viscosity-increasing effect (this is particularly evident in NMP solvent-based systems). Due to this increase in viscosity, the amount of PVP that can be used in battery systems is limited, and as a result, the amount of conductive carbon (or other active materials to be dispersed) that can be provided to the battery system is correspondingly limited. Therefore, it is desirable to replace PVP with an alternative dispersant that provides a lower viscosity profile during use, thereby improving the energy density and promoting the improvement of current battery systems.

Means for Solving the Problems

[0008] The dispersant of the present invention has been found to provide a dispersant with reduced salt or no salt that can render a composition or formulation incorporating the dispersant within the salt tolerance range. In particular, in a composition or formulation using the dispersant of the present invention, undesirable viscosity changes are avoided as compared to known dispersants that are not within the salt tolerance range. More specifically, undesirable thickening of the composition or formulation during use is avoided. One field of use where known dispersants cause undesirable viscosity changes in a composition or formulation is the field of battery systems, and use in battery systems is a very challenging environment for dispersants, and thus is selected to more particularly emphasize the benefits of the present invention. However, those skilled in the art of dispersants will understand that such dispersants are more widely useful in applications other than battery systems.

[0009] More specifically, and surprisingly, it has been found that the dispersants described herein have an improved viscosity profile during use. In addition, they also have improved compatibility with NMP solvent-based systems, thereby making them particularly suitable for use as dispersants in battery systems.

[0010] According to the present invention, there is provided a dispersant comprising a polyester derived from a plurality of poly(carbonylalkyleneoxy) chains (and optionally a fatty acid) and an amine, wherein the acid value of the dispersant is less than 15 mgKOH / g.

[0011] According to another alternative embodiment of the present invention, there is provided a method for producing the dispersant described herein.

[0012] Also provided is a dispersion comprising a continuous phase, particles to be dispersed, and the dispersant described herein.

[0013] Furthermore, there is provided a battery system comprising the dispersion described herein.

[0014] In addition, the use of the dispersant described herein in a battery system is also provided.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Thus, according to one embodiment of the present invention: A dispersant comprising a plurality of poly(carbonylalkyleneoxy) chains, and amine, is provided, and the acid value of the dispersant is less than 15 mgKOH / g.

[0016] The acid value is also referred to as the acid number and is a measure of the amount of potassium hydroxide (KOH) required to neutralize 1 gram (g) of the chemical substance of interest. AOCS ‘Te-1a-64: Method for Testing Acid Value of Fatty Acids provides a method suitable for testing the materials of the present invention.

[0017] The acid value of the dispersant of the present invention is less than 15 mgKOH / g. Preferably, the acid value of the dispersant is less than 10 mgKOH / g, more preferably less than 5 mgKOH / g, even more preferably less than 2 mgKOH / g, and most preferably less than 1 mgKOH / g. Dispersants having an acid value between 0.2 mgKOH / g and 2 mgKOH / g, more preferably between 0.4 mgKOH / g and 1.2 mgKOH / g, have been found to be particularly suitable for use as dispersants in battery systems.

[0018] Preferably, the polyester dispersant of the present invention comprises a plurality of poly(carbonylalkyleneoxy) chains having an alkylene group containing between 3 and 12 carbon atoms. More preferably, the alkylene group contains between 4 and 8 carbon atoms, and most preferably, the alkylene group contains between 5 and 7 carbon atoms.

[0019] The plurality of poly(carbonylalkyleneoxy) chains of the dispersant polyester of the present invention may be formed from two or more poly(carbonylalkyleneoxy) chains having different alkylene group chain lengths. As another option, and more preferably, the poly(carbonylalkyleneoxy) chain of the dispersant of the present invention is formed from one type of alkylene group, that is, has a single chain length, and when a single-length carbon chain is provided, higher consistency may be expected during use.

[0020] Most suitably, the dispersant polyester contains a plurality of poly(carbonylalkyleneoxy) chains in which the alkylene group is a hydroxyhexanoic acid derivative group, and more particularly a 6-hydroxyhexanoic acid derivative group. It is desirable for the dispersant to contain a plurality of poly(carbonylalkyleneoxy) chains that are poly(6-hydroxyhexanoate) derived from ε-caprolactone. The benefits of using such derivative groups are that they are available from commercial sources and the cost.

[0021] The dispersant polyester may preferably contain a fatty acid. Thus, the fatty acid is included in the production method of the dispersant as desired. The presence of the fatty acid in the production method acts to control the chain length of the plurality of poly(carbonylalkyleneoxy) chains, and thus advantages in production and quality control can be obtained. However, in some alternative embodiments, the dispersant does not contain a fatty acid, and the absence of the fatty acid acts to limit the acid introduced into the dispersant production process, and it will limit the amount of acid that needs to be removed or neutralized to obtain a dispersant with an acid value as defined herein. When present in the dispersant, the fatty acid may be saturated or unsaturated. The fatty acid may preferably contain a medium fatty acid chain. Preferably, the fatty acid chain contains between 6 and 18 carbons. More preferably, the fatty acid chain contains 10 to 16 carbons. Even more preferably, the fatty acid may be selected from one or more of oleic acid, caproic acid, lauric acid, stearic acid, and palmitic acid. Most preferably, the fatty acid is lauric acid.

