Furnace atmosphere control for lithium-ion battery cathode material production

Abstract

A method and apparatus for controlling the atmosphere in a multi-zone calcining (combustion) furnace for producing high-quality nickel-rich cathode materials for lithium-ion and solid-state batteries. Maintaining a high-quality oxygen-rich atmosphere ensures cathode material quality. The atmosphere control system continuously measures and analyzes the composition of the calcining furnace atmosphere in different zones and adjusts the flow rate of the oxygen-rich atmosphere into the furnace to optimize the calcining process.

Description

Background Art

[0001] The increasing demand for technologies to reduce greenhouse gas emissions, such as carbon dioxide, requires the development of alternative methods for collecting and storing clean energy. For example, the electrification of mobility can significantly reduce carbon dioxide emissions.

[0002] Rechargeable lithium-ion batteries (LIBs) are widely used in consumer electronics and are rapidly entering the electric vehicle (EV) and large-scale stationary energy storage markets. State-of-the-art LIB systems typically consist of a graphite anode, separator, aqueous electrolyte, and a lithium-containing cathode. Cathode materials determine the battery's energy density and voltage, leading to intensive research into cathode materials to further improve the energy density of the entire battery system.

[0003] Such as LiCoO2, LiMn2O4, LiFePO4 and LiNi x Mn y Co z Conventional cathodes such as O2(NMC) have been commercially used as cathode materials for LIBs. Among these chemistries, nickel-rich LiNi x Mn y Co z O2, where x ≥ 0.5, or nickel-rich NMC, is considered a promising cathode material, especially in the EV market. Nickel-rich NMC exhibits a high achievable discharge capacity (200-220 mAh g-1) and further enhances energy density (~800 Wh kg-1) compared to conventional cathodes. See, for example, W. Liu et al., Angew. Chem. Int. Ed. 54 (2015) 4440-4457; A. Manthiram et al., Adv. Energy Mater. 6 (2016); Y.-K. Sun et al., Nat. Mater. 11 (2012) 942-947 and Y.-K. Sun et al., Nat. Mater. 8 (2009) 320-324.

[0004] Increasing the nickel content in cathode materials (>0.5 mole fraction) requires the use of oxygen as the calcination furnace atmosphere to achieve complete oxidation of metal building chemicals such as lithium nickel manganese cobalt (NMC) and lithium nickel cobalt aluminum (NCA), lithium nickel manganese cobalt aluminum (NMCA), nickel cobalt boron, etc.

[0005] Although these cathode materials exhibit very attractive energy densities, their electrochemical performance is very sensitive to the synthesis method and post-calcination treatment conditions. The synthesis method widely used to prepare these cathode materials includes precursor preparation, lithium source mixing, and calcination at high temperatures of 700-1050 degrees Celsius. See, for example, MHLee et al., Electrochim. Acta 50 (2004) 939-948 and A. van Bommel et al., Chem. Mater. 21 (2009) 1500-1503.

[0006] Understanding and controlling the oxygen-rich furnace atmosphere during the calcination step is crucial to providing high-quality nickel-rich cathode materials. Careful control of the atmosphere during the calcination process can produce nickel-rich cathode materials with improved performance and service life, while reducing the cost of the cathode manufacturing process.

[0007] Existing atmosphere control systems used in other industries for heat treatment processes utilize inert and reactive atmospheres, such as argon, nitrogen, hydrogen, ammonia, natural gas, or mixtures thereof. These heat treatment processes are typically designed to avoid oxidation and decarburization by reducing the oxygen or water content of the atmosphere. Conversely, producing high-quality nickel-rich cathode materials requires calcining the precursor at relatively high temperatures in a strongly oxidizing atmosphere.

[0008] Therefore, there is a need for effective, reliable, and economical equipment and methods to monitor and control the oxygen-rich environment required to produce nickel-rich cathode materials in industrial-scale calciners. Summary of the Invention

[0009] A method and apparatus including an atmosphere control system are described herein. The atmosphere control system is designed to control an oxygen-rich atmosphere in a calcining furnace to produce high-quality nickel-rich cathode materials for lithium-ion and other solid-state batteries. The calcining process is preferably carried out in a furnace having multiple temperature zones. Preferably, there are at least three zones, namely a preheating zone where the cathode precursor material enters the furnace and is heated from ambient temperature to the desired processing temperature. During the preheating process, impurities (moisture, carbon dioxide and other harmful impurities) are exhausted in the form of gases. The material is then moved from the preheating zone of the furnace to the hot zone. The calcined material is then moved from the hot zone to a cooling zone before exiting the furnace.

[0010] The atmosphere control device preferably includes three main components: (1) a network of sensors installed in the multiple temperature zones of the furnace; (2) an oxygen delivery system including mass flow controllers, which are cables that provide a variable flow of oxygen to the multiple temperature zones when connected to an oxygen source; and (3) a process control system capable of communicating with and controlling the sensors and oxygen delivery system. This device can be incorporated into the design of a new furnace or installed as a retrofit to an existing furnace.

[0011] This method involves using an atmosphere control device to monitor and adjust the atmosphere in multiple temperature zones of a furnace. This ensures that the hottest zone of the furnace, where the cathode material is ultimately formed, has a relatively clean, oxygen-rich atmosphere that is significantly lower in impurities (moisture, carbon dioxide, and other harmful impurities) than the preheating zone. The flow rate of oxygen-enriched process gas entering each zone is adjusted to move the furnace atmosphere away from the hot zone and toward the furnace inlet and outlet. This maintains a high-purity, oxygen-rich atmosphere in the hot zone and minimizes undesirable side reactions between the material and harmful impurities (moisture and carbon dioxide) in the hot zone.

