WO2018134485A1

WO2018134485A1 - Method for the manufacture of cathode materials for nanostructured li ion batteries utilising short-term laser pulses

Info

Publication number: WO2018134485A1
Application number: PCT/FI2018/050055
Authority: WO
Inventors: Jari Liimatainen; Ville KEKKONEN
Original assignee: Picodeon Ltd Oy
Priority date: 2017-01-23
Filing date: 2018-01-23
Publication date: 2018-07-26

Abstract

The present invention introduces a method for the manufacture of cathode materials (52) for lithium batteries so that a coating method based on laser ablation is utilised in the manufacture of at least one material layer. The share by volume of the active cathode material used in the invention is at least 30 percent by volume and the average particle size is at most 5 pm. In the method the so-called roll-to-roll method can be used, in which the base material to be coated (15, 22, 42, 65, 75, 85, 95) is directed from one roll (41 a) to the second roll (41 b), and the coating occurs on the area between the rolls (41 a-b). In addition, turning mirrors (31) can be used to direct laser pulses (12, 61, 71 a-b, 81 a-d, 91) as a pulse front (33) to the surface of the target material (13, 62, 72a-b, 82a-d, 82A-D, 92).

Description

Method for the manufacture of cathode materials for nanostructured Li ion batteries utilising short-term laser pulses

Field of the invention The invention relates especially to lithium batteries, their structure and the manufacture of cathode materials. Further, the invention relates to the manufacture of at least one part of the said lithium batteries utilising short-term laser pulses and the so-called PLD (Pulsed Laser Deposition) method.

Background of the invention As the need for mobile devices, electrically operated cars and storing of energy grows, the need for the development of battery technology has increased. Li ion batteries have succeeded well in very many applications, especially due to their good energy density and recharging possibilities compared to, among others, traditional Ni-CD (nickel-cadmium) and Ni-Mn (nickel-manganese) batteries. Li ion battery technology is based on a positive cathode, in which active material is, for example, transition metal oxide, and a commonly used carbon-based negative anode. A microporous polymeric separator is used between the anode and cathode to prevent contact between the anode and cathode, but nevertheless allowing the ions to move through the separator film. In addition, an electrolyte is needed, which in current solutions is principally liquid.

To improve the energy density and service life of ion batteries it has been attempted to develop new cathode materials by utilising new material systems, microstructures and material combinations. There are several alternative materials to be used as cathode coatings for Li ion batteries, and with the new manufacturing technologies and materials the aim is to utilise their advantages and reduce weaknesses relating to different alternatives. With many potential materials, the use is limited, for example, by restrictions relating to safety, service life and, in certain cases, manufacturing technology and costs. A weakness with some materials is the poor ion and/or electron conductivity, weakening of capacity as the number of charge/discharge cycles grows, or reaction with the electrolyte. It must also be possible to prevent the dissolution of doping substances essential for microstructure and functionality with correct material choice and possibly coatings suitable for the electrochemical environment used. Lithium-bearing metal oxides, such as L1C0O2, LiMn20₄ and LiFeP0₄ are currently typically used as cathode materials for Li ion batteries because of their technical overall advantages. There are certain weaknesses related to them; for example, with L1C0O2, poor thermal stability and weakening of capacity with big current den- sities. The weakness with LiMn20₄ again is its long-term durability, among other things, due to the dissolution of manganese. The weakness with LiFeP0₄ again is its poor electron and ion conductivity. Advantages with both LiFeP0₄ and LiMn20₄ are lower raw-material costs compared to the cobalt-doped L1C0O2 cathode material. The cathode material may form as much as 40% of the costs for the Li ion battery so that minimising the raw-material costs for cathode materials is of high significance so that it would be advantageous to develop cheaper microstructures simultaneously offering the same performance into cathode coatings.

The modification and optimisation of micro and nanostructures, adding of small doping substance quantities, changes in the surface structure and chemistry, and man- ufacture of composite structures can make it possible to avoid certain structural weaknesses, or their impacts can be reduced. These changes are not possible by using present manufacturing methods, such as chemical methods, in which cathode material powders are bonded to each other and the background material with different binding agents or in which the size of the cathode particles is very big. Summary of the invention

In the present invention there is introduced a method for the manufacture of cathode materials and coatings used in the manufacture of Li ion batteries, making use of benefits related to the control, doping and multilayer manufacture of microstructures achieved with ultrashort laser pulses. The method is suited for the industrial bulk manufacture of cathode materials. The method makes it possible to optimise the overall performance of the cathode coating, cyclical durability, charge/discharge intensity, and to improve the service life and energy density. These methods and means are illustrated next.

In the method of the invention, ultrashort laser pulses with the length of less than 1000 ps are targeted at the target material to detach material from the target material as atoms, ions, particles, or a combination of these. The material detached from the target is targeted at the surface of the piece to be coated so that a coating with the desired quality or thickness is generated. The quality, structure, quantity, size distribution and energeticity of the materials detached from the target are controlled by parameters used in laser ablation, such as, among others, pulse energy, pulse length, used wavelength, pulse repetition frequency and superposition, coating temperature and background gas pressure. Further, the microstructure (e.g. quantity of crystallinity) and doping of target materials can be controlled together with chosen laser pulse parameters to achieve the desired process, material distribution and coating.

Depending on the cathode material or combination of cathode materials used and on the pursued property profile, the process parameters for laser ablation can be adjusted to achieve the desired microstructure and morphology. An advantage of the ultrashort pulsed laser technology is that it can be utilised with very many mate- rials so that it is possible to produce different material combinations and different microstructure combinations.

The pulsed laser technology can be used to adjust the porosity of the coating layer to be manufactured by ablation, the size of cathode material particles and the free area of cathode materials, which has numerous essential meanings for the Li ion battery and cathode. The coating produced by laser ablation has to be porous in order to make possible the distribution of the electrolyte over the entire cathode material as well as short diffusion ranges of ions and electrons. The short diffusion ranges of ions and electrons make possible the quicker charge and discharge of the Li ion battery. Reducing the particle size shortens the diffusion range of ions and electrons and, further, enhances the contact surface between the electrolyte and cathode material particles, which together with the correct porosity rate accelerates the electrochemical cathode reactions, which are essential for the operation of the Li ion battery.