[0022] Preferably, the polyester is derived with a ratio of a plurality of poly(carbonylalkyleneoxy) chains to fatty acids between 4:1 and 15:1, more preferably the ratio is between 5:1 and 13:1, and most preferably the ratio is between 8:1 and 12:1. The ratio of the plurality of poly(carbonylalkyleneoxy) chains to fatty acids from which the polyester is derived determines the length of the poly(carbonylalkyleneoxy) chains in the polyester material, and the higher the relative ratio of fatty acids, the shorter the polyester chains. It has been found that the relatively long polyester chain lengths obtained from the preferred ratios described herein improve thermal stability.

[0023] The dispersant polyester contains an amine. Suitably, the amine may contain one or more of a primary, secondary, or tertiary amine. Preferably, the amine is a polymeric amine, more preferably the polymeric amine is a poly(alkyleneimine). Most preferably, the polymeric amine is polyethyleneimine. Suitably, the weight average molecular weight of the polymeric amine can be in the range of 1000 to 50000, more preferably 2000 to 30000. Most preferably, the weight average molecular weight of the polymeric amine is up to 25000, because commercially available polymeric amines with a molecular weight exceeding 25000 are supplied as aqueous solutions, which can make the production of the dispersant more complicated due to the need for a water removal step. For this reason, the weight average molecular weight of the particularly preferred polymeric amine can be in the range of 1000 to 25000, more preferably 2000 to 25000, for the benefit of ease of production.

[0024] When the dispersant contains a relatively low level of amine, there may not be enough amine to neutralize the acid present during the dispersant manufacturing process. Other materials may be introduced to achieve neutralization of the acid groups of the plurality of poly(carbonylalkyleneoxy) chains of the polyester, but it is particularly preferred that the neutralization is achieved mainly or solely through reaction with the amine during the dispersant manufacturing process. For this reason, suitably, the dispersant contains at least 1% by weight (percent by weight) of amine. Preferably, the dispersant contains at least 2% by weight of amine. More preferably, the dispersant contains at least 5% by weight of amine, and even more preferably, the dispersant contains at least 7% by weight of amine. On the other hand, the presence of a relatively high level of amine is considered to have an adverse effect on the performance of the dispersant. For this reason, the dispersant may suitably contain 35% by weight or less of amine, preferably 30% by weight or less of amine, more preferably 15% by weight or less of amine, and most preferably 10% by weight or less of amine. Therefore, in order to achieve a good balance between performance and acid neutralization without introducing additional neutralizing materials, the dispersant may advantageously contain from about 1 to 30% by weight of amine, preferably 2 to 15% by weight of amine, more preferably 5 to 10% by weight of amine, and most preferably about 7% by weight of amine.

[0025] In addition or as another option, the dispersant of the present invention may also contain an acid scavenger. The acid scavenger may be included to react with unwanted acid groups that still remain in the dispersant after reaction with the amine. Suitable acid scavengers may be selected from alkali metal soaps and epoxy esters. Preferably, the acid scavenger is a monoepoxy ester because such materials have been found to be advantageously compatible with the active materials present in the battery system. When present, the dispersant may contain from 1 to 20% by weight of the acid scavenger, preferably 5 to 15% by weight, and more preferably 8 to 12% by weight. It is particularly preferred that the dispersant does not contain an acid scavenger, and this embodiment is particularly preferred when the dispersant also does not contain a fatty acid.

[0026] Merely adding a basic material to balance the acid groups present in the dispersant does not result in appropriately improved properties to make the dispersant suitable for use in a battery system. It is considered that in order to obtain the desirable properties realized when using the dispersant of the present invention, the acid content of the dispersant needs to be removed or immobilized. More specifically, it has been found that incorporating caustic soda to neutralize the acid groups present in conventionally known dispersants is not an effective route to obtain a material that avoids an undesired increase in viscosity (thickening of the dispersion) during use. The reason why the addition of a basic material to neutralize the acid groups does not yield desirable results is not fully understood, but the formation of neutralization reaction salts in the dispersant may also contribute to the dispersion thickening effect. In the dispersant, the poly(carbonylalkyleneoxy) chain of the polyester and the amine are linked via crosslinking groups of amides and / or amide salts formed during the reaction between at least one amino group present in the amide and at least one carbonyl group present in the poly(carbonylalkyleneoxy). The presence of these amide and / or amide salt crosslinking groups is thought to contribute to the problems associated with the inappropriate viscosity profile of prior art dispersants. In addition, the removal of amide bases is considered particularly important to avoid the thickening effect of the dispersion seen when used with certain solvents containing NMP.

[0027] In addition or as another option, the amine value of the dispersant is less than 30 mg KOH / g, preferably less than 28 mg KOH / g, and most preferably less than 26 mg KOH / g. The amine value is a measure of the equivalent amount of potassium hydroxide (KOH) relative to the amine alkalinity present in 1 gram (g) of the chemical substance of interest. The indicator method for the total amine value of fatty amines, AOCS Tf-1b-64, provides a suitable method for testing the materials of the present invention. It has been found that a decrease in the amine value corresponds to an improvement in the ability of the dispersant to disperse particulate matter. For this reason, a dispersant with both a low acid value and a low amine value can be particularly preferred.

[0028] Furthermore, it has also been found that the dispersant of the present invention has good thermal stability. As a result, this material is well-suited for use in battery systems that may encounter higher temperatures during battery use. Suitably, the weight loss of the dispersant at 350 °C is less than 20%. The weight loss can be evaluated according to the standard test methods of ASTM E2550 and / or ISO 11358-1.

