Method of manufacturing a carbon material for use as a battery electrode

Abstract

A method of manufacturing a carbon material for use as a battery electrode, comprising: providing a polysaccharide / protein mixture comprising at least one polysaccharide component and at least one protein component; and pyrolysing the polysaccharide / protein mixture.

Description

[0001] METHOD OF MANUFACTURING A CARBON MATERIAL FOR USE AS A BATTERY ELECTRODE

[0002] Field of the Invention

[0003] The present invention relates to a material for electrochemical energy storage, and in particular to a material, often called Hard Carbon, derived from crustaceans utilised as an anode active material in metal-ion batteries.

[0004] Background of the Invention

[0005] As the skilled person will appreciate, a battery comprises a cathode and an anode. The active materials chosen for the cathode and anode have a significant influence upon the environmental impact, technical performance in use and over time, and cost of manufacturing the battery.

[0006] It is known to use hard carbon ("HC") as an anode material for lithium-ion and sodium-ion batteries. HC, also known as "non-graphitizing" carbon, is a nongraphic carbon that cannot be graphitized even at temperatures as high as 3000 °C. The distance between single atomic layers (dooz) is widely accepted to be between 3.4 < doo2 (A) < 3.7, which is somewhat larger than that for graphite which is doo2 = 3.3A. The main difference between graphite and HC is the nature of the carbon / carbon bonds, or hybridisation. Whereas graphite has sp2 bonds, HC has a mixed sp2 and sp3 hybridisation, which leads to cross-linking between the layers and a lack of long-range atomic order. Furthermore, cross-linking induced disorder reduces the density of the material. The density of HC is around 1.5 g-cm-3, which is slightly lower than the density of graphite which is around 2.1 g-cm-3.

[0007] HC is known to be electrochemically active towards metal-ions such as e.g. lithium, sodium, and potassium. In this way, HC has been known to function as an anode active material, opposite cathode active materials in a type of battery initially referred to as a "rocking-chair" battery, as first commercialised by Sony in 1991 in a lithium-ion battery having HC as the anode material. Since then, for lithium-ion applications, HC has mostly been replaced by graphite as the anode material of choice, owing to graphite's higher specific capacity (mAh / g), lower specific surface area (m2 / g) and higher density (g / cm3), which enable overall higher energy density (Wh / kg and Wh / L) batteries. In sodium-ion batteries, HC is known to be used instead of graphite as the anode material of choice because graphite is not electrochemically active towards sodium ions in carbonated electrolytes.

[0008] Known methods of manufacturing HC exist. Methods known to the inventors are described herein.

[0009] US7718307B2 describes the manufacture of HC from petroleum pitch. Pitch is a byproduct of processing fossil fuels which not only comes with considerable equivalent CO2 emissions and high Global Warming Potential but also has an unsustainable future of availability due to diminishing resources and the phasing out of fossil fuel processing altogether.

[0010] US20170125811A1 describes the manufacture of HC from a mixture of pitch and coconut shells in a 70 / 30 mixture. This again suffers from the CO2 associated with use of pitch, and also involves 12+ energy intensive and costly process steps.

[0011] US2016 / 0104889A1 describes the use of HC as an anode material for a sodium-ion battery.

[0012] A list of HC processes from a variety of feedstocks is described in a review paper: 2019 review Dou et al. Mat. Tod. 23 2019, 87 or the 2020 review Xie et al 2020 Prog. Energy 2 042002.

[0013] JP2021077635A and Kamiyama Angew. Chem. Int. Ed. 2021, 60, 5114-5120 describe synthesis of a very high-capacity HC using a process using glucose and magnesium gluconate. Although of academic interest, this process appears to have technical and economic challenges to scale to industrial quantities.

[0014] Conder et al. ACS Appl. Energy Mater. 2019, 2, 4841-4852 describes a direct pyrolysis of de-proteinised chitin and chitosan into HC, which is then demonstrated as a sodium-ion active electrode material. The chitin and chitosan (Sigma Aldrich) are each derived from waste shrimp shells from which both the calcium carbonate and protein have been removed in advance of pyrolysis leaving solely chitin. An acid treatment step is applied after pyrolysis. In the case of chitosan, a further process step, deacetylation, is applied to the chitin to alter the molecular weight. Hao et al. Nano Energy 45 (2018) 220-228 discloses a direct pyrolysis of deproteinised chitin at a range of furnace temperatures to produce HC with SSAs 285 m2g-1and greater. The origin and composition of this chitin is the same as in the Conder case discussed above.

[0015] Known methods of manufacturing HC are complex, and as a result are expensive. And often rely on unsustainable precursors. There is therefore a need for improvements in the manufacture of HC, for use as a battery anode material.

[0016] Summary of the Invention

[0017] Environmental impact and, to some extent, cost are significantly impacted by the choice of feedstock, or precursor, and the energy required to operate the process to the feedstock material into the final battery active material. This invention discloses a process to convert chitin, present in waste crustacean shell produced by the food processing industry, into a battery active material. This is favourable in terms of environmental impact of both the choice of feedstock and the low energy process, in comparison with known processes that convert petroleum pitch and / or needle-coke into the final battery material.