Detrimental reactions of cathode materials with the electrolyte can be prevented or their impact can be reduced by executing a thermomechanical protective layer, coating impacting the properties of the reaction layer or coating increasing the chemical endurance of the cathode material layer during the coating of the cathode material, between the manufacturing steps of different coating layers or as the last step. The porosity or thickness of this coating can be adjusted in accordance with the required functionality. A coating of this type should enable the electrochemical reactions essential for the operation of the Li ion battery and the diffusion essential for the reactions, but reduce or prevent detrimental reactions. One example of such a phenomenon with LiMn2O₄ is the dissolution of manganese and its travel to the electrolyte and the surface of the anode material. By manufacturing a composite structure either layer by layer or by means of two or several simultaneous material flows produced by combinatory ablation, it is possible to control the properties of the cathode material coating in many ways. When one wants to manufacture the composite material as a combination of several different materials, a simultaneous material flow can be directed from two or several targets towards the piece to be coated, separately adjusting the ablation process of both materials to achieve the desired structure and material distribution.

For example, protective coatings can be manufactured to the surface of and around cathode particles by combinatory technology, or the material can be doped, for ex- ample, by adding material enhancing electrical conductivity. A challenge with the combinatory process is to control the material flow in a situation in which the gas atmosphere has to be suitable for the processing of all materials to be ablated separately. For example, the background gas pressure must be appropriate in relation to the morphology of the desired material for all materials to be ablated. If the ob- jective for one material is to generate particles of a certain size, and for the second material the objective is to achieve, for example, particles of a different size or an atomised material flow, the background gas must be suitable for this purpose. In addition, it must be able to prevent undesired reactions between materials leaving from different targets in the material flow or upon generation of the coating. The crystalline structure of the cathode material manufactured by laser ablation can be adjusted, for example, by changing the coating temperature. An amorphic structure is very easily generated in laser ablation, the functionality of which in case of lithium-bearing metal oxides is not good. Because of this, laser ablation must be executed in circumstances, in which the amorphousness of the material to be pro- duced by coating is as low as possible. For example, by raising the temperature, for example, by heating the substrate and by editing the process parameters for laser ablation, the crystallinity of the structure can be promoted.

Ultrashort pulsed laser ablation can be utilised to produce many above-described advantages on the basis of one process technology, with certain preconditions even in one coating process step. The laser ablation process can also be executed alternatively in several steps, for example, by using a coating line, in which, for example, a porous layer consisting of cathode material particles is manufactured in the first step, and in the next step there is performed the doping, for example, with a copper or nickel layer or dispersion and by continuing this coating in steps, until the desired coating thickness has been produced. In principle, it is possible to combine one or some of the above-mentioned methods with a second coating method, for example, as successive process steps so that the ultrashort pulsed laser ablation technology is applied to the coating process step best suited for it, and a second coating technology is used to supplement this. This can be executed either immediately as successive process steps or as separate processes.

The coating process can be performed as a method of the roll-to-roll type or, for example, on sheets, which are fed to the coating line as successive sheets.

For productivity it is essential to perform the coating by utilising a wide laser beam distribution, which is generated by means of turning mirrors. The laser pulse front detaches material from the target material in a desired manner, and the material flow is directed from the target to the surface of the piece to be coated.

The inventional idea of the invention further comprises the final product manufactured with the method, i.e. the different material layers of the Li ion battery, and the cathode material thin film produced with the manufacturing method of the invention.

Brief description of the drawings

Figure 1 illustrates the principle of the coating transaction with different physical components in an example of the invention;

Figure 2 illustrates an exemplary structure of a coated separator film;

Figure 3 illustrates the principle of forming a fan-shaped rectilinear laser pulse front with an apparatus arrangement of the invention;

Figure 4 illustrates an example of the so-called roll-to-roll principle relating to the coating process;

Figure 5 illustrates a typical structure of a lithium ion battery as a cross-sectional view;

Figure 6a illustrates an example of the coating of a cathode material to a base by PLD technology;

Figure 6b illustrates a possible porous structure produced with the principle of Figure 6a, in which one material is used;

Figure 6c illustrates a possible porous structure produced with the principle of Figure 6a, in which two materials are used to generate the composite material;

Figure 6d illustrates a possible porous structure produced with the principle of Figure 6a, in which doped material is used in addition to the principal material; Figure 7 illustrates a combinatory coating method using two simultaneous material flows;

Figure 8a illustrates the use of successive coating stations to improve productivity when manufacturing sandwich structures;

Figure 8b illustrates the use of successive coating stations to improve productivity when manufacturing composite structures;

Figure 8c illustrates the use of successive coating stations to improve productivity when manufacturing a doped material;

Figure 8d illustrates a closer detail of the basic material, in which doped particles are included; and

Figure 9 illustrates an example of the use of a composite target material in the manufacture of a composite coating.

Detailed description of the invention

In the invention of the method, there is manufactured a cathode material layer for a Li ion battery and, when needed, also other layers making use of pulsed laser ablation deposition to manufacture materials applicable to it or gaining relative productivity or quality advantages from it. In pulsed laser ablation, solid material is detached with short laser pulses, the length of which can vary from milliseconds to femtoseconds. In pulsed laser (ablation) deposition (PLD) based on laser ablation, laser pulses with the length of at most 100 000 ps (i.e. at most 100 ns) are typically used. In one embodiment also so called ultrashort pulsed laser deposition (US PLD) can be used, in which the length of the laser pulses is at most 1000 ps.