[0012] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.

[0013] Aspect 1: A method for controlling the furnace atmosphere of a calcining furnace for producing cathode materials for lithium-ion batteries, the method comprising the following steps:

[0014] (a) measuring a first oxygen concentration, a first moisture concentration, and a first carbon oxide concentration of an atmosphere in a first zone of a calcining furnace;

[0015] (b) measuring a second oxygen concentration, a second moisture concentration, and a second carbon dioxide concentration of the atmosphere in a second zone of the calcining furnace, wherein the second zone is adjacent to the first zone and a boundary between the first zone and the second zone is located at a position where the temperature of the atmosphere reaches a predetermined soaking temperature;

[0016] (c) independently supplying an oxygen process gas comprising at least 50% (by volume) oxygen to the first and second zones of the calciner;

[0017] (d) controlling the flow rate of the first oxygen process gas stream entering the first zone based on at least one selected from (i) the first oxygen concentration measured in step (a), (ii) the first moisture concentration measured in step (a), and (iii) the first carbon dioxide concentration measured in step (a);

[0018] (e) controlling the flow rate of the second oxygen process gas stream entering the second zone based on at least one selected from (i) the second oxygen concentration measured in step (b), (ii) the second moisture concentration measured in step (b), and (iii) the second carbon dioxide concentration measured in step (b); and

[0019] (f) maintaining the flow rate of the first oxygen process gas stream equal to or lower than the flow rate of the second oxygen process gas stream to prevent gaseous flow from the first zone into the second zone.

[0020] Aspect 2: The method according to aspect 1, wherein step (d) further comprises increasing the flow rate of the oxygen process gas stream if at least one of the following conditions exists: (i) the first oxygen concentration measured in step (a) is less than a predetermined set point, (ii) the first moisture concentration measured in step (a) is greater than a predetermined set point, and (iii) the first carbon dioxide concentration measured in step (a) is greater than a predetermined set point.

[0021] Aspect 3: The method of any one of Aspects 1 to 2, wherein step (e) further comprises increasing the flow rate of the second oxygen process gas stream if at least one of the following conditions exists: (i) the second oxygen concentration measured in step (b) is less than a predetermined set point, (ii) the second moisture concentration measured in step (b) is greater than a predetermined set point, and (iii) the second carbon dioxide concentration measured in step (b) is greater than a predetermined set point.

[0022] Aspect 4: The method according to any one of aspects 1 to 3, further comprising the following steps:

[0023] (h) Repeating steps (a) through (f) while gradually heating the first zone to a first temperature and maintaining the second zone at a second temperature, wherein the second temperature is greater than or equal to the first temperature.

[0024] Aspect 5: The method according to any one of aspects 1 to 4, further comprising the following steps:

[0025] (i) Repeating steps (a) to (f) while simultaneously injecting a quantity of lithium-ion battery cathode precursor material into the first zone for a time sufficient to heat the material to a predetermined material temperature, and subsequently injecting the material into the second zone.

[0026] Aspect 6: The method according to any one of aspects 1 to 5, further comprising the following steps:

[0027] (j) measuring a third oxygen concentration, a third water concentration, and a third carbon dioxide concentration of the atmosphere in a third temperature zone of the furnace, wherein the third temperature zone is adjacent to the second temperature zone;

[0028] (k) controlling the flow rate of the third oxygen process gas stream entering the third zone based on at least one selected from (i) the third oxygen concentration measured in step (j), (ii) the third moisture concentration measured in step (j), and (iii) the third carbon dioxide concentration measured in step (j); and the flow rate

[0029] (1) Maintaining the flow rate of the third oxygen process gas stream equal to or lower than the flow rate of the second oxygen process gas stream to prevent gaseous flow from the third zone into the second zone.

[0030] Aspect 7: A method as described in any one of Aspects 1 to 6, wherein the lithium-ion cathode precursor material is selected from the following precursors: lithium nickel manganese cobalt (NMC); lithium nickel cobalt aluminum (NCA); lithium nickel manganese cobalt aluminum (NMCA); nickel cobalt boron (NCB) and combinations thereof.

[0031] Aspect 8: The method of any one of aspects 1 to 7, wherein the cathode precursor material comprises a nickel molar ratio greater than 0.5.

[0032] Aspect 9: The method of any one of aspects 1 to 8, wherein the oxygen process gas comprises a purity of at least 90% by volume.

[0033] Aspect 10: The method according to any one of aspects 1 to 9, further comprising the following steps:

[0034] (m) extracting a furnace atmosphere sample from the first zone through a sample line; and

[0035] (n) delivering the sample to at least one external analyzer for measuring a parameter selected from the group consisting of oxygen concentration, carbon dioxide concentration, dew point, ammonia, SO x and NO x .