[0018] The electrochemical performance is largely, but not wholly, governed by specific gravimetric capacity (mAh / g) and specific surface area (m2 / g). This disclosure provides a way to reduce the specific surface area of chitin-derived HC below 100 m2 / g.

[0019] The external (e.g. open pore) specific surface area can be evaluated using Brunauer-Emmett-Teller (BET) theory. The method uses physical adsorption of a probing gas (typically nitrogen) to determine the external surface area of the hard carbon. In a battery, this surface area will be accessible to the electrolyte and a solid-electrolyte interphase ("SEI") will form at this interface.

[0020] During the first few cycles of a new battery, a process termed "formation" occurs whereby components of the electrolyte, anode and cathode decompose and form a solid-electrolyte interphase ("SEI") on the anode surface. This consumption of active components of the battery has well known detrimental effects on performance of the battery as it removes material that can no longer contribute to the electrochemical performance of the battery e.g. sodium or organic components of the electrolyte. This typically results in a lower overall energy density (Wh / kg and Wh / L) of the final cell. A larger anode surface area begets a larger SEI, consumes a higher proportion of active components and causes a larger drop in full cell performance.

[0021] The present inventors have identified that for materials applied as an anode in a metal-ion battery (e.g. lithium-ion or sodium-ion battery anode), a specific surface area ("SSA") less than 100 m2 / g (e.g. a Brunauer-Emmett-Teller (BET) specific surface area of less than 100 m2 / g when measured by N2 sorption at 77 K) is preferable and less than 10 m2 / g (e.g. a Brunauer-Emmett-Teller (BET) specific surface area of less than 10 m2 / g when measured by N2 sorption at 77 K) may be optimal. In accordance with standard practice, the BET specific surface areas stated herein are measured by N2 adsorption isotherms at 77K (e.g. at Relative Pressure (P / Po) 0.05-0.3, where P is the pressure and Po is the saturation pressure).

[0022] The lithium / sodium of the battery anode may be stored in internal closed pores that are not accessible to the BET probing gas / battery electrolyte.

[0023] The inventors have devised a simple, improved, method of manufacturing HC for a sodium-ion battery.

[0024] In accordance with a first aspect of the present invention, there is provided a method of manufacturing a carbon material (e.g. for use as an electrode), comprising: providing a saccharide (e.g. polysaccharide) / protein mixture comprising at least one saccharide component and at least one protein component; and pyrolysing (e.g. carbonizing) the saccharide / protein mixture.

[0025] In this way, a method of manufacturing a carbon material is provided that avoids the need for a protein removal step. Embodiments of the invention are not only highly cost-effective but also offer environmentally sustainable solutions to the problem of battery electrode production.

[0026] In one embodiment, the carbon material is for use as a battery electrode (e.g. metal-ion battery electrode (e.g. lithium-ion or sodium-ion battery electrode)).

[0027] In one embodiment, the electrode (e.g. battery electrode) is an anode or cathode. In one embodiment, the carbon material is hard carbon (e.g. non-graphitizing carbon / amorphous carbon).

[0028] In one embodiment, the carbon material produced by the pyrolysing step has a (e.g. external) specific surface area below 100 m2 / g (e.g. a Brunauer-Emmett- Teller (BET) specific surface area of less than 100 m2 / g).

[0029] In one embodiment, the carbon material produced by the pyrolysing step has a specific surface area below 10 m2 / g (e.g. a BET specific surface area of less than 10 m2 / g).

[0030] In one embodiment, the step of providing a saccharide / protein mixture comprises: providing the saccharide / protein mixture; and (e.g. prior to the pyrolysing step) demineralising the saccharide / protein mixture (e.g. performing a calcium carbonate (CaCOs) removal step). Advantageously, this pre-pyrolysis demineralising step in combination with the absence of a protein removal step maintains the saccharide (e.g. polysaccharide) structure in its natural state (so that, for example, saccharides / polysaccharides with an acetyl or amide group are maintained in a substantially non-deacetylated state (e.g. with the hydrocarbon chain significantly acetylated)) at pyrolysis resulting in a reduction in specific surface area of the carbon material produced by the pyrolysing step. It is noted that this pre-pyrolysis demineralising step has the opposite effect to the step of adding metal oxide / metal species used in many prior art techniques.

[0031] In one embodiment, the demineralising step is performed using an acid (e.g. hydrochloric acid, acetic acid, phosphoric acid, nitric acid, or any other acid having a useful soluble salt by-product).

[0032] In one embodiment, the demineralising step results in the formation of a soluble salt for use in an external process. For example, in one embodiment the demineralising step results in the formation of a (e.g. calcium) salt (e.g. application of hydrochloric acid forms calcium chloride) for use as a fertiliser.

[0033] In one embodiment, the saccharide / protein mixture is a saccharide / protein comprising at least one saccharide component (e.g. polysaccharide component) and at least one protein component. In one embodiment, the at least one saccharide component is a saccharide (e.g. polysaccharide) having at least one acetyl or amide group.