Laser ablation is utilised to control micro and nanostructures to achieve and optimise the previously described functionalities of the Li ion battery. The cathode can be of any material suitable for the cathode material of Li ion batteries, such as lithium-bearing transition metal oxides, such as L1C0O2 and LiMn02, different intercalation cathode materials, such as T1S3 and NbSe3 and LiTiS2 or a polyanion compound, such as LiFeP0₄. Also other materials or composites or sandwich structures formed of these can be used. For example, so-called doping is pos- sible by adding to the surface of the cathode material copper, nickel or platinum particles, for example, as dispersions or coating. The objective of composite materials or doping is to eliminate certain weaknesses of cathode materials, such as poor conductivity or microscopic damages caused by a large change in volume. Detaching materials and producing a material flow from a target or targets to the surface of the piece to be coated occurs by adjusting the parameters for short laser pulses. For each material there exist parameters especially applicable for it, with which the ablation process and the structure of the generating coating can be con- trolled. To detach material from the target material, the energy density (J/cm²) generated by the laser pulses must be adequate on the surface of the target material. The threshold energy density, with which the material detachment begins from the target, is called the ablation threshold, and it is a material-specific parameter, but depends also on, among others, the wavelength of the laser light and the length of laser pulses. The material can detach from the target as atoms, ions, molten particles, broken particles, particles condensed from atoms and ions after detachment from the target, or as a combination of these. The mode of detachment of the material and its behaviour, such as condensation tendency after detaching from the target depends on, among other things, by how much the energy density of laser pulses exceeds the ablation threshold. Depending on the cathode material and the requirements set on its structure and the morphology of the coating, the parameters for laser ablation can be changed. It is essential to note that, after detaching from the target, there may occur changes in the material structure and size distribution in the material flow before the material attaches to the base material. This change process can be controlled by process-technical means, for example, by adjusting the atmosphere in the coating chamber, i.e. composition and pressure of background gas, and the flight range of the material (from the target to the base) in addition to the previously mentioned laser pulse parameters.

Because the objective is to manufacture porous cathode materials, their manufac- ture can be performed based on very different ablation processes and combinations of these. The choice of the ablation process is impacted by the desired porosity, particle size and thus open area, thickness of the coating (particle sizes produced by different ablation mechanisms vary), quantity of crystallinity, productivity requirement and control requirements for stoichiometry. In addition, for the strength of the porous structure it is important to produce a structure, in which, in addition to particles, the material flow contains fine-grained, atomised or ionised material to contribute to the bond between particles and thus the strength of the entire structure, and sufficient kinetic energy of the material flow.

A coating process based on ultrashort pulsed laser ablation differs from other thin film coating methods in that it makes possible to relatively precisely control the particle size producing the porous coating. If it is attempted to produce a desired coating by initially forming an essentially atomised or ionised material, the material's tendency to form so-called clusters depends especially on the velocity and size distribution of the units composing the detached material flow by ablation and on the pressure of the background gas. For example, the condensation of a certain material flow produced from the target by laser ablation into particles can be intensified by increasing the background gas pressure in the coating chamber in a controlled manner. The increase in pressure increases the probability of collisions with gas atoms/molecules. In collisions, the material flow units lose energy and change their direction. Deceleration and changes in direction again increase the probability of collisions with other units in the material flow and thus the formation of clusters. The use of background gas can be used to adjust the energeticity of the material flow and, further, to impact on the composition of the cathode material through a reactive process when performing laser ablation in the desired gas atmosphere. For example, metal oxide coatings can be made in an oxygen atmosphere by the laser abla- tion of pure metal.

To manufacture a porous cathode material, it is also possible to execute the ablation process so that particles are detached from the target material by breaking, for example, along the powder particle interfaces of the target material manufactured from powder material. Alternatively, the laser ablation process can be controlled so that the surface of the target melts locally so that molten particles detach from the target material, which are directed to the surface of the base material. The above-described alternative methods can be chosen according to the type of microstructure which is desired for the cathode material and which material is concerned.

Laser pulses can be brought to the target also in so-called bursts, which are formed of a certain quantity of laser pulses on the selected repetition frequency. For example, laser power of 100 W can be formed by using individual laser pulses of 100 J on the repetition frequency of 1 MHz or by using laser pulse bursts, which have 10 pulses of 10 J on the repetition frequency of 60 MHz, and these bursts are repeated on the frequency of 1 MHz. These laser pulse packages can significantly change the interaction of laser with the material and control the properties of the detaching material and the coating process. For example, laser pulse bursts make possible the reduction in the size of particles forming in laser ablation and thus growing the area of the specific area in the cathode coating material, shortening of diffusion ranges (improvement in ion and electron conductivity) and, with certain materials, better resistance against microfractures caused by changes in the specific volume. The method makes it possible to produce different material and coating concepts even with only one method and apparatus, due to the flexibility of the method and its applicability to very different materials by means of parameter selection. This reduces significantly the quantity of necessary apparatus investments in different cathode coating solutions, accelerates the manufacture and delivery time and reduces the quantity of manufacturing and processing errors.

The method is especially suited for roll-to-roll manufacture, in which the base material (for example, copper strip) is directed from a roll to the coating stations as a continuous strip, after which the cathode material is coated to the strip in the coating stations (of which there can be one or several). Coating stations can also be positioned successively so that either the same cathode material is coated in several successive stations so that the coating efficiency increases or different materials can be coated in different stations to manufacture composite or multilayer structures or by doping, for example, materials increasing conductivity to the surface of the cathode materials. There are later own figure examples of these embodiment alternatives. Different protective layers can also be manufactured to the surface of cathode materials in different layers or, for example, only on top of the last layer, for example, to prevent the dissolution of essential doping substances or detrimental reactions with the electrolyte. Instead of successive coating stations, the coating can alternatively be manufactured in a roll-to-roll method so that the strip to be coated moves first through the coating station so that one layer of material is produced to its surface of a desired material. After this, the direction of motion of the roll in question is changed and the target material is automatically changed in the coating station and the coating of a second material, for example, an additive (i.e. doping material), a second party of a composite material (for example, carbon) or a second layer material in sandwich materials is executed, and this process is repeated so long until the desired total structure is complete.

It is not necessary to use laser ablation for the coating of all material layers, and also other coating and manufacturing methods for the material layers can be linked to the manufacturing chain, if this is optimal for the total solution. Such supporting methods are, among others, chemical vapour deposition (CVD), atomic layer deposition (ALD), and physical vapour deposition (PVD) technologies.