[0029] In addition or as another option, the crystallization temperature (Tc) peak temperature of the dispersant is less than 20 °C (measured by differential scanning calorimetry, DSC), more preferably less than 15 °C, and most preferably less than 10 °C. The crystallization peak temperature is considered to be related to the amount of unreacted poly(carbonylalkyleneoxy) chains present in the dispersant, and a high crystallization peak temperature indicates a high level of unreacted poly(carbonylalkyleneoxy) chains. The low crystallization temperature of the dispersant of the present invention indicates the thermal stability of the dispersant of the present invention at ambient temperature.

[0030] In addition or as another option, the melting temperature (Tm) peak temperature of the dispersant is less than 45 °C (measured by DSC), preferably less than 40 °C. This melting temperature of the dispersant of the present invention facilitates the handling and use of the dispersant in dispersion. DSC is a method widely used for the characterization and analysis of polymeric materials. DSC can be evaluated according to the standard test methods of ASTM D3418 and / or ISO 11357-3.

[0031] In addition, a method for producing the dispersant described above is also provided. A method for producing a dispersant comprising a plurality of poly(carbonylalkyleneoxy) chains, optionally a fatty acid, and an amine comprises the following steps: a) generating a polyester from the polymerization reaction of a plurality of poly(carbonylalkyleneoxy) chains and optionally a fatty acid; b) providing an amine and reacting the polyester of step a) with the amine to form an intermediate reaction product; and c) reducing the acid value of the intermediate reaction product of step b). comprises.

[0032] All of the preferred features described above with respect to the individual components of the dispersant product and the final dispersant product itself equally apply to the materials used in the methods described herein. Thus, in step c), the acid value of the intermediate reaction product is reduced sufficiently to obtain the ultimately desired low acid value dispersant product as defined above.

[0033] Method steps a), b), and / or c) may be carried out simultaneously or sequentially. More specifically, steps b) and c) are preferably carried out simultaneously. Further, in the case where no fatty acid is used as desired in step a), steps a) and b) may most preferably be carried out simultaneously.

[0034] Suitably, step a) may be carried out in a first reaction vessel, and subsequently step b) may be carried out in a second reaction vessel. In that case, when the polymerization reaction of step a) is complete, the first reaction vessel may be cooled as desired, and the polyester produced is discharged to the second reaction vessel for carrying out step b) of the method. In this case, the amine may be introduced into the second reaction vessel before or after the introduction of the polyester, or alternatively, the two reactants may be introduced simultaneously. As another alternative, step b) may preferably be carried out using the same (first) reaction vessel. In this case, there is no need to cool the reaction vessel. Instead, the amine may be introduced into the reaction vessel and reacted with the polyester formed in step a). However, the polyester of step a) may also be discharged to a second reaction vessel for carrying out subsequent step b) (and simultaneous or subsequent step c)) because this can increase the throughput of the process.

[0035] Preferably, the polymerization reaction of step a) may be carried out at a temperature between 130 °C and 250 °C, more preferably between 150 °C and 200 °C.

[0036] In step a), the polymerization reaction may suitably be carried out in the presence of a polymerization catalyst. The suitable polymerization catalyst may be of organic or inorganic nature. Preferably, the polymerization catalyst may be selected from titanium(IV) butyrate, zirconium(VI) butoxide, zinc acetate, and toluenesulfonic acid. Titanium(IV) butyrate and zirconium(VI) butoxide are particularly preferred polymerization catalysts for use in the process of the present invention.

[0037] Suitably, the polymerization reaction of step a) may have a reaction time between 4 hours and 20 hours. If the polymerization reaction is carried out in the absence of a polymerization catalyst, a suitable reaction time may be between 15 hours and 20 hours, preferably between 17 hours and 19 hours. As another option, if the polymerization reaction is carried out in the presence of a polymerization catalyst, a suitable reaction time may be between 4 hours and 12 hours, preferably between 6 hours and 10 hours. Thus, the presence of the catalyst is particularly preferred for shortening the time required to carry out the reaction of step a).

[0038] Suitably, the polymerization reaction is carried out under an inert atmosphere, preferably under nitrogen. It is also preferred that a nitrogen purge is carried out to remove air from the reaction vessel prior to the polymerization reaction.

[0039] Suitably, the polyester produced in step a) contains a plurality of poly(carbonylalkyleneoxy) chains in which the alkylene group contains between 3 and 12 carbon atoms. More preferably, the alkylene group contains between 4 and 8 carbon atoms, and most preferably, the alkylene group contains between 5 and 7 carbon atoms. Most suitably, the polyester contains a plurality of poly(carbonylalkyleneoxy) chains in which the alkylene group is a hydroxyhexanoic acid derivative group, more particularly a 6-hydroxyhexanoic acid derivative group. It is desirable that the dispersant contains a plurality of poly(carbonylalkyleneoxy) chains that are poly(6-hydroxyhexanoate) derived from ε-caprolactone.

[0040] Preferably, the polyester produced in step a) also contains fatty acids used as desired. The fatty acids may be saturated or unsaturated. The fatty acids preferably may contain medium-chain fatty acid chains. Preferably, the fatty acid chain contains between 6 and 18 carbons. More preferably, the fatty acid chain contains 10 to 16 carbons. Even more preferably, the fatty acid may be selected from one or more of oleic acid, caproic acid, lauric acid, stearic acid, and palmitic acid. Most preferably, the fatty acid is lauric acid. As suggested above, the presence of fatty acids makes it possible to control the chain lengths of the plurality of poly(carbonylalkyleneoxy) chains in the polyester produced in step a). When the fatty acids used as desired are included in the production of the polyester in step a), it is preferable that step b) is carried out following step a), that is, when fatty acids are used in the method for producing the dispersant, steps a) and b) are preferably carried out sequentially.