[0036] Aspect 11: A method for controlling the furnace atmosphere of a calcining furnace for producing cathode materials for lithium-ion batteries, the method comprising the following steps:

[0037] (a) measuring a first oxygen concentration of an atmosphere within a first zone of a calciner;

[0038] (b) measuring a second oxygen concentration in a second zone of the calciner, wherein the second zone is adjacent to the first zone and a boundary between the first zone and the second zone is located at a position where the atmosphere temperature reaches a predetermined soaking temperature;

[0039] (c) independently supplying an oxygen process gas comprising at least 50% (by volume) oxygen to the first and second zones of the calciner;

[0040] (d) controlling the flow rate of the first oxygen process gas stream entering the first zone based on the first oxygen concentration measured in step (a);

[0041] (e) controlling the flow rate of the second oxygen process gas stream entering the second zone based on the second oxygen concentration measured in step (b); and

[0042] (f) maintaining the flow rate of the second oxygen process gas stream equal to or lower than the flow rate of the first oxygen process gas stream to prevent gaseous flow from the second zone into the first zone.

[0043] Aspect 12: A device for controlling the atmosphere in a calcining furnace for producing lithium-ion or solid-state battery cathode materials, comprising:

[0044] A first sensor group is installed in the first furnace temperature zone, the first sensor group including a first oxygen sensor, a first moisture sensor and a first carbon dioxide sensor;

[0045] A second sensor group is installed in the second furnace temperature zone, the second sensor group includes a second oxygen sensor, a second moisture sensor and a second carbon dioxide sensor;

[0046] an oxygen delivery system operably configured in fluid flow communication with the oxygen source to deliver independently regulated oxygen flows to the first and second furnace temperature zones;

[0047] A process controller is operable to communicate with the sensors and the oxygen delivery system to control the rate of oxygen delivery to the first and second temperature zones in response to a plurality of signals from the first and second sensor groups.

[0048] Aspect 13: The apparatus according to Aspect 12 further comprises a first sampling line operable to extract an atmosphere sample from the first temperature zone of the furnace and deliver it to a first external sensor; the first external sensor operable to communicate with the process controller.

[0049] Aspect 14: The device of any of aspects 12 to 13, wherein the first oxygen sensor is an in-situ sensor.

[0050] Aspect 15: The apparatus of aspects 12 to 14, wherein the first external sensor is a sensor for measuring a parameter selected from the group consisting of oxygen, pressure, dew point, carbon dioxide, ammonia, SO x 、NO x and pressure differential.

[0051] Aspect 16: The apparatus of any one of aspects 12 to 15, wherein the first sampling line comprises a dehumidification device operable to remove moisture from the furnace atmosphere sample.

[0052] Aspect 17: The apparatus of any one of aspects 12 to 16, wherein the first furnace zone comprises an upper zone and a lower zone; the first oxygen sensor is located in the upper zone, and an inlet is used to deliver oxygen from the oxygen delivery system located in the lower zone.

[0053] Aspect 18: The apparatus of any one of aspects 12 to 17, wherein the first sampling line passes through the furnace wall; the sampling line comprises an inner length formed of ceramic material and located within the furnace wall, and an outer length formed of stainless steel and located outside the furnace wall.

[0054] Aspect 19: The apparatus of any one of aspects 12 to 18, wherein the first sensor group and the first external sensor are operable to communicate with a first sensor node; and the first sensor node is operable to communicate with a process controller.

[0055] Aspect 20: The apparatus of any one of aspects 12 to 19, wherein the first sensor group further comprises a first gas flow rate sensor, and the second sensor group further comprises a second gas flow sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a schematic diagram of an industrial-scale calcining furnace equipped with an atmosphere control system according to an embodiment of the present invention.

[0057] Figure 2 is a flow chart illustrating the control logic of an exemplary furnace zone in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The following detailed description provides only preferred exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the claimed invention. Rather, the following detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description of preferred exemplary embodiments for implementing the claimed invention. Various changes may be made to the function and arrangement of components without departing from the spirit and scope of the claimed invention.

[0059] Component numerals introduced in the specification in association with a drawing may be repeated in one or more subsequent drawings without additional description in the specification, in order to provide context for other features.

[0060] In the claims, letters are used to identify claimed steps (e.g., (a), (b), and (c). These letters are used to describe steps of the recited method and are not intended to indicate the order in which the claimed steps should be performed, unless and only if such an order is explicitly recited in the claims.

[0061] As used herein, the terms "furnace" and "calciner" refer to a device used to heat-treat solid precursor materials to form lithium-ion cathode materials. The temperature of the heat-treating process is preferably between 700 and 1300 degrees Celsius.

[0062] As used herein, the terms "temperature zones," "heating zones," and "zones" refer to regions within a furnace associated with a defined furnace temperature profile. The material being heat treated passes through these zones during processing. A zone can have a constant temperature or a temperature gradient. The boundaries between zones can be defined spatially or by temperature. Zone boundaries can be sharp or gradual, depending on the specific furnace design and application.

[0063] As used herein, the term "NMC" refers to a NMC having the general formula LiNi x Mn y Co z O2. The term "nickel-rich NMC" refers to materials with the general formula LiNi x Mn y Co z O2 materials, wherein the value of x is greater than 0.5. The term "NMC 811" refers to materials with the chemical formula LiNi 0.8 Mn 0.1 Co 0.1 O2 material.

[0064] As used herein, the term "precursor" refers to the raw materials used to produce cathode materials in an unreacted state. Preferred cathode materials, including but not limited to NCA and NMC, are produced by co-precipitating a transition metal hydroxide precursor material and then calcining (lithiation and oxidation) it with a lithium compound (preferably lithium hydroxide). In a preferred embodiment, the precursor is Ni x Mn y Co (1-x-y) (OH)2, the cathode material produced during calcination is NMC.