The composition of the material detached by laser ablation must remain on a correct area for the functionality of the coating. In principle, pulsed laser technology, espe- cially ultrashort pulsed laser technology, is a suitable method to minimise disadvantageous changes in composition, for example, due to the evaporation of the doping substances. By means of ultrashort pulsed laser technology it is possible to minimise the melting of the material and the formation of large molten areas, which increase uneven material losses and complicate the control of stoichiometry. With several target materials, limiting the length of laser pulses to under 5 - 10 ps is adequate to minimise the melting of the target and the excessive loss of doping substances in laser ablation, if the superposition of laser beams is slight. On high repetition frequencies, the superposition of laser beams may cause the material to melt even with short pulse lengths. A change in stoichiometry may cause the loss of a desired structure and correct functionality. In industrial production, the process must remain constantly stable, because of which changes in the target composition are detrimental also in the long run.

When manufacturing composite materials, sandwich structures or by doping the principal material of the cathode coating with a second material, the optimum process parameters and circumstances for different materials are not necessarily the same. This must be taken into account in the planning and combination of different steps in the production process. If it is desired to manufacture a composite material with a combinatory solution, the laser parameters can be tailored in relation to different materials optimally by using two different laser sources, but in this case both materials must be sufficiently well ablatable in the same coating atmosphere, be- cause it can be difficult to control the atmospheres separately. If the adjusting of the coating atmosphere separately for all materials is necessary, this is most easily executable in successive coating steps so that a coating atmosphere advantageous for different materials can be controlled separately. These coating steps can be built several in a process solution depending on what type of a material distribution one wants to produce.

In certain situations, it is also possible to make a desired doping to an individual target material piece, and if the ablation thresholds in relation to each other and the condensation tendency in the chosen gas atmosphere are suitable, the composite structures can be manufactured by blending the desired materials to the target ma- terial in a desired proportion. This situation is separately described in Figure 9.

The basic principle of the method is described in the view of principle in Figure 1 , in which the structural parts and directions of travel of the material involved in the transaction are shown on a level of principle. In Figure 1 , the energy source for the ablation process is the laser light source 1 1 , from which laser light is directed in short pulses 12 towards the target material 13. The laser pulses 12 cause local de- tachment of material in the surface of the target material 13 from the target as particles or other respective parts, which have been mentioned above. This way a particle material flow 14 is generated, which extends towards the piece 15 to be coated. The piece 15 to be coated can also be called the coating base or substrate. The correct orientation can be executed by positioning the direction of the plane of the target material surface 13 appropriately in relation to the piece 15 to be coated so that the direction of motion energy releasing in the form of plasma is towards the piece 15 to be coated. The laser source 1 1 can naturally be transferred in relation to the target 13, or the angle of orientation of the laser beams in relation to the surface of the target 13 can be varied. Further, a separate arrangement can be placed between the laser source 1 1 and the target 13, with which the laser pulse front hitting the target can be parallelised. Of this arrangement there is the separate figure 3. It is also possible to place other kinds of optics and, for example, mirrors between the laser source 1 1 and the target 13. The plasma and particle material flow 14 in Figure 1 can be fan-shaped so that a wider area can be coated with one angle of orientation of the laser pulses on the surface area of the material 15 to be coated; assuming that the material to be coated is not transferred in lateral direction (seen from the figure). In another embodiment, the material to be coated is movable, and of this embodiment there is the separate figure 4.

Generally speaking, in an example of ablation used in the invention the detachment of the target surface material and the formation of particles and the transfer of the material from the target to the base and to the previously formed material layer is achieved by laser pulses directed to the target, in which the timely duration of an individual laser pulse can be between 0.5 - 10000 ps.

In an example of the invention, laser pulses can be produced on a repetition frequency, which is between 50 kHz - 100 MHz.

The film made of a material by laser ablation and transferring as particles from the target material to the base material must form a reliable bond to the base material or to a previously formed material layer. This can be achieved by adequate kinetic energy of the particles, which makes possible sufficient energy to generate a connection between different materials. A very essential process parameter in laser ablation, when manufacturing porous coatings, is the gas pressure used in the process chamber. Increasing the gas pressure promotes the formation and growth of particles during the flight of the material from the target to the surface of the material to be coated. An optimal gas pressure may vary according to which material is being coated and what is the desired particle size distribution, porosity and adhesion between the particles, and the bond of the particles to the rest of the battery material.

In an embodiment, laser ablation and coating occur in a vacuum chamber, i.e. either in a vacuum or background gas, where a desired controlled pressure can be set. An alternative is to set the pressure between 10 ⁸— 1000 mbar. When pursuing porous coatings, a background pressure of 10 ³— 1 mbar is typically used, but also pressures of under 10^"3 mbar can produce the desired porosity by controlling the laser beam parameters.

In an embodiment, laser ablation is executed by using an elevated coating temper- ature, which is at least 300°C, by heating the substrate to be coated i.e. the base in a roll-to-roll method or some other coating arrangement (such as manufacturing on sheets) slightly before its coating.

A coated product can also be subjected to heat treatment after the coating to achieve desired crystallinity. A typical post-heat treatment temperature is at least 450 °C. Nevertheless, this temperature can be selected to be some other temperature value, which is at least 300 °C.

When using an elevated coating temperature or post-heat treatment to control crystallinity, the resistance to temperature of the base material and other materials used in the structure must be taken into account. In Figure 2 there is illustrated an exemplary structural view of a separator film functioning as one part of the Li ion battery after it has been coated using the PLD method. The porosity of the forming coating must be adequate to make possible the diffusion of ions through the coating and film. The separator film 22 typically used in battery applications is polymer-based and it has a microporous structure 23, as has been mentioned above. The pores 23 of the polymer film can be of varying sizes. Also the coating 21 consisting of inorganic material has a porous structure. In the separator films of Li ion batteries, the porosity of microporous polymer films is typically between 30 - 50 percent by volume, and the objective is that the porosity of the inorganic coating would be at least 30 percent by volume. It is essential that the porosity of the inorganic material is mainly through-going, and this makes possible that the electrolyte moistens the film as well as possible. A porous material is achieved by detaching material by laser ablation and by creating circumstances, in which nanoparticles typically of the size of 10 - 100 nm or particle clusters consisting of these are formed as the detached material. As these particles and particle clusters accumulate to the surface of the polymer film, they form a porous coating. Alternatively, the detachment of material by laser ablation occurs entirely or partly through molten particles or particles detaching from the target materials, which form a coating of inorganic material to the surface of the polymer film. The previous mech- anism produces a narrower particle distribution so that also the porous distribution becomes more even. In practice, the coating is often generated with both mechanisms, which is further complemented by the plasma generated as the result of laser ablation. The structure and porosity of the inorganic coating is adjusted by controlling the detachment mechanisms of different materials. To improve uniform quality and productivity, it would be preferable to produce as wide a material flow as possible from the target to the base material. In an example of the invention, this can be accomplished by disintegrating the laser pulses by turning mirrors to form a laser pulse front in the same plane. This arrangement has been described in Figure 3. Instead of the target, the laser pulses 12 of the laser source 1 1 are directed to the turning mirrors 31 , which can, for example, be a hexagonal and rotatable mirror surface. The laser pulses 12 are reflected from the turning mirrors 31 to form a fan-shaped laser pulse front (or laser beam distribution), and the reflected pulses are directed to the telecentric lens 32. The laser pulse front can be directed by the telecentric lens 32 to form an essentially rectilinear laser pulse front 33 so that the laser pulses hit the target material 13 in the same angle. In this example in Figure 3, the said angle is 90°.