[0034] In one series of embodiments, the pyrolysing step comprises at a one-stage pyrolysis process.

[0035] In one embodiment, the one-stage pyrolysis process is performed at above atmospheric pressure (e.g. in a device (e.g. autoclave) operative at an elevated pressure (e.g. O.IMPa to 30MPa) and temperature).

[0036] In another series of embodiments, the pyrolysing step comprises at least a two- stage pyrolysis process comprising: i) a first pyrolysis stage to obtain an intermediate char material; and ii) a subsequent second pyrolysis stage to obtain a (e.g. final) char material.

[0037] In one embodiment, the first pyrolysis stage is performed at above atmospheric pressure (e.g. in a device (e.g. autoclave) operative at an elevated pressure (e.g. O.IMPa to 30MPa) and temperature).

[0038] In one embodiment, the first pyrolysis stage comprises a hydrothermal process (e.g. hydrothermal process at an elevated pressure (e.g. between O.IMPa and 30MPa)).

[0039] In another embodiment, the first pyrolysis stage comprises a solvothermal process (e.g. a solvothermal process at an elevated pressure (e.g. between O.IMPa and 30MPa)).

[0040] In one embodiment, the saccharide / protein mixture is a polysaccharide / protein comprising at least one polysaccharide component and at least one protein component.

[0041] In one embodiment, the polysaccharide / protein mixture is formed with a scleroprotein as the at least one protein component.

[0042] In one embodiment, the polysaccharide / protein mixture is formed with chitin as the at least one polysaccharide component. In one series of embodiments, the polysaccharide / protein mixture comprises a naturally occurring polysaccharide-protein matrix (e.g. naturally occurring biopolymer obtained from biomass (e.g. from marine biomass).

[0043] In one embodiment, the polysaccharide / protein mixture is obtained without any protein removal step (e.g. with no significant removal of protein from the naturally occurring polysaccharide / protein mixture).

[0044] In one embodiment, the polysaccharide / protein mixture contains at least 10% protein by mass (e.g. at least 20% protein by mass, e.g. at least 30% protein by mass).

[0045] In one embodiment, the polysaccharide / protein mixture contains less than 60% protein by mass (e.g. 10%-60% protein by mass, e.g. 20%-60% protein by mass, e.g. 30%-60% protein by mass).

[0046] In one embodiment, the polysaccharide / protein mixture is obtained (e.g. directly) from demineralised biomass material (e.g. from demineralised particulate biomass material).

[0047] In one embodiment, the step of providing the naturally occurring polysaccharide / protein mixture comprises a demineralising step (e.g. calcium carbonate (CaCOs) removal step) prior to the pyrolysing step.

[0048] In one embodiment, the polysaccharide / protein mixture comprises a naturally occurring chitin-scleroprotein matrix (e.g. naturally occurring interwoven fibrous matrix of chitin-scleroprotein).

[0049] In one embodiment, the chitin-scleroprotein matrix is obtained (e.g. directly) from demineralised crustacean shell particulate material.

[0050] In one embodiment, the step of providing a polysaccharide / protein mixture comprises: providing crustacean shell particulate material; and (e.g. prior to the pyrolysing step) demineralising the crustacean shell particulate material (e.g. using an acid). In one embodiment, the demineralised crustacean shell particulate material is washed to pH neutral and dried.

[0051] In one embodiment, pyrolysis of the polysaccharide / protein mixture (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises applying a temperature of at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900°C, e.g. at least 1000°C).

[0052] In one embodiment, pyrolysis of the polysaccharide / protein mixture (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises applying a temperature of at least 500°C for at least 1 minute (e.g. at least 600°C for at least 1 minute, e.g. at least 700°C for at least 1 minute, e.g. at least 800°C for at least 1 minute, e.g. at least 900°C for at least 1 minute, e.g. at least 1000°C for at least 1 minute).

[0053] In one embodiment, pyrolysis of the polysaccharide / protein mixture (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises heating to at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900°C, e.g. at least 1000°C) and dwelling until the massout / massin is less than 40%.

[0054] In one embodiment, pyrolysis of the polysaccharide / protein mixture (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises applying a temperature of at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900°C, e.g. at least 1000°C) until mass loss from thermal decomposition has ceased. This has the advantage of providing a carbon material that has advantageous properties as a battery anode material.

[0055] In one embodiment, pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) is carried out in an inert environment. For example, the pyrolysis is carried in an environment of low oxygen partial pressure (e.g. where the oxygen partial pressure is less than 160mBar), or under a stream of inert gas such as N2, Ar, CO2, CO, or under a vacuum.

[0056] In one embodiment, the method further comprises, after pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis), washing to pH neutral and drying the pyrolysed material. In one embodiment, the method further comprises, after pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis), milling (e.g. jet milling) the pyrolysed material.

[0057] In accordance with a second aspect of the present invention, there is provided a method of manufacturing a metal-ion battery (e.g. lithium-ion or sodium-ion battery), comprising performing the method of any embodiment of the first aspect of the present invention.