[0041] As described above, when fatty acids are used in the method, preferably, the polyester produced in method step a) results in a polyester having a ratio of a plurality of poly(carbonylalkyleneoxy) chains to fatty acids between 4:1 and 15:1, more preferably between 5:1 and 13:1, and most preferably between 8:1 and 12:1.

[0042] Suitably, the amine in step b) may contain one or more of primary, secondary, or tertiary amines. Preferably, the amine is a polymeric amine, more preferably, the polymeric amine is a poly(alkyleneimine). Most preferably, the polymeric amine is a polyethyleneimine. Suitably, the weight average molecular weight of the polymeric amine can be in the range of 1000 to 50000, more preferably 2000 to 30000. As suggested above, most preferably, the weight average molecular weight of the polymeric amine is at most 25000, because commercially available polymeric amines with a molecular weight exceeding 25000 are supplied as aqueous solutions. For this reason, the weight average molecular weight of a particularly preferred polymeric amine can be in the range of 1000 or more to 25000, more preferably 2000 or more to 25000, for ease of production.

[0043] Optionally, the method may include a water removal step. This is preferred when the polymeric amine used in step b) is provided as an aqueous solution, as is typical when the commercially available product has a weight average molecular weight of the amine exceeding 25000. However, such a method is not very preferred.

[0044] Suitably, step b) may be carried out at a temperature between 130 °C and 240 °C, preferably between 150 °C and 220 °C, more preferably between 170 °C and 190 °C.

[0045] In the method of the present invention, the decrease in the acid value of the intermediate reaction product in step c) may be achieved by any suitable means. In particular, the decrease in the acid value of the intermediate reaction product in step c) can be achieved by carrying out the reaction of step b) for a time long enough such that the amine present reacts sufficiently with the polyester of step a) to eliminate the formation of any salts or acids. Additionally or as an alternative, an acid scavenger may be used to achieve the decrease in the acid value of step c).

[0046] Preferably, the reduction of the acid value is achieved by carrying out step b) for a sufficiently long time. In this case, the reaction time of step b) may be between 14 hours and 24 hours, more preferably between 16 hours and 22 hours, and most preferably between 18 hours and 22 hours, during which the acid value of the intermediate reaction product can be reduced to a desirable atypically low level.

[0047] Optionally, process step c) may be terminated at the stage where the acid value of the product is monitored during the process and the desired acid value is obtained. The termination of process step c) can be achieved by cooling the reactants. Cooling the reactants decelerates the reaction until the reactants are below the reaction activation temperature, at which point the reaction of process step c) stops. Thus, preferably, process step c) includes a step of continuously or intermittently monitoring the acid value. When the acid value is to be monitored intermittently, the measurement of the acid value of the product / reactants is preferably carried out at time intervals between 15 minutes and 1 hour, conveniently at 30 - minute time intervals.

[0048] As another option, the reaction stops naturally when there is no free acid left to react. Thus, in the case of a material with a very low acid value, it is not necessary to monitor the reaction of process step c). Instead, it is only necessary to carry out the reaction of step c) for a time sufficient for all the free acid present in the original reactants to react.

[0049] When the acid value reaches the desired low level, step c) of the method may be terminated, and the product is (optionally cooled and) discharged from its reaction vessel. The product is discharged in a state suitable for use as a dispersant without further modification or treatment.

[0050] Suitably, step c) is carried out in situ in the same reaction vessel used for carrying out the reaction of step b), thereby eliminating the need to transport the intermediate reaction product to a further reaction vessel where the acid value can be reduced. However, for higher throughput processing, it may be desirable to discharge the intermediate reaction product from the reaction vessel of step b) to a further reaction vessel for carrying out step c), thereby enabling the recharging of fresh polyester reactant and amine reactant to the reaction vessel of step b) to be carried out in a shorter time frame, and thus a higher throughput process is obtained.

[0051] As another option or in addition, as suggested above, the reduction in the acid value of the intermediate reaction product in step c) may be effected (or assisted) via the introduction of an acid scavenger. The introduction of an acid scavenger can be used to shorten the time required to obtain the desired acid value without an acid scavenger. However, the method of introducing such an acid scavenger is not very preferred because the introduction of the acid scavenger can reduce the suitability for use in some applications of the final dispersant product.

[0052] The present invention also provides a dispersion comprising a continuous phase, particles to be dispersed, and a dispersant as described above.

[0053] The dispersant of the present invention is considered to have a reduced salt content and, in some embodiments, is considered to be salt-free, which results in improved salt tolerance when used compared to conventionally known similar materials. This enables the dispersant of the present invention to be used in applications where problems associated with gelation, thickening, or increased viscosity due to the presence of salt have been identified. As a result of this benefit, as further described below, a higher loading of material can be dispersed in the dispersions of the present invention.

[0054] Preferably, the continuous phase contains a solvent. The solvent may be polar or non-polar. The solvent may be an organic solvent or an inorganic solvent. More preferably, the solvent is selected from n-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and dihydrolevoglucosenone (also known as Cyrene), and such solvents are particularly useful in battery systems. However, for other applications, the continuous phase solvent may be selected from alcohols (especially methanol, ethanol, and terpineol), hydrocarbons (especially toluene), and ketones (especially methyl ethyl ketone).