The laser pulse front can also be executed in other ways; for example, using a rotating monogon mirror, which directs the laser pulses, for example, to a circular target material, of which there is formed an annular material front. In an application example, a part of the Li ion battery is well suited to be coated so that material is discharged from a roll to be coated to a desired width in a coating chamber. A view of principle is shown of this application alternative in Figure 4. Material is directed to the desired coating width from one or several coating sources so that material is continuously discharged from a roll to coating and after it has passed the coating zone, the material is reassembled to the roll. The method can be called a roll-to-roll method, as has already been stated above. In other words, the part 42 of the Li ion battery to be coated is originally around the roll 41 a. The ablation apparatus with its laser source 1 1 and target material 13 is included as has been described above. The laser pulses 12 make the material to detach as a particle flow 14 (in other words, in the form of a material flux) towards the material 42 to be coated, and the coated Li ion battery part 42 is generated as the result of adhesion. The coated film 43 is let to rotate around the second roll 41 b as the direction of motion of the film is left to right in Figure 4. The roll structures 41 a, 41 b can be motor-driven. The Li ion battery film to be coated can be the entire area of the surface, seen from the direction of depth in the Figure, or only part of the surface. Sim- ilarly, a desired part (length) in the direction of motion of the film can be chosen to be coated or, alternatively, the entire roll can be gone through from the beginning to the end so that the entire roll becomes coated.

Figure 5 illustrates a typical structure of the lithium ion battery as a cross-sectional view. Of the parts, the first one from the top is the aluminium film 51 , which functions as current collector for the electric current. Moving down, the next part is the cathode material 52, which is especially discussed in this invention. Next there is the porous polymer membrane 53, which functions as separator film in the battery. It can be made, for example, of polyethylene. The fourth film is the anode material 54. The lowermost, fifth film is the copper film 55, which functions as current collector in a respective way as the uppermost aluminium film 51 .

Figure 6a is a structural view of an arrangement, in which cathode material is coated to a base by using PLD technology. The laser beam pulses 61 have here been marked with thick dashed lines underneath, and the laser pulses arrive at the picture area from bottom right. The laser pulses are focused onto the surface 62 of the target material piece, and preferably the direction of the target surface encountered by the pulses is preferably set in an inclined direction in relation to the direction of arrival of the pulses. The material flow 63 consisting of particles, atoms and/or ions is formed of this interaction. This material flow is seen as a droplet-shaped material cloud in the figure. The base material 65 to be coated is uppermost, and the actual coating 64 is formed to its lower surface, which is here shown as five circles with a uniform diameter. In other words, the material flow hits the lower surface of the base, and adheres to it.

Figure 6b illustrates a possible coating structure produced by the principle in Figure 6a, in which the coating adheres to the lower surface of the base 65. As can be seen in the figure, the coating forming of the material flow is porous, and it consists only of one material, which can here be called the principal material 66. In other words, in this example, also the target used consists of one material, and there is one target to be used.

Figure 6c illustrates a second type of a coating structure produced onto the base 65 using the principle in Figure 6a. In this situation a composite material is generated, which consists of two different materials. The principal material 66 is marked with circles, and among the principal material there is the second material 67. The structure is still porous.

Figure 6d illustrates a possible porous structure produced by the principle in Figure 6a, in which so-called doping material is used in addition to the principal material. The bigger circles seen here on the lower surface of the base 65 illustrate the principal material 66, and the smaller circles illustrate the so-called doping material i.e. additive 68. In this situation it can be determined, for example, that the quantity of the additive 68 is at most 10 percent by volume of the entire volume of the coating. Also this structure is porous. As can be seen in the figure, the additive 68 sets among the principal material 66, and in an advantageous embodiment this distribution of doping material into the principal material is made homogeneous, so that the entire porous coating is similar, i.e. of uniform quality.

Figure 7 illustrates an example of a combinatory coating method using two coincidental material flows. Here, two separate laser beams, i.e. the first pulse string 71 a and the second pulse string 71 b enter the arrangement, and these pulse strings are directed to hit the target material pieces, i.e. the first target 72a and the second target 72b. The material of the first target is different from the material of the second target. Of these interactions, material flows 73a and 73b are formed as the result of laser ablation. Both these material flows comprise particles, atoms and ions, but concerning different materials. The material flows hit the lower surface of the base 75 simultaneously, thus forming the composite coating 74. The compositions of the different substances in the composite coating 74 can be varied, for example, by independently adjusting either one or both of the laser sources, which generate the laser beams 71 a and 71 b. The composite coating 74 consists thus of the material flows 73a and 73b on the lower surface of the base 75 principally at the same time and immediately forming a finished coating.

Figure 8a illustrates the use of successive coating stations to improve productivity when manufacturing sandwich structures. In this example, there are shown four coating stations, and each incoming laser beam (or pulse string) 81 a-d is focused on the appropriate target 82a-d through a mirror (P, each beam having its own). In this situation, the roll-to-roll method can be used, and the lower surface of the base 85 first contacts the first material flow 83a, of which the first coating layer 84a is formed. This first coating layer 84a again contacts the second material flow 83b as the base 85 moves, and this way the second coating layer 84b is produced onto the first coating layer 84a. This process still continues in two coating stations, and the final result is the base material 85 which has contacted the four material flows 83a- d, and this coating has a sandwich-type structure 84a, 84b, 84c, 84d. The targets 82a-d can be of the same material, as has been shown in this figure.