[0058] In accordance with a third aspect of the present invention, there is provided a carbon electrode material for use in a battery, manufactured by pyrolysing a chitinprotein matrix extracted from crustacean shells.

[0059] In one embodiment, the chitin-protein matrix comprises interwoven chitin and protein.

[0060] In one embodiment, the chitin-protein matrix is obtained without any protein removal step (e.g. with no significant removal of protein from the naturally occurring polysaccharide / protein mixture).

[0061] In one embodiment, the chin-protein matrix is a demineralised chitin-protein matrix.

[0062] A fourth aspect of the invention provides a method of manufacturing a carbon material (e.g. hard carbon) for a battery electrode (e.g. battery anode or cathode), comprising: providing a demineralised crustacean shell particulate material, comprising a chitin and protein matrix; and pyrolysing the demineralised crustacean shell particulate material.

[0063] The method of the first aspect has a lower environmental impact, a higher yield, and can be performed at lower cost than any other known processes.

[0064] The step of pyrolysing may comprise applying a temperature of at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900 °C, e.g. at least 1000°C) for at least 1 minute. The step of pyrolysing may comprise heating to at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900 °C, e.g. at least 1000°C) and dwelling until the massout / massin is less than 40%.

[0065] The step of pyrolysing may comprise applying a temperature of at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900 °C, e.g. at least 1000°C) until mass loss from thermal decomposition has ceased. This has the advantage of providing a HC that has advantageous properties as a battery anode material.

[0066] Pyrolysis may be carried out in an atmosphere of low oxygen partial pressure, such as under a stream of inert gas such as N2, Ar, CO2, CO. This has the advantage of avoiding contamination of the HC and enabling efficient pyrolysis.

[0067] The step of providing a demineralised crustacean shell particulate material may comprise providing crustacean shell particulate material, and demineralising the crustacean shell particulate material using an acid. After demineralisation, the demineralised crustacean shell particulate material may be washed to pH neutral and dried. After pyrolysis, the method may comprise a step of washing to pH neutral and drying. This has the advantage of providing an efficient method of manufacturing HC for a battery anode that is both cost-effective and environmentally friendly.

[0068] A fifth aspect of the invention provides a HC anode material configured for use in a metal-ion battery, manufactured by pyrolysing a chitin-protein matrix extracted from crustacean shell. A HC material manufactured in this way is particularly effective as a battery anode material.

[0069] The chitin-protein matrix may comprise interwoven chitin and protein.

[0070] A sixth aspect of the invention provides a metal-ion battery comprising an anode having a carbon material manufactured using the method described hereinabove or comprising the carbon material anode material described hereinabove. A metal-ion battery comprising this material is particularly efficient, having higher energy density, has a lower environmental impact, and can be manufactured at lower cost. In accordance with a seventh aspect of the invention, there is provided a method of manufacturing a carbon material for use as a battery electrode, comprising: providing a saccharide (e.g. polysaccharide) in a substantially chemically naturally occurring state (e.g. with substantially unaltered chemical structure); and pyrolysing the saccharide in the substantially chemically naturally occurring state.

[0071] In one embodiment, the step of providing a saccharide in a substantially chemically naturally occurring state comprises providing a saccharide / protein mixture comprising at least one saccharide component (e.g. polysaccharide component) in a substantially chemically naturally occurring state and at least one protein component.

[0072] In one embodiment, pyrolysing the saccharide in the substantially chemically naturally occurring state comprises pyrolysing the saccharide / protein mixture (e.g. with either: i) no protein removal step; ii) a protein removal step that does not result in a (poly)saccharide in a non-naturally-occurring state; or iii) a protein removal step resulting in a (poly)saccharide in a non-naturally-occurring state followed by a repair step to return the (poly)saccharide to a substantially chemically naturally occurring state).

[0073] In one embodiment, the saccharide is a saccharide (e.g. polysaccharide) having at least one acetyl or amide group.

[0074] In one embodiment, pyrolysing the saccharide in the substantially chemically naturally occurring state comprises pyrolysing the saccharide in a substantially nondeacetylated state.

[0075] In one embodiment, pyrolysing the saccharide in the substantially chemically naturally occurring state comprises pyrolysing the saccharide / protein mixture (e.g. with either: i) no protein removal step; ii) a protein removal step that does not result in a (poly)saccharide in a deacetylated state; or iii) a protein removal step resulting in a (poly)saccharide in a deacetylated state followed by a repair step to return the (poly)saccharide to a substantially non-deacetylated state).

[0076] In another embodiment, the step of providing a saccharide in a substantially chemically naturally occurring (e.g. non-deacetylated) state comprises providing at least one saccharide component in a substantially chemically naturally occurring (e.g. non-deacetylated state) and substantially no protein component.

[0077] In one embodiment, the carbon material is for use as a battery electrode (e.g. metal-ion battery electrode (e.g. lithium-ion or sodium-ion battery electrode)).

[0078] In one embodiment, the electrode (e.g. battery electrode) is an anode or cathode. In one embodiment, the carbon material is hard carbon (e.g. non-graphitizing carbon / amorphous carbon).