[0055] In one particularly preferred embodiment, the solvent is NMP. The dispersant of the present invention is particularly well-suited for use in NMP-based solvent systems because it avoids the undesirable thickening effect seen with conventionally known dispersants.

[0056] Suitably, the particles to be dispersed are particulate battery active materials. Preferably, the particulate battery active material is selected from one or more of conductive carbon, lithium nickel manganese cobalt oxide (NMC, LiNi x Mn y Co z O 2 ), lithium manganese oxide (LMO, LiMn 2 O 4 ), lithium iron phosphate (LFP, LiFePO 4 ), lithium cobalt oxide (LCO, LiCoO 2 ), and lithium nickel cobalt aluminum oxide (NCA, LiNiCoAlO 2 ).

[0057] The dispersion preferably contains particles to be dispersed in an amount between 0.1% by weight and 99.9% by weight, more preferably between 0.5% by weight and 99% by weight, and most preferably between 1% by weight and 95% by weight. More specifically, as will be understood by those skilled in the art, the amount of particles to be dispersed by weight relative to the total dispersion depends greatly on the density of the particles to be dispersed. Thus, in the case of a dispersion useful in a battery system, the dispersion may suitably contain conductive carbon between 1% by weight and 19.9% by weight, preferably between 5% by weight and 18% by weight, and most preferably between 7% by weight and 15% by weight. Additionally, the dispersion may also contain a lithium-containing material between 60% by weight and 80% by weight. Thus, for battery system applications, the dispersion may preferably contain particles to be dispersed in a total amount between 60% by weight and 99.9% by weight of the dispersion. One of the advantages of the present invention is that it is possible to include a greater amount of particles to be dispersed without the problem of unwanted gelation or viscosity increase occurring as compared to conventionally known dispersants.

[0058] The dispersion may contain further additives. Such further additives may include one or more of a binder, an adhesion promoter, a wetting agent, and a corrosion inhibitor, by which the dispersion may become more suitable for use in a battery system. Preferably, the dispersion contains a binder, and suitable binders are known and include, among others, polyvinylidene difluoride (PVDF), cellulose-derived materials, rubbers (e.g., SBR, hydrogenated nitrile), polyacrylonitrile, latex, and polyacrylic acid. These further additives are not battery active materials.

[0059] Furthermore, a battery system containing the dispersion described herein is also provided.

[0060] The battery system may be packaged as a cylindrical battery, a button battery or coin cell, a prismatic battery, or a pouch-type battery depending on its intended use.

[0061] Preferably, the battery system is a lithium-ion battery system.

[0062] The battery system may further contain additional additives. Such additional additives may include one or more of a binder, an adhesion promoter, a wetting agent, and a corrosion inhibitor.

[0063] In addition, the use of the dispersant described herein in a battery system is also provided. Preferably, the dispersant is used in the cathode of the battery system. Preferably, the use of the dispersant of the present invention in a battery system enables the dispersion of a higher loading of active material, and this enables the achievement of a higher energy density. The ability to have a higher loading of active material in this way is due to the viscosity profile obtained with this dispersant, which is improved over other known alternative dispersants.

[0064] Hereinafter, the present invention will be described with reference to the following examples and the accompanying drawings.

Brief Description of the Drawings

[0065]

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Example

[0066] In the following examples, dispersants were prepared according to the following preparation methods.

[0067] In each prepared sample, the weight percentages of the raw materials used were varied to obtain the polyester with the ε-caprolactone: lauric acid ratio shown in Table 1 (where applicable).

[0068] bi) Comparative example - Hypermer KD1 manufactured by Croda Hypermer KD1 is a commercially available material for comparison. As described below, a small-scale process was carried out in accordance with the teachings of European Patent Application Publication No. 0158406 to obtain a chemical substance equivalent to commercially available Hypermer KD1.

[0069] a) Lauric acid, ε-caprolactone, and zirconium(IV) butoxide catalyst (used at a level of 0.1% by weight) were charged into a reaction vessel equipped with a nitrogen headspace purge and a stirrer. The reactants were mixed and heated to a temperature of 180 °C and maintained until the reaction was complete (endpoint determined by GPC, with the raw materials present in the GPC chart < 1% by weight). Next, the reaction product was cooled to 100 °C and discharged from the reaction vessel.

[0070] This product was prepared from the polyester material prepared according to step a) above (see Table 1) and polyethyleneimine, which was charged into a reaction vessel equipped with a nitrogen headspace purge. The reactants were mixed and heated to 150 °C and maintained until the reaction was complete after approximately 5 hours (acid value within the range of 25 - 30 mgKOH / g). Next, the reaction product was cooled to 90 °C and discharged from the reaction vessel. However, it should be noted that in the tests conducted below, commercially available Hypermer KD1 products obtained from plant batches were tested.

[0071] bii) Example according to the present invention - Method 1 (Samples 120, 154A, 154B, 156A, 156B, 158, 159, and 118 in Table 1) a) Lauric acid, ε-caprolactone, and zirconium(IV) butoxide catalyst (used at a level of 0.1% by weight) were charged into a reaction vessel equipped with a nitrogen headspace purge and a stirrer. The reactants were mixed and heated to a temperature of 180 °C and maintained until the reaction was complete (endpoint determined by GPC, with the raw materials present in the GPC chart < 1% by weight). Next, the reaction product was cooled to 100 °C and discharged from the reaction vessel.