Figure 8b illustrates the use of successive coating stations to improve productivity in the manufacture of composite structures. This is otherwise similar to the situation in figure 8a, but now there are chosen two different types of materials as the target material pieces 82A, 82B, and these are placed alternately, one target to one coating station, the next target being of the second material. In other words, seen from the left, the first and third target are of the same first material "A", and the second and fourth target, respectively, are of the same second material "B". The laser pulse strings 81 a-d can still be controlled independently and focused on the targets through the mirrors P. This arrangement provides two different types of material flows 83A, 83B, which alternate. When the material flows hit the moving base 85, a new different layer is formed on top of the older layers, and the final result is the 4- layered composite structure 84A, 84B, 84A, 84B visible in the right edge. In this coating, the material layers thus alternate with each other.

Figure 8c illustrates the use of successive coating stations to improve productivity in the manufacture of doped material. This arrangement is otherwise similar to the one in Figure 8b, but here the first and third target 82C are made of the basic mate- rial, and the second and fourth target 82D, respectively, are made of the additive, i.e. doping material. The laser pulse strings 81 a-d can still be controlled independently, and they can be focused on the targets through the mirrors P. This arrangement produces two material flows 83C, 83D of different types, which alternate. With the respective principle as above, the doped basic material now forms the coat- ing to the base 85, and the relative proportion of doped material of the entire coating can be chosen by independently adjusting the laser parameters. In the coating layers, 84C represents the basic material layer and 84D the additive layer.

Figure 8d illustrates a more exact detail of the basic material, in which doped particles are included. Thus, this describes a more detailed structure of the coating gen- erated by the arrangement in Figure 8c. The basic material 86 is seen as bigger parts in the figure, and the doped material, i.e. additive 87 is seen in the figure as smaller parts among the basic material. The additive 87 is in practice found as particles among the basic material.

Figure 9 illustrates an example of the use of a composite target material in the manufacture of a composite coating. Now there only is one physical element as the tar- get material piece, but this element in itself has a composite structure, i.e. the target 92 consists in this example of two different materials. When laser beam pulses 91 are focused on such target 92, there is generated a material flow 93 consisting of atoms, ions and particles of two different materials. This material flow 93 hits the lower surface of the base material 95, and the final result is a composite coating 94 containing two materials, the composite coating adhering to the lower surface of the base material 95.

As has emerged in many connections above, in addition to the manufacturing method, the inventional idea of the invention further includes the manufactured product, i.e. foil or film-type cathode, which is intended for a Li ion battery, and also the essential components of the entire Li ion battery, of which at least one part has been manufactured using laser ablation.

As a summary, in the invention there is produced a cathode material coating for a Li ion battery so that the share by volume of at least one active cathode material used in the coating is at least 30 percent by volume of the cathode material coating, and the average particle size is at most 5 pm. In addition, at least one material layer of the Li ion battery is manufactured based on laser ablation, i.e. at least the film- type cathode is manufactured using the PLD method. Finally, the Li ion battery is assembled by utilising the manufactured material layers.

Combinatory coating arrangements and successive coating stations according to Figures 7 and 8a can be combined so that, for example, one coating arrangement of another type has been taken at the place of one or some coating stations in Figure 8a, such as a combinatory coating station comprising two or several targets in accordance with the principle of the example in Figure 7.

The invention relates to a method for manufacturing cathode materials (52) for a Li ion battery, the method comprising the following steps of: directing short-term laser pulses (12, 61 , 71 a-b, 81 a-d, 91 ) to at least one target (13, 62, 72a-b, 82a-d, 82A-D, 92);

detaching at least one material (14, 63, 73a-b, 83a-d, 83A-D, 93) from at least one target (13, 62, 72a-b, 82a-d, 82A-D, 92) by laser ablation; directing the at least one detached material (14, 63, 73a-b, 83a-d, 83A-D, 93) to the base material (15, 22, 42, 65, 75, 85, 95) of the coating to at least one surface or part of surface.

A characteristic of the invention is that the method further comprises the step of - producing a cathode material coating for the Li ion battery so that the at least one active cathode material used in the coating, the share by volume of the cathode material coating being at least 30 percent by volume, has the average particle size of at most 5 pm, and the cathode material coating is manufactured based on pulsed laser ablation deposition. In an embodiment of the invention, a Li ion battery is further assembled in the method by using manufactured material layers, which material layers comprise an anode, cathode, and a solid or liquid electrolyte material so that at least the anode material is manufactured by using pulsed laser ablation deposition.

In an embodiment of the invention, when using pulsed laser ablation deposition, the detachment of material, formation of particles and transfer of material from the target (13, 62, 72a-b, 82a-d, 82A-D, 92) to the base material (15, 22, 42, 65, 75, 85, 95) is achieved by laser pulses (12, 61 , 71 a-b, 81 a-d, 91 ) focused on the target (13, 62, 72a-b, 82a-d, 82A-D, 92), in which the timely duration of an individual laser pulse is between 0.5 - 10000 ps. In an embodiment of the invention, laser pulses (12, 61 , 71 a-b, 81 a-d, 91 ) are generated on a repetition frequency, which can be chosen from the range of 50 kHz - 100 MHz.

In an embodiment of the invention, the average particle size of at least one active cathode material used in the coating is under 3 pm, the share of volume of the cath- ode material in the cathode material coating being at least 30 percent by volume.

In an embodiment of the invention, the average particle size of at least one active cathode material used in the coating is under 1 pm, the share of volume of the cathode material in the cathode material coating being at least 30 percent by volume.

In an embodiment of the invention, the average particle size of at least one active cathode material used in the coating is under 600 nm, the share of volume of the cathode material in the cathode material coating being at least 30 percent by volume. In an embodiment of the invention, the cathode material coating has at least 20 percent by volume of oxide containing a chosen transition metal.