[0065] As used herein, the term "communication" refers to the ability to send and receive information, data, signals, controls, or commands via any known technology. For example, communication between components of the disclosed atmosphere control system can be accomplished via one or more technologies, including but not limited to fixed-line or wireless networks, such as a local area network (LAN), a wireless local area network (WLAN), a wide area network (WAN), a personal area network (PAN), a wireless personal area network (WPAN), a telephone network (e.g., a cellular network or a circuit-switched network), an intranet, an extranet, a peer-to-peer network, a virtual private network (VPN), the Internet, or other communication networks / links.

[0066] The production of nickel-rich cathode materials, such as NMC, requires calcination in an oxygen-rich atmosphere (atmosphere with an oxygen content of >50%). Preferably, the oxygen content of the calciner atmosphere is 70% (by volume) or higher, more preferably 90% (by volume) or higher. Previous cathode chemistries (nickel mole fraction less than 0.5) can be calcined in air, which is known to have an oxygen content of 21% (by volume), or in an oxygen-rich atmosphere. The present invention is applicable to all of the above environments.

[0067] Studies of nitrogen-oxygen atmosphere mixtures used to calcine NMC containing more than 0.5 mole fraction nickel have shown that low oxygen content in the gas mixture leads to poor electrochemical and cycling performance of the resulting cathode materials. This correlation is attributed to the oxidation state of the nickel in the product and the size of its atomic radius.

[0068] Various metals can reach different degrees of oxidation according to the number of their atomic groups and electron shells. In the case of nickel, the most stable cation is Ni 2+ , which may be detrimental to the performance of cathode materials. Its negative impact comes from the fact that its atomic radius is similar to that of Li + According to Le Chatelier's principle, increasing the oxygen partial pressure in the furnace atmosphere allows more oxygen to oxidize nickel to its preferred higher oxidation state, namely Ni 3+ .

[0069] Based on these findings, current calcination processes supply oxygen to the furnace at a fixed flow rate, assuming that a high, fixed oxygen flow rate is sufficient to oxidize the cathode material. Little attention has been paid to this important aspect of the process: effectively utilizing the potential of the protective atmosphere and its impact on the final product. Furthermore, process impurities, including but not limited to carbon dioxide (CO2) and water (H2O), can adversely affect oxidation and lead to side reactions with lithium. Careful monitoring and reduction of these impurities must be strictly controlled.

[0070] In addition to the composition of the furnace atmosphere, the direction and speed of the furnace atmosphere flow are also important. Preferably, the calcination process is carried out in a continuous furnace, in which the crucible containing the precursor is transported through multiple temperature zones. The temperature zones and their boundaries depend on the furnace design and the process being performed. Generally, a furnace consists of three main zones: preheating, hot (soaking) and cooling. The preheating zone is the part of the furnace where any part or material gradually increases its temperature from the starting temperature (most commonly the ambient temperature) until it reaches the "soaking temperature". The hot zone of the furnace is the part with the most stable temperature, and this temperature should be fairly "constant" or maintained around the desired soaking temperature (defined specifically for the type of material being processed). The cooling zone is the area where the product is cooled at the desired cooling rate (always specific to the material and properties) throughout the cooling zone.

[0071] Preferably, the depth of the precursor material within the crucible is relatively small to provide sufficient contact between the furnace atmosphere and the precursor material. The atmosphere control system of the present invention optimizes the flow pattern and composition of the furnace atmosphere by measuring the flow direction and velocity of the furnace atmosphere to ensure a more efficient reaction between the precursor material and the oxygen-rich atmosphere.

[0072] Preferably, the process gas is injected on the cooling side of the hot zone with the goal of forcing most of the gas flow towards the furnace inlet (opposite to the direction of belt movement) and allowing some gas flow to the cooling zone and protect the parts that may be most affected.

[0073] In an example of an NMC calcining process, gas inlets (located at the bottom of the furnace) are located throughout the furnace's length, although the flow distribution between these inlets is uneven. Most of the gas is introduced into the cooling end and forced out of the furnace during the preheating section. Most chemical reactions between the material and the atmosphere occur in the preheating zone, with some occurring in the hot zone. It is important to remove impurities released from the material as quickly as possible. Placing gas outlets in the "dirtiest" section of the furnace helps prevent these impurities from entering the hot zone and reversing the chemical reactions.

[0074] However, it is important not only to remove the impurities from the furnace as quickly as possible, but also to allow the oxygen process gas in the furnace to have a sufficient partial pressure to oxidize and distribute the material in the furnace in a manner that more evenly exposes the material to the oxidizing atmosphere.

[0075] In an embodiment, the direction of atmosphere flow in the furnace is determined by measuring the pressure differential between different furnace sections and between the furnace and the external atmosphere. During normal operation, the pressure inside the furnace is preferably slightly higher than the ambient pressure and is uniform throughout the furnace (low pressure differential). This is directly related to the gas flow rate entering the furnace. An increase in the pressure differential between specific furnace sections indicates an uneven distribution of gas flow or, depending on the direction of the pressure change, air entering from one furnace end.

[0076] In an embodiment, the atmosphere control system of the present invention continuously measures and analyzes oxygen, CO2, H2O, furnace pressure, furnace atmosphere flow direction and flow rate in each zone of the calcining furnace. Other parameters can be further measured as needed depending on the type of material being processed. Other parameters may include but are not limited to sulfur oxides (SO x ) and nitrogen oxides (NO x ) and other impurities.