[0072] The polyester material prepared in step a) above (see Table 1) and polyethyleneimine were charged into a reaction vessel equipped with a nitrogen headspace purge. The reactants were mixed and heated to and maintained at 175 °C, and the reaction was continued until the desired atypically low acid value was reached (the acid values obtained are shown in Table 1). Next, the reaction product was cooled to 90 °C and discharged from the reaction vessel.

[0073] bii) Examples according to the invention - Method 2 (Sample 197 in Table 1) Sample 197 was prepared by a process route, an alternative that does not use step a) described above. Instead, this method relates to a direct PEI-initiated polycaprolactone process route as an alternative.

[0074] ε-Caprolactone, polyethyleneimine, and zirconium(IV) butoxide catalyst (used at a level of 0.1 wt%) were charged into a reaction vessel equipped with a nitrogen headspace purge, a stirrer, and a condenser set for removing condensates. The reactants were mixed and heated to a temperature of 180 °C and maintained until the reaction was complete, which in this case was approximately 3 hours (the completion of the reaction was confirmed using endpoint determination by GPC. The ε-caprolactone present in the GPC chart was <1 wt%). Next, the reaction product was cooled to 100 °C and discharged from the reaction vessel.

[0075] In each prepared sample, the weight percentages of the raw materials used were varied to obtain dispersants containing the weight percentages of polyethyleneimine shown in Table 1.

[0076] All the polyethyleneimine (PEI) materials used were commercially available, and their corresponding weight-average molecular weights (MW) are as shown in Table 1.

[0077] The acid value was calculated according to AOCS ‘Te-1a-64: Test Method for Acid Value.

Table 1

[0078] The PEI materials used are as follows: The material with 2000 MW is Lupasol PR8515 manufactured by BASF. The material with 10000 MW is Epomin SP200 manufactured by Nippon Shokubai Co., Ltd. The material with 25000 MW is Lupasol WF manufactured by BASF.

[0079] Test 1. Viscosity of the dispersion Samples of commercially available conductive carbon particles were dispersed in NMP as a solvent in the presence of a dispersant selected from either commercially available PVP (manufactured by Sigma Aldrich, molecular weight 20000), which is a benchmark, the high acid value comparison sample (Hypermer KD1) detailed above, or the low acid value example sample 118 described above.

[0080] Two types of commercially available conductive carbon particles were tested: 1) LITX 50 manufactured by Cabot, which is a conductive additive used in lithium-ion batteries for high-end consumer electronic devices such as hybrid electric vehicles and smartphones. 2) Super C65 manufactured by Imerys Graphite & Carbon, which is a conductive additive used in lithium-ion rechargeable batteries.

[0081] Using an IKA overhead stirrer equipped with a 4-blade propeller stirrer, a dispersion composed of the materials detailed above was prepared at ambient temperature. The dispersant was added at a level of 1 wt% of the total dispersion, and carbon was added at a level of 5 wt%.

[0082] The viscosity profiles of the dispersions for LITX 50 and Super C65 are shown in Figures 1 and 2, respectively. The viscosity profiles were obtained using a TA Instruments DHR-2 rheometer equipped with a 40 mm stainless steel parallel plate at a 500 micrometer gap. From the low acid value samples according to the present invention, an improved lower viscosity profile is obtained compared to the high acid value comparison samples, and even some improvement is obtained compared to the PVP benchmark samples used in combination with Super C65.

[0083] In addition, the cathode formulations of related simple battery systems containing either a commercially available PVP (manufactured by Sigma Aldrich, molecular weight 20,000) benchmark, a high acid value comparison sample, or the low acid value sample 118 according to the present invention detailed above were tested, and the resulting viscosity profiles are shown in Figure 3. These simple cathode formulations also contained LCO and LITX 50 from Cabot as the active material particles to be dispersed, and the solvent in which they were dispersed was NMP.

[0084] In the cathode formulations of the battery system, it is important to have a low viscosity in combination with shear thinning behavior, which allows the formulation to be easily deposited in the required location but to be maintained in place after deposition. In the case of the present invention, the low acid value samples result in a reduced viscosity profile compared to the high acid value samples. This addresses the need identified by battery manufacturers who have reported the unwanted thickening of formulations when using commercially available materials that match this high acid value sample. In addition, the low acid value sample dispersant also exhibits improved shear thinning viscosity when compared to the PVP benchmark dispersant.

[0085] 2. Performance of the dispersion The performance of three dispersants, 1. PVP, 2. Hypermer KD1 with high acid value (comparison), and 3. low acid value dispersant sample 118 according to the present invention, in dispersing conductive carbon LITX 50 in the solvent NMP, was examined in terms of the concentration of the dispersant required to achieve an acceptable dispersion, the packing level of the particles to be dispersed, and the particle size peak data of the dispersed particles. The results obtained are shown in FIGS. 4 to 6 and are discussed below.

[0086] The dispersion was prepared by dissolving the dispersant in NMP while stirring using an overhead stirrer (IKA) equipped with a 4 - blade impeller. LITX 50 was added and stirring was continued until homogeneous.

[0087] Viscosity measurements were performed at 25 °C using a DHR - 2 rheometer (TA Instruments) equipped with a 40 mm stainless - steel parallel plate. The gap was set at 500 μm and an immersion time of 30 seconds was taken before measurement. The flow curve was plotted logarithmically from a shear rate of 0.1 - 1000 s -1 . When specific data points were used for comparison, these were obtained at 10 s -1 .