In an embodiment of the invention, the cathode material coating contains at least 25 percent by weight of either cobalt, manganese, nickel, titanium or iron, or a desired combination of these materials, the share of the combination being at least 25 percent by weight of the cathode material coating.

In an embodiment of the invention, the cathode material coating has at least 50 percent by volume of L1C0O2, LiMn02 or some other as well as oxide containing both lithium and a chosen transition metal. In an embodiment of the invention, the cathode material coating has at least 20 percent by weight of either sulphur, selenium, fluorine, iodide or tellurium, or at least 20 percent by weight of a chosen combination of these substances.

In an embodiment of the invention, the cathode material coating contains at least 5 percent by weight of carbon. In an embodiment of the invention, at least two laser sources are set to operate simultaneously, forming together a combinatory continuous material flow (73a, 73b) from at least two different targets (72a, 72b) to the surface of the base material, forming a cathode material coating (74) consisting of at least two different materials.

In an embodiment of the invention, coating is performed in at least two successive coating stations so that at least one of the coating stations operates so that the material flow generated by it does not meet the second coating station before the generation of the coating to the surface of the base material (85).

In an embodiment of the invention, a carbon-based material is coated in a combinatory manner in at least one coating step by laser ablation together with cathode material particles, the quantity of which is at least 5 percent by volume and the average size of which is at most 3 pm.

In an embodiment of the invention, a carbon-based material is coated onto cathode material particles with the average size of at most 3 pm by means of at least two successive coating stations. In an embodiment of the invention, a metallic material comprising at least 25 percent by volume or copper, silver, gold, tin, nickel, platinum or palladium or a blend of these is coated in a combinatory manner or by means of successive coating stations.

In an embodiment of the invention, the average size of particles containing the said metallic material is at most 500 nm. In an embodiment of the invention, the manufacture of at least one cathode material coating is executed in a partial background gas pressure, which is at least 10^"6 mbar.

In an embodiment of the invention, at least 50 percent by volume of the total volume of the cathode material coating is executed in an atmosphere containing oxygen, nitrogen or argon, in which the total gas pressure is at least 10^"4 mbar. In an embodiment of the invention, the porosity of the cathode material coating is at least 5 percent by volume.

In an embodiment of the invention, the porosity of the cathode material coating is at least 20 percent by volume.

In an embodiment of the invention, the thickness of the cathode material coating is at most 100 pm.

In an embodiment of the invention, the coating is carried out in an elevated temperature concerning at least half of the entire cathode material coating to be coated, in which the elevated temperature is chosen to be at least 300 °C.

In an embodiment of the invention, the coated product is subjected to heat treatment in a temperature of at least 300 °C after the coating of at least one material layer.

In an embodiment of the invention, the coating of an active cathode material occurs from the target material, which comprises either metallic materials and/or carbon, in which, when using metallic materials, the metallic materials comprise at least 25 percent by volume of either copper, silver, gold, tin, nickel, platinum or palladium or a blend of at least two of these substances.

In an embodiment of the invention, the quantity of metallic materials in the target material is at most 15 percent by weight.

In an embodiment of the invention, the quantity of carbon in the target material is at most 80 percent by weight. The inventional idea further comprises a Li ion battery, which comprises cathode material (52) and anode material (54). A characteristic is that the Li ion battery further comprises either a solid or liquid electrolyte, and that at least one embodiment alternative of the above-described method has been utilised in the manufacture of the cathode material (52).

The method of the invention has the following advantages: i. Porous cathode materials for Li ion batteries can be manufactured with a simple arrangement of different compositions or combinations of these

ii. Good adherence is achieved between different material layers without sepa- rate adhesion layers or binding agents

iii. The open area and porosity of the cathode material can be adjusted by changing the laser pulse parameters, background gas or its pressure, and the distance between the target and the base

iv. During the processing and installation of different material layers there is no risk of material damage or contamination, if the method is carried out with one apparatus

v. Sandwich structures can be manufactured to optimise properties

vi. Composite structures can be manufactured to optimally combine different materials

vii. Doping can be performed to add small quantities of doping substances, for example, to improve conductivity

viii. Especially with complex cathode material compositions, it is possible to retain the correct composition of coatings from the target to the base

ix. The use of binding agents can be avoided, which reduces the contamination of battery chemistry in long-term use

x. Several materials important for different functionalities can be manufactured by one manufacturing method or partly even in one manufacturing step xi. The quantity of productional investments can be reduced

xii. Cathode materials with a very small particle size (< 1 pm) can be manufac- tured, which

a. Increases the quantity of active surface in contact with the electrolyte b. Shortens the diffusion range of ions and electrons

xiii. As a result, a nanocrystalline fine-grained structure is achieved, in which the optimised pore distribution endures better the changes in volume occurring in the discharge and charge steps without microcracking or detachment from the background material xiv. An even pore distribution decreases stresses caused by changes in volume induced by charge/discharge cycles of the structure

xv. It is possible to manufacture batteries with a considerably bigger energy density than the traditional anode material solutions In the invention it is possible to combine individual features of the invention mentioned above and in the dependent claims into new combinations, in which two or several individual features can have been included in the same embodiment.

The present invention is not limited to the examples presented, but many variations are possible within the scope of protection defined by the enclosed claims.

Claims

1 . A method for the manufacture of cathode materials (52) for a Li ion battery, the method comprising the following steps:

directing short-term laser pulses (12, 61 , 71 a-b, 81 a-d, 91 ) to at least one tar- get (13, 62, 72a-b, 82a-d, 82A-D, 92);

detaching at least one material (14, 63, 73a-b, 83a-d, 83A-D, 93) from at least one target (13, 62, 72a-b, 82a-d, 82A-D, 92) by laser ablation;

directing at least one detached material (14, 63, 73a-b, 83a-d, 83A-D, 93) to the base material (15, 22, 42, 65, 75, 85, 95) of the coating to at least one surface or part of surface, characterised in that the method further comprises the step of

producing the cathode material coating of the Li ion battery so that the average particle size of at least one active cathode material used in the coating is at most 5 pm, the share by volume of the cathode material in the cathode material coating being at least 30 percent by volume, and the cathode material coating being manufactured based on pulsed laser ablation deposition.