[0079] In one embodiment, the carbon material produced by the pyrolysing step has a specific surface area below 100 m2 / g (e.g. a Brunauer-Emmett-Teller (BET) specific surface area of less than 100 m2 / g).

[0080] In one embodiment, the carbon material produced by the pyrolysing step has a specific surface area below 10 m2 / g (e.g. a BET specific surface area of less than 10 m2 / g).

[0081] In one embodiment, the saccharide is a polysaccharide.

[0082] In one embodiment, the step of providing a saccharide in a substantially chemically naturally occurring (e.g. non-deacetylated) state comprises providing polysaccharide material (e.g. with or without protein component) obtained from crustacean shell particulate material.

[0083] In one embodiment, the polysaccharide is chitin.

[0084] In one embodiment, the method further comprises demineralising (e.g. performing a calcium carbonate (CaCOs) removal step on) the crustacean shell particulate material (e.g. prior to the pyrolysing step).

[0085] In one embodiment, the demineralising step is performed using an acid (e.g. hydrochloric acid, acetic acid, phosphoric acid, nitric acid, or any other acid having a useful soluble salt by-product).

[0086] In one embodiment, the demineralising step results in the formation of a soluble salt for use in an external process. For example, in one embodiment the demineralising step results in the formation of a (e.g. calcium) salt (e.g. application of hydrochloric acid forms calcium chloride) for use as a fertiliser.

[0087] In one series of embodiments, the pyrolysing step comprises at a one-stage pyrolysis process.

[0088] In one embodiment, the one-stage pyrolysis process is performed at above atmospheric pressure (e.g. in a device (e.g. autoclave) operative at an elevated pressure (e.g. O.IMPa to 30MPa) and temperature).

[0089] In another series of embodiments, the pyrolysing step comprises at least a two- stage pyrolysis process comprising: i) a first pyrolysis stage to obtain an intermediate char material; and ii) a subsequent second pyrolysis stage to obtain a (e.g. final) char material.

[0090] In one embodiment, the first pyrolysis stage is performed at above atmospheric pressure (e.g. in a device (e.g. autoclave) operative at an elevated pressure (e.g. O.IMPa to 30MPa) and temperature).

[0091] In one embodiment, the first pyrolysis stage comprises a hydrothermal process (e.g. hydrothermal process at an elevated pressure (e.g. between O.IMPa and 30MPa)).

[0092] In another embodiment, the first pyrolysis stage comprises a solvothermal process (e.g. a solvothermal process at an elevated pressure (e.g. between O.IMPa and 30MPa)).

[0093] In one embodiment, pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises applying a temperature of at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900°C, e.g. at least 1000°C).

[0094] In one embodiment, pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises applying a temperature of at least 500°C for at least 1 minute (e.g. at least 600°C for at least 1 minute, e.g. at least 700°C for at least 1 minute, e.g. at least 800°C for at least 1 minute, e.g. at least 900°C for at least 1 minute, e.g. at least 1000°C for at least 1 minute). In one embodiment, pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises heating to at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900°C, e.g. at least 1000°C) and dwelling until the massout / massinis less than 40%.

[0095] In one embodiment, pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) comprises applying a temperature of at least 500°C (e.g. at least 600°C, e.g. at least 700°C, e.g. at least 800°C, e.g. at least 900°C, e.g. at least 1000°C) until mass loss from thermal decomposition has ceased. This has the advantage of providing a carbon material that has advantageous properties as a battery anode material.

[0096] In one embodiment, pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis) is carried out in an inert environment. For example, the pyrolysis is carried in an environment of low oxygen partial pressure (e.g. where the oxygen partial pressure is less than 160mBar), or under a stream of inert gas such as N2, Ar, CO2, CO, or under a vacuum.

[0097] In one embodiment, the method further comprises, after pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis), washing to pH neutral and drying the pyrolysed material.

[0098] In one embodiment, the method further comprises, after pyrolysis (e.g. in a single pyrolysis step or in the second pyrolysis stage of two-stage pyrolysis), milling (e.g. jet milling) the pyrolysed material.

[0099] In accordance with an eighth aspect of the present invention, there is provided a method of manufacturing a metal-ion battery (e.g. lithium-ion or sodium-ion battery), comprising performing the method of any embodiment of the seventh aspect of the present invention.

[0100] Brief Description of the Drawings

[0101] Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a table showing key performance indicators of a selection of hard carbons synthesized by the inventors;

[0102] Figure 2 is a graph showing X-ray diffraction spectra of hard carbons;

[0103] Figure 3 illustrates a method according to the invention.

[0104] Detailed Description of Embodiments)

[0105] The following detailed description and figures provide examples of how the present invention can be implemented and should not be seen as limiting examples, rather illustrations of how the various features of the material and method disclosed herein can be combined, although other optional combinations will be evident upon a reading of the following description in light of the figures.

[0106] Features of the present invention are defined in the appended claims. While particular combinations of features have been presented in the claims, it will be appreciated that other combinations, such as those provided above, may be used.