[0077] The process controller, which communicates with the sensors (directly with each sensor or sensor group via a node), also communicates with the oxygen delivery system. The oxygen delivery system includes mass flow controllers at the inlet of each furnace zone. The oxygen delivery system is in fluid flow communication with the oxygen source and is used to optimize the oxygen flow to each furnace zone to maintain high oxygen concentration, remove CO2, H2O, and other impurities, and maintain the desired atmosphere flow direction. Preferably, the furnace will have at least three zones: a preheat zone, a hot zone, and a cooling zone.

[0078] Furnace pressure and gas velocity sensors are installed at selected locations to monitor the flow pattern of the furnace atmosphere. This helps to effectively remove moisture, carbon dioxide, and impurities through vents in the furnace wall, thereby maintaining high oxygen levels in the furnace. Parameters including, but not limited to, temperature, oxygen concentration, moisture (measured as dew point), and CO2 concentration are preferably used to verify that the calciner atmosphere is operating under optimal conditions. By correlating the atmospheric conditions with the quality of the finished cathode material, the optimal operation of the calciner atmosphere control system is determined.

[0079] Figure 1 An embodiment of a furnace atmosphere control system 100 for a calcining furnace 101 for producing nickel-rich lithium-ion battery cathode material is shown. For clarity, not all possible configurations or measurement locations are shown, but given the options shown, different configurations can be put together as part of the present invention. The furnace includes a plurality of sequential heating and cooling zones maintained at different temperatures, each equipped with a series of sensors. Figure 1 In the embodiment of the present invention, the furnace includes at least one of a preheating zone 105 , a hot zone 107 and a cooling zone 111 .

[0080] Cathode precursor material 115 enters the furnace at preheating zone 105 and is subsequently conveyed through hot zone 107 before passing through cooling zone 111 to form finished cathode material product 117. The preheating step, in addition to raising the temperature of the raw materials, removes moisture, CO2, and other impurities primarily resulting from precursor decomposition. Moisture, carbon dioxide, and impurities are preferably removed from the material before entering the hot zone, where they could potentially cause undesirable reverse reactions.

[0081] An oxygen source is connected to the oxygen delivery system 119. The source is preferably an oxygen-enriched mixture. Preferred gas mixtures include, but are not limited to, a mixture of O2 and N2, purified air, or a combination thereof. In one embodiment, the gas mixture contains at least 50% (by volume) O2, preferably at least 70% (by volume) O2, and more preferably at least 90% (by volume) O2. Preferably, the oxygen-enriched mixture has a CO2 concentration of less than 1 ppm, a CO concentration of less than 1 ppm, a H2O concentration of less than 5 ppm, a total hydrocarbon concentration of less than 1 ppm, and is substantially free of metallic particles, oil, or grease. Preferably, the remainder of the impurities in the oxygen-enriched mixture are argon and nitrogen, which are inert at process temperatures and should not negatively impact the processed material.

[0082] refer to Figure 1, the oxygen delivery system 119 is in fluid flow communication with mass flow controllers 121, 123, and 125, which deliver the oxygen-enriched mixture into the furnace via inlet 127. The mass flow controllers are in electrical communication with the software logic of the main flow controller 131. The mass flow controllers are adjusted based on signals from the main flow controller to allow more or less restricted flow by proportionally controlling the flow of gas through the mass flow controllers. Preferably, the inlet is located at the bottom of the furnace or on the side wall of the furnace, or both. Gases emitted by the precursor material, including water vapor, CO2 and other impurities, leave the furnace via outlet 129 at the top of the furnace. Preferred oxygen sources include, but are not limited to, liquid oxygen tanks and / or vacuum swing adsorption (VSA) oxygen generators. In embodiments, oxygen from a liquid oxygen tank or a VSA oxygen generator is mixed with purified air or pure nitrogen. When the oxygen is mixed with pure nitrogen, the nitrogen can come from a liquid nitrogen tank or a PSA nitrogen generator.

[0083] The mass flow controllers 121, 123, and 125 on the gas inlet communicate with the central process controller 131. Figure 1 In the illustrated embodiment, the hot zone 107 has fewer gas outlets 129 than the preheat zone 105 and the cooling zone 111, to promote the flow of furnace atmosphere from the hot zone to adjacent zones. Preferably, the majority of the oxygen flows toward the front of the furnace, in the opposite direction of the cathode material's travel. This design helps achieve the richest oxygen atmosphere and the lowest impurities in the hot zone of the furnace, which are the most critical parameters.

[0084] Oxygen sensors 133, 135, and 137 are located at measurement points within the furnace. Preferred oxygen sensors are zirconia probes, paramagnetic probes, electrochemical analyzers, or any other suitable oxygen sensor for measuring oxygen in highly oxidizing atmospheres. Preferably, the oxygen sensors are positioned to measure the oxygen concentration in the atmosphere of each furnace zone. The oxygen sensors are preferably placed close to the solid material being heat treated to measure the atmosphere exposed to the material. In embodiments, each zone will have multiple oxygen sensors and multiple groups of other sensors installed at different locations within the zone. Figure 1 The embodiment shown is provided as an example, wherein there is one set of sensors per zone to simplify this diagram. This also applies to other types of sensors. In an embodiment, additional oxygen sensors (not shown) can be added and placed in the main oxygen-enriched supply line and the main furnace outlet (ventilation) line. Their purpose is to measure the oxygen concentration in the supply line and the main outlet line (after the calcination process). The additional oxygen sensors further communicate with the process controller via a wireless node or are directly electrically connected to the process controller. The purpose of installing these sensors is to measure the oxygen concentration before and after the calcination process. These measurements will allow calculations to be made to determine how much oxygen is used in the process, and this data will be used for thermodynamic analysis of the process and enhanced process control.