2. Method according to claim 1 , characterised in that in the method the Li ion battery is further assembled by using the manufactured material layers comprising an anode, cathode and a solid or liquid electrolyte material so that at least the cath- ode material has been manufactured by using pulsed laser ablation deposition.

3. Method according to claim 1 or 2, characterised in that when using pulsed laser ablation deposition, the detachment of material, formation of particles and transfer of material from the target (13, 62, 72a-b, 82a-d, 82A-D, 92) to the base material (15, 22, 42, 65, 75, 85, 95) is achieved by laser pulses (12, 61 , 71 a-b, 81 a- d, 91 ) focused on the target (13, 62, 72a-b, 82a-d, 82A-D, 92), in which the timely duration of an individual laser pulse is between 0.5 - 10000 ps.

4. Method according to any of the preceding claims 1 - 3, characterised in that laser pulses (12, 61 , 71 a-b, 81 a-d, 91 ) are generated on a repetition frequency, which can be chosen between 50 kHz - 100 MHz.

5. Method according to any of the preceding claims 1 - 4, characterised in that the average particle size of at least one active cathode material used in the coating is less than 3 pm, the share by volume of the cathode material in the cathode material coating being at least 30 percent by volume.

6. Method according to any of the preceding claims 1 - 4, characterised in that the average particle size of at least one active cathode materials used in the coating is less than 1 pm, the share by volume of the cathode material in the cathode material coating being at least 30 percent by volume.

7. Method according to any of the preceding claims 1 - 4, characterised in that the average particle size of at least one active cathode materials used in the coating is less than 600 nm, the share by volume of the cathode material in the cathode material coating being at least 30 percent by volume.

8. Method according to any of the preceding claims 1 - 7, characterised in that the cathode material coating has at least 20 percent by volume of oxide containing a chosen transition metal.

9. Method according to claim 8, characterised in that the cathode material coating contains either cobalt, manganese, nickel, titanium or iron in the quantity of at least 25 percent by volume or a desired combination of these materials, in which the share of the combination is at least 25 percent by volume of the cathode material coating.

10. Method according to claim 8, characterised in that the cathode material coating has at least 50 percent by volume of L1C0O2, LiMn02 or some other as well as lithium and oxide containing a chosen transition metal.

1 1 . Method according to any of the preceding claims 1 - 10, characterised in that the cathode material coating has at least 20 percent by weight of either sulphur, selenium, fluoride, iodide or tellurium or at least 20 percent by weight of a chosen combination of these.

12. Method according to any of the preceding claims 1 - 1 1 , characterised in that the cathode material coating contains at least 5 percent by weight of carbon.

13. Method according to any of the preceding claims 1 - 12, characterised in that at least two laser sources are set to operate simultaneously, forming together a combinatory continuous material flow (73a, 73b) from at least two different targets (72a, 72b) to the surface of the base material (75), forming a cathode material coat- ing (74) consisting of at least two different materials.

14. Method according to any of the preceding claims 1 - 13, characterised in that the coating is performed in at least two successive coating stations so that at least one of the coating stations operates so that the material flow generated by it does not meet the second coating station before the generation of the coating to the surface of the base material (85).

15. Method according to any of the preceding claims 1 - 14, characterised in that a carbon-based material is coated in a combinatory manner by pulsed laser ablation deposition in at least one coating step together with cathode material particles, the quantity of which is at least 5 percent by volume and the average size of which is at most 3 pm.

16. Method according to any of the preceding claims 1 - 15, characterised in that a carbon-based material is coated onto the cathode material particles, the average size of which is at most 3 pm by means of at least two successive coating stations.

17. Method according to any of the preceding claims 1 - 16, characterised in that the cathode material coating has 0.5 - 10 percent by volume of metallic material, the metallic material comprising at least 25 percent by weight of either copper, silver, gold, tin, nickel, platinum or palladium or a mixture of these.

18. Method according to claim 17, characterised in that a metallic material containing copper, silver, gold, tin, nickel, platinum or palladium or a mixture of these in a quantity of at most 25 percent by weight is coated in a combinatory manner or by means of successive coating stations.

19. Method according to claim 17 or 18, characterised in that the average sizes of particles containing metallic material is at most 500 nm.

20. Method according to claim 1 - 19, characterised in that the manufacture of at least one cathode material coating is executed in partial background gas pressure, which is at most 10^"6 mbar.

21 . Method according to any of the preceding claims 1 - 20, characterised in that at least 50 percent by volume of the total volume of the cathode material coating is executed in an atmosphere containing oxygen, nitrogen or argon, in which the total gas pressure is at most 10^"4 mbar.

22. Method according to any of the claims 1 - 21 , characterised in that the po- rosity of the cathode material coating is at least 5 percent by volume.

23. Method according to any of the claims 1 - 21 , characterised in that the porosity of the cathode material coating is at least 20 percent by volume.

24. Method according to any of the claims 1 - 23, characterised in that the thickness of the cathode material coating is at most 100 pm.

25. Method according to any of the claims 1 - 24, characterised in that the coating is executed in an elevated temperature concerning at least half of the entire cathode material coating to be coated, in which the elevated temperature is chosen to be at least 300 °C.

26. Method according to any of the claims 1 - 25, characterised in that after the coating of at least one material layer, the coated product is subjected to a heat treatment in a temperature, which is at least 300 °C.

27. Method according to any of the claims 1 - 26, characterised in that the coating of an active cathode material occurs from the target material, which comprises either metallic materials and/or carbon, in which when using metallic materials, the metallic materials comprise at least 25 percent by weight of either copper, silver, gold, tin, nickel, platinum or palladium or a mixture of at least two of these substances.

28. Method according to claim 27, characterised in that the quantity of metallic materials in the target material is at most 15 percent by weight.

29. Method according to claim 27, characterised in that the quantity of carbon is at most 80 percent by weight.

30. Li ion battery, which comprises

a. a cathode material (52), and

b. an anode material (54),

characterised in that the Li ion battery further comprises

c. either a solid or liquid electrolyte, and in which

d. a method according to any of the claims 1 - 29 has been utilised in the manu- facture of the cathode material (52).