[0088] Figure 4 shows the amount of dispersant required to disperse conductive carbon LITX 50 in the solvent NMP with an acceptable viscosity. In this case, it can be seen that for Hypermer KD1 at 6 wt%, only 2 wt% was required for example sample 118 to achieve an acceptable dispersion. Furthermore, it can also be seen that example sample 118 has a similar dispersant concentration to the case of PVP.

[0089] In addition, Figure 5 shows that in Example Sample 118, compared with Hypermer KD1, higher carbon filling amounts can be achieved at lower viscosities at all carbon filling levels tested. Further, in Example Sample 118, a beneficial higher carbon filling amount is also obtained compared with PVP. Thus, with the materials of the present invention, higher carbon filling amounts can be achieved at the same viscosity in the solvent system. The possibility of such higher filling levels is advantageous for using the dispersant of the present invention in battery systems.

[0090] Particle size measurements were performed using a CPS Disc Centrifuge (CPS Instruments) by measuring 100 μl of particles at a disc speed of 20,000 rpm from 1.0 to 0.01 μm. The gradients used contained NMP and Halocarbon 1.8.

[0091] Figure 6 shows the obtained particle size peak data. The particle size peak data shows that the use of Dispersant 118 results in a decrease in particle size compared to when using PVP, suggesting that the dispersing ability of Example Sample 118 is improved compared to PVP. Although no improvement is obtained compared to Hypermer KD1 (comparative example), the low acid value material of the present invention avoids the viscosity increasing effect seen when using Hypermer KD1 without a significant inferiority in dispersing ability compared to Hypermer KD1, as discussed above. Thus, the materials of the present invention provide benefits compared to both PVP and Hypermer KD1, thereby making them particularly suitable for use in battery systems, but also suitable for use in other dispersion systems where viscosity control and increased particle filling amounts may be attractive.

[0092] 3. Effect of Dispersant on the Capacity of Lithium-Ion Coin Cells Two commercially available battery active materials were tested to evaluate the effect of Dispersant Sample 118 on the capacity of the composite cathode of lithium-ion coin cells. 1) Gelon-made LCO is typically used in batteries for consumer electronic devices. 2) Gelon-made NMC622 is a lithium nickel manganese cobalt (LiNiMnCoO2) cathode composite active material powder typically used in automotive batteries.

[0093] The composition of the solid composite cathode material prepared for the cathode capacity test is shown in Table 2 below. The carbon black used was commercially available CB grade LITX 200 made by Cabot. The binder used was commercially available polyvinylidene fluoride (PVDF) powder Solef 6010 / 1001 made by Solvay. Commercially available dispersant PVP was also tested as an alternative.

Table 2

[0094] To prepare the cathode slurry for testing, first carbon black was pre-dispersed in the solvent NMP using a centrifugal mixer (Thinky Mixer ARE-310) at a carbon:dispersant ratio of 5:1 by weight%. Subsequently, the battery cathode active material (LCO or NMC622) and the binder PVDF were added to the initial carbon black dispersion and mixed for 1 hour using a SPEX-8000M ball mill. The final slurry contained 67 wt% solid composite cathode material filled in 33 wt% solvent NMP.

[0095] A cathode slurry without a dispersant (blank) was also prepared as a reference sample to be tested.

[0096] The cathode slurry to be tested was used to provide a layer of cathode slurry on battery-grade aluminum foil using a doctor blade applicator, and then dried at 110 °C in a vacuum oven to form the cathode layer of the coin cell to be tested. After drying, cathode disks were cut out from the coated film using a high-precision disk puncher, and the disks were transferred to an argon-filled glove box with an oxygen and moisture content of less than 1 ppm. A 2032 coin cell was assembled inside the glove box using the prepared cathode disk, metallic lithium as the reference / counter electrode, a porous polypropylene separator, and a commercial 1 M LiPF 6 electrolyte solution in 50 / 50 (volume / volume) ethylene carbonate / diethyl carbonate. The fabricated coin cell was allowed to stand for 12 hours and then subjected to electrochemical tests. The coin cell was cycled 5 times at a constant current in the potential range of 3.2 - 4.2 V vs. Li / Li+(LCO) and 3.0 - 4.3 V vs. Li / Li+(NMC622) at a current corresponding to a formation C-rate of 0.1 using a battery cycling device. Next, cycling was performed at 0.5 C, 1.0 C, and 2.0 C using the same potential range (5 charge-discharge cycles at each C-rate). The capacity at each C-rate was calculated as the average of 5 cycles.

[0097] Figures 7 and 8 show the rate performance data (discharge capacity vs. C-rate) of coin cells containing LCO and NMC622 cathode active materials, respectively. Both graphs also show the results obtained with a blank sample (i.e., without a dispersant) for comparison with the case where PVP or Sample 118 was included as a dispersant. In the chemistry of both battery active materials tested, it can be seen that the use of a dispersant for carbon resulted in an increase in capacity, and this beneficial effect was greater at higher discharge rates. The improved capacity retention at high rates indicates a more uniform dispersion and better coating of the active material by the carbon particles.

Claims

1. A dispersant for a battery system comprising a polyester derived from a plurality of poly(carbonylalkyleneoxy) chains, and an amine, wherein the amine is a poly(alkyleneimine), has a weight average molecular weight in the range of 1000 to 50000, at least a part of the polyester and the amine form a reaction product therebetween, the acid value of the dispersant is less than 5 mgKOH / g, and the amine value of the dispersant is less than 30 mgKOH / g. A dispersant for a battery system.