[0085] refer to Figure 1 In an embodiment, a first oxygen sensor 133 is located in the preheat zone 105 of the furnace, a second oxygen sensor 135 is located in the hot zone 107 of the furnace, and a third oxygen sensor 137 is located in the cooling zone 111. Sensor nodes 139, 141, and 143 in each zone receive signals from the oxygen sensors 133, 135, and 137 and, in turn, communicate with a central process controller 131. The master process controller may be equipped with a cloud-based data input system 132. In an embodiment (not shown), the oxygen sensors are located outside the furnace in sampling lines, as described below.

[0086] More oxygen sensors can be added to the system to measure oxygen concentrations at other furnace locations (i.e., gas supply lines and furnace ventilation lines). They communicate with the process controller via wireless nodes or are directly electrically connected to the process controller.

[0087] Sensors 145, 147, 149 for measuring flow direction and velocity are located in the preheat zone 105, hot zone 107, and cooling zone 111. The flow direction and velocity sensors 145, 147, 149 are electrically connected to the nodes 139, 141, 143 of their respective zones, and the nodes communicate with the central process controller.

[0088] Sampling lines 151, 153, 155 are located in the preheating zone 105, the hot zone 107, and the cooling zone 111, respectively. The sampling lines allow samples of the atmosphere in each zone to be taken from the furnace for analysis by external sensors to measure dew point and impurities. A section of each sampling line 151, 153, 155 extends through the top furnace wall and has an opening exposed to the furnace. The inner portion is preferably made of ceramic material. Another portion of the sampling line extends from the first portion to a series of monitoring devices. The outer portion of the sampling lines 157, 159, 161 is preferably made of a thermally conductive material, including but not limited to stainless steel, to avoid condensation in the sampling lines when heated. All materials used in the sampling lines are preferably compatible with oxygen and cleaned to appropriate conditions.

[0089] Pumps 175, 177, 179 are used to draw atmospheric samples into a series of sensors through sampling lines 157, 159, 161. Filters 163, 165, 167 are located on each sampling line to remove any particulate matter from the sample.

[0090] Dew point sensors 169, 171, 173 measure the dew point of the atmosphere sample. After the dew point analyzer, condensation cups 181, 183, 185 remove moisture from the sample before the CO2 analyzer 187, 189, 191 and sensor arrays 193, 195, 197. The sensor array preferably includes sensors for measuring pressure and impurities (including but not limited to ammonia, SO x and NOx After passing through sensor arrays 193, 195, and 197, the sample is discharged to a safe location 194, 196, and 198.

[0091] Nodes 139, 141, and 143 in each furnace zone receive signals from the corresponding zone's sensor arrays 193, 195, and 197, CO2 analyzers 187, 189, and 191, dew point sensors 169, 171, and 173, oxygen sensors 133, 135, and 137, and flow sensors 145, 147, and 149. Each node communicates with a central process controller. The central process controller receives and processes signals from all sensors and regulates the oxygen flow rate to each zone by communicating with and controlling mass flow controllers 121, 123, and 125.

[0092] Figure 2 An exemplary embodiment of process control logic 200 for a single furnace zone is provided. The control steps can be executed as a discrete sequence or as a continuous loop. It should be noted that control logic 200 is exemplary only. Many other possible control logics can improve the performance of a calciner to produce nickel-rich cathode material.

[0093] At the beginning of the sequence 202, measurements are taken from the oxygen sensor 204, the CO2 sensor 206, and the dew point sensor 208. The measured values are then compared to default values. The default values can be selected by the operator or can be selected and changed by the main process controller based on readings from other zones to optimize the atmosphere conditions within the furnace.

[0094] Figure 2 Example set points are provided to illustrate one embodiment of the present invention. In the practice of the present invention, these set points will vary and are selected by the process engineer. The set points are customized based on the specific furnace design and the specific processing application. The set points may also vary by furnace zone.

[0095] exist Figure 2 In the illustrated embodiment, the oxygen measurement is treated as the oxygen partial pressure (pO2) and compared to a setpoint of 0.9 bar 210. When pO2 is equal to or below 0.9 bar, the process controller signals the oxygen mass flow controller for that zone to increase the oxygen flow into zone 214. The system continues to read the oxygen measurement 204 from the oxygen sensor until the reading is greater than 0.9 bar 210. As used herein, 0.9 bar corresponds to an oxygen concentration of 90% (by volume of oxygen), assuming for simplicity that the total furnace pressure is approximately 1 bar. The flow controller is preferably capable of proportional control to achieve more precise flow adjustments proportional to the deviation from the setpoint.

[0096] When the oxygen reading is greater than the set point (0.9 bar in this example) 210, the controller will then compare the CO2 sensor's measurement to a default value (50 ppm in this example 212). If the CO2 concentration is equal to or greater than 50 ppm, the process controller will signal the oxygen mass flow controller for that zone to increase the oxygen flow into the zone 218. The system will continue to read the sensor's carbon dioxide measurement 206 until the increased oxygen flow displaces enough CO2 to bring the reading below 50 ppm 212.