[0107] The method of the present invention involves preparation of a saccharide / protein mixture, which in this embodiment is a polysaccharide / protein matrix derived from the sustainable feedstock of crustacean shell waste, specifically, the exoskeletons of crustaceans.

[0108] The exoskeletons of crustaceans principally consist of three components in an interwoven matrix of macrofibrils:

[0109] (1) calcium carbonate (CaCCh),

[0110] (2) chitin (CsH OsN)^ and

[0111] (3) protein.

[0112] In the crustacean exoskeleton, CaCCh offers structural stability, protection and a counter point for muscle leverage. It is commonly also found in rock minerals calcite and aragonite, notably in limestone.

[0113] Protein performs a range of functions, providing the cellular framework for the growth and moulting cycles in the epicuticle. Protein also provides a water-proofing function, forming an impermeable membrane. Proteins are large macromolecules, rarely represented by chemical formulas. They consist of sequences of amino acids bonded together into secondary structures, which interact to form three dimensional tertiary structures which further interact to form quaternary structures. One conventional method of classifying proteins is by their morphology. Scleroprotein (fibrous), globular and membrane.

[0114] Chitin is a model example saccharide. Other examples of saccharides are cellulose and glucose. In a crustacean shell chitin affords flexibility to the CaCOs framework facilitating movement and other functions critical for life. It is a polysaccharide, a natural biopolymer that is synthesised in the biosphere in a range of living organisms at an estimated rate of 100 billion tonnes per year. The main commercial sources of chitin are crab and shrimp shells where an acid treatment to dissolve the calcium carbonate is followed by an alkali treatment to dissolve proteins. Chitosan is the deacetylated form of chitin and although it is often differentiated by degree of deacetylation there is no generally accepted nomenclature to describe chitosan and from herein chitin and chitosan are assumed interchangeable.

[0115] The inventors estimate that globally around 10 million tonnes of shell waste are generated annually, the vast majority of which is disposed of in landfill.

[0116] The inventors have discovered that removing calcium carbonate and processing a chitin-protein matrix in accordance with the method of the present invention provides HC having a lower specific surface area than a comparable method in which calcium carbonate and protein is removed before pyrolysis.

[0117] Compared to a method of manufacturing HC in which protein is removed before pyrolysis, synthesis of HC from a protein-chitin matrix using the method of the present invention also has the following advantages:

[0118] - A higher yield (i.e. relative mass out of the furnace compared to mass into the furnace); and

[0119] - A lower final cost of the process, having not needed to remove the protein. Removing protein is a second wet chemical step which typically involves using alkaline NaOH solution, after the step of removing CaCCh

[0120] Compared to a method of manufacturing HC involving petroleum pitch as a precursor, the method of present invention has the following advantages:

[0121] - A lower environmental impact, in that: (a) Both crustacean shells and fossil fuels have negative CO2 emissions associated with their formation, but there are eight orders of magnitude between the formation timescales. Shells form over roughly 1 year. Coal / oil / gas form over roughly 100 million years.

[0122] (b) The present aspect involves a simpler and lower energy process to form HC, which produces lower CO2 emissions than an equivalent HC manufacturing process having petroleum pitch as a precursor. Longer term sustainability of the process to produce HC. Chitin is produced in the biosphere at a rate of 100 billion tonnes-per- annum. 10 million tonnes-per-annum of waste shell is produced globally. In contrast, petroleum pitch is produced as a by-product of processing fossil fuels which are widely anticipated to be exhausted by 2060. The invention enables a circular economy, as the vast majority of shell waste currently goes to landfill. With reference to the Figures, Figure 1 is a table that contains key performance indicators of a selection of hard carbons synthesised from chitin extracted from crustacean shell, or a chitin-protein matrix extracted from crustacean shell using different processes. Chitin-and-protein is hereon referred to as DMB or "de-mineralised biowaste". Where "de-mineralised" refers to the removal of the mineral calcium carbonate from the shell, leaving chitin-and-protein. DMPB refers to de-mineralised and de-proteinised biowaste (essentially leaving only a chitin skeleton) where the de-mineralisation and de-proteinisation steps are conducted in that order. DPMB refers to de-proteinised and de-mineralised biowaste (also essentially chitin) where the de-proteinisation and de-mineralisation steps have been conducted in that order. The de-mineralisation and de-proteinisation processes were conducted using a known chemical route of reacting with hydrochloric acid (HCI) and sodium hydroxide (NaOH) respectively, as described in Percot et al., Optimization of chitin extraction from shrimp shells, Biomacromolecules 2003, 4, 1, 12-18. "Chitin" in Figure 1 refers to commercially available chitin derived from crayfish, sourced from WellGreen Technology Co. Ltd. and acts as a control experiment. "SSA" is the specific surface area (m2 / g) determined from N2 gas adsorption measurements, "dooz" is the HC average interlayer spacing derived from X-ray diffraction measurements. "Yield" is the ratio of final mass of HC to starting mass of dry shell.