2. The dispersant for a battery system according to claim 1, wherein the dispersant contains a fatty acid.

3. The dispersant for a battery system according to claim 1, wherein the acid value of the dispersant is less than 1 mgKOH / g.

4. The dispersant for a battery system according to any one of claims 1 to 3, wherein the plurality of poly(carbonylalkyleneoxy) chains contain an alkylene group having 3 to 12 carbon atoms.

5. The dispersant for a battery system according to claim 4, wherein the alkylene group contains 4 to 8 carbon atoms.

6. The dispersant for a battery system according to any one of claims 2 to 5, wherein the fatty acid may be selected from one or more of oleic acid, caproic acid, lauric acid, stearic acid, and palmitic acid.

7. The dispersant for a battery system according to any one of claims 1 to 6, wherein the polymer amine is polyethyleneimine.

8. The dispersant for a battery system according to any one of claims 1 to 7, wherein the weight average molecular weight of the polymer amine is in the range of 2000 to 25000.

9. The dispersant for a battery system according to any one of claims 1 to 8, wherein the dispersant contains at least 5 wt% (weight percent) of an amine.

10. The dispersant for a battery system according to claim 9, wherein the dispersant contains at least 7 wt% of an amine.

11. The dispersant for a battery system according to any one of claims 1 to 10, wherein the dispersant contains 35 wt% or less of an amine.

12. The dispersant for a battery system according to any one of claims 1 to 11, wherein the dispersant further contains an acid scavenger.

13. The dispersant for a battery system according to any one of claims 1 to 12, wherein the amine value of the dispersant is less than 28 mgKOH / g.

14. The dispersant for a battery system according to any one of claims 1 to 13, wherein the mass loss when the dispersant is heated to 350 °C according to the standard test method of ASTM E2550 and / or ISO 11358-1 is less than 20%.

15. A method for producing a dispersant for a battery system according to any one of claims 1 to 14, the method comprising the following steps: a) producing a polyester from a polymerization reaction of a plurality of poly(carbonylalkyleneoxy) chains and, optionally, a fatty acid; b) providing an amine and reacting the polyester of step a) with the amine to produce an intermediate reaction product; and c) controlling the reaction time of the reaction to produce the intermediate reaction product of step b), or by a combination of controlling the reaction time of the reaction to produce the intermediate reaction product of step b) and adding an acid scavenger, reducing the acid value of the dispersant to less than 5 mg KOH / g. A method comprising the above steps.

16. The method for producing a dispersant for a battery system according to claim 15, wherein the polymerization reaction of step a) is carried out in the presence of a polymerization catalyst.

17. The method for producing a dispersant for a battery system according to claim 16, wherein the polymerization catalyst may be selected from titanium(IV) butyrate, zirconium(VI) butoxide, zinc acetate, and toluenesulfonic acid.

18. The method for producing a dispersant for a battery system according to any one of claims 15 to 17, wherein the polymerization reaction of step a) is carried out at a temperature between 130 °C and 250 °C.

19. The method for producing a dispersant for a battery system according to any one of claims 15 to 18, wherein the production of the intermediate reaction product in step b) is carried out at a temperature between 130 °C and 240 °C.

20. The method for producing a dispersant for a battery system according to any one of claims 15 to 19, wherein the reaction time of step b) is between 14 hours and 24 hours.

21. The method for producing a dispersant for a battery system according to any one of claims 15 to 20, wherein method step c) further comprises a step of continuously or intermittently monitoring the acid value.

22. The method for producing a dispersant for a battery system according to any one of claims 15 to 21, wherein in step c), the reduction of the acid value of the intermediate reaction product is achieved (or assisted) by the introduction of an acid scavenger.

23. A dispersion comprising a continuous phase, particles to be dispersed, and a dispersant for a battery system according to any one of claims 1 to 14.

24. The dispersion according to claim 23, wherein the continuous phase contains a solvent. **Claim 25** The dispersion according to claim 24, wherein the solvent is n-methyl-2-pyrrolidone (NMP). **Claim 26** The dispersion according to any one of claims 23 to 25, wherein the particles to be dispersed are particulate battery active materials. **Claim 27** The particulate battery active material is selected from one or more of conductive carbon, lithium nickel manganese cobalt oxide (NMC, LiNi ｘ Mn ｙ Co ｚ O ２ ), lithium manganese oxide (LMO, LiMn ２ O ４ ), lithium iron phosphate (LFP, LiFePO ４ ), lithium cobalt oxide (LCO, LiCoO ２ ), and lithium nickel cobalt aluminum oxide (NCA, LiNiCoAlO ２ ), the dispersion according to claim 26. **Claim 28** The dispersion according to any one of claims 23 to 27, containing particles to be dispersed in an amount between 0.1% by weight and 99.9% by weight of the dispersion. **Claim 29** The dispersion according to claim 28, containing particles to be dispersed in an amount between 60% by weight and 99.9% by weight of the dispersion. **Claim 30** The dispersion according to any one of claims 23 to 29, further comprising at least one additional additive selected from one or more of a binder, an adhesion promoter, a wetting agent, and a corrosion inhibitor. **Claim 31** A battery system comprising the dispersion according to any one of claims 23 to 30. **Claim 32** The battery system according to claim 31, wherein the battery system is a lithium-ion battery system. **Claim 33** Use of the dispersion according to any one of claims 26 to 30 in a battery system. **Claim 34** Use of the dispersion according to any one of claims 26 to 30 in the cathode of a battery system.

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