[0097] When the pO2 is above the set point and the CO2 reading is below the set point (50 ppm in this example), the controller compares the dew point sensor's measurement to the set point (0 degrees Celsius in this example) 216. When the dew point is equal to or greater than 0 degrees Celsius, the process controller signals the zone's oxygen mass flow controller to increase the oxygen flow into the zone 222. The system continues to read the sensor's dew point measurement 220 until the increased oxygen flow displaces enough moisture to bring the reading below 0 degrees Celsius.

[0098] When pO2 is above a setpoint and CO2 and dew point measurements are below setpoints, the controller maintains the oxygen flow rate into that zone. Similar closed-loop control logic is used for the sensor arrays for pressure and other impurities. The main process controller is configured with software to simultaneously monitor the readings of all sensors in each zone and manipulate the mass flow controllers to optimize the atmosphere within the furnace.

[0099] Parameter set points in each zone may be different and can be dynamically adjusted by the main process controller based on sensor measurements.

[0100] Pressure differential and / or temperature measurements can be taken at various points. Such measurements of the exhaust flow can indicate flow direction and velocity. Such measurements between a furnace and an exhaust flow, or between two furnace locations, can also indicate flow direction and / or velocity.

[0101] Examples

[0102] Thermogravimetric analysis (TGA) was performed on an NMC 811 precursor mixed with two lithium sources used to prepare cathode materials: lithium hydroxide (LiOH) and lithium carbonate (Li2CO3). This experiment was conducted to understand how these chemicals behave in the presence of oxygen (oxidation reactions) and temperature, in order to better understand material decomposition over temperature profiles.

[0103] Example 1 - NMC 811 precursor and LiOH.

[0104] 18.8070 mg of NMC811 precursor and LiOH mixture (molar ratio 1:1) was placed in a TGA instrument (TGAQ500, TA Instruments, New Castle, DE). In an atmosphere containing 98% oxygen and 2% nitrogen, the temperature was increased from 50 degrees Celsius to 900 degrees Celsius. The process gas (oxygen source) flow rate was set to 50 ml / min. The temperature was maintained at 50 degrees Celsius for 30 minutes and then heated to 900 degrees Celsius at a rate of 3 degrees Celsius per minute. The material was then maintained at 900 degrees Celsius for 20 minutes. The material was then cooled to room temperature. The reaction in the furnace with LiOH as the lithium source was 4Ni 0.8 Mn 0.1 Co 0.1 O+4LiOH+O2à4LiNi 0.8 Mn 0.1 Co 0.1 O2 + 2H2O. Table 1 summarizes the results of Example 1.

[0105] Table 1 - TGA analysis results of NMC 811 precursor and LiOH

[0106]

[0107]

[0108] The results in Table 1 show that water is removed from the precursor material in stages at lower temperatures before the precursor material reaches the maximum process temperature of 900 degrees Celsius.

[0109] Example 2 - NMC 811 Precursor and Li2CO3

[0110] 33.9230 mg of NMC811 precursor and Li2CO3 mixture (molar ratio 2:1) were placed in the TGA apparatus (same as above). The material was first kept at room temperature for 30 minutes. The temperature was then raised from room temperature to 950 degrees Celsius at a rate of 3 degrees Celsius per minute. Throughout the process, the material was in an atmosphere of 98% (by volume) oxygen and 2% (by volume) nitrogen with a gas flow rate of 50 ml / min. Furnace reaction using Li2CO3 as the Li source: 2Ni 0.8 Mn 0.1 Co 0.1 O+2Li2CO3+O2à2LiNi 0.8 Mn 0.1 Co 0.1 O2 + 2CO2. The results of Example 1 are summarized in Table 2.

[0111] Table 2 - TGA analysis results of NMC 811 precursor and Li2CO3

[0112]

[0113] The results in Table 2 show that water is removed from the precursor material in stages at lower temperatures before the precursor material reaches the maximum process temperature of 950 degrees Celsius.

[0114] An invention has been disclosed in terms of preferred embodiments and alternative embodiments thereof. Of course, those skilled in the art may make various changes, modifications, and variations to the teachings of the present invention without departing from the intended spirit and scope of the present invention. It is intended that the present invention be limited only to the terms of the appended claims.

Claims

1. A method for controlling the furnace atmosphere of a calcining furnace for producing cathode materials for lithium-ion batteries, the method comprising the following steps: (a) measuring a first oxygen concentration, a first moisture concentration, and a first carbon dioxide concentration of an atmosphere in a first zone of the calcining furnace; (b) measuring a second oxygen concentration, a second moisture concentration, and a second carbon dioxide concentration of an atmosphere in a second zone of the calcining furnace, wherein the second zone is adjacent to the first zone and a boundary between the first zone and the second zone is located at a position where the temperature of the atmosphere reaches a predetermined soaking temperature; (c) independently supplying an oxygen process gas comprising at least 50% (by volume) oxygen to the first and second zones of the calciner; (d) controlling the flow rate of a first oxygen process gas stream entering the first zone based on at least one selected from (i) the first oxygen concentration measured in step (a), (ii) the first moisture concentration measured in step (a), and (iii) the first carbon dioxide concentration measured in step (a); (e) controlling the flow rate of the second oxygen process gas stream entering the second zone based on at least one selected from (i) the second oxygen concentration measured in step (b), (ii) the second moisture concentration measured in step (b), and (iii) the second carbon dioxide concentration measured in step (b); and (f) maintaining the flow rate of the first oxygen process gas stream equal to or lower than the flow rate of the second oxygen process gas stream to prevent gaseous flow from the first zone into the second zone, wherein step (d) further comprises increasing the flow rate of the first oxygen process gas stream if at least one of the following conditions exists: (i) the first oxygen concentration measured in step (a) is less than a predetermined set point, (ii) the first moisture concentration measured in step (a) is greater than a predetermined set point, and (iii) the first carbon dioxide concentration measured in step (a) is greater than a predetermined set point.