[0123] Figure 3 shows a method 100 of manufacturing HC for a battery anode. The method 100 comprises providing 102 dried crustacean shell. The dried crustacean shell may be formed from crab shell or any other suitable crustacean shells. The drying may be performed by warming to 80°C for 24 hours. The method 100 further comprises a step of grinding 104 the crustacean shell. The grinding 104 can be performed using a grinder. Preferably, the grinding step 104 grinds the crustacean shell into approximately 1 mm sized particles, as controlled by a 1mm mesh sieve. This forms crustacean shell particulate material.

[0124] The method 100 further comprises a step of de-mineralising 106 the crustacean shell particulate material. The step of de-mineralising 106 is performed to remove the CaCOs from the crustacean shell particulate material. This step can be performed by adding an acid to the particulate material. The acid can preferably be HCI solution, but other options such as citric, acetic and formic acids are equally viable reagents. The concentration of the HCI solution may be 10 w / w% but preferably more than 1 w / w% and preferably not more than 30 w / w%. The step of de-mineralising 106 can include a step of stirring the acid with the particulate material in a beaker. The stirring may be performed for one minute. This step 106 may comprise sealing the beaker and leaving at room temperature (~21°C) for at least 24 hours.

[0125] The method 100 further comprises a step of filtering 108. The filtering 108 is performed to recover the solid DMB from the de-mineralising solution (the byproduct of this process is calcium chloride which can advantageously be used as an environmentally friendly fertiliser by-product). The filtering 108 can be performed using a glass frit Buchner funnel. After filtering 108, the method 100 comprises a washing step 110. The washing step 110 washes the DMB of any remaining acid solution. The washing 110 may be performed using tap water until the material is pH neutral. The method 100 further comprises drying 112 the DMB material. The drying 112 may be performed by heating the DMB at 80°C.

[0126] Once the DMB has been obtained according to the above method steps, the next step in producing HC is to pyrolyse the DMB. The step of pyrolysing 114 may be performed using a tube furnace. This step 114 can include placing the DMB in a ceramic boat, placing the boat into the furnace when it is cool, sealing the ends of the furnace, and passing dried nitrogen gas through the tube. The nitrogen gas may be passed through at a rate in the range from 0.01 SLM (Standard-Litre-per- Minute) to 10 SLM. In one example, the nitrogen gas may be passed through at approximately 1 SLM. The furnace may be heated at a rate of between l°C / minute and 10°C / minute to a temperature of between 500°C and 2500°C. In one example, the furnace may be heated at a rate of 3°C / minute to a temperature of 1050°C. The pyrolysing step 114 may comprise holding the DMB in the furnace for at least two hours. After pyrolysing 114, the method 100 comprises cooling 116 the material under the flow of nitrogen gas to room temperature. The step of cooling 116 may comprise removing the material from the furnace once at room temperature.

[0127] Example 1

[0128] In Example 1, a method of manufacturing de-mineralised biowaste for a battery anode was performed, comprising the steps of providing a demineralised crustacean shell particulate material comprising a chitin-protein matrix, for subsequent pyrolysation of the demineralised crustacean shell particulate material.

[0129] DMB was prepared by grinding 5 g of dried crab shell into approximately 1 mm particles using a grinder and a 1mm mesh sieve. The particles were placed in a glass beaker along with 60 ml of 10 w / w% HCI solution and stirred for one minute. The beaker was then covered and left for 24 hours at room temperature and pressure. The solid was recovered by filtering through a glass frit Buchner funnel and washed with tap water until approximately pH neutral. The recovered material was then dried at 80°C for 24 hours and weighed.

[0130] Example 2

[0131] An example of how DMPB can be prepared is provided for information only.

[0132] DMPB was prepared by following the DMB process and then performing the following subsequent steps. 100 ml of 5w / w% NaOH aqueous solution was added to the dried material resulting from the final step of the DMB process, and heated to 90°C for 2 hours. The solid was recovered by filtering through a glass frit Buchner funnel and washed with tap water until approximately pH neutral. The recovered material, essentially chitin, was then dried at 80°C for 24 hours, and weighed.

[0133] Example 3

[0134] An example of how DPMB can be prepared is provided for information only. DPMB was prepared by performing the following steps. First, 5 g of dried crab shell was ground into approximately 1 mm particles using a grinder and 1mm mesh sieve. Then, 100 ml of 5 w / w% NaOH aqueous solution was added to the particles and heated to 90°C for 2 hours. The solid was recovered by filtering through a glass frit Buchner funnel and washed with tap water until approximately pH neutral. The recovered material was then dried at 80 °C for 24 hours, weighed. This was placed in a glass beaker along with 60 ml of 10 w / w% HCI solution and stirred for one minute. The beaker was then covered and left for 24 hours. The solid was recovered by filtering through a glass frit Buchner funnel and washed with tap water until pH neutral. The recovered material was then dried at 80°C for 24 hours, and weighed.