2. The method of claim 1 , wherein step (e) further comprises increasing the flow rate of the second oxygen process gas stream if at least one of the following conditions exists: (i) the second oxygen concentration measured in step (b) is less than a predetermined set point, (ii) the second moisture concentration measured in step (b) is greater than a predetermined set point, and (iii) the second carbon dioxide concentration measured in step (b) is greater than a predetermined set point.

3. The method according to claim 1, further comprising the steps of: (h) repeating steps (a) through (f) while gradually heating the first zone to a first temperature and maintaining the second zone at a second temperature, wherein the second temperature is greater than or equal to the first temperature.

4. The method according to claim 1, further comprising the steps of: (i) repeating steps (a) to (f) while simultaneously injecting a predetermined amount of lithium-ion battery cathode precursor material into the first zone for a time sufficient to heat the material to a predetermined material temperature, and then injecting the material into the second zone.

5. The method according to claim 1, further comprising the steps of: (j) measuring a third oxygen concentration, a third moisture concentration, and a third carbon dioxide concentration of the atmosphere in a third zone of the furnace, wherein the third zone is adjacent to the second zone; (k) controlling the flow rate of the third oxygen process gas stream entering the third zone based on at least one selected from (i) the third oxygen concentration measured in step (j), (ii) the third moisture concentration measured in step (j), and (iii) the third carbon dioxide concentration measured in step (j); and (1) Maintaining the flow rate of the third oxygen process gas flow equal to or lower than the flow rate of the second oxygen process gas flow to prevent gaseous flow from the third zone into the second zone.

6. The method of claim 4, wherein the lithium-ion cathode precursor material is selected from the group consisting of: lithium nickel manganese cobalt (NMC); lithium nickel cobalt aluminum (NCA); lithium nickel manganese cobalt aluminum (NMCA); nickel cobalt boron (NCB), and combinations thereof.

7. The method of claim 6, wherein the cathode precursor material comprises a nickel molar ratio greater than 0.

5.

8. The method of claim 1, wherein the oxygen process gas comprises a purity of at least 90% by volume.

9. The method according to claim 1, further comprising the steps of: (m) extracting a furnace atmosphere sample from the first zone through a sample line; and (n) delivering the sample to at least one external analyzer for measuring a parameter selected from the group consisting of: oxygen concentration; carbon dioxide concentration; dew point; ammonia; SO x and NO x .

10. An apparatus for controlling the atmosphere in a calcining furnace according to the method of any one of claims 1 to 9, wherein the calcining furnace is used to produce lithium ion or solid state battery cathode materials, comprising: A first sensor group is installed in the first furnace temperature zone, wherein the first sensor group includes a first oxygen sensor, a first moisture sensor, and a first carbon dioxide sensor; A second sensor group is installed in the second furnace temperature zone, the second sensor group including a second oxygen sensor, a second moisture sensor and a second carbon dioxide sensor; an oxygen delivery system operably configured to be located in fluid flow communication with an oxygen source to deliver independently regulated oxygen flows to the first and second furnace temperature zones; A process controller is operable to communicate with the sensors and the oxygen delivery system to control the oxygen delivery rate to the first and second furnace temperature zones in response to a plurality of signals from the first and second sensor groups.

11. The apparatus of claim 10, further comprising a first sampling line operable to extract an atmosphere sample from the first furnace temperature zone of the furnace and transport it to a first external sensor; the first external sensor operable to communicate with the process controller.

12. The apparatus of claim 10, wherein the first oxygen sensor is an in-situ sensor.

13. The apparatus according to claim 11, wherein the first external sensor is for measuring a parameter selected from the group consisting of oxygen, pressure, dew point, carbon dioxide, ammonia, SO x 、NO x and differential pressure sensors.

14. The apparatus of claim 11, wherein the first sampling line comprises a dehumidification device operable to remove moisture from the furnace atmosphere sample.

15. The apparatus of claim 10, wherein the first furnace temperature zone comprises an upper zone and a lower zone; the first oxygen sensor is located in the upper zone, and an inlet for delivering oxygen from the oxygen delivery system located in the lower zone.

16. The apparatus of claim 11, wherein the first sampling line passes through a furnace wall; the sampling line comprises an inner length formed of a ceramic material and located within the furnace wall, and an outer length formed of stainless steel and located outside the furnace wall.

17. The apparatus of claim 11, wherein the first sensor group and the first external sensor are operable to communicate with a first sensor node; the first sensor node is operable to communicate with the process controller.

18. The apparatus of claim 10, wherein the first sensor group further comprises a first gas flow rate sensor, and the second sensor group further comprises a second gas flow sensor.

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