[0135] Hard Carbon Preparation

[0136] The hard carbons DMB-HC, DMPB-HC and DPMB-HC were prepared by placing 1 g of DMB, DMPB, DPMB in a ceramic crucible, respectively. Chitin-HC was prepared as a control experiment by placing 1g of crayfish chitin sourced from Wellgreen Technology Co. Ltd. in a ceramic crucible. The crucibles were individually positioned in a cool tube furnace. Both ends were sealed and dried nitrogen gas was passed through at approximately 1 SLM. The furnace was heated at a rate of 3°C / minute to 1050°C where it dwelt for two hours before it was set to cool naturally to room temperature. The mass of the recovered material was measured and divided by the starting mass of dry shell to derive the yield shown in Figure 1.

[0137] SSA Measurement

[0138] The SSA from Figure 1 was estimated from N2 gas sorption measurements. A Quantachrome Quadrasorb Evo Analyser was used for surface area analysis. Prior to analysis, the HC was firstly prepared by hand grinding using a mortar and pestle for 2 minutes before passing through a 100-micrometer sieve, and then a 50- micrometer sieve. This material was then degassed under dynamic vacuum for 3 h at 200°C. Surface areas of the hard carbons were determined from 5 point N2 adsorption isotherms (Relative Pressure (P / Po) 0.05-0.3) measured at 77K. The Brunauer-Emmett-Teller (BET) method was used to treat the data.

[0139] As shown in the table in Figure 1, the HC produced from the DMB material made according to the method described above has the lowest SSA compared to the HC produced from material which had been deproteinised or the as-received chitin. Figure 2 shows X-ray diffraction spectra of HC synthesised from: DMB (chitinprotein matrix), DMPB (calcium carbonate removed, then protein removed, leaving essentially chitin), DPMB (protein removed then calcium carbonate removed, leaving essentially chitin), and chitin (commercially sourced chitin from crayfish, Wellgreen Technology Co. Ltd.). The X-ray diffraction spectra were collected in the following manner. The HC was firstly prepared by hand grinding using a mortar and pestle for 2 minutes before passing through a 100-micrometer sieve, and then a 50-micrometer sieve. The sieved HC was then compacted into a zero background sample holder which was loaded into the XRD machine. This instrument had a copper target set to 40 kV and 15 mA. The scan was conducted from 5 to 80 degrees in 20, with a step size of 0.02 degrees and a speed of 1.2 degrees (20) per minute. The doo2 spacing was extracted from the spectra using the position of the peak in the region 23-24° (20) and Bragg's Law: nA = 2dsin0. Where n = l and the wavelength of the X-rays (A) was 1.540593 A.

[0140] Although a specific form and arrangement of method and material is described and shown in the figures, it will be appreciated that various aesthetic, structural, and operational changes could be made to the material and method shown whilst still performing the function of the present invention as defined in the appended claims. Other variations on the embodiments described can be envisaged without departing from the scope of protection as defined in the appended claims.

Claims

Claims1. A method of manufacturing a carbon material for use as a battery electrode, comprising: providing a polysaccharide / protein mixture comprising at least one polysaccharide component and at least one protein component; and pyrolysing the polysaccharide / protein mixture.

2. The method according to claim 1, wherein the carbon material produced by the pyrolysing step has a specific surface area below 100 m2 / g.

3. The method of claim 2, wherein the carbon material produced by the pyrolysing step has a specific surface area below 10 m2 / g.

4. The method according to any of the preceding claims, wherein the step of providing a polysaccharide / protein mixture comprises: providing crustacean shell particulate material; and demineralising the crustacean shell particulate material prior to the pyrolysing step.

5. The method according to claim 4, wherein the demineralising step is performed using an acid.

6. The method according to claim 4 or claim 5, wherein the demineralising step results in the formation of a salt for use as a fertiliser.

7. The method of any of the preceding claims, wherein the pyrolysing step comprises at a one-stage pyrolysis process.

8. The method of any of the preceding claims, wherein the pyrolysing step comprises at least a two-stage pyrolysis process comprising: i) a first pyrolysis stage to obtain an intermediate char material; and ii) a subsequent second pyrolysis stage to obtain a char material.

9. The method of claim 8, wherein the first pyrolysis stage is performed at above atmospheric pressure.

10. The method of claim 8 or claim 9, wherein the first pyrolysis stage comprises a hydrothermal process.

11. The method of claim 8 or claim 9, wherein the first pyrolysis stage comprises a solvothermal process.

12. The method of any of the preceding claims, wherein the polysaccharide / protein mixture is formed with a scleroprotein as the at least one protein component.

13. The method of any of the preceding claims, wherein the polysaccharide / protein mixture is formed with chitin as the at least one polysaccharide component.

14. The method of any of the preceding claims, wherein the polysaccharide / protein mixture comprises a naturally occurring chitin-scleroprotein matrix.

15. The method of claim 14 wherein the chitin-scleroprotein matrix is obtained directly from demineralised crustacean shell particulate material.

16. The method of preceding claims wherein the polysaccharide / protein mixture contains at least 10% protein by mass.

17. The method of claims 7-11, wherein pyrolysis of the polysaccharide / protein mixture comprises applying a temperature of at least 500°C for at least 1 minute.

18. A method of manufacturing a metal-ion battery, comprising performing the method of any of the preceding claims.